Long-term O<sub>3</sub>–precursor relationships in Hong Kong: field observation and model simulation
Over the past 10 years (2005–2014), ground-level O<sub>3</sub> in Hong Kong has consistently increased in all seasons except winter, despite the yearly reduction of its precursors, i.e. nitrogen oxides (NO<sub><i>x</i></sub> = NO + NO<sub>2</sub>)...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/10919/2017/acp-17-10919-2017.pdf |
| Summary: | Over the past 10 years (2005–2014), ground-level O<sub>3</sub>
in Hong Kong has consistently increased in all seasons except winter,
despite the yearly reduction of its precursors, i.e. nitrogen oxides
(NO<sub><i>x</i></sub> = NO + NO<sub>2</sub>), total volatile organic compounds (TVOCs), and
carbon monoxide (CO). To explain the contradictory phenomena, an
observation-based box model (OBM) coupled with CB05 mechanism was applied in
order to understand the influence of both locally produced O<sub>3</sub> and
regional transport. The simulation of locally produced O<sub>3</sub> showed an
increasing trend in spring, a decreasing trend in autumn, and no changes in
summer and winter. The O<sub>3</sub> increase in spring was caused by the net
effect of more rapid decrease in NO titration and unchanged TVOC reactivity
despite decreased TVOC mixing ratios, while the decreased local O<sub>3</sub>
formation in autumn was mainly due to the reduction of aromatic VOC mixing
ratios and the TVOC reactivity and much slower decrease in NO titration.
However, the decreased in situ O<sub>3</sub> formation in autumn was overridden by
the regional contribution, resulting in elevated O<sub>3</sub> observations.
Furthermore, the OBM-derived relative incremental reactivity indicated that
the O<sub>3</sub> formation was VOC-limited in all seasons, and that the long-term
O<sub>3</sub> formation was more sensitive to VOCs and less to NO<sub><i>x</i></sub> and CO in
the past 10 years. In addition, the OBM results found that the contributions
of aromatics to O<sub>3</sub> formation decreased in all seasons of these years,
particularly in autumn, probably due to the effective control of solvent-related
sources. In contrast, the contributions of alkenes increased, suggesting a
continuing need to reduce traffic emissions. The findings provide updated
information on photochemical pollution and its impact in Hong Kong. |
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| ISSN: | 1680-7316 1680-7324 |