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1.
A new detailed multiphase halogen mechanism, the CAPRAM Halogen Module 2.0 (HM2), has been developed and coupled to the multiphase chemistry mechanism RACM-MIM2ext/CAPRAM 3.0n. The overall mechanism comprises 1,705 reactions including 595 reactions of the HM2. Halogen chemistry box model studies have been, for the first time, performed with a non-permanent cloud scenario for pristine open ocean regions in mid-latitudes. Moreover, detailed time-resolved reaction flux analysis has been used to investigate the multiphase halogen reaction cycles in more detail. Clouds significantly change the multiphase halogen chemical system and new reaction cycles are proposed for in-cloud conditions. While most gas phase concentrations are decreased for chlorine and iodine species, they are increased for bromine. Flux analyses determined the relative contributions of the methylene dihalides CH2IX (X = Cl, Br, I) as the main I atom source with a contribution of about 80 % to the total iodocarbon sources. Furthermore, HOI was confirmed to be important for chlorine activation. It is shown that 25 % of the ozone loss can be attributed to halogens. VOC oxidation by halogens is important as halogens account for about 20 % of the methane oxidation and up to 80 % of the oxidation of other VOCs. In other cases, enhanced VOC and VOC oxidation product concentration levels were found. For example, 15 % of the methyl peroxyl radicals are formed after the reaction of chlorine atoms with methane or methyl hydroperoxide. In the aqueous phase, changes in the oxidation of organics do only occur for highly oxidised organics without a C-H bond. For example, over 80 % of oxalic acid are oxidised by electron transfer with Cl2 ? in deliquescent particles during non-cloud periods.  相似文献   

2.
Halogens in the atmosphere chemically destroy ozone. In the troposphere, bromine has higher ozone destruction efficiency than chlorine and is the halogen species with the widest geographical spread of natural sources. We investigate the relative strength of various sources of reactive tropospheric bromine and the influence of bromine on tropospheric chemistry using a 6-year simulation with the global chemistry transport model MOZART4. We consider the following sources: short-lived bromocarbons (CHBr3, CH2BrCl, CHBr2Cl, CHBrCl2, and CH2Br2) and CH3Br, bromine from airborne sea salt particles, and frost flowers and sea salt on or in the snowpack in polar regions. The total bromine emissions in our simulations add up to 31.7 Gmol(Br)/yr: 63 % from polar sources, 24.6 % from short-lived bromocarbons and 12.4 % from airborne sea salt particles. We conclude from our analysis that our global bromine emission is likely to be on the lower end of the range, because of too low emissions from airborne sea salt. Bromine chemistry has an effect on the oxidation capacity of the troposphere, not only due to its direct influence on ozone concentrations, but also by reactions with other key chemical species like HO x and NO x . Globally, the impact of bromine chemistry on tropospheric O3 is comparable to the impact of gas-phase sulfur chemistry, since the inclusion of bromine chemistry in MOZART4 leads to a decrease of the O3 burden in the troposphere by 6 Tg, while we get an increase by 5 Tg if gas-phase sulfur chemistry is switched off in the standard model. With decreased ozone burden, the simulated oxidizing capacity of the atmosphere decreases thus affecting species associated with the oxidation capacity of the atmosphere (CH3OOH, H2O2).  相似文献   

3.
Summary We have used a multi-phase cloud photochemistry model to investigate the influence of dissolved iron (Fe) and copper (Cu) on the in-cloud production and loss of ozone and ozone-related species. Comparison of the results of our simulations with and without Fe and Cu reactions for three different photochemical scenarios (marine, averaged continental and polluted continental) indicate that Fe and Cu reactions, depending upon the scenario considered, can either increase or decrease the predicted rate of loss of ozone and ozone related species. For the marine and averaged continental scenarios the rate of loss of ozone in the aqueous-phase was decreased by as much as 45% and 70%, respectively, when Fe and Cu reactions were considered. For polluted continental conditions, the rate of loss of ozone in the aqueous phase increased with a factor 2 for low metal concentrations up to a factor 20 for high metal concentrations. In all three scenarios inclusion of the Fe and Cu reactions results in cloud droplets becoming more efficient sinks for gas-phase HO2 and also enhances OH production. The net effect of the decreased losses of ozone from the aqueous phase and the effect of the cloud droplets on HO2 and OH determine the overall impact on ozone and ozone related species, for each of the situations considered. Overall, when Fe and Cu reactions were included the marine cloud was found to be a less efficient sink for ozone, and averaged continental and polluted continental clouds were more efficient sinks for ozone (O3 losses doubled in the averaged continental scenario). The higher OH flux in the aqueous phase also enhances the rate at which organic compounds, such as formaldehyde and formic acid, are oxidized in the cloud.With 4 Figures  相似文献   

