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1.
Concurrent measurements of the surface energy balance components (net radiation, heat storage, and sensible and latent heat fluxes) were made in three communities (open water, Phragmites australis, Scirpus acutus) in a wetland in north-central Nebraska, U.S.A., during May-October, 1994. The Bowen ratio – energy balance method was used to calculate latent and sensible heat fluxes. This paper presents results from the open water area. The heat stored in water (G) was found to play a major role in the energy exchange over the water surface. During daytime, G consumed 45–60% of R n , the net radiation (seasonally averaged daytime G was about 127 W m–2). At night, G was a significant source of energy (seasonally averaged nighttime G was about -135 Wm–). The diurnal pattern of latent heat flux ( E) did not follow that of R n . On some days, E was near zero during midday periods with large R n . The diurnal variability in E seemed to be significantly affected by temperature inversions formed over the cool water surface. The daily evaporation rate (E) ranged from 2 to 8 mm during the measurement period, and was generally between 70 and 135% of the equilibrium rate.  相似文献   

2.
Further laboratory studies of emission by O(1 S) and by O2 A 3 u + ,A3 u andc 1 u – in the oxygen afterglow lead to the conclusion that Barth's mechanism for the excitation of the auroral green line O 2 * +O(3P=O2+O(1S)–(1) is correct and that levelsv=6 and 7 of O2 A 3 u + are Barth precursors. The value ofk 1=7×10–11 cm3 s–1 deduced for these levels is shown to be in fair agreement with atmospheric measurements.  相似文献   

3.
Eddy correlation equipment was used to measure mass and energy fluxes over a soybean crop. A rapid response CO2 sensor, a drag anemometer, a Lyman-alpha hygrometer and a fine wire thermocouple were used to sense the fluctuating quantities.Diurnal fluxes of sensible heat, latent heat and CO2 were calculated from these data. Energy budget closure was obtained by summing the sensible and latent heat fluxes determined by eddy correlation which balanced the sum of net radiation and soil heat flux. Peak daytime CO2 fluxes were near 1.0 mg m–2 (ground area) s–1.The eddy correlation technique was also employed in this study to measure nocturnal CO2 fluxes caused by respiration from plants, soil, and roots. These CO2 fluxes ranged from - 0.1 to - 0.25 mg m–2s–1.From the data collected over mature soybeans, a relationship between CO2 flux and photosynthetically active radiation (PAR) was developed. The crop did not appear to be light-saturated at PAR flux densities < 1800 Ei m–2 s–1. The light compensation point was found to be about 160 Ei m–2 s–1.Published as Paper No. 7402, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Nebraska Agricultural Experiment Station Project 27-003 and Regional Research Project 11–33.Post-doctoral Research Associate, Professor and Professor, respectively. Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0728.  相似文献   

4.
Since 1978, a measuring station has been operated at Cape Point (34°21 S, 18°29 E). In this article, results of measurements of CO, CFCl3, CCl4, O3, N2O and CH4 are presented as monthly means and analyzed with respect to long-term trends and seasonal variations. For CO and CH4, very similar seasonal variations have been observed, indicating strong interrelations between these two gases. For CO and O3, no significant changes of the mean annual concentrations can be established for the observation periods of 10 and 5 years, respectively. The measurements yield a growth rate of 9.1 pptv yr-1 for CFCl3 (1980–1987) and 0.6 ppbv yr-1 for N2O (1983–1987). The concentration increases of CH4 (10.3 ppbv yr-1 for 1983–1987) and of CCl4 (2.1 pptv yr-1 for 1980–1988) are analyzed for temporal changes during the last years.Presented at the Second Conference on Baseline Observations in Atmospheric Chemistry (SABOAC II) in Melbourne, Australia, November 1988.  相似文献   

5.
Rain and air of Florence have been collected in a continuous way andanalysed by flow analysis spectrofluorimetric methods for formaldehydeand hydrogen peroxide. Diurnal and seasonal variations were observed;the mean/maximum concentrations of all data (as gm–3) are 3.3/23.4 for HCHO and 0.4/4.93 forH2O2. The effect of external sources and ofphotochemical reactions produces periods of positive and negativecorrelations for these compounds. The mean/maximum rain concentration ofall data are 98/443 g l–1 for HCHO and 84/685 g l–1 for H2O2. Concentrationratios rain/air and discrepancies to Henry's Law equilibrium arediscussed.  相似文献   

