In this natural intervention study, we evaluated the impact of vehicular shutdown during bandhas (general strikes) and meteorological parameters on ambient PM10 concentrations (particulate matter of aerodynamic diameter 10 μm or less) in the Kathmandu Valley, Nepal. Publicly available PM10 data (January 2003-February 2008) collected at six monitoring stations were combined with meteorological and bandh data. Linear mixed effects regression models were used to examine the effects of bandhas on PM10 concentrations. Lower PM10 concentrations were observed during the monsoon season compared to the winter, across all monitoring stations, with the largest reduction observed for the urban high traffic area (mean ± standard deviation: 290 ± 71 vs 143 ± 36 μg/m(3)). In the high traffic area, there was 36 μg/m(3) decrease in PM10 concentration during the bandh period compared to 2 days preceding the bandh, adjusting for season, rainfall, temperature, and windspeed. The improvements in air quality were short lived: PM10 concentration in the urban high traffic area increased by an average of 26 μg/m(3) within the first 2 days after the bandh. Our results suggest that controlling vehicular traffic can have an immediate impact in improving particulate matter air quality even among the most polluted cities in the world.
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