4.
Two recent gas-phase chemical kinetic mechanisms for tropospheric ozone formation, one based on the lumped-structure approach (CB05) and the other based on the lumped-molecule approach (RACM2), are compared for simulations of ozone over Europe. The host air quality model is POLAIR3D of the Polyphemus modeling platform. A one-month period (15 July to 15 August 2001) is simulated. Model performance is satisfactory with both mechanisms. Overall, the two mechanisms give similar results with a domain-averaged difference of 3 ppb and a mean fractional absolute difference of 5% (values averaged over the month for the daily 8-h average maximum ozone concentrations). This difference results from different treatments in the two mechanisms for both inorganic and organic chemistry. Differences in the treatment of the inorganic chemistry are due mainly to differences in the kinetics of two reactions: NO + O3 \(\longrightarrow\) NO2 + O2 and NO + HO2 \(\longrightarrow\) NO2 + OH. These differences lead to a domain-averaged difference in ozone concentration of 5%, with RACM2 kinetics being more conducive to ozone formation. Differences in the treatment of organic chemistry lead to a domain-averaged difference in ozone concentration of 3%, with CB05 chemistry being more conducive to ozone formation. This average difference results in part from compensating effects among various VOC classes and some significant differences are identified at specific locations (the coastline of northern Africa and eastern Europe: 9%) and for specific organic classes (aldehydes, biogenic alkenes and aromatics). Differences in the treatment of the organic chemistry result from various aspects. For some VOC classes, such as aldehydes and biogenic alkenes, the more detailed explicit treatments using more model species in RACM2 lead to either greater or lower reactivity depending on the assumptions made for the oxidation products. For other VOC species, such as aromatics, the assumptions made about the major chemical oxidation pathways (aromatic alcohol formation in CB05 vs. ring opening in RACM2) affect the ozone formation significantly. Reconciliation of different chemical kinetic mechanisms will require experimental data to reduce current uncertainties in the kinetic (e.g., NO oxidation) and mechanistic (e.g., aromatics oxidation) representations of major chemical pathways.  相似文献   

5.
The mathematical model presented in this paper describes in detail the gas-phase chemistry (22 reactions), gas-phase/liquid-phase equilibrium (18 equilibria) and liquid-phase chemistry (57 reactions and equilibria) in a stratiform cloud system. The model is used to analyze the influence of the liquid phase on the photooxidant formation and destruction for different gaseous SO2 concentrations with and without consideration of organic aqueous phase chemistry. It has been shown that for [SO2]>1 ppb the cloud is quantitatively a sink for H2O2, OH, HO2 and O3. The ozon destruction via O3+O2 -, which is most important in remote areas, is in polluted areas only significant at summer days. The role of organic components in cloud water consists in the transformation OH HO2 where HO2 is further transformed into H2O2.  相似文献   

