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.