6.
During April 1986, as part of an international arctic air chemistry study (AGASP-2), ground level observations of aerosol trace elements, oxides of sulphur and nitrogen and particle number size distribution were made at Alert Canada (82.5N, 62.3W). Pollution haze was evident as indicated by daily aerosol number (size > 0.15 m diameter) and SO4 = concentrations in the range 125 – 260 cm–3 and 1.6 – 4.5 g m–3, respectively. Haze and associated acidic gases tended to increase throughout the period. SO2 and peroxyacetylnitrate (PAN) mixing ratios were in the range 140 – 480 and 370 – 590 ppt(v), respectively. About 88% of the total end-product nitrogen was in the form of PAN. In air dried to 2% relative humidity by warming to room temperature, the aerosol mass size distribution had a major mode at 0.3 m diameter and a minor one at 2.5 m. Aerosol mass below 1.5 m was well correlated with SO4 =, K+ and PAN. There was a steady increase in the oxidized fraction of total airborne sulphur and nitrogen oxide throughout April as the sun rose above the horizon and remained above. The mean oxidation rate of SO2 between Eurasia and Alert was estimated as 0.25 – 0.5% h–1. The molar ratio of total nitrogen oxide to total sulphur oxide in the arctic atmosphere (0.67±0.17) was comparable to that in European emissions. A remarkably strong inverse correlation of filterable Br and O3 led to the conclusion that O3 destruction and filterable Br production below the Arctic surface radiation inversion is associated with tropospheric photochemical reactions involving naturally occurring gaseous bromine compounds.  相似文献   

7.
The formation and occurrence of hydroperoxides in the troposphere have been studied by laboratory experiments and by preliminary field measurements. Nine alkenes were reacted individually with ozone in a reaction chamber in the presence of excess water, and the amounts of hydrogen peroxide and of nine organic hydroperoxides produced in the gas and aerosol phases and deposited on the chamber walls determined by HPLC. The reactions of ethene, propene, 1-butene and isoprene gave hydroxymethyl hydroperoxide as the major product with no hydrogen peroxide observed. In the case of - and -pinene, 2-carene and limonene the major product was hydrogen peroxide. Cis-2-butene produced hydrogen peroxide and methyl hydroperoxide. Preliminary measurements of hydrogen peroxide and five organic hydroperoxides in ambient air were made at Niwot Ridge, Colorado from 24 July–4 August 1989. The gas-phase species were preconcentrated by cryotrapping with subsequent HPLC separation. The gas-phase concentrations of H2O2 ranged from 0.5–2 ppbv with the lowest concentrations being measured at night and the highest under conditions of strong photochemical activity. The maximum concentrations of hydroxymethyl hydroperoxide approximated those of H2O2. Methyl hydroperoxide concentrations ranged from <50 to 800 pptv and three other organic hydroperoxides were detected at concentrations below 200 pptv. High volume aerosol samples yielded H2O2 and methyl hydroperoxide concentrations <10 ng m-3 while H2O2 and six organic species were detected in rainwater at concentrations in the range <0.01–50 M.  相似文献   

