Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 10 3 2010 10.5194/acpd-10-6537-2010 http://www.atmos-chem-phys-discuss.net/10/6537/2010/ http://www.atmos-chem-phys-discuss.net/10/6537/2010/acpd-10-6537-2010.html http://www.atmos-chem-phys-discuss.net/10/6537/2010/acpd-10-6537-2010.pdf 6537 6566 2010-03-09 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 K. Sellegri k.sellegri@opgc.univ-bpclermont.fr P. Laj H. Venzac J. Boulon D. Picard P. Villani P. Bonasoni A. Marinoni P. Cristofanelli E. Vuillermoz Laboratoire de Météorologie Physique, CNRS/University of Clermont-Ferrand, Clermont-Ferrand, France, France Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), CNRS/University of Grenoble, Grenoble, France Institute for Atmospheric Science and Climate (ISAC), CNR, Bologna, Italy Ev-K2-CNR Committee, Bergamo, Italy The present paper investigates the diurnal and seasonal variability of the aerosol total number concentration, number and volume size distribution between 10 nm and 10 μm, from a combination of a scanning mobility particle sizer (SMPS) and an optical counter (OPC), performed over a two-year period (May 2006–May 2008) at the Nepal Climate Observatory-Pyramid (NCO-P) research station, (5079 m a.s.l.). The annual average number concentration measured over the two-year period at the NCO-P is 860 cm^−3. Total concentrations show a strong seasonality with maxima during pre-monsoon and post-monsoon seasons and minima during the dry and monsoon seasons. A diurnal variation is also clearly observed, with maxima between 09:00 and 12:00 UTC. The aerosol concentration maxima are mainly due to nucleation processes during the post-monsoon season, as witnessed by high nucleation mode integrated number concentrations, and to transport of high levels of pollution from the plains by valley breezes during the pre-monsoon season, as demonstrated by high accumulation mode integrated number concentrations. Night-time number concentration of particles (from 03:00 to 08:00 NST) are relatively low throughout the year (from 450 cm^−3 during the monsoon season to 675 cm^−3 during the pre-monsoon season), indicating the level of free_tropospheric background, as a result of downslope winds during this part of the day. However, it was found that these background concentrations are strongly influenced by the daytime concentrations, as they show the same seasonal variability. The resulting free troposphere (FT)/residual layer concentrations are found to be two times higher than at other lower altitudes European sites, such as the Jungfraujoch. Night-time measurements were subsequently selected to study the FT composition according to different air masses, and the effect of long range transport to the station. Bollasina, M., Bertolani, L., and Tartari, G.: Meteorological observations at high altitude in Khumbu Valley, Nepal Himalayas, 1994–1999, Bull. Glaciol. Res., 19, 1–11, 2002. 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 NCO-Pyramid Atmospheric Research Observatory in Himalaya for aerosol, ozone and halocarbon measurements, Sci. Total Environ., 391(2–3), 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, 2010. 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., 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, doi: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, 2010. Hansen, J., Sato, M., Ruedy, R., Lacis, A., and Oinas, V.: Global warming in the twenty-first century: An alternative scenario, PNAS 29~August~2000, 97(18), 9875–9880, 2000. 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, doi:10.1029/2008JD011489, 2009. Kerminen, V.