Characteristics of vertical ozone distribution in the lower troposphere in the Yangtze River Delta at Lin'an in the spring of 2001

摘要

We analyzed vertical distributions of ozone (O_3) in the lower troposphere ( < 5 km above ground) at Lin'an (119.75°E, 30.30°N), Zhejiang Province using electrochemical concentration cell (ECC) ozonesonde data obtained from February 21 to April 13, 2001. The results showed that the vertical O_3 distributions are controlled by metrological conditions and the characteristics of O_3 profiles are related to those of wet bulb potential temperature and wind field. O_3 below 2 km showed that the strongest variability and enhanced O_3 mixing ratios were associated with easterly winds that blow pollutants from the upwind source region of the Yangtze River Delta (YRD) region. Vertical O_3 profiles below 5 km can be grouped into 5 categories: (1) peak mixing ratio type, (2) well-mixed type, (3) layered-structure type, (4) episodic pollution type and (5) alti-tudinal increasing type. Vertical distributions of O_3 affected by regional transport of polluted air masses were investigated. Transport of polluted air from high latitudes of northern China, accompanying subsiding motion of air and stagnant atmospheric conditions are important factors that lead to high mixing ratios of O_3 at Lin'an. The stagnant atmospheric conditions associated with a continental high pressure system and pollution plume transported from the YRD and central-eastern China also lead to regional accumulation of O_3 and high O_3 mixing ratio at Lin'an. Long-range transport of O_3 and pollutants from the Pearl River Delta in South China and in-situ O_3 formation also resulted in elevated O_3 mixing ratios at around 1 km altitudes and layered O_3 distribution in the lower troposphere.