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1.
This work presents a gas chromatographic method that uses a thermal conductivity detector (GC-TCD) to measure the liquid water mass (LWM) of collected aerosols. The method is a modification of the previously developed EA-TCD method (Journal of Aerosol Science 29, 827). A microcomputer was incorporated into the system to control the analytical procedures, improve the measurement precision, and make possible a continuous operation. To validate the method, the aerosol LWMs of NaCl, Na2SO4, NH4NO3, (NH4)2SO4, NH4Cl, and Na2CO3 were measured at room temperature under relative humidities (RHs) varying between 20% and 90%, in both humidifying and dehumidifying conditions. Estimates of aerosol LWMs for varying aerosol chemical compositions and RHs by various measurement methods and predictive models are comprehensively compared. The comparison shows that the GC-TCD measurements agree closely with those of the other methods. The GC-TCD measurements are closer to the ISORROPIA model predictions than those of the AIM2 model. Most notably, our method determines, for the first time, the hygroscopic behavior of Na2CO3 aerosol yielding the deliquescence relative humidity and crystallization relative humidity at 78% and 39% RH, respectively. The hygroscopic characteristics of various NaCl mole fractions in mixed NaCl–Na2SO4 aerosols, determined by GC-TCD, are used to show the discrepancy between the measurements and the model's prediction.  相似文献   

2.
In this study, the water cycles of nine water-soluble organic salts of atmospheric interest were studied using an electrodynamic balance (EDB) at 25°C. Sodium formate, sodium acetate, sodium succinate, sodium pyruvate and sodium methanesulfonate (Na-MSA) particles crystallize as the relative humidity (RH) decreases and they deliquesce as the RH increases. Sodium oxalate and ammonium oxalate form supersaturated particles at low RH before crystallization but they do not deliquesce even at RH=90%. Sodium malonate and sodium maleate particles neither crystallize nor deliquesce. These two salts absorb and evaporate water reversibly without hysteresis. In most cases, the solid states of single particles resulting from the crystallization of supersaturated droplets do not form the most thermodynamically stable state found in bulk studies. Sodium formate, sodium oxalate, ammonium oxalate, sodium succinate, sodium pyruvate and Na-MSA form anhydrous particles after crystallization. Sodium acetate forms particles with a water/salt molar ratio of 0.5 after crystallization. In salts with several hydrated states including sodium formate and sodium acetate, the particles deliquesce at the lowest deliquescence relative humidity (DRH) of the hydrates. Except sodium oxalate and ammonium oxalate, all the salts studied here are as hygroscopic as typical inorganic hygroscopic aerosols. The hygroscopic organic salts have a growth factor of 1.76–2.18 from RH=10–90%, comparable to that of typical hygroscopic inorganic salts such as NaCl and (NH4)2SO4. Further study of other atmospheric water-soluble organic compounds and their mixtures with inorganic salts is needed to explain the field observations of the hygroscopic growth of ambient aerosols.  相似文献   

3.
This paper presents a mathematical model that describes the chemical composition and growth rate of atmospheric aerosols containing sulfate and nitrate, and that is applicable over the entire range of relative humidities. The model describes aerosols as consisting of an insoluble core, a soluble solid shell and an aqueous film. The chemical composition of the solid and aqueous aerosol phases in this model is governed by the following processes:
  • 1.(1) the chemical equilibria between the ambient gas and the aerosol liquid phases and between the aerosol liquid and the soluble solid phases;
  • 2.(2) the diffusion-limited condensation of H2SO4 and
  • 3.(3) the liquid-phase chemical reaction of SO2. At low humidities the liquid phase may not be thermodynamically viable, in which case the model then treats the solid-phase/gas-phase equilibrium.
Model simulations were conducted to study the effect of ambient relative humidity and gas-phase concentrations on the aerosol chemical composition and growth rate. Results indicate that
  • 1.(1) precipitation of (NH4)2SO4 occurs at its point of deliquescence (i.e. at a relative humidity of close to 80%) even in the presence of other electrolytes;
  • 2.(2) within the uncertainty of the thermodynamic data, the saturation products of NH3 and HNO3 for a liquid-coated aerosol and a dry aerosol are in agreement with each other;
  • 3.(3) the aerosol concentrations correspond closely to (NH4) 2SO4 and NH4NO3 for both liquid and solid phases, i.e. NH4HSO4 is predicted to exist in negligible amounts under most conditions and
  • 4.(4) the assumption of either an ideal internal mixture or an external mixture for dry sulfates and nitrate aerosols has little effect on model predictions.
  相似文献   

