Atmospheric Environment (v.40, #16)
Editorial board (i).
Multivariate analysis of the data and speciation of heavy metals in street dust samples from the Organized Industrial District in Kayseri (Turkey) by Şerife Tokalıoğlu; Şenol Kartal (2797-2805).
The concentrations of metals (Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) in 29 dust samples collected from the streets of the Organized Industrial District (OID) in Kayseri (Turkey) were determined by flame atomic absorption spectrometry (FAAS). The modified three-step BCR sequential extraction procedure was used in order to evaluate mobility, availability and persistence of trace elements in street dust samples. Multivariate statistical analysis was applied to the obtained data. Three operationally defined fractions isolated using the BCR procedure were: acid extractable, reducible, and oxidizable. The mobility sequence based on the sum of the BCR sequential extraction stages was: Cd (93.3%)>Zn (83.8%)>Pb (77.2%)>Co (75.9%)>Mn (73.0%)>Ni (60.1%)>Cu (59.0%)>Cr (58.6%). Correlation analysis, principal component analysis (PCA) and cluster analysis (CA) were applied to the data matrix to evaluate the analytical results and to identify the possible pollution sources of metals. PCA revealed that the sampling area was mainly influenced from three sources, namely industrial, traffic and natural sources. Validation of the analytical results was checked by analysis of the BCR-701 certified reference material.
Keywords: Modified BCR sequential extraction; Street dust; Multivariate analysis; BCR-701; Organized Industrial District;
Diurnal variation in methyl halide emission rates from tropical ferns by Takuya Saito; Yoko Yokouchi (2806-2811).
We measured foliar emission rates of methyl chloride (CH3Cl) and methyl bromide (CH3Br) from tropical ferns. The diurnal variation in methyl halide emission rates was quite different between tropical ferns of the same genus: Cyathea podophylla showed diurnal cycles with a midday maximum, whereas Cyathea lepifera showed a midday decline in emission rates. It is likely that the efficiency of methylation of halide ions in the leaves is affected positively or negatively by environmental factors such as temperature and solar radiation, depending on the species. These unique diurnal variations in methyl halide emission rates could be important keys to our understanding of the production of these compounds.
Keywords: Methyl chloride; Methyl bromide; Isoprene; Tropical plants; Stratospheric ozone;
Comparison of ozone simulations using MM5 and CALMET/MM5 hybrid meteorological fields for the July/August 2000 CCOS episode by Bruce Jackson; Daniel Chau; Kemal Gurer; Ajith Kaduwela (2812-2822).
Two sets of meteorological fields were prepared for the July/August 2000 Central California Ozone Study (CCOS) episode. The first set was generated using the MM5 prognostic model. The second set was generated using the CALMET model in which the MM5-generated output was used as the initial guess field and objective analysis was used to improve agreement between simulated fields and observed air temperatures and wind speed components. The resulting CALMET/MM5 hybrid meteorological fields and those generated using MM5 alone were also used as inputs for the CAMx/SAPRC99 air quality model to simulation ozone concentrations for the July/August 2000 episode. Ozone concentrations simulated using the CALMET meteorological inputs resulted in better agreement with observed concentrations than those simulated using the MM5 generated inputs throughout the modeling domain.This analysis suggested that hybrid meteorological fields, developed by merging the results of objective analysis and prognostic models, can improve episodic air quality model performance over using prognostic meteorological fields alone.
Keywords: CALMET; MM5; Hybrid; Objective; CCOS;
Quantitative back-trajectory apportionment of sources of particulate sulfate at Big Bend National Park, TX by Kristi A. Gebhart; Bret A. Schichtel; Michael G. Barna; William C. Malm (2823-2834).
