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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]

The lifetime and concentration of nitrogen oxides (NOx) are susceptible to non-linear production and loss, and con- sequently to the resolution of a chemical transport model (CTM). Here we use the GEOS-Chem CTM in its high performance implementation (GCHP) to investigate NOx simulations over the eastern United States across a wide range of resolutions (13–181 km). Following increasing grid size, daytime surface NOx concentrations over July 2015 generally decrease over the Great Lakes (GL) region and increase over the Southern States (SS), yielding regional biases (181 km vs. 13 km) of −18 % to 9 %; meanwhile hydrogen oxide radicals (HOx) increase over both regions, consistent with their different chemical regimes. Night- time titration of ozone by surface nitric oxide (NO) was found to be more efficient at coarser resolutions, leading to longer NOx lifetimes and higher surface concentrations of nitrogen dioxide (NO2) over the GL in January 2015. The tropospheric NO2 column density at typical afternoon satellite overpass time has spatially more coherent negative biases (e.g., −10 % over the GL) at coarser resolutions in July, which reversed the positive biases of surface NOx over the SS. The reduced NO2 aloft (> 1 km altitude) at coarser resolutions was attributable to the enhanced HOx that intrudes into the upper troposphere. Application of coarse resolution simulations for interpreting satellite NO2 columns will generally underestimate surface NO2 over the GL and overestimate surface NO2 over the SS in summer, while uniformly overestimating NOx emissions over both regions. This study significantly broadens understanding of factors contributing to NOx resolution effects, and the role of fine resolution to accurately simulate and interpret NOx 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]

High-resolution (e.g., 5 km) emission data of nitrogen oxides (NO x = NO + NO 2 ) provide localized knowledge of pollution sources for targeted regulations, yet such data are lacking or inaccurate over most regions at present. Here we improve our PHLET-based inversion method to derive NO x emissions in China at a 5-km resolution in summer 2019, based on the TROPOMI-POMINO satellite product of nitrogen dioxide (NO 2 ) columns. With low computational costs, our inversion explicitly accounts for the effects of horizontal transport and nonlinear chemistry. We find numerous small-to-medium sources related to minor roads and small human settlements at relatively low affluence levels, in addition to clear emission signals along major transportation lines, consistent with road line density and Tencent location data. Many small-to-medium sources and transportation emissions are unclear or missing in the spatial distributions of four widely used emission inventories. Our emissions offer a unique reference for targeted emission control.

Atmospheric transport of fine particulate matter (PM 2.5 ), the leading environmental risk factor for public health, is estimated to exert substantial transboundary effects at present. During the past several decades, human-produced pollutant emissions have undergone drastic and regionally distinctive changes, yet it remains unclear about the resulting global transboundary health impacts. Here we show that between 1950 and 2014, global anthropogenic PM 2.5 has led to 185.7 million premature deaths cumulatively, including about 14% from transboundary pollution. Among four country groups at different affluence levels, on a basis of per capita contribution to transboundary mortality, a richer region tends to exert severer cumulative health externality, with the poorest bearing the worst net externality after contrasting import and export of pollution mortality. The temporal changes in transboundary mortality and cross-regional inequality are substantial. Effort to reduce PM 2.5 -related transboundary mortality should seek international collaborative strategies that account for historical responsibility and inequality., Competing Interests: Conflict of interest The authors declare that they have no conflict of interest., (Copyright © 2021 Science China Press. Published by Elsevier B.V. All rights reserved.)