The local ozone generation was greatly underestimated with current mechanism under high NOx conditions, according to a recent study conducted by researchers led by Prof. XIE Pinhua from the Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS).

This research, based on the observed concentration of HOx free radicals, has pointed a way for future ozone pollution control. Related results were published on Science of the Total Environment.

Radicals are essential driving force of secondary pollution formation. Scientists have observed high concentrations of OH radicals in urban areas and established unconventional regeneration mechanisms. Severe underestimation of ozone formation is not accidental due to regional variations in atmospheric oxidation and the shortcomings of existing box model mechanisms. So, it is necessary to study atmospheric oxidation in different environments.  

In view of this, following a one-month first in-situ HOx radicals measurement in the wintertime of Shanghai with a self-developed HOx instrument, Prof. HU Renzhi and PhD student ZHANG Guoxian, member of the team, conducted a closure analysis on megacity atmospheric chemical processes with a box model. The level of HOx radicals they observed was higher than previous wintertime observations (OH: 2.7×106 cm^-3, HO2: 0.8×108 cm^-3).

Considering the overview of radical concentrations, reactivities and budget channels, they concluded that the complex carbonyls-related oxidation under elevated photochemistry was a possible factor for the discrepancy of the radical sources.

This work was supported by the National Natural Science Foundation of China, the Cultivating Project of Strategic Priority Research Program of CAS, and the Natural Science Foundation of Anhui Province.

Level of HOx radicals was higher than previous wintertime observations. (Image by HU Renzhi)