Abstract: In this paper, the MM5/CALPUFF model was used to simulation the coal combustion pollutants emission and their spatial distribution before and after the Urumqi "Coal to Gas" project. Two scenarios were set based on Urumqi local energy structure adjustment project:one is taking the heating enterprises as the only emission source in 2010 and 2014, and the other is taking the enterprises in which the coal consuming was more than 1 000 tons/year and all the heating enterprises as the emission sources in 2010 and 2014. Prediction of the environmental air quality was conducted during the heating period (October-March). The results show that, in situation one, the daily concentration of SO₂, NO_x, PM₁₀ and PM_2.5 fell by 92.44%, 97.52%, 90.56% and 88.80%, respectively, and the annual average concentration fell by 74.66%, 94.93%, 89.50% and 92.31% respectively. This indicates that after the project, the heating enterprise emissions concentration decreased obviously. In situation two, the daily concentration of SO₂ and NO_x fell by 66.85% and 91.53% respectively, and the annual average concentration fell by 73.89% and 81.03% respectively, the effect of PM_2.5 and PM₁₀ improved finitely. According to "Xinjiang environmental quality statement (2000、2014)", annual average concentration of SO₂, NO_x and PM₁₀ in 2010 fell by 71.9%, 16.41% and -9.77%, respectively, compared with those in 2010. The measured data of SO₂ and PM₁₀ agreed well with the prediction. The reduction of NO_x was offset because the number of motor vehicles in Urumqi increased quickly in recent years. The "coal to gas" project has made radical changes in the energy structure of large heating boiler, which improved the atmospheric environment in Urumqi to a certain extent. Atmospheric pollution has changed from coal burning to mixed automobile vehicle exhaust emission. The annual amount of pollution reduction average concentrations in different districts changed greatly due to the natural causes and adjustment of the city layout. The annual amount of pollution reduction increased successively from south area (Urumqi County and Dabancheng District), middle area (Saybagh District, Tianshan District, Shuimogou District and New Urban District and Toutunhe District)to north area (Midong District). Based on the numerical simulation of MM5 and CALPUFF models, different situation models were established to study the spatial changes of characteristic pollutants distributions before and after the "Coal to Gas" project in Urumqi for the first time. The research is of great practical significance for controlling and tackling the Urumqi pollution problem.

Key words: coal to gas project, air pollutant, CALPUFF, scenario prediction