6.
Using the global chemistry and transport model MOZART,the simulated distributions of tropospheric hydroxyl free radicals(OH) over China and its sensitivities to global emissions of carbon monoxide(CO),nitrogen oxide(NO x),and methane(CH 4) were investigated in this study.Due to various distributions of OH sources and sinks,the concentrations of tropospheric OH in east China are much greater than in west China.The contribution of NO + perhydroxyl radical(HO 2) reaction to OH production in east China is more pronounced than that in west China,and because of the higher reaction activity of non-methane volatile organic compounds(NMVOCs),the contributions to OH loss by NMVOCs exceed those of CO and take the dominant position in summer.The results of the sensitivity runs show a significant increase of tropospheric OH in east China from 1990 to 2000,and the trend continues.The positive effect of double emissions of NO x on OH is partly offset by the contrary effect of increased CO and CH 4 emissions:the double emissions of NO x will cause an increase of OH of 18.1%-30.1%,while the increases of CO and CH 4 will cause a decrease of OH of 12.2%-20.8% and 0.3%-3.0%,respectively.In turn,the lifetimes of CH 4,CO,and NO x will increase by 0.3%-3.1% with regard to double emissions of CH 4,13.9%-26.3% to double emissions of CO and decrease by 15.3%-23.2% to double emissions of NO x.  相似文献   

7.
The Model of Multiphase Cloud Chemistry M2C2 has recently been extended to account for nucleation scavenging of aerosol particles in the cloud water chemical composition. This extended version has been applied to multiphase measurements available at the Puy de Dôme station for typical wintertime anthropogenic air masses. The simulated ion concentrations in cloud water are in reasonable agreement with the experimental data. The analysis of the sources of the chemical species in cloud water shows an important contribution from nucleation scavenging of particles which prevails for nitrate, sulphate and ammonium. Moreover, the simulation shows that iron, which comes only from the dissolution of aerosol particles in cloud water, has a significant contribution in the hydroxyl radical production. Finally, the simulated phase partitioning of chemical species in cloud are compared with measurements. Numerical results show an underestimation of interstitial particulate phase fraction with respect to the measurements, which could be due to an overestimation of activated mass by the model. However, the simulated number scavenging efficiency of particles agrees well with the measured value of 40% of total number of aerosol particles activated in cloud droplets. Concerning the origin of chemical species in cloud water, the model reproduces quite well the contribution of gas and aerosol scavenging estimated from measurements. In addition, the simulation provides the contribution of in-cloud chemical reactivity to cloud water concentrations.  相似文献   

8.
Measurements of OH reactivity were made at the Weybourne Atmospheric Observatory on the North Norfolk coast, UK in May 2004. A wide range of supporting species was also measured concurrently as part of the TORCH-2 field campaign, allowing a detailed study of the OH oxidation chemistry to be carried out. Measurements were made in a variety of air masses, with the 3 most prevalent being air from the Atlantic that arrived at the site from over mainland UK in a South Westerly direction, and much cleaner Northerly air that originated over the far North Sea or Arctic, passed over the North Sea and arrived at the site from a North/North Easterly direction. Direct OH reactivity measurements were made on 6 days during the campaign and with influence of 2 of the 3 air masses prevalent during the study period. The average, minimum and maximum measured OH reactivity are: 4.9, 1.3 and 9.7 respectively. The measured OH reactivity was compared to key OH sinks such as NO2 and CO and a general positive correlation was observed. OH reactivity (k′) was then calculated using the full range of OH sinks species that were measured (including >30 NMHCs) and their pseudo first order rate constants for reaction with OH. For much of the measurement period there is a significant difference between the measured and calculated k′, with an average value of k′meas- k′calc?=?1.9 s-1, indicative of unmeasured OH sinks. A zero-dimensional box model containing a subset of the Master Chemical Mechanism was used to calculate the OH reactivity more accurately. The simultaneously measured trace species were used as inputs to the model and their oxidative degradation was described by a chemical mechanism containing ~5,000 species. The extra OH sinks species produced by the model, resulted in an improvement in the agreement between k′meas and k′calc, however the averaged missing OH reactivity across the entire measurement period remained at 1.4 s-1. Speculation is made as to the source of this missing reactivity, including reference to studies showing that a potentially large number of high molecular weight aromatic species could be unmeasured by standard instrumentation.  相似文献   

