India, Dec. 31 -- Dense fog continued to severely disrupt air and rail travel across the National Capital Region on Tuesday, causing massive delays at Delhi's Indira Gandhi International Airport and affecting over 50 trains, even as air quality showed marginal improvement, but remaining firmly in the hazardous range.

Delhi's 24-hour average Air Quality Index (AQI) registered at 388 ("very poor") at 4pm Tuesday, a marginal decline from Monday's 401 ("severe"). However, the wider region fared worse. Ghaziabad recorded the country's worst air with an AQI of 404 ("severe"), followed by Noida at 400 and Greater Noida at 366 (both "very poor").

Forecasts indicate the reprieve is fleeting. The Air Quality Early Warning System predicts air qual...