| Summary: | Seven scenarios were designed to study the national environmental benefits of ULE in coal-fired power plants (CPPs), ULE in industrial coal burning (ICB) and NH<sub>3</sub> emission reduction by using the GEOS-Chem model. The results showed that although the CPPs have achieved the ULE transformation target, the PM<sub>2.5</sub> concentration across the country has decreased by 4.8% (1.4 μg/m<sup>3</sup>). Due to the complex non-linear chemical competition mechanism among nitrate and sulfate, the average concentration of nitrate in the country has increased by 1.5% (0.1 μg/m<sup>3</sup>), which has reduced the environmental benefits of the power plant emission reduction. If the ULE technology is applied to the ICB to further reduce NO<sub>x</sub> and SO<sub>2</sub>, although the PM<sub>2.5</sub> concentration can be reduced by 10.1% (2.9 μg/m<sup>3</sup>), the concentration of nitrate will increase by 2.7% (0.2 μg/m<sup>3</sup>). Based on the CPPs-ULE, NH<sub>3</sub> emissions reduced by 30% and 50% can significantly reduce the concentration of ammonium and nitrate, so that the PM<sub>2.5</sub> concentration is decreased by 11.5% (3.3 μg/m<sup>3</sup>) and 16.5% (4.7 μg/m<sup>3</sup>). Similarly, based on the CPPs-ICB-ULE, NH<sub>3</sub> emissions can be reduced by 30% and 50% and the PM<sub>2.5</sub> concentration reduced by 15.6% (4.4 μg/m<sup>3</sup>) and 20.3% (5.8 μg/m<sup>3</sup>). The CPPs and ICB use the ULE technology to reduce NO<sub>x</sub> and SO<sub>2</sub>, thereby reducing the concentration of ammonium and sulfate, causing the PM<sub>2.5</sub> concentration to decline, and NH<sub>3</sub> reduction is mainly achieved through reducing the concentration of ammonium and nitrate to reduce the concentration of PM<sub>2.5</sub>. In order to better reduce the concentration of PM<sub>2.5</sub>, NO<sub>x</sub>, SO<sub>2</sub> and NH<sub>3</sub> emission reduction control measures should be comprehensively considered in different regions of China. By comprehensively considering the economic cost and environmental benefits of ULE in ICB and NH<sub>3</sub> emission reduction, an optimal haze control scheme can be determined.
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