9.
Global secondary organic aerosol formation (SOA) is currently assumed to be between 11.2 and 270 Tg/yr. This range of uncertainty is reflected in the gas-phase chemistry. In this study, we focus on the feedback of SOA formation on the concentrations of most important trace gases such as ozone, and compare it to the impact of monoterpene gas-phase chemistry with a newly developed reduced monoterpene mechanism (MMM) for either α- or β-pinene in the global chemistry transport model MATCH-MPIC. With this set-up an uncertainty range of 3.5–4.0% increase in annually averaged tropospheric ozone was found to be caused by the gas-phase chemistry of the investigated monoterpenes. Moreover, a strong feedback has been observed for NOx, HCHO, HNO3 and PAN. These observations are affected remarkably by different SOA formation approaches like partitioning or saturation vapour pressure limitation and by the structure of the monoterpene used, e.g. reducing the impact on tropospheric ozone to 1.2–1.9% by using the partitioning approach versus the simulation with gas-phase chemistry only. Therefore, a consideration of the individual processes associated with SOA formation seems to be necessary to reduce the uncertainty in SOA formation and to understand the impact of VOCs on atmospheric chemistry. An erratum to this article is available at .  相似文献   

10.
A one-dimensional, time-dependent model of the physics and chemistry of a warm stratiform cloud is used to study the possible impact of chemical inhomogeneity among cloud and raindrops on the oxidation of SO2 in clouds. The effects of chemical inhomogeneity are examined using two contrasting models: In Model 1 a bulk-solution parameterization is adopted which effectively treats all cloud and raindrops as if they are chemically homogeneous; in Model 2 we allow the cloud and raindrops to have a dichotomous distribution. The dichotomous distribution in Model 2 is simulated by assuming that the two groups of cloud droplets nucleate from two chemically distinct populations of condensation nuclei; one being acidic and the other being alkaline. While the two models yield essentially identical results when the ambient levels of H2O2 are greater than the ambient levels of SO2, the rate of conversion of SO2 to sulfuric acid and the amount of sulfate removed in the precipitation can be significantly enhanced in Model 2 over that of Model 1 under conditions of oxidant limitation (i.e., H2O2 < SO2). This enhancement is critically dependent upon the fraction of alkaline nuclei assumed to be present in Model 2 and arises from the rapid increase in the aqueous-phase reaction between O3+SIV at high pH. Our results suggest that cloud models which adopt a bulk-solution parameterization for cloud droplet chemistry, may underestimate the amount of in-cloud SO2 oxidation under oxidant-limited conditions.  相似文献   

11.
A chemistry module has been incorporated into a Lagrangian type model that computes the dynamics and microphysics of an orographical cloud formed in moist air flowing over the summit of Great Dun Fell (GDF) in England. The cloud droplets grow on a maritime aerosol which is assumed to be an external mixture of sea-salt particles and ammonium-sulfate particles. The dry particle radii are in the range 10 nm<r<1 µm. The gas-phase chemical reaction scheme considers reactions of nitrogen compounds that are important at night. The treatment of scavenging of gases into the aqueous phase in the model takes into account the different solubilities and accommodation coefficients. The chemistry in the aqueous phase focusses on the oxidation of S(IV) via different pathways.Sensitivity analyses have been performed to investigate deviations from gas-liquid equilibria according to Henry's law and also to study the influence of iron and of nitrogen compounds on the aqueous-phase oxidation of dissolved SO2. When addressing these questions, special attention has been given to the dependence on the droplet size distribution and on the chemical composition of the cloud condensation nuclei on which the droplets have formed. It was found that the oxidation of S(IV) via a chain reaction of sulfur radicals can be important under conditions where H2O2 is low. However, major uncertainties remain with respect to the interaction of iron with the radical chain. It was shown that mixing of individual cloud droplets, which are not in equilibrium according to Henry's law, can result in a bulk sample in equilibrium with the ambient air. The dependence of the aqueous-phase concentrations on the size of the cloud droplets is discussed for iron, chloride and NO3.  相似文献   

