Abstract:Large intra-season differences in mixing ratios of
CO and O3 were detected at Miyun, a rural site north of Beijing,
in summer 2006. Despite an increase in mean daytime
mixing ratio of 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.