Significantly mitigating PM pollution level via reduction of NO emission during wintertime.

Despite considerable decreases in fine particulate matter (PM) in Chinese megacities over the past decade, many second- and third-tier cities that distribute abundant industrial enterprises are still facing great challenges for PM further reduction under the recent policy background of eliminating heavily-polluted weather. In view of core effects of NO on PM, the deeper reductions of NO in these cities are expected to break the plateau of PM decline, however, the link between NO emission and PM mass loading is currently lacking. Herein, we progressively construct an evaluation system for PM productions based on daily NO emissions in a typical industrial city (Jiyuan), considering a sequence of nested parameters involving evolutions of NO into nitric acid and then nitrate, and contributions of nitrate to PM. The evaluation system was subsequently validated to better reproduce real increasing processes for PM pollution based on 19 pollution cases, with root mean square errors of 19.2 ± 16.4 %, suggesting the feasibility of developing NO emission indicators linked to goals of mitigating atmospheric PM. Additionally, further comparative results reveal that currently high NO emissions in this industrial city severely hinder the achievement of atmospheric PM environmental capacity targets, especially in the scenarios of high initial PM level, low planetary boundary layer height and long pollution duration. It is anticipated that these methodologies and findings would supply guidelines for further regional PM mitigation, in which source-oriented NO indicators could also provide some orientations for industrial cleaner production such as denitrification and low nitrogen combustion.