Seasonal variations of acidic air pollutants in Seoul,South Korea

The annular denuder system (ADS) was used to characterize seasonal variations of acidic air pollutants in Seoul, South Korea. Fifty- four 24 h samples were collected over four seasons from October 1996 to September 1997. The annual mean concentrations of HNO₃, HNO₂, SO₂ and NH₃ in the gas phase were 1.09, 4.51, 17.3 and 4.34 μg m^-3, respectively. The annual mean concentrations of PM_2.5(d_p≤2.5 μm in aerodynamic diameter, 50% cutoff), SO^2-₄, NO^-₃ and NH⁺₄ in the particulate phase were 56.9, 8.70, 5.97 and 4.19 μg m^-3, respectively. All chemical species monitored from this study showed statistical seasonal variations. Nitric acid (HNO₃) and ammonia (NH₃) exhibited substantially higher concentrations during the summer, while nitrous acid (HNO₂) and sulfur dioxide(SO₂) were higher during the winter. Concentrations of PM_2.5, SO^2-₄, NO^-₃ and NH⁺₄ in the particulate phase were higher during the winter months. SO^2-₄, NO^-₃ and NH⁺₄ accounted for 26–38% of PM_2.5. High correlations were found among PM_2.5, SO^2-₄, NO^-₃ and NH⁺₄. The mean H⁺ concentration measured only in the fall was 5.19 nmole m^-3.     

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.     

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.     

Cereal waste burning pollution observed in the town of Vitoria (northern Spain)

Agricultural waste burning is a widespread practice throughout the world but there is little information about its pollutant impact. This paper deals with a preliminary study of the pollution observed in Vitoria (Northern Spain) caused by cereal waste burning. The mean hourly flux of pollutants produced by cereal waste burning fires can reach values of 1.4 kt of CO₂, 13 t of TPM and 3 t of NO_x in the area around Vitoria. Measurements obtained in the area of emission and inside fire plumes show high ratios (NO₂/NO_x) indicating that nitrogen oxides emitted by the source undergo a rapid transformation in the same area of emission. Results relating to aerosol composition collected in Vitoria during burning periods show an increase in the concentration of K⁺, NO₃⁻ and Cl⁻ ions, that are inter-correlated. The modification of the ionic composition of aerosols also affects the chemistry of the rain collected in Vitoria. During the burning period, it is particularly noticeable that anthropogenic pollution (usually identifiable by the correlation between SO₄²⁻ and NO₃⁻ concentrations) disappears, indicating the existence of an independent source of NO₃⁻ not linked to the SO₄²⁻ source. Similar results were deduced studying BAPMON data collected in Spain during cereal waste burning. Finally, we note that ozone concentration measured at Vitoria is not affected by the pollution generated by the burning fires.     

Laboratory studies of the impact of aerosol composition on the heterogeneous oxidation of 1-propanol

The effects of (NH₄)₂SO₄, NH₄NO₃, NaCl, NH₄Cl, and Na₂SO₄ aerosols on the kinetics of 1-propanol oxidation in the presence of the hydroxyl radical have been investigated using the relative rate technique. p-Xylene was used as a reference compound. Two different aerosol concentrations that are typical of polluted urban conditions were tested. The total surface areas of aerosols were 1400 (condition I) and 3400 μm² cm⁻³ (condition II). Results indicate that aerosols promote the oxidation of 1-propanol, and the extents of the promoting effects depend on the aerosol composition and concentration. Increases in the relative rates of the 1-propanol/OH reaction vs. the p-xylene/OH reaction were only observed for (NH₄)₂SO₄ aerosol conditions I and II, NH₄NO₃ aerosol condition II, and NH₄Cl aerosol condition II. These results indicate that NH₄⁺ is the species promoting the oxidation of 1-propanol, and suggests the possibility of a strong interaction between NH₄⁺ and 1-propanol that can change the activation energy of the initial OH attack. These results have profound implications on the use of air quality models for the assessment of air pollution control strategies.     

