共查询到20条相似文献,搜索用时 15 毫秒
1.
G.P.J. Draaijers E.P. Van Leeuwen P.G.H. De Jong J.W. Erisman 《Atmospheric environment (Oxford, England : 1994)》1997,31(24):4159-4168
An assessment was made of the capacity of base cations to neutralize acid deposition and of the contribution of base cation deposition to forest nutrition in Europe. In large parts of southern Europe more than 50% of the potential acid deposition was found counteracted by deposition of non-sea salt Mg2+ + Ca2+ + K+. In central and northwestern Europe, base cation deposition usually amounted to less than 25% of the acid input. Smallest base cation deposition relative to potential acid deposition was found in southern Scandinavia, Denmark, northern Germany and The Netherlands. A similar spatial pattern was found for the neutralization of acid anions in precipitation. Whereas in Scandinavia weathering is the dominant supplier of base cation to forest soils, in eastern and southern Europe, forests mainly rely on atmospheric deposition for the supply of base cations. Using error propagation, the random and systematic error in acid neutralization capacity for an average grid cell of 10 × 20 km was estimated to equal 45–55% and 50–55%, respectively. 相似文献
2.
《Atmospheric environment (Oxford, England : 1994)》2007,41(7):1426-1439
This paper focuses on a detailed analysis of the effects of meteorological factors explaining the variability of rain composition.Inorganic composition of 113 individual rain events was measured from May 2002 to October 2005 at a rural site near Chimay, in the western part of the Belgian Ardennes. Original models were fitted for each studied ion (H+, Mg2+, Ca2+, K+, NH4+, Na+, Cl−, NO3− and SO42−) to relate rain event concentration or wet deposition to the rainfall volume (R), the length of the antecedent dry period (ADP), the volume of the previous event (Rprev) as well as to the mean wind speed and the prevailing wind direction during both the dry and the rainy periods. These variables explained from 32% (H+) to 69% (NO3−) of rain concentration variability. Concentrations decreased logarithmically with increasing R values except in case of H+ for which a positive effect of rain volume on rain concentration was observed. ADP affected positively rain concentrations of all ions excluding K+ and H+ for which, respectively, a nonsignificant and a negative effect of this variable was observed. Increasing Rprev strengthened the effect of the variable R on H+, Mg2+, Ca2+, Na+, NH4+ and SO42− concentrations while it softened the effect of ADP on NO3− concentrations. Wind speed and direction during dry and rainy periods explained together from 8% (K+) to 38% (Na+) of rain concentration total variability. R2 coefficients of the wet deposition models ranged from 0.51 (K+) to 0.79 (SO42−). For all ions, wet deposition increased significantly with increasing R values while the effects of the other variables were similar to those on concentrations. Wind conditions during dry and rainy periods explained from 4% (H+) to 24% (Na+) of wet deposition total variability. On an annual scale, the total dry period duration, the total rainfall volume as well as the shape of the distributions of the length of the antecedent dry periods and of the rain event volume are important parameters that influence annual wet deposition. 相似文献
3.
《Atmospheric environment(England)》1987,21(10):2121-2131
A comprehensive framework for model error analysis is applied to the EMEP-W model of longrange transport of sulfur in Europe. This framework includes a proposed taxonomy of model uncertainties. Parameter uncertainties were investigated by Monte Carlo simulation of two source-receptor combinations. A 20% input parameter uncertainty (expressed as a coefficient of variation = standard deviation/mean) yielded a 15–22% output error of total sulfur deposition. The relationship between output error and input uncertainty was approximately proportional. Covariance between parameters can have an important effect on computed model error, and can either exaggerate or reduce errors compared to the uncorrelated case. Of the model state variables, SO2 air concentration and wet deposition had the highest error, and total sulfur deposition the lowest. It was also found that it is more important to specify the dispersion of the input parameter frequency distributions than their shape. The results of the model error analysis were applied to routine calculations of deposition in Europe. An error (coefficient of variation) of 20% for transfer coefficients throughout Europe yielded spatial variations in the order of a few tens to a few hundreds of km in computed deposition isolines of 2 and 5 g sulfur m−2a−1. 相似文献
4.
