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

Mutzel, Anke; Zhang, Yanli; Böge, Olaf; Rodigast, Maria; Kolodziejczyk, Agata; Wang, Xinming; Herrmann, Hartmut

The oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate inline-formulaα-pinene, limonene, and inline-formulam-cresol with regards to their SOA formation potential dependent on relative humidity (RH) under night- (NOinline-formula3 radicals) and daytime conditions (OH radicals) and the resulting chemical composition. It was found that SOA formation potential of limonene with NOinline-formula3 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 inline-formulaα-pinene with NOinline-formula3 slightly exceeds that of the OH-radical reaction, independent from RH. On average, inline-formulaα-pinene yielded SOA with about 6–7 % from NOinline-formula3 radicals and 3–4 % from OH-radical reaction. Surprisingly, unexpectedly high SOA yields were found for inline-formulam-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 inline-formulaα-pinene and inline-formulam-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 inline-formulaα-pinene varied between 2 and 80 % as a function of RH.

Furthermore, SOA from inline-formulaα-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.

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Mutzel, Anke / Zhang, Yanli / Böge, Olaf / et al: Importance of secondary organic aerosol formation of α-pinene, limonene, and m-cresol comparing day- and nighttime radical chemistry. 2021. Copernicus Publications.

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