Abstract
Intensive agricultural activities in the North China Plain (NCP) lead to substantial emissions of nitrogen oxides (NOx) from soil, while the role of this source on local severe ozone pollution is unknown. Here we use a mechanistic parameterization of soil NOx emissions combined with two atmospheric chemistry models to investigate the issue. We find that the presence of soil NOx emissions in the NCP significantly reduces the sensitivity of ozone to anthropogenic emissions. The maximum ozone air quality improvements in July 2017, as can be achieved by controlling all domestic anthropogenic emissions of air pollutants, decrease by 30% due to the presence of soil NOx. This effect causes an emission control penalty such that large additional emission reductions are required to achieve ozone regulation targets. As NOx emissions from fuel combustion are being controlled, the soil emission penalty would become increasingly prominent and shall be considered in emission control strategies.
Highlights
Intensive agricultural activities in the North China Plain (NCP) lead to substantial emissions of nitrogen oxides (NOx) from soil, while the role of this source on local severe ozone pollution is unknown
Despite the fact that the Chinese Action Plan on Air Pollution Prevention and Control implemented in 2013 has significantly reduced the nationwide anthropogenic emissions of primary pollutants including particulate matter (PM) and nitrogen oxides (NOx = NO + NO2)[6,7], summertime ozone pollution, measured as daily 8 h average maximum (MDA8) has been increasing at over 3 ppbv year−1 in the NCP over 2013–2019, among the fastest urban ozone trends in the recent decade reported in the Tropospheric Ozone Assessment Report (TOAR)[8,9,10]
We demonstrate that the presence of soil NOx emissions in the NCP that largely driven by fertilizer application, significantly reduces the sensitivity of surface ozone to anthropogenic NOx emissions, degrades the effectiveness of anthropogenic emissions control measures on surface ozone regulation, and serves as a penalty requiring extra anthropogenic emission reduction
Summary
Intensive agricultural activities in the North China Plain (NCP) lead to substantial emissions of nitrogen oxides (NOx) from soil, while the role of this source on local severe ozone pollution is unknown. Emissions are consistent with the observations with mean differences less than 5%, but if soil NOx emissions are excluded model results would be biased low by 15–20% (P < 0.01) in areas with low anthropogenic/soil emission ratios (Supplementary Fig. 1c), and by 12–14% (P < 0.01) for all the NCP areas.
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