Temperature-dependent association between mortality rate and carbon monoxide level in a subtropical city

The objective of this study was to explore the combined effect of temperature and air pollutant levels on daily non-accidental deaths and cardiovascular causes of mortality. In this study, associations were assessed by means of time-series analyses over the period 1995-1999 for Kaohsiung, Taiwan's largest industrial city, which has a subtropical climate. Ambient exposures to various air pollutants, including carbon monoxide (CO), sulfur dioxide (SO2), ozone (O3), nitrogen dioxide (NO2), and particulate matter (PM10), were estimated from the arithmetic means of all daily measurements taken by an air quality monitoring station nearest to the residential district. Generalized additive models with non-parametric spline were used to identify associations between daily mortality and air pollutants as well as the air pollutant-temperature interaction correlation.

Our findings indicate that CO is associated with increased risks of non-accidental and cardiovascular mortality. For a 0.2 ppm increase in CO, the increased relative daily risk of non-accidental death is at least 4% on the same day, when the mean temperature is above 24.8 °C, while the increased relative risk of mortality due to cardiovascular diseases is 7% 2 days later at below 19.7 °C. The study also suggests a statistically significant interaction between CO concentration and daily mean temperature, with non-accidental mortality increasing with a warm outdoor temperature and the effect of CO on cardiovascular mortality being modified by a cold climate. Further reduction of CO pollution is thus deemed crucial for the benefit of public health.