Spatio-temporal variations in SO2 and NO2 emissions caused by heating over the Beijing-Tianjin-Hebei Region constrained by an adaptive nudging method with OMI data.

The Beijing-Tianjin-Hebei (BTH) region in China suffers from heavy air pollution, especially in heating period. SO2 and NO2 are two of the key primary gaseous pollutants emitted by coal burning. The increase in air pollution caused by heating in the south-central part of the BTH region is higher than that in the northern part. And the distribution of SO2 and NO2 increment has significant differences. In this work, SO2 and NO2 emissions over the BTH region are determined using an adaptive "nudging" constrained method and a variational processing technique based on Ozone Monitoring Instrument (OMI) satellite data and surface measurement data collected in 2015. The application of the method can provide reliable, up-to-date and high-resolution mapping of sources of SO2 and NO2 emissions. These SO2 and NO2 emissions reflect the spatial differences in point and area sources in urban agglomerations and rural areas under different meteorological conditions during the non-heating and heating seasons. The intensity and influence of SO2 and NO2 emissions, particularly those of SO2, are significantly greater during the heating season than those during the non-heating season. Winter increases in SO2 emissions in the northern areas of the BTH region are larger than those in the southern part. In addition, significant increases in SO2 emissions occur mainly in suburban and rural areas, while those of NO2 emissions mainly occur in urban agglomerations. In the major urban areas, where coal has been replaced by natural gas or electric power for heating, winter heating causes much smaller increases in SO2 emissions than in other areas. The large amounts of bulk coal consumption in the suburban and rural areas could cause significant regional air pollution. Clear increases in SO2 and NO2 emissions in winter occur along a belt from southern Beijing to Langfang, Baoding, Shijiazhuang and Xingtai, which is consistent with a special "quasi-steady" air pollutant transport belt in the region. All above results show that the adaptive "nudging" constrained emission method could be an effective tool for air pollution control during certain seasons.