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Atmospheric Environment (v.40, #14)
Modeling regional sulfate during the BRAVO study: Part 2. Emission sensitivity simulations and source apportionment by Michael G. Barna; Bret A. Schichtel; Kristi A. Gebhart; William C. Malm (pp. 2423-2435).
The Regional Modeling System for Aerosols and Deposition (REMSAD) was used to estimate a sulfate source apportionment as part of the Big Bend Regional Aerosol and Visibility Observational Study (BRAVO). Fine particulate sulfate was the main component of haze measured at Big Bend National Park (BBNP) during the BRAVO field measurement campaign (July–October 1999). The sulfate apportionment was estimated using a suite of emission sensitivity simulations in which sulfur dioxide (SO2) emission rates were modified. Four large regional emission source areas were evaluated with respect to their contributions to estimated sulfate at BBNP: the eastern US (14.0×106tonsSO2yr−1), Texas (1.0×106tonsSO2yr−1), Mexico (2.5×106tonsSO2yr−1), and the western US (1.8×106tonsSO2yr−1). In addition to these large regional sources, several sub-regions were considered (e.g., northeastern Texas), as well as a large coal-fired power plant in Mexico located approximately 225km southeast of BBNP (Carbón I/II). During the four-month study period, it was estimated that the eastern US was the largest contributor to sulfate at BBNP (42%), followed by Mexico (23%), Texas (16%), and the western US (9%). Carbón I/II accounted for more than half of the Mexican contribution of sulfate to BBNP. Boundary conditions, which were specified by a global model, contributed 7%. The sum of the sulfate concentrations resulting from the emission sensitivity simulations were within a few percent of the sulfate concentration estimated from the original base emissions simulation, indicating that sulfate predictions responded approximately linearly to gross changes in sulfur dioxide emissions. The source apportionment results presented here are one estimate in a suite of estimates that were considered for the BRAVO study, and do not represent the final BRAVO sulfate source apportionment for BBNP.
Keywords: Sulfate; Modeling; Source apportionment; BRAVO; REMSAD
Modeling regional sulfate during the BRAVO study: Part 1. Base emissions simulation and performance evaluation by Michael G. Barna; Kristi A. Gebhart; Bret A. Schichtel; William C. Malm (pp. 2436-2448).
The Regional Modeling System for Aerosols and Deposition (REMSAD) was employed to predict sulfate formation and transport in the Big Bend Regional Aerosol and Visibility Observational Study (BRAVO). Fine particulate sulfate was the main component of haze measured at Big Bend National Park (BBNP) during the BRAVO field measurement campaign, which was conducted July–October 1999. Predicted sulfate was evaluated against measurements collected from BRAVO and CASTNet (Clean Air Speciation and Trends Network) monitors. During the four month study period, average observed and predicted sulfate concentrations at the 37 BRAVO sites were 3.1 and 3.3μgm−3, respectively, and 4.5 and 5.0μgm−3 at the 62 CASTNet sites, respectively. Spatial and temporal biases were clearly apparent. Underestimations of sulfate during July and August were evident throughout the BRAVO monitoring network (fractional biases of −0.60 and −0.44, respectively), corresponding to a period of increased atmospheric transport from Mexico to Texas. Biases in estimated sulfate in the vicinity of BBNP may be attributed to an overestimation of predicted precipitation rates during July and August. Positive biases within the BRAVO network were apparent in October (fractional bias=0.39), when atmospheric transport from the eastern US was more prevalent. Overall performance statistics for sulfate predictions relative to the BRAVO and CASTNet sites were: correlation coefficient=0.61 and 0.90, respectively; fractional error=0.56 and 0.35, respectively; fractional bias=−0.10 and 0.04, respectively. This simulation provided the basis for a series of emission sensitivity simulations that were used to estimate a sulfate source apportionment for BBNP.
