Transported acid aerosols measured in southern Ontario

During the period 29 June 1986–9 August 1986, a field health study assessing the acute health effects of air pollutants on children was conducted at a summer girls' camp on the northern shore of Lake Erie in SW Ontario. Continuous air pollution measurements of SO₂, O₃, NO_x, particulate sulfates, light scattering, and meteorological measurements including temperature, dew point, and wind speed and direction were made. Twelve-hour integrated samples of size fractioned particles were also obtained using dichotomous samplers and Harvard impactors equipped with an ammonia denuder for subsequent hydrogen ion determination. Particulate samples were analyzed for trace elements by X-ray fluorescence and Neutron Activation, and for organic and elemental carbon by a thermal/optical technique. The measured aerosol was periodically very acidic with observed 12-h averaged H⁺ concentrations in the range < 10–560 nmoles m⁻³. The aerosol H⁺ appeared to represent the net strong acidity after H₂SO₄ reaction with NH₃(g). Average daytime concentrations were higher than night-time for aerosol H⁺, sulfate, fine mass and ozone. Prolonged episodes of atmospheric acidity, sulfate, and ozone were associated with air masses arriving at the measurement site from the west and from the southwest over Lake Erie. Sulfate concentrations measured at the lakeshore camp were more than twice those measured at inland sites during extreme pollution episodes. The concentration gradient observed with onshore flow was potentially due to enhanced deposition near the lakeshore caused by discontinuities in the meteorological fields in this region.     

Intensive studies of Sierra Nevada cloudwater chemistry and its relationship to precursor aerosol and gas concentrations

Measurements of inorganic aerosol and gas phase species are presented for three sites in central California during a 4 day period in April 1988. The measurement sites were located along an east-west transect at Visalia, Ash Mountain, and Lower Kaweah, with elevations of 90, 550 and 1900 m, respectively. Aerosol compositions were nearly neutral at all locations, however large concentrations of NH₃ at Visalia contributed significant excess alkalinity to the air mass sampled there. Concentrations of all major species were observed to decrease with elevation during most of the sampling periods. Concentrations at the upper two sites exhibited diurnal fluctuations, with peaks in the late afternoon, consistent with the transport of pollutants from San Joaquin Valley sources by daytime upslope winds. Concentrations of most of these species reached a maximum at the elevated sites on 28 April, as a weak cold front approached, reducing the atmospheric stability over the valley floor. Concentrations at Visalia on this day were somewhat lower than those observed earlier in the week.Clouds intercepting the mountain slopes on 28 April were sampled at two locations. The coudwater pH at both sites was observed to fall throughout the event, dropping as low as 4.34. Precursor concentrations of aerosol NO₃⁻, SO₄^2- and NH₄⁺, and gas phase HNO₃ and NH₃, were sufficient to account for the observed cloudwater loadings of NO₃⁻, SO₄^2- and NH₄⁺. In-cloud measurements made near the cloud base indicated a considerable S(IV) oxidation potential in the form of H₂O₂, but only low S(IV) concentrations. Cloudwater concentrations of formic acid were approximately three times acetic acid concentrations. Carbonyl concentrations were dominated by formaldehyde and glyoxal.     

Comparison of H2O2 and O3 content in atmospheric samples in the San Bernardino mountains,Southern California

Concentrations of atmospheric H₂O₂ were measured in air, rain, cloud and dew samples in forested areas of the San Bernardino Mountains, southern California, from spring through fall of 1987–1990 O₃ measurements in air were also conducted for comparison. Typical ranges of H₂O₂ concentrations measured were 1–3 ppb in air, 10–90 μM in rain and cloud water, and < μM in dew. The results show that gas-phase H₂O₂ concentrations were slightly higher at nighttime than at daytime or nearly constant throughout a 24-hr period, whereas O₃ concentrations were highest during the afternoon, when polluted air masses from Los Angeles carried by daily sea breezes reached the mountain region. Afternoon concentrations of gaseous H₂O₂ and O₃ in the mountain region were compared with those measured in Los Angeles urban sites to elucidate the regional variation of these oxidants. The results show that ambient concentrations of H₂O₂ and O₃ were about 50–100% higher at the mountains sites than at the Los Angeles sites.     

