London – New research from the London School of Economics finds that denser cities are more likely to have higher levels of harmful air pollution. Urban planners need to address this if we are to have cities that promote health and wellbeing.

London School of Economics researchers Sefi Roth and Felipe Carozzi have published a new study on US cities showing that denser urban locations are associated with higher concentrations of fine particulate matter such as dust and soot (PM2.5). According to their estimates, doubling population density increases PM2.5 concentrations by 0.73 μg/m3, or an increase of 3.6%. This is associated with higher annual mortality costs as much as $630 per capita due to income lost due to disease or a shortened lifespan.

Their findings are turning conventional wisdom onto its head by suggesting that denser cities aren’t necessarily greener cities – at least not when it comes to air pollution. It is true that denser cities are associated with lower emissions thanks to shorter commutes or increased use of public transport, but when it comes to air pollution, what counts is not total emissions but rather the concentration of pollutants in the air. And this, according to their study, is higher in denser cities.

According to Roth and Carozzi, there are many arguments in favour of urban densification, but improved local air quality is not one of them. “Urban planners should take note of these trade-offs when designing the cities of the future,” conclude the researchers.