Validation of Personal Exposure Models for Sulfafe and Aerosol Strong Acidity

Personal exposure models for sulfates (SO₄ ⁼) and aerosol strong acidity (H⁺) were previously developed using concentration and activity pattern data collected from a personal monitoring study conducted in Uniontown, Pennsylvania, during the summer of 1990. Models were constructed based on time-weighted microenvironmental exposures. For SO₄ ⁼, the “best-fit” model included a correction factor, while for H⁺, it included both a correction factor and a neutralization term.

In this paper, we present the validation of these models using data collected in a personal monitoring study conducted in State College, Pennsylvania, during the summer of 1991. Indoor and outdoor concentration and activity pattern data collected in this study were used as inputs for the “best-fit” models for SO₄ ⁼ and H⁺. Predicted personal exposures subsequently were compared to the measured personal exposures from State College to determine their accuracy and precision.

Predicted personal exposures for both SO₄ ⁼ and H⁺ were in excellent agreement with measured personal exposures from State College. The models explained 91 and 62 percent of the variability in personal SO₄ ⁼ and H⁺ exposures, respectively, and were able to estimate personal exposures substantially better than outdoor concentrations alone. Validation results suggest that the models' correction and neutralization factors are not site specific and support the models' future application as a technique to assess the personal acid aerosol exposures of children living in similar rural and semi-rural communities.     

The measurement of H2SO4 and other sulfate species at Tuxedo,New York with a thermal analysis flame photometric detector and simultaneously collected quartz filter samples

A study of major atmospheric particulate sulfate species was conducted during 30 July 1980–1983 September 1980 in Sterling Forest, a rural area in Tuxedo, NY, not affected by major local sources of pollution. In situ measurements of total sulfate, sulfuric acid and ammonium sulfate ammonium bisulfate were made using Thermal Analysis-Flame Photometric Detection (TA-FPD). These measurements were compared to the total sulfate and strong acid (H⁺) concentration measured in simultaneously collected 12 h, treated quartz filter samples. The concentration of NH₄HSO₄ was inferred from the difference between the total strong acid concentration and the sulfuric acid measurements, so that total sulfate and acid concentrations could be balanced. A major sulfate pollution episode occurred during the period of 27–29 August. The concentration of H⁺ showed an excess above that necessary to account for the TA-FPD H₂SO₄ measurement, indicating the presence of NH₄ HSO₄. The maximum 12 h average concentrations of H₂SO₄, NH₄HSO₄ and (NH₄)₂SO₄ were 5.18, 11.42 and 10.08 μg m⁻³ as SO₄²⁻ respectively, and were measured from 9:15 to 21:15 on 28 August. The study demonstrated the usefulness of concurrent measurements of airborne particulate sulfate by filter extraction and TA-FPD to identify acidic sulfate species.     

Chemical differences between event and weekly precipitation samples in northeastern Illinois

We examine the chemical differences between event and weekly samples of precipitation collected in northeastern Illinois from April 1980 to March 1982. Analyses were conducted for H⁺, Ca²⁺, Mg²⁺, NH₄⁺, SO₄²⁻ and NO₃⁻ concentrations as well as for pH and conductivity. In addition, the 1980–1981 samples, were titrated to determine the total, strong and weak acid concentrations. Although seasonal and annual precipitation amounts were different for the two years, the general pattern of event and weekly sample ion concentrations were similar. Weekly samples had significantly less [NH₄⁺] and higher laboratory pH in all seasons and more [SO₄²⁻] in every season but summer. Weekly samples had significantly more [Ca²⁻] and [Mg²⁺] during seasons with little precipitation. Event and weekly [NO₃⁻] were never significantly different. The weekly samples had more total acidity in the spring but less in the summer. The observed differences may be attributed to chemical degradation of the weekly samples while waiting collection and during shipment between the field and the laboratory.     