Spatial and temporal patterns in summertime sulfate aerosol acidity and neutralization within a metropolitan area

A study of sulfate aerosol acidity in Metropolitan Toronto was conducted during the summer of 1986. Fine-fraction aerosol (<2.5-μm) were collected using Teflon membrane filters and analyzed for major ionic species (H⁺, NH⁺₄, NO⁻₃, SO²⁻₄). Samples were collected for 6 weeks at three study sites: one in the Center City and the others 13 km (WNW) and 20 km (NE) away. There were very strong correlations among the three sites with respect to measured aerosol species (r² > 0.9 for 24-h data). However, spatial variations in the magnitude of aerosol acidity were observed during sulfate episodes. For example, the peak concentrations for all sites occurred on 25–26 July 1986. While the 24-h data for sulfate were quite uniform at the three sites (34, 34 and 35 μg m⁻³), H⁺ concentrations were 9.4, 8.3 and 6.0 μg m⁻³ (as H₂SO₄) for the NE, WNW and Center City sites, respectively. For most of the summertime episodes, the downtown area also had lower aerosol acidity compared to the two sites in suburban areas.     

Trace metals in atmospheric fine particles in one industrial urban city: Spatial variations, sources, and health implications

Trace metals in PM2.5were measured at one industrial site and one urban site during September, 2010 in Ji'nan, eastern China. Individual aerosol particles and PM2.5samples were collected concurrently at both sites. Mass concentrations of eleven trace metals(i.e., Al, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Sr, Ba, and Pb) and one metalloid(i.e., As) were measured by inductively coupled plasma atomic emission spectroscopy(ICP-AES). The result shows that mass concentrations of PM2.5(130 μg/m3) and trace metals(4.03 μg/m3) at the industrial site were 1.3 times and 1.7 times higher than those at the urban site, respectively, indicating that industrial activities nearby the city can emit trace metals into the surrounding atmosphere. Fe concentrations were the highest among all the measured trace metals at both sites, with concentrations of 1.04 μg/m3at the urban site and 2.41 μg/m3at the industrial site, respectively. In addition, Pb showed the highest enrichment factors at both sites, suggesting the emissions from anthropogenic activities existed around the city. Correlation coefcient analysis and principal component analysis revealed that Cu, Fe, Mn, Pb, and Zn were originated from vehicular trafc and industrial emissions at both sites; As, Cr, and part of Pb from coal-fired power plant; Ba and Ti from natural soil. Based on the transmission electron microscopy analysis, we found that most of the trace metals were internally mixed with secondary sulfate/organic particles. These internally mixed trace metals in the urban air may have diferent toxic abilities compared with externally mixed trace metals.     

大气PM2.5中水溶性离子在线观测技术的应用研究

为了解北京大气PM2.5污染状况,评估大气细颗粒物快速捕集-化学成分在线分析系统(RCFP-IC)在追踪污染生成-消散过程中的适用性,于2011年3月对北京PM2.5中NO3-、SO24-、NH4+和Cl-这4种污染型水溶性离子浓度变化进行了连续高时间分辨率观测,并结合同期气象要素的变化,探讨了污染过程形成的原因.结果表明,一个月的观测期内捕捉到了5次较为明显的污染过程,4种水溶性离子的浓度变化趋于一致,并呈现出典型的"慢积累、快清除"的锯齿型污染物浓度时间序列变化特征.NO3-和NH4+在典型污染事件中峰值浓度是清洁时期浓度的10倍以上,而SO24-和Cl-污染峰值浓度仅为清洁时期的2～4倍.停暖后4种离子浓度较采暖期下降了15%～60%.RCFP-IC与高分辨率飞行时间气溶胶质谱(HR-TOF-AMS)同期观测结果变化趋势具有高度的一致性,但RCFP-IC定量水溶性离子浓度更为准确.     

Nitrous and nitric acid measurements at sites in South-East England

Measurements of HONO and HNO₃ have been made using annular denuder samplers at sites in south-east England. Whilst concentrations of HNO₃ exhibited a diurnal variation, with a maximum in mid-afternoon nitrous acid shows the opposite diurnal cycle with maximum levels at night due to daytime photolysis. Concentrations of HONO increase with those of NO₂, and elevated nighttime HONO level appear to be followed by high levels of HNO₃ the following day. Average concentrations of HONO (0.45± 0.26 ppb in 24 h samples are comparable to those of HNO₃ (0.56±0.36 ppb in 24 h samples), each representing about 5–10% of the concentration of NO₂. Although NO₂ oxidation provides the source of HNO₃ concentrations of the two compounds are not related, presumably since the formation of NH₄NO₃ aerosol limits HNO₃ concentrations at out site.     

