The Compounding Burden of Heat and Air Pollution
Very hot days are deadlier when the air is dirty: across 620 cities, a very hot day raised deaths by 12.8% when particle pollution was high against 5.3% when it was low. And the two hazards travel together — in 2024 ozone was higher on hot days in 131 of 149 large cities. About 2.6 billion people live in countries that are both hot and polluted, three-quarters of the population of lower-middle-income countries against 4% in high-income ones.