8.
Dimethylsulfide (DMS), sulfur dioxide (SO2), methanesulfonate (MSA), nonsea-salt sulfate (nss-SO4 2–), sodium (Na+), ammonium (NH4 +), and nitrate (NO3 –) were determined in samples collected by aircraft over the open ocean in postfrontal maritime air masses off the northwest coast of the United States (3–12 May 1985). Measurements of radon daughter concentrations and isentropic trajectory calculations suggested that these air masses had been over the Pacific for 4–8 days since leaving the Asian continent. The DMS and MSA profiles showed very similar structures, with typical concentrations of 0.3–1.2 and 0.25–0.31 nmol m–3 (STP) respectively in the mixed layer, decreasing to 0.01–0.12 and 0.03–0.13 nmol m–3 (STP) at 3.6 km. These low atmospheric DMS concentrations are consistent with low levels of DMS measured in the surface waters of the northeastern Pacific during the study period.The atmospheric SO2 concentrations always increased with altitude from <0.16–0.25 to 0.44–1.31 nmol m–3 (STP). The nonsea-salt sulfate (ns-SO4 2–) concentrations decreased with altitude in the boundary layer and increased again in the free troposphere. These data suggest that, at least under the conditions prevailing during our flights, the production of SO2 and nss-SO4 2– from DMS oxidation was significant only within the boundary layer and that transport from Asia dominated the sulfur cycle in the free troposphere. The existence of a sea-salt inversion layer was reflected in the profiles of those aerosol components, e.g., Na+ and NO3 –, which were predominantly present as coarse particles. Our results show that long-range transport at mid-tropospheric levels plays an important role in determining the chemical composition of the atmosphere even in apparently remote northern hemispheric regions.  相似文献   

9.
Vertical distributions of dimethylsulfide (DMS), sulfur dioxide (SO2), aerosol methane-sulfonate (MSA), non-sea-salt sulfate (nss-SO4 2-), and other aerosol ions were measured in maritime air west of Tasmania (Australia) during December 1986. A few cloudwater and rainwater samples were also collected and analyzed for major anions and cations. DMS concentrations in the mixed layer (ML) were typically between 15–60 ppt (parts per trillion, 10–12; 24 ppt=1 nmol m–3 (20°C, 1013 hPa)) and decreased in the free troposphere (FT) to about <1–2.4 ppt at 3 km. One profile study showed elevated DMS concentrations at cloud level consistent with turbulent transport (cloud pumping) of air below convective cloud cells. In another case, a diel variation of DMS was observed in the ML. Our data suggest that meteorological rather than photochemical processes were responsible for this behavior. Based on model calculations we estimate a DMS lifetime in the ML of 0.9 days and a DMS sea-to-air flux of 2–3 mol m–2 d–1. These estimates pertain to early austral summer conditions and southern mid-ocean latitudes. Typical MSA concentrations were 11 ppt in the ML and 4.7–6.8 ppt in the FT. Sulfur-dioxide values were almost constant in the ML and the lower FT within a range of 4–22 ppt between individual flight days. A strong increase of the SO2 concentration in the middle FT (5.3 km) was observed. We estimate the residence time of SO2 in the ML to be about 1 day. Aqueous-phase oxidation in clouds is probably the major removal process for SO2. The corresponding removal rate is estimated to be a factor of 3 larger than the rate of homogeneous oxidation of SO2 by OH. Model calculations suggest that roughly two-thirds of DMS in the ML are converted to SO2 and one-third to MSA. On the other hand, MSA/nss-SO4 2- mole ratios were significantly higher compared to values previously reported for other ocean areas suggesting a relatively higher production of MSA from DMS oxidation over the Southern Ocean. Nss-SO4 2- profiles were mostly parallel to those of MSA, except when air was advected partially from continental areas (Africa, Australia). In contrast to SO2, nss-SO4 2- values decreased significantly in the middle FT. NH4 +/nss-SO4 2- mole ratios indicate that most non-sea-salt sulfate particles in the ML were neutralized by ammonium.  相似文献   

10.
We present here experimental determinations of mass accommodation coefficients using a low pressure tube reactor in which monodispersed droplets, generated by a vibrating orifice, are brought into contact with known amounts of trace gases. The uptake of the gases and the accommodation coefficient are determined by chemical analysis of the aqueous phase.We report in this article measurements of exp=(6.0±0.8)×10–2 at 298 K and with a total pressure of 38 Torr for SO2, (5.0±1.0)×10–2 at 297 K and total pressure of 52 Torr for HNO3, (1.5±0.6)×10–3 at 298 K and total pressure of 50 Torr for NO2, (2.4±1.0)×10–2 at 290 K and total pressure of 70 Torr for NH3.These values are corrected for mass transport limitations in the gas phase leading to =(1.3±0.1)×10–1 (298 K) for SO2, (1.1±0.1)×10–1 (298 K) for HNO3, (9.7±0.9)×10–2 (290 K) for NH3, (1.5±0.8)×10–3 (298 K) for NO2 but this last value should not be considered as the true value of for NO2 because of possible chemical interferences.Results are discussed in terms of experimental conditions which determine the presence of limitations on the mass transport rates of gaseous species into an aqueous phase, which permits the correction of the experimental values.  相似文献   

