Atmospheric Environment (v.41, #10)
Editorial board (i).
Formation of 9,10-phenanthrenequinone by atmospheric gas-phase reactions of phenanthrene by Lin Wang; Roger Atkinson; Janet Arey (2025-2035).
Phenanthrene is a 3-ring polycyclic aromatic hydrocarbon which exists mainly in the gas-phase in the atmosphere. Recent concern over the presence of 9,10-phenanthrenequinone in ambient particles led us to study the products of the gas-phase reactions of phenanthrene with hydroxyl radicals, nitrate radicals and ozone. The formation yields of 9,10-phenanthrenequinone were measured to be ∼3%, 33±9%, and ∼2% from the OH radical, NO3 radical and O3 reactions, respectively. Calculations suggest that daytime OH radical-initiated and nighttime NO3 radical-initiated reactions of gas-phase phenanthrene may be significant sources of 9,10-phenanthrenequinone in ambient atmospheres. In contrast, the ozone reaction with phenanthrene is unlikely to contribute significantly to ambient 9,10-phenanthrenequinone.
Keywords: Phenanthrene; 9,10-phenanthrenequinone; Nitrate radical; Hydroxyl radical; Gas-phase atmospheric reactions;
Association between ionic composition of fine and coarse aerosol soluble fraction and peak expiratory flow of asthmatic patients in São Paulo city (Brazil) by Christine Bourotte; Ana-Paula Curi-Amarante; Maria-Cristina Forti; Luiz A. A. Pereira; Alfésio L. Braga; Paulo A. Lotufo (2036-2048).
Air pollutants are associated with adverse respiratory effects mainly in susceptible groups. This study was designed to assess the impact of the ionic composition of particulate matter on asthmatic respiratory functions in São Paulo city. From May to July 2002, fine and coarse particulate matter fractions were collected and their respective chemical composition with respect to major ions (Na+, Mg2+, K+, Ca2+, NH4 +, Cl−, NO3 − and SO4 2−) were determined in each aqueous-extract fraction. The results showed predominant concentrations of SO4 2− (48.4%), NO3 − (19.6%) and NH4 + (12.5%) in the fine fraction, whereas NO3 − (35.3%), SO4 2− (29.1%), Ca2+ (13.1%) and Cl− (12.5%) were the predominant species in the coarse fraction. The association between the chemical components of both fractions and the daily peak expiratory flow (PEF) measurements (morning and evening) of the 33 asthmatic individuals were assessed through a linear mixed-effects model. The results showed a significant negative correlation (decrease of PEF) between morning PEF and coarse chloride (3-day moving average) and between evening PEF and coarse Na+ (3-day moving average), coarse Mg2+ (3-day moving average) and coarse NH4 + (2- and 3-day moving average). A significant negative correlation has also been observed between morning and evening PEF and Mg2+ in the fine fraction. These results suggest that some particle chemical constituents may increase the responsiveness of airways and that coarse particles that deposit in the upper airways may be more relevant for asthmatic response and irritation. However, the results do not prove a clear causal relationship.
Keywords: PM2.5; PM2.5–10; Aerosol composition; Major ions; Aqueous extracts; PEF; Urban pollution;
Concentration-dependent NH3 deposition processes for mixed moorland semi-natural vegetation by M.R. Jones; I.D. Leith; D. Fowler; J.A. Raven; M.A. Sutton; E. Nemitz; J.N. Cape; L.J. Sheppard; R.I. Smith; M.R. Theobald (2049-2060).
Dry deposition modelling typically assumes that canopy resistance (R c) is independent of ammonia (NH3) concentration. An innovative flux chamber system was used to provide accurate continuous measurements of NH3 deposition to a moorland composed of a mixture of Calluna vulgaris (L.) Hull, Eriophorum vaginatum L. and Sphagnum spp. Ammonia was applied at a wide range of concentrations (1–100 μg m−3). The physical and environmental properties and the testing of the chamber are described, as well as results for the moorland vegetation using the ‘canopy resistance’ and ‘canopy compensation point’ interpretations of the data.Results for moorland plant species demonstrate that NH3 concentration directly affects the rate of NH3 deposition to the vegetation canopy, with R c and cuticular resistance (R w) increasing with increasing NH3 concentrations. Differences in R c were found between night and day: during the night R c increases from 17 s m−1 at 10 μg m−3 to 95 s m−1 at 80 μg m−3, whereas during the day R c increases from 17 s m−1 at 10 μg m−3 to 48 s m−1 at 80 μg m−3. The lower resistance during the day is caused by the stomata being open and available as a deposition route to the plant. R w increased with increasing NH3 concentrations and was not significantly different between day and night (at 80 μg m−3 NH3 day R w=88 s m−1 and night R w=95 s m−1). The results demonstrate that assessments using fixed R c will over-estimate NH3 deposition at high concentrations (over ∼15 μg m−3).
