Qin MR, Chen ZM, Shen HQ, Li H, Wu HH, Wang Y. Impacts of heterogeneous reactions to atmospheric peroxides: Observations and budget analysis study. Atmospheric Environment [Internet]. 2018;183:144-153,. 访问链接Abstract
Atmospheric peroxides play important roles in atmospheric chemistry, acting as reactive oxidants and reservoirsof HOx and ROx radicals. Field measurements of atmospheric peroxides were conducted over urban Beijing from2015 to 2016, including dust storm days, haze days and different seasons. We employed a box model based onRACM2 mechanism to conduct concentration simulation and budget analysis of hydrogen peroxide (H2O2) andperoxyacetic acid (PAA). In this study, heterogeneous reaction is found to be a significant sink for atmosphericH2O2 and PAA in urban Beijing. Here, we recommend a suitable uptake coefficient formula considering thewater effect for model research of peroxides. It is found that H2O2 and PAA unexpectedly maintained considerableconcentrations on haze days, even higher than that on non-haze days. This phenomenon is mainlyascribed to relatively high levels of volatile organic compounds and ozone on haze days. In addition, high levelsof water vapor in pollution episode can promote not only the heterogeneous uptake to aerosol phase but also theproduction of H2O2. Atmospheric PAA formation is suggested to be sensitive to alkenes and NOx in urbanBeijing. In particular, with the help of peroxides, sulfate formation rate from heterogeneous uptake could increaseby ∼4 times on haze days, indicating the potential effect of peroxides on enhancement of aerosol oxidativeproperty and secondary sulfate formation.
Xing YN, Li H, Huang LB, Wu HH, Shen HQ, Chen ZM. The production of formaldehyde and hydroxyacetone in methacrolein photooxidation: New insights into mechanism and effects of water vapor. Journal of Environmental Sciences [Internet]. 2018;66:1-11. 访问链接Abstract
Methacrolein (MACR) is an abundant multifunctional carbonyl compound with highreactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiatedoxidation of MACR at various NO/MACR ratios (0 to 4.04) and relative humidities (< 3% to80%) using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanismwas performed to test our current understanding of the mechanism. In contrast to thereasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde(HCHO) were twice higher than the experimental results. The discrepancy was ascribed tothe existence of unconsidered non-HCHO forming channels in the chemistry of CH3C(=CH2)OO., which account for approx. 50%. In addition, the production of hydroxyacetoneand HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields ofHCHO were higher under humid conditions than that under dry condition. The yields ofhydroxyacetone were higher under humid conditions at low-NOx level, while lower athigh-NOx level. The reasonable explanation for the lower hydroxyacetone yield underhumid conditions at high-NOx level is that water vapor promotes the production ofmethacrolein nitrate in the reaction of HOCH2C(CH3)(OO.)CHO with NO due to the peroxyradical-water complex formation, which was evidenced by calculational results. And theminimum equilibrium constant of this water complex formation was estimated to be1.89 × 10−18 cm3/molecule. These results provide new insights into the MACR oxidationmechanismand the effects of water vapor.
Chen WT, Shao M, Wang M, Lu SH, Liu Y, Yuan B, Yang YD, Zeng LM, Chen ZM, Chang CC, et al. Variation of ambient carbonyl levels in urban Beijing between 2005 and 2012. Atmospheric Environment. 2016;129:105-113.Abstract
Carbonyl compounds are important precursors of secondary air pollutants. With the rapid economic development and the implementation of stricter control measures in Beijing, the sources of carbonyls possibly changed. Based on measurement data obtained at an urban site in Beijing between 2005 and 2012, we investigated annual variations in carbonyl levels and sources during these years. In summer, formaldehyde and acetaldehyde levels decreased significantly at a rate of 9.1%/year and 7.2%/year, respectively, while acetone levels increased at a rate of 4.3%/year. In winter, formaldehyde levels increased and acetaldehyde levels decreased. We also investigated the factors driving the variation in carbonyls levels during summer by determination of emission ratios for carbonyls and their precursors, and calculation of photochemical formation of carbonyls. The relative declines for primary formaldehyde and acetaldehyde levels were larger than those for secondary formation. This is possibly due to the increasing usage of natural gas and liquefied petroleum gas which could result in the rise of carbonyl precursor emission ratios. The increase in acetone levels might be related to the rising solvent usage in Beijing during these years. The influences of these sources should be paid more attention in future research.