12.
The formation of gas-phase products from the reaction of OH radicals with isoprene for low-NOx conditions ([NOx] ≤ 1010 molecule cm?3) has been studied in an atmospheric pressure flow tube (Institute for Tropospheric Research-Laminar Flow Tube, IfT-LFT) operating in the temperature range of 293–343 K and a relative humidity of < 0.5 % up to 50 %. The photolysis of H2O2 or ozone photolysis in the presence of water vapour served as the NOx-free OH radical sources. For dry conditions at 293 K, the measured yields of methyl vinyl ketone (MVK), 0.07?±?0.02, and methacrolein (MACR), 0.12?±?0.04, were in reasonable agreement with literature data. Beside the C4-carbonyls, further product signals have been attributed tentatively to glycolaldehyde, methylglyoxal, hydroxyacetone, 3-methylfuran, C5-hydroperoxyenals (HPALDs) and C5-hydroxy-hydroperoxides. A simplified, “classical” reaction mechanism without efficient HPALD production describes well the observed yield for MVK and MACR. Unexpected high MVK and MACR yields of up to 0.65 in total were measured under conditions of a relative humidity of 50 % using both OH radical sources and two different measurement techniques for organics (proton transfer reaction mass spectrometry and gas chromatography with flame ionization detector). The reaction mechanism applied is not able to describe the strong increase of MVK and MACR yields with increasing water vapour content. The signal attributed to the HPALDs showed a distinct rise of about one order of magnitude increasing the temperature from 293 K to 343 K. A rough estimate leads to a HPALD yield of 0.32 at 343 K with an uncertainty of a factor of two. The results of this study do not support a predominant formation of HPALDs under atmospheric conditions in low-NOx areas. The surprisingly high MVK and MACR yields measured for a relative humidity of 50 % and the formation of glycolaldehyde, methylglyoxal and hydroxyacetone necessitate further research.  相似文献   

13.
Mechanism reductions of the detailed aqueous phase chemistry mechanism CAPRAM 3.0i are performed. Manual methods and automatic techniques are both applied in order to provide a less computationally intensive mechanism which is operational in regional chemistry transport models (CTMs). The finally reduced mechanism contains less than 200 reactions (4 times smaller than the detailed CAPRAM 3.0i) and describes the main characteristics of inorganic and organic aqueous phase processes occurring in tropospheric warm clouds. Most of the chemical reduction potential is realized in the CAPRAM 3.0i organic chemistry. The number of aqueous phase species decreases from 380 in the full mechanism to 130 in the final reduced version. The calculated percentage deviations between the full and reduced mechanism are on average below 5% for the most important organic and inorganic target compounds such as oxidants, inorganic and organic acids, carbonyls and alcohols. Comparisons of the required CPU times between the full and reduced mechanisms show reductions of approximately 40%. 2-D test simulations with the CTM MUSCAT were performed using prescribed meteorological conditions in order to examine the applicability of the reduced mechanism at regional scale. Simulations with the reduced CAPRAM 3.0i mechanism and a much less complex mechanism with only limited inorganic chemistry (INORG) were compared to evaluate the effects of more detailed chemistry. The model results show large differences in the level of oxidants and the inorganic and organic mass processing. Prospectively, the reduced mechanism represents the basis for studying aerosol cloud processing effects at regional scale with future CTMs and will allow more adequate interpretation of field data.  相似文献   

14.
We examine the sensitivities of heterogeneous sulfate chemistry in a mid-latitude and tropical storm using a cloud resolving model. Both thermodynamic environments show unstable conditions favorable for development of intensive convection, with more CAPE in tropical compared to mid-latitude storm. Compared with the observed severe storms, modeled results show a relatively good agreement with the radar and surface chemical observations. Microphysical evaluation indicates that the accretion and autoconversion appear to be most important processes in such considered clouds. This sensitivity simulation is an upper bound for conversion of S (IV) to sulfate. The tropical convective storm produces for about 2.5 times more sulfate compared to mid-latitude storm and converts more SO2 to sulfate, increasing wet deposition of sulfur. The results for a midlatitude run indicate that aerosol nucleation and impact scavenging account for between 18.9% and 28.9% of the in-cloud sulfate ultimately deposited. As a result of greater rainfall efficiency, tropical storm shows about two times higher sub-cloud scavenging rate than mid-latitude storm. The oxidation of S (IV) to SO4 ?2 in cloud droplets and in precipitation is found to be dominant in both convective storms accounting almost with the same percentage contribution of 45.4% and 46.3% to sulfur deposition, respectively. In-cloud oxidation contribute a larger fraction of the total amount of sulfur deposited in tropical case (29.2%) when compared to the mid-latitude case (11.8), respectively. Neglecting aqueous-phase chemistry in ice-phase hydrometeors in both convective clouds led to overpredict deposition of about 40% to 33% relative to the base runs.  相似文献   

