Articles | Volume 11, issue 16
Atmos. Chem. Phys., 11, 8447–8458, 2011
Atmos. Chem. Phys., 11, 8447–8458, 2011

Research article 19 Aug 2011

Research article | 19 Aug 2011

New particle formation infrequently observed in Himalayan foothills – why?

K. Neitola1, E. Asmi1, M. Komppula2, A.-P. Hyvärinen1, T. Raatikainen1,3, T. S. Panwar4, V. P. Sharma4, and H. Lihavainen1 K. Neitola et al.
  • 1Finnish meteorological Institute, Helsinki, Finland
  • 2Finnish meteorological Institute, Kuopio, Finland
  • 3Georgia Institute of Technology, Atlanta, Georgia, USA
  • 4Energy and Resource Institute, New Delhi, India

Abstract. A fraction of the Himalayan aerosols originate from secondary sources, which are currently poorly quantified. To clarify the climatic importance of regional secondary particle formation in the Himalayas, data from 2005 to 2010 of continuous aerosol measurements at a high-altitude (2180 m) Indian Himalayan site, Mukteshwar, were analyzed. For this period, the days were classified, and the particle formation and growth rates were calculated for clear new particle formation (NPF) event days. The NPF events showed a pronounced seasonal cycle. The frequency of the events peaked in spring, when the ratio between event and non-event days was 53 %, whereas the events were truly sporadic on any other seasons. The annual mean particle formation and growth rates were 0.40 cm−3 s−1 and 2.43 nm h−1, respectively. The clear annual cycle was found to be mainly controlled by the seasonal evolution of the Planetary Boundary Layer (PBL) height together with local meteorological conditions. Spring NPF events were connected with increased PBL height, and therefore characterised as boundary layer events, while the rare events in other seasons represented lower free tropospheric particle formation. This provides insight on the vertical extent of NPF in the atmosphere.

Final-revised paper