Ionic composition of precipitation at the Central Anatolia (Turkey)

Concentrations of major ions, SO₄²⁻, NO₃⁻, Cl⁻, H⁺, Ca²⁺, K⁺, Mg²⁺, Ca²⁺ and conductivity were measured in approximately 300 daily, wet-only rain samples collected at a permanent rural station between 1993 and 1998. Concentrations of anthropogenic ions NH₄⁺, SO₄²⁻ and NO₃⁻ were among the highest values reported in whole EMEP network, suggesting that the Anatolian plateau is under strong influence of distant emission sources. Although transport of pollutants have significant influence on the chemical composition of precipitation, average pH of the rainwater is 6.2 due to extensive neutralization of acidity. Approximately 95% of the acidity in collected samples is neutralized, particularly in summer season. The neutralizing agents are primarily CaCO₃ and NH₃. Concentrations of crustal ions are higher in summer season due to enhanced resuspension of soil particles from dry surface soil. Concentrations of anthropogenic ions SO₄²⁻ and NO₃⁻ do not change significantly between summer and winter due to higher intensity of rains in summer season. Although concentrations of ions measured in this study is among the highest reported in EMEP network, wet deposition fluxes are low compared to flux values reported for similar sites in Europe, due to low annual precipitation in the Anatolia. Wet deposition fluxes of all measured parameters are highly episodic. Source regions affecting chemical composition precipitation in the Central Anatolia is investigated using trajectory statistics.     

Relationship between Sulfate Aerosol and Visibility

A PM₁₀ monitoring network was established throughout the South Coast Air Basin (SOCAB) in the greater Los Angeles region during the calendar year 1986. Annual average PM₁₀ mass concentrations within the Los Angeles metropolitan area ranged from 47.0 µg m^-3 along the coast to 87.4 µg m^-3 at Rubldoux, the furthest inland monitoring station. Measurements made at San Nicolas Island suggest that regional background aerosol contributes between 28 to 44 percent of the PM₁₀ aerosol at monitoring sites In the SOCAB over the long term average. Five major aerosol components (carbonaceous material, NO^- ₃, SO⁼ ₄, NH⁺ ₄, and soil-related material) account for greater than 80 percent of the annual average PM₁₀ mass at all on-land monitoring stations. Peak 24-h average mass concentrations of nearly 300 µg m^-3 were observed at inland locations, with lower peak values (?130–150 µg m^-3) measured along the coast. Peak-day aerosol composition was characterized by increased NO^- ₃ Ion and associated ammonium ion levels, as compared to the annual average. There appears to be only a weak dependence of PM₁₀ mass concentration on season of the year. This lack of a pronounced seasonal dependence results from the complex and contradictory seasonal variations in the major chemical components (carbonaceous material, nitrate, sulfate, ammonium ion and crustal material). At most sites within the Los Angeles metropolitan area, PM₁₀ mass concentrations exceeded both the annual and 24-h average federal and state of California PM₁₀ regulatory standards.     

The Contribution of Sulfate and Nitrate to Atmospheric Fine Particles During Winter Inversion Fogs in Cache Valley,Utah

Abstract

Air pollutants were collected in Logan, Cache County, UT, in February 1993 during two periods of atmospheric inversion accompanied by fog. The following atmospheric species were determined: (1) gaseous SO₂, NO₂ (semi-quantitatively),HNO3, NH3, and HF; (2) fine particulate SO₄ ⁼, NO₃ ^-, NH₄ ⁺, F–, H⁺, C, Si, S, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Pb, Se, Br, and Sr, and; (3) fine particulate mass, which was calculated. The major components of fine particulate matter were carbonaceous material, ammonium nitrate, and ammonium sulfate, while the soil component was small. Calculated, fine particulate mass averaged 80 μg/m³ and reached concentrations as high as 120 μg/m³. SO₂/So_x and NO₂/NO_y mole ratios generally varied between 0.2 and 0.1 during inversions. These ratios also showed moderate but consistent diurnal patterns. The emission inventory for Cache County indicates sources of SO₂ and NO_x but not significant amounts of primary sulfate and nitrate. The observations reported here indicate there is significant conversion of SO₂ and NO_x in the presence of excess oxidants to sulfuric and nitric acid that are neutralized by excess ammonia.     

