Origin of the springtime tropospheric ozone maximum over east China at LinAn in 2001

Abstract

Tropospheric ozone (O₃) profiles over the east China coast at LinAn (30.30°N, 119.75°E) were measured by electrochemical concentration cell ozonesondes in the spring of 2001. The measurement revealed that extremely high O₃ with mixing ratios up to 1200 ppbv sometimes penetrated deeply into 8.5–16 km above sea level as a result of lowering of the tropopause across the East Asia strong subtropical jet stream. In addition, high O₃ in the 75–150 ppbv range penetrated into the upper and middle troposphere following the extreme O₃ regimes and caused an overall high O₃ mixing ratio in these regions. The occurrence of the high O₃ regimes followed the propagation of dry air with low relative humidity and high potential vorticity suggesting that the O₃ is of stratospheric origin. High O₃ episodes with O₃ mixing ratios in the 75–100 ppbv range were observed in the lower troposphere and especially in the boundary layer. Trajectory analysis suggested that the O₃-rich air masses had passed through the industrialized and urbanized zones of the Pearl River Delta region of south China, northeast China coast and Yangtze River Delta region of east China. The O₃ is probably of anthropogenic origin resulting from photochemical formation from pollutants emitted from these regions. Our analysis thus revealed that over the east China coast at LinAn, stratospheric O₃ is still the predominant source of O₃ in the middle and upper troposphere, while anthropogenic sources caused a high O₃ pollution episode in the boundary layer.