Academic journal article Environmental Health Perspectives

The Exposure-Response Curve for Ozone and Risk of Mortality and the Adequacy of Current Ozone Regulations

Academic journal article Environmental Health Perspectives

The Exposure-Response Curve for Ozone and Risk of Mortality and the Adequacy of Current Ozone Regulations

Article excerpt

Time-series analyses have shown that ozone is associated with increased risk of premature mortality, but little is known about how [O.sub.3] affects health at low concentrations. A critical scientific and policy question is whether a threshold level exists below which [O.sub.3] does not adversely affect mortality. We developed and applied several statistical models to data on air pollution, weather, and mortality for 98 U.S. urban communities for the period 1987-2000 to estimate the exposure-response curve for tropospheric [O.sub.3] and risk of mortality and to evaluate whether a "safe" threshold level exists. Methods included a linear approach and subset, threshold, and spline models. All results indicate that any threshold would exist at very low concentrations, far below current U.S. and international regulations and nearing background levels. For example, under a scenario in which the U.S. Environmental Protection Agency's 8-hr regulation is met every day in each community, there was still a 0.30% increase in mortality per 10-ppb increase in the average of the same and previous days' [O.sub.3] levels (95% posterior interval, 0.15-0.45%). Our findings indicate that even low levels of tropospheric [O.sub.3] are associated with increased risk of premature mortality. Interventions to further reduce [O.sub.3] pollution would benefit public health, even in regions that meet current regulatory standards and guidelines. Key words: mortality, ozone, regulations, threshold. doi:10.1289/ehp.8816 available via http://dx.doi.org/ [Online 23 January 2006]

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Tropospheric ozone is a common urban area pollutant linked to numerous harmful health effects, including reduced lung function, increased frequency of respiratory symptoms, and development of asthma [Broeckaert et al. 1999; Brunekreef and Holgate 2002; McConnell et al. 2002; U.S. Environmental Protection Agency (EPA) 1996]. Recent meta-analysis and time-series studies have linked short-term [O.sub.3] exposure to premature mortality (Anderson et al. 2004: Bell et al. 2004, 2005; Huang et al. 2005; Ito et al. 2005; Levy et al. 2005), but the exposure-response curve for [O.sub.3] remains unknown. More than 100 million people in the United States live in areas that exceed the current health-based U.S. National Ambient Air Quality Standard (NAAQS) for [O.sub.3] (U.S. EPA 2004). Elevated concentrations of [O.sub.3] are also a growing concern for rapidly developing nations with rising emissions of [O.sub.3] precursors from expanding transportation networks.

The U.S. EPA is currently reviewing the scientific evidence on [O.sub.3] and health to determine if the current NAAQS (80 ppb for the daily 8-hr maximum) should be revised to meet the goal mandated in the Clean Air Act Amendments (1990) to protect human health with an "adequate margin of safety" (U.S. EPA 1997). There are several critical questions regarding the association between [O.sub.3] and mortality as the current NAAQS is reexamined: Can [O.sub.3] affect mortality even at low levels? Are current regulations sufficiently stringent to prevent premature mortality? Is there an attainable threshold [O.sub.3] level that does not affect mortality, and if so, is it below current regulatory limits? Evidence relevant to these questions can be obtained by estimating the exposure-response curve for [O.sub.3] and mortality. The shape of this curve can provide a basis for a) understanding the impacts of low levels of [O.sub.3] pollution on health, b) assessing the adequacy of regulatory standards, c) designing other health-based studies on [O.sub.3], d) estimating the health consequences associated with emissions scenarios and policies (e.g., Hubbell et al. 2005), and e) assessing how climate change might affect human health through altered [O.sub.3] levels (e.g., Knowlton et al. 2004).

Materials and Methods

Data and hierarchical model. To investigate the exposure-response relationship between [O. …

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