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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.

To investigate the reaction mechanisms during the NO 3 - and O 3 -initiated aging of aromatic secondary organic aerosol (SOA), the gases and particles formed from the OH-initiated oxidation of toluene were exposed to NO 3 radicals and O 3 in a laboratory chamber. Hydroxyl radicals for the oxidation of toluene were produced under light conditions through H 2 O 2 photolysis and dark conditions through tetramethylethylene ozonolysis. Aerodyne aerosol mass spectrometer results demonstrated an increase in SOA and nitrate aerosol concentrations only after N 2 O 5 injection, but no clear change after O 3 injection. The results of proton transfer reaction-quadrupole interface-time of flight mass spectrometer showed that the signal of m/z 109.07 decreased and the signals of m/z 123.05 and m/z 154.05 increased after N 2 O 5 injection, suggesting that gaseous cresols formed from toluene oxidation are rapidly degraded and gaseous nitrocresols and methylbenzoquinones are newly formed. The results of liquid chromatography-mass spectrometry analysis showed that nitrocresols and nitrosalicylic alcohols were the major products formed after N 2 O 5 injection in the particle phase. To confirm the contribution of cresols on aging, NO 3 oxidation of o -cresol was carried out, which resulted in the formation of similar products, i.e. gaseous nitrocresols and particulate nitrosalicylic alcohols. Yield curve analysis using two product model estimated that cresol accounted for ~62% of the increase in SOA during NO 3 -initiated aging of toluene SOA. Image 1 • SOA formed from OH oxidation of toluene was exposed to NO 3 radicals and O 3. • SOA increased by 22% only after NO 3 radical addition. • Cresols were rapidly degraded, nitrocresols and nitrosalicylic alcohols were formed. • Cresols accounted for a 57–67% increase in SOA upon exposure to NO 3 radicals. [ABSTRACT FROM AUTHOR]