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- Title
Intensive photochemical oxidation in the marine atmosphere: evidence from direct radical measurements.
- Authors
Zhang, Guoxian; Hu, Renzhi; Xie, Pinhua; Hu, Changjin; Liu, Xiaoyan; Zhong, Liujun; Cai, Haotian; Zhu, Bo; Xia, Shiyong; Huang, Xiaofeng; Li, Xin; Liu, Wenqing
- Abstract
Comprehensive observations of hydroxyl (OH) and hydroperoxy (HO 2) radicals were conducted in October 2019 at a coastal continental site in the Pearl River Delta (YMK site, 22.55 ∘ N, 114.60 ∘ E). The daily maximum OH and HO 2 concentrations were (4.7–9.5) × 10 6 and (4.2–8.1) × 10 8 cm -3 , respectively. The synchronized air mass transport from the northern cities and the South China Sea exerted a time-varying influence on atmospheric oxidation. Under a typical ocean-atmosphere (OCM), reasonable measurement model agreement was achieved for both OH and HO 2 using a 0-D chemical box model incorporating the regional atmospheric chemistry mechanism version 2-Leuven isoprene mechanism (RACM2-LIM1), with daily averages of 4.5 × 10 6 and 4.9 × 10 8 cm -3 , respectively. Land mass (LAM) influence promoted more active photochemical processes, with daily averages of 7.1 × 10 6 and 5.2 × 10 8 cm -3 for OH and HO 2 , respectively. Heterogeneous uptake had certain effects on HO x chemistry, but the influence of the halogen mechanism was limited by NO x level. Intensive photochemistry occurred after precursor accumulation, allowing local net ozone production comparable with surrounding suburban environments (5.52 ppb h -1 during the LAM period). The rapid oxidation process was accompanied by a higher diurnal nitrous acid (HONO) concentration (> 400 ppt). After a sensitivity test, HONO-related chemistry elevated the ozone production rate by 33 % and 39 % during the LAM and OCM periods, respectively. The nitric acid (P (HNO 3)) and sulfuric acid (P (H 2 SO 4)) formation rates also increased simultaneously (∼ 43 % and ∼ 48 % for LAM and OCM sectors, respectively). In the ozone-prediction test, simulated O 3 decreased from ∼ 75 ppb to a global background (∼ 35 ppb) without the HONO constraint, and daytime HONO concentrations were reduced to a low level (∼ 70 ppt). For coastal cities, the particularity of the HONO chemistry tends to influence the ozone-sensitive system and eventually magnifies the background ozone. Therefore, the promotion of oxidation by elevated precursors deserves a lot of attention when aiding pollution mitigation policies.
- Subjects
CHEMICAL models; ATMOSPHERIC chemistry; NITROUS acid; CITIES &; towns; AIR travel
- Publication
Atmospheric Chemistry & Physics, 2024, Vol 24, Issue 3, p1825
- ISSN
1680-7316
- Publication type
Article
- DOI
10.5194/acp-24-1825-2024