Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 13957-13971, 2015
© Author(s) 2015. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
17 Dec 2015
Seasonal variation of ozone and black carbon observed at Paknajol, an urban site in the Kathmandu Valley, Nepal
D. Putero1, P. Cristofanelli1, A. Marinoni1, B. Adhikary2, R. Duchi1, S. D. Shrestha3, G. P. Verza4, T. C. Landi1, F. Calzolari1, M. Busetto1, G. Agrillo1, F. Biancofiore5, P. Di Carlo5, A. K. Panday2, M. Rupakheti6, and P. Bonasoni1 1CNR-ISAC, National Research Council of Italy – Institute of Atmospheric Sciences and Climate, Via Gobetti 101, 40129 Bologna, Italy
2ICIMOD, International Centre for Integrated Mountain Development, G.P.O. Box 3226, Khumaltar, Lalitpur, Kathmandu, Nepal
3Ev-K2-CNR Committee, G.P.O. Box 5109, Paknajol, Kathmandu, Nepal
4Ev-K2-CNR Committee, Via S. Bernardino 145, 24126 Bergamo, Italy
5Center of Excellence CETEMPS, University of L'Aquila, Via Vetoio 1, 67010 Coppito (AQ), Italy
6IASS, Institute for Advanced Sustainability Studies, Berliner Strasse 130, 14467 Potsdam, Germany
Abstract. The Kathmandu Valley in south Asia is considered as one of the global "hot spots" in terms of urban air pollution. It is facing severe air quality problems as a result of rapid urbanization and land use change, socioeconomic transformation, and high population growth. In this paper, we present the first full year (February 2013–January 2014) analysis of simultaneous measurements of two short-lived climate forcers/pollutants (SLCF/P), i.e., ozone (O3) and equivalent black carbon (hereinafter noted as BC) and aerosol number concentration at Paknajol, in the city center of Kathmandu. The diurnal behavior of equivalent BC and aerosol number concentration indicated that local pollution sources represent the major contributions to air pollution in this city. In addition to photochemistry, the planetary boundary layer (PBL) and wind play important roles in determining O3 variability, as suggested by the analysis of seasonal changes of the diurnal cycles and the correlation with meteorological parameters and aerosol properties. Especially during pre-monsoon, high values of O3 were found during the afternoon/evening. This could be related to mixing and entrainment processes between upper residual layers and the PBL. The high O3 concentrations, in particular during pre-monsoon, appeared well related to the impact of major open vegetation fires occurring at the regional scale. On a synoptic-scale perspective, westerly and regional atmospheric circulations appeared to be especially conducive for the occurrence of the high BC and O3 values. The very high values of SLCF/P, detected during the whole measurement period, indicated persisting adverse air quality conditions, dangerous for the health of over 3 million residents of the Kathmandu Valley, and the environment. Consequently, all of this information may be useful for implementing control measures to mitigate the occurrence of acute pollution levels in the Kathmandu Valley and surrounding area.

Citation: Putero, D., Cristofanelli, P., Marinoni, A., Adhikary, B., Duchi, R., Shrestha, S. D., Verza, G. P., Landi, T. C., Calzolari, F., Busetto, M., Agrillo, G., Biancofiore, F., Di Carlo, P., Panday, A. K., Rupakheti, M., and Bonasoni, P.: Seasonal variation of ozone and black carbon observed at Paknajol, an urban site in the Kathmandu Valley, Nepal, Atmos. Chem. Phys., 15, 13957-13971, doi:10.5194/acp-15-13957-2015, 2015.
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Short summary
The aim of this paper is to present a full-year analysis of simultaneous measurements of ozone, black carbon, and aerosol number concentration at Paknajol, in the Kathmandu Valley, one of the global “hot spots” in terms of air pollution. Results indicate persisting poor air quality conditions throughout the measurement period, and suggest that the pollutants' variability is mainly driven by local pollution source activity, local- and large-scale dynamics, photochemistry, and vegetation fires.
The aim of this paper is to present a full-year analysis of simultaneous measurements of ozone,...