4.
ABSTRACT

A thermodynamic equilibrium model was used to investigate the response of aerosol NO3 to changes in concentrations of HNO3, NH3, and H2SO4. Over a range of temperatures and relative humidities (RHs), two parameters provided sufficient information for indicating the qualitative response of aerosol NO3. The first was the excess of aerosol NH4 + plus gas-phase NH3 over the sum of HNO3, particulate NO3, and particulate SO4 2- concentrations. The second was the ratio of particulate to total NO3 concentrations. Computation of these quantities from ambient measurements provides a means to rapidly analyze large numbers of samples and identify cases in which inorganic aerosol NO3 formation is limited by the availability of NH3. Example calculations are presented using data from three field studies. The predictions of the indicator variables and the equilibrium model are compared.  相似文献   

5.
We used an environmental transmission electron microscope to observe deliquescence and hygroscopic growth of atmospheric particles with hygroscopic coatings over the range 0–100% relative humidity (RH). The particles were collected from polluted and clean environments. Types included a sulfate-coated NaCl/silicate aggregate particle, a sulfate-coated sea-salt particle, and a Mg-rich, chloride-coated sea-salt particle. They all exhibited initial water uptake between 50% and 60% RH, although the first major morphological changes occurred at 70% RH. A deliquescence sphere, adjacent to the core particle, formed between 70% and 76% RH when deliquescence occurred or when the liquid phase was able to break out of the solid exterior coating. The deliquescence sphere grew to engulf the particle with increasing RH. Some particles developed a splatter zone associated with a particle coating. Efflorescence occurred over the range 49–44% RH. Our results indicate that some coated particles undergo a multi-step deliquescence process and that composition of the different phases within the coating affects deliquescence and hygroscopic growth below 76% RH. Above 76% RH, the dominant hygroscopic growth was due to water uptake by NaCl. Efflorescence of these particles also was strongly linked to NaCl, although the presence of other phases inhibited formation of a single NaCl crystal. Our results show that the observed coatings can both enhance particle solubility and lower the effective deliquescence RH of the particle. Thus, these coatings cause important phase and size changes for aerosol particles that could feed back into many other chemical and physical processes that contribute to radiative forcing within the atmosphere.  相似文献   

6.
The previously developed theoretical model [Gao, Y., Chen, S.B., Yu, L.E., 2006. Efflorescence relative humidity for ammonium sulfate particles. Journal of Physical Chemistry A, 110, 7602–7608], which has successfully predicted the efflorescence relative humidity (ERH) of ammonium sulfate ((NH4)2SO4) particles at room temperature, is employed to estimate the ERH of sodium chloride (NaCl) particles in sizes ranging from 6 nm to 20 μm. The theoretical predictions well agree with the reported experimental data in literatures. When the NaCl particles are larger than 70 nm, the ERH decreases with decreasing dry particle sizes, and reach a minimum around 44% RH, otherwise the ERH increases with decreasing dry particle sizes (<70 nm) because of the Kelvin effect. Compared with (NH4)2SO4 particles, the Kelvin effect on ERH is stronger for NaCl particles smaller than 30 nm, while the dry particle size exerts weaker influence on NaCl particles larger than 70 nm.  相似文献   

7.
Measurements on size distribution of atmospheric aerosol were made at Dayalbagh, Agra during July to September 1998. A 4-stage cascade particle sampler (CPS - 105) which fractionates particles in sizes ranging between 0.7 and >10.9 μm, was used. Samples were collected on Whatman 41 filters. The filters were analyzed for the major water-soluble ions. The anions (F, Cl, NO3 and SO4) were analyzed by Dionex DX-500 ion chromatograph while atomic absorption and colorimetric techniques were used for the analysis of cations (Na, K, Ca and Mg) and NH4, respectively. The average mass of aerosol was found to be 131.6 μg m−3 and aerosol composition was found to be influenced by terrigeneous sources. The mass size distribution of total aerosol and the ions NH4, Cl, NO3, K, Ca, Mg, SO4 and Na was bimodal while that of F was unimodal. SO4, F, K and NH4 dominated in the fine mode while Ca, Mg, Cl and NO3 were in abundance in coarse fraction. Na was found in both coarse as well as fine mode. Coarse mode SO4 and NO3 have been ascribed to contribution from re-suspension of soil and formation by heterogeneous oxidation on soil derived particles. Preponderance of K in fine mode is attributed to emissions from vegetation and from burning of plant materials. Ca, Mg, Cl and NO3 are largely soil derived and hence dominate in coarse fraction. Equivalent ratios of NH4/(SO4+NO3) were calculated for both fine and coarse aerosols. The coarse mode ratio varied between 0.7 and 1.4 while in fine mode it ranged between 1.4 and 1.9. It shows that aerosol is basic, the basicity of coarse mode is due to higher concentration of soil-derived alkaline components while the basicity in fine mode is due to neutralization of acidity by NH3.  相似文献   

