Atmospheric Environment (v.74, #C)
Editorial board (i).
Surface ozone photolysis rate trends in the Eastern Mediterranean: Modeling the effects of aerosols and total column ozone based on Terra MODIS data by N. Benas; E. Mourtzanou; G. Kouvarakis; A. Bais; N. Mihalopoulos; I. Vardavas (1-9).
The surface ozone photolysis rate (J(O1D)) was computed on a daily basis and on a 50 km × 50 km resolution for the 11-year period 2000–2010 at Finokalia meteorological station in Crete, Greece. A radiative transfer model was used, with climatological data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA's Terra satellite. The area is representative of the Eastern Mediterranean, a region with high variability in aerosol loads and total column ozone. Instantaneous values of J(O1D) computed from the model were validated against corresponding station measurements available during the 5-year period 2002–2006. Monthly mean values of J(O1D) during the 11-year period examined, reveal a statistically significant decreasing trend, based on Terra MODIS data, which shows an overall 13% decrease. The aerosol effect on J(O1D) varies on a daily basis, depending on the aerosol load, and can exceed −10% during dust events, with a median value of −2.3% over the whole period examined. On a seasonal basis, the aerosol effect on J(O1D) follows the seasonal pattern of the aerosol load, with higher values in spring and autumn, due to the increased Saharan dust episodes during these seasons. Linear regression analysis on monthly mean values of total column ozone revealed a statistically significant increasing trend in both Finokalia and Thessaloniki stations. Total column ozone MODIS data were validated against spectroradiometric (columnar) measurements at Thessaloniki station. Sensitivity analysis on the effect of total column ozone on J(O1D) showed that a 10% variation in total ozone causes a corresponding 15–17% change in J(O1D). These results suggest that the decreasing trend in J(O1D) found in the case of Terra MODIS should be attributed mainly to the corresponding increasing trend in total column ozone.
Keywords: Ozone photolysis rate; Aerosol optical thickness; Total column ozone; Enhancement factor;
A new method for estimating greenhouse gases and ammonia emissions from livestock buildings by José Barrancos; Susana Briz; Dácil Nolasco; Gladys Melián; Germán Padilla; Eleazar Padrón; Isabel Fernández; Nemesio Pérez; Pedro A. Hernández (10-17).
It is widely known that carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are the main greenhouse gases contributing to global climate change. Emission factors for the aforementioned gases have been proposed in order to calculate the contribution of livestock farming to global climate change. However, these emission factors depend on many additional factors such as the housing system, environmental conditions, etc., which implies some uncertainties in their estimation. Therefore, works that aim at improving experimental calculation of these emissions are crucial to provide reliable estimates of the emissions produced by livestock. The purpose of this work was to apply a new methodology inspired by the accumulation chamber method to estimate emission rates from livestock buildings. The work was based on measuring the increase of gas emissions inside the livestock building by means of the remote sensing technique Open-Path FTIR (OP-FTIR). Previously to the measurements, livestock building cattle was confined outside of the building. Utilization of fan ventilation system favoured the homogenization of air inside the building. This experiment proved that evolution of CH4 and CO2 concentrations inside the livestock building behaved like an accumulation chamber unlike the N2O which did not show such behaviour. Results showed CH4, CO2 and NH3 emissions of 167 ± 54,700 ± 200 and 1.3 ± 0.2 kg head−1 year−1, respectively. One of the main parameters affecting the estimated emission factors is the type of animal feeding. Therefore, it is essential to investigate the influence of food composition on CH4 and CO2 emission in a relative larger number of operating cattle buildings since the methodology herein proposed is an easy and cheap tool to study livestock emission factors and their variability.
Keywords: Open-Path FTIR; Livestock emissions; Greenhouse gases; Ammonia; Flux chamber;
Distribution of ozone in the marine boundary layer of Arabian Sea prior to monsoon: Prevailing airmass and effect of aerosols by Prabha R. Nair; Liji Mary David; S. Aryasree; K. Susan George (18-28).
Surface ozone (O3) measurements were carried out in the marine environment of the Arabian Sea (AS) during the premonsoon months, April–May 2006, as part of the Integrated Campaign for Aerosols, gases and Radiation Budget. The O3 mixing ratio over the AS varied in the range ∼3–22 ppb with a mean of 13.5 ± 2 ppb. Comparatively high mixing ratios were observed over the southern AS and close to the coast. The spatial pattern did not show any evidence of transport from nearby landmass or in situ photochemistry. Longitudinally separated narrow regions of low and high O3 were seen over the southern AS. The role of aerosols in modifying the O3 concentration was examined based on the co-located measurement of aerosol mass loading, number density, size distribution and optical depth. The O3 mixing ratio showed positive correlation with aerosol loading. Over high O3 regions, large particle concentration showed significant enhancement. The role of chloride ion in depleting O3 was also investigated. The observed spatial features were compared with those measured during the earlier cruises conducted in different seasons and over various oceanic regions. A comparison has been made with the measurements over the Bay of Bengal during the same cruise.
Keywords: Surface O3; Tropospheric chemistry; Mass loading; Aerosols; Aerosol chemistry; Number density;
New particle formation and growth associated with East-Asian long range transportation observed at Fukue Island, Japan in March 2012 by Takafumi Seto; Seyoung Kim; Yoshio Otani; Akinori Takami; Naoki Kaneyasu; Toshiyuki Fujimoto; Kikuo Okuyama; Tamio Takamura; Shiro Hatakeyama (29-36).
Time-resolved data for size distribution, number concentration and chemical composition of atmospheric aerosols were taken from March 9 to 16, 2012 during Fukue Site Atmospheric Aerosol Observation Campaign (128.7°E, 32.8°N) organized by ASEPH (Impacts of Aerosols in East Asia on Plants and Human Health) project. A scanning mobility particle sizer was employed to continuously measure the particle size distribution from 14 nm to 670 nm and the total number concentration of particles (>3 nm) was measured by a condensation particle counter. Very large amount of polluted air mass transportation (PM2.5 > 65 μg m−3) was observed on March 11, associated with a sudden increase in particle number concentration having a mobility diameter from 100 to 300 nm. The transported air mass contained anthropogenic pollutants such as sulfate (>20 μg m−3), nitrate (>15 μg m−3) and black carbon (>3 μg m−3). Typical new particle formation and growth events were also observed on March 12–13. The onset of particle formation and nucleation bursts was identified at around noon and it is considered that these were nucleated species near the island area. It was found that some new particle formation events were associated with the long range transportation of polluted air mass from East Asian region.
Keywords: New particle formation; Aerosol; Nucleation; East Asia;
Measurements of vertical and horizontal distributions of ozone over Beijing from 2007 to 2010 by Pengfei Chen; Jiannong Quan; Qiang Zhang; Xuexi Tie; Yang Gao; Xia Li; Mengyu Huang (37-44).
The vertical distributions of ozone (O3) over a mega city (Beijing, China), and the horizontal O3 distributions in the lower troposphere (2–3.6 km) over Beijing and its surrounding areas located in the North China Plain (NCP), were analyzed based on the aircraft measurements from 159 flights during 2007–2010. The results are highlighted as follows: (1) There was a peak of O3 concentration occurring at ∼1 km over Beijing, and the peak values ranged between 60 and 120 ppbv. (2) There was an O3 minimum at the surface. The minimum was largely caused by the chemical reaction of NO + O3. This process produced about 30 ppbv of the O3 reduction below 0.5 km in the morning (9:00–10:00). (3) There was a transition altitude (∼1 km), below which the ozone formation was in a VOC-limited condition, and above which the ozone formation was in a NOx-limited condition. (4) The analysis of the horizontal distribution shows that O3 concentrations were enhanced in the downwind of the city plumes. This result suggests that there was an important regional O3 chemical production in the NCP region.
Keywords: Ozone; Vertical profile; Horizontal profile; Aircraft measurement; Beijing;
Stochastic reconstruction of multiple source atmospheric contaminant dispersion events by Derek Wade; Inanc Senocak (45-51).
Reconstruction of intentional or accidental release of contaminants into the atmosphere using concentration measurements from a sensor network constitutes an inverse problem. An added complexity arises when the contaminant is released from multiple sources. Determining the correct number of sources is critical because an incorrect estimation could mislead and delay response efforts. We present a Bayesian inference method coupled with a composite ranking system to reconstruct multiple source contaminant release events. Our approach uses a multi-source data-driven Gaussian plume model as the forward model to predict the concentrations at sensor locations. Bayesian inference with Markov chain Monte Carlo (MCMC) sampling is then used to infer model parameters within minutes on a conventional processor. The composite ranking system enables the estimation of the number of sources involved in a release event. The ranking formula allows plume model results to be evaluated based on a combination of error (scatter), bias, and correlation components. We use the 2007 FUSION Field Trial concentration data resulting from near-ground-level sources to test the multi-source event reconstruction tool (MERT). We demonstrate successful reconstructions of source parameters, as well as the number of sources involved in a release event with as many as three sources.
Keywords: Event reconstruction; Bayesian inference; Source term estimation; Gaussian plume model;
Influence of specimen size, tray inclination and air flow rate on the emission of gases from biomass combustion by E.B. Amorim; J.A. Carvalho; T.G. Soares Neto; E. Anselmo; V.O. Saito; F.F. Dias; J.C. Santos (52-59).
Experiments of biomass combustion were performed to determine whether specimen size, tray inclination, or combustion air flow rate was the factor that most affects the emission of carbon dioxide, carbon monoxide, and methane. The chosen biomass was Eucalyptus citriodora, a very abundant species in Brazil, utilized in many industrial applications, including combustion for energy generation. Analyses by gas chromatograph and specific online instruments were used to determine the concentrations of the main emitted gases, and the following figures were found for the emission factors: 1400 ± 101 g kg−1 of CO2, 50 ± 13 g kg−1 of CO, and 3.2 ± 0.5 g kg−1 of CH4, which agree with values published in the literature for biomass from the Amazon rainforest. Statistical analysis of the experiments determined that specimen size most significantly affected the emission of gases, especially CO2 and CO.
