The chemical composition of snow at a rural upland site in Mid-wales

The chemical composition of samples of freshly fallen snow and snow in standing accumulations several days old have been determined for an upland rural site in Mid-Wales. Fresh snow has a lower solute content than incident rainfall at an equivalent time of year, which may be related to the weather conditions, specifically wind direction, during periods of snowfall. The concentrations of solutes in standing snow drifts appear to increase with time and mechanisms by which this might occur are discussed.     

The use of chemical and statistical methods to identify sources of selected elements in ambient air aerosols in Karachi,Pakistan

Concentrations of 23 elements plus NO₃⁻, SO₄²⁻ and Cl⁻ were determined for samples collected continuously every 3 or 6 h during 22–27 July, 1985 at a suburban site in Karachi, Pakistan. Concentrations of lithophilic elements and several anthropogenic elements were ~ 80 % higher during daytime than at night. These elevated levels were attributed to daytime increases in wind velocity and anthropogenic activity. Factor analysis showed that ~ 50% of the variance was associated with soil, and ~ 14 % each with oceanic Na and Cl⁻, anthropogenic Sb and Pb, and Zn, Se and SO₄²⁻. A cement (limestone/dolomite) factor was not separated even though Ca and Mg concentrations were unusually high and a cement factory was located nearby. This led to an investigation of a chemical approach to determine the sources. Concentrations of Na, Mg and Ca were determined in water-extracts of the samples. Assuming soluble Na (~ 92 % of total) to be sea derived, marine components of Mg, SO₄²⁻, Ca and Br were determined. Solubility considerations were then used to reveal the cement source and apportion the aerosol sources. On the average, approximately 48 % of the total aerosol mass could be accounted for by the ‘cement’ and ‘soil’ components; about 12 % by the ‘sea salt’, about 3% by the ‘fossil fuel’ SO₄²⁻ (as (NH₄)₂SO₄); about 1 % by the NO₃⁻ (as NH₄NO₃); the remaining 36 % of the aerosol mass was unassigned.     

A simplified approach to the indirect evaluation of the chemical composition of atmospheric aerosols from PM mass concentrations

The present work shows a straightforward procedure to indirectly estimate the chemical composition at a given site only from the determination of the PM concentrations, and the classification of the days according to the main meteorological scenarios. A previous study based on the mean chemical composition associated to the main meteorological scenarios is required.This experiment has been carried out with data from two monitoring sites in the North-Western Mediterranean, one regional and one suburban background. At both sites, one-year datasets on chemical PM₁₀ composition were obtained. Based on these datasets, the mean PM₁₀ compositions according to the most relevant meteorological situations were calculated for both locations. After that, the reconstruction of the chemical composition for all the days with available PM₁₀ concentrations was completed. Subsequently, the estimated PM₁₀ composition was compared with that determined experimentally. The comparison between the rebuilt and the experimental results was very satisfactory in the case of the regional background site, and relatively replaced in the other case. Furthermore, the validation of the method at the regional background site has been conducted from the reconstruction of a 4-year data base, and subsequent comparison with the experimental chemical composition.Our results show that it is possible to attain a good approach to the chemical composition at regional background sites, where local emission sources are negligible. Conversely, when the local sources rise in importance, i.e., at a suburban background site, the approach is suitable only for those components with a more regional origin and/or those from long range transport of air masses.     

