Atmos. Chem. Phys. Discuss., 13, 13045-13078, 2013
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Ozone weekend effects in the Beijing–Tianjin–Hebei metropolitan area, China
Y. H. Wang1,2, B. Hu1, and Y. S. Wang1
1State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Science, Beijing, 100029, China
2Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Science, Lanzhou University, Lanzhou, 730000, China

Abstract. The ozone weekend effect (OWE) was first investigated in the metropolitan area of Beijing–Tianjin–Hebei (BTH), China, using in situ measurements from the Atmospheric Environment Monitoring Network from July 2009 to August 2011. The results indicate that there is an obvious weekly periodical variation in the surface ozone concentration based on 24 h averaged value. There is a lower ozone concentration from Wednesday to Friday (weekday) and a higher concentration from Saturday to Monday (weekend) over the entire study area. NOx also displays weekly cycle, with the maximum level occurring on weekdays and the minimum level on weekends, especially later on Sunday night and early Monday morning. This pattern may be responsible for the higher concentration of ozone on weekends. Additionally, the vertical variations in O3 and NOx from the 8 m 47 m, 120 m and 280 m observation platforms on the 325 m Beijing meteorological tower displayed obvious weekly cycles that corresponded to the surface results.

A smaller decrease in VOCs (a proxy for CO) and much lower NOx concentrations on the weekend may lead to higher VOC/NOx ratio, which can enhance the ozone production efficiency in VOC-regime areas. Additionally, a clear weekly cycle in the fine aerosol concentration was observed, with maximum values occurring on weekdays and minimum values occurring on weekends. Higher concentrations of aerosol on weekdays can reduce the UV radiation flux by absorption or scattering, which leads to a decrease in the ozone production efficiency. A significant weekly cycle in UV radiation, in consistent with the aerosol concentration, was discovered at the BJT site, validating the assumption. A comprehensive understanding of the ozone weekend effect in the BTH area can provide deep insights into controlling photochemical pollution.

Citation: Wang, Y. H., Hu, B., and Wang, Y. S.: Ozone weekend effects in the Beijing–Tianjin–Hebei metropolitan area, China, Atmos. Chem. Phys. Discuss., 13, 13045-13078, doi:10.5194/acpd-13-13045-2013, 2013.
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