Atmospheric Environment (v.63, #C)

Radiative forcing due to aviation water vapour emissions by L.J. Wilcox; K.P. Shine; B.J. Hoskins (1-13).
Three emissions inventories have been used with a fully Lagrangian trajectory model to calculate the stratospheric accumulation of water vapour emissions from aircraft, and the resulting radiative forcing. The annual and global-mean radiative forcing due to present-day aviation water vapour emissions has been found to be 0.9 [0.3–1.4] mW m−2. This is around a factor of three smaller than the value given in recent assessments, and the upper bound is much lower than a recently suggested 20 mW m−2 upper bound. This forcing is sensitive to the vertical distribution of emissions, and, to a lesser extent, interannual variability in meteorology. Large differences in the vertical distribution of emissions within the inventories have been identified, which result in the choice of inventory being the largest source of differences in the calculation of the radiative forcing due to the emissions.Analysis of Northern Hemisphere trajectories demonstrates that the assumption of an e-folding time is not always appropriate for stratospheric emissions. A linear model is more representative for emissions that enter the stratosphere far above the tropopause.► Radiative forcing due to aviation water vapour emissions was 0.9 [0.3–1.4] mW m−2 in 2006. ► This new value is around a factor of three smaller than recent assessments. ► The upper bound from recent assessments is likely much too high. ► The stratospheric accumulation of emissions is modelled with Lagrangian trajectories. ► The vertical distribution of emissions is key to the estimate of radiative forcing.
Keywords: Aviation; Climate; Radiative forcing; Lagrangian trajectory;

Mechanism and kinetic studies for OH radical-initiated atmospheric oxidation of methyl propionate by Xiaoyan Sun; Yueming Hu; Fei Xu; Qingzhu Zhang; Wenxing Wang (14-21).
DFT molecular orbital theory calculations were carried out to investigate OH radical-initiated atmospheric oxidation of methyl propionate. Geometry optimizations of the reactants as well as the intermediates, transition states and products were performed at the B3LYP/6-31G(d,p) level. As the electron correlation and basis set effect, the single-point energies were computed by using various levels of theory, including second-order Møller–Plesset perturbation theory (MP2) and the coupled-cluster theory with single and double excitations including perturbative corrections for the triple excitations (CCSD(T)). The detailed oxidation mechanism is presented and discussed. The results indicate that the formation of 3-oxo-methyl propionate (HC(O)CH2C(O)OCH3) is thermodynamically feasible and the isomerization of alkoxy radical IM17 (CH3CH(O)C(O)OCH3) can occur readily under the general atmospheric conditions. Canonical variational transition-state (CVT) theory with small curvature tunneling (SCT) contribution was used to predict the rate constants. The overall rate constants were determined, k(T)(CH3CH2COOCH3 + OH) = (1.35 × 10−12)exp(−174.19/T) cm3 molecule−1 s−1, over the possible atmospheric temperature range of 180–370 K.► Mechanism and kinetics for OH-initiated reaction of methyl propionate were studied. ► Detailed reaction mechanism was proposed. ► The overall rate constant have been obtained. ► The atmospheric lifetime determined by OH radicals is about 15.5 days.
Keywords: Methyl propionate; OH radicals; Atmospheric oxidation; Reaction mechanism; Kinetic parameters;

Filter samples of secondary organic aerosols (SOA) generated from the ozone (O3)- and hydroxyl radical (OH)-initiated oxidation of various biogenic (isoprene, α-pinene, limonene, α-cedrene, α-humulene, farnesene, pine leaf essential oils, cedar leaf essential oils) and anthropogenic (tetradecane, 1,3,5-trimethylbenzene, naphthalene) precursors were exposed to humid air containing approximately 100 ppb of gaseous ammonia (NH3). Reactions of SOA compounds with NH3 resulted in production of light-absorbing “brown carbon” compounds, with the extent of browning ranging from no observable change (isoprene SOA) to visible change in color (limonene SOA). The aqueous phase reactions with dissolved ammonium (NH4 +) salts, such as ammonium sulfate, were equally efficient in producing brown carbon. Wavelength-dependent mass absorption coefficients (MAC) of the aged SOA were quantified by extracting known amounts of SOA material in methanol and recording its UV/Vis absorption spectra. For a given precursor, the OH-generated SOA had systematically lower MAC compared to the O3-generated SOA. The highest MAC values, for brown carbon from SOA resulting from O3 oxidation of limonene and sesquiterpenes, were comparable to MAC values for biomass burning particles but considerably smaller than MAC values for black carbon aerosols. The NH3/NH4 + + SOA brown carbon aerosol may contribute to aerosol optical density in regions with elevated concentrations of NH3 or ammonium sulfate and high photochemical activity.Display Omitted► Secondary organic aerosols change color from white to brown in presence of ammonia. ► Browning reaction occurs for a wide range of biogenic and anthropogenic aerosols. ► Aqueous reaction with ammonium ion is equally efficient in producing brown carbon. ► The mass absorption coefficient is comparable to that of biomass burning aerosols. ► Secondary brown carbon may contribute to absorption of solar radiation by aerosols.
Keywords: Brown carbon; Secondary organic aerosol; Ammonia; Mass absorption coefficient;

Smoke plume optical properties and transport observed by a multi-wavelength lidar, sunphotometer and satellite by Yonghua Wu; Lina Cordero; Barry Gross; Fred Moshary; Sam Ahmed (32-42).
Optical characteristics and long-distance transport of smoke plumes are studied using satellite observations and ground-based remote sensing in New York City. Vertical distribution and column optical properties of aerosol plume are derived from a combination of multi-wavelength lidar and sunphotometer measurement. Aloft smoke plumes from two cases are investigated in this paper from U.S. western and south-western forest fires. The smoke source and transport pathway to the U.S. east coast are analyzed by MODIS and CALIOP imageries as well as HYSPLIT backward trajectory analysis. In both cases, the plumes have relatively high optical depth (as much as 1.2 at 500-nm) and Angstrom exponent of up to 1.8, but show different intrusion heights, source regions and transport process. Lidar profiling observations indicate these smoke plumes mixing downward into the planetary-boundary-layer which are coincident with increasing trends of surface PM2.5 (particulate matter, diameter < 2.5 μm) concentrations.► Smoke plumes optical properties and temporal-spatial distributions are presented. ► Intra-continental transport and origins of smoke plumes are investigated. ► Influences on the PBL and surface PM2.5 by smoke-plumes are illustrated.
Keywords: Smoke; Transport; Optical properties; Lidar; Satellite;

A study of four-year HCFC-22 and HCFC-142b in-situ measurements at the Shangdianzi regional background station in China by Bo Yao; Martin K. Vollmer; Lingjun Xia; Lingxi Zhou; Peter G. Simmonds; Frode Stordal; Michela Maione; Stefan Reimann; Simon O’Doherty (43-49).
Atmospheric HCFC-22 (CHClF2) and HCFC-142b (CH3CClF2) in-situ measurements have been recorded by an automated gas chromatograph-electron capture detectors (GC-ECDs) system and a gas chromatography/mass spectrometry (Medusa-GC/MS) system at the Global Atmosphere Watch (GAW) regional background station Shangdianzi (SDZ), China. The mixing ratios of the two HCFCs at SDZ show frequent events with elevated concentrations due to polluted air from urban or industrialized areas. The mean background mixing ratios for HCFC-22 and HCFC-142b were 205.3 ppt (parts per trillion, 10−12, molar) and 20.7 ppt, respectively, for the study period (March 2007–February 2011). The yearly background mixing ratios for the two HCFCs at SDZ are similar to those measured at Trinidad Head and Mace Head located in the Northern Hemisphere (NH), but larger than Cape Grim and Cape Matatula (located in the Southern Hemisphere) due to inter-hemispheric differences caused by predominantly NH emissions. During the study period, background mixing ratios exhibited positive growth rates of 8.7 ppt yr−1 for HCFC-22 and 0.95 ppt yr−1 for HCFC-142b. HCFC’s seasonality exhibits a summer/autumn maximum and a winter minimum. 4-year averaged background seasonal amplitudes (maximum–minimum) are 6.0 ppt for HCFC-22 and 0.9 ppt for HCFC-142b. The seasonal fluctuations (maximum–minimum) in polluted events are 105.4 ppt for HCFC-22 and 29.1 ppt for HCFC-142b, which are much stronger than the fluctuations under background conditions. However, both HCFC-22 and HCFC-142b show summer minima in 2008, which is most likely due to emission control regulations when the Olympic Games were held in Beijing.► We obtained the longest records of HCFC-22 and HCFC-142b in China. ► We compared HCFCs background levels with background stations in other countries. ► Both HCFCs background concentrations show positive trends. ► We performed a seasonal cycle analysis and found an interesting exception of 2008.
Keywords: Hydrochlorofluorocarbons (HCFCs); Shangdianzi; Seasonality; Data analysis;