Evaluation of the UNC toluene-SOA mechanism with respect to other chamber studies and key model parameters

In a companion paper by Hu et al. [2007. A kinetic mechanism for predicting secondary organic aerosol formation from toluene oxidation in the presence of NO_x and natural sunlight. Atmospheric Environment, doi:10.1016/j.atmosenv.2007.04.025], a kinetic mechanism was developed from data generated in the University of North Carolina's (UNC) 270 m³ dual outdoor aerosol smog chamber, to predict secondary organic aerosol (SOA) formation from toluene oxidation in the atmosphere. In this paper, experimental data sets from European Photoreactor (EUPHORE), smog chambers at the California Institute of Technology (Caltech), and the UNC 300 m³ dual-outdoor gas phase chamber were used to evaluate the toluene mechanism. The model simulates SOA formation for the ‘low-NO_x’ and ‘mid-NO_x’ experiments from EUPHORE chambers reasonably well, but over-predicts SOA mass concentrations for the ‘high-NO_x’ run. The model well simulates the SOA mass concentrations observed from the Caltech chambers. Experiments with the three key toluene products, 1,4-butenedial, 4-oxo-2-pentenal and o-cresol in the presence of oxides of nitrogen (NO_x) are also simulated by the developed mechanism. The model well predicts the NO_x time–concentration profiles and the decay of these two carbonyls, but underestimates ozone (O₃) formation for 4-oxo-2-pentenal. It well simulates SOA formation from 1,4-butenedial but overestimates (possibly due to experimental problems) the measured aerosol mass concentrations from 4-oxo-2-pentenal. The model underestimates SOA production from o-cresol, mostly due to its under-prediction of o-cresol decay. The effects of varying temperature, relative humidity, glyoxal uptake, organic nitrate yields, and background seed aerosol concentrations, were also investigated.     

Study of size distribution of atmospheric aerosol at Agra

Measurements on size distribution of atmospheric aerosol were made at Dayalbagh, Agra during July to September 1998. A 4-stage cascade particle sampler (CPS - 105) which fractionates particles in sizes ranging between 0.7 and >10.9 μm, was used. Samples were collected on Whatman 41 filters. The filters were analyzed for the major water-soluble ions. The anions (F, Cl, NO₃ and SO₄) were analyzed by Dionex DX-500 ion chromatograph while atomic absorption and colorimetric techniques were used for the analysis of cations (Na, K, Ca and Mg) and NH₄, respectively. The average mass of aerosol was found to be 131.6 μg m⁻³ and aerosol composition was found to be influenced by terrigeneous sources. The mass size distribution of total aerosol and the ions NH₄, Cl, NO₃, K, Ca, Mg, SO₄ and Na was bimodal while that of F was unimodal. SO₄, F, K and NH₄ dominated in the fine mode while Ca, Mg, Cl and NO₃ were in abundance in coarse fraction. Na was found in both coarse as well as fine mode. Coarse mode SO₄ and NO₃ have been ascribed to contribution from re-suspension of soil and formation by heterogeneous oxidation on soil derived particles. Preponderance of K in fine mode is attributed to emissions from vegetation and from burning of plant materials. Ca, Mg, Cl and NO₃ are largely soil derived and hence dominate in coarse fraction. Equivalent ratios of NH₄/(SO₄+NO₃) were calculated for both fine and coarse aerosols. The coarse mode ratio varied between 0.7 and 1.4 while in fine mode it ranged between 1.4 and 1.9. It shows that aerosol is basic, the basicity of coarse mode is due to higher concentration of soil-derived alkaline components while the basicity in fine mode is due to neutralization of acidity by NH₃.     

The continuous field measurements of soluble aerosol compositions at the Taipei Aerosol Supersite,Taiwan

The characteristics of ambient aerosols, affected by solar radiation, relative humidity, wind speed, wind direction, and gas–aerosol interaction, changed rapidly at different spatial and temporal scales. In Taipei Basin, dense traffic emissions and sufficient solar radiation for typical summer days favored the formation of secondary aerosols. In winter, the air quality in Taipei Basin was usually affected by the Asian continental outflows due to the long-range transport of pollutants carried by the winter monsoon. The conventional filter-based method needs a long time for collecting aerosols and analyzing compositions, which cannot provide high time-resolution data to investigate aerosol sources, atmospheric transformation processes, and health effects. In this work, the in situ ion chromatograph (IC) system was developed to provide 15-min time-resolution data of nine soluble inorganic species (Cl⁻, NO₂⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺). Over 89% of all particles larger than approximately 0.056 μm were collected by the in situ IC system. The in situ IC system is estimated to have a limit of detection lower than 0.3 μg m⁻³ for the various ambient ionic components. Depending on the hourly measurements, the pollutant events with high aerosol concentrations in Taipei Basin were associated with the local traffic emission in rush hour, the accumulation of pollutants in the stagnant atmosphere, the emission of industrial pollutants from the nearby factories, the photochemical secondary aerosol formation, and the long-range transport of pollutants from Asian outflows.     

