Impact of vehicular strike on particulate matter air quality: Results from a natural intervention study in Kathmandu valley Michelle Fransen a , Joanne Pe ´ rodin a , Jayjeev Hada b , Xin He c , Amir Sapkota a,n a Maryland Institute for Applied Environmental Health, University of Maryland School of Public Health, College Park, MD 20742, USA b COMMITTED Nepal, Kamaladi Sadak, Kathmandu, Nepal c Department of Epidemiology and Biostatistics, University of Maryland School of Public Health, College Park, MD 20742, USA article info Article history: Received 2 March 2012 Received in revised form 11 December 2012 Accepted 13 December 2012 Available online 20 February 2013 Keywords: Air pollution Particulate matter Kathmandu Natural intervention Vehicular strike abstract In this natural intervention study, we evaluated the impact of vehicular shutdown during bandhas (general strikes) and meteorological parameters on ambient PM 10 concentrations (particulate matter of aerody- namic diameter 10 mm or less) in the Kathmandu Valley, Nepal. Publicly available PM 10 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 PM 10 concentrations. Lower PM 10 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 (mean7standard deviation: 290 771 vs 143736 mg/m 3 ). In the high traffic area, there was 36 mg/m 3 decrease in PM 10 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: PM 10 concentration in the urban high traffic area increased by an average of 26 mg/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. & 2013 Elsevier Inc. All rights reserved. 1. Introduction Epidemiological studies, primarily from North America and Europe, have linked exposure to particulate matter with adverse health outcomes such as mortality, cardiovascular diseases and hospitalization for asthma exacerbation (Brunekreef and Holgate, 2002; Dockery and Pope III, 1994; Dockery et al., 1993; Le et al., 2002; Pope III et al., 1995). A more recent study with data from 20 large metropolitan cities reported that a 10 mg/m 3 increase of PM 10 (particulate matter of aerodynamic diameter 10 mm or less) was associated with a 0.51 percent increase in all cause mortality and a 0.68% increase in cardiovascular and respiratory mortality (Samet et al., 2000). Other studies have shown exposure to increased levels of PM 10 to be associated with low birth weight (Shah and Balkhair, 2011), preterm birth (Parker et al., 2008; Sapkota et al., 2012; Woodruff et al., 2003), decreased sperm motility (Selevan et al., 2000), cardiovascular disease (Bae et al., 2010; Roux et al., 2008), and lung cancer mortality (Pope III et al., 2002). Although the evidence of adverse health effects associated with particulate matter exposure are compelling, the majority of data used in deriving these conclusions are from high income countries where the particulate matter levels are markedly lower compared to lower income countries. For instance, the daily PM 10 levels in Kathmandu, Nepal can regularly exceed the United States Environ- mental Protection Agency’s 24-hour National Ambient Air Quality Standard of 150 mg/m 3 , especially in the cold winter months (Dongarra et al., 2010; Giri et al., 2008; Joshi, 2003). The high level of air pollution in the Kathmandu Valley is primarily attributable to industries and transportation (Giri et al., 2008). As of 2004, almost 250,000 cars, buses, minibuses, trucks, vans and motorcycles are registered in the Kathmandu Valley. Most of these vehicles are older and, unlike industries, there are no coherent regulations in place to control the emissions from the vehicles that are present in Kath- mandu Valley (Joshi, 2003). Dust resuspension from the poor road quality, tire burning and the use of biofuels for cooking and heating add to the increase in particulate matter concentrations. Under- standing the sources of this unusually high pollution combined with information on the extent to which controlling such sources alleviate the problem is a first step towards improving air quality and protecting health in these areas. Natural experiments consisting of short term cessation of source activity are important from policy perspectives as they offer a very unique opportunity to study the direct impact of these sources on ambient particulate matter (Friedman et al., 2001; Wang et al., 2009). Within the past 20 year period (1990–2010), the political system in Nepal has gone from a party-less political system Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/envres Environmental Research 0013-9351/$ - see front matter & 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.envres.2012.12.005 n Correspondence to: Maryland Institute for Applied Environmental Health, University of Maryland College Park School of Public Health, 2234F SPH Building, College Park, MD 20742, USA. Fax: þ1 301 314 1012. E-mail address: amirsap@umd.edu (A. Sapkota). Environmental Research 122 (2013) 52–57