Keywords: Sulfate; Modeling; BRAVO; REMSAD
Annual variation of particulate organic compounds in PM2.5 in the urban atmosphere of Beijing by X.-F. Xiao-Feng Huang; Ling-Yan He; Min Hu; Yuan-Hang Zhang (pp. 2449-2458).
Beijing, the capital of China, is a rapidly developing mega-city with a huge population in the world. Beijing has been experiencing severe air pollution problems since 1980s due to more and more energy consumption. In the case of severe organic aerosol pollution in Beijing, a one-year-long observation on major organic compounds in PM2.5 was performed at an urban site to gain information of their ambient concentration levels and sources in Beijing. The compound classes identified by GC/MS included alkanes, PAHs, fatty acids, dicarboxylic acids, and hopanes, whose seasonal average concentrations during the year were 39–477, 9–283, 260–483, 16–42, and 2.3–16ngm−3, respectively. Since the molecular distributions of particulate organic matter are indicative of different emission sources, their seasonal characteristics and variations were discussed in detail to explore the major contributing sources in Beijing. Conclusively, organic aerosol pollution in Beijing was found to be mostly associated with vehicle exhaust, coal combustion for residential heating, and cooking emissions, and the latter two sources are unique Chinese pollution sources. The dataset in this paper provides useful information for establishing effective control measures to reduce organic aerosol pollution in Beijing.
Keywords: Pm; 2.5; GC/MS; Particulate organic compounds; Seasonal variation; Sources
Seasonal, diurnal and nocturnal behaviors of lower carbonyl compounds in the urban environment of Beirut, Lebanon by Samar G. Moussa; Mutassem El-Fadel; Najat A. Saliba (pp. 2459-2468).
Lower carbonyl concentrations were measured for the first time in two different sampling sites (American University of Beirut (AUB) and Abdel-Aziz (AA)) in Beirut, Lebanon. Formaldehyde (C1) and acetaldehyde (C2) were the most abundant carbonyls with respective maximum concentrations of 12.2 and 5.2ppbv at AUB and 8.6 and 5.1ppbv at AA. Diurnal variations of carbonyls exhibited similar behaviors, suggesting related formation and decomposition routes. Morning levels of carbonyls were either equal or higher than the ones in the afternoon at the coastal site (AUB) due to atmospheric dilution. However, morning levels were mostly lower than noon levels at a three-busy street intersection (AA) due to the enhancement of photochemical activities. Vehicle emissions constituted the dominant source of carbonyls measured as confirmed by the good correlation between C1, C2 and propanal (C3) and the C1/CO and C2/CO ratios in the mornings. Seasonal variation showed the predominance of summertime photolysis and photo-oxidation reactions of aldehydes. Based on the measured formaldehyde levels, ozone and nitrous acid concentrations, morning and afternoon OH radical fluxes are computed and consequently their contribution to photochemical smog processes are assessed.
Keywords: Low-carbonyl compounds; Primary carbonyl emissions; Lebanon; Eastern Mediterranean; OH radical fluxes; Seasonal carbonyl variation
Temperature effects on Henry's law constants for four VOCs in air-activated sludge systems by J.-H. Jun-Hong Lin; M.-S. Ming-Shean Chou (pp. 2469-2477).
A single equilibration technique (SET) was adopted to measure the air–water dimensionless Henry's law constants (K H) and the air-activated sludge mixed liquor ones (K′ H) for volatile organic compounds (VOCs). Hydrophilic VOCs (methanol and isopropanol) and hydrophobic ones (toluene and p-xylene) were used as target compounds. Deionized water (DI water) and DI water suspended with a pasteurized activated sludge (the mixed liquor) were used as testing liquids. Mixed liquor suspended solid (MLSS) concentrations were from zero to approximately 40,000mgL−1 and the equilibrium temperatures from 288 to 303K. Results indicate that for the hydrophilic compoundsK′ H/K H raised slightly with increasing MLSS in the mixed liquor.K′ H/K H for the hydrophobic compounds raised with the increasing MLSS, and the maximum decreases ofK′ H fromK H were 86–88% (288K) and 68–73% (303K) for MLSS=40,000mgL−1. Temperature variations ofK′ H could reasonably be regressed by the van’t Hoff's equation and the phase change enthalpy Δ H′ increase approximately linearly with increasing MLSS for hydrophobic toluene and p-xylene.K′ H variation can be controlled by MLSS concentration and temperature in activated sludge system. Lower temperatures and higher MLSS concentrations should result in a lowerK′ H for hydrophobic VOCs, while higher MLSS concentrations in a higherK′ H for hydrophilic VOCs.
