Student Research: Marissa Baker
Introduction and Background
In both public health and urban deign and planning disciplines, it is accepted that the built environment can influence the health of a population (Saelens et al. 2003; Frank & Engelke 2001; Frumkin 2002; Jackson 2003; Northridge et al. 2003). Specifically of interest to this thesis, the built environment can serve to promote physical activity through community design aspects, and the built environment can serve to promote physical activity through community design aspects, and the built environment also can influence exposure to air pollution through density, travel patterns, and transportation options. This thesis explores the relationship between the probability of walking and exposure to NO2 at the parcel-level, and at public elementary schools, in Seattle, WA.
NO2 Health Effects and Relation to the Built Environment
NO2 is formed by the incomplete combustion of fossil fuels, and in urban areas such as Seattle mostly can be attributed to emissions from vehicles and industrial power-plants. NO2 is defined as a criteria pollutant under the National Ambient Air Quality Standards (NAAQS) by the US Environmental Protection Agency (EPA), with the annual (arithmetic average) allowable concentration being 53 parts per billion (ppb), and the daily maximum 1-hour average not to exceed 100 ppb (U.S. EPA 2010). Additionally, in the presence of sunlight, NO2 can react with volatile organic compounds to form ozone, and nitrile aerosols from NO2 make up a fraction of PM2.5 both of which are criteria pollutants monitored under the NAAQS.
Previous and ongoing research has characterized the acute and chronic health effects associated with exposure to NO2. Acutely, exposure to NO2 has been found to be associated with eye, nose, throat, and lung irritation, persistent coughing, wheezing, and respiratory infections, especially in asthmatics, those with chronic obstructive pulmonary disease (COPD), small children, or the elderly (Chen et al. 2007). Incidence and exacerbation of asthma and other respiratory conditions has found to be positively associated with NO2 exposure, even at ambient levels below the EPA standards (Brauer et al. 2007; Chen et al. 2007; Vedal et al. 2002). Epidemiological studies also have found a positive association between mortality due to lung cancer and cardiopulmonary disease, and exposure to traffic-related air pollution; in addition to COPD, bronchitis, and emphysema being positively associated with exposure to air pollution in general (Pope III et al. 2002; Dockery et al. 1993; Pope III et al. 1995). The World Health Organization (WHO) estimates that air pollution causes 2 million premature deaths worldwide each year (WHO 2008). This makes the mortality risk from particulate air pollution comparable to that for grade 1 or 2 obesity, but less than the mortality risk associated with extreme (grade 3) obesity (Pope III et al. 2002).
Recently, both public health an urban design and planning research have begun to characterize how aspects of the built environment are related to urban air pollution. Studies suggest that areas of higher residential density have higher average concentrations of urban air pollution, including higher average NO2 concentrations (Weng & Yang, 2006). Additionally, neighborhoods convenient to transportation centers or centers of business and industry have been shown to be exposed to additional air pollution, including NO2 due to increased transportation and industrial output in the area (Beelen et al. 2008; Brunekreef et at. 1997).