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1.
During two measuring campaigns in early spring 1994 and 1995 (March/April) and one campaign in summer 1994, measurements of ozone, PAN, sulfur dioxide, nitric acid, and particulate nitrate, sulfate, and ammonium (only 1995) were recorded in the Arctic. Observations were made by aircraft at various sites in the eastern and western Arctic. Ozone concentrations showed a steady increase with altitude both in spring and summer. During five flights in springtime, low ozone events (LOEs) could be observed near the surface and up to altitudes of 2000 m. SO2 background concentrations, ranging from detection limit (0.5 nmol/m3) to 5 nmol/m3, were observed during both spring and summer. Distinct maxima up to 55 nmol/m3 in lower altitudes were only obtained in springtime. Concentrations of the organic nitrate PAN were within a similar range as those of the inorganic nitrate HNO3 during spring campaigns. In contrast, concentrations of particulate nitrate were one half an order of magnitude lower. HNO3 concentrations increased significantly with altitude. Evidently, HNO3 was intruded from the stratosphere into the troposphere. Sulfate concentrations ranged between 5 and 30 nmol/m3; ammonium concentrations were obtained within a range from 10 to 50 nmol/m3.  相似文献   

2.
Observations of the concentration of several nitrogen containing compounds at five rural Scandinavian sites during March–June 1993 are reported. Total nitrate (NO 3 - + HNO3) and total ammonium (NH 4 + + NH3) were measured by denuder and filter pack. In general the methods agree well. At all sites the particulate fraction dominated, with the largest fraction of NO 3 - and the lowest of NH 4 + at the sites which were closest to the emission sources. The fraction of NO 3 - of total nitrate increased with increasing NO2 concentrations, indicating that the nighttime conversion of NO2 to NO 3 - is an important route of formation for NO 3 - . A positive correlation was found between HNO3 and O3 in June at all sites, while no correlation was found early in the spring. Model calculations were made with a lagrangian boundary layer photooxidant model for the whole period, and compared to the measured concentrations. The calculated ratio between mean observed and modelled daily maximum concentrations of ozone over the measurement period were within +/–10% at all sites. The models ability to describe the daily ozone maximum concentration was satisfactory with an average deviation of 19–22% from the observed concentrations. HNO3 was underestimated by over 50% at all sites except the one closest to the emission sources. The correlation between modelled and observed concentrations was generally best for the sites with shortest transport distance from the sources of emission.  相似文献   

3.
The results from a one-dimensional photochemical model of the troposphere representative of summertime conditions at Northern Hemisphere mid-latitudes are presented. A parameterization of mixing processes within the planetary boundary layer (PBL) has been incorporated into the model for both the daytime convective PBL and the formation of the nocturnal PBL. One result of the parameterized PBL is that the concentrations of some trace species in the free troposphere are 20–30% higher than when mixing processes are described by a vertical eddy diffusion coefficient which is held constant with respect to height and time.The calculations indicate that the lifetime of the oxides of nitrogen (NO x =NO+NO2) against photochemical conversion to nitric acid (HNO3) during summertime conditions is on the order of 6 h. This lifetime is short enough to deplete most of the NO x in the PBL, resulting in the finding that other reactive nitrogen species (HNO3 and peroxyacetyl nitrate) are more abundant than NO x throughout the free troposphere, even though NO x is the most abundant reactive nitrogen species at the surface. The effects of the inclusion of anthropogenic nonmethane hydrocarbon (NMHC) chemistry are also discussed. The inclusion of NMHC chemistry has a pronounced effect on the photochemistry of tropospheric oxone and increases thein situ column production by more than 30%.  相似文献   

