Seasonal PM 10 dynamics in Kathmandu Valley Rupak Kumar Aryal a , Byeong-Kyu Lee b, * , Rahul Karki c , Anup Gurung c , Jaya Kandasamy a , Bipin Kumar Pathak a , Suman Sharma d , Nirita Giri e a Institute for Water and Environmental Resource Management, Faculty of Engineering, University of Technology, Sydney, Australia b Department of Civil and Environmental Engineering, University of Ulsan, San 29, Mugeo2-dong, Nam-gu, Ulsan 680-749, Ulsan, Republic of Korea c Department of Environmental Science and Engineering, Kathmandu University, Kavre, Nepal d Ministry of Population and Environment, Kathmandu, Nepal e Environment and Public Health Organization, Kathmandu, Nepal article info Article history: Received 7 June 2007 Received in revised form 23 May 2008 Accepted 13 August 2008 Keywords: Kathmandu valley PM 10 Seasons Correlation abstract Data on ambient PM 10 levels from six locations in the Kathmandu Valley recorded by means of continuous sampling using low volume air samplers from October 2002 to March 2007 were used to investigate PM 10 concentration dynamics in the valley. Monthly average data of the urban areas, which have much higher concentrations than the rural areas, even exceeded the daily standard level of PM 10 , in Nepal, 120 mmm 3 . Repetitive peaks and troughs each year indicated annual patterns. Monthly average showed seasonal patterns are different between rural area and urban sites. The highest monthly average concen- tration was observed in February, the end of winter in urban areas where as in rural found in spring, and the lowest concentration was observed in July (monsoon period). The continuous increase in PM 10 concentration from December to February in urban areas showed accumulation of PM 10 in the ambient air during the wintertime. Rainfall in June and September, during the monsoon period, caused a PM 10 concentration decrease, demonstrating that precipitation is effective in removing PM 10 from the valley. Cross correlation analyses among the PM 10 levels measured simultaneously at the sampling stations showed a poor relationship in winter; however, there were good relationships in the monsoon and post-monsoon seasons. Both the PM 10 concentration and the air-mixing environment in the valley were closely associated with the temperature and wind speed. Ó 2008 Published by Elsevier Ltd. 1. Introduction Thoracic ambient particulate matter (PM 10 ) is defined as particles less than 10 mm in aerodynamic diameter. It is well-documented that increased exposure to thoracic PM is associated with various adverse health effects, such as respiratory diseases, cardiovascular mortality, morbidity, and probably, malignant lung diseases (Donaldson and MacNee, 2001; Kan and Chen, 2003; Chang et al., 2005; Goldberg et al., 2006; Ostro et al., 2006). Ambient PM 10 represents a complex mixture of anthropogenic and natu- rally occurring airborne particles. There is increased evidence that most of the harmful components in PM 10 are particles formed from incomplete combustion of fossil fuels and pyrolysis of organic materials. A plethora of chemicals has been identified in contaminated ambient air, including polycyclic aromatic hydrocarbons (PAHs) and their nitro- and oxy-derivatives, strong acids and toxic metals (Fang et al., 2000; Lin et al., 2005). There have been many studies of the association between the prevalence of different air pollutants and adverse human health outcomes. PM 10 appears to be one of the most useful single measures of air pollution in a given area (US EPA, 1996; Kunzli et al., 2000; Schwartz, 2001). Most PM 10 studies have been conducted * Corresponding author. Tel.: þ82 52 259 2864; fax: þ82 52 259 2629. E-mail address: bklee@ulsan.ac.kr (B.-K. Lee). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ – see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.atmosenv.2008.08.016 Atmospheric Environment 42 (2008) 8623–8633