Nitrous acid (HONO) and its daytime sources at a rural site during the 2004 PRIDE‐PRD experiment in China

Abstract

[1] High HONO level during daytime was observed at a rural site Xinken in southeastern China during the 2004 Program of Regional Integrated Experiments of Air Quality over Pear River Delta (PRIDE-PRD). The high HONO concentration led to a daytime (9:00-15:00) OH formation up to three times faster than that from O 3 photolysis. An unexplained daytime HONO source, approximately four times faster than the reaction of OH with NO, has been derived from the HONO budget estimation. According to current understanding, this unknown source was attributed to heterogeneous reactions of NO 2 on ground and aerosol surfaces. The good correlation between the unknown source and J values is consistent with the photolytic HONO source observed in laboratory studies.

Quantification of the unknown HONO daytime source and its relation to NO<sub>2</sub>

“…2) Thus, an additional (unknown) HONO daytime source exists. Equation (2), which is similar to that of Su et al (2008b), sums up the processes influencing HONO mixing ratios.…”

“…3.2.2). The magnitude of T v (without the contribution of the rising boundary layer in the morning) can be estimated by using a parameterization for dilution by background air provided by Dillon et al (2002) Su et al (2008b).…”

Light-induced protein nitration and degradation with HONO emission

“…Measured mixing ratios are typically about 1 order of magnitude higher than simulated ones, and an additional source of 200-800 ppt h −1 would be required to explain observed mixing ratios Acker et al, 2006;Li et al, 2012;Su et al, 2008;Elshorbany et al, 2012;Meusel et al, 2016), indicating that estimates of daytime HONO sources are still under debate. It was suggested that HONO arises from the photolysis of nitric acid and nitrate or by heterogeneous photochemistry of NO 2 on organic substrates and soot (Zhou et al, 2001(Zhou et al, , 2002(Zhou et al, and 2003Villena et al, 2011;Ramazan et al, 2004;George et al, 2005;Sosedova et al, 2011;Monge et al, 2010;Han et al, 2016).…”

“…It was suggested that HONO arises from the photolysis of nitric acid and nitrate or by heterogeneous photochemistry of NO 2 on organic substrates and soot (Zhou et al, 2001(Zhou et al, , 2002(Zhou et al, and 2003Villena et al, 2011;Ramazan et al, 2004;George et al, 2005;Sosedova et al, 2011;Monge et al, 2010;Han et al, 2016). Stemmler et al (2006Stemmler et al ( , 2007 found HONO formation on light-activated humic acid, and field studies showed that HONO formation correlates with aerosol surface area, NO 2 and solar radiation (Su et al, 2008;Reisinger, 2000;Costabile et al, 2010;Wong et al, 2012;Sörgel et al, 2015) and is increased during foggy periods (Notholt et al, 1992). Another proposed source of HONO is the soil, where it has been found to be co-emitted with NO by soil biological activities (Oswald et al, 2013;Su et al, 2011;Weber et al, 2015).…”

“…HONO is of great interest for atmospheric composition, as its photolysis forms OH radicals, which are the key oxidant for degradation of most air pollutants in the troposphere (Levy, 1971). In the lower atmosphere, up to 30 % of the primary OH radical production can be attributed to photolysis of HONO, especially during the early morning when other photochemical OH sources are still small (Reaction R1, Kleffmann et al, 2005;Alicke et al, 2002;Ren et al, 2006;Su et al, 2008;Meusel et al, 2016).…”