Employing both map pattern classification and weather typing, this study examines the role of climate in impacting air quality in Cleveland, Ohio from 1998 to 2007. This research creates a large-scale map pattern-classification of 500 mb geopotential heights that characterizes the broad scale flow of the atmosphere and the Spatial Synoptic Classification (SSC), which typifies the weather situation at the surface, where pollutants ultimately interact with the population. Surface weather types are found to have a greater impact on the Air Quality Index (AQI) than typical circulation patterns. Warm (cool) weather types and circulation patterns with a ridge (trough) consistently relate to poor (better) air quality in Cleveland. When weather types and circulation patterns are considered in tandem, these relationships are reinforced. Circulation patterns appear to have considerable influence on air quality in conjunction with moderate surface weather types, with impacts differing by the primary pollutant considered. Spike days of high AQIs (days with an AQI of at least 100) show similar results.► We analyze air quality using two synoptic climatological methods in tandem. ► Warm weather types and ridge patters are associated with high AQIs. ► Cold weather types and trough patterns are associated with low AQIs. ► When types and patterns are examined in tandem, both effects are amplified. ► Weather type and circulation pattern impacts differ by season and pollutant.
Keywords: Synoptic climatology; Air quality; SSC; AQI; Weather types; Circulation patterns;

Rainwater samples from Ahmedabad, an urban site in India are analysed for their chemical composition and Sr isotopic ratio. Dominance of Ca in the cation budget indicates its importance in the acid neutralization whereas SO4 and NO3 dominate the anion budget. The major ion concentrations measured in this study are on the lower side of the range reported in the previous study (Rastogi and Sarin, 2007) from the same site. Na and Cl show very good correlation with ratio similar to the seawater ratio, implying their marine origin. Na concentration in these samples has been used as a proxy to calculate the non sea salt fraction of other major ions. Non sea salt Ca and Mg vary from 99.0% to 99.6% and 24.6% to 89.1% of the measured Ca and Mg respectively whereas non sea salt component of SO4 and HCO3 contribute 84.3% to 98.9% and 99.1% to 99.9% respectively. Sr concentrations in these rainwaters vary from 32 to 191 nM and 87Sr/86Sr ranges from 0.70878 to 0.71027. Sr concentration shows a very good correlation (coefficient 0.93) with the non-sea salt component of Ca and Mg indicating their continental sources and having similar provenances. Carbonates and basalts seem to contribute significantly to dissolved base cations of the rainwaters. The basalts from Deccan region, which is isotopically indistinguishable from the African basalts and the silicate and carbonates from African region along with the sediments from the Ganga plain (which is originated from the Himalayan lithologies) could be potential dust sources for this particular site. The sources of dissolved base cations deduced from Sr isotope composition of the rainwaters are consistent with wind back trajectory data obtained from NOAA HYSPLIT model.► Chemical composition and Sr isotopic ratio are measured in rainwater samples. ► Chemical composition of rainwater display decadal variation. ► Sr isotopic ratio has been used to trace the sources of base cations for the first time in the Indian subcontinent. ► Base cations in the rainwaters of the Ahmedabad are derived from carbonates and basalts in addition to seawater.
Keywords: Rainwater; Chemical composition; Sr isotopic composition; Base cations; Provenance tracer; Ahmedabad, India;

The secondary formation of inorganic aerosols in the droplet mode through heterogeneous aqueous reactions under haze conditions by Xinfeng Wang; Wenxing Wang; Lingxiao Yang; Xiaomei Gao; Wei Nie; Yangchun Yu; Pengju Xu; Yang Zhou; Zhe Wang (68-76).
Secondary inorganic aerosols play important roles in visibility reduction and in regional haze pollution. To investigate the characteristics of size distributions of secondary sulfates and nitrates as well as their formation mechanisms under hazes, size-resolved aerosols were collected using a Micro-Orifice Uniform Deposit Impactor (MOUDI) at an urban site in Jinan, China, in all four seasons (December 2007–October 2008). In haze episodes, the secondary sulfates and nitrates primarily formed in fine particles, with elevated concentration peaks in the droplet mode (0.56–1.8 μm). The fine sulfates and nitrates were completely neutralized by ammonia and existed in the forms of (NH4)2SO4 and NH4NO3, respectively. The secondary formation of sulfates, nitrates and ammonium (SNA) was found to be related to heterogeneous aqueous reactions and was largely dependent on the ambient humidity. With rising relative humidity, the droplet-mode SNA concentration, the ratio of droplet-mode SNA to the total SNA, the fraction of SNA in droplet-mode particles and the mass median aerodynamic diameter of SNA presented an exponential, logarithmic or linear increase. Two heavily polluted multi-day haze episodes in winter and summer were analyzed in detail. The secondary sulfates were linked to heterogeneous uptake of SO2 followed by the subsequent catalytic oxidation by oxygen together with iron and manganese in winter. The fine nitrate formation was strongly associated with the thermodynamic equilibrium among NH4NO3, gaseous HNO3 and NH3, and showed different temperature-dependences in winter and summer.► Size-resolved inorganic aerosol compositions were analyzed for a highly polluted area. ► Humidity-dependent heterogeneous formation of inorganic aerosols was investigated. ► Relationships were given between the SO4 2−, NO3 , NH4 + in the droplet mode and the RH. ► Dominant formation pathways of sulfates and nitrates were analyzed for haze events.
Keywords: Secondary inorganic aerosols; Mass size distribution; Droplet mode; Heterogeneous aqueous reaction; Haze pollution; Jinan;

Net exchanges of CO2, CH4 and N2O between marshland and the atmosphere in Northeast China as influenced by multiple global environmental changes by Lili Wang; Hanqin Tian; Changchun Song; Xiaofeng Xu; Guangsheng Chen; Wei Ren; Chaoqun Lu (77-85).
Natural wetland ecosystem plays an important role in global climate change due to its large amounts of stored carbon and nitrogen. The Sanjiang Plain, Northeast China, encompasses large area of natural freshwater marshy wetlands. However, the magnitude and temporal patterns of major greenhouse gases (GHGs: CO2, CH4 and N2O) in this region remain far from certain. Here we used a process-based ecosystem model to examine GHGs fluxes and their underlying mechanisms in the marshland across the Sanjiang Plain over the period 1949–2008. Simulation results indicated that during the past 60 years, the Sanjiang Plain's marshland acted as a net CO2 sink of 4.20 ± 0.44 Tg C yr−1, while approximately 0.46 ± 0.02 Tg C yr−1 for CH4 and 0.02 ± 0.00 Tg N yr−1 for N2O were released to the atmosphere. Land cover and land use change (LCLUC) was the primary driver for GHGs changes. Climate change and tropospheric ozone (O3) pollution decreased CO2 uptakes, yet elevated CO2 concentration and nitrogen deposition increased CO2 uptake. Tropospheric O3 pollution and nitrogen deposition decreased CH4 emission by 7.94 Gg C and 0.41 Gg C, respectively, while elevated CO2 concentration increased the CH4 emission by 133.81 Gg C. Accumulatively, tropospheric O3 pollution and climate change contributed approximately 5.37% and 4.89% to the increased N2O emission, respectively, while elevated CO2 concentration reduced 2.81% of the N2O emission. The global warming potential (GWP) ranged from −1.81 Tg CO2eq yr−1 in the 1970s to 29.15 Tg CO2eq yr−1 in the 2000s. The decadal GWP by CO2 fluxes shifted from negative values between the 1950s and the 1990s to positive values in the 2000s, while CH4 and N2O emissions enhanced GWP from the 1950s to the 2000s. The total GWP decreased from the 1950s to the 1970s, but increased from the 1980s to the 2000s. This suggested that the reduced GWP by decreased CH4 emissions was gradually offset by the increased GWP by increased N2O emissions and decreased CO2 sink from the 1980s to the 2000s, implying that a full accounting of the greenhouse gas balance is essential in assessing global change impacts.► CO2 uptake and CH4 emissions decreased, while N2O increased in the Sanjiang Plain during 1949–2008. ► Net global warming potential (GWP) increased over recent 3 decades. ► Land cover and land use change was the largest contributor to the increasing GWP.
Keywords: Carbon dioxide; Methane; Nitrous oxide; Marshland; Sanjiang Plain;

