Daily mortality and ozone – which metric?

Abstract

Background: Ozone is an aggressive gas but even worse it indicates a complex air pollution mixture. This highly reactive mixture of often only short-lived chemicals might even be better indicated not by the daily average ozone concentration but by the turn-over of ozone. We hypothesized that the daily variation in ozone concentration (the difference between night time low and early afternoon high half hour mean concentration) is a better predictor of health effects than the daily mean concentration. Methods: We performed a time series analysis on daily deaths (all causes, respiratory and cardiovascular causes as well as death in elderly 65+) in Vienna for the years 1991-2009. We controlled for seasonal and long term trend, day of the week, temperature and humidity using the same basic model for all pollutant metrics. Results: We found model ?t was best for same day variability of ozone concentration (calculated as the difference between daily hourly maximum and minimum) and hourly maximum. Of these the variability displayed a more linear dose-response function. Maximum 8h moving average and daily mean value performed not so well. Nitrogen dioxide (daily mean) in comparison performed better when previous day values were assessed. Same day ozone and previous day nitrogen dioxide effect estimates did not confound each other. Conclusion: Variability in daily ozone levels or peak ozone levels seem to be a better proxy of a complex reactive secondary pollutant mixture than daily average ozone levels in the Middle European setting. If this ?nding is con?rmed this would have implications for the setting of legally binding limit values.