Wet and dry deposition monitoring in Southeastern Michigan

Wet and dry deposition as collected by a bucket were measured at two sites in southeastern Michigan for two years. The precipitation had an average pH of 4.27 and a SO²⁻₄ to NO⁻₃ ratio of 2.0. Particulate dry deposition velocities of 0.6 cm s⁻¹ for SO²⁻₄ and NO⁻₃ and > 2 cm s⁻¹ for Cl⁻, Ca²⁺, Mg²⁺,Na⁺ and K⁺ were calculated. The ambient particle composition, dry bucket collection and wet deposition were compared at two sites, one urban and the other rural. Higher ambient particle concentrations and dry deposition rates were measured at the urban site than the rural site, indicating the influence of local emissions. However, local emissions had no effect on the wet deposition concentrations. The influence of more distant source regions was examined by separating the precipitation events by wind direction. The events from the south and east had the highest SO²⁻₄ to NO⁻₃ ratios, which corresponded to the areas with the highest sulfur emissions. NO⁻₃ showed no directional dependence.Wet deposition was examined for the effect of storm type and seasonal trends. Contrary to a recent study on Long Island, we found higher concentrations of H⁺, SO²⁻₄ and NH⁺₄ in winter rain compared to snow. The wet deposition concentrations of H⁺, SO²⁻₄, and NH⁺₄ were highest in the summer, while only Na⁺ and Cl⁻ concentrations were highest in the winter, presumably due to winter road salting. The total deposition of acidic ions was highest in the summer and lowest in the winter, due both to lower concentrations and lower precipitation volumes in the winter. The dry deposition as collected by a bucket accounted for 1 % of total H⁺ deposition, 21 % of SO²⁻₄ deposition, 27% of NO⁻₃ deposition, 50% of Cl⁻ deposition and 61 % of Ca²⁺ deposition.     

Comparison of Selenium and Sulfur at Remote Sites

Abstract

The Interagency Monitoring of Protected Visual Environments (IMPROVE) particulate monitoring network has been collecting aerosols for visibility apportionment at remote sites in the United States since 1988. The measurements include the major PM_2.5 components, such as sulfur, carbon, and nitrate, and trace elements, such as selenium. This paper will examine the relationship between the sulfurs and selenium concentrations at 61 sites for samples collected in the seasonal year 1993. Maps of mean sulfur and selenium measurements in summer 1993 and winter 1993-1994 indicate that there are well-defined regional patterns for both elements, with concentrations in the Appalachian region that are ten times those in areas of the Pacific Northwest. The S/Se ratios of means are relatively uniform across the United States, at around 2000 in summer and 1000 in winter, indicating a strong sulfur-selenium relationship. The role of conversion of S0₂ to sulfate can also be deduced from the means. For individual samples taken during summer 1993, there is a high correlation between the two variables in the East, especially at sites in the Northeast, where the correlation coefficients (r²) are around 0.9. In the West, the correlation is much lower. This is attributed to fewer sources and differing emission factors.     