Observed chemical characteristics of long-range transported particles at a marine background site in Korea

Deokjeok Island is located off the west coast of the Korean Peninsula and is a suitable place to monitor the long-range transport of air pollutants from the Asian continent. In addition to pollutants, Asian dust particles are also transported to the island during long-range transport events. Episodic transport of dust and secondary particles was observed during intensive measurements in the spring (March 31-April 11) and fall (October 13-26) of 2009. In this study, the chemical characteristics of long-range-transported particles were investigated based on highly time-resolved ionic measurements with a particle-into-liquid system coupled with an online ion chromatograph (PILS-IC) that simultaneously measures concentrations of cations (Li+, Na , NH4+, K+, Ca2+, Mg2+) and anions (F-, C1-, NO3-, SO42-). The aerosol optical thickness (AOT) distribution retrieved by the modified Bremen Aerosol Retrieval (M-BAER) algorithm from moderate resolution imaging spectroradiometer (MODIS) satellite data confirmed the presence of a thick aerosol plume coming from the Asian continent towards the Korean peninsula. Seven distinctive events involving the long-range transport (LRT) of aerosols were identified and studied, the chemical components of which were strongly related to sector sources. Enrichment of acidic secondary aerosols on mineral dust particles, and even of sea-salt components, during transport was observed in this study. Backward trajectory, chemical analyses, and satellite aerosol retrievals identified two distinct events: a distinctively high [Ca2++Mg2]/[Na+] ratio (>2.0), which was indicative of a preprocessed mineral dust transport event, and a low [Ca2++Mg2+]/[Na+] ratio (<2.0), which was indicative of severe aging of sea-salt components on the processed dust particles. Particulate C1- was depleted by up to 85% in spring and 50% in the fall. A consistent fraction of carbonate replacement (FCR) averaged 0.53 in spring and 0.55 in the fall. Supporting evidences of C1- enrichment on the marine boundary layer prior to a dust front were also found. Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of the Air & Waste Management Association for sector and air mass classifications of clean and LRT cases.     

Concentration and composition of atmospheric aerosols from the 1995 SEAVS experiment and a review of the closure between chemical and gravimetric measurements

We summarize the results from the various measurements and the inter-sampler comparisons from Southeastern Aerosol and Visibility Study (SEAVS), a study with one of its objectives to test for closure among chemical, gravimetric and optical measurements of atmospheric aerosol particles. Sulfate and organics are the dominant components of the SEAVS fine particles (nominally, particles with aerodynamic diameter < or = 2.5 microns) but between 28 and 42% (range over various samplers) of the gravimetrically measured total fine particle concentration is unidentified by the chemical measurements. Estimates of water associated with inorganic components and measurement imprecision do not totally explain the observed difference between gravimetric and chemical measurements. We examine the theoretical and empirical basis for assumptions commonly made in the published literature to extrapolate total fine particle concentration on the basis of chemical measurements of ions, carbon and elements. We then explore the more general question of closure using the SEAVS data as well as data from other, similar studies reported in the literature. In so combining the SEAVS measurements with other similar studies, we find a strong association between organic carbon and the unidentified component, that is, the fraction of the total fine particle concentration not identified by chemical measurements. We offer several tenable hypotheses for the relationship between the organic and unidentified components that deserve to be tested in future work. Specifically, we hypothesize that (1) errors in the sampling and analysis of organic carbon; (2) estimates of organic mass from measurements of organic carbon; and/or (3) water absorption by organics may all contribute to the observed relationship.     

The contribution of middle- and long-range transport of tropospheric photochemical ozone to pollution at a rural site in North-West England

Ground-level ozone measurements from a rural site in North-West England are presented. Two distinct types of polluted air mass are identified: one type having passed over the North Sea and Northern England, and the other having travelled from the continent via the South-East and Midlands of England. The former air mass type contains long-range transported ozone originating primarily within continental Europe, whilst the latter type contains both long-range transported ozone and ozone formed from precursors injected during passage of the air mass over middle-distance source areas in England. The monitoring results are compared with the predictions of recent theoretical models of ozone formation in polluted air masses and urban plumes.     

