Variations of O₃ and CO in summertime at a rural site near Beijing

Abstract

Abstract. Large intra-season differences in concentrations of CO and O3 ([CO], [O3]) 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 [O3] dropped from 67 ppbv in June to 50 ppbv in July and August. The observed changes in CO and O3 are attributed to the influence of the summer monsoonal circulation that develops over the North China Plain in July. Photochemical production of O3 is reduced as a consequence of increased cloudiness during July and August, as indicated by the strong negative correlation observed between [O3] 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 O3 during summer in Beijing.