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1.
Dry deposition of ammonia,nitric acid,ammonium, and nitrate to alpine tundra at Niwot Ridge,Colorado
《Atmospheric environment (Oxford, England : 1994)》2001,35(6):1105-1109
Micrometeorological measurements and ambient air samples, analyzed for concentrations of NH3, HNO3, NH4+, and NO3−, were collected at an alpine tundra site on Niwot Ridge, Colorado. The measured concentrations were extremely low and ranged between 5 and 70 ng N m−3. Dry deposition fluxes of these atmospheric species were calculated using the micrometeorological gradient method. The calculated mean flux for NH3 indicates a net deposition to the surface and indicates that NH3 contributed significantly to the total N deposition to the tundra during the August–September measurement period. Our pre-measurement estimate of the compensation point for NH3 in air above the tundra was 100–200 ng N m−3; thus, a net emission of NH3 was expected given the low ambient concentrations of NH3 observed. Based on our results, however, the NH3 compensation point at this alpine tundra site appears to have been at or below about 20 ng N m−3. Large deposition velocities (>2 cm s−1) were determined for nitrate and ammonium and may result from reactions with surface-derived aerosols. 相似文献
2.
《Atmospheric environment (Oxford, England : 1994)》2001,35(13):2405-2415
Deposition of nitric acid (HNO3) vapor to soils has been evaluated in three experimental settings: (1) continuously stirred tank reactors with the pollutant added to clean air, (2) open-top chambers at high ambient levels of pollution with and without filtration reducing particulate nitrate levels, (3) two field sites with high or low pollution loads in the coastal sage plant community of southern California. The results from experiment (1) indicated that the amount of extractable NO3− from isolated sand, silt and clay fractions increased with atmospheric concentration and duration of exposure. After 32 days, the highest absorption of HNO3 was determined for clay, followed by silt and sand. While the sand and silt fractions showed a tendency to saturate, the clay samples did not after 32 days of exposure under highly polluted conditions. Absorption of HNO3 occurred mainly in the top 1 mm layer of the soil samples and the presence of water increased HNO3 absorption by about 2-fold. Experiment (2) indicated that the presence of coarse particulate NO3− could effectively block absorption sites of soils for HNO3 vapor. Experiment (3) showed that soil samples collected from open sites had about 2.5 more extractable NO3− as compared to samples collected from beneath shrub canopies. The difference in NO3− occurred only in the upper 1–2 cm as no significant differences in NO3− concentrations were found in the 2–5 cm soil layers. Extractable NO3− from surface soils collected from a low-pollution site ranged between 1 and 8 μg NO3–N g−1, compared to a maximum of 42 μg NO3–N g−1 for soils collected from a highly polluted site. Highly significant relationship between HNO3 vapor doses and its accumulation in the upper layers of soils indicates that carefully prepared soil samples (especially clay fraction) may be useful as passive samplers for evaluation of ambient concentrations of HNO3 vapor. 相似文献
3.
