Atmospheric Environment (v.43, #39)

Isoprene emissions and climate by F. Pacifico; S.P. Harrison; C.D. Jones; S. Sitch (6121-6135).
Biogenic volatile organic compounds (BVOCs) play an important role in atmospheric chemistry and the carbon cycle. Isoprene is quantitatively the most important of the non-methane BVOCs (NMBVOCs), with an annual emission of about 400–600 TgC; about 90% of this is emitted by terrestrial plants. Incorporating a mechanistic treatment of isoprene emissions within land-surface schemes has recently become a focus for the modelling community, the aim being to quantify the potential magnitude of associated climate feedbacks. However, these efforts are hampered by major uncertainties about why plants emit isoprene and the relative importance of different environmental controls on isoprene emission. The availability and reliability of observations of isoprene fluxes from different types of vegetation is limited, and this also imposes constraints on model development. Nevertheless, progress is being made towards the development of mechanistic models of isoprene emission which, in conjunction with atmospheric chemistry models, will ultimately allow improved quantification of the feedbacks between the terrestrial biosphere and climate under past and future climate states.
Keywords: Isoprene; Biospheric flux measurements; Biosphere emission modelling; Biosphere feedback; Atmospheric chemistry; Climate change; Earth system modelling;

Gases and particulate matter predictions from the UCD/CIT air quality model were used in a visibility model to predict source contributions to visual impairment in the San Joaquin Valley (SJV), the southern portion of California's Central Valley, during December 2000 and January 2001. Within the SJV, daytime (0800–1700 PST) light extinction was dominated by scattering associated with airborne particles. Measured daytime particle scattering coefficients were compared to predicted values at approximately 40 locations across the SJV after correction for the increased temperature and decreased relative humidity produced by “smart heaters” placed upstream of nephelometers. Mean fractional bias and mean fractional error were −0.22 and 0.65, respectively, indicating reasonable agreement between model predictions and measurements. Particulate water, nitrate, organic matter, and ammonium were the major particulate species contributing to light scattering in the SJV. Daytime light extinction in the SJV averaged between December 25, 2000 and January 7, 2001 was mainly associated with animal ammonia sources (28%), diesel engines (18%), catalyst gasoline engines (9%), other anthropogenic sources (9%), and wood smoke (7%) with initial and boundary conditions accounting for 13%. The source apportionment results from this study apply to wintertime conditions when airborne particulate matter concentrations are typically at their annual maximum. Further study would be required to quantify source contributions to light extinction in other seasons.
Keywords: CRPAQS; Source apportionment; UCD/CIT air quality model; Visibility;

This study identified sources of mercury (Hg) in downtown Toronto, Canada by analyzing gaseous elemental mercury (GEM), mercury associated with particles with sizes less than 2.5 microns (PHg < 2.5), and gaseous oxidized inorganic mercury (GOIM), commonly referred to as reactive gaseous mercury (RGM), and air pollutants (CO, NOx, O3, PM2.5, SO2) concentrations between Dec 2003 and Nov 2004. The data were analyzed using Positive Matrix Factorization (PMF) model, Principal Components Analysis (PCA), ratio analysis, back trajectories, and correlation analyses. The analyses suggest industrial sources (chemical production, metal production, sewage treatment), rather than coal combustion, were the major contributors to measured Hg levels. Overlap in source profiles for the Hg sources listed in the Canadian National Pollutant Release Inventory (NPRI) and lack of source profiles for urban sources were the major limitations to positively identifying sources from the PMF and PCA factors. Correlation analyses revealed direct emissions were the sources of GOIM in spring, summer, and fall, and the occurrence of GEM oxidation by ozone in the summer. Elevated Hg events are attributed to emissions from urban sources near the sampling site, regional point sources, and photochemical processes involving ozone.
Keywords: GEM; GOIM; Mercury sources; RGM; Speciation;