15.
Iron is the most abundant transition metal in the atmosphere and can play a significant role in cloudwater chemistry where its reactivity is closely related to the partitioning between Fe(II) and Fe(III). The objective of this work is to determine the total iron content and the iron speciation in a free tropospheric site, and to understand which factors influence these parameters. We collected 147 samples of cloudwater during 34 cloud events over a period of four years at the puy de Dôme summit. Besides iron we measured other chemical compounds, solar radiation, physico-chemical and meteorological parameters potentially connected with iron reactivity. The total iron concentrations ranged from 0.1 to 9.1 μM with the major frequency occurring at low levels. The pH and presence of organic complexants seem to be the most significant factors connected with total dissolved iron; while the iron oxidation state seems to be an independent factor. Light intensity, presence of complexants or oxidants (H2O2) do not influence the Fe(II)/Fe(Total) ratio, that was quite constant at about 0.75. This could be due to the potential redox that forces the Fe(II)-Fe(III) couple to the reduced form or, more probably to the complexation by Natural Organic Matter, that can stabilize iron in its reduced form and prevent further oxidation. Our field measurements did not show the diurnal cycle observed in surface water and predicted by models of atmospheric chemistry. This result prompts a more careful review of the role of iron and, by analogy, all the transition metals in atmospheric liquid phase, often over-estimated in the literature.  相似文献   

16.
A box model is used to explore the detailed chemistry of C2 and C3 organic compounds in the marine troposphere by tracing the individual reaction paths resulting from the oxidation of ethane, ethene, acetylene, propane, propene and acetic acid. The mechanisms include chemical reactions in the gas phase and in the aqueous phase of clouds and aerosol particles at cloud level under conditions resembling those in the northern hemisphere. Organic hydroperoxides are found to be important intermediate products, with subsequent reactions leading partly to the formation of mixed hydroxy or carbonyl hydroperoxides that are readily absorbed into cloud water, where they contribute significantly to the formation of multifunctional organic compounds and organic acids. Organic hydroperoxides add little to the oxidation of sulfur dioxide dissolved in the aqueous phase, which is dominated by H2O2. Next to acetaldehyde and acetone, glycol aldehyde, glyoxal, methyl glyoxal and hydroxy propanone are prominent oxidation products in the gas and the aqueous phase. Acetaldehyde is not efficiently converted to acetic acid in clouds; the major local sources of acetic acid are gas-phase reactions. Other acids produced include hydroperoxy acetic, glycolic, glyoxylic, oxalic, pyruvic, and lactic acid. The mechanism of Schuchmann et al. (1985), which derives glycolic and glyoxylic acid from the oxidation of acetate, is found unimportant in the marine atmosphere. The principal precursors of glyoxylic acid are glyoxal and glycolic acid. The former derives mainly from acetylene and ethene, the latter from glycolaldehyde, also an oxidation product of ethene. The oxidation of glyoxylic acid leads to oxalic acid, which accumulates and is predicted to reach steady state concentrations in the range 30–90 ng m−3. This is greater, yet of the same magnitude, than the concentrations observed over the remote Pacific Ocean.  相似文献   