《Atmospheric environment (Oxford, England : 1994)》2001,35(5):975-983
In the United States, fertilized corn fields, which make up approximately 5% of the total land area, account for approximately 45% of total soil NOx emissions. Leaf chamber measurements were conducted of NO and NO2 fluxes between individual corn leaves and the atmosphere in (1) field-grown plants near Champaign, IL (USA) in order to assess the potential role of corn canopies in mitigating soil–NOx emissions to the atmosphere, and (2) greenhouse-grown plants in order to study the influence of various environmental variables and physiological factors on the dynamics of NO2 flux. In field-grown plants, fluxes of NO were small and inconsistent from plant to plant. At ambient NO concentrations between 0.1 and 0.3 ppbv, average fluxes were zero. At ambient NO concentrations above 1 ppbv, NO uptake occurred, but fluxes were so small (14.3±0.0 pmol m−2 s−1) as to be insignificant in the NOx inventory for this site. In field-grown plants, NO2 was emitted to the atmosphere at ambient NO2 concentrations below 0.9 ppbv (the NO2 compensation point), with the highest rate of emission being 50 pmol m−2 s−1 at 0.2 ppbv. NO2 was assimilated by corn leaves at ambient NO2 concentrations above 0.9 ppbv, with the maximum observed uptake rate being 643 pmol m−2 s−1 at 6 ppbv. When fluxes above 0.9 ppbv are standardized for ambient NO2 concentration, the resultant deposition velocity was 1.2±0.1 mm s−1. When scaled to the entire corn canopy, NO2 uptake rates can be estimated to be as much as 27% of the soil-emitted NOx. In greenhouse-grown and field-grown leaves, NO2 deposition velocity was dependent on incident photosynthetic photon flux density (PPFD; 400–700 nm), whether measured above or below the NO2 compensation point. The shape of the PPFD dependence, and its response to ambient humidity in an experiment with greenhouse-grown plants, led to the conclusion that stomatal conductance is a primary determinant of the PPFD response. However, in field-grown leaves, measured NO2 deposition velocities were always lower than those predicted by a model solely dependent on stomatal conductance. It is concluded that NO2 uptake rate is highest when N availability is highest, not when the leaf deficit for N is highest. It is also concluded that the primary limitations to leaf-level NO2 uptake concern both stomatal and mesophyll components. 相似文献
4.
《Atmospheric environment (Oxford, England : 1994)》1999,33(19):3143-3152
The annular denuder system (ADS) was used to characterize seasonal variations of acidic air pollutants in Seoul, South Korea. Fifty- four 24 h samples were collected over four seasons from October 1996 to September 1997. The annual mean concentrations of HNO3, HNO2, SO2 and NH3 in the gas phase were 1.09, 4.51, 17.3 and 4.34 μg m-3, respectively. The annual mean concentrations of PM2.5(dp≤2.5 μm in aerodynamic diameter, 50% cutoff), SO2-4, NO-3 and NH+4 in the particulate phase were 56.9, 8.70, 5.97 and 4.19 μg m-3, respectively. All chemical species monitored from this study showed statistical seasonal variations. Nitric acid (HNO3) and ammonia (NH3) exhibited substantially higher concentrations during the summer, while nitrous acid (HNO2) and sulfur dioxide(SO2) were higher during the winter. Concentrations of PM2.5, SO2-4, NO-3 and NH+4 in the particulate phase were higher during the winter months. SO2-4, NO-3 and NH+4 accounted for 26–38% of PM2.5. High correlations were found among PM2.5, SO2-4, NO-3 and NH+4. The mean H+ concentration measured only in the fall was 5.19 nmole m-3. 相似文献
5.
《Atmospheric environment (Oxford, England : 1994)》1999,33(11):1757-1766
Results from a 1-year daily rainwater sampling program, employing both wet and bulk deposition samplers with replicate samples, from 1994 to 1995 in Hong Kong are presented and analysed. Analyte concentrations were found to vary over a wide range of several orders of magnitude, with [H+] for example, from 0.16 to 208.9 μeq dm-3. Diurnal pH values less than 3.83 were measured on five occasions. A significant correlation between pH and lognormal windspeed has been found. This is taken to indicate the minor importance of long-range transport in determining rainwater acidity, since local pollutant emissions accumulate and react under conditions of atmospheric stability in the sub-tropical climate. The H+ wet deposition flux onto a polythene surface was 90 meq m-2 yr-1 during 1994–1995 at City University. Dry deposition exerts a neutralizing influence upon the acidity from this wet deposition. Although paired t-tests indicated significant differences between the bulk versus wet deposition datasets for cations, but not anions, the dataset means consequently showed such large standard deviations that t-tests indicated no significant differences. In rainwater, the charges from SO2-4 and NO-3 anions seldom balance the proton charges, implying that they are also derived from solubilization of primary and secondary airborne Ca2+, Mg2+ and NH+4 particulate matter in rainwater. Use of the [SO2-4]/[NO-3] ratios in rainwater in fingerprinting pollutant origins has drawbacks, but is generally indicative of a predominantly regional contribution of these secondary pollutants to rainwater. Bulk deposition pH in Hong Kong would be in the region of 4.1 if basic Ca2+ compounds alone did not neutralize acidity. The regional rainout pH, inferred after exhaustive below-cloud scavenging, is about 5. The temporal trends in Hong Kong rainwater acidity are blurred. 相似文献
6.
