title: Modeling the residential infiltration of outdoor PM(2.5) in the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air).
abstract: BACKGROUND
  Epidemiologic studies of fine particulate matter [aerodynamic diameter ≤ 2.5 μm (PM(2.5))] typically use outdoor concentrations as exposure surrogates. Failure to account for variation in residential infiltration efficiencies (F(inf)) will affect epidemiologic study results.
  
  
  OBJECTIVE
  We aimed to develop models to predict F(inf) for > 6,000 homes in the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air), a prospective cohort study of PM(2.5) exposure, subclinical cardiovascular disease, and clinical outcomes.
  
  
  METHODS
  We collected 526 two-week, paired indoor-outdoor PM(2.5) filter samples from a subset of study homes. PM(2.5) elemental composition was measured by X-ray fluorescence, and F(inf) was estimated as the indoor/outdoor sulfur ratio. We regressed F(inf) on meteorologic variables and questionnaire-based predictors in season-specific models. Models were evaluated using the R² and root mean square error (RMSE) from a 10-fold cross-validation.
  
  
  RESULTS
  The mean ± SD F(inf) across all communities and seasons was 0.62 ± 0.21, and community-specific means ranged from 0.47 ± 0.15 in Winston-Salem, North Carolina, to 0.82 ± 0.14 in New York, New York. F(inf) was generally greater during the warm (> 18°C) season. Central air conditioning (AC) use, frequency of AC use, and window opening frequency were the most important predictors during the warm season; outdoor temperature and forced-air heat were the best cold-season predictors. The models predicted 60% of the variance in 2-week F(inf), with an RMSE of 0.13.
  
  
  CONCLUSIONS
  We developed intuitive models that can predict F(inf) using easily obtained variables. Using these models, MESA Air will be the first large epidemiologic study to incorporate variation in residential F(inf) into an exposure assessment.
authors.affiliation: Faculty of Health Sciences, Simon Fraser University, Burnaby, British Columbia, Canada. allenr@sfu.ca
authors.forename: Ryan W
authors.initials: RW
authors.lastname: Allen
authors.forename: Sara D
authors.initials: SD
authors.lastname: Adar
authors.forename: Ed
authors.initials: E
authors.lastname: Avol
authors.forename: Martin
authors.initials: M
authors.lastname: Cohen
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Curl
authors.forename: Timothy
authors.initials: T
authors.lastname: Larson
authors.forename: L-J Sally
authors.initials: LJ
authors.lastname: Liu
authors.forename: Lianne
authors.initials: L
authors.lastname: Sheppard
authors.forename: Joel D
authors.initials: JD
authors.lastname: Kaufman
mesh_terms: D016902:Air Pollution, Indoor / Q000032:analysis*; D050197:Atherosclerosis / Q000139:chemically induced* / Q000453:epidemiology*; D015331:Cohort Studies; D006798:Housing; D006801:Humans; D008962:Models, Theoretical; D052638:Particulate Matter / Q000633:toxicity*; D011446:Prospective Studies; D012044:Regression Analysis; D013052:Spectrometry, X-Ray Emission; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology
chemical_list: D052638:Particulate Matter