Kathmandu, August 19 Kathmandu Valley has witnessed a decline in air pollution levels since the start of monsoon. According to Department of Environment, due to continuous rainfall very little dust particles are found suspended in the air in the Valley. Information Officer and Senior Divisional Chemist at the Environment Department Shankar Prasad Paudel said air pollution levels normally remained below the national standards during monsoon season. Currently, five air quality monitoring stations are in operation in the Valley. Last year, in August the government had resumed air quality monitoring in Kathmandu Valley by installing a station at Ratnapark. Since then the government has been running three stations in Ratnapark, Pulchowk and Dhulikhel.Besides the government run air quality monitoring stations in Kathmandu, Nepal had begun accessing US Embassy Air Quality Monitor data. Although the practice of monitoring levels of air pollution began in Nepal in 2002 with the installation of seven air quality stations in the Valley by the Danish government, all stations were shut down by 2009.