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

作者：Stemmler K; Vlasenko A; Guimbaud C; Ammann M^*

来源：Atmospheric Chemistry and Physics, 2008, 8(17): 5127-5141.

DOI：10.5194/acp-8-5127-2008

Surface active organic compounds have been observed in marine boundary layer aerosol. Here, we investioate the effect such surfactants have on the uptake of nitric acid (HNO3). an important removal reaction of nitrogen oxides in the marine boundary layer. The uptake of gaseous HNO3 on deliquesced NaCl aerosol was measured in a flow reactor using HNO3 labelled with the short-lived radioactive isotope N-13. The uptake coefficient gamma on pure deliquesced NaCl aerosol was gamma = 0.5 +/- 0.2 at 60% relative humidity and 30 ppb HNO3(g). The uptake coefficient was reduced by a factor of 5-50 when the aerosol was coated with saturated linear fatty acids with carbon chain lengths of 19 and 15 atoms in monolayer quantities. In contrast, neither shorter saturated linear fatty acids with 12 and 9 carbon atoms. nor coatings with the unsaturated oleic acid (C18. cis-double bond) had a detectable effect on the rate of HNO3 uptake. It is concluded that it is the structure of the monolayers formed. which determines their resistance towards HNO3 uptake. Fatty acids (C 18 and C15), which form a highly ordered film in the so-called liquid condensed state, represent a significant barrier towards HNO3 uptake, while monolayers of shorter-chain fait), acids (C9, C12) and of the unsaturated oleic acid form a less ordered film in the liquid expanded state and do not hinder the uptake. Similarly, high contents of humic acids in the aerosol, a structurally inhomogeneous. quite water soluble mixture of oxidised high molecular weight organic compounds did not affect HNO3 uptake. As surfactant films on naturally occurring aerosol

• 出版日期2008