8.
This study investigates ammonium, nitrate, and sulfate (NH4+, NO3?, and SO42?) in size-resolved particles (particularly nano (PM0.01–0.056)/ultrafine (PM0.01–0.1)) and NOx/SO2 collected near a busy road and at a rural site. The average (mass) cumulative fraction of secondary inorganic aerosols (SO42?+NO3?+NH4+) in nano or ultrafine particles at the roadside was found to be three to four times that at the rural site. The above three secondary inorganic aerosol species were present in similar cumulative fractions in particles of size 1–18 μm at both sites; however, dissimilar fractions were observed for Cl?, Na+, and K+. The nitrogen ratios (NRs: NR = NO3??N/(NO3??N + NO2–N)), sulfur ratios (SRs: SR = SO42??S/(SO42??S + SO2–S)), dNR/DP (derivative of NR with respect to DP (particle diameter)), and dSR/DP (derivative of SR with respect to DP) at the roadside were higher than those at the rural site for nano/ultrafine particles. At both sites (particularly the roadside), the nanoparticles had significantly higher dNR/DP and dSR/DP values than differently sized particles, implying that NO3?/SO42? (from NO2/SO2 transformation or NO3?/SO42? deposition) were present on these particles.  相似文献   

9.
Abstract

Annual applications of (NH4)2SO4 NH4NO3 and urea on a Solonetzic soil at 112 kg N/ha for 10 consecutive years reduced pH levels from 5.6 for the check to 4.4, 4.9 and 5.3, respectively for (NH4)2SO4, NH4NO3 and urea. (NH4)2SO4 generated twice as much exchange acidity as NH4NO3 and four times as much as urea. Net extractable cations leached from the Ap horizon closely approximated the amount of exchange acidity generated by (NH4)2SO4 and NH4NO3 fertilizers. The levels of soil extractable Al and Mn were greatly enhanced by (NH4)2SO4 as were plant contents. Similar acidifying effects to that produced by the (NH4)2SO4 occurred when NH4NO3 was applied at 300 kg N/ha annually for 12 consecutive years in another field experiment on the same soil. Liming samples of the field (NH4)2SO4 acidified soils in the greenhouse, significantly increased yields and lowered the Al and Mn contents of the plants to normal levels.  相似文献   

10.
The influence of humidity is considered on the concentration of the suspended particulate matter (SPM) measured with a β-ray counter. The humidity condition inside a small observatory where the counter is located is, in general, different from the ambient condition outside the observatory. From the measured values, the ambient SPM concentration is derived considering the hygroscopic effect of common aerosol species of sea salt (SS), (NH4)2SO4, NH4NO3 and NaNO3. In a case study conducted during September 2005, temperature and humidity were measured both inside and outside the observatory. The average value of the relative humidity is 48% for inside and 78% for outside, resulting in approximately 53% larger SPM mass concentration after the correction. Accordingly, the value of mass extinction efficiency, which is given by the ratio between the optically measured extinction coefficient and the mass concentration, becomes lower after the correction.  相似文献   

