Efforts Made to Reduce Outdoor Air Pollution

Across the world, a wide range of measures has been established to reduce outdoor air pollution. Epidemiologists at LMU carried out a systematic review taking stock of the evidence. They suggest significant attention must be paid on study design and improved evaluation methods.

Several measures have been introduced globally with the objective of reducing outdoor air pollution and at the same time enhancing public health. These efforts include, for instance, the formation of low-emission zones, the subsidies for public transport, the regulation of industrial emissions, and limitations on the use of wood and coal for heating in private households. There is a clear connection between these actions and improved air quality and health, but it is actually hard to determine their effects.

It’s quite a challenge to evaluate the introduction of a measure like the low emission zone.

Jacob Burns, Institute for Medical Information Processing, Biometry and Epidemiology (IBE), Pettenkofer School of Public Health, LMU

It has been well established that there is a negative impact of air pollution on public health related to respiratory and cardiovascular diseases, among others. However, it is less clear whether or not measures developed to enhance outdoor air quality actually decrease the concentration of pollutants present and weaken their impacts on public health.

It’s important to remember how many factors influence both air quality and the relevant health conditions. Levels of energy consumption in industry, transport and domestic households all play a substantial role in air pollution levels, as does the weather.

Jacob Burns, Institute for Medical Information Processing, Biometry and Epidemiology (IBE), Pettenkofer School of Public Health, LMU

With regards to health, the risk of developing cardiovascular disease, for instance, is influenced both by breathing particulate matter and other pollutants and by many genetic, social, and physiological risk factors.

“This illustrates how difficult it can be to attribute changes in air pollutant concentrations, numbers of individuals admitted to hospitals, or mortality rates to any single measure.”

These difficulties are considered in the new review published in the Cochrane Library. Cochrane is a network of over 13,000 scientists, whose main focus was to improve the quality of the scientific understanding based on which policy decisions concerning human health are taken.

The new study’s authors, under the guidance of Professor Eva Rehfuess’ research group from the IBE at the Pettenkofer School of Public Health, presented the first systematic review with the aim to identify and critically value all studies that assess the impact of measures with a focus on improving air quality. The study takes into account 38 specific measures, which range from those to reduce traffic, to the regulation of industrial emissions and opportunities for cleaner and more efficient household heating systems.

For the most part, the studies that we reviewed show either positive or unclear effects. But these studies differ so much from one another that we could not, with confidence, draw general conclusions about what works and what does not work.

Jacob Burns, Institute for Medical Information Processing, Biometry and Epidemiology (IBE), Pettenkofer School of Public Health, LMU

However, the epidemiologists at LMU highlight that this is not an argument against such interventions. Actually, the authors obviously note that “it is important to emphasize that lack of evidence of an association is not equivalent to evidence of no association.” For them, the more significant message is that “the methods of evaluation in this area must be improved, so that decision-makers have a reliable basis on which to base their policy choices,” stated Rehfuess.

In this study, the scientists at LMU make many specific suggestions—especially with respect to the aim of future studies in this area, but of which few were also directed at policymakers.

According to Rehfuess, “At the moment, many studies are conducted retrospectively. Ideally, the evaluation could be incorporated into the planning and introduction of the measure.”