Importance of secondary organic aerosol formation of <i>α</i>-pinene, limonene, and <i>m</i>-cresol comparing day- and nighttime radical chemistry
<p>The oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate <span class="inline-formula"><i>α</i></span>-pinene, limonene, and <span class="inline-formul...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/8479/2021/acp-21-8479-2021.pdf |
| Summary: | <p>The oxidation of biogenic and anthropogenic compounds leads to the formation
of secondary organic aerosol mass (SOA). The present study aims to
investigate <span class="inline-formula"><i>α</i></span>-pinene, limonene, and <span class="inline-formula"><i>m</i></span>-cresol with regards to their SOA
formation potential dependent on relative humidity (RH) under night-
(NO<span class="inline-formula"><sub>3</sub></span> radicals) and daytime conditions (OH radicals) and the resulting
chemical composition. It was found that SOA formation potential of limonene
with NO<span class="inline-formula"><sub>3</sub></span> 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 <span class="inline-formula"><i>α</i></span>-pinene with NO<span class="inline-formula"><sub>3</sub></span>
slightly exceeds that of the OH-radical reaction, independent from RH. On
average, <span class="inline-formula"><i>α</i></span>-pinene yielded SOA with about 6–7 % from NO<span class="inline-formula"><sub>3</sub></span>
radicals and 3–4 % from OH-radical reaction. Surprisingly, unexpectedly
high SOA yields were found for <span class="inline-formula"><i>m</i></span>-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
<span class="inline-formula"><i>α</i></span>-pinene and <span class="inline-formula"><i>m</i></span>-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 <span class="inline-formula"><i>α</i></span>-pinene varied between 2 and 80 % as a
function of RH.</p>
<p>Furthermore, SOA from <span class="inline-formula"><i>α</i></span>-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.</p> |
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| ISSN: | 1680-7316 1680-7324 |