Source apportionment methods applied to the determination of the origin of ambient aerosols that affect visibility in forested areas

An aerosol characterization, visibility, and receptor modeling study was conducted in the Shenandoah Valley, VA between 14 July and 15 August 1980. The objectives of this study were to: (1) determine the origin of the ambient particles, (2) determine the major chemical species contributing to the light extinction coefficient, (3) evaluate analytical methods to characterize aerosols and (4) provide data for comparison with chemical composition of aerosols collected in the Great Smoky Mountains and in the Abastumani Mountains of Georgian Soviet Socialist Republic. The average sulfate concentrations measured in fine particles (<2.5μm) at these three locations were: 12.0μgm⁻³ at Great Smoky Mountains; 13.6 μg m⁻³ at Shenandoah Valley, and 4.6 μg m⁻³ at Abastumani Mountains; the fractions of sulfate in the fine particle mass concentrations at each site were 0.50,0.50 and 0.38, respectively. For the two studies in the United States, the fine particle sulfate during sulfate maxima was mostly in the form of ammonium acid sulfate. Factor analysis of the fine aerosol composition measured in the Shenandoah Valley yielded a persistent factor containing large loadings on mass, SO²⁻₄, S, NH⁺₄, H⁺, Se and total nitrate (sum of particulate nitrate and nitric acid), which is characteristic of coal-fired sources. This factor analysis grouping along with additional emissions information suggests that coal-fired power plants are the principal source of sulfate and nitrate.     

Atmospheric concentrations of ammonia and ammonium at an agricultural site in the southeast United States

In this study, we present ∼1 yr (October 1998–September 1999) of 12-hour mean ammonia (NH₃), ammonium (NH₄⁺), hydrochloric acid (HCl), chloride (Cl⁻), nitrate (NO₃⁻), nitric acid (HNO₃), nitrous acid (HONO), sulfate (SO₄²⁻), and sulfur dioxide (SO₂) concentrations measured at an agricultural site in North Carolina's Coastal Plain region. Mean gas concentrations were 0.46, 1.21, 0.54, 5.55, and 4.15 μg m⁻³ for HCl, HNO₃, HONO, NH₃, and SO₂, respectively. Mean aerosol concentrations were 1.44, 1.23, 0.08, and 3.37 μg m⁻³ for NH₄⁺, NO₃⁻, Cl⁻, and SO₄²⁻, respectively. Ammonia, NH₄⁺, HNO₃, and SO₄²⁻ exhibit higher concentrations during the summer, while higher SO₂ concentrations occur during winter. A meteorology-based multivariate regression model using temperature, wind speed, and wind direction explains 76% of the variation in 12-hour mean NH₃ concentrations (n=601). Ammonia concentration increases exponentially with temperature, which explains the majority of variation (54%) in 12-hour mean NH₃ concentrations. Dependence of NH₃ concentration on wind direction suggests a local source influence. Ammonia accounts for >70% of NH_x (NH_x=NH₃+NH₄⁺) during all seasons. Ammonium nitrate and sulfate aerosol formation does not appear to be NH₃ limited. Sulfate is primarily associated ammonium sulfate, rather than bisulfate, except during the winter when the ratio of NO₃⁻–NH₄⁺ is ∼0.66. The annual average NO₃⁻–NH₄⁺ ratio is ∼0.25.     

The distribution and transport of sulfate “species” in the New York metropolitan area during the 1977 Summer Aerosol Study

The atmospheric distribution of sulfate was analyzed at four sites operated by various cooperating laboratories for the period of 18 July–29 August 1977 in the New York metropolitan subregion. The sulfate concentrations measured in NYC were categorized according to wind trajectory and values ≥ 15 μg m⁻³ were normally associated with a strong westerly component. SO^{2 −}₄ values ≤ 5 μg m⁻³ were associated with other wind trajectories, that had not passed over the Ohio Valley. Comparison of the 1977 study with the New York Summer Aerosol Study (1976) indicated that on the average the SO^{2 −}₄ concentrations were slightly lower in 1977. The highest concentrations (> 20 μgm⁻³) occurred simultaneously with the return flow of ozone-laden high pressure systems.The results of a SO^{2 −}₄ episode which affected the region from 3–9 August 1977 were analyzed using trajectory analyses, satellite imagery and measurements of the chemical species H⁺, NH⁺₄, and SO^{2 −}₄. Transport of SO^{2 −}₄ was observed and the presence of a strong acid distribution in the rural areas was denonstrated. The aerosol in New York City appeared to be more nearly neutral, probably a result of reaction with ammonia.     

