| Krishna Murthy, V., Giri, D., Sanjay Nath Khanal, School of Science, Kathmandu University, Dhulikhel, Kavre, Nepal |
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ABSTRACT
Air borne particulates of smaller size and mass are persistent in the ambient environment; exert health impact to exposed resident population in urban setting. These particulates act as nuclei or substrates on which many other pollutant gases could be adsorbed, form secondary pollutants and result in synergistic health effects. The statistical analysis of PM10 values in Kathmandu valley has been carried to assess spatial distribution and seasonal effects on PM10 in urban area of Kathmandu Valley. For this purpose, one year PM10 mass concentration levels obtained from daily 24-hour air sampling at six air monitoring stations of Kathmandu valley (Matsyagaon, Tribhuvan University, Bhaktapur, Thamel, Patan hospital and Putalisadak) are considered for statistical analysis. The data was available in the public domain of the website of His Majesty's Government, Nepal, Ministry of Population and Environment (MOPE). The difference on the average PM10 in Matsyagaon and Putalisadak is attributable to Matsyagaon, falling under village development category and quality of air in Matsyagaon was under ‘good’ category (67.6% values falling within 0-60 µg/m3). The quality of air in TU was under the ‘moderate’ (60-120µg/m3) category - 38.3% values in good and 43.9% in moderate category, whereas the quality of air in Bhaktapur, Thamel, Patan Hospital and Putalisadak were under ‘Unhealthy’ category since majority of the observations fell in the range prescribed for unhealthy category (121-350 µg/m3); in Thamel it was 58.9%, in Patan hospital it was 76.1% and in Putalisadak it was 79.4%. However, the overall observed PM10 pollution falls in unhealthy category 964 values falling in the ‘unhealthy’ range of 121-350µg/m3, (47.39%) suggesting deteriorating trend of air quality in the valley. The seasonal variation with respect to particulate pollution indicate that pre-monsoon and winter seasons vulnerable to high PM10 concentration in the valley. The disturbing findings were that in Putalisadak commercial area monsoon exerted no beneficial effect in reduction the particulate pollution level; the Thamel and Patan hospital areas are rapidly shifting to high levels of pollution; Bhaktapur area, located outside the ring road, also showed a shift from good category to moderate in monsoon season. Thus majority of areas of the valley are exhibiting shifting trend to a dominance of particulate pollution scenario in the valley and not allowing the particle-reducing induction good effect of rainfall. A guiding principle in mitigating particulate pollution in the valley to a large extent is to allow the monsoon to exert its positive influence to the fullest possible reduction and washing effect of particulates thereby minimizing rate of particulate re-suspension in the ambient air.
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