Direct Observation of the Kinetics of an Atmospherically Important Reaction at the Air−Aqueous Interface

Abstract

Many atmospherically important chemical processes are believed to occur at the interface between the air and aqueous phases. We report the first direct measurement of the kinetics of a reaction between a gas-phase species (ozone) and a compound (anthracene) adsorbed at the air−water interface. The reaction was studied at the “clean” air−water interface and also at an interface consisting of approximately one monolayer of 1-octanol. In both instances, the reaction was seen to follow a Langmuir−Hinshelwood mechanism, in which ozone first adsorbs to the surface and then reacts with adsorbed anthracene. Using typical atmospheric ozone concentrations, a reactive uptake coefficient of approximately 6 × 10-8 at the air−water interface may be estimated; this value increases by about a factor of 5 when the water surface is coated by a monolayer of 1-octanol.

Reaction of gas phase OH with unsaturated self-assembled monolayers and relevance to atmospheric organic oxidations

“…An enhanced reaction probability for the surface reaction is consistent with the fact that the terminal double bond should be the part of the SAM that OH first encounters in the structured monolayer, as also proposed for the NO 3 reaction, 57 and with previous studies showing enhanced reactivity at interfaces compared to the gas phase. [19][20][21][22][23][24][25][26][27][28] Reaction on every collision has also been observed for the reaction of Cl atoms with a C3Q SAM. 22 Although there are a number of studies of the OH oxidation of organics on surfaces and in or on particles, there are 25 measured g = 0.29 for the same surface, indicating that even for saturated alkyl chains, the surface reaction is fast.…”

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols

“…Interestingly, the reactions of ozone with a number of other surface-bound organics which are chemically dissimilar have also been observed to have kinetics consistent with a L-H mechanism. This includes reactions with soot, 245,246 benzo[a]-pyrene on soot, 247 polycyclic aromatic hydrocarbons at the air-water interface 207,211,213,214 chlorophyll at the air-water interface 248 and aqueous salt aerosols containing oleate. 249 More recently, the ozonolysis of the 8-carbon alkene SAM has been revisited using ZnSe and SiO x -coated ZnSe ATR crystals.…”

A new approach to studying aqueous reactions using diffuse reflectance infrared Fourier transform spectrometry: application to the uptake and oxidation of SO2 on OH-processed model sea salt aerosol

“…Thus, the results of the post-OH-processing UV exposure suggest that HOCl/OCl À is the oxidant for S(IV) in region I. Using the rate constants for reactions (12) and (13), and the pK a for HOCl, the relative rate of oxidation of sulfite by HOCl compared to OCl À is given by k 12 [H 1 ]/(3.0 Â 10 À8 k 13 ). At a pH of 12, this ratio is one, i.e.…”