Seasonal variations in atmospheric SOx and NOy species in the adirondacks

This paper reports the results of over 2 years of measurements of several of the species comprising atmospheric SO_x (=SO₂+SO₄²⁻) and NO_y (=NO+NO₂ + PAN + HNO₃+NO₃⁻+ organicnitrates + HONO + 2N₂O₅ …) at Whiteface Mountain, New York. Continuous real-time measurements of SO₂ and total gaseous NO_y provided data for about 50% and 65% of the period, respectively, and 122 filter pack samples were obtained for HNO₃, SO₂ and aerosol SO₄²⁻, NO₃⁻, H⁺ and NH₄⁺. Concentrations of SO₂ and NO_y were greatest in winter, whereas concentrations of the reaction products SO₄²⁻ and HNO₃were greatest in summer. The seasonal variation in SO₄²⁻ was considerably more pronounced than that of HNO₃and the high concentrations of SO₄²⁻ aerosol present in summer were also relatively more acidic than SO₄²⁻ aerosol in other seasons. As a result, SO₄²⁻ aerosol was the predominant acidic species present in summer, HNO₃was predominant in other seasons. Aerosol NO₃⁻ concentrations were low in all seasons and appeared unrelated to simultaneous NO_y and HNO₃concentrations. These data are consistent with seasonal variations in photochemical oxidation rates and with existing data on seasonal variations in precipitation composition. The results of this study suggest that emission reductions targeted at the summer season might be a cost-effective way to reduce deposition of S species, but would not be similarly cost-effective in reducing deposition of N species. kwAcid deposition, seasonal variation, sulfate, nitrate, nitric acid, sulfur dioxide, oxides of nitrogen, hydrogen peroxide, ozone, air pollution, Adirondack Mountains     

A study of long range air pollution problems related to coal development in the Northern Great Plains

Potential environmental problems from coal development in the Northern Great Plains were examined in this paper. A regional-scale air pollution model was used to assess the impact of pollutant emissions on air quality at large distances. This model is based on the numerical solution of the atmospheric diffusion equation. Sulfur dioxide emissions inventories constructed for 1976 and 1986 were used with this model to calculate long range transport, diffusion, and dry deposition of SO₂ and sulfates for three meteorological conditions: a strong-wind winter case, a stagnation spring case, and a moderate-wind summer case. Calculated SO₂ concentrations near point sources are highest for the stagnation spring case, intermediate for the strong-wind winter case, and lowest for the moderate-wind summer case. Long range transport of SO₂, in contrast, appears to be slightly greater in the winter and summer cases than in the spring. For an SO₂/sulfate conversion rate of 0.3% h⁻¹, the predicted sulfate concentrations are not significantly above the background level. A simulation using a rate of 3% h⁻¹, however, yields a maximum 3-h average sulfate concentration of 20 μg m⁻³.     

Application of positive matrix factorization in source apportionment of particulate pollutants in Hong Kong

An advanced algorithm called positive matrix factorization (PMF) in receptor modeling was used to identify the sources of respirable suspended particulates (RSP) in Hong Kong. The compositional data obtained from the Hong Kong Environmental Protection Department from 1992 to 1994 were analyzed. The species analyzed in this study are Al, Ca, Mg, Pb, Na⁺, V, Cl⁻, NH₄⁺, SO₄²⁻, Br⁻, Mn, Fe, Ni, Zn, Cd, K⁺, Ba, Cu, and As. Unlike the conventional receptor modeling algorithm, factor analysis PMF only generates non-negative source profiles. To eliminate sulfate from such factors where it is not physically plausible, special penalty terms were included in the model so that sulfate concentrations could be selectively decreased in specified factors. A 9-factor model containing non-zero sulfate concentrations in three factors gives the most satisfactory source profiles. Ammonium sulfate, chloride depleted marine aerosols and crustal aerosols are the three non-zero sulfate sources. Other factors are marine aerosols, non-ferrous smelters, particulate copper, fuel oil burning, vehicular emission and bromide/road dust. The last two sources can be combined as a single source of vehicle/road dust. The compositional profiles of these factors were also developed. The mass profiles obtained can be improved by further refinement of distribution of sulfate in the sources.     