As part of the Big Bend Regional Aerosol and Visibility Observational (BRAVO) study, a quantitative back-trajectory-based receptor model, Trajectory Mass Balance (TrMB) was used to estimate source apportionment of particulate sulfur measured at Big Bend National Park, Texas, during July–October 1999. The model was exercised using a number of sets of trajectories generated by three different trajectory models, with three different sets of input gridded meteorology, and tracked for 5, 7, and 10 days back in time. The performance of the TrMB model with the different trajectory inputs was first evaluated against perfluorocarbon tracers and synthetically generated sulfate concentrations from a regional air quality model, both of which had known attributions. These tests were used to determine which trajectories were adequate for the TrMB modeling of measured sulfate concentrations, illustrated the magnitude of the daily uncertainties as compared to the uncertainties in the mean attributions, and demonstrated the value of a robust evaluation process. Depending on trajectories, mean sulfate source apportionment results were 39–50% from Mexico, 7–26% from the eastern US, 12–45% from Texas, and 3–25% from the western US. These ranges were inclusive of the best BRAVO attribution estimates for Mexico, Texas, and the western US, but TrMB underestimated the eastern US contribution as compared to the BRAVO best estimates.
Keywords: Receptor modeling; Back-trajectory modeling; Big Bend National Park; Source apportionment; Tracer studies;
Comparison of thermodynamic predictions for in situ pH in PM2.5 by Xiaohong Yao; Tsz Yan Ling; Ming Fang; Chak K. Chan (2835-2844).
In situ aerosol pH is important in the study of atmospheric chemistry because many heterogeneous atmospheric chemical processes are pH dependent, but it is not easy to measure the in situ pH of PM2.5 due to the low liquid water content of aerosol particles. In situ aerosol pH is usually estimated by thermodynamic modeling. This study compared the in situ pH of PM2.5 in Hong Kong estimated by different thermodynamic methods such as AIM-II (Aerosol Inorganics Model-II) with the gas–aerosol partitioning calculation disabled, HCl/Cl−, HNO3/NO3 − and NH3/NH4 + gas–aerosol equilibrium equations, and two thermodynamic gas–aerosol equilibrium models (ISORROPIA and SCAPE2). In the first method, actual measured particulate composition was used as input while only the total (gas+aerosol) composition was used in the other methods. AIM-II with the gas–aerosol partitioning calculation disabled gives the lowest in situ aerosol pH, 3.5, 2.8, 3.1, 2.7 and 4.3 unit (on average) less than that estimated by HCl/Cl−, HNO3/NO3 − and NH3/NH4 + gas–aerosol equilibrium equations, and by SCAPE2 and ISORROPIA, respectively. The differences in estimated in situ pH are discussed in terms of the extent of the gas–aerosol equilibrium achieved, especially the NH3/NH4 + equilibrium. Although the estimated equilibrium concentrations deviated from the measured NH4 + in PM2.5 by only 20–35%, the estimated in situ pH is very sensitive to the deviation. It is possible that approaches based on the assumption of the gas–aerosol equilibrium may not be suitable for estimating in situ aerosol pH in the atmosphere.
Keywords: Aerosol thermodynamics; AIM; SCAPE2; ISORROPIA; Gas–aerosol partitioning; Aerosol acidity; Water content; PM2.5; Hong Kong;
An integrated neural network model for PM10 forecasting by Patricio Perez; Jorge Reyes (2845-2851).
We have developed an integrated artificial neural network model to forecast the maxima of 24 h average of PM10 concentrations 1 day in advance and we have applied it to the case of five monitoring stations in the city of Santiago, Chile. Inputs to the model are concentrations measured until 7 PM at the five stations on the present day plus measured and forecast values of meteorological variables. Outputs are the expected maxima concentrations for the following day at the site of the same five stations. The greatest of the concentrations among the five forecasts defines air quality for the following day. According to the range where the concentrations fall, three levels or classes of air quality are defined: good (A), bad (B) and critical (C). We have adjusted the parameters of the models using 2001 and 2002 data to forecast 2003 conditions and 2002 and 2003 data in order to forecast 2004 values. Forecast values using the neural model are compared with the results obtained with a linear model with the same input variables and with persistence. According to the results reported here, overall, the neural model seems more accurate, although a good choice of input variables appears to be very important.
