ABSTRACT
Organic acids are major contributors to the acidity of precipitation in the remote troposphere. Direct emission into the atmosphere from vegetation has been suggested to be an important source, as has emission from formicine ants. In regions where olefin levels are low, the reaction of hydrated formaldehyde with OH radicals in cloud water is thought to be an important atmospheric source of formic acid. Modeling studies suggest that reactions of carboxylic acid anions with OH radicals in cloud droplets represents an important, and possibly dominant, tropo-spheric removal mechanism for carboxylic acids. The effectiveness of the aqueous-phase sink is strongly pH dependent because the protonated acids are both more volatile and less reactive toward OH(aq) than their unprotonated counterparts. A competitive kinetics technique is employed with thiocyanate used as the reference reactant. The laser flash photolysis-long path absorption (LFP-LPA) technique was employed in this study. The LFP-LPA apparatus and its adaptation for temperature-dependence studies is described elsewhere.
