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The lifetime and concentration of nitrogen oxides (NO x) are susceptible to nonlinear production and loss and to the resolution of a chemical transport model (CTM). This is due to the strong spatial gradients of NO x and the dependence of its own chemical loss on such gradients. In this study, we use the GEOS-Chem CTM in its high-performance implementation (GCHP) to investigate NO x simulations over the eastern United States across a wide range of spatial model resolutions (six different horizontal grids from 13 to 181 km). Following increasing grid size, afternoon surface NO x mixing ratios over July 2015 generally decrease over the Great Lakes region (GL) and increase over the southern states of the US region (SS), yielding regional differences (181 km vs. 13 km) of -16 % (in the GL) to 7 % (in the SS); meanwhile, hydrogen oxide radicals (HO x) increase over both regions, consistent with their different chemical regimes (i.e., NO x -saturated in the GL and NO x -limited in the SS). Nighttime titration of ozone by surface nitric oxide (NO) was found to be more efficient at coarser resolutions, leading to longer NO x lifetimes and higher surface mixing ratios of nitrogen dioxide (NO 2) over the GL in January 2015. The tropospheric NO 2 column density at typical afternoon satellite overpass time has spatially more coherent negative biases (e.g., -8 % over the GL) at coarser resolutions in July, which reversed the positive biases of surface NO x over the SS. The reduced NO x aloft (>1 km altitude) at coarser resolutions was attributable to the enhanced HO x that intrudes into the upper troposphere. Application of coarse-resolution simulations for interpreting satellite NO 2 columns will generally underestimate surface NO 2 over the GL and overestimate surface NO 2 over the SS in summer, but it will uniformly overestimate NO x emissions over both regions. This study significantly broadens understanding of factors contributing to NO x resolution effects and the role of fine-resolution data in accurately simulating and interpreting NO x and its relevance to air quality. [ABSTRACT FROM AUTHOR]

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 NH3 emission reduction by using the GEOS-Chem model. The results showed that although the CPPs have achieved the ULE transformation target, the PM2.5 concentration across the country has decreased by 4.8% (1.4 μg/m3). 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/m3), which has reduced the environmental benefits of the power plant emission reduction. If the ULE technology is applied to the ICB to further reduce NOx and SO2, although the PM2.5 concentration can be reduced by 10.1% (2.9 μg/m3), the concentration of nitrate will increase by 2.7% (0.2 μg/m3). Based on the CPPs-ULE, NH3 emissions reduced by 30% and 50% can significantly reduce the concentration of ammonium and nitrate, so that the PM2.5 concentration is decreased by 11.5% (3.3 μg/m3) and 16.5% (4.7 μg/m3). Similarly, based on the CPPs-ICB-ULE, NH3 emissions can be reduced by 30% and 50% and the PM2.5 concentration reduced by 15.6% (4.4 μg/m3) and 20.3% (5.8 μg/m3). The CPPs and ICB use the ULE technology to reduce NOx and SO2, thereby reducing the concentration of ammonium and sulfate, causing the PM2.5 concentration to decline, and NH3 reduction is mainly achieved through reducing the concentration of ammonium and nitrate to reduce the concentration of PM2.5. In order to better reduce the concentration of PM2.5, NOx, SO2 and NH3 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 NH3 emission reduction, an optimal haze control scheme can be determined. [ABSTRACT FROM AUTHOR]