Keywords: Van’t Hoff; Phase change enthalpy; Partition effect; Volatile organic compounds; Activated sludge
Multi-year trend in fine and coarse particle mass, carbon, and ions in downtown Tokyo, Japan by Hiroaki Minoura; Katsuyuki Takahashi; Judith C. Chow; John G. Watson (pp. 2478-2487).
Long-term measurements of suspended particulate matter (SPM, <7μm), PMfine (<2.1μm), and PMcoarse (2.1–7μm) were obtained from a traffic-dominated site in Tokyo, Japan for the period 1994–2004 to evaluate the effects of emission reduction measures for motor-vehicle emissions. SPM decreased from 1996 forward, with all of the downward trend attributable to the PMfine fraction. Annual average PMcoarse was constant over the 10-yr period. From 1996 to 2004, PMfine decreased at a rate of 2.37μgm−3yr−1 for PM2.1 mass. Most of this decrease was attributable to decreases in organic and elemental carbon. This decrease is consistent with fleet penetration of engines and fuels that complied with a stringent Japanese emission reduction limit which began to take effect in 1994. Sulfate and nitrate concentrations did not decrease over this period. Evidence of Asian dust storm contributions was found in elevated PMcoarse and water-soluble calcium levels during the spring.
Keywords: Japan; Tokyo; Trends; Particulate matter; Chemical composition; Elemental carbon
Can topological indices be used to predict gas-phase rate coefficients of importance to tropospheric chemistry? Free radical abstraction reactions of alkanes by Max R. McGillen; Carl J. Percival; Teresa Raventos-Duran; Gabriela Sanchez-Reyna; Dudley E. Shallcross (pp. 2488-2500).
As tropospheric chemical models become ever more complex, reliable rate coefficient data for gas-phase hydrogen abstraction reactions involving trace hydrocarbons becomes increasingly necessary. There are hundreds of non-methane hydrocarbons (NMHCs) of potential importance to tropospheric chemistry, many of which have not been subjected to experimental inquiry. This study—the first of its kind to investigate hydrocarbons ranging from C2 to C10 using topological indices—aims to provide a reliable and accessible method of estimating rate coefficients for these species.Rate coefficients of free radical abstraction reactions of NMHCs were correlated with the Randić and Balaban topological indices for radical moieties OH, Cl and NO3. These correlations were compared with those of an established frontier orbital approach based on calculated ionization potentials (IPs).The Randić index was found to correlate better than IP for each of the radicals studied, and correlated particularly effectively for the Cl radical. The Balaban index did not correlate for branched alkanes except for NO3. Where only unbranched alkanes were considered, the Balaban index proved most reliable, demonstrating a clear linear relationship.Topological indices present an accurate and diverse method for estimating free radical abstraction rate coefficients that does not require the computing power, specialist software packages, or complex mathematics inherent in ab initio calculations. A further advantage of using topological indices is that they are calculated in an unambiguous manner. More reliable tools for estimating rate coefficients have direct implications for improving models, and may also provide a direction for future laboratory work, either by highlighting particularly reactive species or identifying potentially spurious rate coefficient data.
Keywords: Topological indices; Kinetics; Hydrogen abstraction; Correlations; NMHCs
Formation of secondary organic particle phase compounds from isoprene gas-phase oxidation products: An aerosol chamber and field study by Boge Olaf Böge; Yunkun Miao; Antje Plewka; Hartmut Herrmann (pp. 2501-2509).
