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1.
We measured CO2, CO, CH4, H2, and NO2 in air masses polluted by savanna fires over Côte d'Ivoire, western Africa. Elevated concentrations of these trace gases were found in fire plumes and also in extensive haze layers. Trace gas mixing ratios ranged as high as 605 ppmv for CO2, 14.8 ppmv for CO, 2.7 ppmv for CH4, 4.2 ppmv for H2, and 25 ppbv for NO2. We compare our emission ratios to those obtained in previous field and laboratory studies. The emission ratios, expressed as an average and as a range or as an average only, were: dCO/dCO2 5.3×10–2 (3–18×10–2); dCH4/dCO 5.3×10–2; dH2/dCO 2.4×10–1 and dNO2/dCO2 1.8×10–4 (1.5–2.2×10–4). The values found match those found during similar measurements, though our results point to rather vigorous burning in the savanna of western Africa.  相似文献   

2.
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   

3.
As part of the LBA-CLAIRE-98 experiment, ground level atmosphericconcentrations of O3, CO, hydroperoxides and organic acids weremeasured in the rainforest region in Surinam. Measurements of CO andO3 were also made at a coastal site.The results suggest that a significant consumption of `boundary layer' ozoneoccurs over the forested region of Surinam, with an estimated net ozoneconsumption of about 5% hr–1 during daytime. Thiswould be mainly explained by a low photochemical production and high drydeposition to the forest vegetation. Compared to other tropical sites, lowerlevels of H2O2 were observed at the rainforest site,with an average boundary layer concentration of 0.55± 0.2 nmolmol–1. Also acetic and formic acids showed relatively lowaverage boundary layer mixing ratios; 1.1± 0.4 nmolmol–1 and 1.4± 0.5 nmol mol–1,respectively. Significant correlations were found between both acids andbetween the acids and hydrogen peroxide, suggesting an atmospheric source forthe acids.From the available observations we discuss possible implications of ourmeasurements for the O3, HO2, and NOx budgetsand concentrations in the boundary layer. We conclude that, despite the highsolar irradiation, relatively low levels of O3,H2O2, HCOOH and CH3COOH are observed in theboundary layer of the rainforest of Surinam, probably due to low levels ofNOx and high levels of VOCs, which leads to loss of OH andHO2 radicals. Additionally, high deposition rates of these gasesoccur to the forest vegetation.  相似文献   

4.
The dependence of specific properties of black carbon (BC) soots on fuel type and combustion conditions has been studied, and the effects of these properties on soot particle hydration and reaction with ozone determined. Series of soots were prepared from n-hexane, diesel and JP8 aircraft fuels, utilizing a flow combustion system designed for accurate control of the air/fuel ratio in premixed flames. It has been shown that, for each of these, linear relationships exist between the state of soot surface oxidation, surface area, unpaired electron spin density, and air/fuel ratio. The interrelationship of these properties potentially enables the preparation of soots with pre-selected characteristics by establishing combustion conditions for each fuel type. Predictable variations in these soot characteristics have been demonstrated through preparations near sea level and at higher elevation. Soot hydration and its reactivity with ozone are quantitatively related to surface oxidation and, thus, the air/fuel combustion ratio for soot's formation in premixed flames. The effect of relative humidity (RH) on the soot-ozone reaction over the O3 concentration and RH ranges 2–4.8 ppm and17–78%, respectively, is expressed by–d[O3]/dt =k[O3]2[H2O]0.2and is directly related to particle surface oxidation.  相似文献   

5.
Airborne measurements of volatile organic compounds (VOC) were performed overthe tropical rainforest in Surinam (0–12 km altitude,2°–7° N, 54°–58° W) using the proton transferreaction mass spectrometry (PTR-MS) technique, which allows online monitoringof compounds like isoprene, its oxidation products methyl vinyl ketone,methacrolein, tentatively identified hydroxy-isoprene-hydroperoxides, andseveral other organic compounds. Isoprene volume mixing ratios (VMR) variedfrom below the detection limit at the highest altitudes to about 7 nmol/molin the planetary boundary layer shortly before sunset. Correlations betweenisoprene and its product compounds were made for different times of day andaltitudes, with the isoprene-hydroperoxides showing the highest correlation.Model calculated mixing ratios of the isoprene oxidation products using adetailed hydrocarbon oxidation mechanism, as well as the intercomparisonmeasurement with air samples collected during the flights in canisters andlater analysed with a GC-FID, showed good agreement with the PTR-MSmeasurements, in particular at the higher mixing ratios.Low OH concentrations in the range of 1–3 × 105molecules cm-3 averaged over 24 hours were calculated due to lossof OH and HO2 in the isoprene oxidation chain, thereby stronglyenhancing the lifetime of gases in the forest boundary layer.  相似文献   

6.
We show that photochemical processes in the lower half of the troposphere are strongly affected by the presence of liquid water clouds. Especially CH2O, an important intermediate of CH4 (and of other hydrocarbon) oxidation, is subject to enhanced breakdown in the aqueous phase. This reduces the formation of HO x -radicals via photodissociation of CH2O in the gas phase. In the droplets, the hydrated form of CH2O, its oxidation product HCO2 –, and H2O2 recycle O2 – radicals which, in turn, react with ozone. We show that the latter reaction is a significant sink for O3. Further O3 concentrations are reduced as a result of decreased formation of O3 during periods with clouds. Additionally, NO x , which acts as a catalyst in the photochemical formation of O3, is depleted by clouds during the night via scavenging of N2O5. This significantly reduces NO x -concentrations during subsequent daylight hours, so that less NO x is available for O3 production. Clouds thus directly reduce the concentrations of O3, CH2O, NO x , and HO x . Indirectly, this also affects the budgets of other trace gases, such as H2O2, CO, and H2.  相似文献   

7.
Biomass burning has important impacts on atmospheric chemistry and climate. Fires in tropical forests and savannas release large quantities of trace gases and particulate matter. Combustion of biofuels for cooking and heating constitutes a less spectacular but similarly widespread biomass burning activity. To provide the groundwork for a quantification of this source, we determined in rural Zimbabwe the emissions of CO2, CO, and NO from more than 100 domestic fires fueled by wood, agricultural residues, and dung. The results indicate that, compared to open savanna fires, emissions from domestic fires are shifted towards products of incomplete combustion. A tentative global analysis shows that the source strength of domestic biomass burning is on the order of 1500 Tg CO2–C yr–1, 140 Tg CO–C yr–1, and 2.5 Tg NO–N yr–1. This represents contributions of about 7 to 20% to the global budget of these gases.  相似文献   

8.
A coupled carbon cycle-climate model is used to compute global atmospheric CO2 and temperature variation that would result from several future CO2 emission scenarios. The model includes temperature and CO2 feedbacks on the terrestrial biosphere, and temperature feedback on the oceanic uptake of CO2. The scenarios used include cases in which fossil fuel CO2 emissions are held constant at the 1986 value or increase by 1% yr–1 until either 2000 or 2020, followed by a gradual transition to a rate of decrease of 1 or 2% yr–1. The climatic effect of increases in non-CO2 trace gases is included, and scenarios are considered in which these gases increase until 2075 or are stabilized once CO2 emission reductions begin. Low and high deforestation scenarios are also considered. In all cases, results are computed for equilibrium climatic sensitivities to CO2 doubling of 2.0 and 4.0 °C.Peak atmospheric CO2 concentrations of 400–500 ppmv and global mean warming after 1980 of 0.6–3.2 °C occur, with maximum rates of global mean warming of 0.2–0.3 °C decade–1. The peak CO2 concentrations in these scenarios are significantly below that commonly regarded as unavoidable; further sensitivity analyses suggest that limiting atmospheric CO2 to as little as 400 ppmv is a credible option.Two factors in the model are important in limiting atmospheric CO2: (1) the airborne fraction falls rapidly once emissions begin to decrease, so that total emissions (fossil fuel + land use-induced) need initially fall to only about half their present value in order to stabilize atmospheric CO2, and (2) changes in rates of deforestation have an immediate and proportional effect on gross emissions from the biosphere, whereas the CO2 sink due to regrowth of forests responds more slowly, so that decreases in the rate of deforestation have a disproportionately large effect on net emission.If fossil fuel emissions were to decrease at 1–2% yr–1 beginning early in the next century, emissions could decrease to the rate of CO2 uptake by the predominantly oceanic sink within 50–100 yrs. Simulation results suggest that if subsequent emission reductions were tied to the rate of CO2 uptake by natural CO2 sinks, these reductions could proceed more slowly than initially while preventing further CO2 increases, since the natural CO2 sink strength decreases on time scales of one to several centuries. The model used here does not account for the possible effect on atmospheric CO2 concentration of possible changes in oceanic circulation. Based on past rates of atmospheric CO2 variation determined from polar ice cores, it appears that the largest plausible perturbation in ocean-air CO2 flux due to changes of oceanic circulation is substantially smaller than the permitted fossil fuel CO2 emissions under the above strategy, so tieing fossil fuel emissions to the total sink strength could provide adequate flexibility for responding to unexpected changes in oceanic CO2 uptake caused by climatic warming-induced changes of oceanic circulation.  相似文献   

