Measurement of NO_y during Campaign of Air Quality Research in Beijing 2006 (CAREBeijing‐2006): Implications for the ozone production efficiency of NO_x

Abstract

Total reactive nitrogen oxides (NO y ) are among the key components in the chemistry of ozone production. In order to improve the understanding of the formation mechanisms of high‐ozone events in Beijing, China, an intensive experiment on the reactive nitrogen oxides was carried out at the observatory of Peking University during the Campaign of Air Quality Research in Beijing and surrounding areas in 2006 (CAREBeijing‐2006) campaign. In this study, analysis focusing on the data of high O 3 episodes was performed to examine the relationship between the concentration of total oxidant and the composition of NO y . High levels of NO and NO y were observed in the morning rush hours, indicating the influences of fresh emissions from local traffic. However, the ratio of [NO] to [NO y ] was only 11–60% in the morning, implying that there was a substantial amount of aged air pollutants remained overnight in the stagnant air mass. Significant increases in the NO z mixing ratio (= [NO y ]‐[NO x ]) were observed during the period from the morning toward early afternoon, consistent with the increasing oxidant level. Ozone production efficiency of NO x (OPE x ), which was derived from the NO z ‐O x regression, was found to range from 3.9 to 9.7 mol/mol in Beijing. Furthermore, it was revealed that the daily [NO z ] maximum was proportional to the NO x peak level in the morning, and that OPE x decreased with the increases of [NO z ] in a hyperbolic form. According to the results, abatement in NO x emission would not be effective toward reducing ozone concentrations in Beijing.