《Atmospheric environment (Oxford, England : 1994)》1999,33(27):4421-4430
The dry deposition of sulphur, nitrogen and base cations to a spruce stand was estimated during a five year period using a surrogate surface resembling needles, throughfall and bulk deposition measurements. The deposition was calculated from the ratio between the deposition of an ion and sodium on the surrogate surface and the net throughfall of sodium to the forest. The dry deposition represented a large fraction of the total atmospheric input of base cations. For Na+, Mg2+, Ca2+, and K+ they were 66, 67, 53 and 42%, respectively. The internal circulation was 95% of non-marine net throughfall fro K+ and 76% for Ca2+. The dry deposition of SO2 to the canopies regulates the internal circulation of Ca2+. The dry deposition of SO2 to the canopies regulates the internal circulation of Ca2+. The dry depositions of ammonium and nitrate are close to the net throughfall of Kjeldahl-N and nitrate, respectively. The obtained deposition velocities are comparable to other studies. The calculated dry deposition of ammonium was compared to the net throughfall of ammonium at three nearby forest stands receiving different ammonium amounts on the soils. No correlation to nitrogen level was found, but most ammonium was lost and converted to organic nitrogen in the canopies of the wettest forest stand. 相似文献
5.
《Atmospheric environment(England)》1985,19(11):1819-1827
A study of deposition velocities to snow was conducted during the 1982–1983 and 1983–1984 winters at the University of Michigan Biological Station in northern Michigan. Weekly measurements were made of dry deposition rates to snow and the atmospheric concentrations of the depositing species. SO2, with an average concentration of 2.2 ppb, was the dominant atmospheric sulfur containing species. NO2, with an average concentration of 1.8 ppb, was the dominant atmospheric nitrogenous species. NO−3 deposition was due primarily to HNO3, which averaged 0.2 ppb. The HNO3 deposition velocity averaged 1.4cm s−1. The SO2 deposition velocity varied with temperature, averaging 0.15 cm s−1 for samples with appreciable exposure time above − 3°C, and 0.06 cm s−1 for samples which remained below an ambient temperature of −3°C. Deposition velocities of Ca2+, Mg2+ , Na+, K+ and NH+4 were 2.1, 1.5, 0.44, 0.51 and 0.10cm s−1, respectively. The mass median diameters of these species were 4.4, 2.7, 1.8, 0.9 and 0.46 μm, respectively. 相似文献
6.
《Atmospheric environment(England)》1986,20(6):1171-1178
Wet and dry deposition were monitored at the University of Michigan Biological Station in rural northern Michigan for three winters. Dry deposition was measured by both the conventional bucket method and by measuring increases in concentration in exposed, elevated snow samples. Average results of the two methods were in reasonable agreement. The cumulative wet and dry deposition quantities are in good agreement with snowpack accumulations until the first thaw period. Dry deposition to snow accounts for less than 15% of the total H+, SO2−4, NO−3 and NH+4 and approximately 25% of the Ca 2+, Mg 2+, Na+, K+ and Cl− during an average precipitation year. Snowpack measurements were also made under deciduous and red pine canopies. Decreases in H+ and NO−3 were observed under the red pine canopy. 相似文献
7.
Jeffrey R. Brook Leiming Zhang Yifan Li David Johnson 《Atmospheric environment (Oxford, England : 1994)》1999,33(30):804
Numerical sensitivity tests and four months of complete model runs have been conducted for the Routine Deposition Model (RDM). The influence of individual model inputs on dry deposition velocity as a function of land-use category (LUC) and pollutant (SO2, O3, SO2−4 and HNO3) were examined over a realistic range of values for solar radiation, stability and wind speed. Spatial and temporal variations in RDM deposition velocity (Vd) during June – September 1996 time period generated using meteorological input from a mesoscale model run at 35 km resolution over north-eastern North America were also examined. Comparison of RDM Vd values to a variety of measurements of dry deposition velocities of SO2, O3, SO2−4 and NHO3 that have been reported in the literature demonstrated that RDM produces realistic results. Over northeastern NA RDM monthly averaged dry deposition velocities for SO2 vary from 0.2 to 3.0 cm s−1 with the highest deposition velocities over water surfaces. For O3, the monthly averaged dry deposition velocities are from 0.05 to 1.0 cm s−1 with the lowest values over water surfaces and the highest over forested areas. For HNO3, the monthly averaged dry deposition velocities have the range of 0.5 to 6 cm s−1, with the highest values for forested areas. For SO2−4, they range from 0.05–1.5 cm s−1, with the lowest values over water and the highest over forest. The monthly averaged dry deposition velocities for SO2 and O3 are higher in the growing season compared to the fall, but this behaviour is not apparent for HNO3 and sulphate. In the daytime, the hourly averaged dry deposition velocities for SO2, O3, SO2−4 and HNO3 are higher than that in the nighttime over most of the vegetated area. The diurnal variation is most evident for surfaces with large values for leaf area index (LAI), such as forests. Based on the results presented in this paper, it is concluded that RDM Vd values can be combined with measured air concentrations over hourly, daily or weekly periods to determine dry deposition amounts and with wet deposition measurements to provide seasonal estimates of total deposition and estimates of the relative importance of dry deposition. 相似文献
8.
