Physical and Chemical Properties of 3-Methyl-1,2,3-butanetricarboxylic Acid (MBTCA) Aerosol

The properties and the chemical fate of later generation products of the oxidation of biogenic organic compounds are mostly unknown. The properties of fresh MBTCA aerosol, a later generation product of the oxidation of monoterpenes in the atmosphere, were determined combining an aerosol mass spectrometer (AMS), a thermodenuder, and a scanning mobility particle sizer. Based on its AMS spectrum m/z 141.055 (C7H9O3+) could be used as an MBTCA signature. The MBTCA particle density was 1.43 +/- 0.04 g cm(-3), its saturation concentration was(1.8 +/- 1.3) X 10(-3) mu g m(-3) at 298 K, and its vaporization enthalpy was 150 +/- 15 kJ mol(-1). After OH radical exposure (similar to 1.2 days) and UV illumination the average aerosol O:C ratio decreased from 0.72 to 0.58-0.64 suggesting net fragmentation. Our findings suggest that the reactions of MBTCA with OH lead to CO2 loss with or without an oxygen addition.