Atmospheric pollutant deposition to high-elevation ecosystems

Current knowledge regarding deposition of atmospheric pollutants to mountain ecosystem is reviewed focusing on the mountains of eastern North America. Despite a general paucity of published data on the subject, some generalization emerge. Wet deposition (i.e. precipitation input) of SO₄²⁻, NO₃⁻, H⁺ and Pb tends to increase with elevation, primarily because of the orographic increase in precipitation amount. Cloud water deposition of these substances can be very significant for mountain forests, but is highly variable spatially because of its strong dependence on wind speed, cloud characteristics, and vegetation canopy structure, which are all heterogeneously distributed. Dry deposition has not been quantified sufficiently to draw empirical generalizations, but the processes involved are discussed with regard to expected elevational trends. Based on the few studies in which total annual deposition (wet, dry, plus cloud water inputs for an entire year) has been measured, it appears that some high-elevation sites in the Appalachian Mountains receive substantially more SO₄²⁻, NO₃⁺ deposition than do typical low-elevation sites. The amount of elevational increase depends largely on the amount of cloud water deposition at the mountain site. Data from two clusters of sites in the northern Appalachians indicate that total deposition of SO₄²⁻, NO₃⁻, and H⁺ to mountaintop sites is typically 3–7 times greater than deposition to nearby lowland sites. Similarly, some studies of Pb accumulation in organic soil horizons suggest a two- to four-fold increase from lowlands to mountaintops. Deposition in mountain areas can be highly variable over short distances because of the patchiness of meteorological conditions and vegetation canopy characteristics, and also because exposed trees and forest edges can receive deposition loads much higher than the landscape average. Night-time and early-morning O₃ concentrations are greater at high-elevation than at low-elevation sites. Daytime O₃ levels are equal or slightly higher at high-elevation sites. Additional studies are suggested which would allow better characterization of pollutant exposure along elevational gradients.     

Wintertime measurements of aerosol acidity and trace elements in Wuhan,a city in central China

A 2-week intensive ambient aerosol study was conducted in December 1988 in Wuhan (Hubei Province), a city of nearly 2 million located on the Yangtze River in central China (P.R.C.). This is an industrial region where soft coal burning is widespread, and emission controls for vehicles and industrial facilities are minimal. The sampling site was located in one of the civic centers where residential and commercial density is highest. An Andersen dichotomous sampler was operated with Teflon membrane filters to collect fine (d_p < 2.5 μmad) and coarse (2.5 ⩽ d_p < 10 μmad) particles for total mass and element determinations. An annular denuder system (ADS) was used to collect fine fraction aerosols for analyses of ionic species including strong acidity (H⁺).The study was conducted between 18 and 30 December, which was rainless, consistently cool (3–10°C) and overcast, but without fog or acute stagnation. Fine particulate mass (PM, as μ m⁻³) averaged 139 (range 54–207); coarse PM averaged 86 (range 29–179). Trace element concentrations were also high. Crustal elements (Si, Al, Ca and Fe) were found primarily in the coarse fraction, while elements associated with combustion (S, K, Cl, Zn and Se) were enriched in the fine fraction. The concentrations of arsenic and selenium were evidence of a large source of coal burning, while vanadium levels (associated with fuel oil use) were not especially enriched.Despite the seemingly high PM loadings, ionic concentrations were not especially high. The average composition of soluble fine aerosol species (in neq m⁻³) were SO₄²⁻: 520 (range 180–980), NO₃⁻: 225 (range 50–470), Cl⁻: 215 (range 20–640), and NH₄⁺: 760 (range 280–1660). A deficit in accountable FP components (total mass compared to the total of ionic plus element masses) as well as the black appearance of collected materials indicate an abundance of carbonaceous aerosol, as high as 100 μ m⁻³. (total mass compared to the total of ionic plus element masses) as well as the black appearance of collected materials indicate an abundance of carbonaceous aerosol, as high as 100 μ m⁻³Aerosol acidity was negligible during most monitoring periods, H⁺: 14 (range 0–50 neq m⁻³, equivalent to 0–2.5 μm m⁻³ as H₂SO₄). Sulfur dioxide, measured by the West-Gaeke method for part of the study, concentrations were low. Although not directly measured, the aerosol measurments suggested that gaseous HCl (from refuse incineration) and NH₃ (animal wastes) concentrations might have been high. Higher aerosol acidity might be expected if HCl sources were more prominent and not neutralized by local ammonia or other base components.     

