Reactive Uptake of N₂O₅on Aqueous H₂SO₄Solutions Coated with 1-Component and 2-Component Monolayers

Abstract

Reactive uptake of N(2)O(5) on aqueous sulfuric acid solutions was studied in the presence of 1-component (octadecanol) and 2-component (octadecanol + phytanic acid) monolayers. In the 1-component monolayer experiments, the reactive uptake coefficient depended strongly on the molecular surface area of the surfactant. Also, the 1-component monolayer showed significant resistance to mass transfer even when the fractional surface coverage of the surfactant was less than 1. For example, a monolayer of 1-octadecanol with a fractional surface coverage of 0.75 decreased the reactive uptake coefficient by a factor of 10. This is consistent with previous studies. In the 2-component monolayer experiments, the reactive uptake coefficient depended strongly on the composition of the monolayer. When the monolayer contained only straight-chain molecules (1-octadecanol), the reactive uptake coefficient decreased by a factor of 42 due to the presence of the monolayer. However, when the monolayer contained 0.20 mole fraction of a branched surfactant (phytanic acid) the reactive uptake coefficient only decreased by a factor of 2. Hence, a small amount of branched surfactant drastically changes the overall resistance to reactive uptake. Also, our results show that the overall resistance to reactive uptake of 2-component monolayers can be predicted reasonably accurately by a model that assumes the resistances to mass transfer can be combined in parallel.

The effect of fatty acid surfactants on the uptake of nitric acid to deliquesced NaCl aerosol

“…Obviously, the hydrolysis of the much less soluble N 2 O 5 may already be affected by less densely packed organic coatings, but might also be more sensitive to the water activity of the mixed aqueous particles. In the most recent study, Cosman et al (2008) found effects that are related to what we have observed for HNO 3 in that a monolayer of octadecanol was strongly inhibiting the uptake of N 2 O 5 , while the addition of a branched surfactant strongly decreased the resistance to N 2 O 5 uptake again.…”

“…A number of recent studies have addressed the effects of organic coatings on the phase transfer of atmospherically relevant molecules (Däumer et al, 1992;Jefferson et al, 1997;Folkers et al, 2003;Thornton and Abbatt, 2005;Glass et al, 2006;Gilman and Vaida, 2006;McNeill et al, 2006;Park et al, 2007;Clifford et al, 2007;Cosman et al, 2008). The observed effects different surfactants have vary substantially and depend on the substrate, the monolayer properties and also on the type of trace gas and its sink process in the condensed phase.…”

Gas–particle partitioning of atmospheric aerosols: interplay of physical state, non-ideal mixing and morphology

“…48 The presence of organic coatings on aqueous aerosols can suppress heterogeneous N 2 O 5 hydrolysis by providing a barrier through which N 2 O 5 needs to diffuse in order to undergo hydrolysis. [49][50][51] Reactive uptake of O 3 and NH 3 to organic aerosols exhibits a pronounced decrease as RH decreases owing to the phase transformation from viscous liquid to semi-solid or amorphous solid. 16,52 Therefore, the presence of a semi-solid matrix may effectively shield reactive organic compounds from chemical degradation in long-range transport.…”

On the effectiveness of nitrogen oxide reductions as a control over ammonium nitrate aerosol

“…The heterogeneous loss rate of N 2 O 5 is a function of the total aerosol surface area and of the fraction of gas-particle collisions resulting in N 2 O 5 uptake. The latter is aerosol composition dependent, enhanced at higher aerosol water content (e.g., Hu and Abbatt, 1997;Hallquist et al, 2003;Thornton et al, 2003), reduced in the presence of organic coatings (e.g., Cosman and Bertram, 2008;McNeill et al, 2006), and inversely proportional to NO − 3 (e.g., Wahner et al, 1998;Hallquist et al, 2003;Bertram and Thornton, 2009;Wagner et al, 2013).…”