Analysis of a Serious Haze Event Resulting from Crop Residue Burning in Central Eastern Hubei

Based on surface meteorological parameters, fire spot information, and air pollutant concentrations, a serious haze event that occurred in central eastern Hubei Province during 11-12 June 2014 was investigated. The dominant reason for this air pollution episode was pollutants being released from crop residue burning in the northern regions of Anhui, and then combining with favorable transport flows. Two zones with low visibility formed in eastern areas of Hubei, with the lowest value of daily average visibility being just 2.1 km. The pollutants released from crop residue burning influenced the air quality of Hubei from north to south, playing a major role in areas around Xiaogan, Wuhan, and Xianning, with peak values of PM2.5 concentration of more than 600 μg m^-3 in these three cities. The ratios of the mass concentrations of PM2.5 and PM10 increased to 0.76 and 0.77 in Wuhan and Xiaogan on 12 June 2014, and reached maximum values of 0.96 and 0.93, respectively. With the transmission of polluted air mass, the proportion of PM2.5 decreased significantly. The variations of mass concentration of SO₂ were negligible, while the mass concentration of NO₂ reached its maximum value 1-3 hours before the PM2.5 or PM10 reached their maximum values. CO was the main gas pollutant produced by crop residue burning, which was positively correlated with the concentrations of PM2.5 and PM10, with correlation coefficients of 0.66 and 0.67, respectively. By analyzing the wind using the Vector Sum Technique (VST), it was found that the air flow in central eastern areas of Hubei transported from the heavily polluted regions (northeast to Hubei Province) was significant. The transportation of pollutants was the main factor causing the occurrence of the haze event on 12 June, while the transportation was weakened markedly on 13 June. The small VST value of wind speed in the southeast of Hubei caused pollutants to accumulate, promoting the continuation of the haze event.