Vertical distributions of COS,CS2, DMS and other sulfur compounds in a loblolly pine forest

Measurements of atmospheric COS, CS₂, DMS, SO₂ and aerosol sulfate and methanesulfonate (MSA) concentrations were conducted in a loblolly pine forest in central Georgia between July and September 1990. The daytime profiles obtained for the reduced sulfur gases (COS, CS₂, DMS) often showed significantly higher concentrations at the canopy level than above the forest canopy, indicating a net emission of these gases from the tree tops. No evidence was found for a net uptake of COS by the canopy during daytime. With one exception, all COS concentrations measured during the day were significantly higher than corresponding nighttime values. These results appear to be in conflict with recent studies suggesting a net uptake of atmospheric COS by plants during photosynthetic activity. Possible explanations for these different findings are discussed. Nighttime profiles indicated no major biosphere-atmosphere exchange of COS, CS₂ or DMS. Nighttime DMS concentrations were significantly higher than corresponding daytime values. A clear inverse relationship between the diel variations of DMS and MSA was observed, consistent with rapid photochemical oxidation of DMS under the given conditions.     

Scavenging ratios and deposition of sulphur,nitrogen and chlorine species in eastern England

Measurements of wet deposited NH₄⁺, SO₄²⁻, NO₃⁻ and Cl⁻, as well as airborne concentrations of these species and gaseous HNO₃, HCl and NH₃, have been made at a site in eastern England. Scavenging ratios based solely upon aerosol-associated species and upon aerosol plus gaseous airborne species are presented and compared with literature values. It appears that HCl and HNO₃ have only a rather minor influence upon wet deposition at our site. Gaseous NH₃ influences ground-level air chemistry appreciably, but scavenging ratios for NH₄⁺ are low, even when based upon aerosol NH₄⁺ concentrations alone, presumably due to altitudinal gradients in this species. The problems inherent in interpretation of scavenging ratios are discussed. Deposition of nitrogen in various chemical forms is estimated from rainwater and air composition. If a transport-limited deposition velocity is assumed for ammonia gas, dry deposition of this species accounts for around 40% of total nitrogen deposition to the ground.     

Field studies of the SO2/aqueous S(IV) equilibrium in clouds

Concentrations of S(IV) were measured in cloudwater at Great Dun Fell and compared with theoretical HSO₃⁻ assuming equilibrium between aqueous and gaseous phases in cloud. Detectable concentrations of S(IV) in the range of 1 × 10⁻⁶ to 17.2 × 10⁻⁶ mol dm⁻³ were observed only in samples which contained low H₂O₂ concentrations, generally <1 × 10⁻⁶ mol dm⁻³. Concentrations of S(IV) were below the detection limit of 1 × 10⁻⁶ mol dm⁻³ in samples which contained hign H₂O₂ levels (1 × 10⁻⁶−80 × 10⁻⁶ mol dm⁻³) confirming that either SO₂ or H₂O₂ acts as the limiting reagent in the oxidation of SO₂ in cloudwater.Equilibrium HSO₃⁻ concentrations were estimated from the measured cloudwater pH, the gas phase SO₂ concentration and the ambient temperature and found to be on average about 5 times lower than the measured S(IV) concentrations. The possible role of formaldehyde in stabilizing S(IV) in cloudwater is discussed. The kinetic data available in the literature suggest that the complexation reaction between S(IV) and HCHO is too slow to account for the observed difference between measured and calculated S(IV) concentrations over the typical lifetime of clouds in our study.S(IV) accounted for up to 10% of the SO₄²⁻ measured in stored cloudwater samples.     