11.
The kinetics and mechanism of the reactionNO3+CH2=C(CH3)–CH=CH2productswere studied in two laboratories at 298 K in the pressure range 0.7–3 torr using the discharge-flow mass-spectrometric method. The rate constant obtained under pseudo-first-order conditions with excess of either NO3 or isoprene was: k 1=(7.8±0.6)×10–13 cm3 molecule–1 s–1. The product analysis indicated that the primary addition of NO3 occurred on both -bonds of the isprene molecule.  相似文献   

12.
Summary We measured ionic compounds in rain and fog at two remote sites in the South Island of New Zealand and at two sites in the Fichtelgebirge, F. R. of Germany. In the Fichtelgebirge high concentrations of H3O+, NO 3 – , SO 4 2– and NH 4 + indicate an anthropogenic impact, whereas in New Zealand concentrations were generally very low except for seasalt derived ions such as Na+, Cl– and Mg2+ at one site near the coast which receives precipitation from maritime sources. Remarkable differences occur in the acidity of hydrometeors in New Zealand and the Fichtelgebirge. The low pH values of the Fichtelgebirge (pH 4.2) are due to an excess of strong mineral acids, whereas the acidity of rain and fog in New Zealand is controlled by dissolved CO2 (pH 5.6). In the Fichtelgebirge, acidity in fog is much higher than in rain, whereas no difference could be observed in New Zealand due to marine influences and the lack of strong mineral acids. Rain of different trajectories of air flow in New Zealand is accompanied by a wide range of ionic concentrations.
Zusammenfassung An zwei entlegenen Meßstellen der Südinsel Neuseelands und an zwei Meßstellen im Fichtelgebirge haben wir die Ionen im Regen und Nebel gemessen. Die Luftverschmutzung im Fichtelgebirge ist gekennzeichnet durch hohe Konzentrationen von H3O+, NO 3 – , SO 4 2– und NH 4 + . Die Ionenkonzentrationen im neuseeländischen Niederschlagswasser waren durchwegs sehr gering mit Ausnahme von Na+, Cl– und Mg2+, die aus Seesalzen stammen und nur in einer küstennahen Meßstelle bei günstigen Wetterlagen bestimmt werden konnten. Große Unterschiede bestehen in der Azidität der Hydrometeore. Während im Fichtelgebirge starke Mineralsäuren niedrige pH-Werte (pH 4.2) bewirken, wird die Azidität des Regens und des Nebels an den neuseeländischen Meßstellen durch gelöstes CO2 kontrolliert (pH 5.6). Im Fichtelgebirge ist die Azidität im Nebel erheblich höher als im Regen. Im Gegensatz dazu konnten wir keinen Unterschied in der Azidität zwischen Nebel und Regen in Neuseeland beobachten, was wir mit dem marinen Einfluß und dem Fehlen starker Mineralsäuren erklären. Unterschiedliche Trajektorien der atmosphärischen Strömung in Neuseeland unterscheiden sich zugleich in ihren Ionenkonzentrationen im Regen.

With 6 Figures  相似文献   

13.
Methanesulfonate (MS–) and non-sea-salt sulfate (nss-SO 4 2– ), two of the major oxidation products of atmospheric dimethylsulfide (DMS), have been continuously measured in rainwater at three remote islands in the Southern Indian Ocean: Amsterdam since 1991, Crozet since 1992, and Kerguelen since 1993. The annual volume weighted mean (VWM) concentrations of nss-SO 4 2– in rainwater were 3.19, 3.04 and 4.57 eq l–1 at Amsterdam, Crozet, and Kerguelen, respectively while the VWM of MS– were 0.24, 0.15 and 0.30 eq l–1, respectively. At all three islands, MS– presented a well-distinguished seasonal variation with a maximum during summer whereas the seasonal variation of nss-SO 4 2– was less pronounced, possibly due to the increased anthropogenic influence during the winter period. Furthermore, MS– presented significant interannual variations, in particular at Amsterdam and Crozet, which is closely related to the sea-surface temperature (SST) anomalies). Finally, the nss-SO 4 2– deposition at Crozet Island presented a decreasing interannual trend, reflecting probably reductions in sulfur emissions from Southern Africa. On the contrary no interannual tendency was observed in the nss-SO 4 2– concentrations at Amsterdam Island, indicating that the biogeochemical sulfur cycle at this area is mainly influenced by biogenic emissions.  相似文献   

