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1.
We use a global atmospheric chemistry transport model to study the possible influence of aqueous phase reactions of peroxynitric acid (HNO4) on the concentrations and budgets of NOx, SOx, O3 and H2O2. Laboratory studies have shown that the aqueous reaction of HNO4aq withHSO– 3aq, and the uni-molecular decomposition of the NO4 – anion to form NO2 – (nitrite) occur on a time scale of about a second. Despite a substantial contribution of the reaction of HSO– 3aq with HNO4aq to the overall in-cloud conversion of SO2 to SO4 2–, a simultaneous decrease of other oxidants (most notably H2O2) more than compensated the increase in SO4 2– production. The strongest influence of heterogeneous HNO4 chemistry was found in the boundary layer, where calculated monthly average ozone concentrations were reduced between 2% to 10% andchanges of H2O2 between –20% to +10%compared to a simulation which ignores this reaction. Furthermore, SO2 was increased by 10% to 20% and SO4 2–depleted by up to 10%. Since the resolution of our global model does not enable a detailed comparison with measurements in polluted regions, it is not possible to verify whether considering heterogeneous HNO4 reactions results in a substantial improvement of atmospheric chemistry transport models. However, the conversion of HNO4 in the aqueous phase seems to be efficient enough to warrant further laboratory investigations and more detailed model studies on this topic.  相似文献   

2.
The kinetics of heterogeneous reactions of NO2 with 17 polycyclic aromatic hydrocarbons (PAHs) adsorbed on laboratory generated kerosene soot surface was studied over the temperature range (255–330) K in a low pressure flow reactor combined with an electron-impact mass spectrometer. The kinetics of soot-bound PAH consumption due to their desorption and reaction with NO2 were monitored using off-line HPLC measurements of their concentrations in soot samples as a function of reaction time, NO2 concentrations in the gas phase being analyzed by mass spectrometer. No measurable decay of PAHs due to the reaction with NO2 was observed under experimental conditions of the study (maximum NO2 concentration of 5.5 × 1014 molecule cm−3 and reaction time of 45 min), which allowed to determine the upper limits of the first-order rate constants for the heterogeneous reactions of 17 soot-bound PAHs with NO2: k < 5.0 × 10−5 s−1 (for most PAHs studied). Comparison of these results to previous studies carried on different carbonaceous substrates, showed that heterogeneous reactivity of PAHs towards NO2 is, probably, dependent on the substrate nature even for resembling, although different carbonaceous materials. Results show that particulate PAHs degradation by NO2 alone is of minor importance in the atmosphere  相似文献   

3.
The chemical conversion of emitted SO2 and SO3 to gaseous H2SO4 in nascent aircraft exhaust plumes and subsequent adsorption of the fully oxidized sulfur species on the surfaces of emitted combustion aerosols (soot) is investigated. Results are presented for the mass fractions of SO3 and H2SO4 acquired per soot particle early in the plume, suggesting that sulfur-induced activation is an efficient pathway to increase the ability of exhaust soot emitted at altitude to host heterogeneous chemical reactions and to trigger the formation of cirrus clouds.  相似文献   

4.
The contribution of emissions from agricultural facilities is rapidly becoming a major concern for local and regional air quality. Characterization of particle properties such as physical size distribution and chemical composition can be valuable in understanding the processes contributing to emissions and ultimate fate of particulate matter from agricultural facilities. A measurement campaign was conducted at an Iowa, deep-pit, three-barn swine finishing facility to characterize near-source ambient particulate matter. Size-specific mass concentrations were determined using minivol samplers, with additional size distribution information obtain using optical particle counters. Particulate composition was determined via ion chromatographic analysis of the collected filters. A thermal-CO2 elemental/organic carbon analyzer measured particulate carbon. The chemical composition and size distribution of sub-micron particles were determined via real-time aerosol mass spectrometry. Primary particulate was not found to be a major emission from the examined facility, with filter-based impactor samples showing average near-source increases (~15–50 m) in ambient PM10 of 5.8 ± 2.9 μg m−3 above background levels. PM2.5 also showed contribution attributable to the facility (1.7 ± 1.1 μg m−3). Optical particle counter analysis of the numerical size distributions showed bimodal distributions for both the upwind and downwind conditions, with maximums around 2.5 μm and below the minimum quantified diameter of 0.3 μm. The distributions showed increased numbers of coarse particles (PM10) during periods when wind transport came from the barns, but the differences were not statistically significant at the 95% confidence level. The PM10 aerosols showed statistically increased concentrations of sulfate, nitrate, ammonium, calcium, organic carbon, and elemental carbon when the samplers were downwind from the pig barns. Organic carbon was the major constituent of the barn-impacted particulate matter in both sub-micron (54%) and coarse size (20%) ranges. The AMS PM1 chemical speciation showed similar species increases, with the exception of and Ca+2, the latter not quantified by the AMS.  相似文献   