Modelling ambient ozone in an urban area using an objective model and geostatistical algorithms by Francisco J. Moral; Francisco J. Rebollo; Pablo Valiente; Fernando López; Arsenio Muñoz de la Peña (86-93).
Ground-level tropospheric ozone is one of the air pollutants of most concern. Ozone levels continue to exceed both target values and the long-term objectives established in EU legislation to protect human health and prevent damage to ecosystems, agricultural crops and materials. Researchers or decision-makers frequently need information about atmospheric pollution patterns in urbanized areas. The preparation of this type of information is a complex task, due to the influence of several factors and their variability over time.In this work, some results of urban ozone distribution patterns in the city of Badajoz, which is the largest (140,000 inhabitants) and most industrialized city in Extremadura region (southwest Spain) are shown. Twelve sampling campaigns, one per month, were carried out to measure ambient air ozone concentrations, during periods that were selected according to favourable conditions to ozone production, using an automatic portable analyzer.Later, to evaluate the overall ozone level at each sampling location during the time interval considered, the measured ozone data were analysed using a new methodology based on the formulation of the Rasch model. As a result, a measure of overall ozone level which consolidates the monthly ground-level ozone measurements was obtained, getting moreover information about the influence on the overall ozone level of each monthly ozone measure. Finally, overall ozone level at locations where no measurements were available was estimated with geostatistical techniques and hazard assessment maps based on the spatial distribution of ozone were also generated.Display Omitted► The Rasch model is used as a measurement tool to estimate overall ozone levels. ► Influence of different monthly ozone measures on overall ozone level is determined. ► Predictive and probability maps provide information for hazard assessment.
Keywords: Ground-level tropospheric ozone; Atmospheric pollutant; Rasch model; Kriged map; Geographical Information System;

A bacterial bioreporter panel to assay the cytotoxicity of atmospheric particulate matter by Nivi Kessler; James J. Schauer; Sharon Yagur-Kroll; Sahar Melamed; Ofir Tirosh; Shimshon Belkin; Yigal Erel (94-101).
Numerous studies have demonstrated that elevated concentrations of suspended atmospheric particulate matter (PM) are associated with adverse health effects. In order to minimize the adverse public health effects of atmospheric PM by exposure management, there is a need for a greater understanding of the toxic mechanisms and the components that are responsible for the toxic effects. The aim of this study was to utilize bioassay techniques to investigate these aspects. For this purpose a reporter panel of 9 genetically engineered bacterial (Escherichia coli) strains was composed. Each panel member was designed to report on a different stress condition with a measurable light signal produced by the luciferase enzyme.Toxic mechanisms and components were studied using six anthropogenic PM source samples, including two vehicle combustion particles, three coal fly ash (CFA) samples and an urban dust sample. The most prominent outcome of the panel exposure results were broad panel responses observed for two of the CFA samples, indicating oxidative stress, respiration inhibition and iron deficiency. These responses were relieved when the samples were treated with EDTA, a non-specific metal chelator, suggesting the involvement of metals in the observed effects. Bioavailability analysis of the samples suggests that chromium was related to the toxic responses induced by two of the CFA samples. Oxidative stress was also observed in several samples of ambient atmospheric aerosols and excess metal toxicity in an urban dust sample collected in a parking lot.The reporter panel approach, as demonstrated in this study, has the potential of providing novel insights as to the mechanisms of atmospheric PM toxicity. Furthermore, combining the panel's results with bioavailability data can enlighten about the role of different PM components in the observed toxicity.► A new bacterial bioassay for toxicity of particulate air pollution is presented. ► Bioassay responses indicating toxicity were observed for several PM samples. ► These responses suggest oxidative stress, respiration inhibition and Fe deficiency. ► A metal chelating treatment of the samples relieved the bioassay's responses. ► Bioavailability analysis suggested that Cr was related to these toxic responses.
Keywords: Toxicity; Particles; Air pollution; Biosensors; Metals; Oxidative stress;

Evaluating the effects of sub-zero temperature cycling on mercury flux from soils by Hamish Corbett-Hains; Nicholas E. Walters; Bill J. Van Heyst (102-108).
A number of mechanisms have been shown to facilitate the flux of mercury from soils, although at sub-zero temperatures, there is evidence to suggest that alternate mechanisms may exist. Field studies at sub-zero temperatures have observed spikes in flux under certain conditions however very little laboratory work has been done to characterize the specific effects or mechanisms. A Dynamic Flux Chamber (DFC) and Tekran Model 2537A were used to analyse mercury flux from a naturally enriched soil. Soil moisture contents were varied between 30%, 60%, and 75% of field capacity while temperatures were cycled between 0 and −25 °C. The results, which were compared to room temperature baseline runs, showed that, at sub-zero temperatures, the mercury flux was suppressed in general. However, during the temperature cycling runs, soil flux spikes were evident during positive temperature change or warming. A one-way ANOVA by ranks proved that statistically significant fluxes were occurring during the runs at 30% and 60% of field capacity for positive rates of temperature changes. Arrhenius plots showed that for positive soil temperatures flux and temperature correlated well with the Arrhenius relationship. At sub-zero conditions however, no relationship was present, indicating another mechanism was present. The proposed mechanism for this enhanced flux is the physical evacuation of interstitial pore space gaseous mercury by the expansion and contraction of the freeze–thaw cycle.► Hg flux from sub-zero temperature soil was observed at varying moisture contents. ► While cycling at sub-zero temperatures Hg flux was suppressed. ► Soil warming from sub-zero temperatures produced Hg flux spikes. ► A physical mechanism is proposed to account for Hg flux spikes. ► Mechanism includes the expansion and contraction of soil during freeze–thaw cycle.
Keywords: Elemental mercury flux; Sub-zero temperature; Temperature cycling; Dynamic flux chamber; Soil moisture;

Personal total exposure (E t) is composed of exposure to pollutants of ambient origin (E a) and nonambient origin (E na), both of which are associated with health effects. However, E a is more relevant for estimating the health effects associated with ambient air pollutants. Associations between E a and ambient concentrations (C a) were examined for different subpopulations in the Detroit Exposure and Aerosol Research Study (DEARS). First, E a was estimated for PM2.5, NO2, and O3. The associations between C a and E a were then characterized with mixed effect models. C a served as a good surrogate for E a for PM2.5 in both summer (slope = 0.80) and winter (slope = 0.55), but only in summer for O3 and NO2 (slope = 0.13 for NO2, and slope = 0.03 for O3).The effects of exposure determinants on E aC a associations were examined using mixed effect models. Exposure determinants examined include personal activities, building and household characteristics and ambient apparent temperature (AT). The strength of associations between C a and E a differed between that for the entire study population and different subpopulations, which in turn differed from each other. Personal activities and building characteristics significantly affected the E aC a associations through modifying the air exchange rate (AER). C a was not a significant indicator of E a for O3 and NO2 for homes with central AC or with windows closed. Ambient AT affected the E aC a associations through modifying both AER and personal activities. The fraction of daily time spent outdoors peaked (6%) at about 22 °C, and monotonically decreased when ambient AT departed from 22 °C. Adequate accounting for the effects of exposure determinants on the E aC a associations will lead to a better understanding of the E aC a associations and of the uncertainties associated with using ambient concentrations as surrogates for personal exposures of ambient origin.► Exposures of ambient origin were estimated for PM2.5 and NO2. ► Seasonal impacts on the E aC a association were identified for PM2.5, NO2, and O3. ► Ventilation related exposure factors significantly affected the E aC a associations. ► Ambient apparent temperature significantly affected the E aC a associations.
Keywords: PM2.5; O3; NO2; Exposure of ambient origin; Time activity patterns; Air exchange rates;