Keywords: Air quality forecasting; Particulate matter; PM10; Neural networks; Meteorology forecast;
Numerical analysis of diffusion around a suspended expressway by a multi-scale CFD model by Hiroaki kondo; Kazutake Asahi; Takayuki Tomizuka; Motoo Suzuki (2852-2859).
The diffusion of NO x around Ikegami–Shinmachi crossroads, which are among the most polluted roadside areas in Japan, was analyzed with a CFD model. This is a suspended four-lane express road with a six-lane ground-level road under the expressway and another four-lane ground-level road intersecting the two roads. Three types of boundary conditions for the CFD model were tested. In the first case, the boundary conditions were given with the results from the mesoscale meteorological model; in other words, the model was multi-scale. In the second case, the boundary conditions were given with the local one-point observation. In the third case, the conditions for the wind were given with the observation, and those for the turbulence were given with the mesoscale numerical model. All of the calculations indicated high concentrations in the morning and low ones in the afternoon, but they did not indicate high concentrations in the evening. The reasons for such time variations of NO x concentrations were investigated from the viewpoints of the wind direction, velocity, and boundary layer height. The results suggested that the extremely high concentration was generated by local sources and advection from the large source area of Tokyo. On the whole, the calculation with the boundary condition with the mesoscale model appears to be better than the other calculations.
Keywords: NO x ; Roadside air pollution; Mesoscale model; Boundary conditions; Automobile;
Long term hourly measurement of 62 non-methane hydrocarbons in an urban area: Main results and contribution of non-traffic sources by N. Durana; M. Navazo; M.C. Gómez; L. Alonso; J.A. García; J.L. Ilardia; G. Gangoiti; J. Iza (2860-2872).
We present one of the largest and most complete databases of atmospheric non-methane hydrocarbons in the Iberian Peninsula, not only for its temporal resolution and seasonal extent, but for the number of species routinely measured. Results were obtained using an automatic gas chromatograph, during 1998–2001 (April–October) and 2004 (February–July), optimized for systematic, unattended measurement of 62 C2–C10 non-methane hydrocarbons (NMHC) every hour, 24 times a day, with detection limits below 0.1 ppbv.Annual average concentrations for most of the NMHC show very little variations along the years. Benzene is an exception; during year 2000, its concentration on ambient air decreased down to a half, after the enforcement of environmental regulations reducing the benzene content on fuels.Significant correlations found among various hydrocarbons and the observed daily cycle indicate that traffic is their principal source. However, some compounds like acetylene and benzene, commonly used as tracers of vehicular emissions, show in our case other sources, during working days for acetylene, and continuous for benzene. This is now relevant, especially when considering that such measuring systems are now starting to be deployed around many cities, all over the world, because in urban areas where similar influences by industrial or commercial sources are to be expected, ratios like toluene/benzene or ethene/acetylene, cannot be used to characterize traffic polluted air masses.Isoprene has been found to have mostly an anthropogenic origin during winter, and a dual anthropogenic–biogenic origin during summer, when natural isoprene amounts 55% of the total. A method for the estimation of the anthropogenic fraction of isoprene in urban areas, based on a correlation with 1-butene, is also proposed.
Keywords: NMHC concentrations; On line VOC analysis; C2–C10 annual trends; Non-traffic sources; Anthropogenic isoprene;
Single-particle characterization of municipal solid waste (MSW) ash particles using low-Z particle electron probe X-ray microanalysis by HeeJin Hwang; Chul-Un Ro (2873-2881).