Seasonal Variations in Aerosol Composition and Acidity at Shenandoah and Great Smoky Mountains National Parks

The concentration of elements Na through Pb, select ions, and organic carbon from fine (<2.5 µm) particles has been monitored at Shenandoah and Great Smoky Mountains National Parks from 1988 through 1995. The data obtained from 1988 through 1994 show that significant changes in the concentrations of many aerosol constituents occur on a seasonal basis. Particulate sulfate and organic carbon are shown to exhibit substantially higher concentrations during the summer, while sulfur dioxide and nitrate concentrations are highest during the winter.

A method for estimating the degree of neutralization of particulate sulfate is given. This method uses routinely measured aerosol elemental compositions because ammonium ion, the primary neutralizing species for sulfate, is not measured on a routine basis. Application of this method to the selected data set shows that sulfate aerosol is most acidic during summer with an average molar H_s (moles of hydrogen associated with sulfur) to S (moles of sulfur) ratio of approximately 4. This suggests the average sulfate particle during the summer has a molar coon slightly more acidic than ammonium bisulfate (NH₄HSO₄) which has a molar hydrogen to sulfur ratio of 5. Winter H_s to S ratios, however, are approximately 8, suggesting the aerosol is on average fully neutralized ammonium sulfate [(NH₄)₂SO₄].     

Coarse–fine and day–night differences of water-soluble ions in atmospheric aerosols collected in Christchurch and Auckland,New Zealand

The water-soluble ions in fine (PM_<2.5) and coarse (PM_2.5−10) atmospheric aerosols collected in Christchurch during winter 2001, spring 2000 and summer 2001, and in Auckland during winter 2001 have been studied in terms of coarse–fine and day–night differences. Although the chemical characteristics of the coarse particles were similar in both cities, those of the fine particles collected in the Christchurch winter were significantly different, as manifested by higher concentrations of nss-K⁺, nss-Cl⁻, nss-Ca²⁺, nss-SO₄²⁻, NO₃⁻ and NH₄⁺. It was found that nighttime PM₁₀ and nss-K⁺ concentrations were much higher than their daytime concentrations in the Christchurch winter but a clear day–night difference was not apparent in the Auckland winter. Moreover, in the winter, sea-salt ions did not show a day–night difference; however, nss-SO₄²⁻ had opposite day–night variation in the two cities. An ion balance calculation has shown that in most samples, coarse particles can be neutral or alkaline, however, fine particles can be neutral or acidic. The possibility of ammonium salts existing in the fine particles collected in the Christchurch winter is discussed and it is concluded that a variety of ammonium salts were present. Equivalent ratios suggest that the fine particles may be significantly aged in the Christchurch winter.The evidence from our soluble ion study strongly suggests that wood and coal burning and secondary aerosols make a significant contribution to fine particulate mass in the Christchurch atmosphere. Thus, home-heating, a sheltered geographic location and relatively calm atmospheric condition are thought to be the major causes for the serious atmospheric particulate pollution in the Christchurch winter.     

