The Levels and Sources of Nitrous Acid (HONO) in Winter of Beijing and Sanmenxia

Abstract

AbstractHONO concentrations in Beijing (BJ) and Sanmenxia (SMX) were simultaneously measured in winter with a duration of 1 month, and the sources and sinks of HONO in the two cities were comparably analyzed. BJ and SMX had different pollution characteristics. Direct vehicle emission made a contribution to observed HONO of about 28% in BJ, whereas it contributed to HONO only about 12% in SMX. Additionally, direct emission from coal combustion in SMX also made a significant contribution to atmospheric HONO, which could achieve to be 13%. In BJ, nighttime NO2 conversion on the aerosol and ground surfaces contributed to HONO sources of 15% and 27%, respectively. In SMX, nighttime NO2 conversion on the aerosol and ground surfaces contributed to HONO sources of 40% and 30%, respectively. Daytime NO2 heterogeneous conversion (including photo‐enhanced conversion) on the aerosol and ground surfaces was important in SMX. Daytime NO3− photolysis contributed 9% HONO in SMX and 4% in BJ. The primary OH production rates from photolysis of daytime HONO in both BJ and SMX were three orders of magnitude faster than those from photolysis of O3, revealing the dominant role of HONO in local atmospheric chemistry of the two cities in winter.