Keywords: Canopy resistance; Compensation point; Cuticular resistance; Flux chamber; Dry deposition; Ammonia;
Atmospheric polycyclic aromatic hydrocarbons observed over the North Pacific Ocean and the Arctic area: Spatial distribution and source identification by Xiang Ding; Xin-Ming Wang; Zhou-Qing Xie; Cai-Hong Xiang; Bi-Xian Mai; Li-Guang Sun; Mei Zheng; Guo-Ying Sheng; Jia-Mo Fu; Ulrich Pöschl (2061-2072).
During the 2003 Chinese Arctic Research Expedition from the Bohai Sea to the high Arctic (37–80°N) aboard the icebreaker Xuelong (Snow Dragon), air samples were collected using a modified high-volume sampler that pulls air through a quartz filter and a polyurethane foam plug (PUF). These filters and PUFs were analyzed for particulate phase and gas phase polycyclic aromatic hydrocarbons (PAHs), respectively, in the North Pacific Ocean and adjacent Arctic region. The ∑PAHs (where ∑=15 compounds) ranged from undetectable level to 4380 pg m−3 in the particulate phase and 928–92 600 pg m−3 in the gas phase, respectively. A decreasing latitudinal trend was observed for gas-phase PAHs, probably resulting from temperature effects, dilution and decomposition processes; particulate-phase PAHs, however, showed poor latitudinal trends, because the effects of temperature, dilution and photochemistry played different roles in different regions from middle-latitude source areas to the high latitudes. The ratios of PAH isomer pairs, either conservative or sensitive to degradation during long-range transport, were employed to interpret sources and chemical aging of PAHs in ocean air. In this present study the fluoranthene/pyrene and indeno[123-cd]pyrene/benzo[ghi]pyrene isomer pairs, whose ratios are conservative to photo-degradation, implies that biomass or coal burning might be the major sources of PAHs observed over the North Pacific Ocean and the Arctic region in the summer. The isomer ratios of 1,7/(1,7+2,6)-DMP (dimethylphenanthrene) and anthracene/phenanthrene, which are sensitive to aging of air masses, not only imply chemical evolving of PAHs over the North Pacific Ocean were different from those over the Arctic, but reveal that PAHs over the Arctic were mainly related to coal burning, and biomass burning might have a larger contribution to the PAHs over the North pacific ocean.
Keywords: Polycyclic aromatic hydrocarbons (PAHs); Arctic; North Pacific Ocean; Biomass burning;
Risks of exceeding the hourly EU limit value for nitrogen dioxide resulting from increased road transport emissions of primary nitrogen dioxide by David C. Carslaw; Sean D. Beevers; Margaret C. Bell (2073-2082).
In London, the recent analysis of ambient measurements has shown that directly emitted (primary) nitrogen dioxide ( NO 2 ) has increased as a fraction of total nitrogen oxides ( NO X ) from road transport sources. These increases appear to be mostly due to certain after-treatment devices, such as oxidation catalysts and particle filters fitted to diesel vehicles. This study uses a constrained simple chemical model to predict hourly concentrations of NO 2 at a busy roadside site in central London to investigate the dependence of peak hourly concentrations of NO 2 on the level of assumed primary NO 2 emitted by road vehicles. The model performance is shown to be good across the full range of hourly NO X and NO 2 concentrations over seven years. Monte Carlo simulations are used to predict future hourly NO 2 concentrations and the probability of exceeding the EU hourly limit value for NO 2 by considering the model errors, uncertainties in future NO X trends and the inter-annual variability of meteorology. It is shown that if the NO 2 / NO X emission ratio of 22.0% by volume, as calculated at the end of 2004, is sustained into the future, it is likely that the hourly EU limit value will not be met. However, the probability of not meeting the limit value in 2010 depends strongly on the meteorological year and varies from 16% to 88% depending on the year considered. This work shows that further increases in the NO 2 / NO X ratio beyond those observed at the end of 2004 would considerably increase the probability of the EU hourly limit for NO 2 being exceeded. Additionally, the analysis of road network emissions in London shows that many other roads are likely to be at risk from exceeding the hourly limit value. Further work is required to improve the quantification of NO 2 in vehicle exhausts to determine the likely future risks of exceeding the hourly limit value in other European cities.