Keywords: Biomass combustion; Eucalyptus citriodora; Emission factors;
Variability of CO2 concentrations and fluxes in and above an urban street canyon by Björn Lietzke; Roland Vogt (60-72).
The variability of CO2 concentrations and fluxes in dense urban environments is high due to the inherent heterogeneity of these complex areas and their spatio-temporally variable anthropogenic sources. With a focus on micro- to local-scale CO2-exchange processes, measurements were conducted in a street canyon in the city of Basel, Switzerland in 2010. CO2 fluxes were sampled at the top of the canyon (19 m) and at 39 m while vertical CO2 concentration profiles were measured in the center and at a wall of the canyon. CO2 concentration distributions in the street canyon and exchange processes with the layers above show, apart from expected general diurnal patterns due mixing layer heights, a strong dependence on wind direction relative to the canyon. As a consequence of the resulting corkscrew-like canyon vortex, accumulation of CO2 inside the canyon is modulated with distinct distribution patterns. The evaluation of diurnal traffic data provides good explanations for the vertical and horizontal differences in CO2-distribution inside the canyon. Diurnal flux characteristics at the top of the canyon can almost solely be explained with traffic density expressed by the strong linear dependence. Even the diurnal course of the flux at 39 m shows a remarkable relationship to traffic density for east wind conditions while, for west wind situations, a change toward source areas with lower emissions leads to a reduced flux.
Keywords: Carbon-dioxide; Urban; Street canyon; Flux measurements; Concentration profiles; Eddy-covariance; Basel;
Assessment of composition and origin of airborne bacteria in the free troposphere over Japan by Teruya Maki; Makiko Kakikawa; Fumihisa Kobayashi; Maromu Yamada; Atsushi Matsuki; Hiroshi Hasegawa; Yasunobu Iwasaka (73-82).
Long-range transport of airborne microorganisms through the free troposphere significantly impacts biological ecosystems, human life, and atmospheric processes in downwind areas. However, microbial communities in the free troposphere have rarely been investigated because the direct collection of microbial cells at high altitudes requires sophisticated sampling techniques. In this study, tropospheric air sampling was performed using a balloon and an aircraft at 800 m and 3000 m, respectively, over the Noto Peninsula in Japan (37.5°N, 137.4°E) where free tropospheric winds carry aerosols from continental areas. The air samples were collected during four different sampling periods when air masses came from desert regions of Asian continent (west samples) and from Siberia of Russia North Asia (north samples). The west samples contained higher levels of aerosols, and bacteria from the west samples grew in culture media containing up to 15% NaCl. In contrast, bacteria from the north samples could not be cultured in the same media. All isolates obtained from the NaCl-amended cultures were similar to Bacillus subtilis and classified as Firmicutes. A 16S rDNA clone library prepared from the west samples was mainly composed of one phylotype of Firmicutes that corresponded to the cultured B. subtilis sequence. A clone library prepared from the north samples consisted primarily of two phyla, i.e., Actinobacteria and Proteobacteria, which are known to dominantly inhabit low-temperature environments of North Asia. Our results suggest that airborne bacterial communities at high altitudes include several species that vary by the direction and interaction of free tropospheric winds.
Keywords: Phylogeny; Asian dust; Airborne bacteria; Bioaerosol; Halotolerant bacteria; Free troposphere;
Carbonaceous and ionic components in ultrafine and fine particles at four sampling sites in the vicinity of roadway intersection by Kyung Hwan Kim; Kazuhiko Sekiguchi; Shinji Kudo; Masatoshi Kinoshita; Kazuhiko Sakamoto (83-92).
Ultrafine particles (UFPs; Dp < 0.1 μm) and fine particles (FPs; Dp < 2.5 μm) were simultaneously collected for 11 h periods in the daytime and in the nighttime at four sites (S1–S4) around a roadway intersection in an urban area. Sampling was carried out for 14 consecutive days to determine the effect of the intersection on the chemical composition of atmospheric UFPs and FPs. The relative contributions of organic carbon (OC) and elemental carbon (EC) to total carbon (TC) in the daytime samples were 65–86% (UFPs: 83–86%; FPs: 65–75%) and 14–35% (UFPs: 14–17%; FPs: 25–35%), respectively, whereas those in the nighttime samples accounted for 71–90% (UFPs: 87–90%; FPs: 71–78%) and 10–29% (UFPs: 10–13%, FPs: 22–29%), respectively, indicating that the contribution of EC in both UFPs and FPs was higher during the daytime. The decrease in the concentration of carbonaceous components with distance from the intersection indicated a strong effect of motor vehicles emissions on the composition of UFPs and FPs around the intersection. The diurnal variations of sulfate and nitrate in UFPs are consistent with the seasonal variations of sulfate and nitrate in FPs showing higher sulfate and nitrate concentrations in summer and winter, respectively. Not observed in FPs, the diurnal patterns of sulfate and nitrate in UFPs may be closely related to particle size in comparison with larger particles, because smaller particles are more strongly affected by the surrounding environment, for example, through oxidation and dissociation. The present study provides interesting observation that the emission characteristics of OC and EC fractions can be different in the same roadside environment depending on the distance from roadway intersection and particle sizes. Furthermore, concentration difference between EC and black carbon (BC) was found at specific site indicating different EC emission characteristics at the same roadside environment.
Keywords: Roadside; Ultrafine particle; Chemical composition; Intersection; Black carbon;
Atmospheric heavy metals and Arsenic in China: Situation, sources and control policies by Jingchun Duan; Jihua Tan (93-101).
In recent years, heavy metal pollution accidents were reported frequently in China. The atmospheric heavy metal pollution is drawing all aspects of attention. This paper summarizes the recent research results from our studies and previous studies in recent years in China. The level, temporal variation, seasonal variation and size distribution of the heavy metals of atmospheric Lead(Pb), Vanadium(V), Manganese(Mn), Nickel(Ni), Chromium(Cr), Cadmium(Cd), Copper(Cu), Zinc(Zn) and Arsenic(As) were characterized in China. The emission characteristics and sources of atmospheric heavy metals and As in China were reviewed. Coal burning, iron and steel industry and vehicle emission are important sources in China. Control policies and effects in China were reviewed including emission standards, ambient air quality standards, phase out of leaded gasoline and so on, and further works for atmospheric heavy metals control were suggested. The comprehensive heavy metals pollution control measures and suggestions were put forward based on the summarization of the development and experience of the atmospheric heavy metal pollution control abroad.
Keywords: Emission standards; Source apportionment; Environmental management; Health risk; Control technology;
Complexation of trace metals in size-segregated aerosol particles at nine sites in Germany by Sebastian Scheinhardt; Konrad Müller; Gerald Spindler; Hartmut Herrmann (102-109).
The complexation of trace metal ions (TMI) was studied in size-segregated ambient aerosol particles collected at nine sites in Germany (urban, rural and coastal). Samples were analysed in terms of TMI (Fe, Mn, Cu), potential inorganic and organic ligands and pH. Using a thermodynamic model (E-AIM III), the concentrations of these compounds in the particle liquid phase were estimated. The resulting liquid phase concentrations were then used as input parameters for a speciation model (Visual MINTEQ) and the equilibrium complexation was calculated under realistic conditions. The complexation was found to be controlled by the availability of strong organic ligands, especially oxalate, whose occurrence in turn was governed by the formation of insoluble Ca-oxalate. Likewise, the pH influenced oxalate availability because it alters the concentrations of the chelating mono- and dianions. As a qualitative result, Fe3+ was found to be mainly complexed by oxalate, while Fe2+ and Mn2+ were rather associated with nitrate. Cu2+ showed mixed organic and nitrate complexation. Complexation by HULIS was only significant for Fe3+ and Cu2+ and was generally less important than other ligands like oxalate and nitrate. Oxalate was found to exist mainly in the solid phase while higher dicarboxylic acids mostly did not form complexes due to protonation. Complexation was shown to be influenced by season, air mass origin, particle size and sampling site.
Keywords: Trace metals; Particulate matter; Organic acids; Complexes; Speciation; Germany;
New Directions: Ash dieback and British carbon stocks by Dave S. Reay (110-111).
Conditional extraction of air-pollutant source signals from air-quality monitoring by Andrew R. Malby; J. Duncan Whyatt; Roger J. Timmis (112-122).
Ambient air-quality data contain information about air-pollution sources that is currently under-exploited. This information could be used to assess trends in the emissions performance of specific sources, and to check at an early stage if policies or controls to reduce air-quality impacts from particular sources are working. Previous techniques for extracting such information have tended to adopt complex analyses and to rely on data from monitoring networks with many sites, thus limiting their applicability to non-specialist users and to networks with few sites. This paper describes simple techniques for ‘conditionally’ selecting data from one or two monitors, and for analysing and interpreting concentrations in terms of source performance or policy progress. Our techniques minimise the effects of variations in meteorology and source activity, so that the selected data give a more consistent indication of individual source performance. We demonstrate our techniques with a case study, in which we track the source performance of road traffic on the M4 motorway in London and show how impacts per vehicle have changed over time under different conditions of traffic flow and fleet composition.
Keywords: Conditional analysis; Signal detection; Source performance; Ambient trends; Vehicle emissions;
Impacts of geostationary satellite measurements on CO forecasting: An observing system simulation experiment with GEOS-Chem/LETKF data assimilation system by Keiya Yumimoto (123-133).
