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Volume 17, issue 10 | Copyright

Special issue: Pan-Eurasian Experiment (PEEX)

Atmos. Chem. Phys., 17, 6227-6241, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 May 2017

Research article | 22 May 2017

Long-term analysis of clear-sky new particle formation events and nonevents in Hyytiälä

Lubna Dada1, Pauli Paasonen1, Tuomo Nieminen1,2, Stephany Buenrostro Mazon1, Jenni Kontkanen1, Otso Peräkylä1, Katrianne Lehtipalo1,4, Tareq Hussein1,5, Tuukka Petäjä1, Veli-Matti Kerminen1, Jaana Bäck3, and Markku Kulmala1 Lubna Dada et al.
  • 1Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland
  • 2Department of Applied Physics, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland
  • 3Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 Helsinki, Finland
  • 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen PSI, Switzerland
  • 5Department of Physics, the University of Jordan, Amman 11942, Jordan

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 building on previously accumulated knowledge and by focusing on clear-sky (noncloudy) conditions. We first investigated the effect of cloudiness on NPF and then compared the NPF event and nonevent 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 in discriminating NPF events from nonevents. The formation rate of 1.5nm particles was calculated by using proxies for gaseous sulfuric acid and oxidized products of low volatile organic compounds, together with an empirical nucleation rate coefficient. As expected, our results indicate an increase in the frequency of NPF events under clear-sky conditions in comparison to cloudy ones. Also, focusing on clear-sky conditions enabled us to find a clear separation of many variables related to NPF. For instance, oxidized organic vapors showed a higher concentration during the clear-sky NPF event days, whereas the condensation sink (CS) and some trace gases had higher concentrations during the nonevent days. The calculated formation rate of 3nm particles showed a notable difference between the NPF event and nonevent days during clear-sky conditions, especially in winter and spring. For springtime, we are able to find a threshold equation for the combined values of ambient temperature and CS, (CS (s−1) >−3.091 × 10−5 × T (in Kelvin) + 0.0120), 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.

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We studied new particle formation under clear-sky conditions in the boreal forest in southern Finland. We compared varying conditions between new particle events and nonevents. We then formulated a threshold value that separates new particle events from nonevents and reached a probability distribution for the frequency of new particle formation. This study serves as the basis for scientists aiming to improve their understanding of new particle formation.
We studied new particle formation under clear-sky conditions in the boreal forest in southern...