Lung disease

The EXHAUSTION project finds that more people die of lung diseases in European cities when high temperatures are combined with high levels of air pollution. This is especially true for those of us who are 65 and older.

What does the visualisation show us?

The visualisation shows the health impact of simultaneous exposure to high temperatures and particulate air pollution (PM2.5). It shows the percentage increase in deaths from lung diseases when the temperature increases from moderate to high levels, given low, medium or high air pollution levels. ”Moderate temperatures” are defined as temperature levels where only 25% of the days in a city are warmer, whereas ‘high temperatures’ are defined as temperature levels where 1% of the days are warmer. By ‘low’, ‘medium’ and ‘high’ air pollution levels, we mean the concentration level where, respectively, 95%, 50%, and 5% of the days have higher concentrations.

The researchers in EXHAUSTION have worked together to illustrate the health effects of interaction between air pollution and heat in Europe. Lead partner: Info Design Lab

The colored bars in the figure show the percentage change in number of deaths from lung diseases in European cities associated with hot weather (i.e. when the temperature increases from moderate to high levels), given different levels of air pollution (low, medium and high).  The light grey vertical lines show the confidence intervals, i.e. the range in which we can be quite sure the true mean values lies.

The first part of the figure (148 European cities) shows the result of a so-called meta-analysis. In a meta-analysis city-level analyses (such as those shown in the other parts of the figure for Oslo, Rome and Berlin) are pooled together to provide estimates that are based on a larger number of data points. The meta-analysis takes into consideration the findings in all cities, acknowledges between-city differences (e.g. each city has its own settings and differs from other cities), as well as within-country similarities (e.g. cities from the same country are more similar than cities from different countries), but also takes into consideration that there might be different level of uncertainty across the city-level analyses. Less weight is put on results that are very uncertain. We choose to include some examples of city-level results to show that there may be large differences in the results being pooled into the meta-analysis.

Gregoire Garec from the 7th arrondissement of Paris explains his experiences with heat waves in Paris.

Heart disease

The EXHAUSTION project finds that more people die of heart diseases in European cities when high temperatures are combined with high levels of air pollution. This is especially true for those of us who are 65 and older.

The researchers in EXHAUSTION have worked together to illustrate the health effects of interaction between air pollution and heat in Europe. Lead partner: Info Design Lab

Henna Ristikangas from Helsinki explains her experiences with heat waves in Helsinki.

Why do results differ across cities?

Populations in different cities can respond differently to environmental stressors such as heat and air pollution due to a number of reasons. For example, on average people living in Rome can handle hot temperatures better than people living in Oslo. This is due partly to physiological adaptation to temperature and also to various behavioral factors (e.g., keeping window shutters closed during hot days, dress lightly, keeping hydrated) as well as factors related to infrastructure (e.g., housing, use of fans and AC, access to cooling centers) and heat warning systems (in some cases heat-health action plans are in place). Other factors that can explain differential vulnerability, both to hot weather and air pollution, is the general health status of the population, a function of, e.g., demography (e.g., share of older adults) and prevalence of various diseases. A general challenge in epidemiological studies, which can also lead to differential results, is that it is difficult to estimate the actual individual exposure level of people.

The results of meta-analyses are generally assumed to give reliable indications of health risks, particularly when they are based on many individual results. The evidence based on one single study (here one single city), however, can be difficult to interpret. A major reason for this is the lower sample size, both in terms of population and the number of days where temperature and air pollution levels differ, leading to lower statistical power (i.e. ability to establish statistically significant estimates).

As an example, it is easy to study heat effects in Rome because it has many hot days, but it may be more difficult to study it in Oslo or Helsinki, where there are fewer hot days. Also, it is difficult to study effect modification by air pollution in cities which always have high air pollution levels and rarely any days with low air pollution level. Missing data can also distort the results, and particularly when the sample size is already small. For instance, if there are missing data on exactly the days that had high temperature and high air pollution level, this would lead to an even smaller sample size. For a city like Rome which has a high number of hot days, missing data on hot days would not cause problems, but for smaller and cooler cities, e.g., Oslo, losing a single hot summer day could be critical as gradients in the exposure level are needed to reveal effects. 

Finally, in our case using data from cities in different parts of Europe, another reason for incoherent results can be related to the fact that percentile values, and not absolute values, are used. In a colder region, reaching the 99th percentile temperature does not necessarily imply that a health damaging level is reached (i.e. a temperature level where physiological mechanisms leading to health damage are triggered). In a hot region, it is more likely that the 99th percentile exceeds temperature levels where such mechanisms are triggered.

The EXHAUSTION project finds that more people die of heart diseases in European cities when high temperatures are combined with high levels of air pollution. This is especially true for those of us who are 65 and older.

Download the slides on heart and lung, air pollution and heat here.

Find out more about this study conducted by EXHAUSTION researchers here: Interactive Effects of High Temperature and Air Pollution in Europe

You can also read more in this interview with Dr. Alexandra Schneider, at Helmholtz Munich.

Photo credit background photo: Unsplash.