Light induced conversion of nitrogen dioxide into nitrous acid on submicron humic acid aerosol

Abstract

Abstract. The interactions of aerosols consisting of humic acids with gaseous nitrogen dioxide (NO 2 ) were investigated under different light conditions in aerosol flow tube experiments at ambient pressure and temperature. The results show that NO 2 is converted on the humic acid aerosol into nitrous acid (HONO), which is released from the aerosol and can be detected in the gas phase at the reactor exit. The formation of HONO on the humic acid aerosol is strongly activated by light: In the dark, the HONO-formation was below the detection limit, but it was increasing with the intensity of the irradiation with visible light. Under simulated atmospheric conditions with respect to the actinic flux, relative humidity and NO 2 -concentration, reactive uptake coefficients γ rxn for the NO 2 →HONO conversion on the aerosol between γ rxn <10 −7 (in the dark) and γ rxn =6×10 −6 were observed. The observed uptake coefficients decreased with increasing NO 2 -concentration in the range from 2.7 to 280 ppb and were dependent on the relative humidity (RH) with slightly reduced values at low humidity (<20% RH) and high humidity (>60% RH). The measured uptake coefficients for the NO 2 →HONO conversion are too low to explain the HONOformation rates observed near the ground in rural and urban environments by the conversion of NO 2 →HONO on organic aerosol surfaces, even if one would assume that all aerosols consist of humic acid only. It is concluded that the processes leading to HONO formation on the Earth surface will have a much larger impact on the HONO-formation in the lowermost layer of the troposphere than humic materials potentially occurring in airborne particles.

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends

“…Other aspects of chemistry that are often omitted include the full range of peroxy radical cross reactions (incomplete in even the MCM; Saunders et al, 2003); peroxy radical recycling from isoprene oxidation (e.g., Crounse et al, 2011;Peters et al, 2014), which some studies indicate can affect OH levels and VOC lifetimes over low-NO x forested areas (Archibald et al, 2010b(Archibald et al, , 2011Taraborrelli et al, 2012); nitryl chloride (ClNO 2 ), which has been found to be important in oxidative chemistry, particularly in coastal regions (e.g., Osthoff et al, 2008); and nitrous acid (HONO) formation other than from NO + OH (+M), including from other gas phase sources (Bejan et al, 2007: Li et al, 2008Li et al, 2014), bacteria (Oswald et al, 2013), aerosol reactions (Ammann et al, 1998Stemmler et al, 2007) and heterogeneous processes (Zhou et al, 2001;Stemmler et al, 2006;Su et al, 2011;Mao et al, 2013). In general, heterogeneous processes (Ravishankara, 1997;Jacob, 2000) are simulated in most models, although typically only for a few species (e.g., heterogeneous formation of N 2 O 5 and loss of HO 2 ) and with substantial variation in uptake coefficients, which can have notable effects on modeled abundances and chemical budgets (e.g., Evans and Jacob, 2005;Macintyre and Evans, 2010).…”

Conversion of gaseous nitrogen dioxide to nitrate and nitrite on aqueous surfactants

“…It can be shown that under typical conditions the photochemically-induced conversion of NO 2 (g) on soot particles is much slower than (R1). 12,41,42,52 Note that their relative rates should be proportional to [ 2 ] correlates with the product g X Â (S/V) w rather than with (S/V) w alone, 13 (2) g X cannot be assumed to be constant, 20 but will vary with the anion makeup of aerosol droplets. Thus, g X should depend on the sources and trajectory of air masses, and vary with relative humidity, i.e., with time of day, 9,88,[90][91][92][93] (3) the hydrolytic disproportionation of NO 2 (g) on aqueous aerosol droplets is deemed to be the main mechanism for the production of tropospheric HONO.…”

“…23 The large and lingering discrepancies (up to four orders of magnitude) 10,18,[23][24][25][26][27][28][29][30][31][32][33] among laboratory measurements of NO 2 uptake coefficients ''on water'', g water , has turned attention to airborne particles that could support pathway (A), such as soot and dust. 12,16,20,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] Since HONO emissions from soot exposed to NO 2 decay rapidly in the dark 51 and cease immediately after illumination, 34,52 significant HONO production at nighttime still calls for a thermal process of type (B) that would operate throughout the day. Schwartz et al, at variance with previously held assumptions, on pure water follows second-order kinetics in [NO 2 (g)], has therefore a very low probability (about one in ten million NO 2 /water collisions) and would not contribute significantly to HONO production on cloud or aerosol droplets under atmospheric conditions.…”

Impact of updated traffic emissions on HONO mixing ratios simulated for urban site in Houston, Texas

“…Among the most known chemical sources of HONO is the gas-phase formation from the reaction between OH and nitric oxide (NO) (Pagsberg et al, 1997) and the heterogeneous formation on surfaces from the hydrolysis of nitrogen dioxide (NO 2 ) (Kleffmann et al, 1998;Finlayson-Pitts et al, 2003). Other chemical sources of HONO are described else-where (Kleffmann, 2007;Kleffmann et al, 2005;George et al, 2005;Stemmler et al, 2006Stemmler et al, , 2007Crowley and Carl, 1997;Li et al, 2008Li et al, , 2009Carr et al, 2009;Amedro et al, 2011). Emissions of HONO from traffic were estimated by Kirchstetter et al (1996) and Kurtenbach et al (2001), who performed tunnel studies and reported exhaust emission ratio of HONO to NO x in a range of 0.003-0.008.…”