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.     

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 chemistry of bulk precipitation at a site in southeast england—II. Relationships between ions and comparison with other sites

This paper contains a statistical analysis of bulk precipitation chemistry of rain falling on the Tillingbourne Catchment, Surrey. Over the years 1978–1981, mean volume-weighted concentrations were: pH, 4.15, 70.8 μeq ℓ⁻¹ H⁺; organic, 2.8 mg ℓ⁻¹; total SO²⁻₄, 80.5 μeq ℓ⁻¹; NO⁻₃, 36.2 μeq ℓ⁻¹; NH⁺₄, 40.9 μeq ℓ⁻¹; Cl⁻ (2 years) 97.4 μeq ℓ⁻¹, rainfall 1067mm. Compared to other sites in the U.K. and elsewhere receiving acid precipitation in this pH is at the low end of the range, but levels of the other ions are moderate. Similar relations apply to deposition. Ion concentrations are highly correlated, especially total SO²⁻₄, NO⁻₃ and NH⁺₄. This group is linked more loosely to pH and organic content, while Cl⁻ does not correlate at all with the other ions, implying a totally different source, probably sea salt. H⁺ ions in rain correlate better with NO⁻₃ than with SO²⁻₄ and regression analysis suggests that almost all the NO⁻₃ is probably associated with nitric acid, whereas only about 57% of the SO²⁻₄ is associated with sulphuric acid. Deposition is approximately related to rainfall by a power law relationship in which the exponent of the equation varies between 0.5 and 0.9. However, it is concluded that an adequate estimate of deposition cannot be obtained from rainfall alone.     

The water-soluble ionic composition of PM2.5 in Shanghai and Beijing,China

A year-long field study to characterize the ionic species in PM2.5 was carried out in Shanghai and Beijing, China, in 1999–2000. Weekly samples of PM2.5 were collected using a special low flow rate (0.4 l min⁻¹) sampler. In Shanghai, SO₄²⁻ NO₃⁻ and NH₄⁺ were the dominant ionic species, which accounted for 46%, 18% and 17% of the total mass of ions, respectively. Local SO₂ emissions were an important source of SO₄²⁻ in PM2.5 because the SO₄²⁻ concentration was correlated with the SO₂ concentration (r=0.66). The relatively stable SO₄²⁻/SO₂ mass ratio over a large range of temperatures suggests that gas-phase oxidation of SO₂ played a minor role in the formation of SO₄²⁻. The sum of SO₄²⁻ and NO₃⁻ was highly correlated with NH₄⁺ (r=0.96), but insufficient ammonium was present to totally neutralize the aerosol. In Beijing, SO₄²⁻, NO₃⁻ and NH₄⁺ were also the dominant ionic species, constituting 44%, 25% and 16% of the total mass of water-soluble ions, respectively. Local SO₂ emissions were an important source of SO₄²⁻ in the winter since SO₄²⁻ was correlated with SO₂ (r=0.83). The low-mass SO₄²⁻/SO₂ ratio (0.27) during winter, which had low humidity, suggests that gas-phase oxidation of SO₂ was a major route of sulfate formation. In the summer, however, much higher mass ratios of SO₄²⁻/SO₂ (5.6) were observed and were ascribed to in-cloud sulfate formation. The annual average ratio of NO₃⁻/SO₄²⁻ was 0.4 and 0.6 in Shanghai and in Beijing, respectively, suggesting that stationary emissions were still a dominant source in these two cities.     

Annual and seasonal trends in chemical composition of precipitation in Japan during 1989–1998

Annual and seasonal trends were discussed for precipitation chemistry in Japan on the basis of a nationwide monitoring network by Japan Environment Agency. For this analysis, 17 sites, selected from the 23 network sites after evaluation of data completeness for the present purpose, were grouped into four areas in terms of the sea which could characterize each area: the Pacific Ocean, the Japan Sea, the Seto Inland Sea and the East China Sea areas. Major ion concentrations at each site were subjected to least-squares multiple regression analysis, and discussion was principally focused on the area-groups. Each area showed significant (p<0.05) decreasing trends in non-sea-salt sulfate (nss-SO₄²⁻) concentrations with the annual mean change rate of −3.0% yr⁻¹, whereas no significant trends were detected for NO₃⁻ at 59% of the sites. Ammonium (NH₄⁺) showed significant increasing trends for 35%, and decreasing trends for 18% of the sites; and, the maximum change rate of 3.8% yr⁻¹ was recorded in the Pacific Ocean area. Non-sea-salt calcium (nss-Ca²⁺) concentrations significantly decreased in northern and some industrialized areas. Both the annual cycle-amplitudes and effects of precipitation amounts were significant for the four ions at almost all sites. The maximum concentrations of nss-SO₄²⁻ and -Ca²⁺ occurred from winter to spring at most sites. The seasons when the maximum concentrations of NO₃⁻ and NH₄⁺ occurred, were found to differ from area to area. Furthermore, the trends in precipitation nss-SO₄²⁻, and NO₃⁻ were qualitatively consistent with those of anthropogenic emissions of SO₂, and NO_x in Japan, respectively.     