《Atmospheric environment (Oxford, England : 1994)》2001,35(6):1039-1051
We reconstructed the historical trends in atmospheric deposition of nitrogen to Cape Cod, Massachusetts, from 1910 to 1995 by compiling data from literature sources, and adjusting the data for geographical and methodological differences. The reconstructed data suggest that NO3-N wet deposition to this region increased from a low of 0.9 kg N ha−1 yr−1 in 1925 to a high of approximately 4 kg N ha−1 yr−1 around 1980. The trend in NO3-N deposition has remained since the early 1980s at around 3.6 kg N ha−1 yr−1. In contrast, NH4-N wet deposition decreased from more than 4 kg N ha−1 yr−1 in the mid 1920s to about 1.5 kg N ha−1 yr−1 from the late-1940s until today. Emissions of NOx-N in the Cape Cod airshed increased at a rate of 2.1 kg N ha−1 per decade since 1910, a rate that is an order of magnitude higher than NO3-N deposition. Estimates of NH3 emissions to the northeast United States and Canada have decreased slightly throughout the century, but the decrease in reconstructed N-NH4+ deposition rates does not parallel emissions estimates. The trend in reconstructed total nitrogen deposition suggests an overall increase through the century at a rate of 0.26 kg N ha−1 per decade. This overall increase in deposition may expose coastal forests to rates of nitrogen addition that, if exceeded, could induce nitrogen saturation and increase nitrogen loads to adjoining estuaries. 相似文献
7.
《Atmospheric environment (Oxford, England : 1994)》2007,41(22):4766-4772
Static chamber method was adopted to measure the surface exchanges of NO and NO2 between three kinds of agricultural lands and the atmosphere during spring–summer period in the Yangtze Delta, China. The average NO fluxes were 20.9, 27.4 and 21.4 ng N m−2 s−1, respectively, for cabbage (CA, cultivation of celery occurred along with cabbage), potato (PO) and soybean (SY) fields. The average NO2 fluxes were −1.12, 0.93 and −0.68 ng N m−2 s−1, respectively, for the cabbage, potato and soybean fields. Apparently, negative linear correlation was found between the NO2 fluxes from the CK plot (tilled conventionally but did not cultivate any seeds) and its ambient concentrations, and the compensation point was calculated to be 0.92 ppbv. The total NO emission from the vegetable lands and SY land in this region during spring–summer period was roughly estimated to be 15.9 Gg N, which accounted for about 11.2% of the estimated value of total NO emissions in the July of 1999 from Chinese agricultural fields. 相似文献
8.
