title: Assessing the influence of indoor exposure to "outdoor ozone" on the relationship between ozone and short-term mortality in U.S. communities.
abstract: BACKGROUND
  City-to-city differences have been reported for the increase in short-term mortality associated with a given increase in ozone concentration (ozone mortality coefficient). Although ozone concentrations are monitored at central outdoor locations, a large fraction of total ozone exposure occurs indoors.
  
  
  OBJECTIVE
  To clarify the influence of indoor exposure to ozone of outdoor origin on short-term mortality, we conducted an analysis to determine whether variation in ozone mortality coefficients among U.S. cities might be partly explained by differences in total ozone exposure (from both outdoor and indoor exposures) resulting from the same outdoor ozone concentration.
  
  
  METHODS
  We estimated average annual air change rates (the overall rate at which indoor air is replaced with outdoor air) and used these to estimate the change in total ozone exposure per unit change in outdoor ozone exposure (ozone exposure coefficient) for 18 cities that had been included in the National Morbidity and Mortality Air Pollution Study (NMMAPS). We then examined associations between both parameters and published ozone mortality coefficients.
  
  
  RESULTS
  For the 18 targeted NMMAPS cities, the association between ozone mortality coefficients and ozone exposure coefficients was strong (1-hr ozone metric: R2 = 0.58, p < 0.001; 8-hr ozone: R2 = 0.56, p < 0.001; 24-hr ozone: R2 = 0.48, p = 0.001). When extended to another 72 NMMAPS cities, the associations remained strong (R2 = 0.47-0.63; p < 0.001).
  
  
  CONCLUSIONS
  Differences in ozone mortality coefficients among cities appear to partially reflect differences in total ozone exposure resulting from differences in the amount of outdoor ozone that is transported indoors.
authors.affiliation: Department of Building Science, School of Architecture, Tsinghua University, Beijing, China.
authors.forename: Chun
authors.initials: C
authors.lastname: Chen
authors.forename: Bin
authors.initials: B
authors.lastname: Zhao
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Weschler
mesh_terms: D016902:Air Pollution, Indoor / Q000009:adverse effects* / Q000032:analysis; D002947:Cities; D004781:Environmental Exposure / Q000706:statistics & numerical data; D004784:Environmental Monitoring; D006801:Humans; D009026:Mortality / Q000639:trends; D010083:Oxidants, Photochemical / Q000032:analysis / Q000633:toxicity*; D010126:Ozone / Q000032:analysis / Q000633:toxicity*; D012111:Residence Characteristics; D018570:Risk Assessment; D013997:Time Factors; D014481:United States; D014504:Urban Health / Q000706:statistics & numerical data
chemical_list: D010083:Oxidants, Photochemical; D010126:Ozone
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