5.
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6.
Using the chemical composition of snow and ice of a central Greenland ice core, we have investigated changes in atmospheric HNO3 chemistry following the large volcanic eruptions of Laki (1783), Tambora (1815) and Katmai (1912). The concentration of several cations and anions, including SO 4 2– and NO 3 – , were measured using ion chromatography. We found that following those eruptions, the ratio of the concentration of NO 3 – deposited during winter to that deposited during summer was significantly higher than during nonvolcanic periods. Although we cannot rule out that this pattern originates from snow pack effects, we propose that increased concentrations of volcanic H2SO4 particles in the stratosphere may have favored condensation and removal of HNO3 from the stratosphere during Arctic winter. In addition, this pattern might have been enhanced by slower formation of HNO3 during summer, caused by direct consumption of OH through oxidation of volcanic SO2.  相似文献   

7.
Upto 13% of -pinene and 3-carene had reacted after 213 s in this dark experimental set-up, where O3, NO and NO2 were mixed with terpenes at different relative humidities (RHs). The different experiments were planned according to an experimental design, where O3, NO2, NO, RH and reaction time were varied between high and low settings (25 and 75 ppb, 15 and 42%, 44 and 213 s). An increased amount of -pinene and 3-carene reacted in the chamber was observed, when the level of O3, NO and reaction time was increased and RH was decreased. In the study, it was found that different interactions affected the amount of terpene reacted as well. These interactions were between O3 and NO, O3 and reaction time, NO and RH, and between NO and reaction time.  相似文献   

8.
Epidemiological studies initially considered the impact of total solid particles on human health, but according to the acquired knowledge about the worse effect of smaller particles, those studies turned to consider the impact of PM10. However, for the last decade PM2.5 began to be more important, once as they are smaller they can penetrate deeper in the lungs, being possible their trapping in alveoli and worse effects on human health. Therefore, more information on PM2.5 should be provided namely concerning the levels and elemental composition. Considering the relevance of traffic on the emission of particles of small sizes, this work included the detailed characterization of PM10 and PM2.5, sampled at two sites directly influenced by traffic, as well as at two reference sites, aiming a further evaluation of the influence of PM10 and PM2.5 on public health. The specific objectives were to study the influence of traffic emission on PM10 and PM2.5 characteristics, considering concentration, size distribution and elemental composition. PM10 and PM2.5 samples were collected using low-volume samplers; the element analyses were performed by particle induced X-ray emission (PIXE). At the sites influenced by traffic emissions PM10 and PM2.5 concentrations were 7–9 and 6–7 times higher than at the background sites. The presence of 17 elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn and Pb) was determined in both PM fractions; particle metal contents were 3–44 and 3–27 times higher for PM10 and PM2.5, respectively, than at the backgrounds sites. The elements originated mostly from anthropogenic activities (S, K, V, Mn, Ni, Zn and Pb) were predominantly present in PM2.5, while the elements mostly originated from crust (Mg, Al, Si and Ca) predominantly occurred in PM2.5–10. The results also showed that in coastal areas sea salt spray is an important source of particles, influencing PM concentration and distributions (PM10 increased by 46%, PM2.5/PM10 decreased by 26%), as well as PM compositions (Cl in PM10 was 11 times higher).  相似文献   

9.
The growth of monodisperse particles (0.07 to 0.5 µm) exposed to SO2 (0–860 ppb), H2O2 (0–150 ppb) and sometimes NH3 (0–550 ppb) in purified air at 22 °C at relative humidities ranging from 25 to 75% were measured using the Tandem Differential Mobility Analyzer technique. The experiments were performed in a flow reactor with aqueous (NH4)2SO4 and Na2SO4 droplets. For (NH4)2SO4 droplets the fractional diameter growth was independent of size above 0.3 µm but decreased with decreasing size below that. When NH3 was added the fractional growth increased with decreasing size. Measurements were compared with predictions of a model that accounts for solubility of the reactive gases, the liquid phase oxidation of SO2 by H2O2, and ionic equilibria. Agreement between measured and predicted droplet growth is reasonable when the ionic strength effects are included. Theory and experiments suggest that NH3 evaporation is responsible for the decrease in relative growth rates for small aqueous ammonium sulfate particles. The observed droplet growth rates are too slow to explain observed growth rates of secondary atmospheric sulfate particles.  相似文献   

