Current State of the Science: Health Effect and Indoor Environmental QualityClifford S. Mitchell, Junfeng (Jim) Zhang, Torben Sigsgaard, Matti Jantunen, Paul J. Lioy, Robert Samson and Meryl H. KarolPresented by Snezana DjordjevicEOH 2504 Principles of Environmental ExposureBackgroundIn this article, indoor pollutants have been reviewed along with their relating issues such as source characterization, exposure assessment, health effects associated with indoor exposure and intervention research relating to indoor environments. In the past problem of indoor environment quality (IEQ) focused on indoor constituents(primarily particles, bioaerosols, and chemicals) and comfort factors temperature, air flow and humidity, but recently it has begun as a complex between building occupants and an array of physical, chemical, biological and design factors. Advances in source characterization enable a better understanding of how chemicals are transported and processed within the spaces and the role that other factors such as lighting and building design my play in determining health. Ability to measure exposure remains the challenge particularly for the biological agents. Researches are also examining the effect of multiple exposure as well as the effects of exposures on vulnerable populations such as children and the elderly.Source characterization Outdoor air pollutions is a dynamic system in which the physical and chemical process affecting the accumulation of pollutants in the atmosphere are constantly changing, largely driven by complex meteorology and photochemistry.  The usual approach of modeling indoor air pollution treats the indoor environment as a static box in which physical and chemical transportation of indoor air pollutants are absent or negligible. On this way estimates are made for primary indoor air pollutant concentration but secondary pollutants are ignored.  In –depth studies of indoor air have shown that the concentration of agents in indoor air is a function of outdoor concentration, indoor source strength, removal and deposition rate within the structure, indoor mixing and chemical reaction Indoor production:Primary sources of indoor pollutants include fuel combustion for cooking, heating and lightening; tobacco smoking; bioeffluents from humans and animals; floor and wall coverings; synthetic paints, glues, polishes, and waxes; pesticides; and building products. Also release of gases from solvent used indoors or from water that is used daily-by products (e.g. chloroform). Concentration of many volatile organic compounds (VOCs) are higher indoors than outdoors because of the use of many types of synthetic materials.Secondary sources refer to indoor chemistry that transform a set of indoor pollutants, emitted from primary sources or transported from outdoors, to a new set of indoor pollutants. Outdoor-to-indoor transportPollutants of outdoor origin can be transported indoors via building openings and cracks. Attempts have been made to estimates the fraction of measured indoor concentration contributed by outdoor air due to the outdoor to indoor transport process.One study, the Exposure of Adult Urban Populations in Europe Study(EXPOLIS) compared concentration of ambient particulate matter smaller than 2.5 micrometers PM2.5, its 16 elemental constituents and black carbon, 30 VOCs, and carbon monoxide among urban adult population in seven European cities. The proportion of outdoor PM found indoor for PM2.5 averaged 0.64 for residential structure, 0.47 for workplaces, and 0.35 for subsample of office buildings constructed after 1990. Although attempts have been made to differentiate PM of outdoor origin from PM of indoor origin, analyses have been complicated because the fraction of indoor species contributed by outdoor air depends not only on outdoor concentration but also on home-specific parameters including air exchange rate(AER) typically expressed as air exchange per hour, indoor generation rate , removal rate and house volume. Models of indoor PM exposure have been developed to account for both indoor and outdoor sources, as well as mixing, transport, and removal( Georgopoulos et al.2005; Nazaroff 2004)One of the chemical which outdoor- to- indoor transport considered unimportant is ozone(O3).O3 like PM is regulated in the United States as a criteria pollutant. Weschler at al.(1989) showed t hat indoor exposure to ozone can easily surpass outdoor exposure. Under high AERs indoor O levels can be 50-70% of outdoor levels. Indoor O3 concentration of 20ppb may not be sufficient to cause health concern but this ozone level can drive a complex set of indoor chemical reactions. Indoor-to-outdoor transportSince the late 1970s , the air tight design of buildings, driven mainly by energy conservation , has resulted in reduce AERs. Ventilation is necessary to reduce concentration of pollutants generated indoor, but is also, necessary to reduce the time available for chemical reactions among indoor pollutants. Based on approximately 4,590 measurements of residential AERs conducted across the US, Pandian et al. (1998) reported that its magnitude are undesirable for removing air pollutants that originate indoors and are low enough for certain reactions to occur.( mean, median and SDs of AER s were 0.55, 0.42, and 0.47ach-air exchange per hour, for the north eastern region and 0.71, 0.62, and 0.56 ach for the southeastern region. Indoor chemistryPollutants can be removed from indoor air through both physical and chemical processes. Physical processes include phase change, adsorption or absorption, or dissolving in water or organic films. Indoor chemistry are reactions involving indoor pollutants , occurring either in the gas phase or on the surfaces. These chemical reaction processes represent sinks for the primary indoor pollutants and sources of secondary indoor pollutants.The most extensively studied gas-phase reactions are oxidation reactions involving O3 and free radicals. O3 can react with nitric oxide, nitrogen dioxide, and unsaturated organic compounds ( terpenes, terpenoids, unsaturated fatty acid) to yield reactive intermediates, the hydroxyl radical(OH), the nitrate radical(NO3) and oxygenated organic compounds. Reactions of ozone with NO2 form the NO3 radical that further reacts with VOCs, leading to the formation of indoor nitric acid . The NO3 radical can also react with NO2 to form dinitrogen pentaoxide N2O5 that