17.
The yields of carbonyl-containing reaction products from the ozonolysis of α-pinene have been investigated using concentrations of ozone found in the indoor environment ([O3] ≤ 100 ppb). An impinger was used to collect gas-phase oxidation products in water, where the derivatization agent O-tert-butylhydroxylamine hydrochloride (TBOX) and gas chromatography-mass spectrometry were used to identify carbonyl-containing species. Seven carbonyl-containing products were observed. The yield of the primary product, pinonaldehyde was measured to be 76 %. Using cyclohexane as a hydroxyl radical (?OH) scavenger, the yield of pinonaldehyde decreased to 46 %, indicating the influence secondary OH radicals have on α-pinene ozonolysis products. Furthermore, the use of TBOX, a small molecular weight derivatization agent, allowed for the acquisition of the first mass spectral data of oxopinonaldehyde, a tricarbonyl reaction product of α-pinene ozonolysis. The techniques described herein allow for an effective method for the collection and identification of terpene oxidation products in the indoor environment.  相似文献   

18.
The chemistry of cloud multiphase systems was studied within the Kleiner Feldberg Cloud Experiment 1990. The clouds encountered during this experimental campaign could be divided into two categories according to the origin of air masses in which the clouds formed. From the chemical point of view, clouds passing the sampling site during the first period of the campaign (26 October-4 November) were characterized by lower pollutant loading and higher pH, as compared to clouds during the final period of the experimental campaign (10–13 November). The study of multiphase partitioning of the main chemical constituents of the cloud systems and of atmospheric acidity within the multiphase systems themselves (gas + interstitial aerosol + liquid droplets) are presented in this paper. A general lack of gaseous NH3 was found in these cloud systems, which caused a lack of buffer capacity toward acid addition. Evidence supports the hypothesis that the higher acidity of the cloud systems during this final period of the campaign was due to input of HNO3. Our measurements, however, could not determine whether the observed input was due to scavenging of gaseous HNO3 from the air feeding into the cloud, or to heterogeneous HNO3 formation via NO2 oxidation by O3 to NO3 and N2O5. Sulfate in cloud droplets mainly originated from aerosol SO 4 2– scavenging, since S(IV) to S(VI) liquid phase conversion was inhibited due to both lack of H2O2 and low pH of cloud droplets, which made O3 and metal catalyzed S(IV) oxidation inefficient.  相似文献   

19.
Beijing is one of the largest and most densely populated cities in China. PM2.5 (fine particulates with aerodynamic diameters less than 2.5 μm) pollution has been a serious problem in Beijing in recent years. To study the temporal and spatial variations in the chemical components of PM2.5 and to discuss the formation mechanisms of secondary particles, SO2, NO2, PM2.5, and chemical components of PM2.5 were measured at four sites in Beijing, Dingling (DL), Chegongzhuang (CG), Fangshan (FS), and Yufa (YF), over four seasons from 2012 to 2013. Fifteen chemical components, including organic carbon (OC), elemental carbon (EC), K+, NH4 +, NO3 ?, SO4 2?, Cl?, Al, Ca, Fe, Mg, Na, Pb, Si, and Zn, were selected for analysis. Overall, OC, SO4 2?, NO3 ?, and NH4 + were dominant among 15 components, the annual average concentrations of which were 22.62 ± 21.86, 19.39 ± 21.06, 18.89 ± 19.82, and 13.20 ± 12.80 μg·m?3, respectively. Compared with previous studies, the concentrations of NH4 + were significantly higher in this study. In winter, the average concentrations of OC and EC were, respectively, 3 and 2.5 times higher than in summer, a result of coal combustion during winter. The average OC/EC ratios over the four sites were 4.9, 7.0, 8.1, and 8.4 in spring, summer, autumn, and winter, respectively. The annual average [NO3 ?]/[SO4 2?] ratios in DL, CG, FS, and YF were 1.01, 1.25, 1.08, and 1.12, respectively, which were significantly higher than previous studies in Beijing, indicating that the contribution ratio of mobile source increased in recent years in Beijing. Analysis of correlations between temperature and relative humidity and between SOR ([SO4 2?]/([SO4 2?] + [SO2])) and NOR ([NO3 ?]/([NO3 ?] + [NO2])) indicated that gas-phase oxidation reactions were the major formation mechanism of SO4 2? in spring and summer in urban Beijing, whereas slow gas-phase oxidation reactions and heterogeneous reactions both occurred in autumn and winter. NO3 ? was mainly formed through year-round heterogeneous reactions in urban Beijing.  相似文献   

20.
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