10.
对临安大气本底站2003-2004年冬、夏季二氧化氮(NO2)、二氧化硫(SO2)、臭氧(O3)进行了分析.结果表明:冬季NO2和SO2平均体积分数分别为19.48×10-9和35.74 x10-9,而夏季的平均体积分数分别为4.81×10-9和8.12×10-9,冬季高于夏季;O3在夏季的平均体积分数为33.55×10-9,略高于冬季的25.44×10-9;夜间NO2和SO2体积分数比白天高,并且NO2呈明显的单峰单谷型分布,O3也呈单峰型但峰值出现在白天.NO2、SO2体积分数存在着明显的“假日效应”,假日比非假日低,周五高于假日和非假日;但O3体积分数没有明显的假日效应.降水对SO2有明显的清除作用,但对NO2的清除作用不明显.与风向对比发现,夏季高体积分数的NO2、SO2都受到NW、WNW风的影响,冬季则分别受NE和SW、SSW风的影响;而O3受风向的影响较复杂,与局地光化学反应有关.  相似文献   

11.
Products of the gas-phase reaction of the NO3 radical with thiophene have been investigated using different experimental systems. On the one hand, experiments have been conducted in our laboratory using two different methods, a Teflon static reactor coupled to a gas chromatograph combined with mass-spectrometry (GC-MS) and a discharge flow tube with direct MS spectroscopic detection. A qualitative analysis in these cases indicates that possible products for the reaction of thiophene+NO3 at room temperature include: sulphur dioxide, acetic and formic acids, a short-chain aldehyde, 2-nitrothiophene and 3-nitrothiophene. On the other hand, quantitative experiments have been performed in the European Photoreactor (EUPHORE) in Valencia, Spain. In this case, the major products were: HNO3 (≈80%), nitrothiophenes (≈30%), SO2 (≈20%), propanal (3%) and a fraction of particles (≈10%). The results obtained indicate that at least 70% of the reaction of NO3 with thiophene proceeds by an H-abstraction process at room temperature. The mechanism of the reaction studied is proposed on the basis of experimental results.  相似文献   

12.
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   

13.
The pK 1 * and pK 2 * of H2SO3 have been determined in NaCl solutions as a function of ionic strength (0.1 to 6 m) and temperature (5 and 25 °C). The extrapolated values in water were found to be in good agreement with literature data. The experimental results have been used to determine the Pitzer interaction parameters for SO2, HSO 3 - and SO 3 - in NaCl solutions. The resultant parameters for NaHSO3 and Na2SO3 were found to be in reasonable agreement with the values for NaHSO4 and Na2SO4. It, thus, seems reasonable to assume that the interactions of Mg2+ and Ca2+ with HSO 3 - and SO 3 - can be estimated from the values with HSO 4 - and SO 4 - until experimental values are available. Measurements of pK 1 * and pK 2 * in artificial seawater were found to be in good agreement with the calculated values using the derived Pitzer parameters. It is, thus, possible to make reasonable estimates of the activity coefficients of HSO 3 - and SO 3 - ions and pK 1 * and pK 2 * for the ionization of H2SO3 in marine aerosols.  相似文献   

14.
Products and mechanisms of the reaction between the nitrate radical (NO3) and three of the most abundant reduced organic sulphur compounds in the atmosphere (CH3SCH3, CH3SH and CH3SSCH3), have been studied in a 480 L reaction chamber using in situ FT-IR and ion chromatography as analytical techniques. In the three reactions, methanesulphonic acid was found to be the most abundant sulphur containing product. In addition the stable products SO2, H2SO4, CH2O, and CH3ONO2 were identified and quantified and thionitric acid-S-methyl ester (CH3SNO2) was observed in the i.r. spectrum from all of the three reactions. Deuterated dimethylsulphide (CD3SCD3) showed an isotope effect on the reaction Deuterated dimethylsulphide (CD3SCD3) showed an isotope effect on the reaction rate constant (kH/kD) of 3.8±0.6, indicating that hydrogen abstraction is the first step in the NO3+CH3SCH3 reaction, probably after the formation of an inital adduct.Based on the products and intermediates identified, reaction mechanisms are proposed for the three reactions.  相似文献   

15.
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   

16.
The kinetics of the aqueous phase reactions of NO3 radicals with HCOOH/HCOO– and CH3COOH/CH3COO– have been investigated using a laser photolysis/long-path laser absorption technique. NO3 was produced via excimer laser photolysis of peroxodisulfate anions (S2O 8 2– ) at 351 nm followed by the reactions of sulfate radicals (SO 4 – ) with excess nitrate. The time-resolved detection of NO3 was achieved by long-path laser absorption at 632.8 nm. For the reactions of NO3 with formic acid (1) and formate (2) rate coefficients ofk 1=(3.3±1.0)×105 l mol–1 s–1 andk 2=(5.0±0.4)×107 l mol–1 s–1 were found atT=298 K andI=0.19 mol/l. The following Arrhenius expressions were derived:k 1(T)=(3.4±0.3)×1010 exp[–(3400±600)/T] l mol–1 s–1 andk 2(T)=(8.2±0.8)×1010 exp[–(2200±700)/T] l mol–1 s–1. The rate coefficients for the reactions of NO3 with acetic acid (3) and acetate (4) atT=298 K andI=0.19 mol/l were determined as:k 3=(1.3±0.3)×104 l mol–1 s–1 andk 4=(2.3±0.4)×106 l mol–1 s–1. The temperature dependences for these reactions are described by:k 3(T)=(4.9±0.5)×109 exp[–(3800±700)/T] l mol–1 s–1 andk 4(T)=(1.0±0.2)×1012 exp[–(3800±1200)/T] l mol–1 s–1. The differences in reactivity of the anions HCOO– and CH3COO– compared to their corresponding acids HCOOH and CH3COOH are explained by the higher reactivity of NO3 in charge transfer processes compared to H atom abstraction. From a comparison of NO3 reactions with various droplets constituents it is concluded that the reaction of NO3 with HCOO– may present a dominant loss reaction of NO3 in atmospheric droplets.  相似文献   