Oliver V. Rattigan H. Dirk Felton Min-Suk Bae James J. Schwab Kenneth L. Demerjian 《Atmospheric environment (Oxford, England : 1994)》2010,44(16):2043-2053
Multi-year hourly measurements of PM2.5 elemental carbon (EC) and organic carbon (OC) from a site in the South Bronx, New York were used to examine diurnal, day of week and seasonal patterns. The hourly carbon measurements also provided temporally resolved information on sporadic EC spikes observed predominantly in winter. Furthermore, hourly EC and OC data were used to provide information on secondary organic aerosol formation. Average monthly EC concentrations ranged from 0.5 to 1.4 μg m?3 with peak hourly values of several μg m?3 typically observed from November to March. Mean EC concentrations were lower on weekends (approximately 27% lower on Saturday and 38% lower on Sunday) than on weekdays (Monday to Friday). The weekday/weekend difference was more pronounced during summer months and less noticeable during winter. Throughout the year EC exhibited a similar diurnal pattern to NOx showing a pronounced peak during the morning commute period (7–10 AM EST). These patterns suggest that EC was impacted by local mobile emissions and in addition by emissions from space heating sources during winter months. Although EC was highly correlated with black carbon (BC) there was a pronounced seasonal BC/EC gradient with summer BC concentrations approximately a factor of 2 higher than EC. Average monthly OC concentrations ranged from 1.0 to 4.1 μg m?3 with maximum hourly concentrations of 7–11 μg m?3 predominantly in summer or winter months. OC concentrations generally correlated with PM2.5 total mass and aerosol sulfate and with NOx during winter months. OC showed no particular day of week pattern. The OC diurnal pattern was typically different than EC except in winter when OC tracked EC and NOx indicating local primary emissions contributed significantly to OC during winter at the urban location. On average secondary organic aerosol was estimated to account for 40–50% of OC during winter and up to 63–73% during summer months. 相似文献
9.
Silvano Fares Jeong-Hoo Park Elena Ormeno Drew R. Gentner Megan McKay Francesco Loreto John Karlik Allen H. Goldstein 《Atmospheric environment (Oxford, England : 1994)》2010,44(28):3404-3412
The Citrus genus includes a large number of species and varieties widely cultivated in the Central Valley of California and in many other countries having similar Mediterranean climates. In the summer, orchards in California experience high levels of tropospheric ozone, formed by reactions of volatile organic compounds (VOC) with oxides of nitrogen (NOx). Citrus trees may improve air quality in the orchard environment by taking up ozone through stomatal and non-stomatal mechanisms, but they may ultimately be detrimental to regional air quality by emitting biogenic VOC (BVOC) that oxidize to form ozone and secondary organic aerosol downwind of the site of emission. BVOC also play a key role in removing ozone through gas-phase chemical reactions in the intercellular spaces of the leaves and in ambient air outside the plants. Ozone is known to oxidize leaf tissues after entering stomata, resulting in decreased carbon assimilation and crop yield. To characterize ozone deposition and BVOC emissions for lemon (Citrus limon), mandarin (Citrus reticulata), and orange (Citrus sinensis), we designed branch enclosures that allowed direct measurement of fluxes under different physiological conditions in a controlled greenhouse environment. Average ozone uptake was up to 11 nmol s?1 m?2 of leaf. At low concentrations of ozone (40 ppb), measured ozone deposition was higher than expected ozone deposition modeled on the basis of stomatal aperture and ozone concentration. Our results were in better agreement with modeled values when we included non-stomatal ozone loss by reaction with gas-phase BVOC emitted from the citrus plants. At high ozone concentrations (160 ppb), the measured ozone deposition was lower than modeled, and we speculate that this indicates ozone accumulation in the leaf mesophyll. 相似文献
10.
《Atmospheric environment (Oxford, England : 1994)》1999,33(23):3813-3820
Ozone was measured in six- and NOx in five sampling periods in 1996–97, mostly during summer, at a 1070 m altitude site in northern Peloponnese. Mean values in each sampling period ranged from 43–48 ppb exceeding the European Union 24 h plant protection standard. The background ozone concentration of 43 ppb derived from the correlation of ozone with NO′x also exceeded the EU plant protection standard. Ozone exhibited maxima in the afternoon and minima during the night; in certain 24–48 h periods, however, the ozone concentrations remained practically constant; in these short periods air mass back trajectories indicated air masses which originated in north Africa. NO′x concentrations had maximum of 24 h around noon. Their mean concentrations ranged from 0.5–0.7 ppb, smaller than respective concentrations in north-central Europe. 相似文献
11.