Acid-catalyzed multiphase reactions of isoprene with hydrogen peroxide have been suggested to produce hydroxylated oxidation products, namely the diastereoisomeric 2-methyltetrols (2-methylthreitol and 2-methylerythritol), compounds which were found quite recently in aerosols above forests. In this study aerosol chamber experiments have been performed reacting isoprene or known isoprene oxidation products with hydrogen peroxide in the presence of acidic particles. Starting from isoprene, 2-methyl-3-butene-1,2-diol or 2-methyl-2-vinyloxirane the formation of the 2-methyltetrols could be observed. The reaction was most effective for 2-methyl-2-vinyloxirane. The last process can lead to an annual 2-methyltetrol formation in atmospheric particles of about 1TgC. Additionally, results from size segregated 2-methyltetrol measurements in Melpitz site (Germany) are presented. The concentrations are between 0.5 and 1.7ngm−3. The 2-methyltetrols are enriched in the fine size fraction as expected for secondary organic aerosol compounds.
Keywords: Secondary organic aerosol; Isoprene; Acidic seed particles; Chamber experiments; 2-Methylthreitol; 2-Methylerythritol
Validation studies of turbulence closure schemes for high resolutions in mesoscale meteorological models by S. Trini Castelli; T. Hara; R. Ohba; C.J. Tremback (pp. 2510-2523).
Mesoscale models are often used to reproduce the atmospheric processes at relatively high resolutions, both for meteorological and pollutant dispersion studies and applications. Particularly in non-homogeneous conditions, a proper description of turbulent transport is a fundamental aspect. In this work, we compare two analogous 1.5-order turbulence schemes implemented in RAMS, mainly differing in the form of the turbulent kinetic energy dynamical equation (1D or 3D) and in the relationships linking the closure quantities, such as diffusion coefficients and dissipation terms. We present results from simulations performed in a simple, idealized case, along with results related to two field campaigns carried on in the Tsukuba region (Japan) in 1989 and 1990. Both turbulence schemes are able to well reproduce the mean flow, but different performances are related to the turbulence field.
Keywords: Turbulence closures; Mesoscale models; RAMS; Non-homogenous conditions; Experimental campaign
Sulphur dioxide in Europe: Statistical relationships between emissions and measured concentrations by Marco Giannitrapani; Adrian Bowman; Marian Scott; Ron Smith (pp. 2524-2532).
Air pollution in Europe is the topic of a wide range of studies involving different disciplines. However most of the analyses presented in the literature focus on the study of monitored concentrations with few articles investigating the relationship between trends in concentrations and reported emissions. In this paper a statistical analysis of sulphur dioxide (SO2) concentrations monitored in Europe from 1990 to 2001 uses additive models to test the relationships with emissions from the same and neighbouring countries. This nonparametric approach allows data to determine the shape of trends with time, correctly models the serial correlation and dependence on covariates, and provides model selection procedures and valid statistical inference. The analysis showed that own country emissions adequately represented the trend over time at all but a few of the 112 sites across Europe, but there was clear statistical evidence that change in concentration was not proportionally related to changes in emissions at almost all sites. For 11 sites with collocated meteorological data, covariates were constructed for neighbouring countries’ emissions accounting for distance, wind direction and wind speed. Even with this simple approach, the statistically significant effect of neighbouring countries’ emissions on monitored concentrations was shown for 6 out of the 11 sites. This confirms the benefit of access to meteorological data within these analyses and the possible improvements if emissions data were available on a finer spatial and temporal scale. The successful application of these statistical methods in this case study extends the statistical toolbox available for air pollution studies.
Keywords: Nonparametric smoothing; Trend; Statistical model selection
Source apportionment of PM2.5 in the southeastern United States using receptor and emissions-based models: Conceptual differences and implications for time-series health studies by Amit Marmur; S.-K. Sun-Kyoung Park; James A. Mulholland; Paige E. Tolbert; Armistead G. Russell (pp. 2533-2551).
