Organic acids in the atmosphere are ubiquitous and are often correlated with mineral dust aerosol. Heterogeneous chemistry and the uptake of organic acids on mineral dust particles can potentially alter the properties of the particle. In this study, heterogeneous uptake and reaction of formic acid, HCOOH, the most abundant carboxylic acid present in the atmosphere, on oxide and clays of the most abundant elements � Si and Al � present in the Earth's crustare investigated under dry and humid conditions. In particular, quantitative adsorption measurements using a Quartz Crystal Microbalance (QCM) coupled with spectroscopic studies using Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy are combined to allow for both quantification of the amount of uptake and identification of distinct adsorbed species formed on silica, alumina and kaolinite particle surfaces at 298 K. These oxides and clay particles show significant differences in the extent and speciation of adsorbed HCOOH due to inherent differences in surface �OH group reactivity. Relative humidity plays a key role in the formic acid reaction with mineral oxide surfaces. Higher relative humidity favors the total and irreversible uptake of formic acid on alumina surface. Interestingly, this thin coating of adsorbed formate on the particle surface significantly enhances the hydrophobic nature of the surface, thereby decreasing the amount of water taken up by the surface as measured by QCM. Lower water content on mineral particle surface limits heterogeneous reactions, in particular with water soluble gases (e.g. NOx and SOx). Therefore, the processed aerosols in the presence of organic acids may behave differently in the atmospheric reactions that warrant further investigation.

Heterogeneous uptake and adsorption of gas-phase formic acid on oxide and clay particle surfaces:? The role of adsorbed water in formic acid adsorption and the impact of formic acid adsorption on water uptake

247th National Meeting (2014)

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