Variability of particulate matter in Kathmandu and Pokhara Valley using Purple Air Sensor and an Overview of Origin of Pollutants

The concentration of fine and coarse mode particulate matters at the surface level over two major cities, Pokhara and Pulchowk of Nepal, were observed from January to September of 2020 by using particulate matter sensors. The hourly and daily averaged size segregated particulate matters of different size distributions are obtained for analysis. We have also compared the column-averaged aerosol optical depth (AOD) obtained from AERONET site. The average concentration of PM 2.5 was higher during the winter season, 99.64 μg/m³ and pre-monsoon season, 55.94 μg /m³ in Pulchowk and it was 58.96 μg/m³ and 38.50 μg/m³ in Pokhara. On February 1, the concentration of PM 2.5 raised to 201 μg /m³ in Pulchowk and 108 μg /m³ in Pokhara in the morning, whereas on April 11, it was 255 μg /m³ in Pulchowk and 238 μg /m³ in Pokhara in the morning. These data show that particulate matter concentration might have been significantly affected by traffic activities, and even cooking activities in the evening and morning along with the temperature. It is also observed that the data concentration is degrading particulate during precipitation, which was estimated by comparing data with the relative humidity observed by the sensor and precipitation amount over Pokhara.