ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-10-5859-2010 Aerosol optical properties and radiative forcing in the high Himalaya based on measurements at the Nepal Climate Observatory-Pyramid site (5079 m a.s.l.) Marcq S. 1 Laj P. 1 Roger J. C. 2 Villani P. 1 Sellegri K. 2 Bonasoni P. 3 Marinoni A. 3 Cristofanelli P. 3 Verza G. P. 4 Bergin M. 5 Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), CNRS/University of Grenoble, Grenoble, France Laboratoire de Météorologie Physique, CNRS/University of Clermont-Ferrand, Clermont-Ferrand, France Institute for Atmospheric Science and Climate (ISAC), CNR, Bologna, Italy Ev-K2-CNR Committee, Bergamo, Italy Georgia Institute of Technology, Civil and Environmental Engineering, Atlanta, USA 02 07 2010 10 13 5859 5872 Copyright: © 2010 S. Marcq et al. 2010 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/10/5859/2010/acp-10-5859-2010.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/10/5859/2010/acp-10-5859-2010.pdf

Intense anthropogenic emissions over the Indian sub-continent lead to the formation of layers of particulate pollution that can be transported to the high altitude regions of the Himalaya-Hindu-Kush (HKH). Aerosol particles contain a substantial fraction of strongly absorbing material, including black carbon (BC), organic compounds (OC), and dust all of which can contribute to atmospheric warming, in addition to greenhouse gases. Using a 3-year record of continuous measurements of aerosol optical properties, we present a time series of key climate relevant aerosol properties including the aerosol absorption (&sigma;<sub>ap</sub>) and scattering (&sigma;<sub>sp</sub>) coefficients as well as the single-scattering albedo (<i>w</i><sub>0</sub>). Results of this investigation show substantial seasonal variability of these properties, with long range transport during the pre- and post-monsoon seasons and efficient precipitation scavenging of aerosol particles during the monsoon season. The monthly averaged scattering coefficients range from 0.1 Mm<sup>−1</sup> (monsoon) to 20 Mm<sup>−1</sup> while the average absorption coefficients range from 0.5 Mm<sup>−1</sup> to 3.5 Mm<sup>−1</sup>. Both have their maximum values during the pre-monsoon period (April) and reach a minimum during Monsoon (July–August). This leads to dry <i>w</i><sub>0</sub> values from 0.86 (pre-monsoon) to 0.79 (monsoon) seasons. Significant diurnal variability due to valley wind circulation is also reported. Using aerosol optical depth (AOD) measurements, we calculated the resulting direct local radiative forcing due to aerosols for selected air mass cases. We found that the presence of absorbing particulate material can locally induce an additional top of the atmosphere (TOA) forcing of 10 to 20 W m<sup>−2</sup> for the first atmospheric layer (500 m above surface). The TOA positive forcing depends on the presence of snow at the surface, and takes place preferentially during episodes of regional pollution occurring on a very regular basis in the Himalayan valleys. Warming of the first atmospheric layer is paralleled by a substantial decrease of the amount of radiation reaching the surface. The surface forcing is estimated to range from −4 to −20 W m<sup>−2</sup> for small-scale regional pollution events and large-scale pollution events, respectively. The calculated surface forcing is also very dependent on surface albedo, with maximum values occurring over a snow-covered surface. Overall, this work presents the first estimates of aerosol direct radiative forcing over the high Himalaya based on in-situ aerosol measurements, and results suggest a TOA forcing significantly greater than the IPCC reported values for green house gases.

