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1.
A side-by-side comparison of the Rotating Arm Collector (RAC) and the Caltech Active Strand Cloudwater Collector (CASCC) was conducted at an elevated coastal site near the eastern end of the Santa Barbara Channel in southern California. The CASCC was observed to collect cloudwater at rates of up to 8.5 ml min−1. The ratio of cloudwater collection rates was found to be close to the theoretical prediction of 4.2:1 (CASCC:RAC) over a wide range of liquid water contents (LWC). At low LWC, however, this ratio climbed rapidly, possibly reflecting a predominance of small droplets under these conditions, coupled with a greater collection efficiency of small droplets by the CASCC. Cloudwater samples collected by the RAC had significantly higher concentrations of Na+, Ca2+, Mg2+ and Cl than those collected by the CASCC. These higher concentrations may be due to differences in the chemical composition of large vs small droplets. No significant differences were observed in concentrations of NO3, SO42− or NH4+ in samples collected by the two instruments.  相似文献   

2.
Scavenging of sulfates and nitrates—two most common ions leading the cloudwater acidity—was investigated during field studies atop a site in Mt. Mitchell (35°44′05″N, 82°17′15″W) State Park where the highest peak (2038 m MSL) of the eastern U.S. is located. Experiments were conducted during the growing seasons (15 May–30 September) of 1986 and 1987 using an instrumented meteorological tower (16.5 m tall) and a passive cloudwater collector. A cloud episode that occurred on 12 October 1987, was also comprehensively investigated. Clouds were frequently observed in which the Fraser fir and red spruce stands stayed immersed 28% and 41% of the time during the 1986 and 1987 seasons, respectively. Rate of cloudwater deposition on the forest canopy was determined using an inferential cloud deposition model. It was found by analysing nine short duration (lasting 8 h or less) and 16 long duration cloud events that the ionic concentration (SO42− and NO3) is inversely proportional to the rate (Ic) of cloudwater deposition (in mm h−1) and can be expressed by the following relationship: [SO42−] = aIcb or [NO3] = aIcb. Theoretical arguments leading to these relationships are presented. The b values for predicting NO32− concentration are found in the range of 0.14–1.24 (mean = 0.48) for short duration and 0.062–0.63 (mean = 0.27) for long duration cloud events, respectively. The corresponding b values for predicting NO3 concentrations are 0.19–1.16 (mean = 0.49) and 0.072–0.59 (mean = 0.27), respectively. When the b parameter was between 0.2 and 0.6, the correlation coefficients between measured and predicted ionic concentrations were found to exceed 0.7. The parameter a is shown to represent the maximum ionic flux for a given cloud event. The ratio of the a parameter for SO42− to NO3 varied between 1.75 and 6.95, indicating that the SO42− contributes to the total ionic concentration substantially more than the NO3 leading to the conclusion that the cloudwater acidity is primarily due to the presence of sulfuric acid which has been demonstrated to cause foliar injury and growth retardation in red spruce trees. The above parameterization is similar to the one that is frequently used to relate ionic concentration in precipitation to the rainfall rate. In order to understand physico-chemical processes leading to the proposed parameterization schemes, meteorological and chemical variables are comprehensively analysed for one short duration and two long duration cloud events. The concentrations of principal ions (SO42−, NO3, H+ and NH4+) during the short duration cloud events were found to be much higher than those during the long duration ones, especially at colder temperatures. Such short cloud events have a potential of causing foliar narcosis in red spruce stands because of unusually acidic cloudwater to which these stands stay exposed intermittently during each growing season.  相似文献   

3.
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.  相似文献   

4.
Atmospheric dry deposition to branches of Pinus contorta and P. albicaulis was measured during summer 1987 in a sub-alpine zone at Eastern Brook Lake Watershed (EBLW), eastern Sierra Nevada, California. Results are presented as deposition fluxes of NO3, SO42−, PO43−, Cl, F, NH4+, Ca2+, Mg2+, Na+, K+, Zn2+, Fe3+, Mn2+, Pb2+ and H+, and compared with other locations in California and elsewhere. Deposition fluxes of anions and cations to the pine branches were low, several times lower than the values determined near the Emerald Lake Watershed (ELW), another sub-alpine location in the western Sierra Nevada. The sums of deposition fluxes of the measured cations and anions to pine surfaces were similar, in contrast to the ELW location where the sums of cation fluxes were much higher than the sums of anion fluxes. A strong positive correlation between depositions of NO3 and NH4+, as well as SO42− and Ca2+, suggested that large portions of these ions might have originated from particulate NH4NO3 and CaSO4 deposited on pine surfaces. An estimated total N dry deposition (surface deposition of NO3 and NH4+ and internal uptake of NO2 and HNO3) to the forested area of the EBLW was 29.54 eq ha−1 yr (about 414 g H ha−1 yr−1).  相似文献   