Environmentally benign treatment of municipal solid waste (MSW) ashes has been a worldwide issue since more countries are implementing incineration to reduce waste volume. A single-particle analytical technique, named low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA) was applied to characterize MSW fly- and bottom-ash particle samples collected from two municipal incinerators in Korea. According to their chemical composition, many distinctive particle types were identified. For fly ash sample collected in one incinerator (sample S1), where lime slurry injection is used for acid–gas treatment, CaCO3-containing particles (28.4%) are the most abundantly encountered, followed by carbonaceous (23.6%), SiO2-containing (13.8%), NaCl-containing (13.1%), and iron-containing (10.5%) particles. For fly ash sample collected at the other incinerator (sample S2), NaCl-containing particles (40.4%) are the most abundantly encountered, followed by iron-containing (29.1%), carbonaceous (11.8%), CaCO3-containing (2.2%), and SiO2-containing (7.0%) particles.For bottom ash sample collected at one incinerator (sample S3), iron-containing particles (46.6%) are the most abundantly encountered, followed by CaCO3-containing (17.3%), carbonaceous (16.6%), and Si and/or Al oxide-containing (15.8%) particles. For bottom ash sample collected in the other incinerator (sample S4), iron-containing particles (63.4%) are also the most abundantly encountered, followed by carbonaceous (14.0%), CaCO3-containing (10.0%), and Si and/or Al oxide-containing (6.1%) particles. Chemical compositions of the two bottom ash samples are not much different compared to those of the two fly ash samples.It was demonstrated that the single-particle characterization using this low-Z particle EPMA technique provided detailed information on various types of chemical species in the MSW ash samples. In addition, the technique has advantage over conventional analytical techniques in the point that both crystalline- and glass-like ash particles can be analyzed at the same time.
Keywords: Low-Z particle EPMA; Municipal solid waste (MSW) ashes; Single-particle analysis;
A modified method for diffusive monitoring of 3-ethenylpyridine as a specific marker of environmental tobacco smoke by Leea Kuusimäki; Kimmo Peltonen; Sinikka Vainiotalo (2882-2892).
A previously introduced method for monitoring environmental tobacco smoke (ETS) was further validated. The method is based on diffusive sampling of a vapour-phase marker, 3-ethenylpyridine (3-EP), with 3 M passive monitors (type 3500). Experiments were done in a dynamic chamber to assess diffusive sampling in comparison with active sampling in charcoal tubes or XAD-4 tubes. The sampling rate for 3-EP collected on the diffusive sampler was 23.1±0.6 mL min−1. The relative standard deviation for parallel samples (n=6) ranged from 4% to 14% among experiments (n=9). No marked reverse diffusion of 3-EP was detected nor any significant effect of relative humidity at 20%, 50% or 80%. The diffusive sampling of 3-EP was validated in field measurements in 15 restaurants in comparison with 3-EP and nicotine measurements using active sampling. The 3-EP concentration in restaurants ranged from 0.01 to 9.8 μg m−3, and the uptake rate for 3-EP based on 92 parallel samples was 24.0±0.4 mL min−1. A linear correlation (r=0.98) was observed between 3-EP and nicotine concentrations, the average ratio of 3-EP to nicotine being 1:8. Active sampling of 3-EP and nicotine in charcoal tubes provided more reliable results than sampling in XAD-4 tubes. All samples were analysed using gas chromatography-mass spectrometry after elution with a 15% solution of pyridine in toluene. For nicotine, the limit of quantification of the charcoal tube method was 4 ng per sample, corresponding to 0.04 μg m−3 for an air sample of 96 L. For 3-EP, the limit of quantification of the diffusive method was 0.5–1.0 ng per sample, corresponding to 0.04–0.09 μg m−3 for 8 h sampling. The diffusive method proved suitable for ETS monitoring, even at low levels of ETS.
Keywords: Nicotine; Passive sampling; Hospitality industry; ETS;
Effect of dilution conditions and driving parameters on nucleation mode particles in diesel exhaust: Laboratory and on-road study by Topi Rönkkö; Annele Virtanen; Kati Vaaraslahti; Jorma Keskinen; Liisa Pirjola; Maija Lappi (2893-2901).