 References Anderson, T. L. and Ogren, J. A.: Determining Aerosol Radiative Properties Using the TSI 3563 Integrating Nephelometer, Aerosol Science and Technology, 29(1), 57–69, 1998. Bollasina M., Nigam, S., and Lau, K. M.: Absorbing aerosols and summer monsoon evolution over South Asia: An observational portrayal, J. Climate, 21, 3221–3239, https://doi.org/10.1175/2007JCLI2094.1, 2008. Bonasoni, P., Laj, P., Angelini, F., Arduini, J., Bonafè, U., Calzolari, F., Cristofanelli, P., Decesari, S., Facchini, M. C., Fuzzi, S., Gobbi, G. P., Maione, M., Marinoni, A., Petzold, A., Roccato, F., Roger, J. C., Sellegri, K., Sprenger, M., Venzac, H., Verza, G. P., Villani, P., and Vuillermoz, E.: The ABC-Pyramid Atmospheric Research Observatory in Himalaya for aerosol, ozone and halocarbon measurements, Sci. Tot. Environ., 391, 252–261, 2008. Bonasoni, P., Laj, P., Marinoni, A., Sprenger, M., Angelini, F., Arduini, J., Bonafè, U., Calzolari, F., Colombo, T., Decesari, S., Di Biagio, C., di Sarra, A. G., Evangelisti, F., Duchi, R., Facchini, M. C., Fuzzi, S., Gobbi, G. P., Maione, M., Panday, A., Roccato, F., Sellegri, K., Venzac, H., Verza, G. P., Villani, P., Vuillermoz, E., and Cristofanelli, P.: Atmospheric Brown Clouds in the Himalayas: first two years of continuous observations at the Nepal-Climate Observatory at Pyramid (5079 m), Atmos. Chem. Phys. Discuss., 10, 4823–4885, https://doi.org/10.5194/acpd-10-4823-2010, 2010. Bond, T. C. and Sun, H.: Can Reducing Black Carbon Emissions Counteract Global Warming? Environ. Sci. Technol., 39(16), 5921–5926, 2005. Carrico, C. M., Rood,, M. J., and Ogren, J. A.: Aerosol light scattering properties at Cape Grim, Tasmania, during the First Aerosol Characterization Experiment (ACE 1), J. Geophys. Res., 103(D13), 16565–16574, 1998. Carrico C. M., Rood, M. J., Ogren, J. A., Neusü{ß}, C. Wiedensohler, A., and Heintzenberg, J.: Aerosol optical properties at Sagres, Portugal during ACE-2, Tellus B, 52(2), 69-4-715, https://doi.org/10.1034/j.1600-0889.2000.00049.x, 2000. Carrico, M. C., Bergin, M. H., Shrestha, A. B., Dibb, J. E., Gomes, L., Harris, J. M.: The importance of carbon and mineral dust to seasonal aerosol properties in the Nepal Himalaya, Atmos. Environ., 37, 2811–2824, https://doi.org/10.1016/S1352-2310(03)00197-3, 2003. Clarke, A. D.: Aerosol Light Absorption by Soot in Remote Environments, Aerosol Science and Technology, 10(1), 161–171, 1989. Clarke, A. D., Howell, S., Quinn, P. K., Bates, T. S., Ogren, J. A., Andrews, E., Jefferson, A., Massling, A., Mayol-Bracero, O., Maring, H., Savoie, D., and Cass, G.: INDOEX aerosol: A comparison and summary of chemical, microphysical, and optical properties observed from land, ship, and aircraft, J. Geophys. Res., 107(D19), 8033, https://doi.org/10.1029/2001JD000572, 2002. Cristofanelli, P., Bracci, A., Sprenger, M., Marinoni, A., Bonafè, U., Calzolari, F., Duchi, R., Laj, P., Pichon, J. M., Roccato, F., Venzac, H., Vuillermoz, E., and Bonasoni, P.: Tropospheric ozone variations at the Nepal climate observatory – pyramid (Himalayas, 5079 m a.s.l.) and influence of stratospheric intrusion events, Atmos. Chem. Phys. Discuss., 10, 1483–1516, https://doi.org/10.5194/acpd-10-1483-2010, 2010. Decesari, S., Facchini, M. C., Carbone, C., Giulianelli, L., Rinaldi, M., Finessi, E., Fuzzi, S., Marinoni, A., Cristofanelli, P., Duchi, R., Bonasoni, P., Vuillermoz, E., Cozic, J., Jaffrezo, J. L., and Laj, P.: Chemical composition of PM<sub>10</sub> and PM<sub>1</sub> at the high-altitude Himalayan station Nepal Climate Observatory-Pyramid (NCO-P) (5079 m a.s.l.), Atmos. Chem. Phys., 10, 4583–4596, https://doi.org/10.5194/acp-10-4583-2010, 2010. Delene, D.J. and Ogren, J. A.: Variability of aerosol optical properties at four North American surface monitoring