5.
Estimates of external and internal sources of ions in net througfall deposition were derived for a deciduous and coniferous canopy by use of multiple regression. The external source component appears to be dominated by dry deposition of Ca2+, SO2 and NO3 during dormant and growing seasons for the two canopy types. Increases in the leaching rates of K+ and Mg2+ during the growing season reflect the presence of leaves in the deciduous canopy and increased physiological activity in both canopies. Internal leaching rates for SO42− doubled during the growing season presumably caused by increased physiological activity and uptake of SO2 through stomates. Net deposition of SO42− in throughfall during the growing season appears highly dependent on stomatal uptake of SO2. Estimates of SO2 deposition velocities were 0.06 cm s−1 and 0.13 cm s−1 for the deciduous and coniferous canopies, respectively, during the dormant seasons, and 0.30 cm s−1 and 0.43 cm s−1 for the deciduous and coniferous canopies, respectively, during the growing season. For the ions of major interest with respect to ecosystem effects, namely H+, NO3 and SO42−, precipitation inputs generally outweighed estimates of dry deposition input. However, net throughfall deposition of NO3 and SO42− accounted for 20–47 and 34–50 per cent, respectively, of total deposition of those ions. Error estimates of ion sources were at least 50–100 per cent and the method is subject to several assumptions and limitations.  相似文献   

6.
Chemical composition of precipitation in Albany, NY from July 1986 to December 1988 has been studied. Mean volume-weighted concentrations (μeqℓ−1) were: acidity, 104.0; alkalinity, −63.7; SO42−, 52.8; NO3, 29.8; Cl, 5.6; F, 0.50; NH4+, 19.3; Ca2+, 6.5; Mg2+, 2.8; Na+, 3.5; and K+, 1.4. Mean pH was 4.2 . Seasonal patterns were pronounced for most species. Concentrations of H+, SO42−, NO3, NH4+ and Ca2+ peaked in the summer and spring. Deposition was related to rainfall amount by a power law relationship in which the exponent of the equation was ∮.6. Wet SO42− deposition was 2.35 keq ha−1 over a 30-month period. The SO42− and NO3 deposition rates observed at Albany indicate that transport from midwestern sources have a major influence at this site. On the average, free H+ ion concentrations determined from pH measurements accounted for 51% of the measured total acidity. There were unknown species, most likely organic acids, that could contribute to the acidity. Correlation and regression analyses indicated that major anions, SO42− and NO3, were closely associated with H+ and NH4+ ions. Factor analysis revealed four common factors which are related to fossil-fuel combustion, sea spray, cement factory and biomass burning.  相似文献   

7.
Atmospheric dry deposition of ions to branches of native Pinus contorta and Pinus monticola (natural surfaces), and nylon filters and Whatman paper filters (surrogate surfaces) were measured in the summer of 1987 in the vicinity of Emerald Lake Watershed (ELW) of the Sequoia National Park located on the western slope of the Sierra Nevada in California. Deposition fluxes of airborne NO3, NH+4 and SO2−4 to native pines at the ELW were much higher than in the eastern Sierra Nevada, but several times lower than deposition fluxes to natural and surrogate surfaces at the highly polluted site in the San Gabriel Mountains of southern California. Deposition fluxes of NO3 and NH4+ to the natural and surrogate surfaces at the ELW were much higher than deposition of SO42−, providing the importance of N compounds in atmospheric dry deposition in this part of the western U.S. A deficit of inorganic anions in materials deposited to various surfaces indicated a possibility of substantial participation of organic acids in atmospheric dry deposition processes. Nylon and paper filters proved to be poor surrogate surfaces for the estimation of ionic dry deposition to conifer branches.  相似文献   

8.
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, SO42- and NH4+, and gas phase HNO3 and NH3, were sufficient to account for the observed cloudwater loadings of NO3, SO42- 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.  相似文献   

9.
The precipitation chemistry of Greater Manchester, a Metropolitan County in the northwest of England, has been examined for small scale spatial variability using a network of 18 bulk precipitation collectors. Significant spatial variability was found for concentrations of non-marine SO42−, NO3, NH4+, Ca2+ and H+ ions. The statistical associations between the data were investigated using correlation, partial correlation and principal components analyses. It was found that zero-order correlation coefficients were inadequate for the interpretation of the data and that the computation of first, and higher order partial correlation coefficients was necessary in order to explain the interrelationships between the data and their spatial variability. The statistical associations between the data suggest relationships between Ca2+ and non-marine SO42−, and NO3+ in precipitation which are discussed in terms of their possible precursor species. Potential source effects were examined in conjunction with atmospheric removal processes. The dry deposition of SO4 particles, rather than the dry deposition of SO2, may explain the spatial variability of non-marine SO42−. The erosion of CaSO4 formed from the reaction of SO2 with CaCO3 on urban surfaces with subsequent resuspension is thought to be the basis of the relationship between Ca2+ and non-marine SO42− concentrations in precipitation. The wet and dry deposition of CaCO3 particles from local sources may be partially responsible for the spatial variability of H+, and dry deposition and scavenging of NH3, in conjunction with the predominant wind direction may explain the spatial variability of NO3 and NH4+ ions. Ammonia is thought to originate from sources both outside the study area and within it.  相似文献   