We have studied exhaust particle-size distribution of a heavy-duty diesel vehicle in the laboratory and on road. The vehicle was equipped with an oxidation catalyst and fulfilled the Euro 3 emission standard. Special attention was paid to the characteristics and formation tendency of nucleation mode. On road, the nucleation mode formed already 5 m behind the vehicle and did not change significantly when the chase distance was doubled. The meteorological parameters were found to affect nucleation mode particle formation: low temperature and high relative humidity favour the formation. In addition, the nucleation mode mean diameter and concentration are affected by engine torque. This behaviour was found to be identical both on road and in laboratory measurements, indicating different behaviour in different torque regimes. At moderate to high torques (>200 Nm) the total volume of nucleation mode particles increases with increasing engine torque. At lowest torques (<200 Nm), the nucleation mode particle volume increases with decreasing torque. The hydrocarbon concentration is high at lowest torque values while the exhaust sulphur content is higher at highest torque values. The results indicate that at low torques the hydrocarbons have an important role in the nucleation process, while at high torques the process could be sulphur driven.
Keywords: Diesel exhaust; Particle formation; Nucleation mode; Dilution; On-road measurements;
Culturability and concentration of indoor and outdoor airborne fungi in six single-family homes by Taekhee Lee; Sergey A. Grinshpun; Dainius Martuzevicius; Atin Adhikari; Carlos M. Crawford; Tiina Reponen (2902-2910).
In this study, the culturability of indoor and outdoor airborne fungi was determined through long-term sampling (24-h) using a Button Personal Inhalable Aerosol Sampler. The air samples were collected during three seasons in six Cincinnati area homes that were free from moisture damage or visible mold. Cultivation and total microscopic enumeration methods were employed for the sample analysis. The geometric means of indoor and outdoor culturable fungal concentrations were 88 and 102 colony-forming units (CFU) m−3, respectively, with a geometric mean of the I/O ratio equal to 0.66. Overall, 26 genera of culturable fungi were recovered from the indoor and outdoor samples. For total fungal spores, the indoor and outdoor geometric means were 211 and 605 spores m−3, respectively, with a geometric mean of I/O ratio equal to 0.32. The identification revealed 37 fungal genera from indoor and outdoor samples based on the total spore analysis. Indoor and outdoor concentrations of culturable and total fungal spores showed significant correlations ( r = 0.655 , p<0.0001 and r = 0.633 , p<0.0001, respectively). The indoor and outdoor median viabilities of fungi were 55% and 25%, respectively, which indicates that indoor environment provides more favorable survival conditions for the aerosolized fungi. Among the seasons, the highest indoor and outdoor culturability of fungi was observed in the fall. Cladosporium had a highest median value of culturability (38% and 33% for indoor and outdoor, respectively) followed by Aspergillus/Penicillium (9% and 2%) among predominant genera of fungi. Increased culturability of fungi inside the homes may have important implications because of the potential increase in the release of allergens from viable spores and pathogenicity of viable fungi on immunocompromised individuals.
Keywords: Indoor air; Outdoor air; Total fungal spore; Culturable fungi; Culturability;
Scientific uncertainties in atmospheric mercury models I: Model science evaluation by Che-Jen Lin; Pruek Pongprueksa; Steve E. Lindberg; Simo O. Pehkonen; Daewon Byun; Carey Jang (2911-2928).
Eulerian-based, first-principle atmospheric mercury models are a useful tool to assess the transport and deposition of mercury. However, there exist uncertainty issues caused by model assumptions/simplifications and incomplete understanding of mercury science. In this paper, we evaluate the model science commonly implemented in atmospheric mercury models. The causes of the uncertainties are assessed in terms of gas phase chemistry, aqueous phase chemistry, aqueous phase speciation, aqueous phase sorption, dry deposition, wet deposition, initial and boundary conditions, emission inventory preparation, and domain grid resolution. We also present a new dry deposition scheme for estimating the deposition velocities of GEM and RGM based on RADM formulation. From our evaluation, mercury chemistry introduces the greatest uncertainty to models due to the inconsistent kinetic data and lack of deterministic product identification in the atmosphere. Model treatments of deposition velocities and aqueous Hg(II) sorption can also lead to distinct simulation results in mercury dry and wet depositions. Although model results may agree well with limited field data of GEM concentrations and Hg(II) wet deposition, it should be recognized that model uncertainties may compensate with each other to yield favorable model performance. Future research needs to reduce model uncertainties are projected.