sites, Journal of Atmospheric Science 59&nbsp;pp. 1135–1150, 2002. Dubuisson, P., Buriez, J. C., and Fouquart, Y.: High spectral resolution solar radiative transfer in absorbing and scattering media: application to the satellite simulations, J. Quant. Spectrosc. Ra., 55, 103–126, 1996. Dumka, U. C., Satheesh, S. K., Pant, P., Hegde, P., and Krishna Moorthy, K.: Surface changes in solar irradiance due to aerosols over central Himalayas, Geophys. Res. Lett., 33, L20809, https://doi.org/10.1029/2006GL027814, 2006. Dumka, U. C., Satheesh, S. K., Pant, P., Hegde, P., and Moorthy, K. K.: Reply to comment by S. Ramachandran on "Surface changes in solar irradiance due to aerosols over central Himalayas", Geophys. Res. Lett., 35, L04813, https://doi.org/10.1029/2007GL030556, 2008. Flanner, M.&nbsp;G. and Zender, C.&nbsp;S.: Snowpack Radiative Heating: Influence on Tibetan Plateau Climate, Geophys. Res. Lett., 32(6), L06501, https://doi.org/10.1029/2004GL022076, 2005. Flanner, M. G., Zender, C. S., Randerson, J. T., and Rasch, P. J.: Present-day climate forcing and response from black carbon in snow, J. Geophys. Res., 112, D11202, https://doi.org/10.1029/2006JD008003, 2007. Flanner, M. G., Zender, C. S., Hess, P. G., Mahowald, N. M., Painter, T. H., Ramanathan, V., and Rasch, P. J.: Springtime warming and reduced snow cover from carbonaceous particles, Atmos. Chem. Phys., 9, 2481–2497, https://doi.org/10.5194/acp-9-2481-2009, 2009. Gobbi, G. P., Angelini, F., Bonasoni, P., Verza, G. P., Marinoni, A., and Barnaba, F.: Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory – Pyramid (5079 m a.s.l.), Atmos. Chem. Phys. Discuss., 10, 1193–1220, https://doi.org/10.5194/acpd-10-1193-2010, 2010. Hansen, J., Sato, M., Ruedy, R., Lacis, A., and Oinas, V.: Global warming in the twenty-first century: An alternative scenario, PNAS 29&nbsp;August&nbsp;2000, Vol.&nbsp;97, No.&nbsp;18, 9875–9880, 2000. Henne, S., Furger, M., Nyeki, S., Steinbacher, M., Neininger, B., de Wekker, S. F. J., Dommen, J., Spichtinger, N., Stohl, A., and Prévôt, A. S. H.: Quantification of topographic venting of boundary layer air to the free troposphere, Atmos. Chem. Phys., 4, 497–509, https://doi.org/10.5194/acp-4-497-2004, 2004. Hess, M., Koepke, P., and Schult, I.: Optical properties of aerosols and clouds: the software package, B. Am. Meteorol. Soc., 79, 831–844, 1998. Holben, B. N., Eck, T. F., Slutsker, I., Tanre, D., Buis, J. P., Setzer, A., et al.: AERONET – A federated instrument network and data archive for aerosol characterization, Remote Sens. Environ., 66(1), 1–16, 1998. Huang, Y., Chameides, W. L., and Dickinson, R. E.: Direct and indirect effects of anthropogenic aerosols on regional precipitation over East Asia, J. Geophys. Res., 112, D03212, https://doi.org/10.1029/2006JD007114, 2007. Hyvärinen, A. P., Lihavainen, H., Komppula, M., Sharma, V. P., Kerminen, V. M., Panwar, T. S., and Viisanen, Y.: Continuous measurements of optical properties of atmospheric aerosols in Mukteshwar, northern India, J. Geophys. Res., 114, D08207, https://doi.org/10.1029/2008JD011489, 2009. IPCC: Climate 2007, The scientific basis, Houghton, J. T., et al., (Cambridge Univ. Press., Cambridge), 2007. Jacobson, M. Z.: Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming, J. Geophys. Res., 107(D19), 4410, https://doi.org/10.1029/2001JD001376, 2002. Kivekäs, N., Sun, J., Zhan, M., Kerminen, V.-M., Hyvärinen, A., Komppula, M., Viisanen, Y., Hong, N., Zhang, Y., Kulmala, M., Zhang, X.-C., Deli-Geer, and Lihavainen, H.: Long term particle size distribution measurements at Mount Waliguan, a high-altitude site in inland China, Atmos. Chem. Phys., 9, 5461–5474, https://doi.org/10.5194/acp-9-5461-2009, 2009. Koloutsou-Vakakis, S., Carrico, C. M., Kus, P., Rood, M. J., Li, Z., Shrestha, R., Ogren, J. A., Chow, J. C., and Watson, J. G.: Aerosol properties at a midlatitude Northern Hemisphere continental site, J. Geophys. Res., 106(D3), 3019–3032, 2001. Komppula, M., Lihavainen, H., Hyvärinen, A.