title: Neighborhood walkability and particulate air pollution in a nationwide cohort of women.
abstract: BACKGROUND
  Features of neighborhoods associated with walkability (i.e., connectivity, accessibility, and density) may also be correlated with levels of ambient air pollution, which would attenuate the health benefits of walkability.
  
  
  OBJECTIVE
  We examined the relationship between neighborhood walkability and ambient air pollution in a cross-sectional analysis of a cohort study spanning the entire United States using residence-level exposure assessment for ambient air pollution and the built environment.
  
  
  METHODS
  Using data from the Nurses' Health Study, we used linear regression to estimate the association between a neighborhood walkability index, combining neighborhood intersection count, business count, and population density (defined from Census data, infoUSA business data, and StreetMap USA data), and air pollution, defined from a GIS-based spatiotemporal PM2.5 model.
  
  
  RESULTS
  After adjustment for Census tract median income, median home value, and percent with no high school education, the highest tertile of walkability index, intersection count, business count, and population density was associated with a with 1.58 (95% CI 1.54, 1.62), 1.20 (95% CI 1.16, 1.24), 1.31 (95% CI 1.27, 1.35), and 1.84 (95% CI 1.80, 1.88) µg/m(3) higher level of PM2.5 respectively, compared to the lowest tertile. Results varied somewhat by neighborhood socioeconomic status and greatly by region.
  
  
  CONCLUSIONS
  This nationwide analysis showed a positive relationship between neighborhood walkability and modeled air pollution levels, which were consistent after adjustment for neighborhood-level socioeconomic status. Regional differences in the air pollution-walkability relationship demonstrate that there are factors that vary from region to region that allow for walkable neighborhoods with low levels of air pollution.
authors.affiliation: Department of Epidemiology, Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA. Electronic address: pjames@hsph.harvard.edu.
authors.forename: Peter
authors.initials: P
authors.lastname: James
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA; Channing Division of Network Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Jaime E
authors.initials: JE
authors.lastname: Hart
authors.affiliation: Department of Epidemiology, Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA; Channing Division of Network Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: Francine
authors.initials: F
authors.lastname: Laden
mesh_terms: D015331:Cohort Studies; D005260:Female; D006801:Humans; D052638:Particulate Matter / Q000633:toxicity*; D012111:Residence Characteristics; D014481:United States; D016138:Walking
chemical_list: D052638:Particulate Matter
keywords: Air pollution; Built environment; Geographic information systems; Neighborhood socioeconomic status; Particulate matter