杭州市大气降雨化学组成特征及来源分析

研究了2006-2008年杭州市大气降雨的化学组成及其来源,并与国内外的相关研究结果进行了比较.结果表明,总体来说,杭州市各月的降雨量相对均衡,月均降雨量为7.1～25.3 mm;降雨pH为3.99～5.64,雨量加权平均pH为4.50;降雨电导率为1.30～8.55 mS/m,雨量加权平均值为3.73 mS/m,降雨电导率与雨量、pH均呈负相关;夏季降雨中的水溶性离子平均浓度较低,雨量加权平均pH较高,而其他季节降雨中的水溶性离子平均浓度较高,雨量加权平均pH较低;其中SO2-4和NO-3是降雨中的主要水溶性阴离子,NH+4和Ca2+是降雨中的主要水溶性阳离子;SO2-4/NO-3(当量浓度比)为2.87,低于国内其他城市,降雨类型为硫酸型,但硝酸在降雨酸性中起的作用有增大趋势;降雨中水溶性阳离子总当量浓度/水溶性阴离子总当量浓度为1.11,低于国内外大部分城市;NH+4、Ca2+当量浓度之和与SO2-4、NO-3当量浓度之和之比为0.89,也低于国内外大部分城市,NH+4和Ca2+是主要的酸性中和物质;总体来说,杭州市降雨中各水溶性离子间的相关性均较好,但H+浓度与大部分离子的相关性不明显;杭州降雨中的化学组分主要来源于工业源和地壳源,此外部分来源于海盐粒子.     

Chemical composition of aerosols during a major biomass burning episode over northern Europe in spring 2006: Experimental and modelling assessments

The long-range transported smokes emitted by biomass burning had a strong impact on the PM_2.5 mass concentrations in Helsinki over the 12 days period in April and May 2006. To characterize aerosols during this period, the real-time measurements were done for PM_2.5, PM_2.5–10, common ions and black carbon. Moreover, the 24-h PM₁ filter samples were analysed for organic and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), ions and levoglucosan. The Finnish emergency and air quality modelling system SILAM was used for the forecast of the PM_2.5 concentration generated by biomass burning. According to the real-time PM_2.5 data, the investigated period was divided into four types of PM situations: episode 1 (EPI-1; 25–29 April), episode 2 (EPI-2; 1–5 May), episode 3 (EPI-3; 5–6 May) and a reference period (REF; 24 March–24 April). EPI-3 included a local warehouse fire and therefore it is discussed separately. The PM₁ mass concentrations of biomass burning tracers—levoglucosan, potassium and oxalate—increased during the two long-range transport episodes (EPI-1 and EPI-2). The most substantial difference between the episodes was exhibited by the sulphate concentration, which was 4.9 (±1.4) μg m⁻³ in EPI-2 but only 2.4 (±0.31) μg m⁻³ in EPI-1 being close to that of REF (1.8±0.54 μg m⁻³). The concentration of particulate organic matter in PM₁ was clearly higher during EPI-1 (11±3.3 μg m⁻³) and EPI-2 (9.7±4.0 μg m⁻³) than REF (1.3±0.45 μg m⁻³). The long-range transported smoke had only a minor impact on the WSOC-to-OC ratio. According to the model simulations, MODIS detected the fires that caused the first set of concentration peaks (EPI-1) and the local warehouse fire (EPI-3), but missed the second one (EPI-2) probably due to dense frontal clouds.     

Organic composition of PM2.5 and size-segregated aerosols and their sources during the 2002 Bay Regional Atmospheric Chemistry Experiment (BRACE), Florida,USA