-P., Kerminen, V.-M., Panwar, T. S., Sharma, V. P., and Viisanen, Y.: Physical properties of aerosol particles at a Himalayan background site in India, J. Geophys. Res., 114, D12202, https://doi.org/10.1029/2008JD011007, 2009. Lacis, A. A. and Oinas, V.: A description of the correlated k-distribution method, J. Geophys. Res., 96, 9027–9064, 1991. Lau, K.-M. and Kim, K.-M.: Observational relationship between aerosol and Asian monsoon rainfall, and circulation, Geophys. Res. Lett., 33, L21810, https://doi.org/10.1029/2006GL027546, 2006. Lelieveld, J., Crutzen, P. J., Ramanathan, V., et al.: The Indian Ocean Experiment: Widespread Air Pollution from South and Southeast Asia, Science, 291, 1031–1036, 2001. Marinoni, A., Cristofanelli, P., Laj, P., Duchi, R., Calzolari, F., Decesari, S., Sellegri, K., Vuillermoz, E., Verza, G. P., Villani, P., and Bonasoni, P.: Aerosol mass and black carbon concentrations, two year-round observations at NCO-P (5079 m, Southern Himalayas), Atmos. Chem. Phys. Discuss., 10, 8379–8413, https://doi.org/10.5194/acpd-10-8379-2010, 2010. Marshall, D., Covert, S., and Charlson, R. J.: Relationship between asymmetry parameter and hemispheric backscatter ratio – implications for climate forcing by aerosols, Appl. Optics, 34, 6306–6311, 1995. Nakajima, T., Yoon, S., Ramanathan, V., Shi, G., Takemura, T., Higurashi, A., Takamura, T., Aoki, K., Sohn, B., Kim, S., Tsuruta, H., Sugimoto, N., Shimizu, A., Tanimoto, H., Sawa, Y., Lin, N., Lee, C., Goto, D., and Schutgens, N.: Overview of the Atmospheric Brown Cloud East Asian Regional Experiment 2005 and a study of the aerosol direct radiative forcing in east Asia, J. Geophys. Res., 112, D24S91, https://doi.org/10.1029/2007JD009009, 2007. Nessler, R., Weingartner, E., and Baltensperger, U.: Effect of humidity on aerosol light absorption and its implications for extinction and the single scattering albedo illustrated for a site in the lower free troposphere, J. Aerosol Sci., 36(8), 958–972, 2005a. Nessler, R., Weingartner, E., and Baltensperger, U.: Adaptation of dry nephelometer measurements to ambient conditions at the Jungfraujoch, Environ. Sci. Technol., 39, 2219–2228, 2005b. Ogren, J. A.: A systematic approach to in situ observations of aerosol properties, in: Aerosol Forcing of Climate, edited by: Charlson, R. J. and Heintzenberg, J., John Wiley & Sons, Ltd., 215–226, 1995. Painter, T. H., Barrett, A. P., Landry, C., Neff, J., Cassidy, M. P., Lawrence, C., McBride, K. E., and Farmer, G. L.: Impact of disturbed desert soils on duration of mountain snowcover, Geophys. Res. Lett., 34(12), L12502, https://doi.org/10.1029/2007GL030284R, 2007. Panday, A. and Prinn, R.: The diurnal cycle of air pollution in the Kathmandu Valley, Nepal: Observations, J. Geophys. Res-Atmos., 114, D09305, https://doi.org/10.1029:2008JD009777, 2009. Pant, P., Hegde, P., Dumka, U. C., Sagar, R., Satheesh, S. K., Moorthy, K. K., Saha, A., and Srivastava, M. K.: Aerosol characteristics at a high-altitude location in central Himalayas: Optical properties and radiative forcing, J. Geophys. Res., 111, D17206, https://doi.org/10.1029/2005JD006768, 2006 Petzold, A., Kramer, H., and Schönlinner, M.: Continuous measurement of atmospheric black carbon using a Multi-Angle Absorption Photometer, Environ. Sci. Pollut. R., 4, 78–82, 2002b Ramachandran, S.: Comment on Surface changes in solar irradiance due to aerosols over central Himalayas by U.&nbsp;C.