Free radical chemistry and its concern with indoor air quality: an open problem

Abstract

Large amounts of chemicals are emitted into the troposphere as a result of anthropogenic and biogenic processes, that give rise to a very complex scenario which includes a variety of chemical transformations. During the past decades, it has become well recognized that oxygen-, nitrogen-, and carbon-centered free radicals play a key role in the chemistry of the troposphere. More recently, increasing attention has been devoted to the relevance that free radical chemistry may have in influencing the indoor air quality. Since modern populations typically spend most of their time indoors, indoor air quality is recognized as an important environmental and health problem. Reactive radicals in indoor air may be the result of indoor penetration of outdoor air or of indoor generation from specific sources. There is a great lack of knowledge about the presence and the concentrations of chemically reactive radicals in indoor air, that, in analogy to the processes occurring in the troposphere, may be formed indoors as well. In the present paper, some of the key aspects of outdoor and indoor free radical chemistry are discussed together with the experimental evidences so far obtained for the occurrence of radicals and radical-chain reactions in such environments.