We developed a chemical data assimilation system based on the GEOS-Chem global chemical transport model (CTM) and an ensemble-based data assimilation method, and performed an observing system simulation experiment (OSSE) to evaluate the impact of geostationary (GEO) satellite data obtained with a multi-spectral (thermal infrared (TIR) and near infrared (NIR)) sensor on air quality forecasting in East Asia.Initial conditions determined by assimilation of the three observation sets improved the forecasting of trans-boundary CO outflow. The performance of GEO satellite with TIR sensor (GEO-TIR) was better than that of LEO satellite with TIR sensor (LEO-TIR). However, in Seoul district (the Korean Peninsula) and Northern Kyushu (western Japan), the positive impact of the wider coverage and higher frequency of GEO disappeared when the forecast time was longer than 48 h. GEO satellite with NIR and TIR sensor (GEO-NIR + TIR) improved the forecast most, reducing the root mean square difference (RMSD), normalized mean bias, and normalized mean difference by more than 20% even for a forecast time longer than 48 h.Using the LEO-TIR result as a benchmark, we evaluated the ability of GEO-NIR + TIR to improve the forecast. The 60-h CO forecasting performances of GEO-TIR and GEO-NIR + TIR were about 30% and 120% better, respectively, than that of LEO-TIR. The wider coverage and higher frequency of GEO therefore improved the RMSD by 30%, and the higher sensitivity in the lower troposphere of NIR + TIR improved it by an additional 90%. Thus, the higher sensitivity in the lower troposphere of NIR + TIR as well as the wider coverage and higher frequency of GEO had a notably positive impact on the forecasting of trans-boundary pollutants over East Asia.
Keywords: Data assimilation; Chemical transport model; Ensemble Kalman filter; Observing system simulation experiment; Geostationary satellite; East Asia;
Short-term variability of mineral dust, metals and carbon emission from road dust resuspension by Fulvio Amato; Martijn Schaap; Hugo A.C. Denier van der Gon; Marco Pandolfi; Andrés Alastuey; Menno Keuken; Xavier Querol (134-140).
Particulate matter (PM) pollution in cities has severe impact on morbidity and mortality of their population. In these cities, road dust resuspension contributes largely to PM and airborne heavy metals concentrations. However, the short-term variation of emission through resuspension is not well described in the air quality models, hampering a reliable description of air pollution and related health effects. In this study we experimentally show that the emission strength of resuspension varies widely among road dust components/sources. Our results offer the first experimental evidence of different emission rates for mineral dust, heavy metals and carbon fractions due to traffic-induced resuspension. Also, the same component (or source) recovers differently in a road in Barcelona (Spain) and a road in Utrecht (The Netherlands). This finding has important implications on atmospheric pollution modelling, mostly for mineral dust, heavy metals and carbon species. After rain events, recoveries were generally faster in Barcelona rather than in Utrecht. The largest difference was found for the mineral dust (Al, Si, Ca). Tyre wear particles (organic carbon and zinc) recovered faster than other road dust particles in both cities. The source apportionment of road dust mass provides useful information for air quality management.
Keywords: Brake; Tyre; Wear; Recovery; Precipitation; Climate; Sources; Modelling; PM;
Locating and quantifying gas emission sources using remotely obtained concentration data by Bill Hirst; Philip Jonathan; Fernando González del Cueto; David Randell; Oliver Kosut (141-158).
We describe a method for detecting, locating and quantifying sources of gas emissions to the atmosphere using remotely obtained gas concentration data; the method is applicable to gases of environmental concern. We demonstrate its performance using methane data collected from aircraft. Atmospheric point concentration measurements are modelled as the sum of a spatially and temporally smooth atmospheric background concentration, augmented by concentrations due to local sources. We model source emission rates with a Gaussian mixture model and use a Markov random field to represent the atmospheric background concentration component of the measurements. A Gaussian plume atmospheric eddy dispersion model represents gas dispersion between sources and measurement locations. Initial point estimates of background concentrations and source emission rates are obtained using mixed ℓ 2 − ℓ 1 optimisation over a discretised grid of potential source locations. Subsequent reversible jump Markov chain Monte Carlo inference provides estimated values and uncertainties for the number, emission rates and locations of sources unconstrained by a grid. Source area, atmospheric background concentrations and other model parameters, including plume model spreading and Lagrangian turbulence time scale, are also estimated. We investigate the performance of the approach first using a synthetic problem, then apply the method to real airborne data from a 1600 km2 area containing two landfills, then a 225 km2 area containing a gas flare stack.
Keywords: Remote sensing; Gaseous emissions; Atmospheric background gas; Bayesian inversion; Gaussian mixture model; Random field modelling; Reversible jump MCMC;
The assessment of the impact of aviation NOx on ozone and other radiative forcing responses – The importance of representing cruise altitudes accurately by A. Skowron; D.S. Lee; R.R. De León (159-168).
Aviation emissions of NOx result in the formation of tropospheric ozone (warming) and destruction of a small amount of methane (cooling), positive and negative radiative forcing effects. In addition, the reduction of methane results in a small long-term reduction in tropospheric ozone (cooling) and, in addition, a long-term reduction in water vapour in the stratosphere (cooling) from reduced oxidation of methane, both negative radiative forcing impacts. Taking all these radiative effects together, aircraft NOx is still thought to result in a positive (warming) radiative effect under constant emissions assumptions. Previously, comparative modelling studies have focussed on the variability between models, using the same emissions database. In this study, we rather quantify the variability and uncertainty arising from different estimations of present-day aircraft NOx emissions. Six different aircraft NOx emissions inventories were used in the global chemical transport model, MOZART v3. The inventories were normalized to give the same global emission of NOx in order to remove one element of uncertainty. Emissions differed in the normalized cases by 23% at cruise altitudes (283–200 hPa, where the bulk of emission occurs, globally). However, the resultant short-term ozone chemical perturbation varied by 15% between the different inventories. Once all the effects that give rise to positive and negative radiative impacts were accounted for, the variability of net radiative forcing impacts was 94%. Using these radiative effects to formulate a net aviation NOx Global Warming Potential (GWP) for a 100-year time horizon resulted in GWPs ranging from 60 to 4, over an order of magnitude. It is concluded that the detailed placement of emissions at chemically sensitive cruise altitudes strongly affects the assessment of the total radiative impact, introducing a hitherto previously unidentified large fraction of the uncertainty of impacts between different modelling assessments. It is recommended that future formulations of aircraft NOx emissions focus efforts on the detailed and accurate placement of emissions at cruise altitudes to reduce the uncertainty in future assessments of aviation NOx impacts.
Keywords: Aviation; Radiative forcing; Emissions; Nitrogen oxides; Ozone response;
The contribution of fossil sources to the organic aerosol in the Netherlands by U. Dusek; H.M. ten Brink; H.A.J. Meijer; G. Kos; D. Mrozek; T. Röckmann; R. Holzinger; E.P. Weijers (169-176).
We measured the radiocarbon (14C) content of organic carbon (OC) samples from two locations in the Netherlands, the urban location of Amsterdam and the coastal location of Petten. PM10 samples were collected in Amsterdam and total suspended particles were collected in Petten using high volume samplers. The 14C/12C fraction in the samples is reported as fraction modern (F14C). It can be used to roughly estimate the contribution of fossil sources to OC, since F14C of fossil fuels is 0, whereas biogenic and wood burning sources are characterized by F14C values close to 1. At the coastal location organic carbon has higher F14C values (0.83 ± 0.04 standard uncertainty) than at the urban location (0.68 ± 0.05). A fraction modern of 0.68 is in the range of F14C values published for OC of other European urban areas (0.68–0.81). The coastal F14C of 0.83 agrees well with measurements at the coastal location of Mace Head, even though in Mace Head measurements were made on particles smaller than 1.5 μm (PM1.5). A F14C of 0.83 is on the lower end of F14C(OC) values estimated for continental background sites in Europe. Fossil sources might be contributing slightly more to organic carbon in the Netherlands than in other European regions. However, a bigger data set is needed to substantiate this finding. On average, fossil fuel combustion is responsible for approximately 40% of the organic carbon in Amsterdam and approximately 20% at the coastal location. At the coastal location, F14C was clearly lower than average when polluted air masses reached the measurement site, whereas in the urban area, air mass history did not have a strong influence on F14C.
Keywords: Organic aerosol; Radiocarbon; Fossil carbon; Source apportionment;
Characteristics of fire-generated gas emission observed during a large peatland fire in 2009 at Kalimantan, Indonesia by Yohei Hamada; Untung Darung; Suwido H. Limin; Ryusuke Hatano (177-181).
To investigate the characteristics of gas emissions from a tropical peatland fire, ground-level measurement of fire-generated gases was conducted during a large fire event in Kalimantan, Indonesia in 2009. Concentrations of CO and CH4 showed positive linear correlations with that of CO2. The relationship between concentrations of N2O and CO2 were divided into two parts, suggesting the influence of additional N2O generation during sample storage. The CO2-normalized emission ratio was calculated for CO, CH4, and N2O. The molar ratio of these fire-generated gas emissions was summarized as CO2:CO:CH4:N2O = 1.00:0.382:0.0261:0.000156, whereas the emission ratio calculated on the global warming potential (GWP) basis was CO2:CH4:N2O = 1.00:0.237:0.0465. The GWP emission based on this ratio was 87.8–91.2% of a simple evaluation in which all carbon was assumed to be emitted as CO2. This is the first trial to evaluate the emission ratios of major greenhouse gases on the basis of ground-level observation during an actual tropical peatland fire.
Keywords: Biomass burning; Emission ratio; Fire-generated gas emission; Global warming potential; Indonesia; Tropical peatland;
Assessment of heavy metal contamination of dustfall in northern China from integrated chemical and magnetic investigation by Qingqing Qiao; Baochun Huang; Chunxia Zhang; John D.A. Piper; Yuepeng Pan; Ying Sun (182-193).
