Secondary organic aerosol formation from isoprene photooxidation.
Recent work has shown that the atmospheric oxidation of isoprene (2-methyl-1,3-butadiene, C5H8) leads to the formation of secondary organic aerosol (SOA). In this study, the mechanism of SOA formation by isoprene photooxidation is comprehensively investigated, by measurements of SOA yields over a range of experimental conditions, namely isoprene and NOx concentrations. Hydrogen peroxide is used as the radical precursor, substantially constraining the observed gas-phase chemistry; all oxidation is dominated by the OH radical, and organic peroxy radicals (RO2) react only with HO2 (formed in the OH + H2O2 reaction) or NO concentrations, including NOx-free conditions. At high NOx, yields are found to decrease substantially with increasing [NOx], indicating the importance of RO2 chemistry in SOA formation. Under low-NOx conditions, SOA mass is observed to decay rapidly, a result of chemical reactions of semivolatile SOA components, most likely organic hydroperoxides.
Departments of Environmental Science and Engineering and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Jesse H
JH
Kroll
Nga L
NL
Ng
Shane M
SM
Murphy
Richard C
RC
Flagan
John H
JH
Seinfeld
D000336:Aerosols / Q000032:analysis* / Q000737:chemistry*; D000393:Air Pollutants; D002070:Butadienes / Q000737:chemistry*; D045782:Hemiterpenes / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D013058:Mass Spectrometry; D009569:Nitric Oxide / Q000737:chemistry; D009930:Organic Chemicals / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction; D010420:Pentanes / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry; D010777:Photochemistry
D000336:Aerosols; D000393:Air Pollutants; D002070:Butadienes; D045782:Hemiterpenes; D009930:Organic Chemicals; D016877:Oxidants; D010420:Pentanes; D010545:Peroxides; C005059:isoprene; D009569:Nitric Oxide; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide