Daytime atmospheric oxidation capacity in four Chinese megacities during the photochemically polluted season: a case study based on box model simulation
Atmospheric oxidation capacity is the basis for converting freshly emitted substances into secondary products and is dominated by reactions involving hydroxyl radicals (OH) during daytime. In this study, we present in situ measurements of ROx radical (hydroxy OH, hydroperoxy HO2, and organic peroxy...
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Published in | Atmospheric chemistry and physics Vol. 19; no. 6; pp. 3493 - 3513 |
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Main Authors | , , , , , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Katlenburg-Lindau
Copernicus GmbH
20.03.2019
Copernicus Publications |
Subjects | |
Online Access | Get full text |
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Summary: | Atmospheric oxidation capacity is the basis for
converting freshly emitted substances into secondary products and is
dominated by reactions involving hydroxyl radicals (OH) during daytime. In
this study, we present in situ measurements of ROx radical (hydroxy OH,
hydroperoxy HO2, and organic peroxy RO2) precursors and products;
the measurements are carried out in four Chinese megacities (Beijing,
Shanghai, Guangzhou, and Chongqing) during photochemically polluted seasons.
The atmospheric oxidation capacity is evaluated using an observation-based
model and radical chemistry precursor measurements as input. The radical
budget analysis illustrates the importance of HONO and HCHO photolysis,
which account for ∼50 % of the total primary radical
sources. The radical propagation is efficient due to abundant NO in urban
environments. Hence, the production rate of secondary pollutants, that is,
ozone (and fine-particle precursors (H2SO4, HNO3, and
extremely low volatility organic compounds, ELVOCs) is rapid, resulting in
secondary air pollution. The ozone budget demonstrates its high production
in urban areas; also, its rapid transport to downwind areas results in rapid
increase in local ozone concentrations. The O3–NOx–VOC (volatile
organic compound) sensitivity tests show that ozone production is
VOC-limited and that alkenes and aromatics should be mitigated first for
ozone pollution control in the four studied megacities. In contrast,
NOx emission control (that is, a decrease in NOx) leads to more
severe ozone pollution. With respect to fine-particle pollution, the role of
the HNO3–NO3 partitioning system is investigated using a thermal
dynamic model (ISORROPIA 2). Under high relative humidity (RH) and
ammonia-rich conditions, nitric acid converts into nitrates. This study
highlights the efficient radical chemistry that maintains the atmospheric
oxidation capacity in Chinese megacities and results in secondary pollution
characterized by ozone and fine particles. |
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ISSN: | 1680-7324 1680-7316 1680-7324 |
DOI: | 10.5194/acp-19-3493-2019 |