Temporal and spatial relationships in fine particle strong acidity, sulphate, PM1O, and PM2.5 across multiple canadian locations

The Canadian Acid Aerosol Measurement Program (CAAMP) was established in 1992 to gain a better understanding of the atmospheric behaviour of fine particle strong acidity (“acid aerosols”) and to facilitate an assessment of the potential health risks associated with acid aerosols and particles in general. During 1992. 1993 and 1994, annular denuder and filter measurements were taken at four sites in Ontario, two in Quebec, three in the Atlantic Provinces and one in the greater Vancouver area. Mean fine particle sulphate concentrations (SO₄²⁻) were highest in southern Ontario (annual average ranged from 40–70 nmol m⁻³), lowest at a site in the Vancouver area (average = 16 nmol m⁻³) and second lowest in rural Nova Scotia. However, mean fine particle strong acid concentrations (H⁺) were geographically different. The highest mean concentrations were at the east coast sites (annual average of up to 30 nmol m⁻³). Acidities were lower in areas where the fine particle acidity experienced greater neutralization from reaction with ammonia. This included the major urban centres (i.e. Toronto and Montréal) and areas with greater amounts of agricultural activity, as in rural southern Ontario. On average, ambient concentrations of fine and coarse particle mass were larger in the urban areas and also in areas where SO₄²⁻ levels were higher. All the particle components were episodic. However, compared to SO₄²⁻ and fine particles (PM_2.5 or PM_2.1, depending upon inlet design), episodes of H⁺ tended to be less frequent and of shorter duration, particularly in Ontario. Saint John, New Brunswick, had the highest mean annual H⁺ concentration, which was 30 nmol m⁻³. H⁺ episodes (24 h concentration > 100 nmol m⁻³) were also the most frequent at this location. The high levels in Saint John were partially due to local sulphur dioxide sources and heterogeneous chemistry occurring in fog, which, on average, led to a 50% enhancement in sulphate, relative to upwind conditions.There was a substantial amount of intersite correlation in the day to day variations in H⁺, SO₄²⁻ , PM_2.5 and PM₁₀ (fine + coarse particles) concentrations, which is due to the influence of synoptic-scale meteorology and the relatively long atmospheric lifetime of fine particles. Sulphate was the most regionally homogenous species. Pearson correlation coefficients comparing SO₄²⁻ between sites ranged from 0.6 to 0.9, depending on site separation and lag time. In many cases, particle episodes were observed to move across the entire eastern portion of Canada with about a two-day lag between the SO₄²⁻ levels in southern Ontario and in southern Nova Scotia.     

Comparison of the Annular Denuder System and the Transition Flow Reactor for Measurements of Selected Dry Deposition Species

An intensive field study was conducted in Research Triangle Park, North Carolina in the fall of 1986. Ambient concentrations of the following constituents were obtained: nitric acid, nitrous acid, nitrogen dioxide, sulfur dioxide, ammonia, hydrogen ion, and particulate nitrate, sulfate, and ammonium. Results collected using the annular denuder system (ADS) and the transition flow reactor (TFR) are presented and compared.

Both types of samplers had operational detection limits on daily (22-hour) samples that were generally below 1 μg m_-3 suggesting that both samplers can provide sensitive measurements for most of the constituents of interest. Both the ADS and TFR show reasonable (>25 percent) within-sampler precision for most of the measured species concentrations, except TFR fine particulate nitrate measurements where results were frequently negative (The TFR fine particulate nitrate measurement is calculated using subtraction of positive numbers).

Comparison of ADS and TFR daily results showed good agreement for total particulate sulfate, the sum of total (coarse plus fine) particulate and gaseous nitrate, and ammonia. As a result of different inlet particle collection efficiencies, the ADS fine particulate sulfate exceeded the TFR (5 percent). In the absence of a filter to collect volatilized particulate ammonium in the ADS, the sum of total particulate and gaseous ammonium in the TFR exceeded that in the ADS. Of potentially more importance, ADS measurements of SO₂ and H⁺ exceeded those of the TFR, while TFR measurements of HNO₃ exceeded those of the ADS. Results of this study suggest that the TFR may provide biased measurements of SO₂, H⁺, HNO₃, and Fine NO₃ ^- that cannot be corrected without modifications to the fundamental design of the sampling system.     