Magnetic phases are a common component of dustfall samples and mineral magnetic studies have been increasingly exploited for air quality studies in recent years to assess the source and spatial-temporal distribution of anthropogenic magnetic particulates and associated heavy metals. Here we report a comparative study of magnetic and chemical properties of atmospheric particulate deposits from rural areas of Inner Mongolia and urban regions of Hebei and Beijing. The sample sets were collected at 13 monitoring stations by the gravimetric method between April 2009 and March 2010. At the rural sites paramagnetic clays, complemented by hematite and goethite recognized by Isothermal Remanent Magnetism (IRM) and Diffuse Reflectance Spectra (DRS) investigations, accompany fine grained magnetite as an important fraction. Although present as a residual phase in samples from the urban regions, coarse-grained magnetite of anthropogenic origin dominants the magnetic signatures in these latter environments. Systematic variations with local anthropogenic activity including traffic, the mining of ores and a range of industrial emissions are identified, together with a seasonal signature in the Beijing area. We use correlations between magnetic concentration-related parameters, notably magnetic susceptibility, and the Pollution Load Index to demonstrate how magnetic parameters can be used as a practical tool for mapping degrees of heavy metal pollution and tracing the sources of pollutants in dustfall samples.
Keywords: Environmental magnetism; Dustfall; Heavy metals; Anthropogenic activities; Northern China;
Additive impacts on particle emissions from heating low emitting cooking oils by M. Amouei Torkmahalleh; Y. Zhao; P.K. Hopke; A. Rossner; A.R. Ferro (194-198).
The effect of five additives, including table salt, sea salt, black pepper, garlic powder, and turmeric, on the emission of PM2.5 and ultrafine particles (UFP) from heated cooking oil (200 °C) were studied. One hundred milligrams of the additives were added individually to either canola or soybean oil without stirring. Black pepper, table salt, and sea salt reduced the PM2.5 emission of canola oil by 86% (p < 0.001), 88% (p < 0.001), and 91% (p < 0.001), respectively. Black pepper, table salt, and sea salt also decreased the total particle number emissions of canola oil by 45% (p = 0.003), 52% (p = 0.001), and 53% (p < 0.001), respectively. Turmeric and garlic powder showed no changes in the PM2.5 and total number emissions of canola oil. Table salt and sea salt, decreased the level of PM2.5 emissions from soybean oil by 47% (p < 0.001) and 77% (p < 0.001), respectively. No differences in the PM2.5 emissions were observed when other additives were added to soybean oil. Black pepper, sea salt, and table salt reduced the total particle number emissions from the soybean oil by 51%, 61% and 68% (p < 0.001), respectively. Turmeric and garlic powder had no effect on soybean oil with respect to total particle number emissions. Our results indicate that table salt, sea salt, and black pepper can be used to reduce the particle total number and PM2.5 emissions when cooking with oil.
Keywords: PM2.5; Indoor atmospheres; Cooking; Oil; Ultrafine particles;
Spatial and temporal variation of phthalic acid esters (PAEs) in atmospheric PM10 and PM2.5 and the influence of ambient temperature in Tianjin, China by Shaofei Kong; Yaqin Ji; Lingling Liu; Li Chen; Xueyan Zhao; Jiajun Wang; Zhipeng Bai; Zengrong Sun (199-208).
Phthalic acid esters (PAEs) are produced in large amounts throughout the world and are excessively used in various industries, which have posed a serious threat to human health and the environment. An investigation of six major PAEs congeners in atmospheric PM10 and PM2.5 was synchronously conducted at seven sites belonging to different functional zones in spring, summer and winter in Tianjin, China in 2010. Results showed that the average concentrations of DMP, DEP, DBP, BBP, DEHP and DOP in PM10 were 0.88, 0.73, 12.90, 0.15, 98.29 and 0.83 ng m−3, respectively, and in PM2.5, they were 0.54, 0.30, 8.72, 0.08, 75.68 and 0.33 ng m-3, respectively. DEHP and DBP were the predominant species. The industrial site exhibited highest PAEs values as 135.9 ± 202.8 ng m−3. In winter, the detected percentages for DOP were low. The other five PAEs concentrations were higher in winter than those in spring and summer, which may be related to the influence of emission sources, meteorological parameters and the chemical–physical characteristic of themselves. Except for DOP, other PAEs were negatively correlated with ambient temperature and the relationships were the best fitted as exponential forms. Significant positive correlations were found for PAEs in PM2.5 and PM10, indicating common sources. The PM2.5/PM10 ratios (0.53–0.70) for the six PAEs concentrations suggested that they were preferentially concentrated in finer particles. Principal component analysis indicated the emission from cosmetics and personal care products, plasticizers and sewage and industrial wastewater may be important sources for PAEs in atmospheric particulate matter in Tianjin.
Keywords: Phthalate acid esters; PM10; PM2.5; Distribution; Sources; Temperature;
An evaluation of atmospheric Nr pollution and deposition in North China after the Beijing Olympics by X.S. Luo; P. Liu; A.H. Tang; J.Y. Liu; X.Y. Zong; Q. Zhang; C.L. Kou; L.J. Zhang; D. Fowler; A. Fangmeier; P. Christie; F.S. Zhang; X.J. Liu (209-216).
North China is known for its large population densities and rapid development of industry and agriculture. Air quality around Beijing improved substantially during the 2008 Summer Olympics. We measured atmospheric concentrations of various Nr compounds at three urban sites and three rural sites in North China from 2010 to 2012 and estimated N dry and wet deposition by inferential models and the rain gauge method to determine current air conditions with respect to reactive nitrogen (Nr) compounds and nitrogen (N) deposition in Beijing and the surrounding area. NH3, NO2, and HNO3 and particulate NH4 + and NO3 −, and NH4 +–N and NO3 −–N in precipitation averaged 8.2, 11.5, 1.6, 8.2 and 4.6 μg N m−3, and 2.9 and 1.9 mg N L−1, respectively, with large seasonal and spatial variability. Atmospheric Nr (especially oxidized N) concentrations were highest at urban sites. Dry deposition of Nr ranged from 35.2 to 60.0 kg N ha−1 yr−1, with wet deposition of Nr of 16.3 to 43.2 kg N ha−1 yr−1 and total deposition of 54.4–103.2 kg N ha−1 yr−1. The rates of Nr dry and wet deposition were 36.4 and 33.2% higher, respectively, at the urban sites than at the rural sites. These high levels reflect the occurrence of a wide range of Nr pollution in North China and suggest that further strict air pollution control measures are required.
Keywords: Air pollution; Reactive N; Dry and wet deposition; Inferential method;
Are coarse particles unexpected common reservoirs for some atmospheric anthropogenic trace elements? A case study by Mickaël Catinon; Sophie Ayrault; Omar Boudouma; Louise Bordier; Gregory Agnello; Stéphane Reynaud; Michel Tissut (217-226).
Without specific experimental equipment, it is very difficult to sample long-term atmospheric deposits on a pure state. That is why the composition of air-transferred solid material accumulated for 40 years in the 2 m-high walls, pierced with numerous holes of an outdoor public shelter, Grenoble city, France, was studied. An appropriate fractionation procedure allowed to obtain several fractions which were i) a sand fraction (8.3%) (fraction A), ii) a large mass of organic matter corresponding mostly to large fragments (>250 μm) of plant origin (66.7%) (fraction B) or to pollen fraction C (0.4%), iii) a slowly depositing organo-clay fraction (20%) (fractions D1 and D2) and iv) a solution mixed with non-settable particles (4.3%) (fraction E). The composition of each fraction was determined for 20 elements. The sand fraction showed very high concentrations specifically in Cu, Pb and Fe corresponding respectively to 81.5, 48.2 and 35.2% of the samples content in these elements. In contrast, Cd and Zn were mainly accumulated in the fraction B (67.5 and 62.2%, respectively). The scanning electron microscopy coupled to energy dispersive X-ray analysis (SEM-EDX) study of the fraction A showed the presence of large particles bearing Pb and Fe, particles rich in Cu and typical fly ashes originating mostly from iron industry. Most of these particles had a crystalline shape suggesting that they were formed after emission at a high temperature. The Pb–Fe–Cu deposit seen in fraction A likely originates from the neighbouring road surface contaminated by car traffic for several decades. The 206Pb/207Pb ratio (1.146 ± 0.004) showed that in the coarse sandy fraction A, Pb was represented at 65% by non-gasoline lead and 35% by “gasoline” lead emitted before 1999. The fraction A particles can only be transported on a limited distance by high magnitude events. They constitute a large reservoir for Cu and Pb and may play a major role in the long-term contamination of urban soils.
Keywords: Air pollution; Pb isotopes; Urban; Coarse particles; SEM-EDX; ICP-MS;
Estimating spatio-temporal resolved PM10 aerosol mass concentrations using MODIS satellite data and land use regression over Lombardy, Italy by Francesco Nordio; Itai Kloog; Brent A. Coull; Alexandra Chudnovsky; Paolo Grillo; Pier Alberto Bertazzi; Andrea A. Baccarelli; Joel Schwartz (227-236).
Traditional air pollution epidemiology studies being conducted in large cities can be limited by the availability of monitoring. Satellite Aerosol Optical Depth (AOD) measurements offer the possibility of exposure estimates for the entire population. We previously demonstrated that daily calibration substantially increased the predictive power of satellite AOD measurements for fine particles (PM2.5) in New England, allowing estimation of exposure in locations without monitors. Similar results have not been reported for larger particles (PM10), which are often the only measures that can be used in locations worldwide that do not have comprehensive PM2.5 monitoring; this also applies to PM estimation of historical exposures. Here we extend this methodology by applying it to 2000–2009 PM10 data from Lombardy, Northern Italy a region with high altitude differences, frequent temperature inversions and stationary fronts. Specifically, by 1) incorporating a model for missing AOD data to deal with non-randomness in the missing data; and 2) modeling interactions between land use and meteorological parameters to better capture space–time interactions. We calibrated AOD data through mixed-effect models regressing PM10 measurements using day-specific random intercepts, and fixed and random AOD and temperature slopes. We used inverse-probability weighting to account for nonrandom AOD missingness, while reducing the dimensionality of spatial and temporal predictors and avoiding selecting different predictors in different locations, as common in land-use regression. We take advantage of associations of grid-cell AOD values with PM10 monitoring located elsewhere and with AOD values in neighboring grid cells to develop grid-cell predictions when AOD is missing. By using ten-fold cross-validation to test the accuracy of our predictions, we found high out-of-sample R 2 (R 2 = 0.787, year to year variation 0.738–0.818) for days with available AOD data. Even in days with no available AOD, our model performance was comparable (R 2 = 0.787, year to year variation 0.736–0.841). Our results demonstrate that PM10 can be reliably predicted using this AOD-based prediction model, even in a geographical area with complex geographic and weather patterns.