4.
Four case studies are described, from a three-site field experiment in October/November 1991 using the Great Dun Fell flow-through reactor hill cap cloud in rural Northern England. Measurements of total odd-nitrogen nitrogen oxides (NO y ) made on either side of the hill, before and after the air flowed through the cloud, showed that 10 to 50% of the NO y , called NO z , was neither NO nor NO2. This NO z failed to exhibit a diurnal variation and was often higher after passage through cloud than before. No evidence of conversion of NO z to NO3 - in cloud was found. A simple box model of gas-phase chemistry in air before it reached the cloud, including scavenging of NO3 and N2O5 by aerosol of surface area proportional to the NO2 mixing ratio, shows that NO3 and N2O5 may build up in the boundary layer by night only if stable stratification insulates the air from emissions of NO. This may explain the lack of evidence for N2O5 forming NO3 - in cloud under well-mixed conditions in 1991, in contrast with observations under stably stratified conditions during previous experiments when evidence of N2O5 was found. Inside the cloud, some variations in the calculated total atmospheric loading of HNO2 and the cloud liquid water content were related to each other. Also, indications of conversion of NO x to NO z were found. To explain these observations, scavenging of NO x and HNO2 by cloud droplets and/or aqueous-phase oxidation of NO2 - by nitrate radicals are considered. When cloud acidity was being produced by aqueous-phase oxidation of NO x or SO2, NO3 - which had entered the cloud as aerosol particles was liberated as HNO3 vapour. When no aqueous-phase production of acidity was occurring, the reverse, conversion of scavenged HNO3 to particulate NO3 -, was observed.  相似文献   

5.
Emissions of nitric oxide and other odd nitrogen oxides (NO x ) from a flooded rice field were studied after urea had been broadcast into the floodwater.The NO x flux from the fertilized area was very low (0.2×10-9 g N m-2 s-1) for the first few days after application of urea and was high (0.95×10-9 g N m-2 s-1) in the subsequent period when significant nitrite and nitrate were present in the floodwater. At night, little if any NO x was exhaled but ambient NO2 was absorbed by the floodwater. An uptake velocity for NO2 of 3×10-4 m s-1 was measured during one night. Maximum NO x losses were observed near 1300 h when temperature and solar ultraviolet light were maximum.While the amounts of nitrogen oxides emitted are of little agronomic importance (2×10-3 per cent of the fertilizer nitrogen was lost as NO x during the 10-day study period), they may well be of significance as a source for some gas reactions in the atmosphere and for the global nitrogen cycle.Of the fertilizer nitrogen applied (as urea) approximately 30% was lost to the atmosphere by NH3 volatilization, 15% by denitrification, presumably as N2, and the remainder, less minor losses of NO and N2O, remained in the plant/soil/water system.Now at Forestry Department, Australian National University, G.P.O. Box 4, ACT 2601, Australia.  相似文献   

6.
Results from numerical investigations regarding the exchange of HNO3, NH3, and NH4NO3 between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with group concentrationsc 1=[HNO3]+[NH4NO3] (total nitrate),c 2=[NH3]+[NH4NO3] (total ammonia), andc 3=[HNO3]-[NH3] as well as the fluxes of the individual nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified inferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO3, NH3, and NH4NO3) measured at a reference height by stations of a monitoring network.  相似文献   

7.
Using a single drop experiment, the uptake of NO3 radicals on aqueous solutions of the dye Alizarin Red S and NaCl was measured at 293 K. Uptake coefficients in the range (1.7–3.1) ⋅ 10− 3 were measured on Alizarin Red S solutions. The uptake coefficients measured on NaCl solutions were in the range of (1.1–2.0) ⋅ 10−3 depending on the salt concentration. Both experiments lead to a consistent result for the mass accommodation coefficient of αNO3 = (4.2− 1.7+2.2)⋅ 10−3. The product H(Dl kCl−II)0.5 for the NO3 radical was determined to be (1.9 ± 0.2) M atm− 1 cm s−0.5 M−0.5 s−0.5 by fitting the uptake data for the NaCl solutions to the so-called resistance model. The yield of the chemical NO3 radical source was characterized using UV-VIS and FT-IR spectroscopy. The amount of gas-phase NO3 radicals measured at elevated humidities was less than expected. Instead, a rise of the gas-phase HNO3 concentration was found indicating a conversion of gas-phase NO3 radicals to gas-phase HNO3 on the moist reactor walls.  相似文献   

