2023 – the crossroad: Yearend analysis of PM2.5 pollution in Delhi

December 31, 2023

The gradual long term improvement in annual PM2.5 levels since 2015-17 is halted in 2023. This has happened despite cleaner than usual summer and monsoon seasons, and much lower ingress of smoke from farm stubble fires in northern states. But this winter has witnessed unusually low surface wind speed that has trapped local pollution that is already high.

Due to the impact of the unusual winter levels the overall annual levels have plateaued and even worsened undoing the gains of the long term downward trend. Even with the contribution of stubble burning to Delhi’s pollution going down this year, with more rains in November and less severe cold winter conditions, the annual level should have improved further. Instead, the worsening of meteorology - lowering of wind speed has tilted the scale adversely simply because the local pollution is still very high. Delhi needs more aggressive emissions reduction to meet the national ambient air quality standard.

Interestingly, summer and monsoon months in 2023 were unusually cleaner than the previous years. But winter levels turned out to be one of the worst due to very slow surface wind speed observed. This has impeded dispersion of pollution and further aggravated trapping of pollution and spiked the levels. This trapping of local pollution from all sides has made this winter exceptionally bad despite lesser smoke from farm stubble fires. The meteorology also explains lowerpollution peaks and relatively uniform bad air quality with minimal fluctuations in PM2.5 concentration throughout the season.