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Black Carbon and Ozone Variability at the Kathmandu Valley and at the Southern Himalayas: A Comparison between a “Hot Spot” and a Downwind High-Altitude Site

Category: Aerosol and Atmospheric Chemistry

Accepted Manuscripts
DOI: 10.4209/aaqr.2017.04.0138
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Davide Putero 1, Angela Marinoni1, Paolo Bonasoni, Francescopiero Calzolari1, Maheswar Rupakheti2, Paolo Cristofanelli1

  • 1 National Research Council of Italy – Institute of Atmospheric Sciences and Climate, CNR–ISAC, 40129 Bologna, Italy
  • 2 Institute for Advanced Sustainability Studies, IASS, 14467 Potsdam, Germany

Highlights

Multi-year comparison of BC and O3 at Kathmandu and at the Nepali Himalayas (NCO-P).
BC and O3 at NCO-P are linearly correlated with PBL height over Kathmandu megacity.
22% (16%) of BC (O3) at NCO-P was explained by concurrent variations at Kathmandu.


Abstract

Several studies have reported the transport of short-lived climate forcers/pollutants (SLCF/P) from the highly polluted areas in south Asia (e.g., the Indo-Gangetic Plain and the Himalayan foothills) to the Himalayas, with significant implications for the global and regional climate, crop yields, and human health. In this work, we perform a comparison of nearly three years (February 2013–October 2015) of simultaneous black carbon (BC) and surface ozone (O3) measurements at two sites in Nepal, i.e., Paknajol (1380 m a.s.l.) in the Kathmandu Valley, and the WMO/GAW global station Nepal Climate Observatory-Pyramid (NCO-P, 5079 m a.s.l.), near the base camp of Mt. Everest. The two sites are only 150 km apart, and are characterized by different situations: while the Kathmandu Valley is one of the regional urban “hot spots” for what concerns air pollution, NCO-P is representative of the background conditions of the high Himalayas and the free troposphere. Therefore, the possible role played by emissions occurring in the planetary boundary layer (PBL) of the Kathmandu Valley in influencing the variability of these SLCF/P at NCO-P was investigated. BC and O3 concentrations at NCO-P showed linear correlation with the modeled PBL height over the Kathmandu urban area, providing evidence that the anthropogenic emissions occurring within the Kathmandu PBL could affect the variability of BC and O3 at NCO-P. Furthermore, when introducing an additional constraint in the analysis (i.e., back-trajectories), we show that, on days in which air mass transport between the two measurement sites is observed (10% of the period), at least 22% and 16% of BC and O3 variability at NCO-P can be explained by concurrent variability of these SLCF/P over the Kathmandu Valley.

Keywords

Black carbon Ozone Comparison Planetary boundary layer Himalayas


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