Keywords: Monte Carlo; Nitrogen oxides; Diesel particulate filter; London;
Evaluation of long-term ozone simulations from seven regional air quality models and their ensemble by M. van Loon; R. Vautard; M. Schaap; R. Bergström; B. Bessagnet; J. Brandt; P.J.H. Builtjes; J.H. Christensen; C. Cuvelier; A. Graff; J.E. Jonson; M. Krol; J. Langner; P. Roberts; L. Rouil; R. Stern; L. Tarrasón; P. Thunis; E. Vignati; L. White; P. Wind (2083-2097).
Long-term ozone simulations from seven regional air quality models, the Unified EMEP model, LOTOS-EUROS, CHIMERE, RCG, MATCH, DEHM and TM5, are intercompared and compared to ozone measurements within the framework of the EuroDelta experiment, designed to assess air quality improvement at the European scale in response to emission reduction scenarios for 2020. Modelled ozone concentrations for the year 2001 are evaluated. The models reproduce the main features of the ozone diurnal cycle, but generally overestimate daytime ozone. LOTOS-EUROS and RCG have a more pronounced diurnal cycle variation than observations, while the reverse occurs for TM5. CHIMERE has a large positive bias, which can be explained by a systematic bias in boundary conditions. The other models and the “ensemble model”, whose concentrations are by definition averaged over all models, represent accurately the diurnal cycle. The ability of the models to simulate day-to-day daily ozone average or maxima variability is examined by means of percentiles, root mean square errors and correlations. In general, daily maxima are better simulated than daily averages, and summertime concentrations are better simulated than wintertime concentrations. Summertime correlations range between 0.5 and 0.7 for daily averages and 0.6 and 0.8 for daily maxima. Two health-related indicators are used, the number of days of exceedance of the 120 μ g m - 3 threshold for the daily maximal 8-h ozone concentration and the SOMO35. Both are well reproduced in terms of frequency, but the simultaneity of occurrence of exceedance days between observations and simulations is not well captured.The advantage of using an ensemble of models instead of a single model for the assessment of air quality is demonstrated. The ensemble average concentrations almost always exhibit a closer proximity to observations than any of the models. We also show that the spread of the model ensemble is fairly representative of the uncertainty in the simulations.
Keywords: Air quality; Modelling; Ozone; Model intercomparison; EuroDelta;
A new moss biomonitoring method for detecting sources of small scale pollution by J. Ángel Fernández; Jesús R. Aboal; Carlos Real; Alejo Carballeira (2098-2110).
A new simple method is proposed for identifying sources of small scale pollution, by determining the tissue concentrations of pollutants in terrestrial mosses. The method is based on spatial characterization of the processes that generate accumulation of pollutants in these organisms. The steps involved in implementing and applying the method are: (i) obtaining data on pollutants in moss samples collected at least at 35 pairs of sampling sites (SS) separated by 1 km distance; (ii) study of the distribution of the differences in concentration between the pairs of SS, eliminating pairs affected by foci that generate small scale processes; (iii) characterization of the resulting normal distributions and calculation, for different levels of significance, of the probability of a value lying within these distributions, and (iv) application of the calculated quantiles to data corresponding to the differences in concentrations between pairs of SS in the vicinities of foci of small scale pollution, to determine which elements can be considered as pollutants. Given the small number of data required once the distribution of the differences has been established, the method is an inexpensive, efficient way of establishing the probability that a pollutant is being emitted from a particular source. The method is very useful for verifying the results of pollution inventories, evaluating new technologies and improving the design of regional networks for biomonitoring of air quality with terrestrial mosses.
