Investigations on HONO formation from photolysis of adsorbed HNO₃on quartz glass surfaces

Abstract

During the last few decades, nitrous acid (HONO) has attracted significant attention as a major source of the OH radical, the detergent of the atmosphere. However, the different daytime sources identified in the laboratory are still the subject of controversial discussion. In the present study, one of these postulated HONO sources, the heterogeneous photolysis of nitric acid (HNO3), was studied on quartz glass surfaces in a photo flow-reactor under atmospherically relevant conditions. In contrast to other investigations, a very low HNO3 photolysis frequency for HONO formation of J(HNO3→ HONO) = 2.4 × 10(-7) s(-1) (0° SZA, 50% r.h.) was determined. If these results can be translated to atmospheric surfaces, HNO3 photolysis cannot explain the significant HONO levels in the daytime atmosphere. In addition, it is demonstrated that even the small measured yields of HONO did not result from the direct photolysis of HNO3 but rather from the consecutive heterogeneous conversion of the primary photolysis product NO2 on the humid surfaces. The secondary NO2 conversion was not photo-enhanced on pure quartz glass surfaces in good agreement with former studies. A photolysis frequency for the primary reaction product NO2 of J(HNO3→ NO2) = 1.1 × 10(-6) s(-1) has been calculated (0° SZA, 50% r.h.), which indicates that renoxification by photolysis of adsorbed HNO3 on non-reactive surfaces is also a minor process in the atmosphere.

Light-induced protein nitration and degradation with HONO emission

“…Even when small amounts of HNO 3 would be formed by unknown heterogeneous reactions, photolysis of HNO 3 is only significant at wavelengths < 350 nm, which is close to the lowest limit of the UV wavelength applied in this study. Likewise, the respective photolysis frequency recently proposed by Laufs and Kleffmann (2016) of about 2.4 × 10 −7 s −1 is very low. Integrating the 20 h experiments, 9.23 × 10 15 (4.6 ppb h, VISa), 1.53 × 10 16 (7.7 ppb h, VISb) and 4.01 × 10…”

“…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).…”

Reply to the ‘Comment on “Investigations on HONO formation from photolysis of adsorbed HNO3 on quartz glass surfaces”’ by M. N. Sullivan, L. T. Chu and L. Zhu, Phys. Chem. Chem. Phys., 2018, 20, DOI: 10.1039/C8CP04497J

“…Since the spectral actinic flux was also quantified in our study by a calibrated spectroradiometer, we used the absorption cross sections of adsorbed HNO 3 published by the group of L. Zhu 2,3 to calculate an average quantum yield of adsorbed HNO 3 for NO 2 formation of f(HNO 3 -NO 2 ) = (3.4 AE 2.6) Â 10 À4 , see eqn (4). 1 This value is orders of magnitude lower compared to the studies of Zhu et al 4 and Abida et al 5 and the present comment by Sullivan et al 6 In these studies, quantum yields near unity were observed in excimer laser photolysis experiments at 308 and 351 nm, which cover the same spectral range as we used in our study. If both quantities are applied, the photolytic lifetime of HNO 3 adsorbed on silica surfaces would be only B5 min for atmospheric spectral actinic fluxes (01 SZA), which is highly unlikely.…”

Diurnal fluxes of HONO above a crop rotation

“…These results stimulated laboratory investigations on potential HONO precursors from which the most frequently discussed mechanisms are (i) the photosensitized reduction of nitrogen dioxide (NO 2 ) by organic material, e.g. humic acids (George et al, 2005;Stemmler et al, 2006;2007, Sosedova et al, 2011Han et al, 2016), (ii) the photolysis of adsorbed nitric acid (Zhou et al, , 2011Laufs and Kleffmann, 2016), (iii) biogenic production of nitrite in soil (Su et al, 2011;Ostwald et al, 2013;Maljanen et al, 2013;Oswald et al, 2015;Scharko et al, 2015;Weber, 2015) and (iv) release of adsorbed HONO from soil surfaces after deposition of strong acids (VandenBoer et al, 2013(VandenBoer et al, , 2014(VandenBoer et al, , 2015Donaldson et al, 2014). Another discussed source, the reaction of excited gaseous NO 2 with water (Li et al, 2008), is of minor importance as demonstrated by laboratory (Crowley and Carl, 1997;Carr et al, 2009;Amedro et al, 2011) and modelling studies (Sörgel et al, 2011b;Czader et al, 2012).…”