-M., Pirjola, L., and Kulmala M.: How significantly does coagulational scavenging limit atmospheric particle production?, J. Geophys. Res., 106, 24119–24125, 2001 Kivekás, 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, 2009. Komppula, M., Lihavainen, H., Hatakka, J., Paatero, J., Aalto, P., Kulmala, M., and Viisanen, Y.: Observations of new particle formation and size distributions at two different heights and surroundings in subarctic area in northern Finland, J. Geophys. Res.-Atmos., 108(D9), 4295, doi:10.1029/2002JD002939, 2003. Komppula, M., Lihavainen, H., Hyvarinen, 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, doi:10.1029/2008JD011007, 2009, 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. Mäkelä, J. M., Koponen, I. K., Aalto, P., and Kulmala, M.: One-year data of submicron size modes of tropospheric background aerosol in southern Finland, J. Aerosol Sci., 31, 595–611, 2000. Marcq, S., Laj, P., Roger, J. C., Villani, P., Sellegri, K., Bonasoni, P., Marinoni, A., Cristofanelli, P., Verza, G. P., and Bergin, M.: Aerosol optical properties and radiative forcing in the high Himalaya based on measurements at the Nepal Climate Observatory –pyramid site (5100 m a.s.l), Atmos. Chem. Phys. Discuss., 10, 5627–5663, 2010. Marinoni, A., Cristofanelli, P., Calzolari, F., Roccato, F., Bonafè, U., and Bonasoni, P.:Continuous measurements of aerosol physical parameters at the Mt. Cimone GAW Station (2165 m a.s.l., Italy), Sci. Total Environ., 391(2–3), 241–251, 2008. Marinoni, A., Cristofanelli, P., Duchi, R., Calzolai, F., Decesari, S., Sellegri, K., Laj, P., Vuillermoz, E., Verza, G.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., in preparation, 2010. Nakajima, T., Yoon, S., Ramanathan, V., Shi, G., Takemura, T., Higurashi, A., Takamura, T., K. Aoki, B. Sohn, S. Kim, H. Tsuruta, N. Sugimoto, A. Shimizu, H. Tanimoto, Y. Sawa, N. Lin, C. Lee, D. Goto, and N. Schutgens: 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, doi:10.1029/2007JD009009, 2007. Nishita, C., Osada, K., Matsunaga, K., and Iwasaka, Y., Number-size distributions of free tropospheric aerosol particles at Mt. Norikura, Japan: Effects of precipitation and air mass transportation pathways, J. Geophys. Res., 112, D10213, doi:10.1029/2006JD007969, 2007 Nyeki S., Li, F., Weingartner, E., Streit, N., Colbeck, I., Gäggeler, H. W., and Baltensperger, U.: The background aerosol size distribution in the free troposphere: An analysis of the annual cycle at a high-alpine site, J. Geophys. Res., 103, 31749–31762, 1998. Osada K., Kido, M., Iida, H., Matsunaga, K., Iwasaka, Y., Nagatani, M., and Nakada, H.: Seasonal variation of free tropospheric aerosol particles at Mt. Tateyama, central Japan, J. Geophys. Res.-Atmos., 108(D23), 8667, doi:10.1029/2003JD002344, 2003. Panday A. K. and Prinn R. G.: Diurnal cycle of air pollution in the Kathmandu Valley, Nepal: Observations, J. Geophys. Res., 114, D09305, doi:10.1029/2008JD009777, 2009. Pio, C. A., Legrand, M., Oliveira, T., Afonso, J., Santos, C., Caseiro, A., Fialho, P., Barata, F., Puxbaum, H., Sanchez-Ochoa, A., Kasper-Giebl, A., Gelencsér, A. Preunkert, S., and Schock, M.: Climatology of aerosol composition (organic versus inorganic) at nonurban sites on a west-east transect across Europe, J. Geophys. Res., 112, D23S02, doi:10.1029/2006JD008038, 2007. Raes, F., Van Dingenen, R, Cuevas, E., Van Velthoven, P. F. J., and Prospero, J. M.: Observation of aerosols in the free troposphere and marine boundary layer of the subtropical Northeast Atlantic: discussion of processes determining their size distribution, J. Geophys. Res., 102(N17), 21315–21328, 1997 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, 102(15), 5326–5333, 2005. Ramanathan, V., Ramana, M. V., Roberts, G., Kim, D., Corrigan, C., Chung, C., and