Research and Analysis of a Persistent Heavy Pollution Event in Ningbo, China

Abstract

From 7 to 12 January 2015, there was a rare persistent severe pollution event in Ningbo. Based on the data from routine weather observation, automatic weather station in Zhejiang Province and urban pollutant monitoring in Ningbo City, by using the particle backward trajectory analysis of NOAA HYSPLIT4 model, the diagnosis and analysis of the pollution development and dissipation process were carried out. The results show that: 1) Pollutants carried by cold air are main reason for pollution in the first stage of the pollution process. The transition from near-surface northwest wind to north-northeast wind is the key to air improvement; 2) Favorable atmospheric circulation is the important reason for the long-term persistence of pollution. The long-term control of high-pressure center and low-level inversion between the two cold air effects make the boundary layer particularly stable, while the low horizontal wind speed is beneficial to polluting particles. With the continuous accumulation, the contaminated particles can not effectively diffuse either vertically or horizontally; 3) In the late period of January 11, the supplement of weak cold air in the East Road made the air quality index (AQI) climb to about 300 again. The two advection conveyances of cold air to pollutant particles and the long-term stable maintenance of weather conditions conducive to the accumulation of pollutant particles are two important reasons for this rare and sustained heavy pollution event.