Characterization of atmospheric aerosols by SEM in a rural area in the western part of México and its relation with different pollution sources by A. Campos-Ramos; A. Aragón-Piña; I. Galindo-Estrada; Xavier Querol; Andrés Alastuey (6159-6167).
Samples of particulate matter were collected during the period from October 2006 through September 2007 in a rural station located 12 km from the city of Colima. A total of 3600 particles were analyzed by SEM-EDS and then classified by their chemical composition and morphology in order of abundance: those rich in C, Fe, Si–Al, Cl–Na, Ca, Ba; and to a lesser abundance, particles rich in heavy metals such as Pb and V–Ni were observed. A factorial analysis was carried out to determine the main elements related with the emission sources such as crustal/farming; fuel-oil; marine; volcanic activity and industry. Trough the seasons, the dominant winds causes the presence of anthropogenic particles in the rural site. The information presented in this study aims to give insight and detailed of the analysis of the morphological characteristics and chemical composition of atmospheric particles at individual level in a rural site from Colima State, Mexico.
Keywords: PM10; Electron-microscopy; Statistical analysis; Emission sources;

There is considerable public concern regarding the potential risks to health of electromagnetic fields in general and high-voltage power lines in particular. As epidemiological findings are not supported by a clearly defined mechanism of direct magnetic field interactions with the human body, potential indirect effects are of interest. It has been suggested that an increased exposure to chemical pollutants could occur near high-voltage power lines due to formation and deposition of charged aerosols. The current study reports empirical evidence that seems to support this hypothesis. The deposition of 18 congeners of polychlorinated biphenyls (PCBs) was studied by collecting samples of pine needles under a 400 kV AC power line and at reference sites in the vicinity. Compared to the reference sites, the average deposition of PCB congeners under the power line was almost double. This difference between the two groups of samples was statistically significant. While it is premature to draw any conclusions regarding the human exposure near high-voltage power lines, the issue deserves attention and further investigations.
Keywords: Atmospheric electric field; Corona ions; Nanoparticles; Polychlorinated biphenyls; Semi-volatile organic compounds;

Reducing carbonyl emissions from a heavy-duty diesel engine at US transient cycle test by use of paraffinic/biodiesel blends by Chung-Shin Yuan; Yuan-Chung Lin; Cheng-Hsien Tsai; Chia-Chieh Wu; Yu-Sheng Lin (6175-6181).
Formaldehyde and acetaldehyde are toxic carcinogens so their reductions in diesel-engine emissions are desirable. This study investigated emissions of carbonyl compounds (CBCs) from an HDDE (heavy-duty diesel engine) at US transient cycle test, using five test fuels: premium diesel fuel (D100), P100 (100% palm-biodiesel), P20 (20% palm-biodiesel + 80% premium diesel fuel), PF80P20 (80% paraffinic fuel + 20% palm-biodiesel), and PF95P05 (95% paraffinic fuel + 5% palm-biodiesel). Experimental results indicate that formaldehyde was the major carbonyl in the exhaust, accounting for 70.1–76.2% of total CBC concentrations for all test fuels. In comparison with D100 (172 mg BHP−1 h−1), the reductions of formaldehyde and acetaldehyde emission factor for P100, P20, PF80P20, and PF95P05 were (−16.8%, −61.8%), (−10.0%, −39.0%), (21.3%, 1.10%), and (31.1%, 19.5%), respectively. Using P100 and P20 instead of D100 in the HDDE increased CBC concentrations by 14.5% and 3.28%, respectively, but using PF80P20 and PF95P05 significantly reduced CBC concentrations by 30.3% and 23.7%, respectively. Using P100 and P20 instead of D100 (2867 ton yr−1) in the HDDE increased CBC emissions by 240 and 224 ton yr−1, respectively, but using PF80P20, and PF95P05 instead of D100 in the HDDE decreased CBC emissions by 711 and 899 ton yr−1, respectively. The above results indicate that the wide usage of paraffinic–palmbiodiesel blends as alternative fuels could protect the environment.
Keywords: Carbonyl compounds; Biodiesel; Paraffinic fuel; Diesel engine;

