Importance of secondary organic aerosol formation of α -pinene, limonene, and m -cresol comparing day- and nighttime radical chemistry

摘要

The oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate α -pinene, limonene, and m -cresol with regards to their SOA formation potential dependent on relative humidity (RH) under night- (NO 3 radicals) and daytime conditions (OH radicals) and the resulting chemical composition. It was found that SOA formation potential of limonene with NO 3 under dry conditions significantly exceeds that of the OH-radical reaction, with SOA yields of 15–30?% and 10–21?%, respectively. Additionally, the nocturnal SOA yield was found to be very sensitive towards RH, yielding more SOA under dry conditions. In contrast, the SOA formation potential of α -pinene with NO 3 slightly exceeds that of the OH-radical reaction, independent from RH. On average, α -pinene yielded SOA with about 6–7?% from NO 3 radicals and 3–4?% from OH-radical reaction. Surprisingly, unexpectedly high SOA yields were found for m -cresol oxidation with OH radicals (3–9?%), with the highest yield under elevated RH (9?%), which is most likely attributable to a higher fraction of 3-methyl-6-nitro-catechol (MNC). While α -pinene and m -cresol SOA was found to be mainly composed of water-soluble compounds, 50–68?% of nocturnal SOA and 22–39?% of daytime limonene SOA are water-insoluble. The fraction of SOA-bound peroxides which originated from α -pinene varied between 2 and 80?% as a function of RH. Furthermore, SOA from α -pinene revealed pinonic acid as the most important particle-phase constituent under day- and nighttime conditions with a fraction of 1–4?%. Other compounds detected are norpinonic acid (0.05–1.1?% mass fraction), terpenylic acid (0.1–1.1?% mass fraction), pinic acid (0.1–1.8?% mass fraction), and 3-methyl-1,2,3-tricarboxylic acid (0.05–0.5?% mass fraction). All marker compounds showed higher fractions under dry conditions when formed during daytime and showed almost no RH effect when formed during night.