Keywords: Air pollution; Aerosol Optical Depth (AOD); Epidemiology; PM10; Exposure error;
Modeling temporal and spatial variability of traffic-related air pollution: Hourly land use regression models for black carbon by Evi Dons; Martine Van Poppel; Bruno Kochan; Geert Wets; Luc Int Panis (237-246).
Land use regression (LUR) modeling is a statistical technique used to determine exposure to air pollutants in epidemiological studies. Time-activity diaries can be combined with LUR models, enabling detailed exposure estimation and limiting exposure misclassification, both in shorter and longer time lags.In this study, the traffic related air pollutant black carbon was measured with μ-aethalometers on a 5-min time base at 63 locations in Flanders, Belgium. The measurements show that hourly concentrations vary between different locations, but also over the day. Furthermore the diurnal pattern is different for street and background locations. This suggests that annual LUR models are not sufficient to capture all the variation. Hourly LUR models for black carbon are developed using different strategies: by means of dummy variables, with dynamic dependent variables and/or with dynamic and static independent variables.The LUR model with 48 dummies (weekday hours and weekend hours) performs not as good as the annual model (explained variance of 0.44 compared to 0.77 in the annual model). The dataset with hourly concentrations of black carbon can be used to recalibrate the annual model, resulting in many of the original explaining variables losing their statistical significance, and certain variables having the wrong direction of effect. Building new independent hourly models, with static or dynamic covariates, is proposed as the best solution to solve these issues. R 2 values for hourly LUR models are mostly smaller than the R 2 of the annual model, ranging from 0.07 to 0.8. Between 6 a.m. and 10 p.m. on weekdays the R 2 approximates the annual model R 2. Even though models of consecutive hours are developed independently, similar variables turn out to be significant. Using dynamic covariates instead of static covariates, i.e. hourly traffic intensities and hourly population densities, did not significantly improve the models' performance.
Keywords: Black carbon; Land use regression; Temporal variation; Air pollution; Belgium;
Impact of aircraft plume dynamics on airport local air quality by Steven R.H. Barrett; Rex E. Britter; Ian A. Waitz (247-258).
Air quality degradation in the locality of airports poses a public health hazard. The ability to quantitatively predict the air quality impacts of airport operations is of importance for assessing the air quality and public health impacts of airports today, of future developments, and for evaluating approaches for mitigating these impacts. However, studies such as the Project for the Sustainable Development of Heathrow have highlighted shortcomings in understanding of aircraft plume dispersion. Further, if national or international aviation environmental policies are to be assessed, a computationally efficient method of modeling aircraft plume dispersion is needed. To address these needs, we describe the formulation and validation of a three-dimensional integral plume model appropriate for modeling aircraft exhaust plumes at airports. We also develop a simplified concentration correction factor approach to efficiently account for dispersion processes particular to aircraft plumes. The model is used to explain monitoring station results in the London Heathrow area showing that pollutant concentrations are approximately constant over wind speeds of 3–12 m s−1, and is applied to reproduce empirically derived relationships between engine types and peak NO x concentrations at Heathrow. We calculated that not accounting for aircraft plume dynamics would result in a factor of 1.36–2.3 over-prediction of the mean NO x concentration (depending on location), consistent with empirical evidence of a factor of 1.7 over-prediction. Concentration correction factors are also calculated for aircraft takeoff, landing and taxi emissions, providing an efficient way to account for aircraft plume effects in atmospheric dispersion models.
Keywords: Jets; Plumes; Airports; Dispersion modeling; Buoyancy;
Understanding of the formation mechanisms of ozone and particulate matter at a fine scale over the southeastern U.S.: Process analyses and responses to future-year emissions by Xiao-Huan Liu; Yang Zhang (259-276).
Ozone (O3) and fine particle (PM2.5) formation over the southeastern U.S. are of a major concern due to high emissions of precursors and special weather conditions that are conducive to their formation. In this study, the Community Multiscale Air Quality (CMAQ) modeling system is applied to simulate the formation of major air pollutants over an area in the southeastern U.S. at a 4-km horizontal grid resolution for January, April, July, and October in 2002 and 2018. Model performance evaluation shows an overall satisfactory performance for O3 in all months and for PM2.5 in January and October at rural sites and in January, April, and October at urban sites. Large underpredictions in PM2.5 concentrations occur in April and July at rural sites and in July at urban sites, because of biases in meteorological predictions and underestimation of emissions of precursors. The model performance at 4-km in terms of O3, PM2.5 and PM2.5 components show some improvements but overall are not always better than that at 12-km. O3 chemistry is VOC-limited in urban areas and NO x -limited over the west of the mountain regions and the southern Georgia throughout the year, and VOC-limited over the rest of areas in January but NO x -limited in other months. Among all photochemical indicators examined, PH2O2/PHNO3 and O3/NO y are the most robust indicators. The domain is NH3-rich or neutral in all months, indicating a high potential for NH4NO3 formation and the sensitivity of PM2.5 formation to the emissions of SO2, NO x , and NH3. Surface O3 is accumulated primarily through vertical transport in urban, rural and coastal areas and both horizontal and vertical transport in mountain regions and produced via gas-phase chemistry at non-urban sites during daytime. The loss of O3 is attributed to gas-phase chemistry via NO titration in urban areas, and dry deposition and transport processes in rural and mountain areas. PM2.5 is produced by primary emissions and PM processes and lost through vertical and horizontal transport in urban areas. The combined effects of transport, emissions, and PM processes influence PM concentrations in other areas. The 2018 simulations project a decrease in PM2.5 concentrations and an improvement in visibility over almost the entire domain, slight decreases in O3 mixing ratios in urban areas in July and most non-urban areas in April and October but large increases in the rest of areas in other months, and a decrease in total N deposition fluxes in most areas except for central and eastern North Carolina and northern Georgia. The development of integrated emission control strategies should consider region-specific seasonality and differences in the responses of O3, PM2.5, visibility, and nitrogen deposition.
Keywords: CMAQ; O3; PM2.5; Process analysis; Chemical regime indicators; Future-year air quality;
A novel assessment of odor sources using instrumental analysis combined with resident monitoring records for an industrial area in Korea by Hyung-Don Lee; Soo-Bin Jeon; Won-Joon Choi; Sang-Sup Lee; Min-Ho Lee; Kwang-Joong Oh (277-290).
The residents living nearby the Sa-sang industrial area (SSIA) continuously were damaged by odorous pollution since 1990s. We determined the concentrations of reduced sulfur compounds (RSCs) [hydrogen sulfide (H2S), methyl mercaptan (CH3SH), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS)], nitrogenous compounds (NCs) [ammonia (NH3) and trimethylamine (TMA)], and carbonyl compounds (CCs) [acetaldehyde and butyraldehyde] by instrumental analysis in the SSIA in Busan, Korea from Jun to Nov, 2011. We determined odor intensity (OI) based on the concentrations of the odorants and resident monitoring records (RMR). The mean concentration of H2S was 10-times higher than NCs, CCs and the other RSC. The contribution from RSCs to the OI was over 50% at all sites excluding the A-5 (chemical production) site. In particular, A-4 (food production) site showed more than 8-times higher the sum of odor activity value (SOAV) than the other sites. This suggested that the A-4 site was the most malodorous area in the SSIA. From the RMR analysis, the annoyance degree (OI ≥ 2) was 51.9% in the industrial area. The ‘Rotten’ smell arising from the RSCs showed the highest frequency (25.3%) while ‘Burned’ and ‘Other’ were more frequent than ‘Rotten’ in the residential area. The correlation between odor index calculated by instrumental analysis and OI from the RMR was analyzed. The Pearson correlation coefficient (r) of the SOAV was the highest at 0.720 (P < 0.05), and overall results of coefficient showed a moderately high correlation distribution range (from 0.465 to 0.720). Therefore, the overall results of this research confirm that H2S emitted from A-4 site including food production causes significant annoyance in the SSIA. We also confirm RMR data can be used effectively to evaluate the characteristic of odorants emitted from the SSIA.
Keywords: Reduced sulfur compounds; Resident monitoring records; Odor intensity; Odor activity value; Pearson correlation coefficient;
Temporal variation in airborne microbial populations and microbially-derived allergens in a tropical urban landscape by Anthony C. Woo; Manreetpal S. Brar; Yuki Chan; Maggie C.Y. Lau; Frederick C.C. Leung; James A. Scott; Lilian L.P. Vrijmoed; Peyman Zawar-Reza; Stephen B. Pointing (291-300).
The microbial component of outdoor aerosols was assessed along a gradient of urban development from inner-city to rural in the seasonal-tropical metropolis of Hong Kong. Sampling over a continuous one-year period was conducted, with molecular analyses to characterize bacterial and eukaryal microbial populations, immuno-assays to detect microbially-derived allergens and extensive environmental and meteorological observations. The data revealed bio-aerosol populations were not significantly impacted by the level of urban development as measured by anthropogenic pollutants and human population levels, but instead exhibited a strong seasonal trend related to general climatic variables. We applied back-trajectory analysis to establish sources of air masses and this allowed further explanation of urban bio-aerosols largely in terms of summer-marine and winter-continental origins. We also evaluated bio-aerosols for the potential to detect human health threats. Many samples supported bacterial and fungal phylotypes indicative of known pathogenic taxa, together with common indicators of human presence. The occurrence of allergenic endotoxins and beta-glucans generally tracked trends in microbial populations, with levels known to induce symptoms detected during summer months when microbial loading was higher. This strengthens calls for bio-aerosols to be considered in future risk assessments and surveillance of air quality, along with existing chemical and particulate indices.