PM_2.5 and size-segregated aerosols were collected in May 2002 as part of the Bay Regional Atmospheric Chemistry Experiment (BRACE), Florida, USA. Aerosol organic composition was used to estimate sources of a series of alkanes and polycyclic aromatic hydrocarbons (PAHs) using chemical indices, hierarchical cluster analysis (HCA) and a chemical mass balance receptor model (CMB). Aerosols were collected on quartz fiber filters (QFF) using a PM_2.5 high volume sampler and on aluminum foil discs using a Micro-Orifice Uniform Deposit Impactor (MOUDI, 50% aerodynamic cut diameters were 18, 10, 5.6, 3.2, 1.8, 1.0, 0.56, 0.315 and 0.171 μm). Target compounds included alkanes and PAHs and were solvent extracted using a mixture of dichloromethane, acetone and hexane, concentrated and then analyzed using a gas chromatograph/mass spectrometer (GC/MS). The target compounds in PM_2.5 were dominated by six sources during the study period: mobile sources (39±5%), coal burning (33±5%), biogenic primary emission (20±2%), oil combustion (5±2%), biomass burning (1.0±0.3%) and an unidentified source (3±2%). Results obtained from the chemical indices, HCA and CMB were in very good agreement with each other. PAH size distributions are presented for days dominated by a same source. Seventy-five percent and 50% of the PAH were found below 1.8 and 0.56 μm, respectively (monthly PAH geometric diameters averaged 0.43 μm). Coarse size PAHs were observed on 1 day (15 May) and were correlated with nitrate and sodium size distribution. It is hypothesized that the PAHs, sodium and nitrate were internally mixed and that the PAHs deposited onto a pre-existing marine aerosol. This transfer process has significant implications for PAH deposition and lifetime and warrants further study.     

PM10 concentration levels at an urban and background site in Cyprus: The impact of urban sources and dust storms

Air quality in Cyprus is influenced by both local and transported pollution, including desert dust storms. We examined PM₁₀ concentration data collected in Nicosia (urban representative) from April 1, 1993, through December 11, 2008, and in Ayia Marina (rural background representative) from January 1, 1999, through December 31, 2008. Measurements were conducted using a Tapered Element Oscillating Micro-balance (TEOM). PM₁₀ concentrations, meteorological records, and satellite data were used to identify dust storm days. We investigated long-term trends using a Generalized Additive Model (GAM) after controlling for day of week, month, temperature, wind speed, and relative humidity. In Nicosia, annual PM₁₀ concentrations ranged from 50.4 to 63.8 μg/m³ and exceeded the EU annual standard limit enacted in 2005 of 40 μg/m³ every year. A large, statistically significant impact of urban sources (defined as the difference between urban and background levels) was seen in Nicosia over the period 2000–2008, and was highest during traffic hours, weekdays, cold months, and low wind conditions. Our estimate of the mean (standard error) contribution of urban sources to the daily ambient PM₁₀ was 24.0 (0.4) μg/m³. The study of yearly trends showed that PM₁₀ levels in Nicosia decreased from 59.4 μg/m³ in 1993 to 49.0 μg/m³ in 2008, probably in part as a result of traffic emission control policies in Cyprus. In Ayia Marina, annual concentrations ranged from 27.3 to 35.6 μg/m³, and no obvious time trends were observed. The levels measured at the Cyprus background site are comparable to background concentrations reported in other Eastern Mediterranean countries. Average daily PM₁₀ concentrations during desert dust storms were around 100 μg/m³ since 2000 and much higher in earlier years. Despite the large impact of dust storms and their increasing frequency over time, dust storms were responsible for a small fraction of the exceedances of the daily PM₁₀ limit.

ImplicationsThis paper examines PM₁₀ concentrations in Nicosia, Cyprus, from 1993 to 2008. The decrease in PM₁₀ levels in Nicosia suggests that the implementation of traffic emission control policies in Cyprus has been effective. However, particle levels still exceeded the European Union annual standard, and dust storms were responsible for a small fraction of the daily PM₁₀ limit exceedances. Other natural particles that are not assessed in this study, such as resuspended soil and sea salt, may be responsible in part for the high particle levels.     