The Italian Air Quality legislation underwent sweeping changes with the implementation of the 1996 European Air Quality Framework Directive when the Italian administrative Regions were entrusted with air quality management tasks. The most recent Regional Air Quality Management Plans (AQMPs) highlighted the importance of Non-Technical Measures (NTMs), in addition to Technical Measures (TMs), in meeting environmental targets. The aim of the present work is to compile a list of all the TMs and NTMs taken into account in the Italian Regional AQMPs and to give in the target year, 2010, an estimation of SO2, NOx and PM10 emission reductions, of PM10 concentration and of the health impact of PM2.5 concentrations in terms of Life Expectancy Reduction. In order to do that, RAINS-Italy, as part of the National Integrated Modeling system for International Negotiation on atmospheric pollution (MINNI), has been applied. The management of TMs and NTMs inside RAINS have often obliged both the introduction of exogenous driving force scenarios and the control strategy modification. This has inspired a revision of the many NTM definitions and a clear choice of the definition adopted. It was finally highlighted that only few TMs and NTMs implemented in the AQMPs represent effective measures in reaching the environmental targets.
Keywords: Integrated assessment model; Air quality management Plan; Control policies; Technical/Non-Technical Measures; Air pollution;

Comprehensive primary particulate organic characterization of vehicular exhaust emissions in France by Imad El Haddad; Nicolas Marchand; Julien Dron; Brice Temime-Roussel; Etienne Quivet; Henri Wortham; Jean Luc Jaffrezo; Christine Baduel; Didier Voisin; Jean Luc Besombes; Gregory Gille (6190-6198).
A study to characterize primary particulate matter (PM2.5 and PM10) from the French vehicular fleet was conducted during winter 2008, in a tunnel in Marseille, France. The carbonaceous fraction represents 70% of the aerosol mass and elemental carbon fraction (EC) represent 60% of the carbonaceous fraction. The organic carbon OC was characterized in term of its water soluble fraction, functionalization rate and HULIS content. Seventy trace organic compounds including alkanes, polycyclic aromatic hydrocarbons (PAH), petroleum biomarkers and carboxylic acids were also quantified, in order to determine an organic emission profile for chemical mass balance modeling studies. Such source profiles were still missing in Europe and particularly in France. The profile obtained in this study is consistent with profiles determined in tunnel or dynamometer studies performed in other countries during the last ten years. These results suggest that organic compounds profiles from vehicular exhaust emissions are not significantly influenced by the geographic area and are thus suitable for use in aerosol source apportionment modeling applied across extensive regions. The chemical profile determined here is very similar to those obtained for diesel emissions with high concentrations of EC relative to OC (EC/OC = 1.8) and low concentrations of the higher molecular weight PAH. These results are consistent with the high proportion of diesel vehicles in the French fleet (49%).
Keywords: Organic aerosol; Vehicular emissions; Organic markers; Functional analyses; Tunnel experiment; Marseille;

Indoor acrolein emission and decay rates resulting from domestic cooking events by Vincent Y. Seaman; Deborah H. Bennett; Thomas M. Cahill (6199-6204).
Acrolein (2-propenal) is a common constituent of both indoor and outdoor air, can exacerbate asthma in children, and may contribute to other chronic lung diseases. Recent studies have found high indoor levels of acrolein and other carbonyls compared to outdoor ambient concentrations. Heated cooking oils produce considerable amounts of acrolein, thus cooking is likely an important source of indoor acrolein. A series of cooking experiments were conducted to determine the emission rates of acrolein and other volatile carbonyls for different types of cooking oils (canola, soybean, corn and olive oils) and deep-frying different food items. Similar concentrations and emission rates of carbonyls were found when different vegetable oils were used to deep-fry the same food product. The food item being deep-fried was generally not a significant source of carbonyls compared to the cooking oil. The oil cooking events resulted in high concentrations of acrolein that were in the range of 26.4–64.5 μg m−3. These concentrations exceed all the chronic regulatory exposure limits and many of the acute exposure limits. The air exchange rate and the decay rate of the carbonyls were monitored to estimate the half-life of the carbonyls. The half-life for acrolein was 14.4 ± 2.6 h, which indicates that indoor acrolein concentrations can persist for considerable time after cooking in poorly-ventilated homes.
Keywords: Acrolein; Emission rate; Cooking oil; Carbonyl; Indoor air;