Deposition and forest canopy interactions of airborne sulfur: Results from the integrated forest study

The Integrated Forest Study (IFS) was a long-term research project designed to determine the effects of atmospheric deposition on forest nutrient cycles. Concentrations and fluxes of airborne sulfur compounds were determined for several years at the 13 IFS research forests in North America and Europe using a standard set of protocols. Annual mean air concentrations of sulfur ranged from ∼1.5 to 8 μgSm⁻³ and were generally dominated by SO₂ (∼60% of total sulfur on the average). Atmospheric deposition of sulfate at these forests was highest at the high elevation (∼ 1000–2000 eq ha⁻¹yr⁻¹) and at the southeastern U.S. sites (∼800–1000 eq ha⁻¹yr⁻¹), and lowest in the Pacific northwest (∼300 eq ha⁻¹yr⁻¹). Cloud water contributed significantly to the sulfur flux at the mountain sites (45–50%), and dry deposition was comparable to wet at the drier southeastern sites (>40% of total). Deposited sulfur appeared to behave more or less conservatively in these canopies, showing little net uptake (ofSO₂) and minor foliar leaching (of soil-derived, internal SO₄²⁻) relative to the total atmospheric flux. The estimated fluxes in total deposition were generally within 15% of the measured fluxes in throughfall plus stemflow, indicating that useful estimates of total atmospheric deposition of sulfur can be derived from measurements of throughfall.     

The spatial distribution and particle size of some inorganic nitrogen,sulphur and chlorine species over the North Sea

The use of filter packs and a cascade impactor during a series of research cruises in the southern area of the North Sea has yielded detailed spatial distribution patterns of aerosol concentrations, Cl⁻, NO₃⁻, SO₄²⁻¹ and NH₄⁺ and gaseous concentrations, HCl, HNO₃ and NH₃. The overall distribution of the atmospheric concentrations closely parallels published modelled results for metallic species. The chemical transformations of these aerosols and gases are investigated together with their interactions with the seasalt aerosol. Aerosol chloride loss is greatest in the more polluted areas, whilst concentrations products of NH₃ with HNO₃ and HCl appear insufficient to sustain the existence of NH₄NO₃ and NH₄Cl. Nitrate is associated predominantly with larger particles and appears to be present substantially as a surface coating on marine aerosol. The total dry deposition input for nitrogen species is calculated for the southern sector with extrapolation to the whole of the North Sea, using particle size weighted deposition velocities of 0.63 and 0.21 cm s⁻¹ for NO₃⁻¹ and NH₄⁺, respectively, and literature-derived values for the gaseous constituents. Finally the use of air-mass back trajectories illustrates the role of source regions in influencing the chemical composition of the North Sea atmosphere.     

PM2.5在线水溶性离子与滤膜采集-实验室检测的比对分析

2014年1~12月,使用URG在线及滤膜采集-实验室分析两种方法对北京市大气细颗粒物PM_(2.5)中的水溶性离子进行检测,并对春、夏、秋、冬这4种不同季节下两种测量方法的差异性进行了比对研究.全年测量结果显示,在线URG所获离子总量高于滤膜采集所获离子总量,其中两种方法所测Cl~-、NO_3~-、Mg~(2+)、Ca~(2+)年均浓度差异不大,而在线所测SO_4~(2-)、NH_4~+、Na~+、K~+结果均明显高于滤膜测试结果.4种主要的水溶性离子中SO_4~(2-)、NO_3~-和Cl~-的相关性较好,NH_4~+相关性略差;不同季节两种测量方法所获结果也略有不同,NO_3~-、SO_4~(2-)、Cl-在秋、冬季差异不显著,而NH_4~+仅在冬季拟合性较好.     

A long-term (1975–1988) study of atmospheric SO42−: Regional contributions and concentration trends

