Influence of NO2 on S(IV) oxidation in aqueous suspensions of aerosol particles from two different origins

The influence of soluble compounds leached from real atmospheric aerosol particles (size range D_ae: 0.17–1.6 μm) and dissolved NO₂ on S(IV) oxidation in aqueous solution is presented. Experiments were conducted with aerosol particles of two different origins (i.e., urban and industrial) and at concentrations of trace gases in the gas mixtures (SO₂/air and SO₂/NO₂/air) typical for a polluted atmosphere. During the introduction of SO₂/air into the aqueous aerosol suspensions under dark conditions at pH 4, the formation of SO₄²⁻ was very slow with a long induction period. However, in the presence of NO₂ the oxidation rate of dissolved SO₂ in suspensions of aerosols from both origins increased substantially (about 10 times). The results suggest that soluble compounds eluted from atmospheric aerosols have not only a catalytic (e.g. Fe, Mn), but also a pronounced inhibiting effect (e.g., oxalate, formate, acetate, glycolate) on S(IV) autoxidation. When NO₂ was also introduced into the aerosol suspensions, the inhibition was not so highly expressed. An explanation for this is that the radical chain mechanism is mainly initiated by the interaction of dissolved NO₂ and HSO₃⁻. Therefore, at conditions typical for a polluted atmosphere dissolved NO₂ can have a significant influence on the secondary formation of SO₄²⁻.     

The Berlin smog project—Description and summary of results

The composition of ambient air pollution, emphasising the ambient particulate matter, has been investigated for 14 wintertime smog periods (SO₂ and/or suspended particulate concentrations exceeding 400 μg m⁻³) in Berlin (West). The total aerosol mass concentration, the SO₂, CO, NO and NO₂ and pertinent meteorological parameters were measured. For chemical characterization the aerosol was collected by hi-volume, low-volume samplers and cascade impactors. The samples were analysed for the metals Pb, Cd, Mn, Ni; the water soluble ions: NH₄⁺, SO₄²⁻, NO₃⁻; and the PAH's: Fl, Py, Per, BaP, BghiP and Cor. The aerosol size distribution (0,01 < d_p < 20 μm) was measured by a combination of electrical and optical analysers with a time resolution of 10 min.The smog periods lasted from 6 to 100 h and occured during anticyclonic conditions with restricted vertical mixing and low to moderate wind velocities. The smog producing pollutants originated either in the city of Berlin or in the industrial regions 100–200 km away.Ambient air quality standards were exceeded by SO₂ (highest 24-h concentration: 760 μg m⁻³), NO_x (320), TSP (930) and SO₄²⁻ (190). BaP levels of up to 92 μg m⁻³ were measured. The total sulfate level increases with the SO₂ concentration and exceeds 100 μg m⁻³ for SO₂ levels above 600 μg m⁻³. In 40% of all cases the aerosol sulfate seems to be more acidic than (NH₄)HSO₄. The secondary aerosol fraction, i.e. the sum of SO₄²⁻, NH₄⁺ and NO₂⁻ ranges from 23 up to 65% of TSP and is related to the age of the pollutants.The composition of the pollutants reflects the different emission patterns of the various source regions and chemical conversions during the trip from the sources to the measuring station. Therefore, the patterns of the composition of the pollutants provide a means to apportion the pollutants among contributing source regions. Thus, it seems possible to develop a scheme to determine during an ongoing smog condition the major contributing source region on the basis of real time measurements of selected physical and chemical parameters of ambient pollutants.     

The air pollution caused by the burning of fireworks during the lantern festival in Beijing

The effects of the burning of fireworks on air quality in Beijing was firstly assessed from the ambient concentrations of various air pollutants (SO₂, NO₂, PM_2.5, PM₁₀ and chemical components in the particles) during the lantern festival in 2006. Eighteen ions, 20 elements, and black carbon were measured in PM_2.5 and PM₁₀, and the levels of organic carbon could be well estimated from the concentrations of dicarboxylic acids. Primary components of Ba, K, Sr, Cl⁻, Pb, Mg and secondary components of C₅H₆O₄²⁻, C₃H₂O₄²⁻, C₂O₄²⁻, C₄H₄O₄²⁻, SO₄²⁻, NO₃⁻ were over five times higher in the lantern days than in the normal days. The firework particles were acidic and of inorganic matter mostly with less amounts of secondary components. Primary aerosols from the burning of fireworks were mainly in the fine mode, while secondary formation of acidic anions mainly took place on the coarse particles. Nitrate was mainly formed through homogeneous gas-phase reactions of NO₂, while sulfate was largely from heterogeneous catalytic transformations of SO₂. Fe could catalyze the formation of nitrate through the reaction of α-Fe₂O₃ with HNO₃, while in the formation of sulfate, Fe is not only the catalyst, but also the oxidant. A simple method using the concentration of potassium and a modified method using the ratio of Mg/Al have been developed to quantify the source contribution of fireworks. It was found that over 90% of the total mineral aerosol and 98% of Pb, 43% of total carbon, 28% of Zn, 8% of NO₃⁻, and 3% of SO₄²⁻ in PM_2.5 were from the emissions of fireworks on the lantern night.     

