Field observational constraints on the controllers in glyoxal (CHOCHO) reactive uptake to aerosol
<p>Glyoxal (CHOCHO), the simplest dicarbonyl in the troposphere, is a potential precursor for secondary organic aerosol (SOA) and brown carbon (BrC) affecting air quality and climate. The airborne measurement of CHOCHO concentrations during the KORUS-AQ (KORea–US Air Quality study) campaign in...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/805/2022/acp-22-805-2022.pdf |
| Summary: | <p>Glyoxal (CHOCHO), the simplest dicarbonyl in the
troposphere, is a potential precursor for secondary organic aerosol (SOA)
and brown carbon (BrC) affecting air quality and climate. The airborne
measurement of CHOCHO concentrations during the KORUS-AQ (KORea–US Air
Quality study) campaign in 2016 enables detailed quantification of loss
mechanisms pertaining to SOA formation in the real atmosphere. The
production of this molecule was mainly from oxidation of aromatics (59 %)
initiated by hydroxyl radical (OH). CHOCHO loss to aerosol was found to be
the most important removal path (69 %) and contributed to roughly
<span class="inline-formula">∼</span> 20 % (3.7 <span class="inline-formula">µ</span>g sm<span class="inline-formula"><sup>−3</sup></span> ppmv<span class="inline-formula"><sup>−1</sup></span> h<span class="inline-formula"><sup>−1</sup></span>,
normalized with excess CO) of SOA growth in the first 6 h in Seoul
Metropolitan Area. A reactive uptake coefficient (<span class="inline-formula"><i>γ</i></span>) of
<span class="inline-formula">∼</span> 0.008 best represents the loss of CHOCHO by surface uptake
during the campaign. To our knowledge, we show the first field observation
of aerosol surface-area-dependent (<span class="inline-formula"><i>A</i><sub>surf</sub></span>) CHOCHO uptake, which diverges
from the simple surface uptake assumption as <span class="inline-formula"><i>A</i><sub>surf</sub></span> increases in<span id="page806"/> ambient
condition. Specifically, under the low (high) aerosol loading, the CHOCHO
effective uptake rate coefficient, <span class="inline-formula"><i>k</i><sub>eff,uptake</sub></span>, linearly increases
(levels off) with <span class="inline-formula"><i>A</i><sub>surf</sub></span>; thus, the irreversible surface uptake is a
reasonable (unreasonable) approximation for simulating CHOCHO loss to
aerosol. Dependence on photochemical impact and changes in the chemical and
physical aerosol properties “free water”, as well as aerosol viscosity,
are discussed as other possible factors influencing CHOCHO uptake rate. Our
inferred Henry's law coefficient of CHOCHO, <span class="inline-formula">7.0×10<sup>8</sup></span> M atm<span class="inline-formula"><sup>−1</sup></span>, is <span class="inline-formula">∼</span> 2 orders of magnitude higher than those
estimated from salting-in effects constrained by inorganic salts only
consistent with laboratory findings that show similar high partitioning into
water-soluble organics, which urges more understanding on CHOCHO solubility
under real atmospheric conditions.</p> |
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| ISSN: | 1680-7316 1680-7324 |