Aerosol number size distribution in the boreal environment: spatio-temporal variation
Swedish Polar Research Secretariat, Abisko Scientific Research Station2016 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Ilmakehän pienhiukkasten kokojakauman alueellinen ja ajallinen vaihtelu havumetsäympäristössä (Finnish)
Atmospheric aerosols have an impact on the global radiation budget, and thus on climate, they reduce the air quality and visibility, and have multiple harmful health effects. The climatic significance of aerosols result from their ability to scatter and absorb solar radiation, and, if being large enough, mediate the cloud albedo and lifetime by acting as cloud condensation nuclei (CCN). The climatic effect, however, has a notable uncertainty. Particles can be either directly emitted to atmosphere or they can form there from precursor vapors. The latter is called new particle formation (NPF). Globally, NPF has been estimated to be responsible for even half of CCN sized tropospheric particles. The understanding of the NPF mechanisms and the spatial and temporal variation of NPF in many scales is necessary to correctly represent aerosols in climate models. In this work, we quantified the importance of biogenic organic vapours and anthropogenic sulfuric emissions in the NPF in northern boreal environment. Aerosol number size distribution data from three measurement sites were used to calculate the average continuous increase in aerosol particle diameter and number concentration when air masses travelled over land. A 14-year-long time series of aerosol and gas measurements were used to determine the effect of reduced Kola Peninsula SO2 emissions on aerosol population at Eastern Finnish Lapland. Secondly, this thesis describes in-situ aerosol measurements conducted with a light aircraft within the lowest 4 km of the troposphere. The data were used to determine the vertical and horizontal extent and variability of the NPF events in the surroundings of the Hyytiälä SMEAR II station. The airborne and ground level measurements were compared to find out the representativeness of the on ground measurements in the lowest parts of the atmosphere, in the planetary boundary layer. The results showed that the Aitken mode particles grew, on average, at the apparent rate of around 1 nm h−1 when they travelled over the northern boreal environment during the growing season. The average calculated growth rates during the NPF events were 3 6 times higher than this apparent average growth rate. The result implied that the condensation has a significant role in the particle growth even when NPF is not explicit. Also, the NPF events inside the planetary boundary layer were found to occur in area over a hundred kilometers. However, within this area, a notable variation in nucleation mode particles was observed.
Place, publisher, year, edition, pages
Helsinki: University of Helsinki, 2016. , 61 p.
Report series of aerosol science, ISSN 0784–3496 ; 192 (2016)
IdentifiersURN: urn:nbn:se:polar:diva-3510ISBN: 978-952-7091-67-8 (print)ISBN: 978-952-7091-68-5 (electronic)OAI: oai:DiVA.org:polar-3510DiVA: diva2:1083544
Petäjä, Tuukka, Ph.D. ProfessorKulmala, Markku, Ph.D. ProfessorKrejci, Radovan, Ph.D.Manninen, Hanna E., Ph.D.