Semi-quantitative understanding of source contribution to nitrous acid (HONO) based on 1 year of continuous observation at the SORPES station in eastern China
<p>Nitrous acid (HONO), an important precursor of the hydroxyl radical (OH), has long been recognized as of significance to atmospheric chemistry, but its sources are still debated. In this study, we conducted continuous measurement of HONO from November 2017 to November 2018 at the SORPES sta...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/13289/2019/acp-19-13289-2019.pdf |
| Summary: | <p>Nitrous acid (HONO), an important precursor of the hydroxyl radical (OH),
has long been recognized as of significance to atmospheric
chemistry, but its sources are still debated. In this study, we conducted
continuous measurement of HONO from November 2017 to November 2018 at the
SORPES station in Nanjing of eastern China. The yearly average mixing ratio
of observed HONO was <span class="inline-formula">0.69±0.58</span> ppb, showing a larger contribution to
OH relative to ozone with a mean OH production rate of 1.16 ppb h<span class="inline-formula"><sup>−1</sup></span>. To
estimate the effect of combustion emissions of HONO, the emitted ratios of
HONO to <span class="inline-formula">NO<sub><i>x</i></sub></span> were derived from 55 fresh plumes (<span class="inline-formula">NO∕NO<sub><i>x</i></sub></span> > 0.85), with a mean value of 0.79 %. During the nighttime, the chemistry of
HONO was found to depend on RH, and heterogeneous reaction of <span class="inline-formula">NO<sub>2</sub></span> on
an aerosol surface was presumably responsible for HONO production. The average
nighttime <span class="inline-formula">NO<sub>2</sub></span>-to-HONO conversion frequency (<span class="inline-formula"><i>C</i><sub>HONO</sub></span>) was determined
to be <span class="inline-formula">0.0055±0.0032</span> h<span class="inline-formula"><sup>−1</sup></span> from 137 HONO formation cases. The
missing source of HONO around noontime seemed to be photo-induced, with an
average <span class="inline-formula"><i>P</i><sub>unknown</sub></span> of 1.04 ppb h<span class="inline-formula"><sup>−1</sup></span>, based on a semi-quantitative
HONO budget analysis. An over-determined system of equations was applied to
obtain the monthly variations in nocturnal HONO sources. Besides the
burning-emitted HONO (accounting for about 23 % of the total concentration), the
contribution of HONO formed heterogeneously on ground surfaces to measured HONO was an
approximately constant proportion of 36 % throughout the year. The soil
emission revealed clear seasonal variation and contributed up to 40 % of
observed HONO in July and August. A higher propensity for generating HONO on
aerosol surfaces occurred in severe hazes (accounting for 40 % of the total concentration in
January). Our results highlight ever-changing contributions of HONO sources
and encourage more long-term observations to evaluate the contributions from
varied sources.</p> |
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| ISSN: | 1680-7316 1680-7324 |