Environmental Engineering, Yale University, New Haven, CT 06511, USA.
J Expo Sci Environ Epidemiol. 2010 Jan;20(1):2-11. doi: 10.1038/jes.2008.69. Epub 2008 Nov 5.
Several exposure metrics have been applied in health research and policy settings to represent ozone exposure, such as the 24 h average and daily 8 h maximum. Frequently, results calculated using one exposure metric are converted using a simple ratio to compare or combine findings with results using a different metric. This conversion, however, assumes that such a ratio is constant across locations and time periods. We investigated the appropriateness of this conversion method by examining the relationships among various forms of ozone concentrations (24 h average, daily 1 h maximum, and daily 8 h maximum) within and between communities for 78 US communities from 2000 to 2004 and compared results to commonly used conversion ratios. We explored whether the relationships between ozone exposure metrics differ by region, weather, season, and city-specific characteristics. Analysis revealed variation in the relationship among ozone metrics, both across communities and across time within individual communities, indicating that conversion of ozone exposure metrics with a standard ratio introduces uncertainty. For example, the average ratio of the daily 8 h maximum to the daily concentration ranged from 1.23 to 1.83. Within a community, days with higher ozone levels had lower ratios. Relationships among metrics within a community were associated with daily temperature. The community-average exposure metric ratios were lower for communities with higher long-term ozone levels. Ozone metric ratios differed by season because of the different rate of change of ozone metrics throughout the year. We recommend that health effects studies present results from multiple ozone exposure metrics, if possible. When conversions are necessary, more accurate estimates can be obtained using summaries of data for a given location and time period if available, or by basing conversion ratios on data from a similar city and season, such as the results provided in this study.
已有多种暴露指标被应用于健康研究和政策制定中，以表示臭氧暴露，如 24 小时平均浓度和每日 8 小时最大浓度。通常，使用一种暴露指标计算出的结果会通过简单的比率转换来进行比较，或者将其与使用不同指标的结果进行结合。然而，这种转换假设该比率在不同地点和时间段是恒定的。我们通过检验 2000 年至 2004 年间美国 78 个社区内和社区之间各种形式的臭氧浓度（24 小时平均浓度、每日 1 小时最大浓度和每日 8 小时最大浓度）之间的关系，来研究这种转换方法的恰当性，并将结果与常用的转换比率进行了比较。我们还探讨了这种关系在不同地区、天气、季节和城市特征之间是否存在差异。分析结果表明，臭氧暴露指标之间的关系存在差异，无论是在社区之间还是在单个社区内部的不同时间内，这表明使用标准比率转换臭氧暴露指标会引入不确定性。例如，每日 8 小时最大浓度与日浓度之间的平均比值范围为 1.23 至 1.83。在一个社区内，臭氧水平较高的日子比值较低。一个社区内各指标之间的关系与日温度有关。长期臭氧水平较高的社区，其社区平均暴露指标比值较低。由于臭氧指标在全年的变化率不同，因此各季节的指标比值也存在差异。我们建议，如果可能的话，健康影响研究应展示多种臭氧暴露指标的结果。如果需要进行转换，则如果有给定地点和时间段的数据汇总，则可以使用更准确的估计值；或者可以根据类似城市和季节的数据来建立转换比率，例如本研究中提供的结果。