Determining the influence of different atmospheric circulation patterns on PM10 chemical composition in a source apportionment study by Mauro Masiol; Stefania Squizzato; Daniele Ceccato; Giancarlo Rampazzo; Bruno Pavoni (117-124).
This study combines a set of chemometric analyses with a source apportionment model for discriminating the weather conditions, local processes and remote contributions having an impact on particulate matter levels and chemical composition. The proposed approach was tested on PM10 data collected in a semi-rural coastal site near Venice (Italy). The PM10 mass, elemental composition and the water soluble inorganic ions were quantified and seven sources were identified and apportioned using the positive matrix factorization: sea spray, aged sea salt, mineral dust, mixed combustions, road traffic, secondary sulfate and secondary nitrate. The influence of weather conditions on PM10 composition and its sources was investigated and the importance of air temperature and relative humidity on secondary components was evaluated. Samples collected in days with similar atmospheric circulation patterns were clustered on the basis of wind speed and direction. Significant differences in PM10 levels and chemical composition pointed out that the production of sea salt is strongly depending on the intensity of local winds. Differently, typical primary pollutants (i.e. from combustion and road traffic) increased during slow wind regimes. External contributions were also investigated by clustering the backward trajectories of air masses. The increase of combustion and traffic-related pollutants was observed when air masses originated from Central and Northwestern Europe and secondary sulfate was observed to rise when air masses had passed over the Po Valley. Conversely, anthropogenic contributions dropped when the origin was in the Mediterranean area and Northern Europe. The chemometric approach adopted can discriminate the role local and external sources play in determining the level and composition of airborne particulate matter and points out the weather circumstances favoring the worst pollution conditions. It may be of significant help in designing local and national air pollution control strategies.► Elements and ions in 193 PM10 samples were studied by Positive Matrix Factorization. ► Results were geochemically interpreted in relation to weather data. ► Days with similar circulation patterns were clustered on the basis of wind data. ► Samples with similar air mass histories were grouped using back-trajectories. ► The major components of PM10 chemistry and dynamics in NE Italy were identified.
Keywords: PM10; Atmospheric circulation; Regional transport; Source apportionment; Lagoon of Venice;

Traditional Eulerian air quality models are unable to accurately simulate sub-grid scale processes, such as the near-source transport and chemistry of point source plumes, because they assume instantaneous mixing of the emitted pollutants within the grid cell containing the release, and neglect the turbulent segregation effects that limit the near-source mixing of emitted pollutants with the background atmosphere (e.g., Kramm and Meixner, 2000). Observations by Dlugi et al. (2010) show that the segregation of chemically reactive species can slow effective second-order reaction rates by as much as 15%, due to inhomogeneous mixing of the reactants. This limitation of traditional grid models applies to both “off-line” models, in which externally derived meteorology is used to drive the chemistry model, and newer “on-line” models, such as the Weather Research and Forecasting model with Chemistry (WRF/Chem), that simulate the emissions, transport, mixing, and chemical transformation of trace gases and aerosols simultaneously with the meteorology. While a number of approaches have been used in the past to address this limitation, the approach that has been most effectively used in operational models is the plume-in-grid (PinG) approach, in which a reactive plume model is embedded within the grid model to resolve sub-grid scale plumes. This paper describes the implementation of such a PinG treatment in WRF/Chem, based on a similar extension to the U.S. EPA Community Multi-scale Air Quality (CMAQ) model. The treatment, referred to as Advanced Plume Treatment, has been tested in CMAQ over more than a decade and has been used successfully in both episodic and long-term applications for assessing point source contributions to ozone and particulate matter. This paper presents the application of the PinG version of WRF/Chem for a three-day episode in July 2001, including a model performance evaluation and comparison of model results with and without PinG treatment. The results from the model application show that overall model performance is only slightly affected when the PinG treatment is used, although there are some generally small improvements, with the PinG treatment showing a 5% lower bias in predicting ozone concentrations, and 3% lower bias in sulfate predictions. However, the predicted spatial patterns of ozone and PM2.5 concentrations from the two simulations show both large decreases of up to 40 ppb ozone and 14 μg m−3 PM2.5, and increases of up to 80 ppb ozone and 33 μg m−3 PM2.5 as a result of using the PinG treatment. These differences are attributed to both direct effects of the PinG treatment (i.e., differences in dispersion, transport and chemistry of point source emissions) and indirect effects (i.e., impacts of air quality changes on meteorology).► First implementation of plume-in-grid (PinG) treatment in online-coupled WRF/Chem. ► Improved model capability in simulating sub-grid scale plumes with PinG. ► Large differences in predicted spatial patterns of pollutants with and without PinG. ► Important implications to simulated aerosol direct and indirect feedbacks.
Keywords: Coupled meteorology and chemistry models; Advanced plume treatment; Sub-grid scale processes; WRF/Chem;

This work presents a systematic analysis and evaluation of the historic and current levels of atmospheric pollution in the Athens metropolitan region, regarding nitrogen oxides (NO x  = NO + NO2), ozone (O3) and the NO2/NO x and NO/NO2 concentration ratios. Hourly, daily, monthly, seasonal and annual pollutant variations are examined and compared, using the results of concentration time series from three different stations of the national network for air pollution monitoring, one urban-traffic, one urban-background and one suburban-background. Concentration data are also related to meteorological parameters. The results show that the traffic affected station of Patission Street presents the higher NO x values and the lower concentrations of O3, while it is the station with the highest number of NO2 limit exceedances. The monitoring data suggest, inter alia, that there is a change in the behaviour of the suburban-background station of Liossia at about year 2000, indicating that the exact location of this station may need to be reconsidered. Comparison of NO x concentrations in Athens with concentrations in urban areas of other countries reveal that the Patission urban-traffic station records very high NO x concentrations, while remarkably high is the ratio of NO2 concentrations recorded at the urban-traffic vs. the urban-background station in Athens, indicating the overarching role of vehicles and traffic congestion on NO2 formation. The NO2/NO x ratio in the urban-traffic station appears to be almost constant with time, while it has been increasing in other urban areas, such as London and Seoul, suggesting an increased effect of primary NO2 in these areas. Diesel passenger cars were only recently allowed in Athens and, therefore, NO2 trends should be carefully monitored since a possible increase in primary NO2 may affect compliance with NO2 air quality standards.► The urban-traffic station presents very high NO x values and NO2 limit exceedances. ► The location of the suburban-background station needs to be carefully considered. ► The NO2 urban traffic vs. background ratio is very high due to traffic contribution. ► The NO2/NO x concentration ratio at the urban-traffic station is constant with time. ► Allowance of diesel cars in Athens in 2011 may affect NO2 trends and NO2/NO x ratio.
Keywords: Air pollution; Traffic; Monitoring stations; Air quality standards; NO2/NO x ratio; NO/NO2 ratio;

Use of a passive sampling network for the determination of urban NO2 spatiotemporal variations by S. Caballero; R. Esclapez; N. Galindo; E. Mantilla; J. Crespo (148-155).
Nitrogen dioxide levels were systematically measured by means of passive samplers at 79 sites in the city of Elche (southeastern Spain) with the aim of investigating the factors affecting NO2 spatiotemporal variations and quantitatively assessing the impact of traffic on urban NO2 concentrations. One-week sampling campaigns were performed approximately once a month during 2007 and 2008. The average NO2 concentration during the two-year period was 32 ± 12 μg m−3, with minima in summer and maxima from fall to early spring. Temporal variations of nitrogen dioxide concentrations were mainly affected by meteorological factors. On the other hand, the relative spatial distribution of NO2 levels, which remained fairly constant during the study period, was controlled by both traffic flow allocation and urban street layout. Using cluster analysis, the sampling sites were grouped into four representative classes of urban NO2 pollution, indicating that a considerable reduction in the number of measurement points for monitoring the spatial and temporal variability of nitrogen dioxide levels is feasible. By means of regression analysis, we estimated a weekly average concentration decrease of ∼1 μg NO2 m−3 if a reduction of 4000 vehicles per week occurred in city centre streets. These results can be useful for improving urban air quality management and control efficiency.► Temporal trends in NO2 concentrations mostly controlled by ambient conditions. ► Spatial NO2 distribution dependent on urban structure and traffic flow allocation. ► Seventy-nine sites divided into 4 groups with similar NO2 levels by cluster analysis. ► Dependence of NO2 levels on traffic flows determined by correlation analyses. ► A reduction of 20,000 vehicles per week would cause a decrease of 4–6 μg NO2 m−3.
Keywords: Nitrogen dioxide; Passive sampling; Urban air pollution; Cluster analysis; Traffic;

