An assessment of the impact of black carbon on air quality and climate in the Kathmandu Valley and surroundings - a model study

• Applicant: Professorin Dr. Andrea Mues
• Subject Area: Atmospheric Science
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262641669

• Final Report Year: 2019

Final Report Abstract

The general objective of the BERLiKUM project was to design and conduct studies aimed at getting better insights into the processes and mechanisms relevant to air quality in the Kathmandu Valley and its surroundings. Adverse air quality is a major environmental and health concern in Nepal and particularly in the urban areas of the Kathmandu Valley. The studies designed for the BERLiKUM project included an analysis of the meteorological conditions and dynamical processes in the valley and their effect on the mixing of pollutants in the atmosphere. In addition to meteorology, local and regional emissions are expected to play a key role for the observed air pollution. Another part of the project was therefore to analyze the black carbon emission in the Kathmandu Valley with measurement and to compare the results with sateof-the-art emission databases for this region. The main focus in this project was on particulate matter and black carbon in particular. The main tool to address these research questions was the Weather Research and Forecasting Model version 3.5.1 (WRF – meteorology only) and an extended version including chemistry and aerosols (WRF-Chem). An evaluation of the simulated meteorology and air pollutants using the WRF and WRF-Chem model for the region of south Asia and Nepal with a focus on the Kathmandu Valley was conducted. The results show that the model is often able to capture important meteorological parameters inside the Kathmandu Valley. The results for most meteorological parameters are well within the range of biases found in other WRF studies especially in mountain areas. However, the evaluation results also clearly highlight the difficulties of capturing meteorological parameters in such complex terrain and reproducing subgrid-scale processes. The measured black carbon concentrations were systematically and strongly underestimated by WRF-Chem. To address these issues, a higher horizontal resolution in the model would be necessary, which would then also require a higher resolution of the input data. Such input data are currently not available for this region. The results strongly suggest that the applied emission data of black carbon are underestimated for the valley and there is a strong need for further improvements of the local emissions data. High-resolution emission data for the valley were not available. In the BERLiKUM project a method was developed to estimate black carbon emission fluxes for the Kathmandu Valley from measured mixing layer height data and black carbon concentrations. Based on the assumption that black carbon aerosols are vertically well mixed within the mixing layer and the finding that the mixing layer varies only little during night time and morning hours, black carbon emission fluxes are estimated for these hours and per month. Even though this method is relatively simple, it can give an observationally based first top-down estimate of the black carbon emissions in this region, especially illuminating the seasonal cycle of the emission fluxes. A model sensitivity study with WRF-Chem using the estimated emission values in the Kathmandu Valley shows significantly reduced biases. This confirms the strong need for an updated black carbon emission database for this region. However, it also became clear that a simple correction of the emission fluxes using the top-down method also has several limitations and uncertainties. One of these limitations is an over-representation of emissions which are relatively constant throughout the day (e.g. from brick kilns) while under-representing emissions which are mainly occurring during the daytime (e.g. traffic). Another important module of the project was the cooperation with regional scientists and other experts as well as the transfer of results and outreach activities. The project cooperated with other scientist especially modelers in order to discuss modelling results and to compare work. The results of the research in the BERLiKUM project have be published in first author and co-author paper in scientific journals. Furthermore, an international workshop was planned and organized together with colleagues from the Center for International Climate Research (CICERO, Norway) and the University Oslo. The workshop discussed various aspects of air pollution science, and to which extend modeling tools may increase our current understanding in this research field.

Publications

• Air quality modelling in the Kathmandu Valleyand surroundings - International REKLIM conference "Our climate our future; regional perspectives on a global challenge". Conference proceedings, programme, abstracts, (Terra Nostra ; 2014), International REKLIM conference "Our climate our future; regional perspectives on a global challenge" (Berlin, Germany 2014), p. 83-84
  Mues, A., Lauer, A.
  
• Measurement and modeling activities in Nepal in framework of the SusKat project. - In: Mitto, T., Fallmann, J., Mikolajczyk, U., Suppan, P., Singh, V., Sokh, R. S. (Eds.), - Proceedings of Abstracts 9th International Conference on Air Quality – Science and Application, 9th International Conference on Air Quality – Science and Application (Garmisch- Partenkirchen, Germany 2014), p. 193
  Mues, A., Lauer, A., Rupakheti, M., Panday, A.
  
• (2015): Atmospheric brown clouds reach the Tibetan Plateau by crossing the Himalayas. - Atmospheric Chemistry and Physics, 15, 11, p. 6007-6021
  Lüthi, Z. l., Škerlak, B., Kim, S.-W., Lauer, A., Mues, A., Rupakheti, M., Kang, S.
  
• (2016): PM Modelling over Nepal with WRF-Chem. - In: Steyn, D. G., Chaumerliac, N. (Eds.), Air Pollution Modeling and its Application XXIV, (Springer Proceedings in Complexity), Cham : Springer International Publishing, 1, p. 319-323
  Mues, A., Lauer, A., Rupakheti, M.
  
• The seasonal cycle of the mixing layer height and its impact on black carbon concentrations in the Kathmandu Valley (Nepal), Geophysical Research Abstracts ; Vol. 18, EGU2016-7832, 2016, General Assembly European Geosciences Union (EGU) Vienna, Austria 2016
  Mues, A., Rupakheti, M., Hoor, P., Bozem, H., Münkel, C., Lauer, A., Butler, T. M.
  
• (2017): Investigation of the mixing layer height derived from ceilometer measurements in the Kathmandu Valley and implications for local air quality. - Atmospheric Chemistry and Physics, 17, 13, p. 8157-8176
  Mues, A., Rupakheti, M., Münkel, C., Lauer, A., Bozem, H., Hoor, P., Butler, T. M., Lawrence, M. G.
  
• (2018): Observation and analysis of spatiotemporal characteristics of surface ozone and carbon monoxide at multiple sites in the Kathmandu Valley, Nepal. - Atmospheric Chemistry and Physics, 18, 19, p. 14113-14132
  Mahata, K., Rupakheti, M., Panday, A. K., Bhardwaj, P., Naja, M., Singh, A., Mues, A., Cristofanelli, P., Pudasainee, D., Bonasoni, P., Lawrence, M. G.
  
• (2018): Variations in surface ozone and carbon monoxide in the Kathmandu Valley and surrounding broader regions during SusKat-ABC field campaign: Role of local and regional sources. - Atmospheric Chemistry and Physics, 18, 16, p. 11949-11971
  Bhardwaj, P., Naja, M., Rupakheti, M., Lupascu, A., Mues, A., Panday, A. K., Kumar, R., Mahata, K., Lal, S., Chandola, H. C., Lawrence, M. G.
  
• (2018): WRF and WRF-Chem v3.5.1 simulations of meteorology and black carbon concentrations in the Kathmandu Valley. - Geoscientific Model Development, 11, 6, p. 2067-2091
  Mues, A., Lauer, A., Lupascu, A., Rupakheti, M., Kuik, F., Lawrence, M. G.