Keywords: Air quality; Heavy metals; Biomonitoring; Pseudoscleropodium purum;
Perennial observations of molecular hydrogen ( H 2 ) at a suburban site in Switzerland by M. Steinbacher; A. Fischer; M.K. Vollmer; B. Buchmann; S. Reimann; C. Hueglin (2111-2124).
Semi-continuous measurements of atmospheric molecular hydrogen ( H 2 ) and carbon monoxide (CO) were performed at a suburban sampling site in Switzerland from November 2002 to February 2005. The presented data provide information about time series, seasonal and diurnal cycles as well as sources and sinks in a suburban environment. Such records become increasingly important for the assessment of the effects of a possible future hydrogen economy on the environment. No significant trend of background H 2 concentrations could be observed for the considered period. Seasonal cycles show the expected pattern with maxima in winter and minima in summer and autumn. When extracting the background H 2 mixing ratios, the absolute levels as well as the seasonal amplitude agree well with literature data from semi-rural and remote sites. The H 2 dry deposition velocity for summer days with low winds is estimated to be between 0.5 × 10 - 4 to 1 × 10 - 4 m s - 1 . Diurnal cycles are dominated by H 2 emissions from nearby traffic. The influence of traffic-related emissions is also corroborated by a high H 2 to CO correlation. Typical molar H 2 to CO ratios from traffic were found to be 0.33 on a molar basis (ppb/ppb). A reduction of 37–62% in European anthropogenic H 2 emissions is estimated for a period covering the last 25 years. Since the ambient H 2 concentration did not decline during the same period, other simultaneous changes of sinks or sources of H 2 must have compensated this reduction.
Keywords: H 2 ; Molecular hydrogen; H 2 to CO ratio; Anthropogenic emissions; Deposition velocity;
Measurement of nucleation and soot mode particle emission from a diesel passenger car in real world and laboratory in situ dilution by Roberto Casati; Volker Scheer; Rainer Vogt; Thorsten Benter (2125-2135).
Uncertainties still remain in the size and number emission of nucleation and soot mode particles from diesel vehicles and understanding of the nucleation process under different ambient conditions. Particle emission measurements were carried out with a EURO-3 certified European diesel passenger car running on low (<10 ppm S) and high (310 ppm S) sulfur fuel. A newly developed in situ diluter which sampled exhaust continuously from the tailpipe and diluted in two steps by a factor of 500–6000 was employed to study nucleation particle formation under well-controlled temperature and humidity conditions. Particle emission measurements were also carried out with a mobile laboratory chasing the exhaust plume of the same vehicle in summer (19–25 °C) and winter (9 °C), with no significant difference of the nucleation or soot mode particle emission found. The particle size distributions compared well with those measured in the laboratory with the same vehicle under identical driving conditions. Simple nucleation and coagulation calculations were compared with the atmospheric and laboratory measurements. It was shown that the primary dilution step had the largest impact on the nucleation mode formation, while the model overpredicted the influence of temperature and humidity. No nucleation mode particles were observed running the diesel vehicle on low (<10 ppm S) fuel.
Keywords: Nucleation particles; Nanoparticles; Exhaust sampling; Real-world emission; Diesel fuel; Particle number;
A study on nighttime–daytime PM10 concentration and elemental composition in relation to atmospheric dispersion in the urban area of Milan (Italy) by R. Vecchi; G. Marcazzan; G. Valli (2136-2144).
In this paper, results on a PM10 daytime–nighttime measurement campaign carried out in Milan to study the evolution of PM10 concentration and composition in relation to atmospheric dispersion conditions are shown. To account for the evolution of atmospheric dispersion conditions, Radon hourly concentration measurements were performed. The significant correlation between PM10 and 222Rn daytime concentrations evidences the dominant role of atmospheric dispersion in determining the temporal variation of PM10 levels. Whenever 222Rn concentrations accumulate during the night (indicating the formation of nocturnal atmospheric stability conditions), PM10 concentrations are higher than those registered during the daytime before, despite a decrease in emissions from active sources. On the contrary, when 222Rn concentrations do not accumulate during night hours, PM10 levels are lower than those measured during the daytime before.As concerns the average elemental concentrations (in ng m−3), the nighttime–daytime variations are in the range −17% to +37%; during the night, soil-related elements (Al, Si, Ca, Ti) decrease while anthropogenic elements (Zn, Cu, Fe, Pb) increase.A case study concerning a ‘green’ Sunday (when traffic was forbidden from 8 a.m. to 8 p.m.) is also discussed. The difference of PM10 concentration and elemental composition registered during the ‘green’ Sunday daytime and the following nighttime, together with the information on atmospheric dilution power obtained by Radon measurements, allowed the characterisation of the traffic source elemental profile and increased the comprehension of the low effectiveness of some PM10 reduction strategies.