8.
The simultaneous measurements of NO, NO2 and HNOA mixing‐ratio profiles carried out on the Stratoprobe balloon flight of 22 July 1974 have been simulated with a time‐dependent model using the measured temperature and ozone profiles. The calculated ratios of NO/NO2, HNO3/NO2 using currently accepted photochemistry are consistent with the measured ratios within the experimental errors of the measurements. The measured NO2/NO ratio is almost a factor of two smaller than predicted, although the discrepancy is still within the experimental errors. A remarkable proportionality in the NO2 and O3 profiles has been noted and is unexplained. A time‐dependent simulation has been employed to convert the measurements into diurnally‐averaged profiles suitable for intercomparison with two‐dimensional stratospheric models and a comparison with constituent profiles from Prinn et al. (1975) is carried out as an example. The NOV mixing ratio, formed from the sum of the NO, NO2 and HNO2 measurements is similar to the NOV mixing ratio from several one‐ and two‐dimensional models used to predict the effects of SST's on the ozone layer. The odd nitrogen mixing ratio is roughly constant from 20 to 35 km at 11 ppbv.  相似文献   

9.
Gaseous nitric acid and ammonia were sampled with annular denuders at a forest savannah site from April to December 1987. The analysis of the extract was made spectrophotometrically and by a selective electrode for NO3 – and NH4 +, respectively. Higher concentrations were observed during the vegetation burning period at the end of the dry season. In the studied savannah area, large soil emissions of NO occur during the rainy season, although very low concentrations of HNO3 (0.035 ppb) and also of particulate NO3 – (0.43 g m-3) were observed; it is likely that NOx are lost by fast vertical transport to the upper troposphere. During the nonburning period, the average concentration of NH3 was 2.7 ppb, which is much lower than values given in the literature for the tropical America atmosphere. The concentrations of HNO3 and NH3 were always below the values needed to produce ammonium nitrate aerosols.  相似文献   

10.
A catalytic reduction technique for the measurement of total reactive odd-nitrogen NO y in the atmosphere was evaluated in laboratory and field tests. NO y component species include NO, NO2, NO3, HNO3, N2O5, CH3COO2NO2(PAN), and particulate nitrate. The technique utilizes the reduction of the higher oxides to NO in reaction with CO on a metal catalyst and the subsequent detection of NO by chemiluminescence produced in reaction with O3. The efficiency and linearity of the conversion of the principal NO y species were examined for mixing ratios in the range of 0.1 to 100 parts per billion by volume (ppbv). Results of tests with Au, Ni, and stainless steel as the catalyst in the temperature range of 25–500°C showed Au to be the preferred catalyst. NH3, HCN, N2O, CH4, and various chlorine and sulfur compounds were checked as possible sources of NO y interference with the Au catalyst. The effects of pressure, O3, and H2O on NO y conversion were also examined. The results of the checks and tests in the laboratory showed the technique to be suitable for initial NO y measurements in the atmosphere. The technique was subsequently tested in ambient air at a remote ground-based field site located near Niwot Ridge, Colorado. The results of conversion and inlet tests made in the field and a summary of the NO y data are included in the discussion.  相似文献   

11.
The objective of this study was to reconstruct light extinction coefficients (b ext ) according to chemical composition components of particulate matter up to 2.5 μm in size (PM 2.5 ). PM 2.5 samples were collected at the monitoring station of the South China of Institute of Environmental Science (SCIES, Guangzhou, China) during January 2010, and the online absorbing and scattering coefficients were obtained using an aethalometer and a nephelometer. The measured values of light absorption coefficient by particle (b ap ) and light scattering coefficient by particle (b sp ) significantly correlated (R 2 > 0.95) with values of b ap and b sp that were reconstructed using the Interagency Monitoring of Protected Visual Environments (IMPROVE) formula when RH was <70%. The measured b ext had a good correlation (R 2 > 0.83) with the calculated b ext under ambient RH conditions. The result of source apportionment of b ext showed that ammonium sulfate [(NH 4 ) 2 SO 4 ] was the largest contributor (35.0%) to b ext , followed by ammonium nitrate (NH 4 NO 3 , 22.9%), organic matter (16.1%), elemental carbon (11.8%), sea salt (4.7%), and nitrogen dioxide (NO 2 , 9.6%). To improve visibility in Guangzhou, the effective control of secondary particles like sulfates, nitrates, and ammonia should be given more attention in urban environmental management.  相似文献   