Keywords: Airborne microorganisms; Bio-aerosols; Bacteria; Fungi; Urban aerosol;
Variations of carbonaceous aerosols from open crop residue burning with transport and its implication to estimate their lifetimes by X.L. Pan; Y. Kanaya; Z.F. Wang; Y. Komazaki; F. Taketani; H. Akimoto; P. Pochanart (301-310).
Studying the correlations of carbonaceous aerosols (element carbon, EC, and organic carbon, OC) from open biomass burning helps to reduce uncertainties in emission inventories and provides necessary constraints for model simulations. In the present study, we measured apparent elemental carbon (ECa) and OC concentrations at the summit of Mount Tai (Mt. Tai) during intensive open crop residue burning (OCRB) episodes using a Sunset OCEC analyzer. In the fine particle mode, OC and ECa showed strong correlations (r > 0.9) with carbon monoxide (CO). Footprint analysis using the FLEXPART_WRF model indicated that OCRB in Central East China had a significant influence on ambient carbonaceous aerosol loadings at the summit of Mt. Tai. During campaign, ΔECa/ΔCO ratios of OCRB plumes were found to be 14.3 ± 1.0 ng m−3 ppbv at Mt. Tai. This ratio was twice larger than those for urban pollution in CEC, demonstrating that significant emissions of soot particles emitted from OCRB. ΔOC/ΔCO ratio of OCRB plumes was found to be 41.9 ± 2.6 ng m−3 ppbv averagely. The transport time of smoke particles was estimated using the FLEXPART_WRF tracer model by releasing particles from the ground layer inside geographical regions where large numbers of hotspots were detected by the MODIS sensor. The relationship between transport time and observed ΔECa/ΔCO and ΔOC/ΔCO ratios was fitted by an e-folding exponential function. Results showed that the loss rate of OC (normalized by CO) with transport was much quicker than that of ECa mass, and the corresponding lifetime of OC mass was estimated to be 28.0–44.2 h (1.2–1.8 days), much shorter than that 98.4–136.9 h (4.1–5.7 days) of ECa. Lifetime of ECa estimated for the OCRB events in CEC in the study was comparably lower than the values normally calculated by the transport models. Short lifetime of OC highlighted its vulnerability to cloud scavenging in the presence of water-soluble organic species from biomass combustion.
Keywords: Black carbon; Lifetime; Open crop residue burning; Mount Tai experiment 2006 (MTX2006);
Air quality comparison between two European ceramic tile clusters by M.C. Minguillón; E. Monfort; A. Escrig; I. Celades; L. Guerra; G. Busani; A. Sterni; X. Querol (311-319).
The European ceramic tile industry is mostly concentrated in two clusters, one in Castelló (Spain) and another one in Modena (Italy). Industrial clusters may have problems to accomplish the EU air quality regulations because of the concentration of some specific pollutants and, hence, the feasibility of the industrial clusters can be jeopardised. The present work assesses the air quality in these ceramic clusters in 2008, when the new EU emission regulations where put into force. PM10 samples were collected at two sampling sites in the Modena ceramic cluster and one sampling site in the Castelló ceramic cluster.PM10 annual average concentrations were 12–14 μg m−3 higher in Modena than in Castelló, and were close to or exceeded the European limit. Air quality in Modena was mainly influenced by road traffic and, in a lower degree, the metalmechanical industry, as evidenced by the high concentrations of Mn, Cu, Zn, Sn and Sb registered. The stagnant weather conditions from Modena hindering dispersion of pollutants also contributed to the relatively high pollution levels. In Castelló, the influence of the ceramic industry is evidenced by the high concentrations of Ti, Se, Tl and Pb, whereas this influence is not seen in Modena. The difference in the impact of the ceramic industry on the air quality in the two areas was attributed to: better abatement systems in the spray-drier facilities in Modena, higher coverage of the areas for storage and handling of dusty raw materials in Modena, presence of two open air quarries in the Castelló region, low degree of abatement systems in the ceramic tile kilns in Castelló, and abundance of ceramic frit, glaze and pigment manufacture in Castelló as opposed to scarce manufacture of these products in Modena. The necessity of additional measures to fulfil the EU air quality requirements in the Modena region is evidenced, despite the high degree of environmental measures implemented in the ceramic industry.The Principal Component Analysis (PCA) identified four factors in Modena, attributed to: road traffic + metalmechanical industry, mineral, ceramic, and background; and three factors in Castelló, attributed to: mineral, ceramic (with influence of road traffic) and regional background. The additional measures to improve the air quality should be focused mainly on road traffic in Modena, and on the ceramic industry in Castelló.
Keywords: Ceramic industry; PM; Metals; Cluster; Road traffic;
Shipping emissions associated with increased cardiovascular hospitalizations by Linwei Tian; Kin-fai Ho; Peter K.K. Louie; Hong Qiu; Vivian C. Pun; Haidong Kan; Ignatius T.S. Yu; Tze Wai Wong (320-325).
Previous studies have suggested nickel (Ni) and vanadium (V) as the likely constituents that are partially responsible for health effects associated with particulate matter pollution. The authors aimed to examine the effects of Ni and V in PM10, the indices of shipping emissions, on emergency hospitalizations for cardiovascular diseases (CVD) in Hong Kong. Daily PM10 speciation data across six monitoring stations in Hong Kong during 1998–2007 were collected. Generalized additive Poisson models with single-day lags were used to estimate the excess risks of emergency hospital admissions for CVD associated with Ni and V, after adjusted for major PM10 chemical species and criteria gaseous pollutants. The excess risks for inter-quartile range (IQR) increases of Ni and V on the same day and previous six days (lag0 ∼ lag6) were estimated. Ni in PM10 was associated with a 1.25% (95%CI: 0.81–1.68%) increase of total emergency CVD admissions on the same day, while lag0 V was associated with a 0.95% (95%CI: 0.55–1.35%) elevated CVD admissions. The associations were not sensitive to the further adjustment for co-pollutants. Ni appeared to correspond better than V to cardiovascular health. Controlling shipping emissions from residual oil combustion in the port cities like Hong Kong is particularly important.Display Omitted
Keywords: Cardiovascular disease; Emergency hospital admission; Nickel; Particulate matter; Shipping emission; Vanadium;
Particle number emission factors for an urban highway tunnel by Jessica L. Perkins; Luz T. Padró-Martínez; John L. Durant (326-337).
Exposure to traffic-related air pollution has been linked to increased risks of cardiopulmonary disease, asthma, and reduced lung function. Ultrafine particles (UFP; aerodynamic diameter < 100 nm), one component of traffic exhaust, may contribute to these risks. This paper describes the development of UFP emission factors, an important input parameter for dispersion models used for exposure assessment. Measurements of particle number concentration (PNC), a proxy for UFP, were performed in the Central Artery Tunnel on Interstate-93 in Boston (MA, USA). The tunnel system consists of two, unidirectional bores, which each carry ∼9 × 104 vehicles per day (diesel vehicles comprise 2–5% of the fleet in the southbound tunnel and 1–3% in the northbound tunnel). A tunnel was chosen for study because it provided an enclosed environment where the effects of lateral and vertical dispersion by ambient air and photochemical reactions would be minimized. Data were collected using a mobile platform equipped with rapid-response instruments for measuring PNC (4–3000 nm) as well as NOx. Because Boston is located in a temperate region (latitude 42° N), we were interested in studying seasonal and diurnal differences in emission factors. To characterize seasonal differences, mobile monitoring was performed on 36 days spaced at 7–14 day intervals over one year (Sept. 2010–Sept. 2011); to characterize diurnal differences intensive mobile monitoring (n = 90 total trips through the tunnels) was performed over the course of two consecutive days in January 2012. All data collected during congested traffic conditions (∼7% of total data set) were removed from the analysis. The median PNC inside the two tunnels for all trips during the 12-month campaign was 3–4-fold higher than on I-93 immediately outside the tunnel and 7–10-fold higher than on I-93 4 km from the tunnel. The median particle number emission factors (EFPN) (±median absolute deviation) for the southbound and northbound tunnels were 5.1 × 1014 (2.3 × 1014) and 1.4 × 1014 (4.2 × 1013) particles vehicle−1 km−1, respectively. EFPN values were ∼2-fold higher in winter and spring (average ambient temperature at the time of monitoring = 6.9 °C) compared to summer and fall (12.9 °C), and ∼2-fold higher in the morning (−7.9 °C) compared to the afternoon/evening (−0.9 °C) on two consecutive winter days. Our results suggest that seasonal and diurnal variations in particulate emissions from highway vehicles may be important to consider in developing EFPN values.
Keywords: Traffic-related air pollution; Ultrafine particles; Roadway tunnel; Highway; Temporal variation; Mobile monitoring;
Use of beryllium-7 as a surrogate to determine the deposition of metal and polycyclic aromatic hydrocarbon through urban aerosols in Nantes, France by Stéphane Percot; Véronique Ruban; Pierre Roupsard; Denis Maro; Maurice Millet (338-345).
