Trends and Source Contribution Characteristics of SO₂, NO_X, PM₁₀ and PM_2.5 Emissions in Sichuan Province from 2013 to 2017

As one of the most populated regions in China, Sichuan province had been suffering from deteriorated air quality due to the dramatic growth of economy and vehicles in recent years. To deal with the increasingly serious air quality problem, Sichuan government agencies had made great efforts to formulate various control measures and policies during the past decade. In order to better understand the emission control progress in recent years and to guide further control policy formulation, the emission trends and source contribution characteristics of SO₂, NO_X, PM₁₀ and PM_2.5 from 2013 to 2017 were characterized by using emission factor approach in this study. The results indicated that SO₂ emission decreased rapidly during 2013–2017 with total emission decreased by 52%. NO_X emission decreased during 2013–2015 but started to increase slightly afterward. PM₁₀ and PM_2.5 emissions went down consistently during the study period, decreased by 26% and 25%, respectively. In summary, the contribution of power plants kept decreasing, while contribution of industrial combustion remained steady in the past 5 years. The contribution of industrial processes increased for SO₂ emission, and decreased slightly for NO_X, PM₁₀ and PM_2.5 emissions. The on-road mobile sources were the largest emission contributor for NO_X, accounting for about 32–40%, and its contribution increased during 2013–2015 and then decreased. It was worth mentioning that nonroad mobile sources and natural gas fired boilers were becoming important NO_X contributors in Sichuan. Fugitive dust were the key emission sources for PM₁₀ and PM_2.5, and the contribution kept increasing in the study period. Comparison results with other inventories, satellite data and ground observations indicated that emission trends developed in this research were relatively credible.