ABSTRACT: Large intra-season differences in concentrations of CO and O<sub>3</sub> ([CO], [O<sub>3</sub>]) were detected at Miyun, a rural site north of Beijing, in summer 2006. Despite an increase in mean daytime [CO] from 500 ppbv in June to 700 ppbv in July, mean daytime [O<sub>3</sub>] dropped from 67 ppbv in June to 50 ppbv in July and August. The observed changes in CO and O<sub>3</sub> are attributed to the influence of the summer monsoonal circulation that develops over the North China Plain in July. Photochemical production of O<sub>3</sub> is reduced as a consequence of increased cloudiness during July and August, as indicated by the strong negative correlation observed between [O<sub>3</sub>] and satellite observations of cloud optical depth, with cloudiness having little effect on CO. The analysis suggests a strategy for emission controls that could be implemented in an economically efficient manner to minimize the frequency of high levels of O<sub>3</sub> during summer in Beijing.
Atmospheric Chemistry and Physics Discussions. 01/2008;