A Diagnostic Study of an Enhanced Tropospheric Ozone Event over Lin-An, China, in Spring 2001

Abstract

ABSTRACT An extraordinary ozone enhancement event was observed at Lin-An (30.30° N, 119.75° E) from 29 to 30 March 2001. In this event, one or more secondary ozone peaks with the concentration up to 1200 ppbv occurred in the upper troposphere (above 10km). The cause of the ozone enhancement was studied utilizing synoptic meteorology diagnosis from conventional weather data, the National Centers for Environmental Protection data, the Total Ozone Mapping Spectrometer data, Brewer data, and Geostationary Meteorological Satellite images of the water vapor channel. It was revealed that the observed secondary ozone peaks in the upper troposphere in this event were associated with a remarkable intrusion of the stratospheric air downward into the troposphere. The stratosphere-troposphere exchange was related to a synoptic system, including a cold high moving southward at surface, an upper trough, a shift of the subtropical jet (STJ) and the polar front jet, and a subsidence at the left side of the STJ entrance. Furthermore, an analysis of potential vorticity (PV) at 200hPa and vertical PV cross-sections indicated that an obvious tropopause fold occurred blow the STJ core. This fold resulted in the downward transportation of ozone-rich stratospheric air into the upper troposphere.