Spatial and temporal characterization of traffic emissions in urban microenvironments with a mobile laboratory by L. Pirjola; T. Lähde; J.V. Niemi; A. Kousa; T. Rönkkö; P. Karjalainen; J. Keskinen; A. Frey; R. Hillamo (156-167).
A measurement campaign by a mobile laboratory van was performed in urban microenvironments bounded by a busy street Mannerheimintie in the city center of Helsinki, Finland. The characteristics of spatiotemporally high-resolution pollutant concentrations were studied such as ultrafine particles in the size range of 3–414 nm, black carbon BC, fine particle mass PM2.5, as well as nitrogen oxides NO and NO2. In addition, the effects of street geometry and roadside structure on the local dispersion of traffic emissions were analyzed as well. Meteorological conditions stayed stable and the wind direction was perpendicular to Mannerheimintie during the campaign. The highest particle concentrations were ∼8 × 105 cm−3, of which around 94% was smaller than 40 nm. At the pavement, the average concentration was in maximum 5 × 104 cm−3; around 80% of the particles was smaller than 40 nm. The volatility fraction was 75% by number. Due to the street canyon effect by the surrounding buildings, the downwind concentrations were around 24% of the upwind concentrations for particle number, 28% of NO, 39% of BC and 70% of NO2 concentrations. Furthermore, the upwind concentrations were higher than the simultaneously measured concentrations within the traffic flow. In fact, the particle count was around 3-fold, BC 2.5-fold, PM2.5 and NO2 1.5-fold compared to the concentrations while driving. Thus, for this measurement site and under these meteorological conditions, the exposure to pedestrians and cyclist on the upwind pavement is even higher than the driver's exposure. If the downwind buildings were parallel to Mannerheimintie, the concentrations dropped significantly at the pavement and continued decreasing slightly in the courtyards. When the downwind buildings were perpendicular to Mannerheimintie, a gradual reduction in the concentrations between the buildings was observed. However, at a distance of approximately a hundred meters a parallel side street which was a street canyon, started to affect the concentrations resulting in an increased exposure risk for pedestrians and cyclists. Understanding the local transport and the dispersion of traffic emissions are important for city planning and air quality assessment.Display Omitted► Major part of traffic particles are smaller than 40 nm and volatile. ► Street canyon effect accumulates particulate and gaseous concentrations to upwind side. ► Exposure at the pavement upwind is even higher than while driving. ► Downwind concentrations highly depend on wind direction and roadside structure.
Keywords: Ultrafine particles; Mobile measurements; Street canyon; Traffic pollutants; Pedestrian exposure;

Meteorological factors influencing the 7Be and 210Pb concentrations in surface air from the southwestern Iberian Peninsula by R.L. Lozano; M.A. Hernández-Ceballos; E.G. San Miguel; J.A. Adame; J.P. Bolívar (168-178).
During a seven-year period (April 2004–July 2011), the 210Pb and 7Be activity concentrations in surface air were determined at El Arenosillo, located on the coastline of the southwestern Iberian Peninsula. The 210Pb and 7Be activity concentrations have been classified in four ranges according to the values of percentiles, 0–P10 (lowest concentrations), P10–P50 (intermediate concentrations), P50–P90 (high concentrations), and P90–Maximum (peaks of concentrations).The computation of both backward trajectories and cluster techniques has been used for identifying the types of air masses that arrive at the sampling station for each range of 210Pb and 7Be activity concentrations. Meteorological parameters, such as the wind roses and daily cycles of specific and relative humidity, and the potential temperature have been calculated (or measured) for each one of the sampling periods and grouped according to the ranges of 210Pb and 7Be activity concentrations.The results indicate that different synoptic patterns are associated with different 210Pb and 7Be activities in this area, which indicates the differences between the arrival of maritime and continental air masses based on the 210Pb and 7Be activities. In addition, the study on the evolution of air masses from the lowest and highest ranges of 7Be/210Pb confirms that both radionuclides can be used as two independent atmospheric transport markers.► 210Pb and 7Be activity concentrations have been measured in southwestern Spain. ► Influence of meteorological scenarios in the 210Pb and 7Be was studied. ► Identification of synoptic patterns associated to the 210Pb concentration ranges. ► Identification of synoptic patterns associated to the 7Be concentration ranges.
Keywords: 210Pb; 7Be; Air masses; Backward trajectories;

Naturally ventilated dairy cattle buildings are a major source of ammonia and greenhouse gas emissions. Accurate estimation in gas emissions constitutes the first step towards reducing the negative impact of emissions on the local environment. The greatest uncertainty in the emission estimation from a naturally ventilated livestock building with large openings is the determination of the air exchange rate (AER) and the choice of the gas sampling positions for representative outlet gas concentration. To reduce the uncertainties in the emission estimation, the performances of three techniques – integrating volume flow rates (VFR), tracer gas decay (TGD) and constant tracer gas (CTG) for determination of ventilation rates were assessed in this paper by Computational fluid dynamics (CFD). In the developed CFD model, the animal occupied zone (AOZ) was treated as porous media and the resistance coefficient of porous zone was derived by pressure drops across AOZ using a sub-CFD model. The results showed that AERs predicted by VFR and TGD were in good agreement with each other within a large range of wind speeds. The large difference in AER estimation using CTG and VFR indicates that the mean CO2 concentration of the entire room may not represent the concentration at the air exit. It may be not suitable to calculate AER using mean concentration of internal sampling positions. When wind became stronger, the accuracy of CTG decreased. The gas sampling positions should be close to the openings or even in the openings; the gas sampling positions should be located adjacent to the openings or even in the openings. To reduce the uncertain introduced by wind direction, all the openings especially of different azimuths should possess sampling tubes. The maximum gas concentrations in the different openings could be the optimum value to represent the concentration in the exit air.► Methods for calculating natural ventilation rate were assessed using a CFD model. ► Internal gas sampling may cause large errors to estimate ventilation rate. ► Gas sampling positions should be close to the sidewall openings. ► Maximum gas concentration in different openings may represent that in exit air.
Keywords: Porous media; Ventilation; Tracer gas; Emission; Sampling position;

This paper presents a computational investigation of the residence of atmospheric contaminants in the wake of an isolated cubical building under different stability conditions, using the computational fluid dynamics code ADREA-HF. Characteristic concentration decay times describing the detrainment behaviour of gas in the near-wake are assessed for different atmospheric stability conditions and the results are compared with experiments conducted in the field (Mavroidis et al., 1999). The flow and concentration fields are also investigated computationally. Two building orientations are examined, with the mean wind direction normal to or at 45° to the leading face of the cubical building. Characteristic decay time patterns calculated by the model agree in general with the experimental ones, while there is a tendency for the model to overestimate dilution rates for the wind direction normal to the face of the building. The residence time (T d), defined as the time it takes for gas concentration to decay to 1/e of its original value, depends on atmospheric stability, with higher values observed in general under stable conditions; T d is especially influenced by the prevailing wind speeds, with a tendency for higher values under lower wind speeds. On the other hand, the non-dimensional residence time (τ = UT d/H) is to a large extent independent of the atmospheric stability conditions, as also indicated by the experimental measurements. Residence times are in general larger when the cube is oriented at 45° to the wind than when it is normal to the wind. Finally, the spatial variability of the calculated residence time T d is also presented and discussed.► Gas residence in the wake of an isolated cube was investigated using a CFD model. ► Residence times were compared with field results for different stability conditions. ► For the cube normal to the flow the model underestimated residence times. ► Non-dimensional residence times are in general independent of atmospheric stability. ► A power law dependence was observed between residence times and wind speed.
Keywords: Pollutant dispersion; Atmospheric stability; CFD models; Isolated building; Residence time; Wake region;