A long-term study of aerosol SO₄²⁻ concentrations ([SO₄²⁻]) has been conducted at Mayville in the western and Whiteface Mountain in the northeastern New York State. From 1975 to 1988, 2382 daily aerosol samples were collected at Whiteface Mountain using high-volume samplers. Similarly, 1863 samples were collected at Mayville for the 1981–1988 period. Both sites are downwind of large SO₂ sources in the Midwest. Whiteface Mountain is located approximately 600 km to the northeast of Mayville. The [SO₄²⁻] at Mayville were approximately twice that of Whiteface Mountain. The highest concentrations at both locations were observed in summer and the lowest during winter. Photochemical reactions appear to be the primary reason for this behavior. Air trajectories (Hefter model) were used to relate the observed [SO₄²⁻] with the upwind SO₂ source regions. In addition, a method based on V/Se ratios was used to resolve SO₄²⁻ contributions between Midwestern sources and those in the East Coast. Approximately, two-thirds or more of the total SO₄²⁻ at the two sites was derived from the Midwestern emissions. At Whiteface Mountain the [SO₄²⁻] for summer months from 1975 to 1988 suggest a decrease of approximately 3% per year between 1978 and 1988. A similar decrease was also observed in SO₂ emissions.     

Cloud chemistry at Mt Rigi,Switzerland: Dependence on drop size and relationship to precipitation chemistry

The chemical composition of winter and spring cloud water sampled at 1620 masl elevation on Mt Rigi in central Switzerland was dominated by NO₃⁻, SO₄²⁻, NH₄⁺ and H⁺. A wide range of concentration levels was observed, with maxima of 3700, 1800 and 4600 micronormal for NO₃⁻, SO₄²⁻ and NH₄⁺, respectively. Concentrations at a lower elevation (1030 masl) site on the mountain were higher due to lower cloud liquid water contents and higher pollutant levels at that site. The lowest pH observed was 2.95; large concentrations of NH₃ in the region prevented pH values from falling even lower. A comparison of simultaneously sampled cloud water and precipitation revealed much higher concentrations for most species in the cloud water, except in one case of extreme precipitation riming when the concentrations in the two phases converged. An exception to the pattern was H⁺; at times the precipitation was more acidic than the cloud water. The chemical composition of the cloud drops varied with drop size. Drops smaller than 10 μm diameter were enriched in NO₃⁻, SO₄²⁻ and NH₄⁺ relative to larger drops. Since the larger drops are the ones most effeciently captured by snow crystals, knowledge of their composition is essential to understanding the chemical implications of accretional growth of precipitation.     

Atmospheric concentrations and deposition of nitrogen and major ions in conifer forests in the United States and Federal Republic of Germany

Emission densities of air pollutants are higher in Europe than in the U.S. as a whole, suggesting similar differences in atmospheric deposition. We determined air concentrations and deposition during the warm season at conifer forests in Tennessee and northern Germany. Our results confirmed major differences in both chemistry and fluxes. Atmospheric and precipitation concentrations of all ions except H⁺ were higher at the German site, most significantly for the nitrogen species. The much higher levels of NH₄⁺ at this site reflect higher emissions of NH₃, which was the species largely responsible for the lower levels of H⁺. Total airborne nitrate was dominated by HNO₃ in Tennessee. In Germany we found comparable amounts of HNO₃ and aerosol NO₃⁻, the concentration of which varied seasonally, apparently in response to agricultural emissions of NH₃ that reacted to form NH₄NO₃. Total deposition of all major ions was much higher at the German site, particularly for the nitrogen species, which exhibited a marked edge effect in throughfall. Dry deposition was determined from air concentrations by using a canopy resistance model and from a statistical model of throughfall fluxes, each of which yielded comparable fluxes for several ions. Dry deposition contributed 10–70% of the ion input and was most important at the German site. Both forest canopies absorbed 40–50% of total deposited nitrogen, primarily from dry deposition.     

Rainwater composition in Athens,Greece

Wet precipitation-only samplers were used to collect wet deposition at two sites in the Athens basin, Greece for the period March 1986–February 1987.Concentrations of major cations (H⁺, NH⁺₄, Na⁺, K⁺, Ca²⁺ and Mg²⁺) and major anions (Cl⁻, NO⁻₃ and SO²⁻₄) were determined for the first time in rainwater samples in Greece. Bicarbonate concentrations were calculated. The relative importance of natural and anthropogenic sources were estimated by a chemical balance. The majority of rain collected has a neutral or alkaline character. Acidity was due to the presence of H₂SO₄ and HNO₃. The statistical analysis of the correlation between the concentration of chemical species confirm the influence of natural and anthropogenic sources. In all samples, SO²⁻₄ concentrations exceed NO⁻₃ concentrations despite the dominance of low S oil burning in the region. The wet flux of S was calculatd to be 0.34 gm⁻²a⁻¹.