Atmospheric deposition and canopy exchange processes in alpine forest ecosystems (northern Italy) 总被引:2,自引:0,他引:2
Raffaella Balestrini Antonio Tagliaferri 《Atmospheric environment (Oxford, England : 1994)》2001,35(36):1799
Throughfall and bulk precipitation chemistry were studied for five years (June 1994–May 1999) at two high elevation forest sites (Val Gerola and Val Masino) which were known to differ in terms of tree health, as assessed by live crown condition. The ion concentration of bulk precipitation samples did not differ significantly between sites, except for Mg2+, while the throughfall concentrations differed in the measured values of H+, N-NO3−, Cl−, Na+, K+, DOC and weak organic acids. The results of the application of the canopy exchange model indicated a higher contribution from the dry deposition of N-NO3−, N-NH4+ and H+ at Val Gerola, where the damage symptoms were more evident. In addition, the canopy leaching of Ca2+, K+ and weak organic acids were 47%, 21% and 27% higher at Val Gerola than at Val Masino. Annual SO42− deposition fluxes (21.3 kg ha−1 yr−1 at Val Masino and 23.6 kg ha−1 yr−1 at Val Gerola) were similar to those reported for moderately polluted European and U.S. sites. Annual N loads were 13.6 and 13.1 kg ha−1 yr−1 in the bulk input, and 15.0 and 18.0 kg ha−1 yr−1 in throughfall inputs, at Val Masino and Val Gerola, respectively. The contribution of the organic fraction to the total N atmospheric deposition load is significant, constituting 17% of the bulk flux and 40% of the throughfall flux. Measured nitrogen loads exceed the critical nutrient loads by several kg N ha−1 at both stations. In particular the nitrogen throughfall load at Val Gerola was about 3 times higher than the critical values. 相似文献
9.
K. Osada Y. Shido H. Iida M. Kido 《Atmospheric environment (Oxford, England : 1994)》2010,44(3):347-353
Atmospheric deposition is an important removal process of aerosol particles and gases from the atmosphere. To elucidate the relative contributions of wet and dry processes and in-cloud and below-cloud scavenging based on deposition amounts in winter at Mt. Tateyama, central Japan, we obtained daily samples (December, 2006–March, 2007) of size-segregated aerosol particles and precipitation at Senjyugahara (SJ; 475 m a.s.l.) and vertical samples of spring snow cover at Murododaira (MR, 2450 m a.s.l., 13 km distance from SJ) on the western flank of Mt. Tateyama. The NH4+ and nssSO42? in aerosols were mostly found in the fine fraction (<2 μm), although Na+, NO3?, and nssCa2+ were mainly detected in the coarse fraction (>2 μm). Average ionic concentrations (μg g?1) in precipitation at SJ were higher about 3.8 for Na+ and nssCa2+, 3.4 for NO3?, 3.7 for NH4+, 2.5 for nssSO42? than those at MR, whereas cumulative precipitation amounts at SJ and MR were, respectively, 84 and 175 cm of water equivalent. Wet and dry deposition amounts during the study period were estimated for sites using size-segregated aerosol data, winter averages of HNO3, NH3, and SO2 concentrations, and dry deposition velocities. Particle-dry deposition comprised about 3% (Na+) to 11% (NH4+) of the total deposition at MR. The maximum amounts of gas dry deposition were estimated, respectively, as 4, 13, and 3% of the total deposition at MR for NH4+, NO3?, and nssSO42?. The relative contributions of below-cloud scavenging (BCS) between MR and SJ were estimated as considering the wet only deposition amount at MR. Higher contributions of BCS were obtained for Na+ (56%) and nssCa2+ (45%), whereas BCSs for NH4+, NO3?, and nssSO42? were lower than 28%. Ionic constituents existing predominantly in the coarse fraction showed a large contribution of BCS. 相似文献
10.