Formation of secondary organic carbon and long-range transport of carbonaceous aerosols at Mount Heng in South China by Shengzhen Zhou; Zhe Wang; Rui Gao; Likun Xue; Chao Yuan; Tao Wang; Xiaomei Gao; Xinfeng Wang; Wei Nie; Zheng Xu; Qingzhu Zhang; Wenxing Wang (203-212).
To understand the sources and formation processes of atmospheric carbonaceous aerosols in rural and mountainous areas of South China, an intensive measurement campaign was conducted at the summit of Mount Heng (27°18′N, 112°42′E, 1269 m asl) during the spring of 2009. The observed average concentrations of organic carbon (OC) and elemental carbon (EC) were 3.01 ± 2.2 and 0.54 ± 0.3 μg m−3, respectively. The total carbonaceous aerosols (TCA) averagely contributed to 20.7% of PM2.5. High OC/EC ratios (range: 1.6–10.4; average: 5.2 ± 1.8) were observed, suggesting the transport and secondary origins of the carbonaceous aerosols at Mount Heng. The amount of secondary organic carbon (SOC) was estimated using the EC-tracer method and accounted for 53.9% of the total OC on average. Good correlations were found between SOC and droplet-mode sulfate, and oxalate and droplet-mode sulfate, indicating the occurrence of in-cloud secondary organic aerosol (SOA) formation at Mount Heng. The concentrations of SOC and water soluble organic acids also displayed positive relationship with aerosol acidity, suggesting the enhancement of SOC formation by acid-catalyzed heterogeneous reactions. Backward trajectory analysis revealed that the observed aerosols at Mount Heng were predominantly associated with the air masses from the Pearl River Delta region (PRD) and Eastern China, which brought significant amounts of anthropogenic pollutants to the site. In addition, strong signals of biomass burning (elevated carbonaceous concentrations, OC/EC ratios and K+ concentrations) were observed in air masses from Southeast Asia, demonstrating that the biomass burning emissions in Southeast Asia could reach the boundary layer of South China and affect the air quality there during the spring season.► Characteristics of carbonaceous aerosols at Mount Heng in South China. ► SOC estimated from the EC-tracer method accounted for more than half of the total OC. ► In-cloud processing and acid-catalyzed reactions both contributed to SOA formation. ► Long-range transport of carbonaceous aerosol from PRD and eastern China was observed. ► Biomass burning emissions in Southeast Asia affected the air quality of South China.
Keywords: Carbonaceous aerosols; Secondary organic carbon (SOC); Cloud processing; Acid-catalyzed reactions; Long-range transport;

Episodes of exceptionally high surface ozone (O3) levels were measured in the Seoul Metropolitan Area (SMA) from July 6 to July 8. During the episode period, the 1-h average O3 concentration exceeded the daily maximum of 80 ppb over three consecutive days. In order to understand the mechanisms behind the increased O3 concentrations on consecutive days, several numerical experiments were conducted using the atmospheric dynamic model WRF for assessing the atmospheric flow as well as CMAQ for the estimation of the amount of photochemical ozone.Gradually increasing ozone concentration during episode period in SMA depends not only on the variation of meteorological conditions and the emission rate of precursors but also on the accompanying precursors within the air mass recirculation that are emitted from the SMA and its surrounding areas. The impact from the recirculation of precursors responsible for the increased ozone concentration was clarified for numerical studies using the particle dispersion model FLEXPART. Results obtained from our experimental model also demonstrated that recirculated O3 precursors such as nitrogen oxide (NO x) and volatile organic compounds (VOCs) significantly influenced O3 levels. During the episode period, NO x and VOCs concentrations in the PBL increased by an average of 2.9% and 19.7%, respectively, through recirculation. The recirculated precursors also are involved in the activation of photochemical reactions responsible for the formation of O3, leading to an average increase in the local O3 production of 10.9 ppb. And overall effect due to recirculation is dependent on the actual path and direction of recirculation.► We clarify the impact of atmospheric recirculation on consecutive high-O3 cases. ► Precursors behavior due to atmospheric recirculation can vary ozone formation. ► High-O3 concentration was more sensitive to VOCs concentration than NO x in Seoul.
Keywords: Ozone; Seoul; FLEXPART; Recirculation; CMAQ;

Multi-year black carbon emissions from cropland burning in the Russian Federation by Jessica L. McCarty; Evan A. Ellicott; Vladimir Romanenkov; Dmitry Rukhovitch; Polina Koroleva (223-238).
Cropland fires are an important source of black carbon (BC) emissions. Previous research has suggested that springtime cropland burning in Eastern Europe, more specifically Russia, is a main contributor of BC in the Arctic atmosphere, acting as a short-lived climate forcer strongly influencing snow-ice albedo and radiation transmission. BC emissions from cropland burning were estimated for the Russian Federation for years 2003 through 2009 using three satellite fire products, the 1 km MODIS Active Fire Product, 0.5° MODIS Fire Radiative Power monthly climate modeling grid product, and the 500 m MODIS Burned Area Product, and a agricultural statistics approach based on a modified method developed and published by the All-Russian Institute of Organic Peat and Fertilizers to estimate farm- and regional-level residue loading from straw surplus left after grain harvesting, while accounting for agricultural management and agrometeorological inputs. The satellite-based emission calculations utilized several different land cover classification schemas for defining croplands in Russia for both the 1 km MODIS Land Cover Product and the 300 m MERIS GlobCover v2.2 data sets. In general, the peaks of BC emissions from cropland burning occurred during the spring (April–May), summer (July–August), and the fall (October). 2008 had the highest annual BC emissions. The range of average annual BC emissions from cropland burning calculated from the different satellite fire products was 2.49 Gg–22.2 Gg, with the agricultural statistics approach annual average equal to 8.90 Gg. The Global Fire Emissions Database (GFED) version 3 reported an annual average of 11.9 Gg of BC from agricultural burning. The results from this analysis showed that the majority of BC emissions originated in European Russia, followed by smaller contributions from West Siberia, Far East Russia, and East Siberia macro-regions. An uncertainty assessment on data used to calculate the BC emissions found moderate uncertainty in some of the input data used in this first attempt to produce spatially and temporally explicit BC emission estimates from cropland burning in the Russian Federation.► Quantified cropland fire and black carbon emissions for the Russian Federation. ► Peaks of BC emissions occurred in the spring, summer, and fall. ► Highest BC emissions occurred during spring in European Russia and West Siberia. ► The range of average annual BC emissions was 2.49 Gg–22.2 Gg.
Keywords: Cropland fires; Remote sensing; Black carbon; Biomass burning; Russian Federation;

Emissions characterization of residential wood-fired hydronic heater technologies by John S. Kinsey; Abderrahmane Touati; Tiffany L.B. Yelverton; Johanna Aurell; Seung-Hyun Cho; William P. Linak; Brian K. Gullett (239-249).
Residential wood-fired hydronic heaters (RWHHs) can negatively impact the local ambient air quality and thus are an environmental concern in wood burning areas of the U. S. Only a few studies have been conducted which characterize the emissions from RWHHs. To address the lack of emissions data, a study was conducted on four appliances of differing design using multiple fuel types to determine their thermal, boiler, and combustion efficiency as well as the emissions of carbon dioxide (CO2), carbon monoxide (CO), total hydrocarbons (THC), nitrous oxide (N2O), methane (CH4), total particulate matter (PM) mass, and particle number as well as particle size distribution (PSD). Three of these appliances were fired with split-log cordwood with the fourth unit using hardwood pellets. The measured thermal efficiencies for the appliances tested varied from 22 to 44% and the combustion efficiencies from 81 to 98%. Depending on appliance and fuel type, the emission factors ranged from about 1300 to 1800 g kg−1 dry fuel for CO2, 8–190 g kg−1 dry fuel for CO, <1–54 g kg−1 dry fuel for THC and 6–120 mg kg−1 for N2O. For the particle phase pollutants, the PM mass emission factors ranged from 0.31 to 47 g kg−1 dry fuel and the PM number emission factors from 8.5 × 1010 to 2.4 × 1014 particles kg−1 dry fuel, also depending on the appliance and fuel tested. The PSD for all four appliances indicated a well established accumulation mode with evidence of a nucleation mode present for Appliances A and B. The average median aerodynamic particle diameters observed for the four appliances ranged from 84 to 187 nm while burning red oak or pellets. In general, the pellet-burning appliance had the highest overall operating efficiency and lowest emissions of the four units tested.► Four residential wood-fired hydronic heaters were tested with multiple fuels. ► Combustion efficiency as well as gas and particle emissions were determined. ► The emissions varied widely depending on the technology and fuel utilized. ► The pellet-burning appliance had the highest efficiency and lowest emissions.
Keywords: Residential wood-fired hydronic heaters; Thermal efficiency; Gaseous emissions; Particle emissions;

Ultrafine particle size distributions near freeways: Effects of differing wind directions on exposure by Kathleen H. Kozawa; Arthur M. Winer; Scott A. Fruin (250-260).
High ambient ultrafine particle (UFP) concentrations may play an important role in the adverse health effects associated with living near busy roadways. However, UFP size distributions change rapidly as vehicle emissions dilute and age. These size changes can influence UFP lung deposition rates and dose because deposition in the respiratory system is a strong function of particle size. Few studies to date have measured and characterized changes in near-road UFP size distributions in real-time, thus missing transient variations in size distribution due to short-term fluctuations in wind speed, direction, or particle dynamics. In this study we measured important wind direction effects on near-freeway UFP size distributions and gradients using a mobile platform with 5-s time resolution. Compared to more commonly measured perpendicular (downwind) conditions, parallel wind conditions appeared to promote formation of broader and larger size distributions of roughly one-half the particle concentration. Particles during more parallel wind conditions also changed less in size with downwind distance and the fraction of lung-deposited particle number was calculated to be 15% lower than for downwind conditions, giving a combined decrease of about 60%. In addition, a multivariate analysis of several variables found meteorology, particularly wind direction and temperature, to be important in predicting UFP concentrations within 150 m of a freeway (R 2 = 0.46, p = 0.014).► UFP size distributions were measured in real-time with a mobile platform. ► Wind direction shown critical to ultrafine number and size downwind of freeways. ► Particle number decreases up to half as winds deviate from perpendicular. ► Particle size also increases, further reducing lung deposition and dose by ∼15%.
Keywords: Ultrafine particles; Size distribution; Wind direction; Freeways;