Sampling artefacts,concentration and chemical composition of fine water-soluble organic carbon and humic-like substances in a continental urban atmospheric environment

Water-soluble organic carbon (WSOC) and atmospheric humic-like substances (HULIS) were investigated for urban PM2.5-fraction aerosol samples, which were collected with the tandem filter method on quartz fibre filters over a non-heating spring season. Sampling artefacts were of importance for all organic chemical fractions, and the back-to-front-filter concentration ratios were on average 28% for WSOC and 17% for HULIS and organic carbon (OC). The difference in the ratios indicates that the water-soluble organics play a more important role in adsorptive artefacts than the organic matter (OM) in general. The results emphasize the need for an appropriate sampling and/or correction method for measuring particulate organic substances in urban environments. The corrected atmospheric concentration of HULIS, obtained by subtracting the back-filter from the front-filter data, was on average 2 μg m⁻³; which represented 6% of the mean PM2.5 particulate mass, and it made up 45% of the secondary OC. The HULIS carbon accounted for 20% of the OC and 62% of the WSOC, while WSOC made up 32% of OC. The major element composition of HULIS, expressed in molar ratios, was C:H:O:N=22:32:10:1. The molar H/C ratio of 1.49 implies the presence of unsaturated organic compounds, although these were depleted in comparison with rural aerosol or standard fulvic acids. The molar O/C ratio of 0.47 indicates the existence of oxygenated functional groups; comparison to rural aerosol suggests that the (fresh) urban-type aerosol is less oxidized (and, therefore, less water soluble as well) than the rural one. The OM/OC mass conversion factor for the isolated (water-soluble) HULIS was derived to be 1.81. It was inferred from comparisons with published data that there are substantial differences in abundance and chemical composition of HULIS for different environments.     

Carbonaceous and inorganic composition in long-range transported aerosols over northern Japan: Implication for aging of water-soluble organic fraction

To better understand the influence of sources and atmospheric processing on aerosol chemical composition, we collected atmospheric particles in Sapporo, northern Japan during spring and early summer 2005 under the air mass transport conditions from Siberia, China and surrounding seas. The aerosols were analyzed for inorganic ions, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and the major water-soluble organic compound classes (i.e., dicarboxylic acids and sugars). SO₄^2? is the most abundant inorganic constituent (average 44% of the identified inorganic ion mass) followed by NH₄⁺ (21%) and NO₃^? (13%). Concentrations of OC, EC, and WSOC ranged from 2.0–16, 0.24–2.9, and 0.80–7.9 μg m^?3 with a mean of 7.4, 1.0, and 3.1 μg m^?3, respectively. High OC/EC ratios (range: 3.6–19, mean: 8.7) were obtained, however WSOC/OC ratios (0.23–0.69, 0.44) do not show any significant diurnal changes. These results suggest that the Sapporo aerosols were already aged, but were not seriously affected by local photochemical processes. Identified water-soluble organic compounds (diacids + sugars) account for <10% of WSOC. Based on some marker species and air mass back trajectory analyses, and using stable carbon isotopic compositions of shorter-chain diacids (i.e., C₂–C₄) as photochemical aging factor of organic aerosols, the present study suggests that a fraction of WSOC in OC is most likely influenced by aerosol aging, although the OC loading in aerosols may be more influenced by their sources and source regions.     

Chemical characterization and source identification of polycyclic aromatic hydrocarbons in aerosols originating from different sources

To obtain the characteristic factors or signatures of particulate polycyclic aromatic hydrocarbons (PAHs) to help identify the sources of particulate PAHs in the atmosphere, different carbonaceous aerosols were generated by burning different fossil fuels and biomass under different conditions in the laboratory, and the chemical characteristics of 14 PAHs were studied in detail. The results showed that (1) carbonaceous aerosols derived from domestic burning of coal, diesel fuel, and gasoline have much higher concentrations of PAHs than those derived from domestic burning of biomass; (2) carbonaceous aerosols derived from domestic burning of diesel fuel/gasoline have similar PAH components as those derived from high-temperature combustion of diesel fuel/gasoline, although the former have much higher concentrations of PAHs than the latter, suggesting that the burning temperature obviously affects the emitting amount of particulate PAHs, but only slightly influences the PAHs components; and (3) the ratios of benzo[b]fluoranthene/acenaphthylene, benzo[b]fluoranthene/fluorene, dibenzo[a,h]anthracene/acenaphthylene, dibenzo[a,h]anthracene/fluorine, and benzo[b]fluoranthene/benzo[k]fluoranthene in carbonaceous aerosols are sensitively dependent on their sources, indicating that these ratios are suitable for use as characteristic factors or signatures of particulate PAHs in the atmosphere.     