Winkle, 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., amd Kim, D.: Corrigan CE, Nguyen H, Stone EA, Schauer JJ, Carmichael GR, Adhikary B, and Yoon SC: Atmospheric Brown Clouds: Hemispherical and regional variations in long range transport, absorption and radiative forcing, J. Geophys. Res., 112, D22, doi:10.1029/2006JD008124, 2007b. Ramanathan, V., Agrawal, M., Akimoto, H., Aufhanner, M., Devotta, S., and Emberson, L.: Atmospheric Brown Clouds: Regional Assessment Report with Focus on Asia. Published by the United Nations Environment Programme, Nairobi, Kenya, 2008. Richter, A., Burrows, J. P., Nüß, H., Granier, C., and Niemeier, U.: Increase in tropospheric nitrogen dioxide over China observed from space, Nature, 437, 129–132, 2005. Shaw, E.: Aerosols at a mountaintop observatory in Arizona, J. Geophs. Res., 112, D07206, doi:10.1029/2005JD006893, 2007. Spracklen, D. V., Carslaw, K. S., Merikanto, J., Mann, G. W., Pickering, S., Ogren, J. A., Andrews, E., Baltensperger, U., Weingartner, E., Boy, M., Kulmala, M., Laakso, L., Lihavainen, H., Kivekäs, N., Mihalopoulos, N., Kouvarakis, G., Jennings, S. G., Birmili, W., Wiedensohler, A., Weller, R., Laj, P., Sellegri, K., Bonn, B., and Krejci, R.: Explaining global surface aerosol number concentrations in terms of primary emissions and particle formation, Atmos. Chem. Phys. Discuss., 9, 26377–26419, 2009. Tunved, P., Hansson, H.-C., Kulmala, M., Aalto, P., Viisanen, Y., Karlsson, H., Kristensson, A., Swietlicki, E., Dal Maso, M., Ström, J., and Komppula, M.: One year boundary layer aerosol size distribution data from five nordic background stations, Atmos. Chem. Phys., 3, 2183–2205, 2003. Tunved, P., Nilsson, E. D., Hansson, H.-C., and Ström, J.: Aerosol characteristics of air masses in northern Europe: Influences of location, transport, sinks, and sources, J. Geophys. Res., 110, D07201, doi:10.1029/2004JD005085, 2005. Van Dingenen, R., Putaud, J.-P., Martins-Dos Santos, S., and Raes, F.: Physical aerosol properties and their relation to air mass origin at Monte Cimone (Italy) during the first MINATROC campaign, Atmos. Chem. Phys., 5, 2203–2226, 2005. Venzac, H., Sellegri, K., and Laj, P.: Nucleation events detected at the high altitude site of the Puy de Dôme Research Station, France, Boreal Env. Res., 12, 345–359, 2007. Venzac, H., Sellegri, K., Laj, P., Villani, P., Bonasoni, P., Marinoni, A., Cristofanelli, P., Calzolari, F., Fuzzi, S., Decesari, S., Facchini, M.-C., Vuillermoz, E., and Verza, G. P.: High Frequency New Particle Formation in the Himalayas, PNAS, 105(41), 15666–15671, 2008. Venzac, H., Sellegri, K., Villani, P., Picard, D., and Laj, P.: Seasonal variation of aerosol size distributions in the free troposphere and residual layer at the puy de Dôme station, France, Atmos. Chem. Phys., 9, 1465–1478, 2009. Villani, P., Picard, D., Michaud, V., et al.: Design and Validation of a Volatility Hygroscopic Tandem Differential Mobility Analyzer (VH-TDMA) to Characterize the Relationships Between the Thermal and Hygroscopic Properties of Atmospheric Aerosol Particles, Aerosol Sci. Technol., 42(9) 729–741, 2008. Weingartner, E., Nyeki, S., and Baltensperger, U.: Seasonal and diurnal variation of aerosol size distributions (10<D<750 nm) at a high-alpine site Jungfraujoch (3580 m a.s.l.), J. Geophys. Res., 104, 26809–26820, 1999. Whitby, K. T.: The physical characteristics of sulphur aerosols, Atmos. Environ., 12, 135–159, 1978. 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 onto snow surface from NCO-P data and its possible impact on snow albedo changes over Himalayan glaciers during the pre-monsoon season, Atmos. Chem Phys. Discuss., in preparation, 2010.