14.
Aerosol chemical composition and trace gas measurements were made at twolocations on the northeastern peninsula of Tenerife during the ACE-2HILLCLOUD experiment, between 28 June and 23 July 1997. Measurementswere made of coarse (#gt;2.5 m aerodynamic diameter) and fine (#lt; 2.5m) aerosol Cl–, NO3 –,SO4 2–, non-sea saltSO4 2– (NSSS),CH3SO3 – (MSA) andNH4 +, and gas phase dimethylsulphide (DMS), HCl,HNO3, SO2, CH3COOH, HCOOH andNH3. Size distributions were measured using a cascadeimpactor. Results show that in marine air masses NSSS and MSA wereformed via DMS oxidation, with additional NSSS present in air massescontaining a continental component. Using a Eulerian box model approachfor aerosols transported between upwind and downwind sites, a mean NSSSproduction rate of 4.36 × 10–4 gm–3 s–1 was calculated for daytimeclear sky periods (highest insolation), with values for cloudy periodsduring daytime and nighttime of 3.55 × 10–4 and2.40 × 10–4 g m–3s–1, respectively. The corresponding rates for MSA were6.23 × 10–6, 8.49 × 10–6and 6.95 × 10–6 g m–3s–1, respectively. Molar concentration ratios forMSA/NSSS were 8.7% (1.8–18.2%) and 1.9%(1.3–3.5%) in clean and polluted air masses, respectively.Reactions occurring within clouds appeared to have a greater influenceon rates of MSA production, than of NSSS, while conversely daytime gasphase reactions were more important for NSSS. For MSA, nighttimein-cloud oxidation rates exceeded rates of daytime gas phase productionvia OH oxidation of DMS. NSSS, MSA and ammonium had trimodal sizedistributions, with modes at 0.3, 4.0 and >10.0 m (NSSS andNH4 +), and 0.3, 1.5 and 4.0 m (MSA). Nosignificant production of other aerosol species was observed, with theexception of ammonium, which was formed at variable rates dependent onneutralisation of the aerosol with ammonia released from spatiallynon-uniform surface sources. Seasalt components were mainly present incoarse particles, although sub-micrometre chloride was also measured.Losses by deposition exceeded calculated expectations for all species,and were highest for the seasalt fraction and nitrate.  相似文献   

15.
Kinetics and products of the gas-phase reactions of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and dimethylsulphone (DMSO2) with Br atoms and BrO radicals in air have beeninvestigated using on-line Fourier Transform Infrared Spectroscopy (FT-IR) as analytical technique at 740 ± 5 Torr total pressure and at 296 ± 3 K in a480 L reaction chamber. Using a relative rate method for determining the rate constants; the following values (expressed in cm3molecule–1 s–1) were found: kDMS+Br = (4.9 ±1.0) ×10–14, kDMSO + Br < 6 × 10–14,kDMSO 2 + Br 1 × 10–15,kDMSO + BrO = (1.0 ± 0.3) × 10–14 andkDMSO 2 + BrO 3 × 10–15 (allvalues are given with one on the experimental data). DMSO, SO2, COS, CH3SBr andCH3SO2Br were identified as the main sulphur containing products of the oxidation of DMS by Br atoms. From the reaction between DMSO and Br atoms, DMSO2and CH3SO2Br were the only sulphur containing products thatwere identified. DMSO, DMSO2 and SO2 were identified as themain sulphur containing products of the reaction between DMS and BrO.DMSO2 was found to be the only product of the reaction between DMSO and BrO. For the reactions of DMSO2 with Br and BrO no products were identified because the reactions were too slow.The implications of these results for atmospheric chemistry are discussed.  相似文献   