High time-resolved measurements of organic air toxics in different source regimes by J.M. Logue; K.E. Huff-Hartz; A.T. Lambe; N.M. Donahue; A.L. Robinson (6205-6217).
High time-resolved (HTR) measurements can provide significant insight into sources and exposures of air pollution. In this study, an automated instrument was developed and deployed to measure hourly concentrations of 18 gas-phase organic air toxics and 6 volatile organic compounds (VOCs) at three sites in and around Pittsburgh, Pennsylvania. The sites represent different source regimes: a site with substantial mobile-source emissions; a residential site adjacent to a heavily industrialized zone; and an urban background site. Despite the close proximity of the sites (less than 13 km apart), the temporal characteristic of outdoor concentrations varied widely. Most of the compounds measured were characterized by short periods of elevated concentrations or plume events, but the duration, magnitude and composition of these events varied from site to site. The HTR data underscored the strong role of emissions from local sources on exposure to most air toxics. Plume events contributed more than 50% of the study average concentrations for all pollutants except chloroform, 1,2-dichloroethane, and carbon tetrachloride. Wind directional dependence of air toxic concentrations revealed that emissions from large industrial facilities affected concentrations at all of the sites. Diurnal patterns and weekend/weekday variations indicated the effects of the mixing layer, point source emissions patterns, and mobile source air toxics (MSATs) on concentrations. Concentrations of many air toxics were temporally correlated, especially MSATs, indicating that they are likely co-emitted. It was also shown that correlations of the HTR data were greater than lower time resolution data (24-h measurements). This difference was most pronounced for the chlorinated pollutants. The stronger correlations in HTR measurements underscore their value for source apportionment studies.
Keywords: Air toxics; High time-resolved instrumentation; Air toxics temporal patterns; Meteorological effects on pollutant concentrations;

Long-term relationships between mercury wet deposition and meteorology by Lynne E. Gratz; Gerald J. Keeler; Eric K. Miller (6218-6229).
Daily-event precipitation samples collected in Underhill, VT from 1995 to 2006 were analyzed for total mercury and results suggest that there were no statistically significant changes in annual mercury wet deposition over time, despite significant emissions reductions in the Northeast United States. Meteorological analysis indicates that mercury deposition has not decreased as transport of emissions from major source regions in the Midwest and East Coast have consistently contributed to the largest observed mercury wet deposition amounts over the period. In contrast, annual volume-weighted mean (VWM) mercury concentration declined slightly over the 12-years, and a significant decrease was observed from CY 2001 to 2006. An increase in the total annual precipitation amount corresponded with the decline in annual VWM mercury concentration. Analysis suggests that the increase in precipitation observed was strongly related to changes in the amount and type of precipitation that fell seasonally, and this departure was attributed to a response in meteorological conditions to climate variability and the El Niño-Southern Oscillation (ENSO) cycle. Increased amounts of rainfall and mixed precipitation (mixture of rainfall and snowfall), particularly in the spring and fall seasons, enhanced annual precipitation amounts and resulted in declining VWM mercury concentrations during these periods. Thus, declines in concentration at the more remote Underhill site appear to be more directly linked to local scale meteorological and climatological variability than to a reduction in emissions of mercury to the atmosphere.
Keywords: Underhill, VT; Precipitation; Speciation; Seasonality; Climate variability; ENSO;