Keywords: Atmospheric mercury; Modeling; Chemical mechanism; Deposition; Mercury speciation; Aqueous sorption; Cloud water; Emission inventory; Initial and boundary conditions;
QSPR prediction of the Dubinin–Radushkevich's k parameter for the adsorption of organic vapors on BPL carbon by Pablo R. Duchowicz; Heriberto Castañeta; Eduardo A. Castro; Francisco M. Fernández; José Luis Vicente (2929-2934).
We propose a QSPR treatment to model a diverse set of pure organic vapors including 36 k parameters from the Dubinin–Radushkevich adsorption isotherm equation. From 814 molecular descriptors provided by the Dragon 5 software and the Replacement Method, we obtain an appropriate four-variables model with R=0.9334 and Rl–10%–o=0.8047. By means of this relationship, we predict 33 unknown values of k for structurally related vapors, enabling now to build their isotherms on BPL adsorbent at any desired temperature.
Keywords: QSPR theory; Physical adsorption; Isotherm; Carbon adsorbent; Modeling;
The ion chemistry, seasonal cycle, and sources of PM2.5 and TSP aerosol in Shanghai by Ying Wang; Guoshun Zhuang; Xingying Zhang; Kan Huang; Chang Xu; Aohan Tang; Jianmin Chen; Zhisheng An (2935-2952).
Daily total suspended particulate (TSP), particle size smaller than 100 μm and particle size smaller than 2.5 μm (PM2.5) aerosol samples were collected at two sites in Shanghai in four seasons from September 2003 to January 2005. Concentrations of the water-soluble ions (SO4 2−, NO3 −, Cl−, F−, PO4 3−, HCOO−, CH3COO−, NO2 −, MSA, C2O4 2−, NH4 +, Ca2+, Na+, K+, Mg2+) were measured for a total of 202 samples. Daily TSP and PM2.5 mass concentrations ranged from 66.1 to 666.8 μg m−3 and 17.8 to 217.9 μg m−3, with annual average concentrations of 230.5 and 94.6 μg m−3, respectively. The sum of ions contributed an average of 26% and 32% of TSP and PM2.5 mass concentrations, respectively. In PM2.5, the concentration of the major ions followed the order of SO4 2−>NO3 −>NH4 +>Cl−>Ca2+>K+, while in TSP was SO4 2−>NO3 −>Cl−>Ca2+>NH4 +>Na+. These major ions were mainly in the form of (NH4)2SO4, Ca(NO3)2, CaCl2, and CaSO4 in aerosol particles. The aerosol was slightly acidic in the fine particle size range, and alkaline in the coarse mode. Seasonal variation of ion concentrations was significant, with the highest concentrations observed in winter and spring and the lowest in summer and autumn. Three types of air masses, i.e. marine, mixing, and continental, were frequently observed, and their distribution in four seasons might result in the clear seasonal variation. It is Shanghai that has the highest NO3 −/SO4 2− value among all of those cities in China, indicating that as the biggest city in China the mobile source of the air pollution becomes more and more predominant. However, stationary emissions were still the dominant source in Shanghai indicated by the NO3 −/SO4 2− ratio of lower than 1. The formation of NO3 − was largely from the gas-phase photochemical reaction in the cold season, and from the heterogeneous reaction in the warm season, while the formation of SO4 2− might be from the heterogeneous reaction in the entire year round. NH4 +, K+, Cl−, NO3 −, and SO4 2− were mainly influenced by the anthropogenic emissions in land, meanwhile Cl− and SO4 2− might be partly influenced by the sea. Na+, Mg2+, and Ca2+ were derived from both inland crustal and marine sources. Chloride depletion was found especially in summer. The air pollution in Shanghai has proved to be under the influence of both the local emissions and the long-range transport from outside areas.
Keywords: Water-soluble ions; Speciation; Temporal variation; Secondary transformation; Sources; Shanghai;
Precision and repeatability of the TRAKER vehicle-based paved road dust emission measurement by V. Etyemezian; H. Kuhns; G. Nikolich (2953-2958).
