title: Measurements of secondary organic aerosol formed from OH-initiated photo-oxidation of isoprene using online photoionization aerosol mass spectrometry.
abstract: Isoprene is a significant source of atmospheric organic aerosol; however, the secondary organic aerosol (SOA) formation and involved chemical reaction pathways have remained to be elucidated. Recent works have shown that the photo-oxidation of isoprene leads to form SOA. In this study, the chemical composition of SOA from the OH-initiated photo-oxidation of isoprene, in the absence of seed aerosols, was investigated through the controlled laboratory chamber experiments. Thermal desorption/tunable vacuum-ultraviolet photoionization time-of-flight aerosol mass spectrometry (TD-VUV-TOF-PIAMS) was used in conjunction with the environmental chamber to study SOA formation. The mass spectra obtained at different photon energies and the photoionization efficiency (PIE) spectra of the SOA products can be obtained in real time. Aided by the ionization energies (IE) either from the ab initio calculations or the literatures, a number of SOA products were proposed. In addition to methacrolein, methyl vinyl ketone, and 3-methyl-furan, carbonyls, hydroxycarbonyls, nitrates, hydroxynitrates, and other oxygenated compounds in SOA formed in laboratory photo-oxiadation experiments were identified, some of them were investigated for the first time. Detailed chemical identification of SOA is crucial for understanding the photo-oxidation mechanisms of VOCs and the eventual formation of SOA. Possible reaction mechanisms will be discussed.
authors.affiliation: National Synchrotron Radiation Laboratory, School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230029, China. fangwz@mail.ustc.edu.cn
authors.forename: Wenzheng
authors.initials: W
authors.lastname: Fang
authors.forename: Lei
authors.initials: L
authors.lastname: Gong
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.forename: Maoqi
authors.initials: M
authors.lastname: Cao
authors.forename: Yuquan
authors.initials: Y
authors.lastname: Li
authors.forename: Liusi
authors.initials: L
authors.lastname: Sheng
mesh_terms: D000336:Aerosols / Q000032:analysis* / Q000737:chemistry; D000390:Air Ionization; D002070:Butadienes / Q000032:analysis* / Q000737:chemistry; D045782:Hemiterpenes / Q000032:analysis* / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods*; D009862:Online Systems; D009930:Organic Chemicals / Q000032:analysis* / Q000737:chemistry; D010084:Oxidation-Reduction; D010420:Pentanes / Q000032:analysis* / Q000737:chemistry; D010777:Photochemistry / Q000379:methods*
chemical_list: D000336:Aerosols; D002070:Butadienes; D045782:Hemiterpenes; D009930:Organic Chemicals; D010420:Pentanes; C005059:isoprene; D017665:Hydroxyl Radical