11.
The light extinction and direct forcing properties of the atmospheric aerosol were investigated for a midwestern rural site (Bondville, IL) using field measurements, a semi-empirical light extinction model, and a radiative transfer code. Model inputs were based on the site measurements of the physical and chemical characteristics of atmospheric aerosol during the spring, summer, fall and winter of 1994. The light scattering and extinction coefficients were calculated and apportioned using the elastic light scattering interactive efficiency (ELSIE) model (Sloane and Wolff, 1985, Atmospheric Environment 19(4), 669–680). The average efficiencies calculated for organic carbon (OC, carbon measured as organic multiplied by 1.2) ranged from 3.81 m2/g OC at lower relative humidities (<63%) to 6.90 m2/g OC at higher relative humidities (>75%) while sulfate (assumed as ammonium sulfate) efficiencies ranged from 1.23 m2/g (NH4)2SO4 to 5.78 m2/g (NH4)2SO4 for the same range of relative humidities. Radiative transfer calculations showed that the rural aerosol at Bondville is most likely to have an overall negative (cooling) forcing effect on climate. Elemental carbon (EC), however, acts to counter sulfate forcing to a degree that has a significant seasonal variation, primarily due to the seasonal variation in the sulfate concentrations. Taking the loading to be the mean summer EC+ammonium sulfate loading and assuming [EC]/[(NH4)2SO4] to be zero in one case (i.e. no soot present) and 0.025 (summer mean at Bondville) in another leads to a 37% difference in calculated forcing.  相似文献   

12.
Vertical concentration profiles for NH3, HNO3 and HCl-gas and for NH4+, NO3, SO2−4, Cl and Na+ aerosol were obtained from a meteorological tower in the central part of the Netherlands. An upward NH3 flux of 0.12 μgm−2 s−1 was calculated from the NH3 profiles and meteorological data. From the HNO3 profiles a maximum HNO3 dry deposition velocity of 4 cm s−1 was calculated. Good agreement was found between the measured concentration products [NH3](g) × [HNO3](g) and the theoretical values at temperatures above 0°C and relative humidities below 80%. In other cases, higher NH3 and/or HNO concentrations in the gas phase were measured than theoretically predicted.  相似文献   

13.
Chemical composition of rainwater was studied in the northeastern Romania, Iasi region, and the concentrations of major inorganic and organic ions were measured in samples collected between April 2003 and December 2006. The pH of the rainwater is 5.92 (volume weighted mean average, VWM) suggesting a sufficient load of alkaline components neutralizing its acidity. On average, 97% of the acidity in the collected samples is neutralized by CaCO3 and NH3. Clear seasonal variations were observed for some of the identified ions (e.g., SO42−, NO3, Ca2+, NH4+). The data obtained during this work revealed that both concentrations and fluxes of anthropogenic source-related ions (e.g., SO42−, NO3 and NH4+) are among the highest reported for European sites. It is shown that meteorology and long-range transport processes may concur to their high levels.  相似文献   

14.
Airborne gaseous and particulate matter in winter was measured over for 37 days in January and December 1997 at 2 sampling sites in northern Kyushu, Japan. One sampling site, Goto Island (an isolated island in the East China Sea), was about 200 km southwest of the other sampling site, Dazaifu city. In winter, acidic sulfates generated over the East Asian continent were transported to northwest Kyushu, to places such as Goto Island and the inland Kyushu area, and high sulfate concentrations were observed at the 2 sampling sites when strong NW winds blew. Acidity around Goto was mainly influenced by particulate NH4HSO4. The concentrations of NH3 at Goto Island were lower than at Dazaifu city. The difference in NH3 levels at the 2 sampling sites plays an important role in the chemical forms and sizes of the particulate matter. Nitrates at Goto Island were mostly present as NaNO3 and Ca(NO3)2 in coarse-size particles. During the process of long-range transport of air pollutants from the Asian continent to Goto, gaseous HNO3 was produced by a photochemical reactions of nitrogen oxides in the atmosphere, and particulate NaNO3 and gaseous HCl were formed by a chlorine-loss reaction between NaCl and gaseous HNO3. When strong NW winds blew, acidic sulfates together with some of the NaNO3 and/or Ca(NO3)2 and some of gaseous HCl and HNO3, which exist in the sea to the west of Kyushu and Goto Island, were transported to inland Kyushu such as Dazaifu city. During the process of transport, most of the acidic sulfates and acidic gases were mixed with regional air pollutants such as chlorides and nitrates existing around Dazaifu city, and neutralized forming (NH4)2SO4, NH4Cl and NH4NO3 in an environment of excess NH3. Therefore, the main chemical forms of NO3 at Dazaifu city varied day-by-day from fine-sized NH4NO3 to coarse-sized NaNO3 and/or Ca(NO3)2. The appearance of NO3 in coarse-size particles at Dazaifu city was due to the transport of NO3 from around the sea to the west of Kyushu.  相似文献   

