Both natural processes and human activities emit a variety of volatile organic compounds (VOCs) into the atmosphere. The atmospheric oxidation of VOCs influences the global climate and planetary health by modulating atmospheric oxidant levels, controlling radical cycling, and producing air pollutants such as fine particulate matter and ozone. A key branching point in essentially all atmospheric VOC oxidation involves organic peroxy radicals (RO2) which can undergo bimolecular reactions and isomerization. The relative importance of each reaction channel determines the products that are ultimately formed. In this presentation, I will first present the state of knowledge regarding formation of organic nitrates in reactions of RO2 with NO. We conducted systematic lab studies of the yields of organic nitrates from the OH-initiated oxidation of linear and branched alkanes containing 4-7 carbon atoms. I will discuss nitrate yields as a function of molecular size and temperature (250 K to 295 K), as well as the effect of the RO2 structure (primary, secondary and tertiary nitrates). Next, I will present temperature-dependent composition and volatility of pure biogenic nucleated particles from alpha-pinene oxidation. By using a temperature-programed desorption chemical ionization mass spectrometer, our results show that highly oxygenated organic molecules formed from RO2 autooxidation are much more abundant in particles formed at higher temperatures, shifting the compounds toward high oxygen to carbon ratio and lower intrinsic (300 K) volatility. Our measurements indicate that during new-particle formation from alpha-pinene oxidation, gas-phase chemistry directly determines the properties of materials in the particle phase.

Atmospheric organic peroxy radical chemistry and its impacts on the formation of organic nitrates and the composition of nucleated particles

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