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[ABSTRACT]Increasing experience of periods of impaired visibility is assumed to be due to increased air pollution in Kathmandu valley. It is observed that the number of clear days in Kathmandu Valley is decreasing since the past two decades. In Nepal, very few studies have focused on the status of visibility in Kathmandu Valley. This study tries to find a linkage between Visibility, Particulate matter 10 (PM10) and Meteorological parameters in the Kathmandu valley. In this study we have considered daily 24-hour average PM10 concentration recorded in six air monitoring site in Kathmandu Valley as the PM10 concentration of Kathmandu Valley. The duration of the PM10 data ranges from 2003 to 2005. Similarly, meteorological data were obtained from the weather monitoring station of the Department of Hydrology and Meteorology located at Tribhuvan International Airport (TIA) for the period 2003 to 2005. For better representation of the influence of PM10 and meteorological parameters, only those days were considered with data from 6 air monitoring sites, and meteorological data from the weather station. The trend in the mean visibility is increasing as we go from 2003 to 2005 i.e. 7.5467 km to 8.1267 km respectively. The mean visibility is highest in monsoon 8.6131 km, which decreases with post monsoon 7.8781 km, pre monsoon 7.0356 km and winter 6.5363 km respectively in a descending order. The Chi-square test of independence at 0.05 level of significance, reveled that mean visibility in the Kathmandu Valley depends on the different seasons of Kathmandu Valley. In the case, of variation of visibility, with the time of the day, it was found to increase gradually with the commencement of day peaking at 2:45 P.M and declining with the onset of night. Irrespective of season, it is observed that as the day progresses the temperature increases, the wind becomes turbulent, humidity decreases and foggy weather disappears. This might be the reason for highest visibility during the noon time. The analysis of variance of mean visibility with different time of the day shows that the mean visibility was found to differ significantly with the different time of the day. Meteorological parameters like temperature (minimum and maximum), rainfall, wind speed, pressure, total cloud and humidity were also found to affect mean visibility.

This study comprised of air quality monitoring during the day time at three municipalities of Banepa, Dhulikhel and Panauti(Known as Banepa Valley) in Kavre district of Nepal. The study was conducted in order to establish a baseline air quality data for those municipalities as the first time ever in the district. In each of those municipalities three air monitoring stations were established representing predominant industrial, commercial and residential areas. Nitrogen Dioxide (NO2) had been estimated from air sampling programme which spanned 7 months and a total of 126 days reflecting winter, premonsoon and monsoon seasons. Low Volume Air (LVA) Sampler and Personal air sampler were used for sampling. UV spectrophotometer was used for estimation of the NO2. The study found that during winter season the concentration of NO2 was more and among the areas commercial area found to be highest level pollution. The over all mean, minimum and maximum level of NO2 was found to be 24.62μg/m3, 11.26μg/m3, 91.20μg/m3 in the Banepa valley. The seasonal trend in pollution levels show that winter > pre-monsoon > monsoon. The pollution concentration trend noted among the areas was commercial > industrial > residential on almost all the occasions. This finding conclude that, most of the time NO2 level are below the National Ambient Air Quality Standards (NAAQS) and World Health Organization (WHO) guideline representing little risk at present in Banepa Valley however commercial area of Banepa is more polluted and is associated with higher NO2 concentration compared to other areas. Keywords: NO2, Nepal, Banepa, air quality, personal air sampler DOI: 10.3126/kuset.v4i1.2878 Kathmandu University Journal of Science, Engineering and Technology Vol.4, No.1, September 2008, pp 1-11