Kinetics and mechanism of the uptake of N<sub>2</sub>O<sub>5</sub> on mineral dust at 298 K

Abstract

Abstract. The heterogeneous reaction of N 2 O 5 with mineral (Saharan) dust has been studied at T=298 K using a combination of Knudsen and DRIFTS cells for kinetic and product investigations, respectively. The initial uptake coefficient has been determined to be γ =(8.0±0.3)·10 −2 . This uptake slowly saturates into a steady state uptake of γ =(1.3±0.3)·10 −2 suggesting that reaction of N 2 O 5 with the mineral dust surface and hydrolysis of N 2 O 5 on the surface take place simultaneously. Both uptake coefficients have been calculated on the basis of the geometric (projected) surface area of the sample and must therefore be regarded as upper limits. In addition, the product investigations show that N 2 O 5 is irreversibly taken up to form nitrate on the surface. Recent model calculations suggest that the uptake rates of N 2 O 5 on Saharan dust which we measured may be large enough to influence the photo-oxidant budget of the atmosphere.

Heterogeneous reaction of N<sub>2</sub>O<sub>5</sub> with airborne TiO<sub>2</sub> particles and its implication for stratospheric particle injection

“…The kinetics of the uptake of N 2 O 5 onto desert dust particles and their surrogates (e.g., Arizona Test Dust, illite) has been reported by several previous studies (Karagulian et al, 2006;Mogili et al, 2006;Seisel et al, 2005;Tang et al, 2010Tang et al, , 2012Tang et al, , 2014Wagner et al, 2008Wagner et al, , 2009). In addition, Seisel et al (2005) observed the formation of nitrate on mineral dust particles due to the uptake of N 2 O 5 using diffuse reflectance FTIR (Fourier transform infrared spectroscopy), and Tang et al (2012) further confirmed that the yield of nitrate is ∼ 2 (as expected from Reaction R1) within the experimental uncertainty, and that the formation of NO 2 is negligible.…”

“…In addition, Seisel et al (2005) observed the formation of nitrate on mineral dust particles due to the uptake of N 2 O 5 using diffuse reflectance FTIR (Fourier transform infrared spectroscopy), and Tang et al (2012) further confirmed that the yield of nitrate is ∼ 2 (as expected from Reaction R1) within the experimental uncertainty, and that the formation of NO 2 is negligible. However, to the best of our knowledge, the reaction of N 2 O 5 with TiO 2 has never been studied.…”

“…4 further suggests that γ (N 2 O 5 ) may decrease with increasing RH between 5 and 20 % RH and reaches a minimum around 20 % RH, and above that γ (N 2 O 5 ) starts to increase with RH. The heterogeneous uptake of N 2 O 5 onto mineral surfaces is suggested to proceed with two pathways: the reaction of N 2 O 5 with surface OH groups or the heterogeneous hydrolysis of N 2 O 5 by surfaceadsorbed water, whereas the reaction with surface OH groups is faster (Seisel et al, 2005;Tang et al, 2014). FTIR observations showed that surface OH groups on Saharan dust particles were depleted during the exposure to N 2 O 5 , leading to the decrease of γ (N 2 O 5 ) with reaction time (Seisel et al, 2005).…”

“…The heterogeneous uptake of N 2 O 5 onto mineral surfaces is suggested to proceed with two pathways: the reaction of N 2 O 5 with surface OH groups or the heterogeneous hydrolysis of N 2 O 5 by surfaceadsorbed water, whereas the reaction with surface OH groups is faster (Seisel et al, 2005;Tang et al, 2014). FTIR observations showed that surface OH groups on Saharan dust particles were depleted during the exposure to N 2 O 5 , leading to the decrease of γ (N 2 O 5 ) with reaction time (Seisel et al, 2005). The uptake coefficient of N 2 O 5 onto illite was found to decrease with increasing RH, and this is suggested to be due to the coverage of OH groups by adsorbed water at high RH (Tang et al, 2014).…”

Heterogeneous Uptake of Amines by Citric Acid and Humic Acid

“…14,16 A similar phenomenon was also observed for the uptake of HNO 3 on soot 47 and N 2 O 5 and H 2 O on mineral dust. 48,49 This implies a very small probe depth or a large true uptake coefficient of amines on citric acid. On the other hand, as discussed above, the reaction degree is lower than 0.05% even for the whole exposure time for all of these amines on citric acid.…”