New insight into the spatiotemporal variability and source apportionments of C<sub>1</sub>–C<sub>4</sub> alkyl nitrates in Hong Kong
C<sub>1</sub>–C<sub>4</sub> alkyl nitrates (RONO<sub>2</sub>) were measured concurrently at a mountain site, Tai Mo Shan (TMS), and an urban site, Tsuen Wan (TW), at the base of the same mountain in Hong Kong from September to November 2010. Although the levels...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/8141/2016/acp-16-8141-2016.pdf |
| Summary: | C<sub>1</sub>–C<sub>4</sub> alkyl nitrates (RONO<sub>2</sub>) were measured concurrently at a
mountain site, Tai Mo Shan (TMS), and an urban site, Tsuen Wan (TW), at
the base of the same mountain in Hong Kong from September to November 2010.
Although the levels of parent hydrocarbons were much lower at TMS
(<i>p</i> < 0.05), similar alkyl nitrate levels were found at both sites
regardless of the elevation difference, suggesting various source
contributions of alkyl nitrates at the two sites. Prior to using a positive
matrix factorization (PMF) model, the data at TW were divided into "meso"
and "non-meso" scenarios for the investigation of source apportionments
with the influence of mesoscale circulation and regional transport,
respectively. Secondary formation was the prominent contributor of alkyl
nitrates in the meso scenario (60 ± 2 %,
60.2 ± 1.2 pptv), followed by biomass burning and oceanic emissions,
while biomass burning and secondary formation made comparable contributions
to alkyl nitrates in the non-meso scenario, highlighting the strong
emissions of biomass burning in the inland Pearl River delta (PRD) region. In
contrast to TW, the alkyl nitrate levels measured at TMS mainly resulted from
the photooxidation of the parent hydrocarbons at TW during mesoscale
circulation, i.e., valley breezes, corresponding to 52–86 % of the alkyl
nitrate levels at TMS. Furthermore, regional transport from the inland PRD
region made significant contributions to the levels of alkyl nitrates
(∼ 58–82 %) at TMS in the non-meso scenario, resulting in
similar levels of alkyl nitrates observed at the two sites. The simulation of
secondary formation pathways using a photochemical box model found that the
reaction of alkyl peroxy radicals (RO<sub>2</sub>) with nitric oxide (NO) dominated
the formation of RONO<sub>2</sub> at both sites, and the formation of alkyl
nitrates contributed negatively to O<sub>3</sub> production, with average reduction
rates of 4.1 and 4.7 pptv pptv<sup>−1</sup> at TMS and TW, respectively. |
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| ISSN: | 1680-7316 1680-7324 |