Elevated levels of fine particulate matter (PM2.5) have been associated with adverse effects on human health, but whether specific components of PM2.5 are responsible for specific health effects is still under investigation. A complementary approach to examining species-specific associations is to assess associations between health outcomes and sources contributing to PM2.5. This approach could help target and regulate the sources that contribute most to adverse health effects. Various techniques have been developed to quantify source impacts on air quality, allowing examination of their health impacts. We compare two conceptually different approaches to source apportionment (SA): a receptor model and an emissions-based air-quality model. Daily source impacts for July 2001 and January 2002 at four sites in the southeastern US were calculated using CMB-LGO, an extended chemical mass balance receptor model incorporating the Lipschitz global optimizer, and EPA's Models-3 emissions-based air-quality modeling system (MM5–SMOKE–community multiscale air-quality (CMAQ)). The receptor model captured more of the temporal variation in source impacts at a specific receptor site compared to the emissions-based model. Driven by data at a single site, receptor models may have some significant shortcomings with respect to spatial representativeness (unless a reduced study area is used or data from multiple sites are available). SA results from emissions-based models, such as CMAQ, may be more spatially representative as they represent an average grid-cell value. Limitations in the ability to model daily fluctuations in emissions, however, lead to results being driven mainly by regional meteorological trends, likely underestimating the true daily variations in local source impacts. Using results from either approach in a health study would likely introduce an attenuation of the observed association, due to limited spatial representativeness in receptor modeling results and to limited temporal representativeness in emissions-based models results.
Keywords: CMAQ; CMB; LGO; Source apportionment; Health effects; PM; 2.5
Trends of particulate matter in four cities in India by Indrani Gupta; Rakesh Kumar (pp. 2552-2566).
Particulate matter (PM) in all the four Metropolitan cities in India are higher than the prescribed standards of Central Pollution Control Board, India as well as WHO guidelines. Over last 10 years various changes in fuel quality, vehicle technologies, industrial fuel mix and domestic fuel mix have taken place resulting in changes in air quality in these cities. A set of time series analysis methods viz. t-test adjusted for seasonality, Seasonal Kendall test and Intervention analysis have been applied to identify and estimate the trend in PM10 and total suspended particles (TSP) levels monitored for about 10 years at three monitoring sites at each of the four cities in India. These tests have indicated that overall PM10 levels in all four metro cities have been decreasing or stationary. The distinct trends for the monthly averages of PM10 concentrations at Parel, Kalbadevi in Mumbai and Thiruvattiyar in Chennai for the period 1993–2003 were declining by 10%, 6% and 5% per annum, respectively. This is ascribed to a shift in the magnitude and spatial distribution of emissions in the city. However, the monthly averages of TSP do not have a clear trend over the period 1991–2003.
Keywords: Air pollution trends; Particulate matter; Time series models
Emission reduction potential of using ethanol–biodiesel–diesel fuel blend on a heavy-duty diesel engine by Xiaoyan Shi; Xiaobing Pang; Yujing Mu; Hong He; Shijin Shuai; Jianxin Wang; Hu Chen; Rulong Li (pp. 2567-2574).
Oxygenated diesel fuel blends have a potential to reduce the emission of particulate matter (PM) and to be an alternative to diesel fuel. This paper describes the emission characteristics of a three compounds oxygenated diesel fuel blend (BE-diesel), on a Cummins-4B diesel engine. BE-diesel is a new form of oxygenated diesel fuel blends consisted of ethanol, methyl soyate and petroleum diesel fuel. The blend ratio used in this study was 5:20:75 (ethanol: methyl soyate: diesel fuel) by volume. The results from the operation of diesel engine with BE-diesel showed a significant reduction in PM emissions and 2%–14% increase of NO x emissions. The change of CO emission was not conclusive and depended on operating conditions. Total hydrocarbon (THC) from BE-diesel was lower than that from diesel fuel under most tested conditions. Formaldehyde, acetaldehyde, propionaldehyde and acetone in the exhaust were measured, and the results indicated that use of BE-diesel led to a slight increase of acetaldehyde, propionaldehyde and acetone emissions. A small amount of ethanol was also detected in the exhaust from burning BE-diesel.