Keywords: PM10; Nighttime/daytime concentration; Traffic source; Atmospheric dispersion;
The role of ambient temperature for particle number concentrations in a street canyon by Gustavo Olivares; Christer Johansson; Johan Ström; Hans-Christen Hansson (2145-2155).
Two and a half years (June 2002 to September 2004) of air pollution and meteorological parameters in a street canyon in Stockholm were analyzed. A distinctive dependence of particle number concentration, normalized by NO x , with ambient temperature was found. By comparison with NO x , it is concluded that this variation is not related to variability in the emissions nor due to changes in atmospheric dilution. The observed ratio between total particle number and NO x increases from ca. [ 150 ± 60 ] particles per picogram of NO x [ pg NO x - 1 ] at + 15 ∘ C to [ 380 ± 50 ] [ pg NO x - 1 ] at - 15 ∘ C . The increase in particle number concentration with decreasing temperatures is different for different particle sizes. For particle sizes smaller than 40 nm the variation is more pronounced while for particle sizes larger than 100 nm the change is not statistically significant. This reflects the impact of temperature dependent processes that affect mainly particles smaller than 100 nm in diameter. Modeling results indicate that condensation of volatile compounds onto pre-existing aerosols gives similar changes in the particle size distribution as those observed. Coagulation is shown to have only minor effects on the particle size distribution. Even though, with the present data set is not possible to quantify the impact of an increased nucleation rate with low temperatures, it was shown that nucleation mode particles are largely influenced by relative humidity with high concentrations during high relative humidity periods and therefore it is expected that for cold periods, when the relative humidity is higher, nucleation is enhanced by the water content of the air.
Keywords: Particle size distribution; Exhaust emissions; Urban aerosol; Condensation; Coagulation;
Primary emissions of fine carbonaceous particles in Europe by Kaarle Kupiainen; Zbigniew Klimont (2156-2170).
The European emissions of BC and OC in fine particles are calculated for the years 1990, 1995 and 2000 applying the RAINS model that, beyond fuel-sector distinction, explicitly includes various combustion technologies and the penetration of abatement options. The emission factors used are developed considering specific European conditions. The main sources of carbonaceous aerosols in Europe are emissions from traffic and residential combustion of solid fuels. Between 1990 and 2000, the BC and OC emissions are estimated to decline from 0.89 to 0.68 Tg and from 1.4 to 1.0 Tg, respectively. Most of the reduction occurred in the early 1990s in Eastern Europe owing to structural changes that resulted in energy efficiency improvements in industry and lower consumption of solid fuels in residential–commercial sector; the latter having strong impact on BC and OC emissions. Furthermore, the growth in transport volumes, and expected increase in emissions, was offset by introduction of stricter legislation for road transport from 1995. Focusing on the most important sectors, transport and residential combustion, the variation in measured carbonaceous emission shares and its impact on total emissions was evaluated. This analysis indicates a range of about −25% to +20% for BC and −7% and +15% for OC, compared to the central case.
Keywords: Black and organic carbon; Emission modelling; Combustion; Anthropogenic sources;
Photochemical ozone formation at Portugal West Coast under sea breeze conditions as assessed by master chemical mechanism model by M.G. Evtyugina; C. Pio; T. Nunes; P.G. Pinho; C.S. Costa (2171-2182).
Results on photochemical pollutants monitoring obtained in the field campaign CZCM-2001 were used as a database in photochemical trajectory model using the explicit mechanism Master Chemical Mechanism version 3 (MCM v3) aiming to simulate the formation of photochemical pollutants in air masses during the sea breeze circulation at Portugal West Coast. The modelling results were in good agreement with experimental data. The sensitivity analysis of MCM v3 revealed that under experimental sea breeze conditions, the initial concentrations of air pollutants such as NO x and VOCs at the coast are crucial factors influencing the level of ozone production in inland rural areas.