12.
Difunctional organic nitrates are important products of the atmospheric reaction of NO3 radicals with unsaturated hydrocarbons about which relatively little is known. In a continuation of the investigation of the atmospheric chemistry of such compounds, the UV absorption spectra of the following organic dinitrates and keto nitrates have been quantitively measured in the gas phase at 298±2 K and atmospheric pressure: 1,2-propandiol dinitrate, CH3CH(ONO2)CH2(ONO2); 1,2-butandiol dinitrate, CH3CH2CH(ONO2)CH2(ONO2); 2,3-butandiol dinitrate, CH3CH(ONO2)CH(ONO2)CH3;cis 1,4-dinitrooxy-2-butene, CH2(ONO2)CH=CHCH2(ONO2); 3,4-dinitrooxy-1-butene, CH2(ONO2CH(ONO2)CH=CH2; -nitrooxy acetone, CH3COCH2(ONO2); 1-nitrooxy-2-butanone, CH3CH2COCH2(ONO2); 3-nitrooxy-2-butanone, CH3CH(ONO2)COCH3.Although the UV spectra of the nitrates are all very similar in shape those of the keto nitrates are red-shifted compared to the dinitrates and in the spectral range of atmospheric interest (>290 nm) their absorption cross-sections are approximately a factor of 5 higher. The cross-sections of the dinitrates are a factor of 2 higher than those reported in the literature for the corresponding alkyl mononitrates.The UV absorption cross-sections of the difunctional nitrates were used in combination with solar actinic flux data to estimate photolysis frequencies and consequently atmospheric lifetimes for these compounds. The results indicate that for the saturated difunctional nitrates studied in this work photolysis will generally be somewhat some important than reaction with OH radicals as an atmospheric removal process. However, for unsaturated nitrates loss due to reaction with OH will dominate over photolysis as an atmospheric sink.Preliminary FT-IR analyses of the photolysis products of -nitrooxy acetone, 3-nitrooxy-2-butanone and 2,3-butandiol dinitrate using both mercury and fluorescent lamps indicate that NO2 is released in the primary step. The further reactions of the radicals thus produced result in the formation of CO, aldehydes and PAN. The possible significance of the results for difunctional organic nitrate as reservoirs for reactive odd nitrogen NO y in the atmosphere, especially during the night, is briefly discussed.  相似文献   

13.
A latitudinal profile (30° W, from 30° N to 30° S) of mixing ratios of nitric acid and particulate nitrate was determined on the Atlantic Ocean during the Polarstern cruise ANT VII/1 from Bremerhaven, Germany, to Rio Grande, Brazil. The detection of HNO3 was performed simultaneously by laser-photolysis fragment-fluorescence (LPFF) and by nylon filter packs. The detection limit was about 30 pptv for a signal accumulation time of 1 h for LPFF and about 5 pptv for the filters at a collection time of 4 h. In general, the mixing ratios of HNO3 in the Northern Hemisphere were found to be significantly higher than those in the Southern Hemisphere. The Atlantic background concentrations frequently varied between 80 pptv and the detection limit. Larger deviations from this trend were found for the more northern latitudes and for episodes like crossings of exhaust plumes from ships or from continental pollutions sources.  相似文献   

14.
The applicability of the tungsten oxide denuder tube technique for the measurement of nitric acid in the rural troposphere was investigated. The technique is based on selective chemisorption of HNO3 from the gas stream, thermal desorption, conversion to NO, and analysis by NO–O3 chemiluminescence. Ammonia, which is also collected and desorbed as NH3 and NO, was separated from the HNO3-derived NO by linear temperature-programed thermal desorption. Possible interferences by NO2, HCN, PAN, and n-propyl nitrate (NPN) were tested and found to be significant under conditions found in the lower troposphere. Simultaneous ambient measurements of HNO3 were made with the tungsten oxide denuder tube and nylon filter methods at a rural site in the Colorado mountains (Niwot Ridge, CO). Nitric acid levels measured by the tungsten oxide denuder tube averaged a factor of 3 higher than levels measured by the nylon filter technique. Tests involving the placement of nylon materials in front of the tungsten oxide denuder tube show that there are species, as yet unidentified, present in the atmosphere that interfere with the measurement of HNO3 by the tungsten oxide technique.  相似文献   