Keywords: Diesel engine; Biodiesel; Ethanol; Alternative fuel; Emissions
Radiocarbon determination of woodsmoke contribution to air particulate matter in Launceston, Tasmania by Timothy B. Jordan; Andrew J. Seen; Geraldine E. Jacobsen; John L. Gras (pp. 2575-2582).
The radiocarbon (14C) content of ambient air particulate matter (PM) collected in Launceston (Australia) through routine state government PM10 sampling has been measured by accelerator mass spectrometry (AMS) to determine the contribution of woodsmoke to wintertime air pollution. For AMS sample preparation a modified combustion method was required for determination of the non-carbonate carbon fraction of PM collected on borosilicate filter media to minimise the effects of the filter melting during combustion to CO2. Negligible differences in the radiocarbon content of atmospheric aerosols were observed for samples using different filter media, particle-size fraction, sample storage, and sample combustion conditions.14C analyses revealed that contemporary carbon sources contribute 97–99% of the total non-carbonate carbon mass of wintertime ambient PM, supporting the conclusion that woodsmoke is the main contributor to Launceston air pollution. Conversely, fossil carbon sources were found to contribute a relatively constant 1.0±0.7μgCm−3 throughout the year, characteristic of transport-related emissions.
Keywords: Biomass combustion; 14; C; Woodheater; Tracer
Uncertainty assessment of localNO2 concentrations derived from error-in-variable external drift kriging and its relationship to the 2010 air quality standard by J. Jan van de Kassteele; Guus J.M. Velders (pp. 2583-2595).
LocalNO2 concentrations near Rotterdam (Netherlands) were assessed for the year 2010, focusing on the uncertainties and the changes in exceedance of European air quality standards. In the first step of the 2-step assessment method, the background contribution was determined by error-in-variable external drift kriging, where measurements and dispersion model output in the 1987–2003 period were combined. The result was subsequently extrapolated using dispersion model output and an emission scenario for 2010. In the second step, the local traffic contribution was added on the basis of a local generic dispersion model with use of an emission scenario for 2010. This resulted in maps showing localNO2 concentrations, upper and lower limits, and probabilities of exceeding the40μgm-3 air quality standard. The probabilistic measures were calculated in numbers and translated into words for easier communication. Using this method and scenario we found that within about 100m from the highways near Rotterdam the meanNO2 concentrations are likely to exceed the standard in 2010. The chance of exceeding the standard is unlikely up to 1km from the highways, where the mean is expected to be below the standard in 2010.
Keywords: Air quality; Policy making; Bayesian geostatistics
Personal monitoring of benzene in Perth, Western Australia: The contribution of sources to non-industrial personal exposure by A. Horton; F. Murray; M. Bulsara; A. Hinwood; D. Farrar (pp. 2596-2606).
Personal monitoring using passive samplers was conducted in Perth, Western Australia, to determine the concentrations of benzene to which residents were exposed during their daily activities. An additional aim of the study was to assess the contribution of different microenvironments to non-industrial exposure, and the extent to which lifestyle and behaviour influence personal exposure. Fifty participants were recruited and wore passive samplers over 24-h periods for 5 consecutive days (including weekends) in summer (November–March) and winter (June–September). The study commenced in June 2001 and was completed in April 2002. The mean benzene exposure of the participants in summer was 1.76 and 1.98μgm−3 in winter. Statistical analysis using a generalized linear mixed model revealed that refuelling and commuting were the most significant contributors to non-industrial exposure to benzene in summer and winter for Perth residents.
Keywords: Personal exposure; Benzene; Source contributions; Passive monitoring
Chemical characterization of air pollution in Eastern China and the Eastern United States by Xuexi Tie; Guy P. Brasseur; ChunSheng Zhao; Claire Granier; Steven Massie; Yu Qin; PuCai Wang; Geli Wang; PeiCai Yang; Andreas Richter (pp. 2607-2625).