Keywords: Photochemical pollution; Master chemical mechanism;
A review of particle formation events and growth in the atmosphere in the various environments and discussion of mechanistic implications by N.S. Holmes (2183-2201).
This review highlights recent observations from a large number of studies investigating formation and growth within different environments and discusses the importance of various mechanisms of particle formation and growth between the different environments. Whilst, several mechanisms for new particle formation which proposed the importance of each mechanism are still the centre of much debate. Proposed nucleation mechanisms include condensation of a binary mixture of sulphuric acid and water; ternary nucleation of sulphuric acid, water and a third molecule, most likely ammonia; ion-induced nucleation; secondary organic aerosol formation involving condensation of low- or non-volatile organic compounds and homogeneous nucleation of iodine oxides. Laboratory and modelling studies have shown these mechanisms can occur in the atmosphere although the contribution depends on the concentrations of precursor compounds present. In addition, atmospheric particle formation events are significantly affected by environmental factors, such as temperature, humidity and the surface area of pre-existing particles, which is also discussed here. One major problem hampering our current understanding is that these new particles are smaller than the lower size detection limit of most instruments and are only observed after some particle growth has occurred.Particles growth occurs through condensation of supersaturated vapours on the surface of the nucleated particles. This requires a lower degree of supersaturation than nucleation and thus condensation of the nucleating species reduces the rate of particle formation. Therefore, it is believed that particle growth often occurs through the condensation of other gases, including organic and inorganic compounds, than those responsible for nucleation. This decoupling of nucleation and growth means that the individual gases responsible for nucleation and growth can be unclear.Since observations of particle formation only occur following growth to observable sizes it is possible that a pool of undetectable particles exist at all times but are only observed following significant condensational growth.
Keywords: Particle formation; Nucleation; Growth; Mechanisms; Modelling studies;
Assessment of the impacts on health due to the emissions of Cuban power plants that use fossil fuel oils with high content of sulfur. Estimation of external costs by L. Turtós Carbonell; E. Meneses Ruiz; M. Sánchez Gácita; J. Rivero Oliva; N. Díaz Rivero (2202-2213).
Fossil fuel electricity generation has been demonstrated to be a main source of atmospheric pollution. The necessity of finding out a balance between the costs of achieving a lower level of environmental and health injury and the benefits of providing electricity at a reasonable cost have lead to the process of estimating the external costs derived from these impacts and not included in the electricity prices as a quantitative measure of it that, even when there are large uncertainties involved, can be used by decision makers in the process of achieving a global sustainable development.The external costs of the electricity generation in three Cuban power plants that use fossil fuel oils with high sulfur content have been assessed. With that purpose a specific implementation of the Impact Pathways Methodology for atmospheric emissions was developed. Dispersion of atmospheric pollutants is modeled at local and regional scales in a detailed way. Health impacts include mortality and those morbidity effects that showed relation with the increment of selected pollutant concentration in national studies. The external cost assessed for the three plants was 40,588,309 USD yr−1 (min./max.: 10,194,833/169,013,252), representing 1.06 USD Cent kWh−1. Costs derived from sulfur species (SO2 and sulfate aerosol) stand for 93% of the total costs.
Keywords: External costs; Electricity generation; Dispersion modeling; Health impacts; Sulfur;
The impact of using different land cover data on wind-blown desert dust modeling results in the southwestern United States by Dazhong Yin; Slobodan Nickovic; William A. Sprigg (2214-2224).
Olson World Ecosystem (OWE) land cover data based on data sources of the 1970s and 1980s with a 10-min spatial resolution, and up-to-date Moderate Resolution Imaging Spectroradiometer (MODIS) land cover data with a 30-s resolution, were used, respectively, in modeling wind-blown desert dust in the southwest United States. The model using different land cover data sets preformed similarly in modeling meteorological field patterns, vertical profiles and surface wind and temperature, in comparisons against observations. The differences of wind and temperature at a specific time and location can be big. Compared against satellite and ground measurements, modeled dust spatial distributions using MODIS land cover data were considerably better than those using OWE land cover. Site against site comparisons of modeled and observed surface PM2.5 concentration time series showed that model performance improved significantly using MODIS land cover data. Modeled surface PM2.5 contour distributions using MODIS land cover data compared more favorably against observations. The performance statistics for modeled PM2.5 concentrations at 40 surface sites increased from 0.15 using OWE data, to 0.58 using MODIS data. This demonstrates that the survey updates and spatial resolution of land cover data are critical in correctly predicting dust events and dust concentrations. Using land cover data such as MODIS data from satellite remote sensing is promising in improving wind-blown dust modeling and forecasting.
