The Correlation Analyze Of NO₂,SO₂ And AOD In China From Satellite

Recently, haze happens more and more frequently in China. Secondary aerosol contributes significantly to pariculate air pollution in China which has become an increasely serious threat to the public health and the economic development. Nitrogen Dioxide （NO₂） and Sulfur Dioxide （SO₂） are two of the most important precursors to secondary inorganic aerosol. To study the relations between atmospheric aerosol and NO₂ and SO₂ is helpful to reveal the source and the formation mechanism of PM2.5 （particulate matter with an aerodynamic diameter less than 2.5 μm） in China.In this study, spatial and temporal correlations among NO₂, SO₂ and aerosol optical depth （AOD） in Central and Eastern China were investigated using combined satellite observations from NASA "A-train" constellation, including aerosol optical depth （AOD） from the Moderate Resolution Imaging Spectroradiometer （MODIS） on board Aqua and Terra satellite and troposphere column integrated Nitrogen Dioxide （NO₂）, Sulfur Dioxide （SO₂） from the Ozone Monitoring Instrument （OMI） on board Aura satellite from 2005 to 2014.This study contains 2 main parts, event studies （Oct 2013 to Nov 2013） and long-term statistics（10years from Jan 2005 to Dec 2014）.First, the mean spatial distribution of AOD, NO₂ and SO₂ is calculated. And the correlation of AOD and NO₂ and AOD and SO₂ is analyzed. In both event studies and long-term statistics significant positive spatial correlations were found between AOD and NO₂, and between AOD and SO₂ in all studying areas in China. This means NO₂ and SO₂ can affect the aerosol by forming secondary aerosol. Unlike the spatial correlations, the daily temporal correlations among AOD, SO₂ and NO₂, however, are not significant in general. Heavy haze days with great AOD are not accompanied by high SO₂ and NO₂ necessarily. In given areas, the day-to-day variations of AOD are more affected by the meteorology condition rather than the concentration of SO₂ and NO₂.Second, the slopes of linear regression of AOD as a function of SO₂ and the slope of NO₂ is analyzed. However, the effects of NO₂ and SO₂ on AOD do not share even importance in urban areas and rural areas. In giant cities and their surrounding areas, such as Beijing-Tianjin-Hebei, Jiangsu-Zhejiang-Shanghai and Guangdong area, the slopes of linear regression of AOD as a function of SO₂ （hereafter the slopes） are close to the slopes of AOD/NO₂. It indicates the contributions from sulfate aerosol and nitrate aerosol to the total AOD are comparable in these areas. In the contrast, in Heilongjiang-Jilin-Liaoning, Shanxi-Shandong-Henan, and Sichuan-Chongqing-Guizhou area, the slopes of AOD/SO₂ are smaller than the slopes of AOD/NO₂. This shows that sulfate aerosol still dominates the total aerosol in the relatively more rural areas in China. Satellite observational studies imply that the chemical composition of particulate air pollution in China may be distinct between cities and rural areas.Then, the seasonal variation of the slopes of of linear regression of AOD/NO₂ and AOD/SO₂ is studied. Significant seasonal variations were also found in the correlation coefficients and the slopes of AOD/NO₂ and AOD/SO₂ in all studying areas. Generally, the slopes peaked in summer and minimized in winter. Such seasonal variations are more evident in Northern China, probably due to the increased combustion of fossil fuel for heating in winter. In contrast, the correlations and slopes in Southern China show relatively smaller seasonal variations. No significant inter-annual trend of those slopes were found during the 10-year period and this indicates the relative contributions of SO₂ and NO₂ to the total aerosol are stable. The only exception is a weak increase of the slope of AOD/NO₂ in Sichuan-Chongqing-Guizhou area, which implies the NO₂-induced aerosol may have increased in recent years.What’s more, annual variation tendency of NO₂ and SO₂ in each point is under research in China. NO₂ in most areas in our country increases except Guangzhou and Taiwan. While SO₂ decreases in most places.At last, probability distribution function of AOD to NO₂ and SO₂ is studied with different meteorological condition and seasons.As a satellite observational study, the results provide direct information on the source and the formation mechanism of air pollution in China at large spatial scale and in long-term durations. The associated explanations and hypotheses require further proofing from modeling and laboratory studies. In addition, the results help to fill the gap in doing studies with ground-based measurements and can provide reference to evaluate the atmospheric chemistry and to transport modeling results.