Abstract
Ethanol (EtOH) and tert-Butyl methyl ether (MTBE) are both finding increased use as oxygenated additives to fuels. However, the environmental fate in the troposphere of these species is unclear when they escape as fugitive emissions. In several locations there are reports of human illness in response to MTBE in particular. Volatile organic compounds (VOC`s) such as these are generally thought to react by a variety of homogeneous free-radical mechanisms, usually beginning with attack by OH radical. However, we show by laboratory kinetic studies that the heterogeneous photoreaction on solid suspended metal-oxide particulates such as fly ash proceeds with a comparable rate, especially in urban environments. EtOH reacts to form acetaldehyde, and EtOH forms isobutene, methanol, and formaldehyde. Our work appears to be the first-ever demonstration that VOC`s can react as fast by a heterogeneous mechanism as by a homogeneous one in the atmosphere. Experiments by various optical and kinetic techniques show that the active phases in fly ash are Fe oxides, which are fairly abundant in other atmospheric particulates as well.