9.
We describe a fast response methane sensor based on the absorption of radiation generated with a near-infrared InGaAsP diode laser. The sensor uses an open path absorption region 0.5 m long; multiple pass optics provide an optical path of 50 m. High frequency wavelength modulation methods give stable signals with detection sensitivity (S/N=1, 1 Hz bandwidth) for methane of 65 ppb at atmospheric pressure and room temperature. Improvements in the optical stability are expected to lower the current detection limit. We used the new sensor to measure, by eddy correlation, the CH4 flux from a clay-capped sanitary landfill. Simultaneously we measured the flux of CO2 and H2O. From seven half-hourly periods of data collected after a rainstorm on November 23, 1991, the average flux of CH4 was 17 mmol m–2 hr–1 (6400 mg CH4 m–2 d–1) with a coefficient of variation of 25%. This measurement may underrepresent the flux by 15% due to roll-off of the sensor response at high frequency. The landfill was also a source of CO2 with an average flux of 8.1 mmol m–2 hr–1 (8550 mg CO2 m–2 d–1) and a coefficient of variation of 26%. A spectral analysis of the data collected from the CH4, CO2, and H2O sensors showed a strong similarity in the turbulent transfer mechanisms.  相似文献   

10.
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   

11.
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   

12.
Summary Vertical profiles of H2O, CO2, O3, NO and NO2 were measured during the Hartheim Experiment (HartX) to develop and calibrate a multi-layer resistance model to estimate deposition and emission of the cited gaseous species. The meteorological and gas concentration data were obtained with a 30 m high telescopic mast with 7 gas inlets located at 5 m intervals and meteorological sensors at 5, 15 and 30 m above ground; a complete gas profile was obtained every 9 min 20 s. Measured profiles were influenced by several exchange processes, namely evapotranspiration, dewfall, assimilation of CO2 in the tree crowns, soil respiration, deposition of NO2 and O3 to the soil and advection of NOx from the nearby highway. Surprisingly, no decrease in O3 concentration was observed in the crown layer during daytime, probably due to the relatively low density of foliage elements and strong turbulent mixing.The advantage of measuring in-canopy profiles is that turbulent exchange coefficients need not be estimated as a prerequisite to obtaining vertical flux estimates. In recent years, flux-gradient relationships in canopies have been subject to many criticisms. If fluxes are calculated at several heights considering only the transfers between the turbulent air and the interacting surfaces at a certain height, and those fluxes are then integrated vertically in a subsequent step, then exchange estimates (deposition or emission) can be obtained independent of turbulent exchange conditions.Typical estimated deposition velocities calculated for a 3-day period are between 4 and 10 mm/s for NO2 and about 4–9 mm/s for O3 (day and night values respectively). This leads to deposition rates of about 20–40 ng N/m2s for NO2 and about 30–40 mg O3/m2 deposited daily under the conditions encountered during HartX. Sensitivity tests done with the best available and most realistic values for model parametrization have shown that sensitivity is large with respect to the soil and cuticula resistances as well as for gas-phase ozone destruction and that more research is required to describe the effectiveness of cuticula and soil in modifying sink characteristics for NO2 and O3.With 12 Figures  相似文献   

13.
To systematically explain relations between light hydrocarbons, CO, and CO2 concentrations/emissions of biomassburning, we measured concentrations/emissions of carbon gases – CO,CO2, light hydrocarbons (CH4, C2H6,C2H4, C2H2, C3H8, C3H6,n-C4H10, i-C4H10, n-C5H12,i-C5H12), and THC (total hydrocarbon) – in the burning of dead plant material, mainly Imperata grass, byclosed-chamber experiments and by time-series analyses of gas concentrations in combustion plumes in relatively efficient and inefficient combustion situations. Concentrations of hydrocarbons measured were well correlated to [CO] although [C2H2] was exceptionally well correlated to[CO2]. The phase diagrams (relation between [CO]/ [CO2] and [hydrocarbon]/ [CO2]) obtained by the time-seriesexperiments well illustrated the variation in the overall emission rates of the closed-chamber experiments. The higher rates of decrease in hydrocarbon concentration with increasing carbon number in the efficient case compared with the inefficient case probably reflected the rate of oxidation and the amount of radicals. The overall concentrations (or emissions) of C2H4 and C3H6 were higher thanthose of C2H6 and C3H8, suggesting a linkage to mechanisms in whichthe predominant path of hydrocarbon oxidation is through the degradation of alkyl radicals, which can be immediately converted into or formed from alkenes. For C3 and C4 species, normal-chain species hadhigher emissions than iso-chain species under lower combustion efficiency. This may be attributable to the presence of tertiary C–H bonds in iso-species,which show more reactivity in the abstraction of H than secondary C–H bonds unless the carbon number is large.  相似文献   

