Ozone in China: Spatial Distribution and Leading Meteorological Factors Controlling O3 in 16 Chinese Cities

Tropospheric ozone (O-3) is one of the major air pollutants in China This paper examined theO(3) concentration in 16 important Chinese cities including 7 megacities and developed a statistical model named Generalized Additive Model (GAM) as a function of different factors to estimate the maximum daily 8 h (MDA8)O-3 during 2014-2016 and how the leading factors impacts O-3 . We found that: (1) Three seasonal patterns of O-3 have been summarized in the spatial-temporal analysis and summer is the highest season in most of the cities. (2) GAM performs very well that it can capture 43-90% of daily O-3 variations. (3) DOY (day of year) and 6 meteorological factors of daily average relative humidity at 1000 mb, daily maximum temperature at 2 m, daily average zonal wind speed at 700 mb, distance of trajectory back 12-hour, surface pressure and geopotential height at 500 mb are sensitive for all 16 cities. The sequence of the leading factors is the same in each group respectively (3 group categories: Beijing, Shijiazhuang and Kunming; Harbin, Hohhot and Dalian; Chengdu and Wuhan). The other 8 cities have different leading factor combination. (4) HYSPLIT back trajectory data can help us to know the importance of transport direction for O-3 concentration in Beijing and other three coastal cities Dalian, Shanghai and Guangzhou. (5) During the Beijing Parade Blue period in the summer of 2015, NO2 was reduced by 44.6% butO(3) was only reduced by 15.7%. Most of these O(3 )changes can be explained by meteorological variations such as wind direction and air temperature.