《Atmospheric environment (Oxford, England : 1994)》2007,41(4):745-756
The contribution of dry deposition to the total atmospheric input of acidifying compounds and base cations is of overwhelming importance. Throughfall measurements provide an estimate of the total deposition to forest soils, including dry deposition, but some uncertainties, related to the canopy interaction processes, affect this approach. We compared the concentrations and the fluxes of the main ions determined in wet-only, bulk and throughfall samples collected at five forest sites in Italy. The contribution of coarse particles deposited onto the bulk samplers was of prime importance for base cations, representing on average from 16% to 46% of the bulk deposition. The extent of this dry deposition depended on some geographical features of the sites, such as the distance from the sea and the annual rainfall. The possibility of applying specific bulk/wet ratios to estimate the wet deposition proved to be limited by the temporal variability of these ratios, which must be considered together with the spatial variability. A direct comparison of the dry contribution deriving from the bulk–wet and the throughfall–wet demonstrated that an extensive natural surface (forest canopy) performs better than a small synthetic surface (funnel of the bulk sampler) in collecting dry deposition of SO42−, NO3− and Na+. The canopy exchange model was applied to both bulk and wet data to estimate the contribution of dry deposition to the total input of base cations, and the uncertainty associated to the model discussed. The exclusive use of bulk data led to a considerable underestimation of base cation dry deposition, which varies among the study sites. 相似文献
11.
Chemical characteristics of precipitation at metropolitan Newark in the US East Coast 总被引:5,自引:0,他引:5
To investigate the chemical characteristics of precipitation in the polluted coastal atmosphere, a total of 46 event-based precipitation samples were collected using a wet-only automatic precipitation collector from September 2006 to October 2007 at metropolitan Newark, New Jersey in the US East Coast. Samples were analyzed by ion chromatography for the concentrations of major inorganic ions (Cl−, NO3−, SO42−, F−, NH4+, Ca2+, Mg2+, Na+, K+) and organic acid species (CH3COO−, HCOO−, CH2(COO)22−, C2O42−). Selected trace metals (Sb, Pb, Al, V, Fe, Cr, Co, Ni, Cu, Zn, Cd) in samples were determined by ICPMS. Mass concentration results show that SO42− was the most dominant anion accounting for 51% of the total anions, controlling the acidity of the precipitation. NH4+ accounted for 48.6% of the total cations, dominating the precipitation neutralization. CH3COO− and HCOO− were the two dominant water-soluble organic acid species, accounting for 42% and 40% of the total organic acids analyzed, respectively. Al, Zn and Fe were the three major trace metals in precipitation, accounting for 34%, 27%, and 25% of the total mass of metals analyzed. The pH values in precipitation ranged from 4.4 to 4.9, indicating an acidic nature. Enrichment Factor (EF) Analysis showed that Na+, Cl−, Mg2+ and K+ in the precipitation were primarily of marine origin, while most of the Fe, Co and Al were from crust sources. Pb, V, Cr, Ni were moderately enriched with EFs ranging 43–410, while Zn, Sb, Cu, Cd and F− were highly enriched with EFs > 700, indicating significant anthropogenic influences. Factor analysis suggests 6 major sources contributing to the observed composition of precipitation at this location: (1) nitrogen-enriched soil, (2) secondary pollution processes, (3) marine sources, (4) incinerations, (5) oil combustions, and (6) malonate–vanadium enriched sources. To further explore the source–precipitation event relationships and seasonality, cluster analysis was performed for all precipitation events. Results show that about half of the precipitation events were characterized by mixed sources. Significant influences of nitrogen-enriched soil and marine sources were associated with precipitation events in spring and autumn, while secondary pollution processes, incineration and oil combustion contributed greatly in summer. 相似文献
12.