The chemical and strontium isotope composition of atmospheric aerosols over Japan: the contribution of long-range-transported Asian dust (Kosa)

Atmospheric aerosols have been collected at four sites around Japan during 2000. From systematically monitoring the major (Na, Mg, Al, K, Ca, and Fe) and trace (Rb and Sr) elements, along with the Sr isotope composition, we have tried to estimate the contribution of long-range-transported Asian dust (“Kosa”) to the atmospheric aerosols.The results are summarized as follows:(1) The concentration of each element in the aerosols increased during the “Kosa” period. The increase was particularly obvious in samples collected on 8 April 2000, when the “Kosa Phenomenon” was observed at all the sampling sites in Japan, 2 days after a very heavy dust storm had occurred in China.(2) The Rb–Sr isotopic diagram shows a two-component mixing relationship: one with a high ⁸⁷Sr/⁸⁶Sr ratio and a high ⁸⁷Rb/⁸⁶Sr ratio, and the other with a low ⁸⁷Sr/⁸⁶Sr ratio and a low ⁸⁷Rb/⁸⁶Sr ratio. There is a significant difference between that of the expected end member of the Asian dust and that of the reported Asian loess, which is thought to be the possible source of the components of the “Kosa”, although the lower component is consistent with the local component at Wako.(3) Plots of the ⁸⁷Sr/⁸⁶Sr ratio vs the Ca/Al and Sr/Al ratios support a two-component mixing suggested by the Rb–Sr systematics, and they indicate that the contributing continental soil components to the “Kosa” aerosols should be composed of the silicate fraction of Asian loess.(4) The discrepancy in the Rb–Sr systematics between the expected end member and the possible sources may be caused by the dissolution of the Ca-bearing minerals via long-range dust transport, or by a combination of source characteristics and grain size separation.     

The quartz content and elemental composition of aerosols from selected sites of the EPA inhalable particulate network

The elemental composition and concentration of quartz in ambient aerosols collected on dichotomous filters from the EPA Inhalable Particulate Network (IPN) in 1980 have been determined by X-ray fluorescence and mass calibration methods of X-ray diffraction (XRD). Quartz concentrations were also determined by reference intensity ratio methods of XRD from high-volume (hi-vol) filters from ten U.S. cities and were compared with data obtained from the dichotomous samples. Twenty five individual sites are represented in the quartz analysis phase of the study.These analyses demonstrate that for all IPN sites, an average of only 4.9 (±2.3) weight per cent of the coarse particle mass as measured by the dichotomous samplers consists of quartz and 0.4 (±0.7) weight per cent as quartz in the fine fraction. Continental interior sites show the highest average quartz content as well as the greatest variability. Except for highly industrialized sites, the Coastal regions and Eastern interior sites reveal the lowest quartz concentrations. The quartz levels observed at Research Triangle Park, NC, Seattle, WA, and Portland, OR, are the lowest of the dichotomous data set, whereas those at Boston, MA, and Five Points, CA, represent the highest levels.The Si concentrations obtained from the quartz analyses were compared with Si measured directly by X-ray fluorescence on the same filters. The complete aerosol X-ray spectra from some samples such as Portland, OR, shows that the Si comes primarily from minerals such as feldspars, whereas the Si in the Buffalo, NY, aerosol comes primarily from quartz. The concentration of quartz combined with elemental composition and other crustal or anthropogenic constituents observed on the filters provides a means for developing unique geographical airshed signatures for use in detailed source apportionment studies.