FT-IR product study of the OH-initiated oxidation of DMS in the presence of NOx

The influence of NO_x (NO+NO₂) concentrations on the product distribution of the OH-initiated oxidation of DMS has been studied at room temperature using total NO_x concentrations varying from 0 to ∼1800 ppbv (30–600 ppbv NO₂ and 140–1760 ppbv NO). Clear trends in the formation yields of the products SO₂, COS, MSA, MTF (methyl thiolformate), MSPN (methanesulphonyl peroxynitrate), DMSO and DMSO₂ have been observed with variation in NO_x. The presence of low levels of NO reduces the yields of both MTF and COS to zero. The formation yields of MSA and DMSO₂ increase with increasing NO_x concentration, whereas the yields of DMSO and SO₂ decrease. The following approximate changes in the yield, not corrected for possible loss processes, have been measured for variation of NO_x between 0 and ∼1800 ppbv: DMSO decreases from 20 to 3%S; DMSO₂ increases from 3 to 15%S, SO₂ decreases from 70 to 30%S and MSA increases from 4 to 17%S. Under the experiments conditions NO_x levels of several tens of ppbv are required before a perceptible change is observed in the MSA yield. If applicable to the atmosphere such a situation is only likely to be observed near coastal areas affected by pollution. MSPN (CH₃SO₂O₂NO₂) is observed as an oxidation product in the presence of NO₂ even at low levels (e.g. 60 ppbv). Its possible role as a NO_x reservoir in the troposphere is considered.     

The effects of increasing atmospheric ozone on biogenic monoterpene profiles and the formation of secondary aerosols

Monoterpenes are biogenic volatile organic compounds (BVOCs) which play an important role in plant adaptation to stresses, atmospheric chemistry, plant–plant and plant–insect interactions. In this study, we determined whether ozonolysis can influence the monoterpenes in the headspace of cabbage. The monoterpenes were mixed with an air-flow enriched with 100, 200 or 400 ppbv of ozone (O₃) in a Teflon chamber. The changes in the monoterpene and O₃ concentrations, and the formation of secondary organic aerosols (SOA) were determined during ozonolysis. Furthermore, the monoterpene reactions with O₃ and OH were modelled using reaction kinetics equations. The results showed that all of the monoterpenes were unequally affected: α-thujene, sabinene and d-limonene were affected to the greatest extend, whereas the 1,8-cineole concentration did not change. In addition, plant monoterpene emissions reduced the O₃ concentration by 12–24%. The SOA formation was dependent on O₃ concentration. At 100 ppbv of O₃, virtually no new particles were formed but clear SOA formation was observed at the higher ozone concentrations. The modelled results showed rather good agreements for α-pinene and 1,8-cineole, whereas the measured concentrations were clearly lower compared to modelled values for sabinene and limonene. In summary, O₃-quenching by monoterpenes occurs beyond the boundary layer of leaves and results in a decreased O₃ concentration, altered monoterpene profiles and SOA formation.     

Influence of the surface microlayer on atmospheric deposition of aerosols and polycyclic aromatic hydrocarbons

Atmospheric dry deposition is an important process for the introduction of aerosols and pollutants to aquatic environments. The objective of this paper is to assess, for the first time, the influence that the aquatic surface microlayer plays as a modifying factor of the magnitude of dry aerosol deposition fluxes. The occurrence of a low surface tension (ST) or a hydrophobic surface microlayer has been generated by spiking milli-Q water or pre-filtered seawater with a surfactant or octanol, respectively. The results show that fine mode (<2.7 μm) aerosol phase PAHs deposit with fluxes 2–3 fold higher when there is a low ST aquatic surface due to enhanced sequestration of colliding particles at the surface. Conversely, for PAHs bound to coarse mode aerosols (>2.7 μm), even though there is an enhanced deposition due to the surface microlayer for some sampling periods, the effect is not observed consistently. This is due to the importance of gravitational settling for large aerosols, rendering a lower influence of the aquatic surface on dry deposition fluxes. ST (mN m⁻¹) is identified as one of the key factor driving the magnitude of PAH dry deposition fluxes (ng m⁻² d⁻¹) by its influence on PAH concentrations in deposited aerosols and deposition velocities (v_d, cm s⁻¹). Indeed, v_d values are a function of ST as obtained by least square fitting and given by Ln(v_d)=−1.77 Ln(ST)+5.74 (r²=0.95) under low wind speed (average 4 m s⁻¹) conditions.     