Keywords: Desert dust modeling; Air-borne particulate matter pollution; PM2.5 concentrations; Model performance;
Coarse particle speciation at selected locations in the rural continental United States by William C. Malm; Marc L. Pitchford; Charles McDade; Lowell L. Ashbaugh (2225-2239).
A few short-term special studies at National Parks have shown that coarse mass (CM) (2.5– 10 μ m ) may not be just crustal minerals but may consist of a substantial amount ( ≈ 40 –50%) of carbonaceous material and inorganic salts such as calcium nitrate and sodium nitrate. To more fully investigate the composition of coarse particles, a program of coarse particle sampling and speciation analysis at nine of the Interagency Monitoring of Protected Visual Environments (IMPROVE) sites was initiated 19 March 2003 and operated through the year 2004. Only the data for 2004 are reported here. Sites were selected to be representative of the continental United States and were operated according to IMPROVE protocol analytical procedures. Crustal minerals (soil) are the single largest contributor to CM at all but one monitoring location. The average fractional contributions range from a high of 76% at Grand Canyon National Park to a low of 34% at Mount Rainier National Park. The second largest contributor to CM is organic mass, which on an average annual fractional basis is highest at Mount Rainier at 59%. At Great Smoky Mountains National Park, organic mass contributes 40% on average, while at four sites organic mass concentrations contribute between 20% and 30% of the CM. Nitrates are on average the third largest contributor to CM concentrations. The highest fractional contributions of nitrates to CM are at Brigantine National Wildlife Refuge, Great Smoky Mountains, and San Gorgonio wilderness area at 10–12%. Sulfates contribute less than about 5% at all sites.
Keywords: Coarse particle; Speciation; Particulate matter; Monitoring;
Precipitation chloride at West Point, NY: Seasonal patterns and possible contributions from non-seawater sources by J.B. Shapiro; H.J. Simpson; K.L. Griffin; W.S.F. Schuster (2240-2254).
Chloride derived from the atmosphere can be a valuable tracer in ecosystem and watershed processes. For these purposes and other environmental studies, it is important to establish temporal patterns and sources for Cl - in wet deposition. Weekly composite precipitation samples have been analyzed by the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) at West Point, NY during 1981–2003, although systematic contamination of precipitation Na + significantly perturbed data for Na + prior to 1998. Chloride and sodium ion seasonal wet deposition were highest in winter and lowest in summer through most of the record, probably as a result of more frequent marine-trajectory storms in winter. During 1998–2003, the period of highest quality Na + data, the ratio of [ Cl - ] / [ Na + ] was significantly higher than average in summer and lower in winter. Higher summer [ Cl - ] / [ Na + ] occurred consistently throughout the record, often reaching values four times the seawater ratio. Based on the ratio of [ Cl - ] / [ Na + ] in seawater ( 1.16 ) ∼ 16 % of annual wet deposition of Cl - during 1998–2003 was in excess of that for surface seawater. Additionally, a minor terrestrial dust Na + component was approximated, which had the net effect of increasing annual excess Cl - wet deposition to ∼ 22 % ( 2.56 mEq m - 2 or 0.90 kg ha - 1 ) of the mean annual Cl - wet deposition at West Point ( 11.9 mEq m - 2 or 4.2 kg ha - 1 ). Consistent with plausible sources of non-seawater Cl - , we attribute excess Cl - wet deposition to HCl emission from coal fired generating stations, HCl emissions from domestic and industrial waste incineration and to HCl formation in the regional atmosphere from reactions of sea-salt aerosols with S and N acidic gases.
Keywords: NADP; HCl; Coal combustion; Incineration; Sea-salt dechlorination;