title: Has reducing fine particulate matter and ozone caused reduced mortality rates in the United States?
abstract: OBJECTIVE
  Between 2000 and 2010, air pollutant levels in counties throughout the United States changed significantly, with fine particulate matter (PM2.5) declining over 30% in some counties and ozone (O3) exhibiting large variations from year to year. This history provides an opportunity to compare county-level changes in average annual ambient pollutant levels to corresponding changes in all-cause (AC) and cardiovascular disease (CVD) mortality rates over the course of a decade. Past studies have demonstrated associations and subsequently either interpreted associations causally or relied on subjective judgments to infer causation. This article applies more quantitative methods to assess causality.
  
  
  METHODS
  This article examines data from these "natural experiments" of changing pollutant levels for 483 counties in the 15 most populated US states using quantitative methods for causal hypothesis testing, such as conditional independence and Granger causality tests. We assessed whether changes in historical pollution levels helped to predict and explain changes in CVD and AC mortality rates.
  
  
  RESULTS
  A causal relation between pollutant concentrations and AC or CVD mortality rates cannot be inferred from these historical data, although a statistical association between them is well supported. There were no significant positive associations between changes in PM2.5 or O3 levels and corresponding changes in disease mortality rates between 2000 and 2010, nor for shorter time intervals of 1 to 3 years.
  
  
  CONCLUSIONS
  These findings suggest that predicted substantial human longevity benefits resulting from reducing PM2.5 and O3 may not occur or may be smaller than previously estimated. Our results highlight the potential for heterogeneity in air pollution health effects across regions, and the high potential value of accountability research comparing model-based predictions of health benefits from reducing air pollutants to historical records of what actually occurred.
authors.affiliation: Cox Associates and University of Colorado, Denver, CO; NextHealth Technologies, Englewood, CO. Electronic address: tcoxdenver@aol.com.
authors.forename: Louis Anthony Tony
authors.initials: LA
authors.lastname: Cox
authors.affiliation: Cox Associates and University of Colorado, Denver, CO; NextHealth Technologies, Englewood, CO.
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Popken
mesh_terms: D000393:Air Pollutants / Q000009:adverse effects / Q000032:analysis*; D000397:Air Pollution / Q000009:adverse effects* / Q000032:analysis; D002318:Cardiovascular Diseases / Q000139:chemically induced / Q000401:mortality*; D004784:Environmental Monitoring; D006801:Humans; D009026:Mortality / Q000639:trends*; D010126:Ozone / Q000009:adverse effects*; D052638:Particulate Matter / Q000009:adverse effects*; D018570:Risk Assessment; D014481:United States / Q000453:epidemiology
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D010126:Ozone
keywords: Accountability research; Air pollution; Cardiovascular mortality risks; Causality; Fine particulate matter; Health effects; Ozone; PM10; PM2.5; Respiratory mortality risk