10.
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.  相似文献   

11.
Rainwater samples in S. Paulo city were collected on an event basis from October 1983 to October 1985 covering two dry and two rainy periods. Bulk samples only were obtained. At the same site and period, fine, coarse and inhalable particles were also collected. Na+, Ca2+, K+, Mg2+, NO3, SO42− and NH4+ contents were determined in rainwater samples, while Na, Ca, K, Cl and S concentrations were measured in aerosol samples. Rainwater is slightly acid (mean pH = 5.0), and contains high concentrations of Ca2+, NO3, SO42− and NH4+. Dry and wet fluxes and washout ratios were determined for some elements. Results obtained suggest that the atmospheric composition in this city is strongly influenced by anthropogenic sources.  相似文献   

12.
The potentially catastrophic environmental consequences of the conflict in Iraq, Kuwait and Saudi Arabia, from mid 1990 to early 1991, have highlighted the need for background atmospheric chemistry measurements for the region. The only known cloudwater chemistry data obtained in the Arabian Peninsula are presented here. The samples were collected near the coast, in the Dhofar region of southern Oman, from 22 to 30 July 1990, immediately prior to the start of the conflict on 2 August. Analysis of the samples for pH, 10 major ion concentrations and 23 trace elements, demonstrates that the cloud water was very clean. Enrichment factor calculations showed the ions have oceanic and crusal origins, whereas trace elements such as B, V, Mn, Ni, Zn, Se, Sr, Mo and Ba have anthropogenic sources. In comparison with three mountain cloudwater sampling sites in eastern North America, the Omani site has higher pH values, higher Na+ and Cl concentrations, and lower SO42− and NH4+ concentrations.  相似文献   

13.
Fog, aerosol, and gas samples were collected during the winter of 1986 at Riverside, California. The dominant components of the aerosol were NH4+, NO3, and SO42−. Gaseous NH3 was frequently present at levels equal to or exceeding the aerosol NH4+. Maximum level were 3800, 3100, 690 and 4540 neq m−3 for NH4+, NO32− and NH3(g), respectively. The fogwater collected at Riverside had very high concentrations, particularly of the major aerosol components. Maximum concentrations were 26,000 29,000 and 6200 μM for NH4+, NO3 and SO42−, respectively. pH values in fogwater ranged from 2.3 to 5.7. Formate and acetate concentrations as high as 1500 and 580 μM, respectively, were measured. The maximum CH2O concentration was 380 μM. Glyoxal and methylglyoxal were found in all the samples; their maximum concentrations were 280 and 120 μM, respectively. Comparison of fogwater and aerosol concentrations indicates that scavenging of precursor aerosol by fog droplets under the conditions at Riverside is less than 100% efficient.The chemistry at Riverside is controlled by the balance between HNO3 production from NOx emitted throughout the Los Angeles basin and NH3 emitted from dairy cattle feedlots just west of Riverside. The balance is controlled by local mixing. Acid fogs result at Riverside when drainage flows from the surrounding mountains isolate the site from the NH3 source. Continued formation of HNO3(g) in this air mass eventually depletes the residual NH3(g). A simple box model that includes deposition, fog scavenging, and dilution is used to assess the effect of curtailing the dairy cattle feedlot operations. The calculations suggest that the resulting reduction of NH3 levels would decrease the total NO3 in the atmosphere, but nearly all remaining NO3 would exist as HNO3. Fogwater in the basin would be uniformly acidic.  相似文献   

14.
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, NO3 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 NO3 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.  相似文献   