Air concentrations of polybrominated diphenyl ethers (PBDEs) in 2002–2004 at a rural site in the Great Lakes by Yushan Su; Hayley Hung; Kenneth A. Brice; Ky Su; Nick Alexandrou; Pierrette Blanchard; Elton Chan; Ed Sverko; Phil Fellin (6230-6237).
Atmospheric PBDEs were measured on a monthly basis in 2002–2004 at Point Petre, a rural site in the Great Lakes. Average air concentrations were 7.0 ± 13 pg m−3 for Σ14BDE (excluding BDE-209), and 1.8 ± 1.5 pg m−3 for BDE-209. Concentrations of 3 dominant congeners (i.e., BDE-47, 99, and 209) were comparable to previous measurements at remote/rural sites around the Great Lakes, but much lower than those at urban areas. Weak temperature dependence and strong linear correlations between relatively volatile congeners suggest importance of advective inputs of gaseous species. The significant correlation between BDE-209 and 183 implies their transport inputs associated with particles. Particle-bound percentages were found greater for highly brominated congeners than less brominated ones. These percentages increase with decreasing ambient temperatures. The observed gas/particle partitioning is consistent with laboratory measurements and fits well to the Junge–Pankow model. Using air mass back-trajectories, atmospheric transport to Point Petre was estimated as 76% for BDE-47, 67% for BDE-99, and 70% for BDE-209 from west–northwest and southwest directions. During the same time period, similar congener profiles and concentration levels were found at Alert in the Canadian High Arctic. Different inter-annual variations between Point Petre and Alert indicate that emissions from other regions than North America could also contribute PBDEs in the Arctic. In contrast to weak temperature effect at Point Petre, significant temperature dependence in the summertime implies volatilization emissions of PBDEs at Alert. Meanwhile, episodic observations in the wintertime were likely associated with enhanced inputs through long-range transport during the Arctic Haze period.
Keywords: Polybrominated diphenyl ether; Atmosphere; The Great Lakes; The Arctic;

A comparison of mesh-adaptive LES with wind tunnel data for flow past buildings: Mean flows and velocity fluctuations by Elsa Aristodemou; Tom Bentham; Christopher Pain; Roy Colvile; Alan Robins; Helen ApSimon (6238-6253).
In this paper we address two important aspects of micro-scale urban airflow model evaluation: (a) the identification of key flow features as dictated by the physics of the problem and as captured by the simulations, and (b) the comparison of important model output parameters (mean flows and fluctuations) with experimental data. A series of mesh-adaptive large eddy simulations (LES) was carried out for the study of air flows within two intersecting street canyons with varying building configurations. The novelty of the approach lies in the combination of LES with mesh adaptivity, which allows a variable-filter length and the implementation of an anisotropic eddy-viscosity model. Both coarse and fine-mesh simulations were carried out, using single and parallel-processor systems respectively. The simulations showed clearly that the expected flow patterns such as the street canyon recirculation and the street-mouth vortices, as well as the exchange of air flow at the street intersections, can readily be captured by the mesh-adaptive LES.In addition, the detailed comparisons of mean flows and fluctuations of the resolved velocity field with the measured data showed that the simulation results agreed well with the patterns and trends of the wind tunnel measurements. In most cases the finer-mesh simulations improved considerably the accuracy of the mean flows, especially for the symmetrical configuration. The improvement in the predicted fluctuations was less obvious, with several detector locations underpredicting the measured values, although the overall comparison was also satisfactory. The typical errors for the mean flows for all three building configurations were less than 30%, whilst for the velocity fluctuations less that 40%. Both the simulated means flows and turbulence levels were generally more accurate in the streets parallel to the wind (streamwise direction) than in the streets normal to the wind.
Keywords: Large eddy simulation; Mesh adaptivity; Urban air pollution modelling;