PM2.5–10, PM2.5 and associated water-soluble inorganic species at a coastal urban site in the metropolitan region of Rio de Janeiro

The concentrations of PM_2.5−10, PM_2.5 and associated water-soluble inorganic species (WSIS) were determined in a coastal site of the metropolitan region of Rio de Janeiro, Southeastern Brazil, from October 1998 to September 1999 (n=50). Samples were dissolved in water and analyzed for major inorganic ions. The mean (± standard deviation; median) concentrations of PM_2.5−10 and PM_2.5 were, respectively, 26 (± 16; 21) μg m⁻³ and 17 (± 13; 14) μg m⁻³. Their mean concentrations were 1.7–1.8 times higher in dry season (May–October) than in rainy season (November–April). The WSIS comprised, respectively, 34% and 28% of the PM_2.5−10 and PM_2.5 masses. Chloride, Na⁺ and Mg²⁺ were the predominant ions in PM_2.5−10, indicating a significant influence of sea-salt aerosols. In PM_2.5, SO₄²⁻ (∼97% nss-SO₄²⁻) and NH₄⁺ were the most abundant ions and their equivalent concentration ratio (SO₄²⁻/NH₄⁺ ∼1.0) suggests that they were present as (NH₄)₂SO₄ particles. The mean concentration of (NH₄)₂SO₄ was 3.4 μg m⁻³. The mean equivalent PM_2.5 NO₃⁻ concentration was eight times smaller than those of SO₄²⁻ and NH₄⁺. The PM_2.5 NO₃⁻ concentration in dry season was three times higher than in rainy season, probably due to reaction of NaCl (sea salt) with HNO₃ as a result of higher levels of NO_y during the dry season and/or reduced volatilization of NH₄NO₃ due to lower wintertime temperature. Chloride depletion was observed in both size ranges, although more pronouncely in PM_2.5.     

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.     

Spatial distribution of wet deposition of nitrogen in South Korea

A method is developed to estimate wet deposition of nitrogen in a 11×14 km (0.125°Lon.×0.125°Lat.) grid scale using the precipitation chemistry monitored data at 10 sites scattered over South Korea supplemented by the routinely available precipitation rate data at 65 sites and the estimated emissions of NO₂ and NH₃ at each precipitation monitoring site. This approach takes into account the contributions of local NO₂ and NH₃ emissions and precipitation rates on wet deposition of nitrogen. Wet deposition of nitrogen estimated by optimum regression equations for NO₃⁻ and NH₄⁺ derived from annual total monitored wet deposition and that of emissions of NO₂ and NH₃ is incorporated to normalize wet deposition of nitrogen at each precipitation rate class, which is divided into 6 classes. The optimum regression equations for the estimation of wet deposition of nitrogen at precipitation monitoring sites are developed using the normalized wet deposition of nitrogen and the precipitation rate at 10 precipitation chemistry monitoring sites. The estimated average annual total wet depositions of NO₃⁻ and NH₄⁺ are found to be 260 and 500 eq ha⁻¹ yr⁻¹ with the maximum values of 400 and 930 eq ha⁻¹ yr⁻¹, respectively. The annual mean total wet deposition of nitrogen is found to be about 760 eq ha⁻¹ yr⁻¹, of which more than 65% is contributed by wet deposition of ammonium while, the emission of NH₃ is about half of that of NO₂, suggesting the importance of NH₃ emission for wet deposition of nitrogen in South Korea.     