15.
中亚热带典型林分不同层次氮硫湿沉降动态变化   总被引:8,自引:3,他引:5  
孙涛  马明  王定勇  黄礼昕 《环境科学》2014,35(12):4475-4481
基于野外定点监测的方法,于2012年9月~2013年8月对四面山常绿阔叶林大气降水、穿透水、枯透水、土壤渗滤液进行了持续1 a的氮、硫湿沉降动态变化的研究.结果表明:四面山大气降水全年p H平均值为4.89,最大值为5.14,大气降水明显偏酸性;土壤层和林冠层能使降雨的p H值有所升高,其中土壤层对p H值的调升幅度最大,其次为森林冠层;森林冠层对NO-3、NO-2、SO2-4有一定的吸附净化作用,平均截留率分别为56.68%、45.84%、35.51%;研究结果也表明:枯枝落叶的降解是导致各离子质量浓度在枯透水中增加的原因;森林土壤能够吸附中和NO-3、SO2-4、NH+4,释放出NO-2.中亚热带常绿阔叶林生态系统对大气降水中NO-3、NO-2、NH+4、SO2-4的总截留率分别为92.86%、57.86%、87.24%、87.25%,对酸性降雨有一定的缓冲作用.  相似文献   

16.
Rainwater and atmospheric bulk deposition samples were collected at a station on the rooftop of the Research Institute of King Fahd University of Petroleum and Minerals in Dhahran. Continuous sampling was carried out manually throughout the rainy season between December 1987 and February 1988, and for one rainfall event in March 1987. A total number of 13 samples were collected and investigated for pH and dissolved ionic composition using inductivity coupled plasma emission spectrometry (ICP) and ion chromatography (IC). The range and volume-weighted average pH were 5.1–7.2 and 5.48, respectively. Significant negative linear correlations were observed between the precipitation pH and rain depth, and between pH and the summation of dissolved {(Ca2+ + Mg2+)−(SO42− + NO3 + NO2)} (in μeqℓ−1). The ionic summation also correlated negatively with rain depth. The ionic abundance in rainwater (in μeqℓ−1) expressed in concentration order showed the general trend SO42− > HCO3−1 = Cl = NO3 > NO2 for anions and Ca2+ > Na+ > Mg2+ > NH4+ > K+ > H+ > Sr2+ for cations. Good mass balance between cations and anions was observed. Total NO3 contribute equally to precipitation acidity as SO42− and Ca2+ plus Mg2+ in alkaline suspended particulates from natural sources are the major ions which buffer the acidity of precipitation. The NH4+ ion which is also present plays an insignificant role in the acid/base equilibrium of rainwater.  相似文献   

17.
Daily measurements the atmospheric cocnentrations of HNO3, NO3-, NO2, SO2, SO42−, NH4+, and several trace metals were made at the University of Michigan Biological Station over a 124-day period during the 1984–1985 winter. The composition of the daily precipitation was also determined. The relative contributions of scavenged NO3 and HNO3 to the precipitation was estimated by assuming that the NO3 scavenging ratio was the same as that of trace metals with a similar particle size. Similarly, the SO42− and SO2 contributions were based on the scavenging ratios of NH4+ and trace metals. On this basis, it was determined that the event median NO3 and HNO3 scavenging ratios were 500 and 3500, respectively. HNO3 scavenging accounted for 83% of the total scavenged NO3. Scavenging of SO42− accounted for all the snow SO42− in 67% of the events. In the remaining events, some SO2 was scavenged, with a median scavenging ratio of 219. Overall, 67% of the snowfall acidity appeared to be due to HNO3 scavenging. Backward air-mass trajectories that were calculated for each event were used to determine the general source regions of the acidic species. Snow associated with air masses from the south and west accounted for 81 and 75% of the deposited NO3 and SO42−, respectively.  相似文献   

18.
Vertical profiles (surface to 5 km) of aerosol particle number concentration, NOy′ mixing ratio, and cloudwater SO42− and NO3 equivalent concentration were obtained in three field studies: North Bay, Ontario, during the summer of 1982 and the winter of 1983–1984, and Syracuse, New York, during the fall of 1984. The measurements from these locations and different seasons are compared. Generally, airborne concentrations are highest with air-mass back trajectories from the south and lowest with back trajectories from the north. For the southerly trajectories, median particle number concentrations (0.2–2 μm) near ground level (950 mb) vary from 1700 cm−3 during the summer project to 800 cm−3 during the winter project. At 700 mb, the south trajectory particle number concentration ranged between 60 and 170 cm−3. Median NOy′ mixing ratios for southerly back trajectories were approximately 6 and 9 ppb at 950 mb and 0.4 and 0.8 ppb at 700 mb for the fall and winter projects, respectively. Comparison of particle number concentration profiles outside of cloud with cloud droplet plus interstitial aerosol particle number concentrations inside cloud indicate that cumulus clouds can transport aerosols vertically from below cloud base. In contrast, stratiform clouds have similar concentrations inside the clouds as outside at the same altitude. The vertical variations of cloudwater sulphate and nitrate concentrations and the NO3/SO42− equivalent concentration ratio are discussed for each of the three field studies.  相似文献   

19.
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.  相似文献   

20.
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.  相似文献   

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