Interactive short-term effects of equivalent temperature and air pollution on human mortality in Berlin and Lisbon
Introduction
Many epidemiological studies have demonstrated an association between air pollution and adverse health effects, linking high levels of several pollutants to increases in all-cause and cause-specific mortality and morbidity (Dockery et al., 1993, Samet et al., 2000). Specifically, particulate matter (PM) has been linked to severe health outcomes (Pope and Dockery, 2006, Brook et al., 2010, Rückerl et al., 2011), and ozone (O3), one of the most toxic photochemical pollutants, has consistently been associated with cardio-respiratory and all-cause mortality with varying effects across seasons and geographic regions (Bell et al., 2004, Bell et al., 2005, Ito et al., 2005, Levy et al., 2005). In addition to air pollution, the effects of temperature on human health have been increasingly recognised (Patz et al., 2000, Basu and Samet, 2002, Curriero et al., 2002, Medina-Ramón and Schwartz, 2007, Baccini et al., 2008, Basu, 2009). The majority of studies have identified U-, V-, or J-shaped temperature-mortality curves with increasing mortality levels at high and low temperatures. Although cold exerts an adverse effect on human health, with mortality increasing with decreasing temperatures over a wide range of values, the tremendous excess mortality observed during heat waves (e.g., the Chicago heat wave of 1996 and the European heat wave of 2003) has led to an extensive research effort on high temperatures and mortality (Schär and Jendritzky, 2004, Kaiser et al., 2007, Robine et al., 2007). In this context, urban populations are of major interest because of their high-density of susceptible individuals and often risk-aggravating environmental conditions (Smoyer et al., 2000, Kinney et al., 2008). Furthermore, higher ambient temperatures in urban areas caused by the anthropogenic modification of the urban climate (i.e., urban heat islands) are likely to increase adverse heat-related health effects.
While most studies investigating the effects of air pollution have adjusted for temperature as a confounder, the role of air pollution is often not considered when assessing the effects of temperature. So far, only a few studies have focused on the potential interactions between air pollution and temperature or effect modification (Samet et al., 1998, Roberts, 2004, Ren and Tong, 2006, Ren et al., 2006, Ren et al., 2008a, Ren et al., 2008b, Li et al., 2011, Cheng and Kan, 2012, Meng et al., 2012). However, air pollution may make people more vulnerable to the effects of temperature variability, and similarly (extreme) temperature may make people more vulnerable to the effects of air pollution (Gordon, 2003, Ren et al., 2006).
In this study, we aimed to investigate the joint or interactive effects of meteorological conditions (i.e., thermal conditions) and air pollution (using ozone and particulate matter as predictors). We chose Berlin and Lisbon as study areas as we aimed to investigate differences in interactive effects in a temperate and a Mediterranean/subtropical climate. Southern European regions are of great interest as they – unlike Southern cities in the US – show augmented heat effects in comparison to more Northern areas (Curriero et al., 2002, Medina-Ramón and Schwartz, 2007, Baccini et al., 2008; D'Ippoliti et al., 2010). While the climate differs, there are several similarities between the two cities which facilitate conclusions about the role of climate or other modifiers. Both cities are metropolitan areas and capital cities and they feature comparable characteristics regarding age structure, death rate, life expectancy, size and air pollution levels. We addressed the research matter by (1) visually examining the relationship between mortality, equivalent temperature and air pollution using so-called response surface models; and (2) categorizing the data sets by air pollution level and equivalent temperature respectively and conducting parametric regression analysis to quantify atmospheric interactive effects.
Section snippets
Mortality data
Daily death counts for Berlin were provided by the State Statistical Institute Berlin-Brandenburg for the time period from 1998 to 2010. For Lisbon, daily death counts from 1998 to 2008 were provided by the Instituto Nacional de Estatística. We abstained from a further stratification by cause of death to retain a sufficient number of cases for statistical analysis, which was important for the response surface analysis and the analysis categorizing by air pollution level and equivalent
Description of atmospheric conditions
Both Berlin and Lisbon are classified as mesothermal “C”-climates according to the Koeppen–Geiger classification (Kottek et al., 2006). Furthermore, Berlin is classified as maritime temperate or oceanic “Cfb”-climate and Lisbon as dry summer subtropical or Mediterranean “Csa”-climate. Berlin shows considerable precipitation in all seasons, while Lisbon is rather dry during the summer months from June to September (Fig. 1). The annual average temperature for the study period in Berlin is
Discussion
This study demonstrated the influence of thermal conditions and air pollution on human all-cause mortality in Berlin and Lisbon. Moreover, the findings provided evidence for the interactive effects between air pollution (i.e., O3 and PM10) and equivalent temperature. We found that air pollution modified thermal effects (essentially heat effects) and that thermal conditions modified air pollution effects.
In general, we found a J- or V-shaped equivalent temperature–mortality relationship with
Conclusions
This study provides evidence for the interactive effects between equivalent temperature and air pollution. Our study clearly demonstrated increased heat effects during periods of high air pollution levels. Particularly, O3 seemed to interact with high (equivalent) temperatures resulting in augmented mortality, observed for both cities. Interactive effects between PM10 and high (equivalent) temperatures were mostly observed for Lisbon while such interactions were less obvious for Berlin.
Acknowledgements
This research was partially funded by the German Academic Exchange Service (DAAD) and by the Conselho de Reitores das Universidades Portuguesas (CRUP). We are very grateful to the Berlin Senate Department for Urban Development and Environment for their kind provision of air quality data.
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