Recently, Professor XIE Pinhua's research group from the Hefei Institutes of Physical Science (HFIPS), Chinese Academy of Sciences (CAS), provided direct evidence of intensive photochemical oxidation in the marine atmosphere through radical measurement.
The research results were published in Atmospheric Chemistry and Physics.
The increasing background ozone concentration in typical regions highlights the significant impact of human activities on the atmospheric oxidizing capacity in the marine boundary layer (MBL). However, research on radical chemistry and oxidation mechanisms in China's MBL regions is limited.
In this study, researchers utilized a self-developed laser-induced fluorescence system (AIOFM-LIF) for the first time to obtain a high-quality timeseries of HOx (OH and HO2) radical concentrations in a marine site in Shenzhen, Pearl River Delta. By combining the observed data with box model analysis, they elucidated the intense photochemical oxidation processes in the marine atmosphere, focusing on radical concentrations, sources, and removal rates.
The results show that in the transition zone between land and sea, the interaction of upwind cities, ships, and other anthropogenic emissions results in the accumulation of precursors and their coupling with radical chemistry, enhancing the atmospheric oxidizing capacity in the marine environment. Influenced by inland air masses, active photochemical processes lead to higher net ozone production.
Moreover, under the high background of precursors in China, heterogeneous uptake processes play a role in HOx radical chemistry, but the influence of halogen mechanisms is limited by NOx levels.
The unique distribution of HONO in the marine atmosphere increases daytime ozone production rates by approximately 40%. Removing the constraint of HONO in the box model allows ozone concentrations to return from pollution levels to global background levels.
"In the stage of secondary pollution control, the coupling effects of precursor emissions and radical chemistry should be additionally considered," said Professor XIE Pinhua.
Median diurnal profiles of the observed and modelled OH, HO2, kOH during LAM and OCM episodes. The coloured shadows for OH and HO2 radicals denote the 25 and 75% percentiles. The grey areas denote nighttime. (Image by HU Renzhi)