Trace gas and aerosol measurements at a remote site in the northeast U.S.

This paper presents the results of continuous measurements of trace atmospheric gases and aerosol composition made at the summit of Whiteface Mountain, New York, for 28 days in July 1982. The gas phase species NO, NO_x ( = NO + NO₂ + PAN), HNO₃, SO₂ and NH₃ were measured, as well as aerosol SO₄²⁻, NO₃⁻, H⁺ and NH₄⁺. Mean and median NO_x concentrations were 1.1 and 1.0 ppb, respectively, with maximum and minimum values of 3.2 and 0.3 ppb. HNO₃ concentrations were variable, occasionally exceeding the simultaneously measured NO_x levels. Mean and median SO₂ were 0.8 and 0.3 ppb, with concentrations up to 12 ppb in pollution episodes. Mean and median NH₃ were both 2.2 ppb. Monthly mean SO₄²⁻ was 5.3 μg m⁻³, with values in clean air of about 1.5 μg m⁻³, and in polluted air up to 80 μg m⁻³. Trajectory calculations indicate that episodes of high pollutant concentrations occur in air masses arriving at Whiteface from the southwest. These episodes contributed most of the SO₄²⁻, HNO₃ and aerosol acidity, and about half the SO₂ and NO_x to which the site was exposed during the measurement period. Limited comparisons of air chemistry data with the composition of cloudwater collected during the program are also presented.     

Background levels of air and precipitation quality for Europe

This paper is intended to be used by specialists engaged in air and precipitation quality management on regional and continental scales. Major goals are to establish definition, methodology and specific values of background air and precipitation quality for sulfur (S) and nitrogen (N) species to be used in practical applications of air resources management. Major findings are the following:

• 1.(a) 69% of SO₂ and 63 % of NO₂ concentration over Europe originate from continental scale anthropogenic sources,
• 2.(b) 15% of precipitation sulfate and 11% of precipitation nitrate over Europe are contributed by hemispheric background,
• 3.(c) hemispheric background pollution values for Europe were found as 1.25 μg (SO₂-S)m⁻³, 0.80 μg (SO₄²⁻-S)m⁻³, 0.157 mg (SO₄²⁻-S)l⁻¹ and 0.04 mg (NO₃⁻-N)ℓ⁻¹.

     

Investigation of the removal mechanism of Cr(VI) in groundwater using activated carbon and cast iron combined system

Zero-valent iron (Fe⁰) has been widely used for Cr(VI) removal; however, the removal mechanisms of Cr(VI) from aqueous solution under complex hydrogeochemical conditions were poorly understood. In this research, the mixed materials containing cast iron and activated carbon were packed in columns for the treatment of aqueous Cr(VI)-Cr(III) in groundwater with high concentration of Ca²⁺, Mg²⁺, HCO₃ ⁻, NO₃ ⁻, and SO₄ ²⁻. We investigate the influences of those ions on Cr(VI) removal, especially emphasizing on the reaction mechanisms and associated precipitations which may lead to porosity loss by using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) techniques. The results show that the precipitations accumulated on the material surface were (Fe/Cr) (oxy)hydroxide, mixed Fe(III)-Cr(III) (oxy)hydroxides, Fe₂O₃, CaCO₃, and MgCO₃. During these reactions, the Cr(VI) was reduced to Cr(III) coupled with the oxidated Fe⁰ to Fe(II) through the galvanic corrosion formed by the Fe⁰-C and/or the direct electron transfer between Fe⁰ and Cr(VI). In addition, Cr(VI) could be reduced by aqueous Fe(II), which dominated the whole removal efficiency. The primary aqueous Cr(III) was completely removed together with Cr(III) reduced from Cr(VI) even when Cr(VI) was detected in the effluent, which meant that the aqueous Cr(III) could occupy the adsorption sites. In general, the combined system was useful for the Cr(VI)-Cr(III) treatment based on galvanic corrosion, and the hardness ions had a negative effect on Cr(VI) removal by forming the carbonates which might promote the passivation of materials and decrease the removal capacity of the system.

