Average concentrations of small, hazardous airborne particles known as PM2.5 hit 91.8 micrograms per cubic metre (mg/cu m) last year in the country, slightly higher than 2022. The WHO recommends levels of no more than 5 mg/cu m, a standard met by only 17% of cities last year. India, fifth in the smog rankings behind Chad, Bangladesh, Pakistan and the Democratic Republic of Congo, saw average PM2.5 fall 7% on the year to 50.6 mg/cu m. But it accounted for 12 of the top 20 most polluted cities, with Byrnihat, in a heavily industrialised part of the country's northeast, in first place, registering an average PM2.5 level of 128 mg/cu m.