《Atmospheric environment (Oxford, England : 1994)》2002,36(4):619-628
A method is developed to estimate wet deposition of nitrogen in a 11×14 km (0.125°Lon.×0.125°Lat.) grid scale using the precipitation chemistry monitored data at 10 sites scattered over South Korea supplemented by the routinely available precipitation rate data at 65 sites and the estimated emissions of NO2 and NH3 at each precipitation monitoring site. This approach takes into account the contributions of local NO2 and NH3 emissions and precipitation rates on wet deposition of nitrogen. Wet deposition of nitrogen estimated by optimum regression equations for NO3− and NH4+ derived from annual total monitored wet deposition and that of emissions of NO2 and NH3 is incorporated to normalize wet deposition of nitrogen at each precipitation rate class, which is divided into 6 classes. The optimum regression equations for the estimation of wet deposition of nitrogen at precipitation monitoring sites are developed using the normalized wet deposition of nitrogen and the precipitation rate at 10 precipitation chemistry monitoring sites. The estimated average annual total wet depositions of NO3− and NH4+ are found to be 260 and 500 eq ha−1 yr−1 with the maximum values of 400 and 930 eq ha−1 yr−1, respectively. The annual mean total wet deposition of nitrogen is found to be about 760 eq ha−1 yr−1, of which more than 65% is contributed by wet deposition of ammonium while, the emission of NH3 is about half of that of NO2, suggesting the importance of NH3 emission for wet deposition of nitrogen in South Korea. 相似文献
12.
Zhao-Yang Meng Xiao-Bin Xu Tao Wang Xing-Ying Zhang Xiao-Lan Yu Shu-Feng Wang Wei-Li Lin Yi-Zhen Chen Yi-An Jiang Xing-Qin An 《Atmospheric environment (Oxford, England : 1994)》2010,44(21-22):2625-2631
We present two years (January 2007–December 2008) of atmospheric SO2, NO2 and NH3 measurements from ten background or rural sites in nine provinces in China. The measurements were made on a monthly basis using passive samplers under careful quality control. The results show large geographical and seasonal variations in the concentrations of these gases. The mean SO2 concentration varied from 0.7 ± 0.4 ppb at Waliguan on Qinghai Plateau to 67.3 ± 31.1 ppb at Kaili in Guizhou province. The mean NO2 concentration ranged from 0.6 ± 0.4 ppb at Waliguan to 23.9 ± 6.9 ppb at Houma in southern Shanxi. The mean NH3 concentration ranged from 2.8 ± 3.0 ppb at Shangdianzi in northeastern Beijing to 13.7 ± 8.4 ppb at Houma. At most sites, SO2 and NO2 peaked in winter and reached minima in summer, while NH3 showed maximum values in summer and lower values in cold seasons. On the whole, the geographical distributions of the observed gas concentrations are consistent with those of emissions. The ground measurements of SO2 and NO2 are contrasted to the SCIAMACHY SO2 and OMI NO2 tropospheric columns, respectively. Although the satellite data can capture the main features of emissions and concentrations of SO2, they do not reflect the variations of SO2 in the surface layer. The situation is better for the case of NO2. The OMI NO2 columns capture the geographical differences in the ground NO2 and correlate fairly well with the ground levels of NO2 at six of the ten sites. 相似文献
13.
Gui-Peng Yang Hong-Hai Zhang Lu-Ping Su Li-Min Zhou 《Atmospheric environment (Oxford, England : 1994)》2009,43(13):2196-2203
Seawater, atmospheric dimethylsulfide (DMS) and aerosol compounds, potentially linked with DMS oxidation, such as methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO42?) were determined in the North Yellow Sea, China during July–August, 2006. The concentrations of seawater and atmospheric DMS ranged from 2.01 to 11.79 nmol l?1 and from 1.68 to 8.26 nmol m?3, with average values of 6.20 nmol l?1 and 5.01 nmol m?3, respectively. Owing to the appreciable concentration gradient, DMS accumulated in the surface water was transferred into the atmosphere, leading to a net sea-to-air flux of 6.87 μmol m?2 d?1 during summer. In the surface seawater, high DMS values corresponded well with the concurrent increases in chlorophyll a levels and a significant correlation was observed between integrated DMS and chlorophyll a concentrations. In addition, the concentrations of MSA and nss-SO42? measured in the aerosol samples ranged from 0.012 to 0.079 μg m?3 and from 3.82 to 11.72 μg m?3, with average values of 0.039 and 7.40 μg m?3, respectively. Based on the observed MSA, nss-SO42? and their ratio, the relative biogenic sulfur contribution was estimated to range from 1.2% to 11.5%, implying the major contribution of anthropogenic source to sulfur budget in the study area. 相似文献
14.
