Potential reactions among indoor pollutants

Abstract

Reactions among indoor pollutants can produce products that, otherwise, might not be present in an indoor environment. To be relevant in an indoor setting, a chemical reaction must occur within a time interval shorter than or comparable to the residence time for a packet of indoor air. At typical air exchange rates, the reactions that meet this criterion include those of ozone with nitric oxide, nitrogen dioxide, and selected unsaturated hydrocarbons; thermal decomposition of peroxyacyl nitrates; numerous free radical reactions; and selected heterogeneous processes. Stable products include aldehydes, ketones, carboxylic acids and various organic nitrates. These reactions also generate free radicals, starting with the nitrate radical, Criegree biradicals, and peroxyacyl radicals, and leading to the hydroxyl, alkyl, alkylperoxy, hydroperoxy, and alkoxy radicals. Such radicals can react with other indoor species yielding additional aldehydes, ketones, carboxylic acids, dinitrates and peroxyacyl nitrates. Some of the potential products are known or suspected to be irritating (e.g. methacrolein, nonanoic acid, 1,2-propanediol dinitrate, peroxybenzoyl nitrate, and radical anions of the type [Cl… NO 2] −) However, some of these same products are difficult to detect using the sampling and analysis techniques currently applied to indoor air.