《Atmospheric environment(England)》1985,19(5):789-796
Wet and dry deposition as collected by a bucket were measured at two sites in southeastern Michigan for two years. The precipitation had an average pH of 4.27 and a SO2−4 to NO−3 ratio of 2.0. Particulate dry deposition velocities of 0.6 cm s−1 for SO2−4 and NO−3 and > 2 cm s−1 for Cl−, Ca2+, Mg2+,Na+ and K+ were calculated. The ambient particle composition, dry bucket collection and wet deposition were compared at two sites, one urban and the other rural. Higher ambient particle concentrations and dry deposition rates were measured at the urban site than the rural site, indicating the influence of local emissions. However, local emissions had no effect on the wet deposition concentrations. The influence of more distant source regions was examined by separating the precipitation events by wind direction. The events from the south and east had the highest SO2−4 to NO−3 ratios, which corresponded to the areas with the highest sulfur emissions. NO−3 showed no directional dependence.Wet deposition was examined for the effect of storm type and seasonal trends. Contrary to a recent study on Long Island, we found higher concentrations of H+, SO2−4 and NH+4 in winter rain compared to snow. The wet deposition concentrations of H+, SO2−4, and NH+4 were highest in the summer, while only Na+ and Cl− concentrations were highest in the winter, presumably due to winter road salting. The total deposition of acidic ions was highest in the summer and lowest in the winter, due both to lower concentrations and lower precipitation volumes in the winter. The dry deposition as collected by a bucket accounted for 1 % of total H+ deposition, 21 % of SO2−4 deposition, 27% of NO−3 deposition, 50% of Cl− deposition and 61 % of Ca2+ deposition. 相似文献
13.
Jeffrey R. Brook Leiming Zhang Franco Di-Giovanni Jacob Padro 《Atmospheric environment (Oxford, England : 1994)》1999,33(30):1
This paper describes the development of a detailed dry deposition model for routine computation of dry deposition velocities of SO2, O3, HNO3 and fine particle SO42− across much of North America. Four different dry deposition/surface exchange sub-models have been combined with the current Canadian weather forecast model (Global Environmental Multiscale model) with a 3 h time resolution and a horizontal spatial resolution of 35 km. The present model uses the US Geological Survey North American Land Cover Characteristics data to obtain fourteen different land use and five seasonal categories. The four sub-models used are a multi-layer model for gaseous species over taller canopy land-use types, a big-leaf model for gaseous species over lower canopies (including bare soil and water) and for HNO3 under all surface types and, two different models for SO42−, one for tall canopies and the other for short canopies. All necessary parameters for each sub-model, chemical species, land-use and seasonal categories have been selected from available data libraries or from the values reported in the literature. The purpose for developing this model (referred to as the Routine Deposition Model (RDM)), when coupled with air concentration data, is to provide estimates of seasonal dry deposition, which can be combined with wet deposition to produce total deposition estimates. Model theory is discussed in this paper and model sensitivity tests and results will be presented in a companion paper. 相似文献
14.
K. Treier K. Pajuste J. Frey 《Atmospheric environment (Oxford, England : 1994)》2004,38(40):7009-7019
Monthly and annual means of main anions (SO42−, NO3−, Cl−) and summed base cations (Ca2+, Mg2+, K+, Na+) in bulk precipitation were studied at 10 stations during an 8-year monitoring period. The data showed statistically significant decreasing trends in most cases. Average declines of mean annual volume-weighted concentrations for both anions and cations were about two-fold. Despite the decrease, the loads of S and cations are still relatively high in Estonia (about 4–14 kg S ha−1 and 0.6–1.2 keq ha−1, respectively) compared with the loads in Finland and Sweden. Estimated linear decline trends followed the same pattern as annually combusted oil shale from Estonian power plants and emissions of SO2 and fly ash. Recent trends in chemical composition of bulk precipitation at the monitoring stations reflected economic changes in Estonia as well as transboundary fluxes from neighbouring countries. 相似文献
15.
《Atmospheric environment (Oxford, England : 1994)》1999,33(26):4283-4290
Wind tunnel measurements of particle dry deposition to wavy and flat surfaces were made to estimate the enhancement of deposition rates due to waves on water surfaces. Measurements were made of 4.0 and 6.7 μm uranine particles at wind speeds of 5 and 10 m s−1 to sinusoidal waves with height to length ratios 2a/λ=0.1 and 0.03 and to flat surfaces. Results showed that deposition was greatest to the upslope portion of the wave, accounting for 40–45% of the total mass, followed by the trough (30%), downslope (15%), and crest (10–15%). These results generally agreed within experimental variability with modeling predictions (Zufall et al., 1999). Deposition was enhanced at the upslope due to the effects of particle interception and impaction on the wave. Total deposition to the wave surfaces was greater than deposition to the flat surface for a large majority of the cases. The average increase in deposition to both wave surfaces for both particle sizes and wind speeds over deposition to the flat surface was 80%. 相似文献
16.