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.     

Observational study of ozone pollution at a rural site in the Yangtze Delta of China

Ozone and related trace gases (CO, NO_x, and SO₂) were measured from June 1999 to July 2000 at a rural site in the Yangtze Delta of China, a region of intensive anthropogenic activity. Elevated ozone levels were frequently observed during the study period, with the highest frequency in late spring and early summer. Over a 1 yr period, 21 d were found to have ozone concentrations exceeding the new US 8-h 80 ppb health standard. Calculation of the “SUM06” exposure index also shows relatively high (>15 ppm h) values for each season except winter. At these levels ozone may have adverse effects on human health as well as agricultural crops. Analysis of meteorological data shows that the high ozone days were associated with large-scale stagnation, intense solar radiation, and minimum rainfall. Large-scale back trajectories indicate a slow-moving/re-circulating airmass during the episodic days. Examination of chemical data shows that the observed daytime high ozone concentrations were due to downward mixing of ozone-rich air, in situ photochemical formation, and in some cases, advection to the site of aged plumes. The very high CO levels (and high CO to NO_x ratios) were found to coincide with many of the ozone episodes, suggesting a contribution from sources of emission involving incomplete combustion. It is suggested that the burning of biomass (e.g., biofeuls and crop residues) may be an important source for the observed high CO and O₃ values.     

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⁻.     

Secondary organic aerosol formation from cyclohexene ozonolysis in the presence of water vapor and dissolved salts

A series of 90 experiments were conducted in the UC Riverside/CE-CERT environmental chamber to evaluate the impact of water vapor and dissolved salts on secondary organic aerosol formation for cyclohexene ozonolysis. Water vapor (low – 30 ± 2% RH, medium – 46 ± 2% RH, high – 63 ± 2% RH) was found to directly participate in the atmospheric chemistry altering the composition of the condensing species, thus increasing total organic aerosol formation by ～22% as compared to the system under dry (<0.1% RH) conditions. Hygroscopicity measurements also indicate that the organic aerosol composition is altered in the presence of gaseous water. These results are consistent with water vapor reacting with the crigee intermediate in the gas phase resulting in increased aldehyde formation. The addition of dissolved salts ((NH₄)₂SO₄, NH₄HSO₄, CaCl₂, NaCl) had minimal effect; only the (NH₄)₂SO₄ and NaCl were found to significantly impact the system with ～10% increase in total organic aerosol formation. These results indicate that the organics may be partitioning to an outer organic shell as opposed to into the aqueous salt. Hygroscopicity measurements indicate that the addition of salts does not alter the aerosol composition for the dry or water vapor system.     

Size-resolved sulfate and ammonium measurements in marine boundary layer over the North and South Pacific

Marine background levels of non-sea-salt- (nss-) SO₄²⁻ (5.0–9.7 neq m⁻³), NH₄⁺ (2.1–4.4 neq m⁻³) and elemental carbon (EC) (40–80 ngC m⁻³) in aerosol samples were measured over the equatorial and South Pacific during a cruise by the R/V Hakuho-maru from November 2001 to March 2002. High concentrations of nss-SO₄²⁻ (47–94 neq m⁻³), NH₄⁺ (35–94 neq m⁻³) and EC (130–460 ngC m⁻³) were found in the western North Pacific near the coast of the Asian continent under the influence of the Asian winter monsoon. Particle size distributions of ionic components showed that the equivalent concentrations of nss-SO₄²⁻ were balanced with those of NH₄⁺ in the size range of 0.06<D<0.22 μm, whereas the concentration ratios of NH₄⁺ to nss-SO₄²⁻ in the size range of D>0.22 μm were decreased with increase in particle size. We estimated the source contributions of those aerosol components in the marine background air over the equatorial and South Pacific. Biomass burning accounted for the large fraction (80–98% in weight) of EC and the minor fraction (2–4% in weight) of nss-SO₄²⁻. Marine biogenic source accounted for several tens percents of NH₄⁺ and nss-SO₄²⁻. In the accumulation mode, 70% of particle number existed in the size range of 0.1<D<0.2 μm. In the size rage of 0.06<D<0.22 μm, the dominant aerosol component of (NH₄)₂SO₄ would be mainly derived from the marine biogenic sources.     