16.
Stratospheric volume mixing ratio profiles of N2O5, CH4, and N2O have been retrieved from a set of 0.052 cm–1 resolution (FWHM) solar occultation spectra recorded at sunrise during a balloon flight from Aire sur l'Adour, France (44° N latitude) on 12 October 1990. The N2O5 results have been derived from measurements of the integrated absorption by the 1246 cm–1 band. Assuming a total intensity of 4.32×10–17 cm–1/molecule cm–2 independent of temperature, the retrieved N2O5 volume mixing ratios in ppbv (parts per billion by volume, 10–9), interpolated to 2 km height spacings, are 1.64±0.49 at 37.5 km, 1.92±0.56 at 35.5 km, 2.06±0.47 at 33.5 km, 1.95±0.42 at 31.5 km, 1.60±0.33 at 29.5 km, 1.26±0.28 at 27.5 km, and 0.85±0.20 at 25.5 km. Error bars indicate the estimated 1- uncertainty including the error in the total band intensity (±20% has been assumed). The retrieved profiles are compared with previous measurements and photochemical model results.Laboratoire associé aux Universités Pierre et Marie Curie et Paris Sud.  相似文献   

17.
Within the framework of IDAF (IGAC DEBITS AFRICA: International GlobalAtmospheric Chemistry/DEposition of Biogeochemically Important TraceSpecies/Africa) network, data analysis is realised on precipitation chemical composition collected in Zoétélé, in Southern Cameroon. This station, located atabout 200 km from the Atlantic Ocean, is representative of a so-called `Evergreen Equatorial Forest' ecosystem. An automatic wet-only precipitation collector was operated at the station from 1996 to 2000. The rainfall regime, associated with eastward advection of moist and cool monsoon air masses, amounts to an average of 1700 mm/year. Inorganic and organic content of the precipitation were determined by IC in 234 rainfall events, representing a total 4,583 mm of rainfall from an overall of 7,100 mm.The mean annual precipitation chemistry and wet deposition fluxes characteristic of an African equatorial forest are quantified. Typical atmospheric gases and particles sources influence the precipitation chemical content and the associated deposition of chemical species. Indeed, hydrogen concentration is the highest (12.0 eq.L–1) of the IDAF measurements, leading to acid rains with a low mean pH 4.92. The mineral species are dominated by nitrogenous compounds (NH4 +:10.5 and NO3 –: 6.9 eq.L–1), Ca2+ (8.9 eq.L–1) and SO4 2 – 5.1 eq.L–1. Relationship between Ca2 + and SO4 2 – indicated aterrigeneous particulate source and an additional SO4 2 – contributionprobably due to swamps and volcano emissions. Na+ and Cl–concentrations, around 4.0 eq.L–1, seem very low for this site,accounting for the marine source. Besides, strong correlations between NH4 +/K+/Cl– indicate the biomass burning originof these species. Accordingly, precipitation chemistry in Zoétéléis influenced by three major sources: biogenic emissions from soil and forest ecosystems, biomass burning from savannah, and terrigenous signature from particles emissions of arid zones; and three minor sources: marine, volcano and anthropogenic. In spite of the relatively low concentration of all these elements, the wet deposition is quite significant due to the high precipitation levels, with for example a nitrogenous compounds deposition of 34 mmol.m–2.yr–1.  相似文献   

