Exploration of the Atmospheric Oxidative Capacity and Regional Secondary Air Pollution Control in China (Invited Presentation)

Air pollution in China has become a social and scientific problem of high concerns by citizens and the government. Ambitious control strategy and national action plan were implemented in 2013 to reduce emission of major primary air pollutants. As a consequence, significant air quality improvement was achieved in most of Chinese cities. However, severe pollution episodes still occurred frequently with characteristics of high O₃ in summer and high secondary aerosol (PM_2.5) in autumn and winter. The control of O₃ and PM_2.5 mostly relies on the elucidation of the atmospheric oxidation capacity, especially HOx radical chemistry, which is the central driving force of secondary air pollution formation.

We have performed five Chinese comprehensive field campaigns centered on measurement of OH radicals with laser induced fluorescence technique, in rural and suburban areas in both North China Plain and Pearl River Delta. In the present work, we summarized the observed ambient characteristics of the OH radicals with a number of classical functional dependences. The primary OH productions during daytime were all the time diagnosed to be dominated by the HONO photolysis channel. OH budget analysis showed that a missing OH source was determined for the summer and autumn campaigns. The underestimation of the observed OH was explained by a so far unrecognized OH regeneration new scheme (RO₂ + X à HO₂, HO₂ + X à OH). The impact of HONO, aerosol and RO₂ radical on O₃ production rate were evaluated, which uncertainties might cause underestimation of O₃ peak concentration in the regional air quality model. Furthermore, the new HOx scheme was used to evaluate the sensitivity of O₃ and secondary aerosol production rate with NOx and VOCs, revealing extremely importance of VOCs reduction for air quality improvement.

National key research and development program “air pollution formation mechanism and control techonology“ was setup in 2015 to provide scientific supporting for regional air pollution control. The reserch on atmospheric oxidation capacity and regional secondary air pollution control will be intensified in next five years. It is a great chance for us to establish a general atmospheric HOx mechanism suited for all the studied Chinese megacities and enable a better air pollution predication for setting up the air pollution mitigation strategies.