Seasonal variation in atmospheric aerosol concentration and composition at urban and rural sites in northern England

Seasonal variations in atmospheric aerosol concentration and composition have been determined at two nearby sites, one urban and one rural, near Leeds, W. Yorkshire. Aerosols, sampled on a daily basis and collected in the size ranges < 2.5 μm and 2.5−15 μm, were analysed for total mass, SO²⁻₄, NO⁻₃, Cl⁻ and NH⁺₄. Dark smoke and SO₂ were also measured at both sites. Results are given covering the period October 1982–September 1983. The average concentration of particles was higher at the urban site. The urban-rural difference in coarse particle concentration, which was about a factor of 2, was more significant than the difference in the fine particle concentration, which was only 1.3. Smoke and SO₂ concentrations showed strong wintertime maxima and summertime minima. Fine NO⁻₃ and Cl⁻ concentrations also had pronounced wintertime maxima and summertime minima attributed to the variation in volatility of their ammonium salts. Total mass, SO²⁻₄ and NH⁺₄ did not show any clear seasonal variations. Anti-cyclonic conditions in summer resulted in elevated mass concentrations of secondary pollutants, e.g. SO²⁻₄. The fine fraction contained ca 50% water-soluble inorganic ions at Leeds and slightly more at the rural site. These proportions showed little seasonal variation.     

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.     

Wintertime wet and dry deposition in northern Michigan

Wet and dry deposition were monitored at the University of Michigan Biological Station in rural northern Michigan for three winters. Dry deposition was measured by both the conventional bucket method and by measuring increases in concentration in exposed, elevated snow samples. Average results of the two methods were in reasonable agreement. The cumulative wet and dry deposition quantities are in good agreement with snowpack accumulations until the first thaw period. Dry deposition to snow accounts for less than 15% of the total H⁺, SO²⁻₄, NO⁻₃ and NH⁺₄ and approximately 25% of the Ca ²⁺, Mg ²⁺, Na⁺, K⁺ and Cl⁻ during an average precipitation year. Snowpack measurements were also made under deciduous and red pine canopies. Decreases in H⁺ and NO⁻₃ were observed under the red pine canopy.     

Study of aerosol transport through precipitation chemistry over Arabian Sea during winter and summer monsoons

Precipitation samples over the Arabian Sea collected during Arabian Sea Monsoon Experiment (ARMEX) in 2002–2003 were examined for major water soluble components and acidity of aerosols during the period of winter and summer monsoon seasons. The pH of rain water was alkaline during summer monsoon and acidic during winter monsoon. Summer monsoon precipitation showed dominance of sea-salt components (∼90%) and significant amounts of non-sea salt (nss) Ca²⁺ and SO₄²⁻. Winter monsoon precipitation samples showed higher concentration of NO₃⁻ and NH₄⁺ compared to that of summer monsoon, indicating more influence of anthropogenic sources. The rain water data is interpreted in terms of long-range transport and background pollution. In summer monsoon, air masses passing over the north African and Gulf continents which may be carrying nss components are advected towards the observational location. Also, prevailing strong southwesterly winds at surface level produced sea-salt aerosols which led to high sea-salt contribution in precipitation. While in winter monsoon, it was observed that, air masses coming from Asian region towards observational location carry more pollutants like NO₃⁻and nss SO₄²⁻ that acidify the precipitation.     

Vertical distribution of gases and aerosols: The behaviour of ammonia and related components in the lower atmosphere

Vertical concentration profiles for NH₃, HNO₃ and HCl-gas and for NH₄⁺, NO₃⁻, SO²⁻₄, Cl⁻ and Na⁺ aerosol were obtained from a meteorological tower in the central part of the Netherlands. An upward NH₃ flux of 0.12 μgm⁻² s⁻¹ was calculated from the NH₃ profiles and meteorological data. From the HNO₃ profiles a maximum HNO₃ dry deposition velocity of 4 cm s⁻¹ was calculated. Good agreement was found between the measured concentration products [NH₃]_(g) × [HNO₃]_(g) and the theoretical values at temperatures above 0°C and relative humidities below 80%. In other cases, higher NH₃ and/or HNO concentrations in the gas phase were measured than theoretically predicted.     

