Large conversion rates of NO₂ to HNO₂ observed in air masses from the South China Sea: Evidence of strong production at sea surface?

Abstract

Nitrous acid (HONO) plays important roles in tropospheric chemistry, but its source(s) are not completely understood. Here we analyze measurements of HONO, nitrogen dioxide (NO 2 ), and related parameters at a coastal site in Hong Kong during September-December 2012. The nocturnal NO 2 -to-HONO conversion rates were estimated in air masses passing over land and sea surfaces. The conversion rates in the "sea cases" (3.17-3.36 × 10 À2 h À1 ) were significantly higher than those in the "land cases" in our study(1.20-1.30 × 10 À2 h À1) and in previous studies by others. These results suggest that air-sea interactions may be a significant source of atmospheric HONO and need to be considered in chemical transport models.

Nitrous acid (HONO) in a polluted subtropical atmosphere: Seasonal variability, direct vehicle emissions and heterogeneous production at ground surface

“…The black arrow represents a period in which the data were used to calculate the heterogeneous conversion rate of the NO 2 . obtained in a semi-rural area in Germany (Kleffmann et al (2003), but lower than the values at most other sites, including those in the PRD region: Xinken (Su et al, 2008a), Back Garden (Li et al, 2012), and Hok Tsui (a coastal background site in Hong Kong) (Zha et al, 2014). The low C HONO in TC might have been related to the large area of forest near the site.…”

“…A recent study at a coastal site in Hong Kong reported a large rate of 3.3 Â 10 À2 h À1 in air traveling over the oceans (Zha et al, 2014).…”

Potential sources of nitrous acid (HONO) and their impacts on ozone: A WRF‐Chem study in a polluted subtropical region

“…Zha et al . [] recently reported a NO 2 ‐to‐HONO conversion rate of 3.17–3.36 × 10 −2 h −1 in air masses passing over sea surfaces, which is almost 3 times the rate over land surfaces (1.20–1.30 × 10 −2 h −1 ), at a clean coastal site in Hong Kong. Although the exact mechanism is not yet clear, formation of HONO on the ocean surface could be a nonnegligible contributor to atmospheric HONO in areas adjacent to the ocean such as Hong Kong.…”

“…The most commonly accepted new HONO source is the heterogeneous conversion from NO 2 to HONO on humid ground and particle surfaces, but whether the conversion mainly occurs on ground surfaces or on aerosol surfaces remains a subject of debate [ Kleffmann , ]. A recent study observed faster conversions of NO 2 in air passing over the sea surface, suggesting that oceans may contribute to the production of HONO [ Zha et al , ]. Direct emission from vehicles has also been identified as a source of HONO, with a molar emission ratio of HONO to nitrogen oxide (NO x ) ranging from 10 −4 to 10 −2 [ Kurtenbach et al , ].…”

Combined impacts of nitrous acid and nitryl chloride on lower-tropospheric ozone: new module development in WRF-Chem and application to China

“…al., 2010). HONO can be heterogeneously formed via conversions of NO 2 (Reaction R1) on particle, land, and sea surfaces (Kleffmann, 2007;Zha et al, 2014), directly emitted by traffic and biological activities (Kurtenbach et al, 2001;Oswald et al, 2013), and formed via photolysis of nitric acid (Zhou et al, 2011). During the day, HONO is then photochemically converted into OH radicals and NO (Reaction R2), both of which have an impact on the oxidation capacity (Kleffmann, 2007).…”