《Atmospheric environment (Oxford, England : 1994)》2004,38(10):1403-1415
Size-resolved fog drop chemical composition measurements were obtained during a radiation fog campaign near Davis, California in December 1998/January 1999 (reported in Reilly et al., Atmos. Environ. 35(33) (2001) 5717; Moore et al., Atmos. Environ. this issue). Here we explore how knowledge of this size-dependent drop composition—particularly from the newly developed Colorado State University 5-Stage cloud water collector—helps to explain additional observations in the fog environment. Size-resolved aerosol measurements before and after fog events indicate relative depletion of large (>2 μm in diameter) particles during fog accompanied by a relative increase in smaller aerosol particle concentrations. Fog equivalent air concentrations suggest that entrainment of additional particles and in-fog sedimentation contributed to observed changes in the aerosol size distribution. Calculated deposition velocities indicate that sedimentation was an important atmospheric removal mechanism for some species. For example, nitrite typically has a larger net deposition velocity than water and its mass is found preferentially in the largest drops most likely to sediment rapidly. Gas–liquid equilibria in fog for NO3−/HNO3, NH4+/NH3, and NO2−/HONO were examined. While these systems appear to be close to equilibrium or relative equilibrium during many time periods, divergences are observed, particularly for low liquid water content (<0.1 g m−3) fogs and in different drop sizes. Knowledge of the drop size-dependent composition provided additional data useful to the interpretation of these deviations. The results suggest that data from multi-stage cloud water collectors are useful to understanding fog processes as many depend upon drop size. 相似文献
15.
《Atmospheric environment (Oxford, England : 1994)》1999,33(21):3515-3529
Dry deposition of sulphur is estimated in three climatic regions of Mpumalanga, South Africa, using the inferential method. Data from June 1996 to May 1997 are used at Elandsfontein and Palmer on the industrialised highveld, as well as data from two-week monitoring campaigns in the late-winter and in summer at Blyde on the eastern escarpment and at Skukuza in the lowveld. Total dry deposition rates for sulphur range across the Mpumalanga highveld from 13.1 kg ha-1 a-1 at Elandsfontein to 3.1 kg ha-1 a-1 at Palmer, are associated with the strong SO2 gradient between the two stations and are attributed mostly to dry deposition of sulphur from SO2. The deposition flux varies less from Palmer eastward over the escarpment and the lowveld and ranges from 3.9 kg S ha-1 a-1 at Blyde to 3.3 kg S ha-1 a-1 at Skukuza. A weak seasonal variation in sulphur dry deposition flux occurs on the central highveld with the maximum in summer and the minimum in winter. Conversely, the maximum sulphur dry deposition on the periphery of the highveld, the escarpment and in the lowveld occurs in winter with the minimum in summer. More than 80% of the dry deposition of sulphur in Mpumalanga occurs during daytime in all seasons. 相似文献
16.