18.
An investigation of the influence of mineral dust ontrace gas cycles in the troposphere is carried out inthis study. A 3D regional scale atmospheric chemistrymodel (STEM-III) which includes aerosol processes isused for the numerical simulations for May 1987.Heterogeneous interactions between gaseous species(SO2, N2O5, HNO3, HO2andH2O2) and the dust particles are considered.Emissions of dust behind convective cold fronts aremodeled. The transport and distribution of mineraldust predicted from the model is compared withsatellite measurements (aerosol index from TOMS). Themodel is shown to capture the synoptic variability inthe observed aerosol index. Calculations show twomajor dust events in May 1987, during which thedust levels close to the source reach more than500 g/m3. The transport of dust is mostlyrestricted towards the north, with the net continentaloutflow of 6 Tg for the entire month. Results showthat the presence of mineral aerosol can greatlyimpact sulfate and nitrate distributions. Averagedover the month of May, the presence of dust isestimated to increase particulate sulfate and nitratelevels in east Asia by 40%. Furthermore, the sulfateand nitrate on the dust particles are predicted to beassociated with the coarse mode (3–5 m particlediameter), consistent with observations over Japan.The influence of mineral dust on the photochemicaloxidant cycle is also investigated. For the entiremonth, a5–10% decrease in boundary layer ozone ispredicted by the model closer to regions of higherdust levels. The ratio of nitric acid to NOx overmarine regions is reduced by a factor between 1 and 2in the boundary layer to more than 2 in the freetroposphere as a result of aerosol processes.  相似文献   

19.
This paper presents dry deposition flux and deposition velocity of atmospheric particles on white marble and red stone at Dayalbagh, a suburban site of semi arid region, which is 10 km away from the industrial sector of the Agra city where due to agricultural practices vegetation predominates. The wind speed at Agra is mostly in the range of 1–2 m s–1. The atmospheric calm conditions at Agra in summer, monsoon, and winter seasons are 47%, 35%, and 76%, respectively. Industrial areas of the city are away from Dayalbagh and are located in the NE, E, SE, and SW sectors. The main industrial activities, which are in operation in Agra city and its outskirts, are foundry and forging industry. The other industrial activities in Agra are rubber processing, lime oxidation and pulverization, chemicals, engineering and brick refractory kilns. Dry deposition samples were collected on dry days on white marble and red stone (0.224 m × 0.224 m × 0.02 m) using surface washing method. Both slabs were fixed to an iron stand (1.5 m height) at an angle of about 80 from the horizontal and exposed for 24 h on the roof of the faculty building. The order of deposition flux on white marble is NH4+ > Mg2+ > Ca2+ > Na+ > Cl– > K+ > NO3– > SO42– > F– and that on red stone is NH4+ > Mg2+ > Ca2+ > SO42– > Na+ > NO3– > K+ > F– > Cl–. Average dry deposition flux of major ions varies from 3.4 to 128.5 M m–2 d–1. The sum of major cations on white marble and red stone are 516.4 and 450.4 eq m–2 d–1, respectively while sum of major anions are 425.3 and 400.4 eq m–2 d–1 on white marble and red stone, respectively. Higher deposition of all ions was observed when wind blows from NE as most of the Agra Iron foundries and Ferozabad glass industries lie in this direction. The mean values of dry deposition velocity of ions vary between 0.22 cm s–1 to 1.49 cm s–1. Deposition velocity for all ions is higher on white marble than red stone inspite of rougher surface of red stone as compared to white marble. This could be due to the chemical nature of white marble, which is made of dolomite and hence adds significant amount of ions by dissolution during washing. Seasonally the deposition velocity was highest in winter.  相似文献   

20.
Henry's law constantsK H (mol kg–1 atm–1) have been determined at 298.15 K for the following organic acids: formic acid (5.53±0.27×103); acetic acid (5.50±0.29×103); propionic acid (5.71±0.34×103);n-butyric acid (4.73±0.18×103); isobutyric acid (1.13±0.12×103); isovaleric acid (1.20±0.11×103) and neovaleric acid (0.353±0.04×103). They have also been determined fromT=278.15 K toT=308.15 K forn-valeric acid (ln(K H)=–14.3371+6582.96/T);n-caproic acid (ln(K H)=–13.9424+6303.73/T) and pyruvic acid (ln(K H)=–4.41706+5087.92/T). The influence of 9 salts on the solubility of pyruvic acid at 298.15 K has been measured. Pyruvic acid is soluble enough to partition strongly into aqueous atmospheric aerosols. Other acids require around 1 g of liquid water m–3 (typical of clouds) to partition significantly into the aqueous phase. The degree of partitioning is sensitive to temperature. Considering solubility and dissociation (to formate) alone, the ratio of formic acid to acetic acid in liquid water in the atmosphere (at equilibrium with the gas phase acids) is expected to increase with rising pH, but show little variation with temperature.  相似文献   

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