&nbsp;Dumka et al., Geophys. Res. Lett., 35, L04814, https://doi.org/10.1029/2007GL030060, 2008. Ramanathan, V., Krutzen, P. J., Kiehl, J. T., and Rosenfeld, D.: Aerosols, climate, and the hydrology, Science, 294, 2119–2124, 2001. Ramanathan, V., Chung, C., Kim, D., Bettge, T., Buja, L., Kiehl, J. T., Washington, W. M., Fu, Q., Sikka, D. R., and Wild, M.: Atmospheric Brown Clouds: Impacts on South Asian Climate and Hydrological Cycle, PNAS, Vol.&nbsp;102, No.&nbsp;15, 5326–5333, 2005. Ramanathan, V., Ramana, M. V., Roberts, G., Kim, D., Corrigan, C., Chung, C., and Winkler, D.: Warming trends in Asia amplified by brown cloud solar absorption, Nature, 448, 575–578, 2007a. Ramanathan, V., Li, F., Ramana, M. V., Siva, P. S., Kim, D., Corrigan, C. E., Nguyen, H., Stone, E. A., Schauer, J. J., Carmichael, G. R., Adhikary, B., and Yoon, S. C.: Atmospheric Brown Clouds: Hemispherical and regional variations in long range transport, absorption and radiative forcing, J. Geophys. Res., 112, https://doi.org/10.1029/2006JD008124, 2007b. Richter A., Burrows, J. P., Nüâ, H., Granier, C., and Niemeier, U.: Increase in tropospheric nitrogen dioxide over China observed from space, Nature, 437, 129–132, 2005. Roger, J.-C., Mallet, M., Dubuisson, P., Cachier, H., Vermote, E., Dubovik, O., and Despiau, S.: A synergetic approach for estimating the local direct aerosol forcing: Application to an urban zone during the Expérience sur Site pour Contraindre les Modèles de Pollution et de Transport d'Emission (ESCOMPTE) experiment J. Geophys. Res., 111(D13), D13208, https://doi.org/10.1029/2005JD006361 (AGU), 2006. Scott, N. A.: A direct method of computation of the transmission function of an inhomogeneous gaseous medium-I: Description of the method, J. Quant. Spectrosc. Ra., 14, 691–704, 1974. Stamnes, K., Tsay, S., Wiscombe, W., and Jayaweera, K.: Numerically stable algorithm for discrete-ordinate-method radiative transfer in multiple scattering and emitting layered media, Appl. Optics, 27, 2502–2509, 1988. Sellegri, K., Laj, P., Venzac, H., Boulon, J., Picard, D., Villani, P., Bonasoni, P., Marinoni, A., Cristofanelli, P., and Vuillermoz, E.: Seasonal variations of aerosol size distributions based on long-term measurements at the high altitude Himalayan site of Nepal Climate Observatory-Pyramid (5079 m), Nepal, Atmos. Chem. Phys. Discuss., 10, 6537–6566, https://doi.org/10.5194/acpd-10-6537-2010, 2010. Venzac, H., Sellegri, K., Laj, P., Villani, P., Bonasoni, P., Marinoni, A., Cristofanelli, P., Calzolari, F., Fuzzi, S., Decesari, S., Facchini, M.-Cr., Vuillermoz, E., and Verza, G. P.: High Frequency New Particle Formation in the Himalayas; PNAS, 105(41), 15666–15671, 2008. Villani, P., Picard, D., Marchand, N., and Laj, P.: Design and Validation of a 6-Volatility Tandem Differential Mobility Analyzer (VTDMA), Aerosol Sci. Technol., 41(10), 898–906, 2007. Welton, E. J., Voss, K. J., Quinn, P. K., Flatau, P. J., Markowicz, K., Campbell, J. R., Spinhirne, J. D., Gordon, H. R., and Johnson, J. E.: Measurements of aerosol vertical profiles and otical properties during INDOEX 1999 using micropulse lidars, J. Geophys. Res., 107, 8019, https://doi.org/10.1029/2000JD000038, 2002. Xu, J., Bergin, M. H., Greenwald, R., Schauer, J. J., Shafer, M. M., Jaffrezo, J. L., and Aymoz, G.: Aerosol chemical, physical, and radiative characteristics near a desert source region of northwest China during ACE-Asia, J. Geophys. Res., 109(D19), D19S0310, https://doi.org/1029/2003JD004239, 2003. Yasunari, T. J., Bonasoni, P., Laj, P., Fujita, K., Vuillermoz, E., Marinoni, A., Cristofanelli, P., Duchi, R., Tartari, G., and Lau, K.-M.: Preliminary estimation of black carbon deposition from Nepal Climate Observatory-Pyramid data and its possible impact on snow albedo changes over Himalayan glaciers during the pre-monsoon season, Atmos. Chem. Phys. Discuss., 10, 9291–9328, https://doi.org/10.5194/acpd-10-9291-2010, 2010.