《Atmospheric environment (Oxford, England : 1994)》2001,35(27):4617-4628
We have developed a modelling system for predicting the traffic volumes, emissions from stationary and vehicular sources, and atmospheric dispersion of pollution in an urban area. This paper describes a comparison of the NOx and NO2 concentrations predicted using this modelling system with the results of an urban air quality monitoring network. We performed a statistical analysis to determine the agreement between predicted and measured hourly time series of concentrations at four permanently located and three mobile monitoring stations in the Helsinki Metropolitan Area in 1996–1997 (at a total of ten urban and suburban measurement locations). At the stations considered, the so-called index of agreement values of the predicted and measured time series of the NO2 concentrations vary between 0.65 and 0.82, while the fractional bias values range from −0.29 to +0.26. In comparison with corresponding results presented in the literature, the agreement between the measured and predicted datasets is good, as indicated by these statistical parameters. The seasonal variations of the NO2 concentrations were analysed in terms of the relevant meteorological parameters. We also analysed the difference between model predictions and measured data diagnostically, in terms of meteorological parameters, including wind speed and direction (the latter separately for two wind speed classes), atmospheric stability and ambient temperature, at two monitoring stations in central Helsinki. The modelling system tends to overpredict the measured NO2 concentrations both at the highest (u⩾6 m s−1) and at the lowest wind speeds (u<2 m s−1). For higher wind speeds, the modelling system overpredicts the measured NO2 concentrations in certain wind direction intervals; specific ranges were found for both monitoring stations considered. The modelling system tends to underpredict the measured concentrations in convective atmospheric conditions, and overpredict in stable conditions. The possible physico-chemical reasons for these differences are discussed. 相似文献
17.
László Bencs Agnieszka Krata Benjamin Horemans Anna J. Buczyńska Alin C. Dirtu Ana F.L. Godoi Ricardo H.M. Godoi Sanja Potgieter-Vermaak René Van Grieken 《Atmospheric environment (Oxford, England : 1994)》2009,43(24):3786-3798
Daily and seasonal variations in dry and wet atmospheric nitrogen fluxes have been studied during four campaigns between 2004 and 2006 at a coastal site of the Southern North Sea at De Haan (Belgium) located at coordinates of 51.1723° N and 3.0369° E. Concentrations of inorganic N-compounds were determined in the gaseous phase, size-segregated aerosol (coarse, medium, and fine), and rainwater samples. Dissolved organic nitrogen (DON) was quantified in rainwater. The daily variations in N-fluxes of compounds were evaluated with air-mass backward trajectories, classified into the main air-masses arriving at the sampling site (i.e., continental, North Sea, and Atlantic/UK/Channel).The three, non-episodic campaigns showed broadly consistent fluxes, but during the late summer campaign exceptionally high episodic N-deposition was observed. The average dry and wet fluxes for non-episodic campaigns amounted to 2.6 and 4.0 mg N m?2 d?1, respectively, whereas during the episodic late summer period these fluxes were as high as 5.2 and 6.2 mg N m?2 d?1, respectively.Non-episodic seasons/campaigns experienced average aerosol fluxes of 0.9–1.4 mg N m?2 d?1. Generally, the contribution of aerosol NH4+ was more significant in the medium and fine particulate fractions than that of aerosol NO3?, whereas the latter contributed more in the coarse fraction, especially in continental air-masses. During the dry mid-summer campaign, the DON contributed considerably (~15%) to the total N-budget.Exceptionally high episodic aerosol-N inputs have been observed for the late summer campaign, with especially high deposition rates of 3.6 and 2.9 mg N m?2 d?1 for Atlantic/UK/Channel and North Sea-continental (mixed) air-masses, respectively. During this pollution episode, the flux of NH4+ was dominating in each aerosol fraction/air-mass, except for coarse continental aerosols. High deposition of gaseous-N was also observed in this campaign with an average total N-flux of 2–2.5-times higher than in other campaigns. 相似文献
18.
