Go outside and take a long, deep breath. Do your lungs feel suitably refreshed? If you’re in any one of a growing number of cities, the answer to that question may well be ‘no’. According to the World Health Organization (WHO), a staggering 98% of large cities (those with more than 100,000 inhabitants) in low- and middle-income countries do not meet minimum air quality guidelines. The situation is better in high-income countries, but still, less than half of cities are up to standard.

Hydrocarbons are precursors to hazardous air pollutants including ozone and particulate matter. Hydrocarbons from diesel make up over 50% of all hydrocarbons in the air in London, a new study has found. The authors also estimate that they contribute up to half of total ozone production potential in London, and say future air quality control strategies must focus more on these pollutants.