Kathmandu, Sept. 24 -- Kathmandu's air quality has just got considerably worse, not just because of dirtier air, but because the World Health Organisation (WHO) has revised its Global Air Quality Guidelines, halving the recommended value for annual average pollution levels.

Safe exposure to concentrations of harmful particles below 2.5 microns (PM2.5) in diameter every year has now been halved, meaning that many Kathmandu residents could be breathing much morepolluted airthan they throught.

On 22 September the WHO updated its Air Quality Guidelines (AQG) such that annual mean concentrations of PM2 should not exceed 5 kg/m3and NO2not exceed 10 kg/m3. In addition, peak season mean 8-hr ozone concentration should not exceed 60 kg/m3.

The ...