Affiliations: Graduate School of Engineering, Department of
Environmental Engineering, Osaka University, Japan | Environmental Pollution Control Center, Osaka
Prefecture, Japan | Institute of Engineering, Pulchok, Tribhuvan
University, Nepal
Abstract: The monthly concentrations of NO_2, NOx,
SO_2 and O_3 measured by a passive
sampler from February 2003 to January 2004 showed that the air pollution during
the winter season in Kathmandu valley was higher than the summer season. The
O_3 level was found the highest during April, May and June
due to strong radiation. The hourly concentrations of NO_2,
NOx, O_3 and suspended particulate matter (SPM) were also
measured by automatic instruments on December 2003. Temperature at the height
of 60 m and 400 m at Raniban Mountain in the northwest of Kathmandu valley was
measured on February 2001 in the winter season and the average potential
temperature gradient was estimated from observed temperature. Wind speed was
also measured at the department of hydrology, airport section, from 18 February
to 6 March 2001. It was found that the stable layer and the calm condition in
the atmosphere strongly affected the appearance of the maximum concentrations
of NO_2 and SPM in the morning, and that the unstable layer
and the windy condition in the atmosphere was considerably relevant to the
decrease of air pollution concentrations at daytime. The emission amounts of
NOx, HCs and total suspended particle (TSP) from transport sector in 2003 were
estimated from the increasing rate of vehicles on the basis of the emission
amounts in 1993 to be 3751 t/a, 30570 t/a and 1317 t/a, respectively. The
diurnal concentrations in 2003 calculated by the two-layers box model
reproduced the characteristics of air pollution in Kathmandu valley such as the
maximum value of O_3 and its time, the maximum value of NO
in the morning, and the decrease of NO and NO_2 at daytime.
The comparison with the concentrations in 1993 calculated suggested that the
main cause of air pollution was the emission from transport sector.
Keywords: air pollution concentration, Kathmandu vallay, box model
