| Summary: | The gas-particle mixture produced in a smog chamber from the ozonolysis of limonene was further oxidised with NO3 radicals, O3 and OH radicals to study the NO3, O3 and OH initiated aging of biogenic secondary organic aerosol (SOA). The results of aerosol mass spectrometry analysis showed that similar yields of SOA were produced by all three oxidants used in the experiments after 1-h of aging, suggesting that NO3 and O3 initiated aging have similar SOA formation potentials to OH initiated aging. The results of proton transfer reaction-quadrupole interface time-of-flight mass spectrometry analysis showed that the signals of m/z 139, m/z 151, m/z 153 and m/z 167 decreased upon subsequent oxidation by all three oxidants, suggesting the degradation of gaseous unsaturated first-generation products formed from limonene ozonolysis such as limonaketone, limononaldehyde, limonalic acid and limononic acid. The results of liquid chromatography-mass spectrometry analysis showed that chromatographic peaks of m/z 185 and m/z 199 degraded upon subsequent oxidation, indicating that particle phase unsaturated products, including limonic acid and 5- or 7-hydroxylimononic acid, reacted in the gas or the particle phase with all three oxidants injected. The results of chemical kinetic and gas-particle partitioning calculations suggest that unsaturated particle phase products decrease due to reactions with NO3 radicals, O3 and OH radicals in the gas phase, whereas reactions in the particle phase are not excluded. New organic nitrate products were produced by NO3 initiated aging whereas saturated organic compounds, including ketolimonic acid, 5- or 7-hydroxyketolimononic acid, and a portion of highly functionalised limonene ozonolysis products of m/z 215 and m/z 217 increased by O3 and OH initiated aging.
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