Ask anyone who polluting Kathmandu's air, you'll be told it's the old car-six wheelers, two wheelers, three wheelers and all. It's true to an extent but there are other culprits that are as, if not more, guilty. Welcome to the Valley's booming brick industry, which has grown with urbanisation, unchecked and unquestioned.

Environmentalists say Kathmandu residents breathe less oxygen and more pollutants throughout the year. Toxic intake touches a high December-May, which is when all the bricks needed for the city's expansion are baked.

Kathmandu has been growing every year and the kilns feed the construction. A 1992 study on kilns by the Metropolitan Environment Improvement Programme (MEIP) says there were 200 registered brick-makers in the Valley and none with any pollution control devices. Of these, 134 were operating in Lalitpur, 60 in Bhaktapur and six in Kathmandu district.

Clean Energy Nepal, a newly formed group that advocates reduced use of fossil fuels and promotion of renewable energy, is urging Valley residents who think this is a problem to speak up. The kilns burn anything-coal, rice husk, fuel wood, sawdust, lignite and sometime scrap tyres. Coal accounts for 65 percent of the total fuel burnt. Also there seem to be no rules governing where one can set up a kiln: you find them next to schools, residential suburbs and dense settlements on the Valley's outskirts.

Pollution from the kilns is worst during the dry season when there's no wind to dissipate the dust and smoke released by brick making. In addition to air pollution, the brick industry also degrades land. The report circulated by Clean Energy Nepal says one kiln occupies about 0.45 hectares of land for its smoke shaft and another 3.5 hectares to prepare mud and organise brick making. This land serves brick making for a few years after which it is rendered useless for agriculture.