15.
A model with spectral microphysics was developed to describe the scavenging of nitrate aerosol particles and HNO3 gas. This model was incorporated into the dynamic framework of an entraining air parcel model with which we computed the uptake of nitrate by cloud drops whose size distribution changes with time because of condensation, collision-coalescence and break-up. Significant differences were found between the scavenging behavior of nitrate and our former results on the scavenging behavior of sulfate. These reflect the following chemical and microphysical differences between the two systems:
  1. nitrate particles occur in a larger size range than sulfate particles.
  2. HNO3 has a much greater solubility than SO2 and is taken up irreversibly inside the drops in contrast to SO2.
  3. nitric acid in the cloud water is formed directly on uptake of HNO3 gas whereas on uptake of SO2 sulfuric acid is formed only after the reaction with oxidizing agents such as e.g., H2O2 or O3.
  4. nitrate resulting from uptake of HNO3 is confined mainly to small drops, whereas sulfate resulting from uptake of SO2 is most concentrated in the largest, oldest drops, which have had the greatest time for reaction.
Sensitivity studies showed that the nitrate concentration of small drops is significantly affected by the mass accommodation coefficient.  相似文献   

16.
The nitric acid formed from trans-2-butene, propene, ethene, toluene, and n-butane in single hydrocarbon/NO2/purified air systems was examined in smog chamber experiments. The effect of hydrocarbon and NO2 concentrations on the maximum HNO3 yield, defined as percentages of initial NO2 converted to HNO3, was studied in two sets of experiments. In every hydrocarbon system, we found no effect of hydrocarbon concentration variation on the nitric acid formed. Out of initially added 100 ppb NO2, in the hydrocarbon-rich systems, ethene formed most HNO3 (45%), followed by propene, toluene, and n-butane (24%), and trans-2-butene (13%). When the initial NO2 concentration was varied with a constant hydrocarbon concentration, the amount of HNO3 formed was found to linearly increase with the added NO2 down to |HC|/|NO2| ratios, which depended on the nature of the hydrocarbon studied. The initial rate of HNO3 formation in hydrocarbon excess experiments varied between 50, 35, 23, 16, and 8 ppb/hr for butene, propene, toluene, ethene, and butane systems, respectively.  相似文献   

17.
The concentrations of H+, nitrate (NO3 -), and sulfate (SO4 2-) in rainwater and their temporal changes were analyzed on the basis of continuous observation from 1 July 1991 to 30 June 1992 at a suburb of Nagoya, Japan. The yearly average for pH was 4.4. In general, an increasing pH with increase in precipitation amount was observed for rain events. Relatively high pH rainwater was sometimes observed at the beginning of rainfall, even though high concentrations of NO3 - and SO4 2- were involved. The high pH values were considered to be caused by the neutralization process with particulate matter containing cations. The yearly averaged ratio of equivalent concentration of nitrate to sulfate (N/S) in rainwater was 0.58. In the early stage of rain, the N/S value was usually more than 1.0 due to the difference of scavenging process between NO3 - and SO4 2-. High values of N/S ranging from 5 to 10 were found under the atmospheric conditions of calm winds and low humidity, during which it is possible that atmospheric particles float for a long time in the air before a rain event. The adsorption of NO3 - in the early stage of rainfall by particulate matter was suggested from the difference in scavenging processes of NO3 - and SO4 2-. A possible scavenging process, called limb cloud scavenging, is presented to explain the interaction of particles and nitrate ions at the early stage of rain. In limb cloud scavenging, the repeated migration of cloud particles or raindrops between the inside and outside of clouds increases the absorption of ions to a highly condensed level, thus increasing the N/S value of rainwater. The influence of global scale seasonal phenomena with large amounts of particulates, such as typhoons or Asian dust storms, was also studied.  相似文献   

