Vertical distribution of summer tropospheric ozone over the northern Tibetan Plateau

Tropospheric ozone (O₃) has significance impacts on climate and air quality, yet observations of tropospheric O₃ is not sufficient. In this study, vertical distribution of tropospheric O₃ and associated meteorological processes from 25 July to 22 August 2016 observed at Golmud, a city in Qinghai province on the Northern Tibet Plateau (TP), is analyzed to better understand characteristics and mechanism of tropospheric O₃ variation there. One general feature is that high (low) O₃ corresponds to low (high) water vapor and high (low) potential vorticity. Except for the tropospheric O₃ enhancement associated with the passage of a low-pressure trough from 25 to 27 July, the impacts of a warm blocking high and the passage of a deep convective system from the main area of the TP on the distribution of tropospheric O₃ are observed and analyzed for the first time in the northern TP. After the formation of the blocking warm high to the northeast of the observation site, easterly winds maintain in the whole troposphere at Golmud from 31 July to 8 August, but tropospheric O₃ concentration is only slightly higher on 2 August due to the anticyclonic shear along the northeast-southwest direction. Pollutant air mass with high O₃ and specific humidity (q) below 6 km appear due to westward transport. The lowest O₃ and the highest q during the entire observational period appear at the height above 10 km from 12 to 14 August with the passage of a deep convective system. Compared with the historical tropospheric O₃ observed in Xining (from July to early August 1996), O₃ at Golmud exhibits a seasonal low value in August, which is consistent with seasonal influences of the summer monsoon. Compared with historical tropospheric O₃ observations in Linzhi (July 2014), Naqu (from late July to mid-August 2011) and Lhasa (August 1998), it is found that latitude has certain influences on O₃ over the Tibetan Plateau.