Satellite data (MODIS, GOME, and MOPITT) together with a chemical transport global model of the atmosphere (MOZART-2) are used to characterize air pollution in Eastern China and the Eastern US to assess the differences between the photochemical conditions in these two regions. Observations show that aerosol concentrations (both fine (radius<0.5μm) and coarse modes (radius>0.5μm)) are higher in Eastern China than in the Eastern US. The NO x concentrations in both regions are substantially higher than in remote regions such as over the oceans (150 compared to 5 (1014#cm−2) over the Pacific Ocean). The CO concentrations are high in both urbanized areas (30 compared to 10 (1017#cm−2) over the Pacific Ocean). However, the concentrations of non-methane hydrocarbons from both anthropogenic and biogenic sources are considerably lower in Eastern China than in the Eastern US. As a result, the rate of photochemical ozone production and ozone concentrations during summer is significantly lower in Eastern China (daily averaged concentrations of 40–50ppbv in summer) than in the Eastern US (daily averaged values of 60–70ppbv). The analysis also shows that in Eastern China, the O3 production is mainly due to the oxidation of carbon monoxide (54% of total O3 production), while, in the Eastern US, the O3 production is attributed primarily to the oxidation of reactive hydrocarbons (68% of total O3 production). The results also indicate that biogenic emissions of hydrocarbons contribute substantially to the production of O3 in the Eastern US. The O3 production due to the oxidation of biogenic hydrocarbons represents approximately one third of total O3 photochemical production in this region. Measurements of surface ozone in the Eastern US and Eastern China seem to support that the summer ozone production is lower in Eastern China than in the Eastern US. However, additional surface measurements, especially of reactive hydrocarbons and ozone are needed in Eastern China in order to improve the present analysis and to confirm our current conclusions. A sensitivity study shows that with increase in anthropogenic emissions of HCs, the surface ozone concentrations significantly increase in Eastern China, indicating that the increase in the emissions of HCs plays an important role for the enhancement in surface ozone in this region.
Keywords: Ozone production; The Eastern US; Eastern China
Characterisation of airborne particulates and associated trace metals deposited on tree bark by ICP-OES, ICP-MS, SEM-EDX and laser ablation ICP-MS by Keiko Suzuki (pp. 2626-2634).
Particulate matter accumulated on tree bark specimens was examined in order to investigate its potential use as a natural monitor to study the impact on local atmospheric conditions. Tree bark from sargent cherry ( Prunus sargentii) and sugar maple ( Acer saccharum Marsh) trees was collected from four locations: Drax (North Yorkshire), Darley Dale (Derbyshire), Galway (Ireland) and Tristan da Cunha. Particulates accumulated on tree bark were prepared for analysis using a microwave-assisted HNO3 digestion. The bulk elemental content was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and trace metals were analysed by inductively coupled plasma mass spectrometry (ICP-MS). Analysis of bulk tree bark samples revealed that the highest mean Pb concentration was obtained in Darley Dale samples, 1069ngg−1, with 147 and 3.2ngg−1Pb in Drax and Galway samples, respectively. In Tristan da Cunha samples 0.12ngg−1 of Pb was detected. Pb, As, Cr, Sb, Sn and Zn were enriched by factors of 10–8650 relative to the background elemental abundance in tree bark obtained from Tristan da Cunha. Particulates accumulated on the tree bark were characterised by SEM-EDX and LA-ICP-MS to provide information on the particle composition and morphology. This study supports the suggestion that the major particulate sources are high-temperature combustion processes. Direct analysis by LA-ICP-MS revealed the potential of this alternative method to investigate the distribution of suspended particulates and their elemental association on the bark specimen.
Keywords: Suspended particulate matter; Tree bark; Trace metals; ICP-OES; ICP-MS; SEM-EDX; LA-ICP-MS