Something in the air


Epidemiologists are using increasingly precise means to determine just how much fine dust we inhale. This may help us to find out more about the health risks of these particles. By Angelika Jacobs

(From "Horizons" no. 105, June 2015)

​There are hundreds of scientific publications describing the health effects of breathing in the fine dust and chemical compounds that arise principally from combustion processes. It seems obvious to everyone today that air pollution contributes to respiratory illness, but in fact such links are difficult to prove.

One major criticism of epidemiological studies on air pollution is that they rely on data from just a few central measuring stations that don’t necessarily reflect the actual exposure of the participants in the study. The concentration of pollutants can vary greatly according to location.

Individual exposure

For some time now, epidemiologists have been focussing particularly on so-called ultrafine particles (UFPs). Their very small size – less than 100 nanometres – means they can enter the bloodstream and quite possibly even advance into the brain. However, the health effects of this fine dust have been little researched until now. UFPs are distributed very unevenly in the air. So when epidemiological studies use data gathered at a central measuring location, there’s no way to be sure just how reliable it is.

This issue has been under investigation by Nino Künzli and Reto Meier of the Swiss Tropical and Public Health Institute (SwissTPH) in Basel. They have compared UFP measurements from central reference stations in 80 residential locations. Their research is part of the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults (SAPALDIA) headed by Professor Nicole Probst-Hensch. “The measurements can differ by a factor of two and more”, says Meier. UFP concentrations depend on the distance from the emission source, which is primarily road traffic. This is why attention has to be paid to the proximity to roads and to the wind direction when choosing locations for making representative measurements.

Indoor air, outdoor air

All the same, doubts remain as to just how representative such data really is. Most people spend a large portion of their time indoors, but most measurements have always been made in the open air. This is why Meier and his colleagues have also investigated the connection between the air quality in living spaces and the air quality outside. Exposure inside buildings was generally rather lower, but in fact correlated pretty well with measurements made outside during the course of the day. As Meier explains, this means that data from outside measuring stations could actually allow us to estimate the concentration of indoor pollutants. “But there are also sources of pollutants in people’s apartments. UFPs occur while cooking, for example”. So there was a clear, corresponding rise in air pollution indoors at mealtimes, namely at midday and in the evening.

There has already been a series of studies on the relationship between indoor and outdoor air quality, says Josef Cyrys of the Environmental Science Center at the University of Augsburg, who was not involved in the current project. “But the available data is meagre, especially on UFPs, and every new study helps us to get a clearer picture”. However, what he finds the study lacks is a perspective on how the new findings might be useful to epidemiologists.

Reto Meier cautions that this question can become exceedingly complex. Particles indoors can also be composed differently from outdoor particles. “These contrasts will probably only become greater in future, as buildings are constructed or renovated according to new energy standards and become more and more sealed off from the outside”, confirms Künzli. In future, people will be able to carry out personal pollutant measurements with their smartphones. This, says Künzli, will open up whole new possibilities for matching the impact of particles to their different sources.

Angelika Jacobs is a science journalist and is currently working for the Neue Zürcher Zeitung.

R. Meier et al.: Ambient Ultrafine Particle Levels at Residential and Reference Sites in Urban and Rural Switzerland. Environmental Science & Technology, 2015.

R. Meier et al.: Differences in indoor versus outdoor concentrations of ultrafine particles, PM2.5, PMabsorbance and NO2 in Swiss homes. Journal of Exposure Science and Environmental Epidemiology, 2015.