《Atmospheric environment (Oxford, England : 1994)》2007,41(23):4931-4939
The current study uses resampling to investigate the impacts of cyclic seasonal behavior on 1- and 5-year period means composed from seasonal mean values in the presence of missing data. This is an empirical study using complete years of seasonal monitoring data collected in the eastern US and extracted from the clean air status and trends network (CASTNET) dry and the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) wet deposition data archives. Estimators of period means with missing seasonal data are determined using means of the non-missing values as estimates of the missing data. Estimates are evaluated in terms of 95% inclusion intervals (e.g., estimates are within ±X% of the true value ⩾95% of the time). For dry deposition, missing transition seasons (i.e., spring or fall) usually yield estimates of annual means that are within ±20% of the true annual mean ⩾95% of the time. Missing summers or winters usually have larger impacts on estimates of annual means of dry deposited species than missing transition seasons. A missing summer has the largest impact on estimates of annual means of dry deposition for all constituents, except SO2, where winter is especially important. For wet deposition, a missing season yields estimates of annual means that are within ±30% of the true annual mean ⩾95% of the time. A missing summer has the largest impact on estimates of annual means of wet deposition for all constituents, except NH4+, where spring and fall are important. A strategy requiring at least 3 years of seasonal representation for three seasons with the fourth season having at least two seasonal values, yields estimates of wet deposition that are within ±17% of the true 5-year means ⩾95% of the time for all species. Corresponding confidence statements for dry deposition results are considerably stronger, with estimates that are within ±10% of the true 5-year mean ⩾95% of the time. 相似文献
17.
A.M.M. Manders M. Schaap X. Querol M.F.M.A. Albert J. Vercauteren T.A.J. Kuhlbusch R. Hoogerbrugge 《Atmospheric environment (Oxford, England : 1994)》2010,44(20):2434-2442
The oceans are a major source for particles that play an important role in many atmospheric processes. In Europe sea salt may contribute significantly to particulate matter concentrations. We have compiled sodium concentration data as a tracer for sea salt for 89 sites in Europe to provide more insight in the distribution of sea salt across Europe. The annual average sea salt concentrations above land were estimated to range between 0.3 and almost 13 μg m?3. Maximum concentrations are found at the Irish coast. At coastal sites along the Atlantic and North Sea coast concentrations tend to be around 5 μg m?3. More inland locations up to about 300 km away from the coast tend to show concentrations between 2 and 5 μg m?3, whereas sites further away from the coast are characterized by lower concentrations. An analysis of the representativity of the data with respect to a long term average showed that the long average is associated with a standard deviation of around 15%. The compilation of observations provides an improved overview of sea salt concentrations in Europe as well as an improved basis for model validation. Verification of the results of the LOTOS-EUROS model learned that the model represents well the spatial variability of the observed sea salt concentrations very well. However, the absolute concentrations are significantly overestimated due to large uncertainties in the emission and dry deposition parameterizations. Using the high explained variability in the gradients across Europe, the bias-corrected modelled distribution serves as a best estimate of the sea salt distribution across Europe for 2005. 相似文献
18.
