The Short Version
The underlying science is sound — winter temperature inversions and low winds in North India do trap pollutants near the ground, and stubble-burning smoke contributes to smog episodes. However, no primary CPCB document in the available evidence contains the specific statement attributed to the board. The claim relies on secondary academic citations of CPCB data, which is not the same as a direct institutional declaration. Additionally, the framing overstates stubble burning's role; research shows winter smog often intensifies after farm fires fade, driven by multiple emission sources.