Spatio-temporal variability of the atmospheric boundary layer depth over the Paris agglomeration: An assessment of the impact of the urban heat island intensity by S. Pal; I. Xueref-Remy; L. Ammoura; P. Chazette; F. Gibert; P. Royer; E. Dieudonné; J.-C. Dupont; M. Haeffelin; C. Lac; M. Lopez; Y. Morille; F. Ravetta (261-275).
Within the framework of a French nationally funded project (CO2-MEGAPARIS) for quantifying the CO2 emissions of the Paris area, a lidar-based experimental investigation of the variability of the atmospheric boundary layer (ABL) depths was performed over four days in March 2011 under clear sky conditions. The prevailing synoptic settings were mainly characterized by anti-cyclonic situations with low wind. The key aim of this paper is to assess the impact of the urban heat island intensity (UHII) on the spatio-temporal variability of the ABL depths over the Paris megacity. A network of fixed aerosol lidars was deployed inside the city and in the vicinity of sub-urban and rural areas. Additionally, the spatial heterogeneity of the nocturnal boundary layer (NBL) depths over greater Paris area is addressed, thanks in particular, to the deployment of a 355-nm elastic lidar in a mobile van to measure the aerosol distributions. Radiosonde-derived profiles (twice a day) of thermodynamic variables over the sub-urban site helped investigate the temperature inversion above ground and hence to compare the lidar-derived ABL depths. Comparing these two results, an excellent concordance was found with a correlation coefficient of 0.994.Five important factors closely related to the ABL circulation, namely, spatio-temporal variability of the ABL depths, growth rate of the ABL depths, entrainment zone thickness, and near-surface temperature fields including resultant UHII were considered to infer the urban–rural contrasts. The mean NBL depth over the urban area was on average 63 m (45%) higher than its adjacent sub-urban area which was, on occasion, as much as (74 m) 58% higher mainly due to the effect of UHII. Daytime well-mixed convective boundary layer and associated strong turbulent mixing near its top over the urban area showed higher entrainment zone thickness (326 m) than over sub-urban (234 m) and rural (200 m) areas. Temperature growth rates during sunrise increased up to more than 3 °C h−1 over the sub-urban area while over the urban region it was 2.5 °C h−1 or even less. The ABL depths over the urban site decayed more slowly (500 m h−1) than over the sub-urban area (600 m h−1) during the late afternoon transition period suggesting an impact of the UHII on the ABL dynamics over the urban area.► Multi-lidar investigation of spatio-temporal variability of the ABL depth around Paris. ► First mobile lidar-based study of the spatial variability of NBL depth around a megacity. ► Assessment of impact of urban heat island (UHI) intensity and urban–rural contrast on ABL depth evolution. ► Higher entrainment zone thickness over urban area than over rural and sub-urban areas.
Keywords: Atmospheric boundary layer depth; Entrainment zone thickness; Lidar; Nocturnal boundary layer; Urban heat island; Wavelet analysis;

The objective of this field study is to evaluate temporal reduction efficiency of air cleaner emitting plasma ion on airborne pollutants emitted from pig building. The operation principle of air cleaner based on plasma ion is that hydrogen atoms and oxygen ions combine to form hydroperoxyl radicals (HOO), which surround and attach to surface of airborne microorganisms and eliminate them by breaking the hydrogen bond in their protein structure. In gaseous pollutants, it was found that there is no reduction effect of the air cleaner on ammonia and hydrogen sulfide (p > 0.05). In particulate pollutants, the air cleaner showed mean 79%(±6.1) and 78%(±3.0) of reduction efficiency for PM2.5. and PM1, respectively, compared to the control without air cleaner (p < 0.05). However, there is no significant difference in TSP and PM10 between the treatment with air cleaner and the control without air cleaner (p > 0.05). In biological pollutants, the mean reduction efficiencies for airborne bacteria and fungi by application of air cleaner were 22%(±6.6) and 25%(±8.7), respectively (p < 0.05). Based on the results obtained from this study, it was concluded that the air cleaner had a positive reduction effect on PM2.5, PM1, airborne bacteria and airborne fungi among airborne pollutants distributed in pig building while it did not lead to significant reduction of ammonia and hydrogen sulfide.► This is the first study wholly which applies air cleaner to livestock house. ► The air cleaner showed a positive reduction effect on dust and bioaerosol. ► Ammonia and hydrogen sulfide were not lowered significantly by air cleaner.
Keywords: Air cleaner; Plasma ion; Pig building; Airborne contaminant;

Black carbon aerosols variation in Kathmandu valley, Nepal by R.K. Sharma; B.K. Bhattarai; B.K. Sapkota; M.B. Gewali; B. Kjeldstad (282-288).
Black carbon (BC) aerosols were measured using an aethalometer (AE-31) at Pulchowk Campus, an urban location of Kathmandu valley, Nepal from May 2009 to April 2010. The amount of BC in the total mass of the suspended particulate matter (TSP) were estimated by comparing the average BC with mass of particulate matter simultaneously measured with frm Omni Ambient Air Sampler for the last two months (March–April, 2010). BC concentration shows significant temporal variation with monthly mean concentration varying between 14.9 μg m 3 and 3.0 μg m 3. The highest daily mean concentration was recorded as high as 39.9 μg m 3. The highest concentration of BC occurred during winter and pre-monsoon seasons. The lowest concentration of BC was found during monsoon and post-monsoon seasons. A distinct diurnal variation of BC with two high peaks occurred; one in around 09:00 morning and another late evening around 20:00 local time. Minimum BC concentration was also observed in the afternoon. The annual average of BC for observation period was 8.6 ± 4.4 μg m 3. The seasonal, monthly and diurnal variation of BC were found to be significantly influenced by the local traffic movements, the domestic and industrial fuel consuming activities, wind speed, wind direction and rain. The amount of BC in the total mass of particulate matters during the observed period varied between 11.6 and 56.2 percent. This variation is attributed to the high amount of re-suspension of dust particles in the atmosphere of the valley.► For the first time Black Carbon (BC) was continuously monitored for one year from May 2009 to April 2010 in Kathmandu, Nepal. ► Diurnal, monthly and seasonal variation of BC was observed. ► Anti-correlation of BC with rain was better than BC with wind. ► Local events also effect in the variation of BC concentration in the valley. ► Percentage of BC in particulate matters varies between 11.6 and 56.2 percent.
Keywords: Black carbon; Aethalometer; Frm Omni Sampler; Aerosol; Diurnal; Seasonal;

Comparison of wintertime CO to NO x ratios to MOVES and MOBILE6.2 on-road emissions inventories by H.W. Wallace; B.T. Jobson; M.H. Erickson; J.K. McCoskey; T.M. VanReken; B.K. Lamb; J.K. Vaughan; R.J. Hardy; J.L. Cole; S.M. Strachan; W. Zhang (289-297).
The CO-to-NO x molar emission ratios from the US EPA vehicle emissions models MOVES and MOBILE6.2 were compared to urban wintertime measurements of CO and NOx. Measurements of CO, NO x , and volatile organic compounds were made at a regional air monitoring site in Boise, Idaho for 2 months from December 2008 to January 2009. The site is impacted by roadway emissions from a nearby busy urban arterial roads and highway. The measured CO-to-NO x ratio for morning rush hour periods was 4.2 ± 0.6. The average CO-to-NO x ratio during weekdays between the hours of 08:00 and 18:00 when vehicle miles travelled were highest was 5.2 ± 0.5. For this time period, MOVES yields an average hourly CO-to-NO x ratio of 9.1 compared to 20.2 for MOBILE6.2. Off-network emissions are a significant fraction of the CO and NO x emissions in MOVES, accounting for 65% of total CO emissions, and significantly increase the CO-to-NO x molar ratio. Observed ratios were more similar to the average hourly running emissions for urban roads determined by MOVES to be 4.3.► Observed CO-to-NO x molar ratio much lower than MOVES (20.2) and MOBILE (9.1). ► Morning winter rush hour CO-to-NO x molar ratio was 4.2 ± 0.06. ► Off-network emissions account for 65% of hourly emitted CO and 23% of the NO x .
Keywords: Air quality; Urban emissions; Roadway emissions; MOVES; CO; NO x ;

