Sensitivity of PM_2.5 to NO_X emissions and meteorology in North China based on observations

摘要

This study examines the sensitivity of daily PM_(2.5) to NO_X emissions and meteorology using in situ observations from main cities of North China (NC). NC cities are divided into low-, medium-, and high-emission groups by the ranking of their 4-year mean NO_2. For each emission group, daily NO_2 levels are used to divide the days into good-, medium-, and bad-meteorological conditions. Regardless of their emission levels, all cities reveal significant decreases (96%-172%) in daily PM_(2.5) levels from bad to good meteorological conditions. The largest difference in PM_(2.5) concentrations between the emissions groups is found under bad meteorological conditions, with 56% higher PM_(2.5) in high-emission cities than low-emission cities, indicating PM_(2.5) under bad meteorological conditions has the largest sensitivity to emissions. The high-emission, bad-meteorology group saw a 24% decrease in mean daily PM_(2.5) levels from 2017, a high-emission year, to 2019, a low-emission year. However, under good meteorological conditions, the high-emissions group shows an increase of 8.8 μg/m~3 in mean daily PM_(2.5) from 2017 to 2019 with a 2.6% increase in the possibility of high PM_(2.5). These results suggest the current emission reduction measures are more effective in controlling PM_(2.5) in high-emission cities under bad meteorological conditions than under other meteorological conditions.