气候变化领域集成服务门户(CCPortal): Effects of inorganic salts on the heterogeneous OH oxidation of organic compounds: Insights from methylglutaric acid-ammonium sulfate

CCPortal

DOI	10.5194/acp-19-9581-2019
	Effects of inorganic salts on the heterogeneous OH oxidation of organic compounds: Insights from methylglutaric acid-ammonium sulfate
	Lam H.K.; Shum S.M.; Davies J.F.; Song M.; Zuend A.; Chan M.N.
发表日期	2019
ISSN	16807316
起始页码	9581
结束页码	9593
卷号	19 期号:14
英文摘要	Atmospheric particles, consisting of inorganic salts, organic compounds and a varying amount of water, can continuously undergo heterogeneous oxidation initiated by gas-phase oxidants at the particle surface, changing the composition and properties of particles over time. To date, most studies focus on the chemical evolution of pure organic particles upon oxidation. To gain more fundamental insights into the effects of inorganic salts on the heterogeneous kinetics and chemistry of organic compounds, we investigate the heterogeneous OH oxidation of 3-methylglutaric acid (3-MGA) particles and particles containing both 3-MGA and ammonium sulfate (AS) in an organic-to-inorganic mass ratio of 2 in an aerosol flow tube reactor at a high relative humidity of 85.0 %. The molecular information of the particles before and after OH oxidation is obtained using the direct analysis in real time (DART), a soft atmospheric pressure ionization source coupled to a high-resolution mass spectrometer. Optical microscopy measurements reveal that 3-MGA-AS particles are in a single liquid phase prior to oxidation at high relative humidity. Particle mass spectra show that C6 hydroxyl and C6 ketone functionalization products are the major products formed upon OH oxidation in the absence and presence of AS, suggesting that the dissolved salt does not significantly affect reaction pathways. The dominance of C6 hydroxyl products over C6 ketone products could be explained by the intermolecular hydrogen abstraction by tertiary alkoxy radicals formed at the methyl-substituted tertiary carbon site. On the other hand, kinetic measurements show that the effective OH uptake coefficient, ?eff, for 3-MGA-AS particles (0:99±0:05) is smaller than that for 3-MGA particles (2:41±0:13) by about a factor of ~ 2:4. A smaller reactivity observed in 3-MGA-AS particles might be attributed to a higher surface concentration of water molecules and the presence of ammonium and sulfate ions, which are chemically inert to OH radicals, at the particle surface. This could lower the collision probability between the 3-MGA and OH radicals, resulting in a smaller overall reaction rate. Our results suggest that inorganic salts likely alter the overall heterogeneous reactivity of organic compounds with gas-phase OH radicals rather than reaction mechanisms in well-mixed aqueous organic-inorganic droplets at a high humidity, i.e., 85%relative humidity (RH). It also acknowledges that the effects of inorganic salts on the heterogeneous reactivity could vary greatly, depending on the particle composition and environmental conditions (e.g., RH and temperature). For instance, at lower relative humidities, aqueous 3-MGA-AS droplets likely become more concentrated and more viscous before efflorescence, possibly giving rise to diffusion limitation during oxidation under relatively dry or cold conditions. Further studies on the effects of inorganic salts on the diffusivity of the species under different relative humidities within the organic-inorganic particles are also desirable to better understand the role of inorganic salts in the heterogeneous reactivity of organic compounds. © 2019 Author(s).
语种	英语
scopus关键词	atmospheric chemistry; concentration (composition); heterogeneity; heterogeneous medium; hydroxyl radical; inorganic salt; organic compound; oxidation
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/144249
作者单位	Earth System Science Programme, Faculty of Science, Chinese University of Hong Kong, Hong Kong, China; Department of Chemistry, University of California, Riverside, CA, United States; Department of Earth and Environmental Sciences, Chonbuk National University, Jeollabuk-do, South Korea; Department of Atmospheric and Oceanic Sciences, McGill University, Montréal, QC, Canada; Institute of Environment, Energy, and Sustainability, Chinese University of Hong Kong, Hong Kong, China
推荐引用方式 GB/T 7714	Lam H.K.,Shum S.M.,Davies J.F.,et al. Effects of inorganic salts on the heterogeneous OH oxidation of organic compounds: Insights from methylglutaric acid-ammonium sulfate[J],2019,19(14).
APA	Lam H.K.,Shum S.M.,Davies J.F.,Song M.,Zuend A.,&Chan M.N..(2019).Effects of inorganic salts on the heterogeneous OH oxidation of organic compounds: Insights from methylglutaric acid-ammonium sulfate.Atmospheric Chemistry and Physics,19(14).
MLA	Lam H.K.,et al."Effects of inorganic salts on the heterogeneous OH oxidation of organic compounds: Insights from methylglutaric acid-ammonium sulfate".Atmospheric Chemistry and Physics 19.14(2019).