Atmospheric sulfate aerosols have important impacts on air quality, climate, and human and ecosystem health. However, current air-quality models generally underestimate the rate of conversion of sulfur dioxide (SO2) to sulfate during severe haze pollution events, indicating that our understanding of sulfate formation chemistry is incomplete. This may arise because the air-quality models rely upon kinetics studies of SO2 oxidation conducted in dilute aqueous solutions, and not at the high solute strengths of atmospheric aerosol particles. Here, we utilize an aerosol flow reactor to perform direct investigation on the kinetics of aqueous oxidation of dissolved SO2 by hydrogen peroxide (H2O2) using pH-buffered, submicrometer, deliquesced aerosol particles at relative humidity of 73 to 90%. We find that the high solute strength of the aerosol particles significantly enhances the sulfate formation rate for the H2O2 oxidation pathway compared to the dilute solution. By taking these effects into account, our results indicate that the oxidation of SO2 by H2O2 in the liquid water present in atmospheric aerosol particles can contribute to the missing sulfate source during severe haze episodes.

Biogenic organosulfates (OSs) are important markers of secondary organic aerosol (SOA) formation involving cross reactions of biogenic precursors (terpenoids) with anthropogenic pollutants. Until now, there has been rare information about biogenic OSs in the air of highly polluted areas. In this study, fine particle (PM 2.5 ) samples were separately collected in daytime and nighttime from summer to fall 2010 at a site in the central Pearl River Delta (PRD), South China. Pinene-derived nitrooxyorganosulfates (pNOSs) and isoprene-derived OSs (iOSs) were quantified using a liquid chromatograph (LC) coupled with a tandem mass spectrometer (MS/MS) operated in negative electrospray ionization (ESI) mode. The pNOSs with MW 295 exhibited higher levels in fall (151 ± 86.9 ng m −3 ) than summer (52.4 ± 34.0 ng m −3 ), probably owing to the elevated levels of NOx and sulfate in fall when air masses mainly passed through city clusters in the PRD and biomass burning was enhanced. In contrast to observations elsewhere where higher levels occurred at nighttime, pNOS levels in the PRD were higher during the daytime in both seasons, indicating that pNOS formation was likely driven by photochemistry over the PRD. This conclusion is supported by several lines of evidence: the specific pNOS which could be formed through both daytime photochemistry and nighttime NO 3 chemistry exhibited no day− night variation in abundance relative to other pNOS isomers; the production of the hydroxynitrate that is the key precursor for this specific pNOS was found to be significant through photochemistry but negligible through NO 3 chemistry based on the mechanisms in the Master Chemical Mechanism (MCM). For iOSs, 2-methyltetrol sulfate ester which could be formed from isoprene-derived epoxydiols (IEPOX) under low-NOx conditions showed low concentrations (below the detection limit to 2.09 ng m −3 ), largely due to the depression of IEPOX formation by the high NOx levels over the PRD. ■ INTRODUCTIONBiogenic volatile organic compounds (BVOCs) including isoprene and monoterpenes 1 contribute significantly to the global secondary organic aerosol (SOA) budget. 2 Recent studies have shown that the conversion of BVOCs to SOA can be significantly promoted in the presence of high anthropogenic emissions. 3−6 As notable SOA products of BVOCs reacting with anthropogenic pollutants under acidic conditions, organosulfates (OSs) have been detected in both laboratory-generated SOA 7−10 and ambient aerosols. 11−18 Moreover, OSs could contribute a significant fraction of fine particles, accounting for up to 30% of organic matter (OM) 9,19−23 and up to 10% of total sulfate. 24,25 The formation mechanisms of OSs are still unclear. Previous chamber studies have demonstrated that both OH-photooxidation and NO 3 dark reactions can form pinene-derived nitrooxy-organosulfates (pNOSs) on acidic particles. 9 The pNOSs were only detected in nighttime samples in northeastern Bavaria, Germany, suggesting a role for nighttime NO 3 chemistry in pNOS formation. 15 How...

Atmospheric oxidation of sulfur dioxide (SO2) forms sulfate-containing aerosol particles that impact air quality, climate, and human and ecosystem health. It is well-known that in-cloud oxidation of SO2 frequently dominates over gas-phase oxidation on regional and global scales. Multiphase oxidation involving aerosol particles, fog, and cloud droplets has been generally thought to scale with liquid water content (LWC) so multiphase oxidation would be negligible for aerosol particles due to their low aerosol LWC. However, recent field evidence, particularly from East Asia, shows that fast sulfate formation prevails in cloud-free environments that are characterized by high aerosol loadings. By assuming that the kinetics of cloud water chemistry prevails for aerosol particles, most atmospheric models do not capture this phenomenon. Therefore, the field of aerosol SO2 multiphase chemistry has blossomed in the past decade, with many oxidation processes proposed to bridge the difference between modeled and observed sulfate mass loadings. This review summarizes recent advances in the fundamental understanding of the aerosol multiphase oxidation of SO2, with a focus on environmental conditions that affect the oxidation rate, experimental challenges, mechanisms and kinetics results for individual reaction pathways, and future research directions. Compared to dilute cloud water conditions, this paper highlights the differences that arise at the molecular level with the extremely high solute strengths present in aerosol particles.

Abstract. We describe here characterization of a new stateof-the-art smog chamber facility for studying atmospheric gas-phase and aerosol chemistry. The chamber consists of a 30 m 3 fluorinated ethylene propylene (FEP) Teflon film reactor housed in a temperature-controlled enclosure equipped with black lamps as the light source. Temperature can be set in the range from −10 to 40 • C at accuracy of ±1 • C as measured by eight temperature sensors inside the enclosure and one just inside the reactor. Matrix air can be purified with non-methane hydrocarbons (NMHCs) < 0.5 ppb, NO x /O 3 /carbonyls < 1 ppb and particles < 1 cm −3 . The photolysis rate of NO 2 is adjustable between 0 and 0.49 min −1 . At 298 K under dry conditions, the average wall loss rates of NO, NO 2 and O 3 were measured to be 1.41 × 10 −4 min −1 , 1.39 × 10 −4 min −1 and 1.31 × 10 −4 min −1 , respectively, and the particle number wall loss rate was measured to be 0.17 h −1 . Auxiliary mechanisms of this chamber are determined and included in the Master Chemical Mechanism to evaluate and model propene-NO x -air irradiation experiments. The results indicate that this new smog chamber can provide high-quality data for mechanism evaluation. Results of α-pinene dark ozonolysis experiments revealed secondary organic aerosol (SOA) yields comparable to those from other chamber studies, and the two-product model gives a good fit for the yield data obtained in this work. Characterization experiments demonstrate that our Guangzhou Institute of Geochemistry, Chinese Academy Sciences (GIG-CAS), smog chamber facility can be used to provide valuable data for gas-phase chemistry and secondary aerosol formation.

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Cooking emissions have been identified as a major source of primary organic aerosol (POA) in urban environments. Cooking may also be a potential source of secondary organic aerosol (SOA) because of the abundant emissions of non-methane organic gases. We studied SOA formation from the photooxidation of emissions from seven vegetable oils heated at 200 °C under high-NO x conditions in a smog chamber. After the samples had been aged under an OH exposure of 1.0 × 10 10 molecules cm −3 s, the SOA formation rate was generally 1 order of magnitude higher than the POA emission rate. We determined that alkenals, which are not traditional SOA precursors in chemical transport models, accounted for 5−34% of the observed SOA. The unexplained SOA may be attributed to the oxidation of primary semivolatile and intermediate-volatility organic compounds (SVOCs and IVOCs, respectively), which were estimated to contribute an additional 9−106% of the observed SOA assuming the volatility distribution of heated cooking oils is the same as that of vehicle exhaust. Our results suggest that cooking can potentially be an important source of SOA in urban areas and that there is a need to characterize both SVOCs and IVOCs emitted from cooking and their SOA yields.

h i g h l i g h t sWe measured aromatic hydrocarbons at four contrasting sites in the PRD region. Diagnostic ratios were used to imply sources of aromatic hydrocarbons. Sources of aromatic hydrocarbons were apportioned by PMF receptor model. Solvent use, vehicle exhaust and biomass burning contributed over 89% AHs. Biomass burning contributed to AHs, particularly for Benzene in the rural. t r a c tAromatic hydrocarbons (AHs) are both hazardous air pollutants and important precursors to ozone and secondary organic aerosols. Here we investigated 14 C 6 -C 9 AHs at one urban, one suburban and two rural sites in the Pearl River Delta region during November-December 2009. The ratios of individual aromatics to acetylene were compared among these contrasting sites to indicate their difference in source contributions from solvent use and vehicle emissions. Ratios of toluene to benzene (T/B) in urban (1.8) and suburban (1.6) were near that of vehicle emissions. Higher T/B of 2.5 at the rural site downwind the industry zones reflected substantial contribution of solvent use while T/B of 0.8 at the upwind rural site reflected the impact of biomass burning. Source apportionment by positive matrix factorization (PMF) revealed that solvent use, vehicle exhaust and biomass burning altogether accounted for 89-94% of observed AHs. Vehicle exhaust was the major source for benzene with a share of 43-70% and biomass burning in particular contributed 30% to benzene in the upwind rural site; toluene, C 8 -aromatics and C 9 -aromatics, however, were mainly from solvent use, with contribution percentages of 47-59%, 52-59% and 41-64%, respectively.

Abstract. Cooking emissions can potentially contribute to secondary organic aerosol (SOA) but remain poorly understood. In this study, formation of SOA from gas-phase emissions of five heated vegetable oils (i.e., corn, canola, sunflower, peanut and olive oils) was investigated in a potential aerosol mass (PAM) chamber. Experiments were conducted at 19-20 • C and 65-70 % relative humidity (RH). The characterization instruments included a scanning mobility particle sizer (SMPS) and a high-resolution time-offlight aerosol mass spectrometer (HR-TOF-AMS). The efficiency of SOA production, in ascending order, was peanut oil, olive oil, canola oil, corn oil and sunflower oil. The major SOA precursors from heated cooking oils were related to the content of monounsaturated fat and omega-6 fatty acids in cooking oils. The average production rate of SOA, after aging at an OH exposure of 1.7 × 10 11 molecules cm −3 s, was 1.35±0.30 µg min −1 , 3 orders of magnitude lower compared with emission rates of fine particulate matter (PM 2.5 ) from heated cooking oils in previous studies. The mass spectra of cooking SOA highly resemble field-derived COA (cookingrelated organic aerosol) in ambient air, with R 2 ranging from 0.74 to 0.88. The average carbon oxidation state (OS c ) of SOA was −1.51 to −0.81, falling in the range between ambient hydrocarbon-like organic aerosol (HOA) and semivolatile oxygenated organic aerosol (SV-OOA), indicating that SOA in these experiments was lightly oxidized.