Ambient suspended particulate matters and related chemical species study in central Taiwan,Taichung during 1998–2001

Ambient suspended particulate (PM_2.5, PM_2.5–10, TSP) was collected from June 1998 to February 2001 in Taichung, central Taiwan. In addition, the related water-soluble ionic species (Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺) and metallic species (Fe, Zn, Pb, Ni) were also analyzed in this study. The results showed that the concentrations of particulate mass are higher in the traffic site (CCRT) than the other sampling sites in this study. Also, the fine particle (PM_2.5) concentration is the dominant species of the total suspended particles in Taichung, central Taiwan. The dominant species for PM_2.5 are sulfate and ammonium at all sampling sites during the period of 1998–2001. The results of diurnal variation at THUC sampling site are also discussed in this study. Overall, acidic and secondary aerosol (Cl⁻, NO₃⁻, SO₄²⁻ and NH₄⁺) is a more serious air pollutant issue in southern and central Taiwan than at several sites around the world. Therefore, ambient suspended particulate monitoring in Taichung, central Taiwan will be continuing in our following study to provide more information for the government to formulate environmental strategy.     

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     

Chemical composition of rainwater and anthropogenic influences in the Piracicaba River Basin,Southeast Brazil

The influences of different kinds of anthropogenic activities on rainwater chemistry in a tropical area were studied during one uninterrupted year at Piracicaba River Basin (Southeast Brazil). A total of 272 rainwater samples collected continuously from August 1997 to July 1998 at four different sites were analyzed for F⁻, CH₃COO⁻, HCOO⁻, MSA, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, SO₄²⁻, C₂O₄²⁻, PO₄³⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, DOC (dissolved organic carbon), DIC (dissolved inorganic carbon), pH and conductivity. The most abundant ion was H⁺ and rain acidity was significant at all sampling sites (average pH of 4.4–4.5). The sources of this free acidity differ among sites and appear to be correlated to the different land-uses. The composition of rainwater appeared to be controlled mostly by three sources: soil dust, sugar cane burning and industrial emissions.     

Association between ionic composition of fine and coarse aerosol soluble fraction and peak expiratory flow of asthmatic patients in São Paulo city (Brazil)

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 SO₄²⁻) were determined in each aqueous-extract fraction. The results showed predominant concentrations of SO₄²⁻ (48.4%), NO₃⁻ (19.6%) and NH₄⁺ (12.5%) in the fine fraction, whereas NO₃⁻ (35.3%), SO₄²⁻ (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.     

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.     

Atmospheric concentrations and the deposition velocity to snow of nitric acid,sulfur dioxide and various particulate species

A study of deposition velocities to snow was conducted during the 1982–1983 and 1983–1984 winters at the University of Michigan Biological Station in northern Michigan. Weekly measurements were made of dry deposition rates to snow and the atmospheric concentrations of the depositing species. SO₂, with an average concentration of 2.2 ppb, was the dominant atmospheric sulfur containing species. NO₂, with an average concentration of 1.8 ppb, was the dominant atmospheric nitrogenous species. NO⁻₃ deposition was due primarily to HNO₃, which averaged 0.2 ppb. The HNO₃ deposition velocity averaged 1.4cm s⁻¹. The SO₂ deposition velocity varied with temperature, averaging 0.15 cm s⁻¹ for samples with appreciable exposure time above − 3°C, and 0.06 cm s⁻¹ for samples which remained below an ambient temperature of −3°C. Deposition velocities of Ca²⁺, Mg²⁺ , Na⁺, K⁺ and NH⁺₄ were 2.1, 1.5, 0.44, 0.51 and 0.10cm s⁻¹, respectively. The mass median diameters of these species were 4.4, 2.7, 1.8, 0.9 and 0.46 μm, respectively.     

Sampling and chemical analysis of ice crystals as a function of size

Size-classified ice crystal samples were collected during the Spring of 1998, at the Jungfraujoch High-Alpine Research Station (3454 m), located in Switzerland. A procedure modified from the Guttalgor method, originally developed for size-selective sampling of raindrops by Bächmann et al. (Atmos. Environ. 26A (1992) 1795) was used to sample ice crystals during precipitation events. The size-classified ice crystal samples were analyzed using ion chromatography to determine the concentrations of Na⁺, NH₄⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃⁻, and SO₄²⁻ in each size class. For ions associated with coarse mode aerosol, Na⁺, K⁺, Ca²⁺, Mg²⁺, and Cl⁻, concentration increased with decreasing ice crystal size, suggesting scavenging by nucleation. For the remaining ions, mixed behavior was observed suggesting a combination of gas phase scavenging and scavenging via riming.