The survey of pollution data in 6,475 cities on Tuesday showed that no country met the World Health Organisation’s (WHO) air quality standard in 2021. The survey also showed that smog even rebounded in some regions after a COVID-related dip. The global health body recommends that average annual readings of small and hazardous airborne particles known as PM2.5 should not exceed five micrograms per cubic metre. The WHO announced this after changing its guidelines in 2021 saying even low concentrations caused significant health risks. However, only 3.4 per cent of the surveyed cities met the stan…