1Department of Physical Sciences, P.O. Box 64, 00014 Helsinki, Finland
2ACD, NCAR, P.O. Box 3000, 80305 Boulder, Colorado, USA
3Leibniz Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany
4Department of Plant Physiology, Estonian University of Life Sciences, Kreutzwaldi 64, 51014 Tartu, Estonia
Abstract. New particle formation is of interest because of its influence on the properties of aerosol population, and due to the possible contribution of newly formed particles to cloud condensation nuclei. Currently no conclusive evidence exists as to the mechanism or mechanisms of nucleation and subsequent particle growth. However, nucleation rates exhibit a clear dependence on ambient sulphuric acid concentrations and particle growth is often attributed to the condensation of organic vapours. A detailed study of new particle formation in the Front Range of the Colorado Rocky Mountains is presented here. Gas and particle measurement data for 32 days was analyzed to identify event days, possible event days, and non-event days. A detailed analysis of nucleation and growth is provided for four days on which new particle formation was clearly observed. Evidence for the role of sesquiterpenes in new particle formation is presented.