<P> Smog is a regular problem in Southeast Asia caused by land and forest fires in Indonesia, especially Sumatra and Kalimantan, although the term haze is preferred in describing the problem . Farmers and plantation owners are usually responsible for the fires, which they use to clear tracts of land for further plantings . Those fires mainly affect Brunei, Indonesia, Philippines, Malaysia, Singapore and Thailand, and occasionally Guam and Saipan . The economic losses of the fires in 1997 have been estimated at more than US $9 billion . This includes damages in agriculture production, destruction of forest lands, health, transportation, tourism, and other economic endeavours . Not included are social, environmental, and psychological problems and long - term health effects . The second - latest bout of haze to occur in Malaysia, Singapore and the Malacca Straits is in October 2006, and was caused by smoke from fires in Indonesia being blown across the Straits of Malacca by south - westerly winds . A similar haze has occurred in June 2013, with the PSI setting a new record in Singapore on June 21 at 12pm with a reading of 401, which is in the "Hazardous" range . </P> <P> The Association of Southeast Asian Nations (ASEAN) reacted . In 2002, the Agreement on Transboundary Haze Pollution was signed between all ASEAN nations . ASEAN formed a Regional Haze Action Plan (RHAP) and established a co-ordination and support unit (CSU). RHAP, with the help of Canada, established a monitoring and warning system for forest / vegetation fires and implemented a Fire Danger Rating System (FDRS). The Malaysian Meteorological Department (MMD) has issued a daily rating of fire danger since September 2003 . Indonesia has been ineffective at enforcing legal policies on errant farmers . </P> <P> Since start of winter season heavy smog loaded with pollutants covered major part of Punjab especially the city of Lahore, causing breathing problems and disrupting normal traffic . </P> <P> Doctors advised residents to stay indoors and wear facemasks outside . </P>

What is the chemistry behind formation of smog