Regulatory control of mercury emission from anthropogenic sources has become a global concern in the recent past. Coal-fired power plants are one of the largest sources of anthropogenic mercury emission into the atmosphere. This paper summarizes the current reducing trend of mercury emission as co-beneficial effect by more stringent regulation changes to control primary air pollutants with introducing test results from the commercial coal-fired facilities and suggesting a guideline for future regulatory development in Korea. On average, mercury emission concentrations ranged 16.3–2.7 μg Sm−3, 2.4–1.1 μg Sm−3, 3.1–0.7 μg Sm−3 from anthracite coal-fired power plants equipped with electrostatic precipitator (ESP), bituminous coal-fired power plants with ESP + flue gas desulphurization (FGD) and bituminous coal-fired power plants with selective catalytic reactor (SCR) + cold side (CS) − ESP + wet FGD, respectively. Among the existing air pollution control devices, the best configuration for mercury removal in coal-fired power plants was SCR + CS − ESP + wet FGD, which were installed due to the stringent regulation changes to control primary air pollutants emission such as SO2, NOx and dust. It was estimated that uncontrolled and controlled mercury emission from coal-fired power plants as 10.3 ton yr−1 and 3.2 ton yr−1 respectively. After the installation of ESP, FGD and SCR system, following the enforcement of the stringent regulation, 7.1 ton yr−1 of mercury emission has been reduced (nearly 69%) from coal-fired power plants as a co-benefit control. Based on the overall study, a sample guideline including emission limits were suggested which will be applied to develop a countermeasure for controlling mercury emission from coal-fired power plants.
Keywords: Mercury emission; Coal combustion; Air pollution control devices; Emission regulation; Co-beneficial effect;

Global temperature change from the transport sectors: Historical development and future scenarios by Ragnhild Bieltvedt Skeie; Jan Fuglestvedt; Terje Berntsen; Marianne Tronstad Lund; Gunnar Myhre; Kristin Rypdal (6260-6270).
Transport affects climate directly and indirectly through mechanisms that operate on very different timescales and cause both warming and cooling. We calculate contributions to the historical development in global mean temperature for the main transport sectors (road transport, aviation, shipping and rail) based on estimates of historical emissions and by applying knowledge about the various forcing mechanisms from detailed studies. We also calculate the development in future global mean temperature for four transport scenarios consistent with the IPCC SRES scenarios, one mitigation scenario and one sensitivity test scenario. There are large differences between the transport sectors in terms of sign and magnitude of temperature effects and with respect to the contributions from the long- and short-lived components. Since pre-industrial times, we calculate that transport in total has contributed 9% of total net man-made warming in the year 2000. The dominating contributor to warming is CO2, followed by tropospheric O3. By sector, road transport is the largest contributor; 11% of the warming in 2000 is due to this sector. Likewise, aviation has contributed 4% and rail ∼1%. Shipping, on the other hand, has caused a net cooling up to year 2000, with a contribution of −7%, due to the effects of SO2 and NOx emissions. The total net contribution from the transport sectors to total man-made warming is ∼15% in 2050, and reaches 20% in 2100 in the A1 and B1 scenarios. For all scenarios and throughout the century, road transport is the dominating contributor to warming. Due to the anticipated reduction in sulphur content of fuels, the net effect of shipping changes from cooling to warming by the end of the century. Significant uncertainties are related to the estimates of historical and future net warming mainly due to cirrus, contrails and aerosol effects, as well as uncertainty in climate sensitivity.
Keywords: Transport sectors; Radiative forcing; Temperature; Historical emissions; Scenarios;

The influence of passenger activities on exposure to particles inside buses by W.W. Song; M.R. Ashmore; A.C. Terry (6271-6278).
Elevated personal exposures to particles have been reported in buses, but the factors associated with these high exposures are uncertain, and the potential role of passenger activities within buses has not been quantified. To improve understanding of this factor we measured particle number concentrations in the range 0.3–15 μm simultaneously inside and outside buses in the city of York (UK), while carefully noting passenger activities. We also developed a box model to simulate the effects of passenger activities, and parameterised this from independent studies with controlled passenger activities. The number concentrations inside buses were significantly higher than those outside in all size classes, and the inside/outside ratios increased with particle size. The model showed broad agreement with measured particle concentrations inside buses, and demonstrated, for particles in the range 3–15 μm, that both re-suspension by passenger activities and deposition to the surface of the passengers had significant effects on concentrations. Hence, understanding of the effects of passenger activities on both particle deposition and re-suspension is essential to interpret exposure measurements inside buses. Exposure of regular commuters inside buses could be of potential health significance and needs further assessment.
Keywords: Bus; Particulate matter; Modeling; Personal exposure; Transport; Box model;