Testing re-entrained aerosol kinetic emissions from roads (TRAKER), a vehicle based measurement system, has been reported as an alternative to silt measurements for estimating PM10 paved road dust emissions. The precision of the TRAKER system was quantified with repeated measurements over the same roads. A prescribed driving route in Las Vegas, Nevada was traversed with the TRAKER on four consecutive days. The 154 km of paved roads were divided into 645 road segments each representing at least 20 data points and corresponding to links used in the county traffic demand and forecasting model. The TRAKER emission potential, which is related to the emission factor by a multiple of travel speed and provides a measure of a road segment's inherent PM10 dust loading, was averaged over each road segment. Comparing the 4 days of sampling, the coefficient of variation (COV), the standard deviation divided by the average, was <10%, <20%, <50%, and <70% for 126, 402, 619, and 639 of the 645 road segments, respectively. The COV decreased with the speed at the time of measurement from 26% at 5–10 m s−1 to 14% at 25–30 m s−1. No discernible relationships were found between COV and number of data points per road segment, length of road segment, or direction of travel. Over the entire 154 km route, emission potentials on the 4th day were slightly lower than the prior 3 days, owing either to actual changes in road conditions or bias introduced into the measurement by surface wind speed which was highest on the 4th day.
Keywords: TRAKER; Las Vegas; Emissions inventory; Fugitive dust; PM10;
Composition of the fine organic aerosol in Yosemite National Park during the 2002 Yosemite Aerosol Characterization Study by Guenter Engling; Pierre Herckes; Sonia M. Kreidenweis; William C. Malm; Jeffrey L. Collett (2959-2972).
The Yosemite Aerosol Characterization Study (YACS) was conducted during the summer of 2002 to investigate regional haze in Yosemite National Park by characterizing the chemical, physical and optical properties of the ambient aerosol. Previous analyses reveal that the composition of PM2.5 during YACS was dominated by carbonaceous material derived primarily from contemporary carbon sources rather than fossil fuel combustion. In addition to several local wildfires and prescribed burns, two regional haze episodes during YACS were strongly influenced by smoke from biomass burning that was subject to long-range transport. Several classes of biomass burning smoke tracers, including anhydrosugars, methoxyphenols, and resin acids, were used to determine contributions of primary biomass burning smoke to PM2.5. Levoglucosan was measured with peak concentrations of 234 ng/m3 during periods with smoke influence from local fires, and primary biomass burning smoke contributions to fine particle organic carbon were estimated to be as high as 100% on individual days during that period. Relatively high concentrations of monoterpene oxidation products and other organic compounds of secondary origin, such as dicarboxylic acids, indicated secondary organic aerosol (SOA) to be an important contributor to contemporary carbon. Biomass combustion plumes impacting the measurement site are likely a significant contributor to the observed SOA. Low concentrations of organic compounds of anthropogenic origin, such as hopanes and steranes, indicated contributions from automobile exhaust to organic carbon of approximately 10% on average. Overall, the fine aerosol in Yosemite National Park during the summer of 2002 was dominated by natural sources, in particular by smoke from wildfires and by secondary organic aerosol of biogenic origin.
Keywords: Wildfires; Biomass burning; Wood smoke; Haze; Levoglucosan; SOA;
Characteristics and sources of lead pollution after phasing out leaded gasoline in Beijing by Yele Sun; Guoshun Zhuang; Wenjie Zhang; Ying Wang; Yahui Zhuang (2973-2985).
