Heterogeneous reaction of N<sub>2</sub>O<sub>5</sub> with illite and Arizona test dust particles

Abstract

Abstract. The heterogeneous reaction of N 2 O 5 with airborne illite and Arizona test dust (ATD) particles was investigated at room temperature and at different relative humidities using an atmospheric pressure aerosol flow tube. N 2 O 5 at concentrations in the range 8 to 24 × 10 12 molecule cm −3 was monitored using thermal-dissociation cavity ring-down spectroscopy at 662 nm. At zero relative humidity a large uptake coefficient of N 2 O 5 to illite was obtained, γ (N 2 O 5 ) = 0.09, which decreased to 0.04 as relative humidity was increased to 67 %. In contrast, the uptake coefficient derived for ATD is much lower (∼ 0.006) and displays a weaker (if any) dependence on relative humidity (0-67 %). Potential explanations are given for the significant differences between the uptake behaviour for ATD and illite and the results are compared with uptake coefficients for N 2 O 5 on other mineral surfaces.

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

“…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). The minimum of γ (N 2 O 5 ) onto TiO 2 at 20 % RH may indicate that the increase of RH up to 20 % could cause the more reactive surface OH groups to be covered by surface-adsorbed water, while further increase in RH will promote the heterogeneous hydrolysis of N 2 O 5 by surface-adsorbed water, i.e.…”

“…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.…”

“…Real desert dust and clay minerals show much higher heterogeneous reactivity towards N 2 O 5 : the uptake coefficient of N 2 O 5 , γ (N 2 O 5 ), is (1-2) × 10 −2 for Saharan dust Wagner et al, 2008), and (4-9) × 10 −2 for illite (Tang et al, 2014), explained by the high density of OH groups in illite (Hatch et al, 2011). γ (N 2 O 5 ) was reported to be (4.5-8.6) × 10 −3 for SiO 2 (Wagner et al, 2008) and (5-10) × 10 −3 for Arizona Test Dust (Wagner et al, 2008;Tang et al, 2014), whose main components are SiO 2 and feldspar (Broadley et al, 2012), and the lower heterogeneous reactivity of SiO 2 and Arizona Test Dust towards N 2 O 5 is mainly attributed to the low amount of surface-adsorbed water on the surface of the two particles, compared to clay and Saharan dust. The reactivity of CaCO 3 with N 2 O 5 is very low at 0 % RH with γ (N 2 O 5 ) of ∼ 5 × 10 −3 but increases quickly with RH with γ (N 2 O 5 ) of ∼ 2 × 10 −2 at 71 % (Wagner et al, 2009).…”

“…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).…”

Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: volume 1. Inorganic compounds

“…large uptake coefficients) and big particles, gas phase diffusion of X can limit the overall rate of the uptake of X onto the surface. A method used to calculate diff for poly-dispersed aerosol particles has also been developed (Tang et al, 2012(Tang et al, , 2014. As shown in Eqs.…”