Fig. 4: Influence of agricultural NOx emissions on the design of optimal reactive nitrogen emission control pathways over the North China Plain.
a, d The bar plots show the decline in population-weighted SIA concentrations (\(\Delta {PWC}\)) due to 20–80% reductions in emissions from agricultural NH3 (gray), agricultural Nr (NOx and NH3) (yellow), and combustion Nr emissions (red) (left axis). The blue (green) lines show the ratio of SIAs decrease due to reductions of agricultural Nr (NH3) and combustion Nr emissions (right axis). b, c, e, f Diagrams illustrating the effectiveness of controlling Nr emissions from agricultural and combustion sources in mitigating population SIA concentrations. The background color indicates the population-weighted SIA concentrations over NCP, and the red lines show the optimal emission reduction pathways. Panels (b, e) are based on estimates that include only agricultural NH3 emission reductions, while panels (c, f) include both NH3 and NOx emissions in agricultural emission reductions. The arrows indicate the relative magnitude of SIA reductions contributed by reductions in agricultural and combustion reactive nitrogen emissions. The top panels (a–c) use 2019 emissions, and the bottom panels (d–f) use emissions reduced to the 2040 level predicted by the SSP1-26 scenario.