A 5-year long-term programme of Pb-monitoring from 2000 to 2004 was carried out at three representative urban sites (a traffic, an industrial, and a residential site), and a suburban site to evaluate the pollution level of Pb in Beijing. For comparison, aerosol samples were also collected in four other cities, Shanghai, Qingdao, Duolun, and Yulin in China. Pb pollution in Beijing has been very serious when compared with other sites over the world, as the concentration of Pb in Beijing remained as high as ∼100–300 ng m−3 in fine particles (PM2.5). Significant spatial variation of Pb in summer with the highest concentration at the industrial site was observed, while relatively even spatial variation was found in winter in urban area, although much heavier in the urban area than at suburban site. Strong seasonal variation of ∼2–3 times higher Pb concentration in winter than that in summer was found. Pb exhibited a unimodal size distribution with most of it in fine fraction. Pb in fine particles was enriched by a factor of 200–1600 relative to its abundance in crust. Besides industry emission, motor vehicle emission, and coal burning, long-range transported dust from outside Beijing and the re-suspended soil containing the deposition of those from previously emitted leaded gasoline could be the important sources of Pb in Beijing.
Keywords: Lead; Urban pollution; Atmospheric pollution; Sources; China; Beijing;
The role of multimedia mass balance models for assessing the effects of volatile organic compound emissions on urban air quality by Karen L. Foster; Steven Sharpe; Eva Webster; Donald Mackay; Randy Maddalena (2986-2994).
A multimedia mass balance model is described that has the potential to contribute to improved assessment of the levels and fate of volatile organic compounds (VOCs) in urban environments. It determines the fate and concentration of organic chemicals in the urban atmosphere under both steady-state and dynamic conditions. It can be used to estimate the fraction of the mass emitted that may participate in photochemical reactions leading to ozone formation, as distinct from the fraction which is dissipated by other processes. Five compartments are included: air (including aerosols), surface water, soil, vegetation and a non-polar organic urban film that coats impervious urban surfaces. Five test chemicals are assessed, viz. pentane, toluene, naphthalene, anthracene and pyrene, representing a range in volatility and atmospheric reactivity. The steady-state results suggest that the more volatile chemicals (pentane and toluene) remain almost entirely in the gaseous phase and advection and atmospheric reaction losses are the only important processes. For the less volatile chemicals, with liquid vapor pressures below a “cut-off” of approximately 10 Pa, partitioning to other media increases, notably to soil and water, thus a lower fraction of the emitted mass reacts in the atmosphere and is a potential ozone precursor. The dynamic results show how changes in the hydroxyl radical (OH) concentrations and advection rates affect chemical fate. It is suggested that the model can contribute to improved assessment of the fate of a variety of organic chemicals in urban areas, especially if certain inter-media partitioning and transport parameters can be better quantified.
Keywords: Volatile organic chemical; Ozone; Urban; Model; Volatility;
A GIS based methodology for gridding of large-scale emission inventories: Application to carbon-monoxide emissions over Indian region by Mohit Dalvi; Gufran Beig; Uday Patil; Akshara Kaginalkar; C. Sharma; A.P. Mitra (2995-3007).
Chemical simulations in most of the atmospheric chemistry models require surface emissions in a specific form (gridded), which are often not available. Simple interpolation of broader level emissions to obtain gridded data may lead to erroneous results. An attempt has been made in this paper to develop a geographical information system (GIS) based methodology for distributing the emissions from a broader level inventory to finely gridded emission values, considering local micro-level details and activity data. Given the importance of Carbon Monoxide emissions in ozone pollution chemistry over India, an emission inventory for CO from various sources for India has been used to demonstrate the GIS-based gridding methodology. The total CO emissions over India for 2001, which are estimated to be around 69.0 Tg year−1, have been downscaled source-wise (distinguishing between rural and urban bio-fuel, vehicular traffic, coal and biomass burning) from state-level (28 points) to district level (∼500 points) before mapping through a GIS utility and finally gridded to a 1°×1° resolution with a data loss of only about 13%. The final results provide detailed information with emission “hot spots” and the relative contribution of various sources. This article focuses on usage of the GIS based statistical methodology for gridding the inventory and the results obtained thereof are discussed.
Keywords: Carbon monoxide; Indian inventory; Geographical information systems; Spatial distribution; Gridded emissions;
New Directions: How representative are aerosol radiative impact assessments? by S.K. Satheesh; J. Srinivasan; V. Vinoj; S. Chandra (3008-3010).