Effect of Different Combustion Processes on Atmospheric NitrousAcid Formation Mechanisms: A Winter Comparative Observation inUrban, Suburban and Rural Areas of the North China Plain

:atmospheric nitrous acid (HONO) is a dominantprecursor of hydroxyl (OH) radicals, and its formation mechanismsare still controversial. Few studies have simultaneously explored effects ofdifferent combustion processes on HONO sources. Hereby, synchro-nous HONO measurement in urban (BJ), suburban (XH) and rural(DBT) areas with different combustion processes is performed in theNorth China Plain in winter. A box model is utilized to analyze HONOformation mechanisms. HONO concentration is the highest at the DBTsite (2.51 +/- 1.90 ppb), followed by the XH (2.18 +/- 1.95 ppb) and BJ(1.17 +/- 1.20 ppb) sites. Vehicle exhaust and coal combustionsignificantly contribute to nocturnal HONO at urban and rural sites, respectively. During a stagnant pollution period, the NO+OH reaction and combustion emissions are more crucial to HONO in urban and rural areas; meanwhile, the heterogeneousreaction of NO2is more significant in suburban areas. Moreover, the production rate of OH from HONO photolysis is about 2orders of magnitude higher than that from ozone photolysis. Consequently, vehicle exhaust and coal combustion can effectively emitHONO, further causing environmental pollution and health risks. It is necessary to expand the implementation of the clean energytransition policy in China, especially in areas with substantial coal combustion.