Ozone Decomposition on Kaolinite As a Function of Monoterpene Exposure and Relative Humidity

Atmospheric processing of mineral aerosol by trace gases results in the formation of surface-adsorbed products that have the capacity to alter the chemical and physical properties of these airborne particulates. To investigate one potential impact of aerosol processing by biogenic volatile organic compounds (BVOCs), we investigated the heterogeneous decomposition of ozone on pure and monoterpene-processed kaolinite. We used a laminar flow reactor to measure O-3 reactive uptake coefficients on kaolinitecoated tubes as a function of relative humidity, O-3 concentration, and pre-exposure to gaseous limonene and apinene. At 26% RH, kaolinite has a near equivalent of a monolayer of adsorbed water, and the ozone steady-state uptake coefficient was gamma(av) = 2.9 x 10(-9) assuming the BET surface area. Pre-exposing kaolinite to limonene and alpha-pinene increased O-3 uptake coefficients by nearly 2 orders of magnitude to 2.1 X 10(-7) and 2.5 X IF', respectively. At all humidities studied (10-50% RH), O-3 uptake was at least 1 order of magnitude higher for monoterpene-processed kaolinite compared to that of pure kaolinite. This dramatic increase in O-3 reactivity is attributed to surface-adsorbed organics, namely limonenediol and a-terpineol, which contain alkene functionalities susceptible to ozonolysis. Increasing relative humidity decreased O-3 uptake for monoterpene-processed kaolinite consistent with competitive adsorption of water resulting in lower organic surface concentrations. These results demonstrate the significant impact adsorbed organics can have on O-3 uptake coefficients on mineral aerosol, which should he accounted for in atmospheric modeling studies.