Reassessing the relationship between ozone and short-term mortality in U.S. urban communities

Abstract

Time-series studies that use daily mortality and ambient ozone concentrations exhibit estimates of ozone effects that are variable across cities. We investigate this inter-city variability, as well as the sensitivity of the ozone-mortality associations to modeling assumptions and choice of daily ozone metric, based on reanalysis of data from the National Morbidity, Mortality and Air Pollution Study (NMMAPS). Previous work from NMMAPS reported a statistically significant association between ambient 24-hour ozone and short-term mortality when averaged across 98 U.S. cities.Separation of ozone health associations from effects due to weather and co-pollutants is central to their interpretation. We examined the sensitivity of city-specific ozone-mortality estimates to adjustments for confounders and effect modifiers, showing substantial sensitivity. We examined ozone-mortality associations in different concentration ranges, finding a larger incremental effect in higher ranges, but also larger uncertainty. Alternative ozone exposure metrics defined by maximum 8-hour averages or 1-hour maxima show different ozone-mortality associations that cannot be explained by simple scaling relationships.The emphasis in earlier studies based on NMMAPS has been on the reporting of "national" effects, together with prediction intervals that suggest that these national values are precisely estimated. Our view is that ozone-mortality associations, based on time-series epidemiologic analyses of daily data from multiple cities, reveal still-unexplained inconsistencies and show sensitivity to modeling choices and data selection, that contribute to serious uncertainties when epidemiological results are used to discern the nature and magnitude of possible ozone-mortality relationships or are applied to risk assessment.2

Review of some effects of climate change on indoor environmental quality and health and associated no-regrets mitigation measures

“…The ratio of indoor to outdoor air concentration in homes is typically 0.2 to 0.4, but closer to 0.1 with air conditioning [68]. There is evidence that ozone less strongly affects health in cities with a higher prevalence of central air conditioning [68,83], presumably because of less window opening and lower outdoor air ventilation rates during warm weather. In analyses for 18 U.S. cities, the increase in mortality per unit increase in outdoor air ozone concentration was smaller in cities with lower predicted annual average outdoor air ventilation rates in homes [91].…”

“…Populations with increased susceptibility to adverse health effects from ozone include asthmatics, people with chronic obstructive pulmonary disease, the elderly, and people with cardiovascular disease [79--82]. Occupants of homes without air conditioning, who maintain windows open more often during warm weather will also have an increased vulnerability [68,83,84]. Table 2 summarizes published estimates of how CC is anticipated to influence the health effects of outdoor ozone.…”

A rapid assessment of the impact of hazard reduction burning around Sydney, May 2016

“…There is evidence of effects even at low levels that seems hard to reconcile with chamber study results, which nevertheless look at relatively healthy subjects for a short time. Smith, Xu & Switzer (2009), in a reassessment of the evidence for the United States, reported larger effects in higher ranges. The curves reported usually correspond to annual effects, but due to the importance of seasonal adjustment in the investigation of the short-term effects of ozone, research should report season-specific curves.…”

“…Other reviews include the quantitative systematic review of the literature conducted by St George's, University of London for the United Kingdom Department of Health, using data in the peer-reviewed literature indexed up to January 2006 (Anderson et al, 2007). A more recent meta-analysis of ozone associations was provided by Smith, Xu & Switzer (2009). A review of the Asian time-series literature also includes associations between ozone and mortality published up to May 2009 (Atkinson et al, 2010).…”

Metrics in Urban Health: Current Developments and Future Prospects

“…The primary interest, historically, in studying urban climate and health has been the relationship of ozone exposure to mortality (70,88). Numerous studies using measures of ozone concentration at 1 day, 8 hours, or hourly levels have correlated its impact on mortality with mixed results.…”