Measurement and Analysis of the Relationship between Ammonia,Acid Gases,and Fine Particles in Eastern North Carolina

Abstract

An annular denuder system, which consisted of a cyclone separator; two diffusion denuders coated with sodium carbonate and citric acid, respectively; and a filter pack consisting of Teflon and nylon filters in series, was used to measure acid gases, ammonia (NH₃), and fine particles in the atmosphere from April 1998 to March 1999 in eastern North Carolina (i.e., an NH₃?rich environment). The sodium carbonate denuders yielded average acid gas concentrations of 0.23 μg/m³ hydrochloric acid (standard deviation [SD] ± 0.2 μg/m³); 1.14 μg/m³ nitric acid (SD ± 0.81 μg/m³), and 1.61 μg/m³ sulfuric acid (SD ± 1.58 μg/m³). The citric acid denuders yielded an average concentration of 17.89 μg/m³ NH₃ (SD ± 15.03 μg/m³). The filters yielded average fine aerosol concentrations of 1.64 μg/m³ ammonium (NH₄ ⁺;SD ± 1.26 μg/m³); 0.26 μg/m³ chloride (SD ± 0.69 μg/m³), 1.92 μg/m³ nitrate (SD ± 1.09 μg/m³), and 3.18 μg/m³ sulfate (SO₄ ^2?; SD ± 3.12 μg/m³). From seasonal variation, the measured particulates (NH₄ ⁺,SO₄ ^2?, and nitrate) showed larger peak concentrations during summer, suggesting that the gas-to-particle conversion was efficient during summer. The aerosol fraction in this study area indicated the domination of ammonium sulfate particles because of the local abundance of NH₃, and the long-range transport of SO₄ ^2? based on back trajectory analysis. Relative humidity effects on gas-to-particle conversion processes were analyzed by particulate NH₄ ⁺ concentration originally formed from the neutralization processes with the secondary pollutants in the atmosphere.     

Influence of meteorological factors and polluting environment on rain chemistry and wet deposition in a rural area near Chimay,Belgium

This paper focuses on a detailed analysis of the effects of meteorological factors explaining the variability of rain composition.Inorganic composition of 113 individual rain events was measured from May 2002 to October 2005 at a rural site near Chimay, in the western part of the Belgian Ardennes. Original models were fitted for each studied ion (H⁺, Mg²⁺, Ca²⁺, K⁺, NH₄⁺, Na⁺, Cl⁻, NO₃⁻ and SO₄²⁻) to relate rain event concentration or wet deposition to the rainfall volume (R), the length of the antecedent dry period (ADP), the volume of the previous event (R_prev) as well as to the mean wind speed and the prevailing wind direction during both the dry and the rainy periods. These variables explained from 32% (H⁺) to 69% (NO₃⁻) of rain concentration variability. Concentrations decreased logarithmically with increasing R values except in case of H⁺ for which a positive effect of rain volume on rain concentration was observed. ADP affected positively rain concentrations of all ions excluding K⁺ and H⁺ for which, respectively, a nonsignificant and a negative effect of this variable was observed. Increasing R_prev strengthened the effect of the variable R on H⁺, Mg²⁺, Ca²⁺, Na⁺, NH₄⁺ and SO₄²⁻ concentrations while it softened the effect of ADP on NO₃⁻ concentrations. Wind speed and direction during dry and rainy periods explained together from 8% (K⁺) to 38% (Na⁺) of rain concentration total variability. R² coefficients of the wet deposition models ranged from 0.51 (K⁺) to 0.79 (SO₄²⁻). For all ions, wet deposition increased significantly with increasing R values while the effects of the other variables were similar to those on concentrations. Wind conditions during dry and rainy periods explained from 4% (H⁺) to 24% (Na⁺) of wet deposition total variability. On an annual scale, the total dry period duration, the total rainfall volume as well as the shape of the distributions of the length of the antecedent dry periods and of the rain event volume are important parameters that influence annual wet deposition.