Atmospheric nucleation: highlights of the EUCAARI project and future directions

Abstract

Abstract. Within the project EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions), atmospheric nucleation was studied by (i) developing and testing new air ion and cluster spectrometers, (ii) conducting homogeneous nucleation experiments for sulphate and organic systems in the laboratory, (iii) investigating atmospheric nucleation mechanism under field conditions, and (iv) applying new theoretical and modelling tools for data interpretation and development of parameterisations. The current paper provides a synthesis of the obtained results and identifies the remaining major knowledge gaps related to atmospheric nucleation. The most important technical achievement of the project was the development of new in-struments for measuring sub-3 nm particle populations, along with the extensive application of these instruments in both the laboratory and the field. All the results obtained during EUCAARI indicate that sulphuric acid plays a central role in atmospheric nucleation. However, also vapours other than sulphuric acid are needed to explain the nucleation and the subsequent growth processes, at least in continental boundary layers. Candidate vapours in this respect are some organic compounds, ammonia, and especially amines. Both our field and laboratory data demonstrate that the nucleation rate scales to the first or second power of the nucleating vapour concentration(s). This agrees with the few earlier field observations, but is in stark contrast with classical thermodynamic nucleation theories. The average formation rates of 2-nm particles were found to vary by almost two orders of magnitude between the different EUCAARI sites, whereas the formation rates of charged 2-nm particles varied very Published by Copernicus Publications on behalf of the European Geosciences Union. 10830V.-M. Kerminen et al.: Highlights of the EUCAARI project and future directions little between the sites. Overall, our observations are indicative of frequent, yet moderate, ion-induced nucleation usually outweighed by much stronger neutral nucleation events in the continental lower troposphere. The most concrete outcome of the EUCAARI nucleation studies are the new semiempirical nucleation rate parameterizations based on field observations, along with updated aerosol formation parameterizations.

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

“…Recent laboratory experiments have shown the importance of sulfuric acid and low-volatile oxidized organic vapors to NPF Kirkby et al, 2011;Petäjä et al, 2011;Kulmala et al, 2013;Ehn et al, 2014;Riccobono et al, 2014). Additionally, atmospheric observations confirm the importance of these precursor vapors in the initial steps of NPF and in the further growth of newly formed particles (Kulmala et al, 1998;Smith et al, 2005;Kerminen et al, 2010;Paasonen et al, 2010;Ahlm et al, 2012;Bzdek et al, 2014;Nieminen et al, 2014;Vakkari et al, 2015). The Station for Measuring Forest Ecosystem-Atmosphere Relations (SMEAR II), located in Hyytiälä, southern Finland, compiles almost 21 years of particle number size distribution and extensive complementary data, providing the longest size distribution time series in the world, and hence allows for robust NPF analysis which is not readily possible at other sites.…”

A statistical analysis of North East Atlantic (submicron) aerosol size distributions

“…The EUCAARI intensive measurement programme was throughout the full year of 2008. As one of the 12 atmospheric supersites EUCAARI supersites, Mace Head (Ireland) is uniquely located on the interface between the NE Atlantic and Europe, thus enabling sampling of both the cleanest air entering into Europe along with some of the most polluted air being exported out of Europe into the N. Atlantic (Jennings et al, 2003;. Asmi et al (2011) presented a combined statistical analysis of 22 stations (including all the 12 EUCAARI supersites) for the year 2008-2009 in terms of means and extremes of the number concentration size distributions encountered.…”

Measurement of neutral sulfuric acid-dimethylamine clusters using CI-APi-TOF-MS

“…Measurements suggest that atmospheric boundary layer nucleation proceeds mainly via a neutral process and ion-induced nucleation usually plays only a minor role 16 . Therefore, it is of importance to study the neutral pathway.…”