Shen XL, Wu HH, Zhao Y, Huang D, Huang LB, Chen ZM. Heterogeneous reactions of glyoxal on mineral particles: A new avenue for oligomers and organosulfate formation. Atmospheric Environment. 2016;131:133-140.Abstract
Glyoxal (GL) plays a crucial role in the formation of secondary organic aerosols (SOA), because it is highly water soluble and capable of oligomerization. This is the first study to describe irreversible heterogeneous reactions of GL on clean and acidic gas-aged SiO2, a-Al2O3, and CaCO3 particles, as models of real mineral particles, at various relative humidity and without irradiation and gas phase oxidants. A series of products, including oligomers, organosulfates, and organic acids, which contribute to SOA formation, were produced. GL uptake on SO2-aged a-Al2O3 enabled the oxidation of surface S(IV) to S(VI). The presence of adsorbed water on particles favored GL uptake and the formation of oligomers and organosulfate, but it suppressed organic acid formation. In addition, the aging process enhanced the positive effect of adsorbed water on GL uptake. These findings will further our understanding of the GL sink and SOA sources in the atmosphere.
Li H, Chen ZM, Huang LB, Huang D. Organic peroxides' gas-particle partitioning and rapid heterogeneous decomposition on secondary organic aerosol. Atmospheric Chemistry and Physics. 2016;16(3):1837-1848.Abstract
Organic peroxides, important species in the atmosphere, promote secondary organic aerosol (SOA) aging, affect HOx radicals cycling, and cause adverse health effects. However, the formation, gas-particle partitioning, and evolution of organic peroxides are complicated and still unclear. In this study, we investigated in the laboratory the production and gas-particle partitioning of peroxides from the ozonolysis of a-pinene, which is one of the major biogenic volatile organic compounds in the atmosphere and an important precursor for SOA at a global scale. We have determined the molar yields of hydrogen peroxide (H2O2), hydromethyl hydroperoxide (HMHP), peroxyformic acid (PFA), peroxyacetic acid (PAA), and total peroxides (TPOs, including unknown peroxides) and the fraction of peroxides in a-pinene/O3 SOA. Comparing the gas-phase peroxides with the particle-phase peroxides, we find that gas-particle partitioning coefficients of PFA and PAA are 104 times higher than the values from the theoretical prediction, indicating that organic peroxides play a more important role in SOA formation than previously expected. Here, the partitioning coefficients of TPO were determined to be as high as (2–3)*104 m3 mg-1. Even so, more than 80% of the peroxides formed in the reaction remain in the gas phase. Water changes the distribution of gaseous peroxides, while it does not affect the total amount of peroxides in either the gas or the particle phase. Approx. 18% of gaseous peroxides undergo rapid heterogeneous decomposition on SOA particles in the presence of water vapor, resulting in the additional production of H2O2. This process can partially explain the unexpectedly high H2O2 yields under wet conditions. Transformation of organic peroxides to H2O2 also preserves OH in the atmosphere, helping to improve the understanding of OH cycling.
Wang Y, Chen ZM, Wu QQ, Liang H, Huang LB, Li H, Lu KD, Wu YS, Dong HB, Zeng LM, et al. Observation of atmospheric peroxides during Wangdu Campaign 2014 at a rural site in the North China Plain. Atmospheric Chemistry and Physics. 2016;16(17):10985-11000.Abstract
Measurements of atmospheric peroxides were made during Wangdu Campaign 2014 at Wangdu, a rural site in the North China Plain (NCP) in summer 2014. The predominant peroxides were detected to be hydrogen peroxide (H2O2), methyl hydroperoxide (MHP) and peroxyacetic acid (PAA). The observed H2O2 reached up to 11.3 ppbv, which was the highest value compared with previous observations in China at summer time. A box model simulation based on the Master Chemical Mechanism and constrained by the simultaneous observations of physical parameters and chemical species was performed to explore the chemical budget of atmospheric peroxides. Photochemical oxidation of alkenes was found to be the major secondary formation pathway of atmospheric peroxides, while contributions from alkanes and aromatics were of minor importance. The comparison of modeled and measured peroxide concentrations revealed an underestimation during biomass burning events and an overestimation on haze days, which were ascribed to the direct production of peroxides from biomass burning and the heterogeneous uptake of peroxides by aerosols, respectively. The strengths of the primary emissions from biomass burning were on the same order of the known secondary production rates of atmospheric peroxides during the biomass burning events. The heterogeneous process on aerosol particles was suggested to be the predominant sink for atmospheric peroxides. The atmospheric lifetime of peroxides on haze days in summer in the NCP was about 2–3 h, which is in good agreement with the laboratory studies. Further comprehensive investigations are necessary to better understand the impact of biomass burning and heterogeneous uptake on the concentration of peroxides in the atmosphere.
