ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-5-57-2005 Measurements in a highly polluted Asian mega city: observations of aerosol number size distribution, modal parameters and nucleation events Mönkkönen P. 1 Koponen I. K. 1 Lehtinen K. E. J. 1 Hämeri K. 1 2 Uma R. 3 Kulmala M. 1 University of Helsinki, Department of Physical Sciences, Finland Finnish Institute of Occupational Health, Helsinki, Finland The Energy and Resources Institute (TERI), New Delhi, India 19 01 2005 5 1 57 66 Copyright: © 2005 P. Mönkkönen et al. 2005 This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 Generic License. To view a copy of this licence, visit https://creativecommons.org/licenses/by-nc-sa/2.5/ This article is available from https://acp.copernicus.org/articles/5/57/2005/acp-5-57-2005.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/5/57/2005/acp-5-57-2005.pdf

Diurnal variation of number size distribution (particle size 3-800nm) and modal parameters (geometric standard deviation, geometric mean diameter and modal aerosol particle concentration) in a highly polluted urban environment was investigated during October and November 2002 in New Delhi, India. Continuous monitoring for more than two weeks with the time resolution of 10min was conducted using a Differential Mobility Particle Sizer (twin DMPS). The results indicated clear increase in Aitken mode (25-100nm) particles during traffic peak hours, but towards the evenings there were more Aitken mode particles compared to the mornings. Also high concentrations of accumulation mode particles (&gt;100nm) were detected in the evenings only. In the evenings, biomass/refuse burning and cooking are possible sources beside the traffic. We have also shown that nucleation events are possible in this kind of atmosphere even though as clear nucleation events as observed in rural sites could not be detected. The formation rate of 3nm particles (J3) of the observed events varied from 3.3 to 13.9cm<sup>-3</sup>s<sup>-1</sup> and the growth rate varied from 11.6 to 18.1nmh<sup>-1</sup> showing rapid growth and high formation rate, which seems to be typical in urban areas.