     

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     

Deposition of sulphur,nitrogen and acidity in precipitation over Ireland: chemistry,spatial distribution and long-term trends

The chemical composition of pollutant species in precipitation sampled daily or weekly at 10 sites in Ireland for the five-year period, 1994–1998, is presented. Sea salts accounted for 81% of the total ionic concentration. Approximately 50% of the SO₄²⁻ in precipitation was from sea-salt sources. The proportion of sea salts in precipitation decreased sharply eastwards. In contrast, the concentration of NO₃⁻ and the proportion of non-sea-salt SO₄²⁻ increased eastwards reflecting the closer proximity to major emission sources. The mean (mol_c) ratio of SO₄²⁻:NO₃⁻ was 1.6 for all sites, indicating that SO₄²⁻ was the major acid anion.The spatial correlation between SO₄²⁻, NO₃⁻ and NH₄⁺ concentrations in precipitation was statistically significant. The regional trend in NO₃⁻ concentration was best described by linear regression against easting. SO₄²⁻ concentration followed a similar pattern. However, the regression was improved by inclusion of elevation. Inclusion of northing in the regression did not significantly improve any of the relationships except for NH₄⁺, indicating a significant increase in concentrations from northwest to southeast.The spatial distribution of deposition fluxes showed similar gradients increasing from west and southwest to east and northeast. However, the pattern of deposition shows the influence of precipitation volume in determining the overall input. Mean depositions of sulphur and nitrogen in precipitation were ≈30 ktonnes S yr⁻¹ and 48 ktonnes N yr⁻¹ over the five-year period, 1994–1998, for Ireland.Least-squares linear regression analysis indicated a slight decreasing trend in precipitation concentrations for SO₄²⁻ (20%), NO₃⁻ (13%) and H⁺ (24%) and a slight increasing trend for NH₄⁺ (15%), over the period 1991–1998.     

On the difference between SO2−4 and NO−3 in wintertime precipitation

Winter rains have lower NO⁻₃ levels but higher SO²⁻₄ levels than snows in the NE United States. In this study, four years of winter precipitation data from SE Michigan were examined to help understand these differences. Although NO⁻₃ levels were indeed higher in snow than winter rain, the higher concentrations could be attributed to the generally lower precipitation depths associated with snow events than with rain events. The NO⁻₃ concentrations are inversely correlated with precipitation depth. There was no evidence that snow scavenged HNO₃ in the air more efficiently than rain.Conversely, SO²⁻₄ was far higher in winter rain than in snow. This could not be explained in terms of ground-level ambient S concentrations or the wind direction from which the storm originated. However, the cloud temperatures were high enough in the case of rain to suggest that the cloud hydrometeors could have been present as liquid droplets rather than ice crystals. The SO²⁻₄ concentrations of the precipitation were highly correlated with the temperatures of the cloud layers. The data suggest that SO₂ is incorporated and oxidized to SO²⁻₄ in clouds most efficiently when the hydrometeors are present as liquid droplets. The fact that NO⁻₃does not show the same relationship suggests that incorporation of N species into cloud water followed by oxidation is not as important a process for N as for S.     

Indications of nonlinearities in processes of wet deposition

Numerical simulations have been carried out with a model consisting of clear-air chemistry, in- cloud chemical reactions, and dynamic processes of cloud development in order to examine the time history of cloudwater pH and sulfate production in a cumulus cloud and the relationship between pollutant precursors and corresponding acidic chemical species in wet deposition. Preliminary results indicate that the molar ratio SO₄²⁻/NC₃⁻ in cloud water increases as the ratio SO₂/NO₂ increases, that the relationship between the increase of precursor SO₂/NO₂ and the increase of SO₄²⁻/NO₃⁻ in cloud water is nonlinear, and that the degree of this nonlinearity becomes more significant for cases when the cloud condensation nuclei content in air is assumed to be invariant.     

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.     

