On the importance of multiphase photolysis of organic nitrates on their global atmospheric removal
<p>Organic nitrates (RONO<span class="inline-formula"><sub>2</sub></span>) are secondary compounds, and their fate is related to the transport and removal of NO<span class="inline-formula"><sub><i>x</i></sub></span>...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-05-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/5851/2023/acp-23-5851-2023.pdf |
| Summary: | <p>Organic nitrates (RONO<span class="inline-formula"><sub>2</sub></span>) are secondary
compounds, and their fate is related to the transport and removal of
NO<span class="inline-formula"><sub><i>x</i></sub></span> in the atmosphere. While previous research studies have focused on
the reactivity of these molecules in the gas phase, their reactivity in
condensed phases remains poorly explored despite their ubiquitous presence
in submicron aerosols. This work investigated for the first time the
aqueous-phase photolysis-rate constants and quantum yields of four
RONO<span class="inline-formula"><sub>2</sub></span> (isopropyl nitrate, isobutyl nitrate, <span class="inline-formula"><i>α</i></span>-nitrooxyacetone,
and 1-nitrooxy-2-propanol). Our results showed much lower photolysis-rate
constants for these RONO<span class="inline-formula"><sub>2</sub></span> in the aqueous phase than in the gas phase.
From alkyl nitrates to polyfunctional RONO<span class="inline-formula"><sub>2</sub></span>, no significant increase
of
their aqueous-phase photolysis-rate constants was observed, even for
RONO<span class="inline-formula"><sub>2</sub></span> with conjugated carbonyl groups, in contrast with the
corresponding gas-phase photolysis reactions. Using these new results,
extrapolated to other alkyl and polyfunctional RONO<span class="inline-formula"><sub>2</sub></span>, in combination
with estimates for the other atmospheric sinks (hydrolysis, gas-phase
photolysis, aqueous- and gas-phase ⚫OH oxidation, dry and
wet
deposition), multiphase atmospheric lifetimes were calculated for 45
atmospherically relevant RONO<span class="inline-formula"><sub>2</sub></span> along with the relative importance of
each sink. Their lifetimes range from a few minutes to several hours
depending on the RONO<span class="inline-formula"><sub>2</sub></span> chemical structure and its water solubility. In
general, multiphase atmospheric lifetimes are lengthened when RONO<span class="inline-formula"><sub>2</sub></span>
partition to the aqueous phase, especially for conjugated carbonyl nitrates
for which lifetimes can increase by up to 100 %. Furthermore, our
results
show that aqueous-phase ⚫OH oxidation is a major sink for
water-soluble RONO<span class="inline-formula"><sub>2</sub></span> (<span class="inline-formula"><i>K</i><sub>H</sub><i>></i>10<sup>5</sup></span> M atm<span class="inline-formula"><sup>−1</sup></span>)
ranging from 50 % to 70 % of their total sink at high liquid water content (LWC)
(0.35 g m<span class="inline-formula"><sup>−3</sup></span>). These results highlight the importance of
investigating the
aqueous-phase RONO<span class="inline-formula"><sub>2</sub></span> reactivity to understand how it affects their
ability to transport air pollution.</p> |
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| ISSN: | 1680-7316 1680-7324 |