17.
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   

18.
Generally, it is assumed that UV-light, high temperature or reactive molecules like O3 and OH are needed to activate gas reactions in air. In consequence, the catalytic activity on natural materials such as sand and soil on the earth's surface is assumed to be insignificant. We have measured O2-dissociation rates on natural quartz sand at 40˚C and compared these with O2-dissociation rates near 500˚C on materials with well-known catalytic activity. In terms of probabilities for dissociation of impinging O2-molecules the measured rates are in the 10−12–10−4 range. We have also measured dissociation rates of H2 and N2, water-formation from H2 and O2 mixtures, exchange of N between N2, NO x and a breakdown of HNO3, NO2 and CH4 on natural quartz sand at 40˚C. The measured rates together with an effective global land area have been used to estimate the impact of thermodynamically driven reactions on the earth's surface on the global atmospheric budgets of H2, NO2 and CH4. The experimental data on natural quartz sand together with data from equilibrium calculations of air suggest that an expected increase in anthropogenic supply of air pollutants, such as NO x or other “reactive” nitrogen compounds, hydrogen and methane, will be counter-acted by catalysis on the earth's surface. On the other hand, at Polar Regions and boreal forests where the “reactive” nitrogen concentration is below equilibrium, the same catalytic effect activates formation of bio-available nitrogen compounds from N2, O2 and H2O.  相似文献   

19.
Long-pathlength infrared absorption spectroscopy wasused to investigate nitric acid-soot aerosol chemistryat 298 K and 0.5% relative humidity. Experimentswere performed by introducing nitric acid vapor(PHNO 3 3 Pa, Ptotal 40 kPa) intoateflon-coated chamber and initiating acquisition ofinfrared spectra at 3 minute time intervals. After 36minutes of data collection, soot powder was rapidlyexpanded into nitric acid contained in the chamber togenerate a soot-HNO3 aerosol. Infrared spectracollected before, and after, soot introduction to thechamber were used to characterize chamber wallreaction processes and soot aerosol chemistry,respectively. Three soot types were investigated(Degussa FW2, Cabot Monarch 1000, and crystallinegraphite), each yielding similar chemistry. Upon sootintroduction to the chamber both HNO3 uptake andNO2 production occurred, with the molar ratio ofHNO3 uptake to NO2 production varying from1.2 to 2.9 for the three soot types studied. Unreacted HNO3 was present at the conclusion ofeach of the aerosol experiments, indicating incompleteconversion of HNO3 into NO2. Thisobservation suggested that `active' sites at the sootsurface responsible for the reduction of HNO3 arenot regenerated (i.e., formed) in the reactionprocess. In essence, a titration occurred betweenthese active sites and HNO3. The NO2concentrations produced, the soot mass concentrationsused, and the BET measured specific surface area ofthe powders allowed computation of the surface densityof active sites of 4.0 × 10-18 m2/active site(describing all three powders studied). This is thefirst reported measurement of surface density ofactive sites for nitric acid chemistry on soot. Sinceatmospheric heterogeneous reactions that exhibitsurface deactivation may, in principle, affect tracegas concentration, we perform an assessment in thisregard.  相似文献   

20.
A method for the estimation of the reaction probability of the heterogeneous N2O5+H2O 2HNO3 reaction using the deposition profile in a laminar flow tube, in which the walls are coated with the condensed aqueous phase of interest, is presented. The production of gas phase nitric acid on the surface followed by its absorption complicates the deposition profiles and hence the calculation of the reaction probability. An estimation of the branching ratio for this process enables a more appropriate calculation to be carried out. Reaction probabilities of N2O5 on substances including some normally constituting atmospheric aerosols, NaCl, NH4HSO4, as well as Na2CO3 are estimated and found to depend on relative humidity and characteristics of the coating used. These fell within the range (0.04–2.0)×10–2.  相似文献   

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