A series of experiments using bulk precipitation collectors of the type used in the UK precipitation chemistry network measured the amounts of NH4+, SO42− and other ions that could be washed from funnels (diameter 15 cm) exposed to a wide range of NH3 and SO2 concentrations over periods from hours to days. In dry conditions, the average deposition flux of NH3 was between 50 and 120 nmol NH4+ funnel−1 d−1 (0.1–0.3 kg N ha−1 yr−1), and was independent of the concentration of NH3. Dry deposition of NH3 to wet funnels at small NH3 concentrations was almost 5 times that to dry funnels under the same conditions (average 240 nmol funnel−1 d−1; 0.7 kg ha−1 yr−1), and increased with increasing NH3 concentrations. The amount of NH4+ ions remaining on the funnel surface was inversely proportional to the vapour pressure deficit during the experiment. This result was interpreted as a dependence on the duration of surface wetness, with greater deposition of NH4+ when evaporation rates of surface water were small.The amount of SO2 deposited on funnel surfaces was closely related to the amount of NH3 deposited, in both wet and dry conditions, but was not strongly correlated with the SO2 concentration. At low NH3 and SO2 concentrations the average deposition to dry funnels was 70 nmol SO42− funnel−1 d−1 (0.5 kg ha−1 yr−1), and to wet funnels was approximately 2.5 times larger. The results are interpreted in terms of the balance between the rate of evaporation of surface water, and the rate of oxidation of SO2, which leads to the ‘fixing’ of NH4+ ions on the surface as involatile salts.It is predicted that dry deposition of NH3 to funnel surfaces across the UK Secondary Network could account for as much as one-half of the measured bulk wet deposition at sites where wet deposition of NH4–N is small. The amount of dry deposition depends on how long and how often funnel surfaces are wetted by rain or dew, and on the air concentrations of NH3. These predictions are based on funnels being wetted only once per day. More frequent wetting would increase the contribution from dry deposition, and the consequent overestimate of wet deposition of NH4–N across the UK by using data obtained from bulk collectors. To some extent this overestimate may be offset by microbial degradation and loss of NH4–N in weekly bulk precipitation samples during collection and storage. 相似文献
19.
《Atmospheric environment (Oxford, England : 1994)》2001,35(34):5989-6002
Concentrations of major ions, SO42−, NO3−, Cl−, H+, Ca2+, K+, Mg2+, Ca2+ and conductivity were measured in approximately 300 daily, wet-only rain samples collected at a permanent rural station between 1993 and 1998. Concentrations of anthropogenic ions NH4+, SO42− and NO3− were among the highest values reported in whole EMEP network, suggesting that the Anatolian plateau is under strong influence of distant emission sources. Although transport of pollutants have significant influence on the chemical composition of precipitation, average pH of the rainwater is 6.2 due to extensive neutralization of acidity. Approximately 95% of the acidity in collected samples is neutralized, particularly in summer season. The neutralizing agents are primarily CaCO3 and NH3. Concentrations of crustal ions are higher in summer season due to enhanced resuspension of soil particles from dry surface soil. Concentrations of anthropogenic ions SO42− and NO3− do not change significantly between summer and winter due to higher intensity of rains in summer season. Although concentrations of ions measured in this study is among the highest reported in EMEP network, wet deposition fluxes are low compared to flux values reported for similar sites in Europe, due to low annual precipitation in the Anatolia. Wet deposition fluxes of all measured parameters are highly episodic. Source regions affecting chemical composition precipitation in the Central Anatolia is investigated using trajectory statistics. 相似文献
20.
《Atmospheric environment(England)》1989,23(12):2761-2766
Pine pollen concentrations in air at a semi-remote site in northern Wisconsin attained levels of 18 and 25 μ m−3 in late May and early June of 1979 and 1981, respectively. The upper and lower limits for the deposition velocity of pine pollen at this site are approximately 30 and 1.3 cm s−1, respectively. Consequently, the average annual pine pollen flux at this location for 1979 and 1981 was between 8.0 and 0.35 g m−2. Deposition of total phosphorus and organic C by pollen dispersal are about 5–100% and 11–240%, respectively, of the measured bulk atmospheric loading rate in the region. Pine pollen fluxes of water-extractable K are about 10–230% of the average annual wet deposition, while the fluxes of waterextractable NO3− and SO4−2 by pollen appear to be negligible in comparison to the total atmospheric deposition (wet plus dry deposition) by other particles. The annual pine pollen flux to Crystal Lake, an oligotrophic seepage lake in the region, was estimated to be 6.5 g m−2 during 1981. The deposition of total P by pollen to this lake was 5.8 kg a−1, which is 45 % of the external input of total phosphorus. About 60% of the total P in samples of Pinus strobus and P. resinosa was dissolved reactive P, which is readily available for plant uptake. Because P is the limiting nutrient for many lacustrine systems and pine pollen dispersal coincides with the period of phytoplankton blooms in temperate-region lakes, this episodic input of P may represent an important source for seepage lakes whose external inputs are dominated by atmospheric deposition. 相似文献