Long-term analysis of clear-sky new particle formation events and
non-events in Hyytiälä
Lubna Dada1, Pauli Paasonen1, Tuomo Nieminen1,2, Stephany Buenrostro Mazon1, Jenni Kontkanen1, Otso Peräkylä1, Tareq Hussein1,4, Tuukka Petäjä1, Veli-Matti Kerminen1, Jaana Bäck3, and Markku Kulmala11Department of Physics, University of Helsinki, P.O. Box 64, FIN-00014 Helsinki, Finland 2Department of Applied Physics, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland 3Department of Forest Sciences, University of Helsinki, P.O. Box 27, FIN-00014 Helsinki, Finland 4Department of Physics, the University of Jordan, Amman 11942, Jordan
Received: 26 Sep 2016 – Accepted for review: 18 Oct 2016 – Discussion started: 19 Oct 2016
Abstract. New particle formation (NPF) events have been observed all around the world and are known to be a major source of atmospheric aerosol particles. Here we combine 20 years of observations in a boreal forest at the SMEAR II station (Station for Measuring Ecosystem-Atmosphere Relations) in Hyytiälä, Finland, by utilizing previously accumulated knowledge, and by focusing on clear-sky (non-cloudy) conditions. We first investigated the effect of cloudiness on NPF and then compared the NPF event and non-event days during clear-sky conditions. In this comparison we considered, for example, the effects of calculated particle formation rates, condensation sink, trace gas concentrations and various meteorological quantities. The formation rate of 1.5 nm particles was calculated by using proxies for gaseous sulfuric acid and oxidized products of low volatile organic compounds. As expected, our results indicate an increase in the frequency of NPF events under clear-sky conditions. Also, focusing on clearsky conditions enabled us to find a clear separation of many variables related to NPF. For instance, oxidized organic vapors showed higher concentration during the clear-sky NPF event days, whereas the condensation sink (CS) and some trace gases had higher concentrations during the non-event days. The calculated formation rate of 3 nm particles showed a notable difference between the NPF event and non-event days during clear-sky conditions, especially in winter and spring. For spring time, we are able to find a threshold value for the combined values of ambient temperature and CS, above which practically no clear-sky NPF event could be observed. Finally, we present a probability distribution for the frequency of NPF events at a specific CS and temperature.
Dada, L., Paasonen, P., Nieminen, T., Buenrostro Mazon, S., Kontkanen, J., Peräkylä, O., Hussein, T., Petäjä, T., Kerminen, V.-M., Bäck, J., and Kulmala, M.: Long-term analysis of clear-sky new particle formation events and
non-events in Hyytiälä, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-859, in review, 2016.