Abstract
Abstract. A series of aggressive measures was launched by the Chinese government to reduce pollutant emissions from Beijing and surrounding areas during the Olympic Games. Observations at Miyun, a rural site 100 km downwind of the Beijing urban center, show significant decreases in concentrations of O3, CO, NOy, and SO2 during August 2008, relative to August 2006–2007. The mean daytime mixing ratio of O3 was lower by about 15 ppbv, reduced to 50 ppbv, in August 2008. The relative reductions in daytime SO2, CO, and NOy were 61%, 25%, and 21%, respectively. Changes in SO2 and in species correlations from 2007 to 2008 indicate that emissions of SO2, CO, and NOx were reduced at least by 60%, 32%, and 36%, respectively, during the Olympics. Analysis of meteorological conditions and interpretation of observations using a chemical transport model suggest that although the day-to-day variability in ozone is driven mostly by meteorology, the reduction in emissions of ozone precursors associated with the Olympic Games had a significant contribution to the observed decrease in O3 during August 2008, accounting for 80% of the O3 reduction for the month as a whole and 45% during the Olympics Period (8–24 August). The model predicts that emission restrictions such as those implemented during the Olympics can affect O3 far beyond the Beijing urban area, resulting in reductions in boundary layer O3 of 2–10 ppbv over a large region of the North China Plain and Northeastern China.
Highlights
Ozone is produced in the troposphere by photochemical oxidation of carbon monoxide (CO) and volatile organic carbon (VOCs), initiated by reaction with OH in the presence of NOx
We show that the reduction in pollution levels during the Olympics, far exceeding the magnitude attributed to year-to-year changes in meteorology, reflects most a response to the emission reductions
Using species concentrations and their correlations observed at Miyun, quantitative estimates are derived for the magnitude of emission reductions for SO2, CO, and NOx during the Olympics employing a “top-down” approach independent of any modeling or bottom-up information
Summary
Ozone is produced in the troposphere by photochemical oxidation of carbon monoxide (CO) and volatile organic carbon (VOCs), initiated by reaction with OH in the presence of NOx. Examining the day-of-week variations of O3 provides a useful methodology to improve understanding of nonlinear ozone chemistry for many western cities and downwind regions (Murphy et al, 2006, 2007) No such “weekend” effect has been observed for precursor emissions in China (Beirle et al, 2003), likely due to different emission patterns related to social-economic factors in China. Using species concentrations and their correlations observed at Miyun, quantitative estimates are derived for the magnitude of emission reductions for SO2, CO, and NOx during the Olympics employing a “top-down” approach independent of any modeling or bottom-up information The latter part of the paper focuses on a model-based analysis.
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