Influence of ship direct emission on HONO sources in channel environment.

Nitrous acid (HONO) is the primary source of hydroxyl radical (OH) during daytime and significantly contribute to the formation of secondary organic compounds (SOA) and atmospheric oxidizing capacity. One month simultaneous observations at ship channel site (SCS) and background site (BGS) in Shanghai, China were conducted to aim at estimating the HONO concentration from ship direct emission and analyzing the nocturnal budget of HONO during non-clean period in SCS. The HONO average concentrations at both BGS and SCS during non-clean period were 0.37 ± 0.42 ppbv and 0.91 ± 0.78 ppbv, respectively. The diurnal variation of HONO from ship direct emission presented a double-peak trend with a maximum value 0.38 ± 0.18 ppbv at 07:00 in the morning. The proportion of HONO emission from ships was in a range of 43%~74% in the daytime, while, the proportions were 42%~63% and 14%~28% at night in clean and non-clean periods, respectively. HONO nocturnal conversion frequencies from NO 2 were 0.29%/h at both sites in non-clean period, during which the deposition velocities of HONO were 0.21–1.4 cm/s and 0.34–1.4 cm/s at BGS and SCS, respectively. • HONO emission from ships is identified and measured by long-path DOAS. • Difficult-calculate and unknown HONO source substituted by background site observation. • Proportion of ship direct HONO emission was estimated on different cases. • The NO 2 -to-HONO conversion frequencies on ship channel site and background site were equal. [ABSTRACT FROM AUTHOR]