18.
The role of trace gases and aerosol particles in the control of sulfur and nitrogen levels in atmospheric precipitation is estimated on the basis of the enrichment factor in the precipitation of these elements relative to particulate matter in the air. By using air and precipitation chemistry data obtained at a Hungarian background air pollution station (K-puszta) it is found that the fraction of ammonium, nitrate and sulfate in precipitation, due to the removal of particulate matter is at least 59, 27 and 31%, respectively. The relationship between wet depositions and air concentrations of different species is determined statistically by applying daily data set. The regression equations obtained make the estimation of the sub-cloud scavenging ratios possible and they give some information on the magnitude of in-cloud scavenging processes. The results show that the in-cloud scavenging is a determining factor for precipitation sulfate, while it is relatively unimportant in the case of ammonium. The sub-cloud scavening of NO2 and SO2 is not too significant. However, for HNO3, and NH3 it is an effective process. The sub-cloud scavenging ratio of sulfur and nitrogen-containing particles varies around 0.25×106.  相似文献   

19.
Biological characterization of Corylus avellana L. and Pinus nigra L. pollen samples was carried out to determine the actual value of pollen as a bio-indicator of the effects of atmospheric pollution, using samples from plants naturally developed in sites controlled for air pollution. In Trentino (North Italy), we selected six stations at three different levels of air pollution, which are constantly monitored with automatic gauges by the Environmental Protection Agency of Trento.First results showed that pollen viability of both species, germinability and pollen tube length of P. nigra, were higher in areas with no road traffic compared to heavy traffic ones. Pollen viability of P. nigra was positively correlated to ozone (O3) concentrations and altitude but negatively to sulphur dioxide (SO2), particulate matter with a diameter less than 10 m (PM10), nitrogen oxides (NOx) and nitrogen dioxide (NO2) concentrations.  相似文献   

20.
Atmospheric nitric acid measurements by ACIMS (Active Chemical Ionization Mass Spectrometry) are based on ion-molecule reactions of CO3 -(H2O) n and NO3 -(H2O) n with HNO3. We have studied these reactions in the laboratory using a flow tube apparatus with mass spectrometric detection of reactant and product ions. Both product ion distributions and rate coefficients were measured. All reactions were investigated in an N2-buffer (1–3 hPa) at room temperature. The reaction rate coefficients of OH-, O2 -, O3 -, CO4 -, CO3 -, CO3 -H2O, NO3 -, and NO3 -H2O were measured relative to the known rate k=3.0×10-9 cm3 s-1 for the reaction of O- with HNO3. The main product ion of the reaction of CO3 -H2O with HNO3 was found to be (CO3HNO3)- supporting a previous suggestion made on the basis of balloon-borne ACIMS measurements. For the reaction of bare CO3 - with HNO3 three product ions were observed, namely NO3 -, (NO3OH)-, and (CO3HNO3)-. The reaction rate coefficients for CO3 -H2O (1.7×10-9 cm3 s-1) and NO3 -H2O (1.6×10-9 cm3 s-1) were found to be close to the collision rate. The measured k values for bare CO3 - (1.3×10-9 cm3 s-1) and NO3 - (0.7×10-9 cm3 s-1) are somewhat smaller. The collisional dissociations of CO3 -(H2O) n , NO3 -(H2O) n (n=1, 2), (CO3HNO3)- and (NO3HNO3)-, occasionally influencing ACIMS measurements, were also studied. Fragment ion distributions were measured using a triple quadrupole mass spectrometer. The results showed that previous stratospheric nitric acid measurements were unimpaired from collisional dissociation processes whereas these processes played a major role during previous tropospheric measurements leading to an underestimation of nitric acid concentrations. Previous ACIMS HNO3 detection was also affected by the conversion of CO3 -(H2O) n to NO3 -(H2O) n due to ion source-produced neutral radicals. A novel ACIMS ion source was developed in order to avoid these problems and to improve the ACIMS method.  相似文献   

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