Indoor Chemistry: Materials, Ventilation Systems, and Occupant Activities

Indoor Chemistry: Materials, Ventilation Systems, and Occupant Activities G.C. Morrison l , R.L. Corsi 2 , H. Destaillats 3 , W.W. Nazaroft, and J.R. Wells s [University of Missouri, Civil, Architectural and Environmental Engineering Dept., Rolla, Missouri, USA 65409-0030 email: gcm@umr.edu http://www.umr.eduJ-gcm 2 The University of Texas, Dept. of Civil, Architectural and Environmental Engineering, Austin, Texas 78758 3Lawrence Berkeley National Laboratory, Berkeley, California, USA, 94720 4University of California, Civil & Environmental Engineering Dept., Berkeley, California, USA 94720-1710 5National Institute for Occupational Safety and Health, Morgantown, West Virginia, USA 26505-2888 Summary: Chemical processes taking place in indoor environments can significantly alter the nature and concentrations ofpollutants. Exposure to secondary contaminants generated in these reactions needs to be evaluated in association with many aspects of buildings to minimize their impact on occupant health and well-being. Focusing on indoor ozone chemistry, we describe alternatives for improving indoor air quality by controlling chemical changes related to building materials, ventilation systems, and occupant activities. Keywords: indoor chemistry, building materials, controls 1 Introduction Indoor chemistry is now recognized as an important factor influencing occupant exposure to air pollutants, including ozone, organic compounds, and particulate matter. Here, we examine how ozone-initiated indoor reactive chemistry is influenced by building materials, ventilation systems and occupant activities. By investigating indoor chemistry in this way, we demonstrate the importance of intelligent decisions by each of the major stakeholders for controlling indoor air chemistry, and thereby improving the healthfulness of buildings. primary emissions, but also the formation of secondary pollutants. Evidence is emerging that the same principle applies for indoor environments. Several broad classes of chemical reactions may occur in indoor air. These include oxidation-reduction reactions, acid-base reactions, hydrolysis reactions, and decomposition reactions. Ozone is an important carrier of oxidative chemical potential. Ozone from ambient air enters buildings along with ventilation. Some products used indoors also may generate ozone. Indoor ozone levels exceeding 20 ppb on a transient basis are not uncommon. Pollutants that react at a meaningful rate with ozone include nitrogen oxides, unsaturated volatile organics, terpenoids, and unsaturated fatty acids and oils. The products of ozone-initiated indoor chemistry are diverse, including free radicals (e.g., OH), peroxides (e.g., H 2 0 2), short-lived organics (e.g., ozonides), and stable organics (e.g., carbonyls). Ozone-initiated indoor air chemistry causes both positive and negative effects. Homogeneous and heterogeneous ozone decomposition reduces human inhalation exposure to this respiratory irritant. On the other hand, the products of ozone-initiated chemistry can also have adverse health effects. At present, it is not clear whether the net effects of uncontrolled ozone-initiated chemistry are beneficial or harmful. However, it is feasible to improve indoor air quality through engineering control that is targeted at simultaneously reducing ozone concentrations and limiting the fonnation of harmful byproducts. The next three sections explore ozone-induced chemistry associated with building materials and furnishings, building ventilation systems, and occupant activities. 2 Indoor reactive chemistry Chemical transformations occur indoors. Such transformations influence the kind and amounts of pollutants to which people are exposed. To ensure healthy environments, those with responsibilities for indoor environmental quality should recognize the potential for chemical transformations and seek to limit their adverse effects. An analogy exists with motor vehicle emissions into urban air. Primary pollutants are directly emitted from motor vehicles, including unburned and partially oxidized organics from fuel, nitrogen oxides from high-temperature combustion, and carbon monoxide from fuel-rich combustion. In the atmosphere, primary pollutants may be chemically transfonned. Nitrogen oxides and volatile organic compounds combine in the presence of sunlight to form secondary pollutants, among which are ozone, aldehydes, organic acids, and secondary particulate matter. Thus, if one seeks to understand the health risks associated with motor vehicle use, one should not only consider the