On the widespread winter fog in Northeastern Pakistan and India

During the last two winters widespread fog frequently occurred in northeast ern India and Pakistan, in a region extending over 1500 km. A particularly severe fog episode lasted from midDecember, 1998 to early January, 1999. Th e fog caused extensive economic damage and disruptions in transport. We det ermined concentrations of SO42-, NO3-, and selected trace elements at Lahor e, Pakistan during and after the fog event by collecting aerosols on Whatma n 41 filters every 12 h. SO42- concentrations of up to 100 mu g/m(3) were o bserved during fog. The SO42-/Se ratios and trace element data suggest a di stant source of SO42- aerosols, hundreds of kms away. Lahore was downwind o f coal-burning in India during the fog. The high concentrations of SO42- ob served suggest a more extensive investigation of the chemistry and transpor t processes in this region is necessary to delineate emission sources and d evelop control strategies as there are serious likely effects on human heal th and economy in a region populated by hundreds of millions of people, and on global climate change through direct;md indirect forcing.