14.
The photochemical oxidation of SO2 in the presence of NO and C3H6 was studied in a 18.2 liter pyrex reactor. When light intensity, irradiation time and SO2 concentration were constant, SO4 2- concentration, derived from the total volume of aerosol produced, peaked when [C3H6]/[NO] was approximately 6.0. Another increase im SO4 2- formation was reached at very high ratios (>50). The experimental observations are consistent with the two SO2 oxidation mechanisms. At low [C3H6]/[NO] ratios, the processes proceed via the HO–SO2 reaction, while at high ratios the O3–C3H6 adduct is assumed to oxidize SO2 to produce SO4 2- aerosols.  相似文献   

15.
A new sensitive method for measuring atmospheric concentrations of sulfur dioxide is presented. Samples are obtained using the mist chamber, which collects highly water-soluble gases with high efficiency, and concentrates them in a small volume of water. Particles are removed from the sampled air stream with a teflon filter, before it enters the mist chamber. After collection, the pH of the water is raised above pH 10 using sodium carbonate, then hydrogen peroxide (H2O2) is added to oxidize sulfur that may be present in the sulfur (IV) oxidation state, to sulfate. After a reaction time of at least 16 hours, the sulfate concentration is measured by ion chromatography. From the sulfate concentration, the water volume used in the mist chamber, and the volume of air sampled, the atmospheric concentration of SO2 is computed. The method is not sensitive to other atmospheric sulfur gases such as DMS, SC2, H2S, COS, or MSH. The estimated overall precision of the method is 10%. The detection limit at the present stage of technique development is approximately 20 ppt (parts per trillion, or 10-12 mol · mol-1) for a 45 minute sampling time, with lower concentrations being detectable with lower precision.  相似文献   

16.
Nitrite oxidation in the tropospheric aqueous phase by freezing was evaluated by freezing a field sample. Nitrite oxidation by dissolved oxygen in the freezing process is much faster than by other oxidation processes, such as reactions with ozone, hydrogen peroxide or dissolved oxygen in an aqueous solution at pHs 3 to –6. At pH 4.5 and 25°C, the lifetime of nitrite in the aqueous phase is ca. 1 hr in oxidation by ozone (6×10-10 mol dm-3), ca. 10 hr in oxidation by H2O2 (2×10-4 mol dm-3), and 7.5 hr (Fischer and Warneck, 1996) in photodissociation at midday in summer. Under the same conditions at a temperature below 0°C, the lifetime of nitrite in the freezing process is estimated as ca. 2 sec when the droplets are frozen within a second. The reaction by freezing is affected by the presence of salts, such as NaCl or KCl, or orgnaic compounds, such as methanol or acetone. The results of freezing a field rain or fog sample showed that nitrite oxidation proceeds below pH 6, and the conversion ratio of nitrate from nitrite increases with decreasing pH. The oxidation of nitrite by freezing was also observed in freezing fog particles generated by an ultrasonic humidifier. The ratios of the concentrations of ions in the winter sample to those in the summer sample (or those in the fog sample) were almost the same values. However, the concentration of nitrite in the winter sample was lower than that estimated by the ratios of other ions. From the present study, it seems that the freezing process plays an important role in the nitrite sink process in the tropospheric aqueous phase.  相似文献   

17.
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   

18.
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   

19.
大气过氧化氢（H2O2）是一种重要的光化学产物,也是硫酸盐气溶胶生成及降水酸化过程的关键氧化剂。然而,我国对H2O2的观测研究较少,尤其对雾霾期间H2O2浓度变化特征认识不足。该文介绍了冬春时段（2016年12月-2017年4月）在北京城区中国气象局的H2O2观测结果,并结合同期O3,PAN,NOX,PM2.5等污染物和气象要素观测数据,分析H2O2浓度变化特征与影响因素。观测结果表明:观测期间H2O2体积混合比（简称为浓度）为（0.65±0.59）×10-9,其中,春季浓度（0.83±0.67）×10-9高于冬季浓度（0.51±0.47）×10-9;H2O2平均日变化基本呈现单峰特征,峰值出现在18:00-21:00,比其他地区峰值出现稍晚,并滞后于O3峰值时间4~7 h;相对湿度对H2O2日峰值时间和浓度水平有影响,小于55%时日峰值出现于18:00-24:00,平均峰值浓度1.52×10-9;大于65%时日峰值出现于11:00-16:00,日峰值浓度均小于1×10-9。H2O2,O3和PAN虽然同属光化学产物,但在不同污染状况下浓度水平和变化趋势差异明显;H2O2清洁日峰值浓度高于污染日,但11:00-15:00污染日浓度略高于清洁日。  相似文献   

20.
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   

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