《Atmospheric environment (Oxford, England : 1994)》2005,39(37):7095-7105
Potassium carbonate sulfation plates, monitored monthly for 11 years from 48 sites in 11 cities in Gansu Province, China, provide a crude estimate of cumulative SO2 dry depositions. Measured SO2 dry deposition rates were 1.6–472 mg m−2 day−1 and had seasonal variations with maxima in winter and minima mainly during summer as a result of higher winter and lower summer SO2 concentrations. The 11-year monthly average SO2 dry deposition rates are 23.2–248.97 and 11.7–175.6 mg m−2 day−1 in the eleven cities in winter and summer, respectively. A monthly average SO2 deposition velocity was also estimated from 0.06 to 9.72 cm s−2 in the 11 cities studied with a 11-year average maximum value of about 1.1–2.7 cm s−2 in April and July and a 11-year average minimum value of about 0.2–1.0 cm s−1 in January. The SO2 dry deposition velocity also exhibits an increasing with wind speed in basins of less than 500 mm annual precipitation. In contrast, due to influences of the relative humidity in valleys of more than 500 mm annual precipitation, it shows a decreasing trend with wind speed increasing. 相似文献
19.
《Atmospheric environment (Oxford, England : 1994)》2007,41(32):6909-6915
Altitude profiles of the mass concentrations of aerosol black carbon (BC) and composite aerosols were obtained from the collocated measurements of these quantities onboard an aircraft, over the urban area of Kanpur, in the Ganga basin of northern India during summer, for the first time in India. The enhancement in the mean BC concentration was observed at ∼1200 m in the summer, but the vertical gradient of BC concentration is less than the standard deviation at that altitude. The difference in the BC altitude profile and columnar concentration in the winter and summer is attributed to the enhanced turbulent mixing within the boundary layer in summer. This effect is more conspicuous with BC than the composite aerosols, resulting in an increase in the BC mass fraction (FBC) at higher levels in summer. This high BC fraction results in an increase in the lower atmospheric heating rate in both the forenoon, FN and afternoon, AN, but with contrasting altitude profile. The FN profile shows fluctuating trend with highest value (2.1 K day−1) at 300 m and a secondary peak at 1200 m altitudes, whereas the AN profile shows increasing trend with highest value (1.82 K day−1) at 1200 m altitude. 相似文献
20.
《Atmospheric environment (Oxford, England : 1994)》2007,41(2):394-406
During the course of one year (March 2004–March 2005), PM2.5 particulate nitrate concentrations were semi-continuously measured every 10 min at a Madrid suburban site using the Rupprecht and Patashnick Series 8400N Ambient Particulate Nitrate Monitor (8400N). Gaseous pollutants (NO, NO2, O3, HCHO, HNO2) were simultaneously measured with a DOAS spectrometer (OPSIS AR-500) and complementary meteorological information was obtained by a permanent tower. The particulate nitrate concentrations ranged from the instrumental detection limit of around 0.2 μg m−3, up to a maximum of about 25 μg m−3. The minimum monthly average was reached during August (0.32 μg m−3) and the maximum during November (3.0 μg m−3). Due to the semi-volatile nature of ammonium nitrate, peaks were hardly present during summer air pollution episodes. A typical pattern during days with low dispersive conditions was characterized by a steep rise of particulate nitrate in the morning, reaching maximum values between 9 and 14 UTC, followed by a decrease during the evening. On some occasions a light increase was observed at nighttime. During spring episodes, brief diurnal nitrate peaks were recorded, while during the autumn and winter episodes, later and broader nitrate peaks were registered. Analysis of particulate nitrate and related gaseous species indicated the photo-chemical origin of the morning maxima, delayed with respect to NO and closely associated with secondary NO2 maximum values. The reverse evolution of nitrate and nitrous acid was observed after sunrise, suggesting a major contribution from HNO2 photolysis to OH formation at this time of the day, which would rapidly produce nitrate in both gaseous and particulate phase. Some nocturnal nitrate maxima appeared under high humidity conditions, and a discussion about their origin involving different possible mechanisms is presented, i.e. the possibility that these nocturnal maximum values could be related to the heterogeneous formation of nitrous and nitric acid by the hydrolysis of NO2 on wet aerosols. 相似文献