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 particles and size-segregated ionic species measured during fall season in three urban sites in Korea

Twelve hours integrated fine particles (PM_2.5) and 24-h average size-segregated particles were collected to investigate the chemical characteristics and to determine the size distribution of ionic species during October–December 1999 in three cities of different urban scale; Chongju, Kwangju, and Seoul, Korea. Concentrations of 5-min PM_2.5 black carbon (BC) and hourly criteria air pollutants (PM₁₀, CO, NO_x, SO₂, and O₃) were also measured using the Aethalometer and ambient air monitoring system, respectively.Highest PM_2.5 mass concentrations at Chongju, Kwangju, and Seoul sites were 63.0, 77.9, and 143.7 μg m⁻³, respectively. For the time period when highest PM_2.5 mass occurred, BC level out of PM_2.5 chemical species was highest at both Chongju and Kwangju, and highest NO₃⁻ (23.6 μg m⁻³) followed by BC (23.1 μg m⁻³) were observed at Seoul site, indicating that highest PM_2.5 pollution is closely associated with the traffic emissions. Strong relationships of Fe with BC and Zn at both Kwangju and Seoul sites support that the Fe and Zn measured there are originated partly from same source as BC, i.e. diesel traffics. However, it is suggested that the Fe measured at Chongju is most likely derived from dispersion of soil dust.The size distributions of SO₄²⁻, NO₃⁻, and NH₄⁺ ionic species indicated similar unimodal distributions at all sampling sites. However, different unimodal patterns in the accumulation mode size range with a peak in the smaller size (0.28–0.53 μm, condensation mode) in both Kwangju and Seoul, and in the relatively larger size (0.53–1.0 μm, droplet mode) in Chongju, were found. The potassium ion under the study sites dominates in the fine mode, and its size distribution showed unimodal character with a maximum in the size range 0.56–1.0 μm.     

Dry deposition of ammonia,nitric acid,ammonium, and nitrate to alpine tundra at Niwot Ridge,Colorado

Micrometeorological measurements and ambient air samples, analyzed for concentrations of NH₃, HNO₃, NH₄⁺, and NO₃⁻, were collected at an alpine tundra site on Niwot Ridge, Colorado. The measured concentrations were extremely low and ranged between 5 and 70 ng N m⁻³. Dry deposition fluxes of these atmospheric species were calculated using the micrometeorological gradient method. The calculated mean flux for NH₃ indicates a net deposition to the surface and indicates that NH₃ contributed significantly to the total N deposition to the tundra during the August–September measurement period. Our pre-measurement estimate of the compensation point for NH₃ in air above the tundra was 100–200 ng N m⁻³; thus, a net emission of NH₃ was expected given the low ambient concentrations of NH₃ observed. Based on our results, however, the NH₃ compensation point at this alpine tundra site appears to have been at or below about 20 ng N m⁻³. Large deposition velocities (>2 cm s⁻¹) were determined for nitrate and ammonium and may result from reactions with surface-derived aerosols.     

Regional-scale impacts of Phase I of the Clean Air Act Amendments in the USA: the relation between emissions and concentrations,both wet and dry

A comparison of data records in the 1990s, both before (1991–1994) and after (1995–1997) implementation of Phase I of the Clean Air Act Amendments (CAAA) of 1990 for the eastern US, shows a significant reduction in SO₂ emissions for most states, except for Texas, North Carolina, Illinois, Florida, and Alabama. However, of the major NO_x emitting states, only two eastern states (New York and Pennsylvania) show significant declines in NO_x. A pattern of large declines in SO₂ emissions (>20%) after CAAA implementation, and large declines in precipitation SO₄²⁻ and H⁺, as well as air concentrations of SO₂ and SO₄²⁻ (components of dry deposition), exists for most regions of the eastern US. In most cases, the emission/concentration relations are close to 1 : 1 when the source region based on 15-h back trajectories is used for the New England region, and source regions based on 9-h back trajectories are used for the six other eastern US regions that were studied. The southern Appalachian Mountain region, an acid-sensitive area receiving high levels of acidic deposition, has not seen an appreciable improvement in precipitation acidity. This area has also shown the least improvement in wet and dry sulfur concentrations, of the areas examined. Precipitation base cations (Ca²⁺ and Mg²⁺) show a pattern of either increasing or level concentrations when comparing 1990–1994 to 1995–1998 data, for six of the seven regions examined. Ammonium concentrations have generally changed <10%, except for the Illinois and southern Appalachian Mtn. regions, which increased >15%.