The aerodynamic size distribution of the natural radionuclide beryllium-7 (7Be) and associated trace metals, pesticides and polycyclic aromatic hydrocarbons (PAHs) in Nantes (France) was determined during 6 campaigns (conducted from June 2010 to March 2012) using a low-pressure impactor. The activity distribution of 7Be, as measured by a gamma ray spectrometer, was associated with the accumulation mode (with around 85% of the mass < 1 μm) and explained by post condensation processes on the airborne particle. The mass size distribution of heavy metals and PAHs was mainly focused on the accumulation mode as well. Trace metals generally show a unimodal distribution, although bimodal distributions for Zn, Cu, As and Cr could also be observed; these were attributed to re-suspension processes. For PAHs, the size distribution remained unimodal with a mass median diameter (MMD) ranging from 0.31 to 0.68 μm, thus confirming the urban origin. Pesticide concentrations in the atmosphere were low and did not allow determining the size distribution. Given their identical aerodynamic distribution as 7Be, trace metals and PAHs are expected to display a similar dry deposition velocity, which will then allow us to calculate the dry deposition fluxes over this urban area.
Keywords: Activity median aerodynamic diameter; 7Be; Heavy metals; PAHs; PM10; Urban aerosol;
Ensemble and enhanced PM10 concentration forecast model based on stepwise regression and wavelet analysis by Yuanyuan Chen; Runhe Shi; Shijie Shu; Wei Gao (346-359).
An ensemble and enhanced PM10 (particulate matter with a diameter less than 10 μm) concentration forecast model was established in eastern China based on data from 2005 to 2009. The enhanced model consists of a single stepwise regression forecast model and a combined forecast model based on wavelet decomposition and stepwise regression. Six individual forecast results were obtained with a combined model that can predict PM10 concentrations at multiple scales. By decomposing variables into detailed and approximated components in six scales and with the application of stepwise regression, the best-fitted forecast models were established in each component of the different scales. Then, the predicted results of the detail and approximation components were reconstructed in each scale as the enhanced prediction. A regional model was established for eastern China. The accuracy rate of each forecasted result by the regional model was calculated using testing data from 2010 based on the needs of operational forecasting. Precision evaluations were also performed. A comparatively higher accuracy was obtained by the combined model. The advantage of predicting the PM10 concentration with the combined model had wide spatial and temporal suitability. An enhanced forecast model was established for each city of eastern China with improvements, where all the predicted results in each city were evaluated by the accuracy rate and precision validation. In each city, the best-fitted model with the highest precision was selected and combined in an ensemble. The ensemble and enhanced forecast model had a significant improvement in accuracy rate and the highest precision of PM10 concentration forecasting in eastern China.
Keywords: PM10 concentration; Wavelet analysis; Stepwise regression; Enhanced model; Ensemble model;
Factors affecting the comparisons of planetary boundary layer height retrievals from CALIPSO, ECMWF and radiosondes over Thessaloniki, Greece by E. Leventidou; P. Zanis; D. Balis; E. Giannakaki; I. Pytharoulis; V. Amiridis (360-366).
The aim of this study is to propose an evaluation methodology of CALIPSO retrievals of the planetary boundary layer (PBL) height using the analyses of the operational early-delivery assimilation system of the European Centre for Medium-Range Weather Forecast (ECMWF) and Radiosonde observations. The investigation is performed over Thessaloniki, Greece, for a period of almost 5 years between 2006 and 2011. Low correlations between CALIPSO and ECMWF are found when CALIPSO aerosol classification scheme reveals dust presence over Thessaloniki. When eliminating cases of dust advection, the correlation between CALIPSO and ECMWF improves considerably, reaching a value of 0.82, while the correlation between CALIPSO and radiosondes reaches 0.74. The proposed methodology for evaluation shows a good potential for future work when more stations will be considered. Taking into account the aforementioned limitations due to the presence of advected dust layers for the Mediterranean site investigated here, the CALIPSO PBL height could be considered a valuable satellite product for investigating the atmospheric boundary layer processes and for evaluating global and regional atmospheric models.
Keywords: Planetary boundary layer; CALIPSO;
Influence of local air flow regimes on the ozone content of two Pyrenean valleys by A. Ezcurra; B. Benech; A. Echelecou; J.M. Santamaría; I. Herrero; E. Zulueta (367-377).
The Pyrenees Mountains, the natural border between France and Spain, have experienced a large increase in road traffic in the last decade. Due to this fact, a research program named PAP (Pollution Atmospheric in the Pyrenees) was established in 2004 by several laboratories from Spain and France to address the influence of meteorological regimes on the pollution levels of two adjacent valleys, Aspe valley (France) and Canfranc valley (Spain), situated in the center of the Pyrenean range. Pollution measurements show that mean ozone concentrations increase with height. In Sarrance, the site placed at the bottom of the valleys at 335 m above sea level (ASL), the mean ozone value was 23 ppb, whereas at the Pic Midi observatory (2877 m ASL), the top of the PAP network, the value found for mean ozone values was 52 ppb. A linear trend fits this altitudinal variation with a vertical gradient of 17 ppb km−1. The data demonstrate that the observatories located over 1400 m ASL do not show the classical mean daily ozone cycle, and that mean ozone concentrations throughout the day are nearly constant. By contrast, below 1400 m ASL, the classical mean daily ozone cycle is clear, reaching a maximum around noon. These findings indicate that the photochemical reactions are almost inactive at the elevated observatories and, as a result, it can be concluded that ozone levels at those locations are mostly caused by advection of aged air masses. Consequently, we could find that the gradient inside the valleys follows a linear trend of 29 ppb km−1. Finally, it has been observed that in north Foehn situations, intrusions of polluted air coming from the Free Troposphere (FT) can be detected in the upper part of the Spanish valley of Canfranc, where the mean daily ozone cycle changes significantly and becomes similar to the ones measured at the stations situated above 1400 m ASL. However, the results also pointed out that, except for the Foehn situations, the different local air flow regimes do not strongly affect the mean diurnal cycle of ozone and the mean ozone concentrations.
Keywords: Ozone; Mountain pollution; Mountain meteorology; Pyrenees;
Forest Filter Effect: Role of leaves in capturing/releasing air particulate matter and its associated PAHs by Elisa Terzaghi; Edward Wild; Gabriele Zacchello; Bruno E.L. Cerabolini; Kevin C. Jones; Antonio Di Guardo (378-384).
Plants play a key role in removing particulate matter and their associated Semi-volatile Organic Compounds (SVOCs) from the atmosphere. Understanding the processes involved in particle capture by vegetation is essential to understand the interactions between SVOCs, particles and plants. In the present study Two Photon Excitation Microscopy (TPEM) was used to visualise particle matter uptake and encapsulation, together with its distribution on leaf/needle surface of different broadleaf (cornel and maple) and conifer species (stone pine). Phenanthrene accumulation, the number of particles associated with this compound and its migration from particles into the leaf cuticle was also identified and quantified. Species-specific deposition velocities were estimated to model temporal PM10 leaf/needle accumulation and to investigate the role of Planet Boundary Layer (PBL) height variation in influencing PM10 flux to plants. Particles at the leaf/needle surface were visualised to range in size from 0.2 to 70.4 μm, but cuticular encapsulation was negligible for particles larger than 10.6 μm, which were removed by a washing procedure. Phenanthrene concentration varied between ≈5 and ≈10 ng g−1 dw according to plant species and between ≈10 and ≈200 ng g−1 dw depending on needle age; this compound was visualized to migrate from particles into the adjacent leaf cuticle. Species-specific deposition velocity range between 0.57 and 1.28 m h−1 and preliminary simulations showed that the diel variability of PBL structure influenced the temporal PM10 flux and leaf/needle concentration, e.g. during daytime hours characterized by high PBL height, PM10 accumulated on cornel leaves was about 65% lower than the amount accumulated during night time. The capability of vegetation to capture particles from the atmosphere, retain, encapsulate them into the cuticle and release them to soil and/or lower biomass, highlighted the value of vegetation in removing pollutants from the atmosphere and influencing their environmental fate.Display Omitted
Keywords: Forest Filter Effect; Particulate matter; SVOCs; TPEM; PBL height;
Impact of diffuse light on isoprene and monoterpene emissions from a mixed temperate forest by Q. Laffineur; M. Aubinet; N. Schoon; C. Amelynck; J.-F. Müller; J. Dewulf; K. Steppe; B. Heinesch (385-392).
This study investigated the impact of diffuse light on canopy scale emission of isoprene and monoterpenes measured continuously above a mixed temperate forest, using the disjunct eddy-covariance by mass scanning technique with a proton transfer reaction-mass spectrometer (PTR-MS) instrument. To assess this impact, the relationship between emissions/radiation and emissions/gross primary production (GPP) under clear sky and cloudy conditions were analysed.Under cloudy conditions (high proportion of diffuse radiation), the isoprene and monoterpene fluxes were enhanced compared to clear sky conditions (low proportion of diffuse radiation) at equivalent temperature and above-canopy total radiation. The whole-canopy enzymatic activity of the metabolic isoprene production pathway, however, was suggested to be lower under cloudy conditions than under clear sky conditions at equivalent temperature. The mechanisms behind these observations are probably linked to the better penetration of diffuse radiation in the canopy. Shade leaves/needles receive more radiation in cloudy conditions than in clear sky conditions, thereby inducing the observed effects.
Keywords: Forest ecosystems; Monoterpenes; Isoprene; Disjunct eddy-covariance; PTR-MS;
Investigating the impacts of anthropogenic and biogenic VOC emissions and elevated temperatures during the 2003 ozone episode in the UK by Jonathan Strong; J. Duncan Whyatt; Sarah E. Metcalfe; Richard G. Derwent; C. Nicholas Hewitt (393-401).
