Add time:09/25/2019         Source:sciencedirect.com

The detailed molecular composition of laboratory-generated secondary organic aerosols (SOA) during the high-NO photooxidation of β-pinene (βP) was investigated using a novel thermal desorption dichloromethane-assisted low-pressure photoionization mass spectrometry (TD-CH2Cl2-assisted LPPI-MS) technique. We found that protonated norpinone gave the highest signal intensity, which supported that assumption that this compound was the key oxidation species responsible for promoting βP-SOA formation. In addition to the previously identified monomers (i.e., 2,2-dimethylcyclobutyl-1,3-dicarboxaldehyde (m/z 140), pinene aldehyde (m/z 150), myrtenol (m/z 152), (2,2-dimethyl-3-acetyl)-cyclobutylformate (m/z 156), pinene acid (m/z 166), and isomers of pinalic-3-acid (m/z 170)), two additional nitrogen-containing species (i.e., C10 hydroxy nitrate and C10 carbonyl nitrate) were also observed at m/z values of 214 and 216 in the mass spectrum of βP-SOA. Furthermore, the losses of 18 (H2O), 46 (NO2), and 64 (H2O + NO2) were attributed to the typical fragmentation pathways of the two nitrogen-containing species. Overall, these results not only contribute to an improved understanding of βP-SOA formation, but they also indicate that TD-CH2Cl2-assisted LPPI-MS can be used as a novel detection means to study SOA formation.

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