Huang LB, Zhao Y, Li H, Chen ZM. Hydrogen peroxide maintains the heterogeneous reaction of sulfur dioxide on mineral dust proxy particles. Atmospheric Environment. 2016;141:552-559.Abstract
The heterogeneous oxidation of sulfur dioxide (SO2) on a-Al2O3 particles was investigated using a flow reactor coupled with a transmission-Fourier transform infrared (T-FTIR) spectrometer at different relative humidities (RH) in the absence or presence of hydrogen peroxide (H2O2), with an emphasis on the saturation coverage of SO2 and the timescale on which the reaction reaches saturation. It is found that the saturation coverage of SO2 in the absence of H2O2 increases with rising RH due to the hydrolysis of SO2 by surface adsorbed water. However, the reaction ultimately reaches saturation since the produced sulfite/bisulfite cannot be further converted to sulfate/bisulfate in the absence of oxidants. In addition, the presence of H2O2 can significantly increase the saturation coverage of SO2 by efficiently oxidizing sulfite/bisulfite to sulfate/bisulfate. Under humid conditions, adsorbed water facilitates the hydrolysis of SO2 and mitigates the increase of surface acidity, which can inhibit the hydrolysis of SO2. Hence, in the presence of H2O2, the saturation coverage of SO2 as well as the time of reaction reaching saturation increases with rising RH and the surface is not saturated on the timescale of the experiments (40 h) at 60% RH. Furthermore, the increase of saturation coverage of SO2 in the presence of H2O2 was observed on chemically inactive SiO2 particles, indicating that the hydrolysis of SO2 and subsequent oxidation by H2O2 likely occurs on other types of particles. Our findings are of importance for understanding the role of water vapor and trace gases (e.g., H2O2) in the heterogeneous reaction of SO2 in the atmosphere.
Wu HH, Wang Y, Li H, Huang LB, Huang D, Shen HQ, Xing YN, Chen ZM. The OH-initiated oxidation of atmospheric peroxyacetic acid: Experimental and model studies. Atmospheric Environment. 2017;164:61-70.Abstract
Peroxyacetic acid (PAA, CH3C(O)OOH) plays an important role in atmospheric chemistry, serving as reactive oxidant and affecting radical recycling. However, previous studies revealed an obvious gap between modelled and observed concentrations of atmospheric PAA, which may be partly ascribed to the uncertainty in the kinetics and mechanism of OH-oxidation. In this study, we measured the rate constant of OH radical reaction with PAA (kPAA+OH) and investigated the products in order to develop a more robust atmospheric PAA chemistry. Using the relative rates technique and employing toluene and metaxylene as reference compounds, the kPAA+OH was determined to be (9.4-11.9)*10-12 cm3 molecule-1 s-1 at 298 K and 1 atm, which is about (2.5-3.2) times larger than that parameter used in Master Chemical Mechanism v3.3.1 (MCM v3.3.1) (3.70*10-12 cm3 molecule-1 s-1). Incorporation of a box model and MCM v3.3.1 with revised PAA chemistry represented a better simulation of atmospheric PAA observed during Wangdu Campaign 2014, a rural site in North China Plain. It is found that OH-oxidation is an important sink of atmospheric PAA in this rural area, accounting for ~30% of the total loss. Moreover, the major terminal products of PAA-OH reaction were identified as formaldehyde (HCHO) and formic acid (HC(O)OH). The modelled results show that both primary and secondary chemistry play an important role in the large HCHO and HC(O)OH formation under experimental conditions. There should exist the channel of methyl H-abstraction for PAA-OH reaction, which may also provide routes to HCHO and HC(O)OH formation.