The Lagrangian tropospheric ozone model ELMO-v2 (Edinburgh Lancaster Model for Ozone) is applied to the intense 2003 ozone episode in SE England. When using model parameters representative of typical episodes, ELMO-v2 was found to underestimate ozone levels substantially during peak ozone days, but, by increasing three parameters (temperature, biogenic and anthropogenic VOC emission rates) to levels close to those observed, good agreement between modelled and observed ozone was achieved. Using attribution techniques possible with a Lagrangian model, the episode was divided into five phases with each exhibiting different geographical origins for ozone precursor emissions. Anthropogenic VOCs, primarily of European (non-UK) origin, made the biggest contribution to modelled ozone levels. European biogenic VOC emissions significantly contributed to ozone levels on some days, whereas the contribution from UK biogenic VOC emissions was comparatively small throughout. The VOC:NO x ratio was also shown to change during the episode, with high ozone days being less VOC-sensitive. The implications of both variable NO x /VOC sensitivity and the possibility of more frequent heatwaves due to climate change need to be taken into account in planning effective future emissions reductions to control ground-level ozone in the UK.
Keywords: ELMO; Lagrangian; Temperature; Source attribution; VOC:NO x ratio;
Ambient and personal PM2.5 exposure assessment in the Chinese megacity of Guangzhou by Heiko J. Jahn; Alexander Kraemer; Xiao-Cui Chen; Chuen-Yu Chan; Guenter Engling; Tony J. Ward (402-411).
Due to the rapid economic development and the associated increase of transportation, agricultural and industrial activities, the densely populated Pearl River Delta, China has significant problems with air pollution. With a population of almost 13 million residents, the megacity of Guangzhou is of particular interest with respect to environmental health due to its large population and numerous anthropogenic and industrial sources of fine airborne particulate matter (≤ 2.5 μm in aerodynamic diameter [PM2.5]).During the winter months of November and December 2011, extensive ambient PM2.5 monitoring was simultaneously conducted within nine of 12 districts of Guangzhou. In addition, personal PM2.5 monitoring was carried out within eight of the 12 districts to determine the levels of PM2.5 to which individuals were exposed to over 24-h periods.Results of the ambient monitoring showed average PM2.5 mass concentrations ranging from 52.4 ± 24.1 (SD, standard deviation) μg m−3 (Median: 53.7) in the Conghua District to 106.6 ± 31.7 μg m−3 (Median: 108.1) in the Yuexiu District. Results of the personal monitoring showed average concentrations ranging from 45.4 ± 21.2 μg m−3 (Median: 53.1) in the Conghua District to 92.5 ± 33.2 μg m−3 (Median: 102.4) in the Luogang District. Three of the districts showed moderate to high correlations between ambient and personal PM2.5 (Yuexiu: Spearman's Rho [r s] = 0.77, p = 0.072; Panyu: r s = 0.59, p = 0.033; Luogang: r s = 0.79, p = 0.021). Five of the seven districts had ambient PM2.5 concentrations higher than personal PM2.5 concentrations. An overall correlation analysis of all ambient and personal data shows a high and significant correlation (r s = 0.7, p = 0.01).This study revealed elevated PM2.5 mass concentrations throughout all of Guangzhou's districts, with ambient PM2.5 levels that consistently exceeded the 24-h standards of both the World Health Organization and the United States Environmental Protection Agency. Results from the PM2.5 personal monitoring program also revealed elevated concentrations.Firstly, based on findings from previous epidemiological studies, one can conclude that this level of PM2.5 burden has strong adverse effects on the inhabitants' health. Secondly, as only three of the districts showed moderate to high correlations between ambient and personal PM2.5 (with two of them being statistically significant), it is likely that the personal monitoring results were greatly influenced by indoor sources of PM2.5. The weak correlations between the ambient PM mass and personal exposure levels underline the demand for future studies measuring personal exposure in different environments with high temporal and spatial resolution, while taking into account detailed activity analyses.
Keywords: Urban health; Urban air pollution; Particulate matter; Ambient and personal monitoring; China;
Erratum to “Aerosol optical and radiative properties during summer and winter seasons over Lahore and Karachi” [Atmos. Environ. 50 (2012) 234–245] by Khan Alam; Thomas Trautmann; Thomas Blaschke; Hussain Majid (412).
The vertical distribution of PM2.5 and boundary-layer structure during summer haze in Beijing by Yang Sun; Tao Song; Guiqian Tang; Yuesi Wang (413-421).
Between August 1, 2009, and August 16, 2009, physical observations of the atmospheric boundary layer and synchronous vertical observations of atmospheric particles were conducted from the Beijing 325 m meteorological tower, where the particulate matter with a diameter of 2.5 μm or less (PM2.5) analysis meters were stationed at a three-floor platform with altitudes of 8 m, 120 m and 280 m, respectively. Meanwhile, the atmospheric temperatures, relative humidity, wind speeds and wind directions between 8 m and 320 m were observed online at 15 different altitude intervals. The backscattering coefficient of aerosols in the boundary-layer atmosphere within 2.5 km height was also observed using a backscattered laser ceilometer. The observations showed that the PM2.5 pollution in the atmosphere from the ground up to 280 m in Beijing was quite high on August 2009, with a maximum of 200 μg m−3. Within 280 m, the vertical distribution of PM2.5 was inhomogeneous, with a maximum difference of up to 116 μg m−3 between levels in the night residual layer and at the ground. The high concentration of particles in the residual layer reached the ground by the next morning through convection, thus becoming severe pollutants. The PM2.5 in the near-surface layer was directly related to the reduction of ultra-violet radiation (UV), with a correlation coefficient of −0.57. Under steady weather conditions, the topographic mountain-valley breezes in Beijing superposed the land-sea breezes, resulting in a specific breath-like diurnal variation in wind direction. As a result, the PM2.5 mixed and increased in the regional area, leading to serious dust-haze pollution. Within 320 m of the boundary layer, the vertical distributions of temperature, humidity, wind speed and wind direction were inhomogeneous, and these patterns were the major factors influencing the distribution and variation of PM2.5 concentration. Under steady weather conditions, the reverse distribution of relative humidity became more significant, while the low temperatures at higher altitudes facilitated the formation of organic aerosols. Sometimes, the PM2.5 levels increased due to long-range transmission of smoke plume into the residual layer. By the synchronous effect of these factors, the moisture absorption of PM2.5 in the upper layer increased, at times resulting in a “higher-top and lower-bottom” pattern of the PM2.5 distribution.
Keywords: Profile; PM2.5; Residue layer; Aerosol-backscattering coefficient; Haze;
Transcontinental methane measurements: Part 1. A mobile surface platform for source investigations by Paige Farrell; Daniel Culling; Ira Leifer (422-431).
The potent greenhouse gas, methane, CH4, originates from a wide range of anthropogenic and natural sources. A ground-based, satellite-scale, transcontinental (Florida to California) survey was conducted to understand better emissions from key sources including wetlands, forest fire, and geologic sources, as well as to acquire desert background values and lower atmosphere vertical profiling in the San Bernardino Mountains. A total of 6600 measurements along 7020 km of roadways were made by flame ion detection, gas chromatography (GC) onboard a recreational vehicle in 2010, and during a second survey with a cavity ring-down spectrometer system in Southern California in 2012. Significant vibration reduction efforts allowed near continuous mobile GC measurements.Nocturnal CH4 measurements tended to be higher compared to daytime values, sometime significantly, for similar sources and were concluded due to day/night meteorological differences. The lowest GC observations were 1.80 ppm, observed in the California desert, ∼60 ppb less than minimum desert CH4 observed in 2012. Thanks to smoke visualization of a brush fire plume, the flux from the fire was estimated at 0.15 kiloton day−1. Geologic CH4 emissions from the La Brea tar pit and surrounding areas were surprisingly strong, with peak concentrations of nearly 50 ppm and highly elevated CH4 concentrations extending over at least ∼100 km2, and accounting potentially for a significant fraction of the LA basin CH4 emissions. Geologic CO2 emissions also were observed.► First-ever cross-country continent scale methane measurements. ► First quantification of methane emissions from the La Brea tar pit/seepage area geologic source. ► Desert background methane measurements. ► Lower atmospheric vertical profiling using a mountain descending road.
Keywords: Methane; Gas chromatography; Wetlands; Greenhouse gas; Fire; Geologic methane; Seepage; La Brea tar pits; Southern California; Emission; South US;
Transcontinental methane measurements: Part 2. Mobile surface investigation of fossil fuel industrial fugitive emissions by Ira Leifer; Daniel Culling; Oliver Schneising; Paige Farrell; Michael Buchwitz; John P. Burrows (432-441).
The potent greenhouse gas, methane, CH4, has a wide variety of anthropogenic and natural sources. Fall, continental-scale (Florida to California) surface CH4 data were collected to investigate the importance of fossil fuel industrial (FFI) emissions in the South US. A total of 6600 measurements along 7020-km of roadways were made by flame ion detection gas chromatography onboard a nearly continuously moving recreational vehicle in 2010. A second, winter survey in Southern California measured CH4 at 2 Hz with a cavity ring-down spectrometer in 2012.Data revealed strong and persistent FFI CH4 sources associated with refining, oil/gas production, a presumed major pipeline leak, and a coal loading plant. Nocturnal CH4 mixing ratios tended to be higher than daytime values for similar sources, sometimes significantly, which was attributed to day/night meteorological differences, primarily changes in the boundary layer height. The highest CH4 mixing ratio (39 ppm) was observed near the Kern River Oil Field, California, which uses steam reinjection. FFI CH4 plume signatures were distinguished as stronger than other sources on local scales. On large (4°) scales, the CH4 trend was better matched spatially with FFI activity than wetland spatial patterns.Qualitative comparison of surface data with SCIAMACHY and GOSAT satellite retrievals showed agreement of the large-scale CH4 spatial patterns. Comparison with inventory models and seasonal winds suggests for some seasons and some portions of the Gulf of Mexico a non-negligible underestimation of FFI emissions. For other seasons and locations, qualitative interpretation is not feasible. Unambiguous quantitative source attribution is more complex, requiring transport modeling.
Keywords: Methane; Gas chromatography; SCIAMACHY; Fugitive emissions; Refinery emissions; Pipeline leak; Greenhouse gas;