Five years of air chemistry observations in the Canadian Arctic

Arctic air chemistry observations made in Canada between 1979 and 1984 are discussed. The weekly average concentration of 25 aerosol constituents has been measured routinely at three locations. Anthropogenic pollution typified by SO₄²⁻ and V has a persistent seasonal cycle. SO₄²⁻ concentrations are similar at all three locations, although they tend to be somewhat higher at Alert than at Mould Bay and Igloolik. The seasonal variation of an aerosol constituent depends on its source. There are four distinctive seasonal variations for:

• 1.(i) anthropogenic constituents Cr, Cu, Mn, Ni, Pb, Sr, V, Zn, H⁺, NH₄⁺, SO₄²⁻, NO₃⁻,
• 2.(ii) halogens (excepting Cl) Br, I, F,
• 3.(iii) sea salt elements Na, Mg, Cl and
• 4.(iv) soil constituents Al, Ba, Ca, Fe and Ti. In the Arctic winter, the mean concentrations of anthropogenic aerosol constituents, except SO₄²⁻, are 2–4 times lower than annual mean concentrations in southern Sweden near a major source region. SO₄²⁻ concentrations are only 30% lower mainly because of production from SO₂. Light scattering (b_scat) and SO₄²⁻ observations indicate that the SO₄²⁻ fraction of the fine particle mass fluctuates between 3 and 65% during the polluted winter months. Daily mean b_sact, at Mould Bay that exceeds 50 × 10⁻⁶m⁻¹ is associated with air originating from the northwest. The soluble major ion composition of aerosols during winter varies markedly with particle size. H⁺, NH₄⁺ and SO₄²⁻ dominate submicrometre particles while sea-salt ions Mg²⁺, Na⁺ and Cl⁻ predominate in supermicrometre particles. Winter SO₂ concentrations at Mould Bay and Igloolik ranged from 0.2 to 1.5 ppb
• 5.(v). The fraction of airborne S as SO₂ ranged from 20 to 90% and peaked in late December-early January. The concentration of total NO₃⁻ (0.025–0.090 ppb(v)) is much lower than that of SO₄²⁻ (0.3–1.2 ppb (v)).

     

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.     

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.     

Description and intercomparison of techniques to measure n and s compounds in the Western Atlantic Ocean experiment

The data set of N and S compound measurements from WATOX-85 has been examined in detail to assess that data quality and suitability for use in addressing the goals of the Western Atlantic Ocean Experiment. Accuracy estimates for particulate SO₄²⁻ and NO₃⁻, SO₂ and HNO₃ have been made on the basis of the investigators' estimates and the results of intercomparisons. Intercomparisons of ground-based particulate SO₄²⁻ and all filter SO₂ and HNO₃ measurements show them to be consistent with the 20% accuracies quoted by the investigators. Ground-based particulate NO₃⁻ and aircraft particulate SO₄²⁻ show inconsistencies such that the accuracies can be no better than 28% and the aircraft particulate NO₃ has an accuracy of no better than 60%.     

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.     

Chemical composition of nucleation and accumulation mode particles collected in Vienna,Austria

Atmospheric aerosol samples were collected by six-stage low pressure impactors in Vienna downtown. Aerosol particles were deposited on aluminum foils in five size fractions in the size range of 0.04–25 μm AD. The concentration of the components Cl⁻, Br⁻, NO₃⁻, SO₄²⁻, Ca, Cu, Fe, Mg, Pb. Sr, Zn and total C was determined by multi-element analytical methods. A comparison of the relative composition of the size fractions containing nucleation mode and accumulation mode particles showed the components derived from traffic emissions (Pb, Br⁻ and C) to be significantly enriched in the nucleation mode size fraction. On the other hand, each of the components Cl⁻, SO₄²⁻,Ca, Cu, Fe, Mg and Sr has a similar relative concentration in the nucleation mode and in the accumulation mode size fraction. For all samples collected on days with prevailing westerly winds a strong negative correlation between wind speed and sulfate particle size as well as sulfate concentration was observed.     

The air pollution episode of January 1985 as revealed by background data measured in Hungary

The air pollution level in January 1985 is discussed on the basis of the concentrations of NO₂ and SO₂ measured at three regional background stations in Hungary. For one background air pollution station some aerosol components (SO₄²⁻, NO₃⁻, NH₄⁺) are also included in the study. The data obtained are compared to average values for January. This comparison makes a severe country-wide pollution episode evident. The fossil fuel consumption and emission data as well as the meteorological parameters observed in this month are analyzed and backward trajectories are calculated to gain some information on the causes of this unusual situation.     

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.     

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.