Different Response Mechanisms of N‐Bearing Components to Emission Reduction Across China During COVID‐19 Lockdown Period

Abstract

AbstractThe response characteristics of secondary inorganic aerosols to COVID‐19 lockdown measures have been extensively reported, while spatial disparities of these response characteristics across China and key deriving mechanisms still remained poorly understood. In our study, a chemical transport model (GEOS‐Chem) was applied to simulate the national concentrations of four N‐bearing components during lockdown periods in 2020 and business‐as‐usual (BAU) period (the same period in 2019). Three distinct regional response mechanisms were distinguished across China. The increases of levels in the northern part of Beijing‐Tianjin‐Hebei (BTH) might be attributable to increased relative humidity (RH) and abundant ammonia (NH3) level (13.5 μg/m3). The dramatic decreases of secondary inorganic nitrogen in Southeast China were contributed by substantial emission reduction (−15.3%) and slightly favorable (pollutant removal) meteorological conditions (−4.36%). The consistent increases of levels, but decreased NH3 levels in tropical regions suggested extremely high RH (84%) and enhanced atmospheric oxidation capacity were dominant factors. The response mechanisms of secondary N‐bearing components showed the distinct characteristics between urban and rural regions, which might be closely associated with variations of emission reduction and meteorology during the COVID‐19 period. The natural experiment demonstrates priority control of NH3 emission might be the primary target for BTH, while the coordinated controls of VOCs and NOx emissions should be exerted in Southeast China especially the tropical regions.