Intake fractions of primary conserved air pollutants emitted from on-road vehicles in the United States by Agnes B. Lobscheid; William W. Nazaroff; Michael Spears; Arpad Horvath; Thomas E. McKone (298-305).
Vehicular air pollutant emissions are characterized by a high degree of spatial variability that is correlated with the distribution of people. The consequences of the spatial association between emissions and exposed populations have not been fully captured in lifecycle and other impact assessments. The intake fraction (iF) quantifies aggregate air-pollutant exposures attributable to sources. Utilizing source–receptor (S–R) relationships derived from the US Environmental Protection Agency's AERMOD steady-state plume model, we quantify the intake fraction of conserved pollutants emitted from on-road mobile sources and report here the first characterization across approximately 65,000 census tracts of the conterminous United States. Considering exposures out to 50 km from the source, the population-weighted mean iF is 8.6 parts per million (ppm). The population-weighted median generally increases with geographic scale, from 3.6 ppm for census tracts to 4.2 ppm for counties, and 5.1 ppm for states, while the population-weighted interquartile range (IQR) progressively narrows as geographic scale increases: 0.85–8.8 ppm for census tracts, 1.5–8.5 ppm for counties, and 3.2–7.5 ppm for states. Across the four US Census regions, the population weighted median iF varies from 2.2 ppm (South) to 7.5 ppm (West), and the census-tract IQR spans an order of magnitude in each region (2.1–17 ppm in the West; 0.55–6.9 ppm in the Midwest; 0.45–5.5 ppm in the South; and 1.8–18 ppm in the Northeast). The population-weighted mean intake fraction for populous urban counties is about two orders of magnitude greater than for sparsely populated rural counties. On a population-weighted average basis and considering the 50 km analysis range, 75% of the intake occurs in the same county as emissions.► We use source–receptor relationships to estimate intake fraction (iF) due to traffic. ► The iF is quantified with high spatial resolution across the conterminous US. ► Across all census tracts, the national population-weighted mean iF is 8.6 ppm. ► The mean iF is about two orders of magnitude greater for urban than rural counties. ► On average, 75% of the intake occurs in the same county as emissions.
Keywords: Air toxics; Exposure assessment; Mobile sources; Traffic; AERMOD; Source–receptor modeling;

Indoor contaminants from Hardcopy Devices: Characteristics of VOCs in photocopy centers by Maryam Sarkhosh; Amir Hossein Mahvi; Mohammad Reza Zare; Yadolah Fakhri; Hamid Reza Shamsolahi (307-312).
Indoor air pollution in working places is widely recognized as one of the most serious potential environment risks to human health. Mean volatile organic compound (VOC) concentrations of 144 samples from four copy centers in Tehran, Iran in two seasons were monitored for the purpose of quantifying the various VOCs in these areas. Area samples were collected in thermal desorption tubes and were analyzed using gas chromatography/mass selective detector. Real-time personal total volatile organic compounds were measured using a data-logging photo-ionization detector. Simultaneously, BTEX (benzene, toluene, ethylbenzene, xylenes) outdoor measurements were performed in the same manner as were the indoor measurements. Nineteen different VOCs were detected in the area samples. The results show that in all photocopy centers, the indoor levels of toluene were much higher than the outdoor levels. During business hours, the VOC levels increased, especially toluene indoor concentration. The ventilation decreased the indoor VOC concentrations. The background and indoor VOC concentrations were higher in winter than in spring. The minimum ratio of the indoor to outdoor concentration of BTEX was estimated to be more than 42. This value proved that buildings with photocopiers can be a site of VOC accumulation.► Nineteen VOCs were detected on the background samples of copy centers. ► Indoor to outdoor fraction (in/out) value of BTEX for all samples are more than 42. ► In this regards minimum value (42) of in/out is related to Benzene in winter. ► In addition to toluene, other BTEXs have a high concentration in winter and spring. ► Average concentrations of BTEX compounds were not the same in winter and spring.
Keywords: BTEX; Toluene; Indoor air quality; Volatile organic compounds; Outdoor levels; Background concentration;

This paper investigates influence of pavement macrotexture on paved road PM10 emissions. This study was conducted on different paved roadway types (local, collector and minor arterial) in the Las Vegas Valley, Nevada. Pavement macrotexture was measured using the ASTM E 965 sand patch method and the Digital Surface Roughness Meter™ (DSRM™). A controlled constant soil loading with known PM10 fraction was applied to cleaned road surfaces. The Desert Research Institute's (DRI) Mini-PI-SWERL™ (Portable In-Situ Wind ERosion Lab) was used to estimate PM10 mass emissions and cumulative mass emitted from pavement surfaces. PM10 mass emissions using controlled applied soil loadings generally declined with increasing pavement macrotexture at all applied shear levels. The relationships were statistically significant, and indicate that pavement macrotexture may need to be included in future development of revised paved road PM10 emissions factors.A change in the slope of emitted PM10 mass and pavement macrotexture occurred between 0.8 and 0.9 mm mean texture depth (MTD). Anomalies in PM10 mass emissions were observed at MTDs exceeding 1.2 mm. Two-way frequency distributions of pavement surface features obtained from DSRM measurements were analyzed to explain the observed anomalies. Results showed that pavement surface feature size distributions may influence on PM10 emissions from paved roads at similar MTDs.PM10 mass emissions were found to linearly depend on adjusted mode size of the pavement surface aggregate. A sharp decrease in friction velocities, computed from wind erosion theory, at MTDs above 0.9 mm matched an observed sharp decrease in PM10 emissions rates at MTDs above 0.9 mm, indicating that classical wind erosion theory could be adapted for non-erodible pavement surfaces and linearly relate PM10 emissions rates to applied shear stress at an aerodynamic roughness height of 0.075 mm.Display Omitted► PM10 emissions declined with increasing asphalt pavement macrotexture. ► PM10 emissions exceeded portion applied PM10, indicating coarse particle break up. ► Two-way pavement frequency distributions explain PM10 emissions at high MTDs. ► Pavement mode sizes used to estimate friction velocity and aero roughness height. ► Wind erosion theory explained PM10 emissions rates from the asphalt pavement.
Keywords: Aggregate mode; Mean texture depth; Pavement macrotexture; PM10 emission; Soil loading; Wind erosion theory;

Effect of beef cattle manure application rate on CH4 and CO2 emissions by Nhu-Thuc Phan; Ki-Hyun Kim; David Parker; Eui-Chan Jeon; Jae-Hwan Sa; Chang-Sang Cho (327-336).
In a series of field experiments, emissions of two major greenhouse gases (GHGs), methane (CH4) and carbon dioxide (CO2) were measured using a closed chamber technique in summer 2010 to evaluate the effects of solid beef cattle manure land application techniques. The treatments included a control (C: no manure), two manure application rates (40 and 80 T ha−1), and two injection layers (surface vs. subsurface (5 cm)): (1) 40 T ha−1 on surface (S40), (2) 80 T ha−1 on surface (S80), (3) 40 T ha−1 at subsurface (D40), and (4) 80 T ha−1 at subsurface (D80)). The exchange patterns of CH4 and CO2 in the control were variable and showed both emission and deposition. However, only emissions were seen in the manure treatments. Emissions of CH4 were seen systematically on the ascending order of 5.35 (C), 59.3 (S40), 68.7 (D40), 188 (S80), and 208 μg m−2 h−1 (D80), while those of CO2 also showed a similar trend: 12.9 (C), 37.6 (S40), 55.8 (D40), 82.4 (S80), and 95.4 mg m−2 h−1 (D80). The overall results of our study suggest that the emissions of CH4 and CO2 are affected most noticeably by the differences in the amount of manure application.► The application of solid manure can release large quantities of greenhouse gases (GHG). ► Its implication has scarcely been evaluated with respect to solid beef cattle manure. ► The behavior of CH4 and CO2 was examined in relation to manure treatment conditions. ► This study will help establish a management scheme for the GHGs from manure treatment.
Keywords: Beef cattle manure; Greenhouse gas (GHG); Emission; Flux; CH4; CO2;