15.
We use an inorganic aerosol thermodynamic equilibrium model in a three-dimensional chemical transport model to understand the roles of ammonia chemistry and natural aerosols on the global distribution of aerosols. The thermodynamic equilibrium model partitions gas-phase precursors among modeled aerosol species self-consistently with ambient relative humidity and natural and anthropogenic aerosol emissions during the 1990s.Model simulations show that accounting for aerosol inorganic thermodynamic equilibrium, ammonia chemistry and dust and sea-salt aerosols improve agreement with observed SO4, NO3, and NH4 aerosols especially at North American sites. This study shows that the presence of sea salt, dust aerosol and ammonia chemistry significantly increases sulfate over polluted continental regions. In all regions and seasons, representation of ammonia chemistry is required to obtain reasonable agreement between modeled and observed sulfate and nitrate concentrations. Observed and modeled correlations of sulfate and nitrate with ammonium confirm that the sulfate and nitrate are strongly coupled with ammonium. SO4 concentrations over East China peak in winter, while North American SO4 peaks in summer. Seasonal variations of NO3 and SO4 are the same in East China. In North America, the seasonal variation is much stronger for NO3 than SO4 and peaks in winter.Natural sea salt and dust aerosol significantly alter the regional distributions of other aerosols in three main ways. First, they increase sulfate formation by 10–70% in polluted areas. Second, they increase modeled nitrate over oceans and reduce nitrate over Northern hemisphere continents. Third, they reduce ammonium formation over oceans and increase ammonium over Northern Hemisphere continents. Comparisons of SO4, NO3 and NH4 deposition between pre-industrial, present, and year 2100 scenarios show that the present NO3 and NH4 deposition are twice pre-industrial deposition and present SO4 deposition is almost five times pre-industrial deposition.  相似文献   

16.
The concentrations of PM2.5−10, PM2.5 and associated water-soluble inorganic species (WSIS) were determined in a coastal site of the metropolitan region of Rio de Janeiro, Southeastern Brazil, from October 1998 to September 1999 (n=50). Samples were dissolved in water and analyzed for major inorganic ions. The mean (± standard deviation; median) concentrations of PM2.5−10 and PM2.5 were, respectively, 26 (± 16; 21) μg m−3 and 17 (± 13; 14) μg m−3. Their mean concentrations were 1.7–1.8 times higher in dry season (May–October) than in rainy season (November–April). The WSIS comprised, respectively, 34% and 28% of the PM2.5−10 and PM2.5 masses. Chloride, Na+ and Mg2+ were the predominant ions in PM2.5−10, indicating a significant influence of sea-salt aerosols. In PM2.5, SO42− (∼97% nss-SO42−) and NH4+ were the most abundant ions and their equivalent concentration ratio (SO42−/NH4+ ∼1.0) suggests that they were present as (NH4)2SO4 particles. The mean concentration of (NH4)2SO4 was 3.4 μg m−3. The mean equivalent PM2.5 NO3 concentration was eight times smaller than those of SO42− and NH4+. The PM2.5 NO3 concentration in dry season was three times higher than in rainy season, probably due to reaction of NaCl (sea salt) with HNO3 as a result of higher levels of NOy during the dry season and/or reduced volatilization of NH4NO3 due to lower wintertime temperature. Chloride depletion was observed in both size ranges, although more pronouncely in PM2.5.  相似文献   

17.
The effects of (NH4)2SO4, NH4NO3, NaCl, NH4Cl, and Na2SO4 aerosols on the kinetics of 1-propanol oxidation in the presence of the hydroxyl radical have been investigated using the relative rate technique. p-Xylene was used as a reference compound. Two different aerosol concentrations that are typical of polluted urban conditions were tested. The total surface areas of aerosols were 1400 (condition I) and 3400 μm2 cm−3 (condition II). Results indicate that aerosols promote the oxidation of 1-propanol, and the extents of the promoting effects depend on the aerosol composition and concentration. Increases in the relative rates of the 1-propanol/OH reaction vs. the p-xylene/OH reaction were only observed for (NH4)2SO4 aerosol conditions I and II, NH4NO3 aerosol condition II, and NH4Cl aerosol condition II. These results indicate that NH4+ is the species promoting the oxidation of 1-propanol, and suggests the possibility of a strong interaction between NH4+ and 1-propanol that can change the activation energy of the initial OH attack. These results have profound implications on the use of air quality models for the assessment of air pollution control strategies.  相似文献   

18.
Determination of the chemical compositions of atmospheric single particles in the Yellow Sea region is critical for evaluating the environmental impact caused by air pollutants emitted from mainland China and the Korean peninsula. After ambient aerosol particles were collected by the Dekati PM10 cascade impactor on July 17–23, 2007 at Tokchok Island (approximately 50 km west of the Korean coast nearby Seoul), Korea, overall 2000 particles (on stage 2 and 3 with cut-off diameters of 2.5–10 μm and 1.0–2.5 μm, respectively) in 10 samples were determined by using low-Z particle electron probe X-ray microanalysis. X-ray spectral and secondary electron image (SEI) data showed that soil-derived and sea-salt particles which had reacted or were mixed with SO2 and NOx (or their acidic products) outnumbered the primary and “genuine” ones (59.2% vs. 19.2% in the stage 2 fraction and 41.3% vs. 9.9% in the stage 3 fraction). Moreover, particles containing nitrate in the secondary soil-derived species greatly outnumbered those containing sulfate. Organic particles, mainly consisting of marine biogenic species, were more abundant in the stage 2 fraction than in the stage 3 fraction (11.6% vs. 5.1%). Their relative abundance was greater than the sum of carbon-rich, K-containing, Fe-containing, and fly ash particles, which exhibited low frequencies in all the samples. In addition, many droplets rich in C, N, O, and S were observed. They tended to be small, exhibiting a dark round shape on SEI, and generally included 8–20 at.% C, 0–12 at.% N, 60–80 at.% O, and 4–10 at.% S (sometimes with <3 at.% Mg and Na). They were attributed to be a mixture of carbonaceous matter, H2SO4, and NH4HSO4/(NH4)2SO4, mostly from the reaction of atmospheric SO2 with NH3 under high relative humidity. The analysis of the relationship between the aerosol particle compositions and 72-h backward air-mass trajectories suggests that ambient aerosols at Tokchok Island are strongly affected not only by seawater from the Yellow Sea but also by anthropogenic pollutants emitted from China and the Seoul–Incheon metropolis, resulting in the dominance of complex secondary aerosol particles.  相似文献   

19.
Previous workers have shown that simultaneous SO2/NOX removal can be obtained in a dry scrubbing system with Ca(OH)2 promoted by an additive such as NaOH, and that fly ash and product recycle improve the reactivity of the solids toward SO2. To test SO2/NOX removal with fly ash and product recycle, bench-scale experiments with a packed bed reactor were performed at bag filter conditions. The most reactive solid for NOX removal was prepared by slurrying Ca(OH)2 with fly ash, CaSO3, and NaOH. The best conditions for NOX removal were the greatest temperature (125°C) and greatest concentrations of SO2 (1500 ppm) and O2 (20 percent). At the best conditions, NOX removed in 1 hour was 3-4 moles per 100 moles Ca(OH)2, compared to 5-10 moles SO2 removed per 100 moles Ca(OH)2. The best SO2 removal was obtained at the highest relative humidities/lowest temperatures (55% RH/ 65°C) with solids prepared by slurrying Ca(OH)2 with fly ash and NaOH. At these conditions, SO2 removed In 1 hour was 60-80 moles per 100 moles Ca(OH)2, compared to 0.5 to 1 moles NOX removed per 100 moles Ca(OH)2.  相似文献   

20.
High concentrations (>15 μm3 cm?3) of CaSO4, Ca(NO3)2 and (NH4)2SO4 were selected as surrogates of dry neutral, aqueous neutral and dry acidic inorganic seed aerosols, respectively, to study the effects of inorganic seeds on secondary organic aerosol (SOA) formation in irradiated m-xylene/NOx photooxidation systems. The results indicate that neither ozone formation nor SOA formation is significantly affected by the presence of neutral aerosols (both dry CaSO4 and aqueous Ca(NO3)2), even at elevated concentrations. The presence of high concentrations of (NH4)2SO4 aerosols (dry acidic) has no obvious effect on ozone formation, but it does enhance SOA generation and increase SOA yields. In addition, the effect of dry (NH4)2SO4 on SOA yield is found to be positively correlated with the (NH4)2SO4 surface concentration, and the effect is pronounced only when the surface concentration reaches a threshold value. Further, it is proposed that the SOA generation enhancement is achieved by particle-phase heterogeneous reactions induced and catalyzed by the acidity of dry (NH4)2SO4 seed aerosols.  相似文献   

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