TUTCRIS - Tampereen teknillinen yliopisto

TUTCRIS

Measurement of the Physical Properties of Secondary Organic Aerosol Particles

Tutkimustuotos

Yksityiskohdat

AlkuperäiskieliEnglanti
KustantajaTampere University of Technology
ISBN (painettu)978-952-15-2902-3
TilaJulkaistu - 2012
OKM-julkaisutyyppiG4 Monografiaväitöskirja

Julkaisusarja

NimiTampereen teknillinen yliopisto, Julkaisuja
KustantajaTampere University of Technology
Numero1071
ISSN (painettu)1459-2045

Tiivistelmä

The work of this thesis concentrates on applying the Electrical Low Pressure Impactor (ELPI, Dekati Ltd.) and scanning/differential mobility particle sizer (SMPS/DMPS) to estimate the particle density and particle solidity of secondary organic aerosols (SOA) dme<200 nm. The density estimation method has been extended to smaller particle sizes and the data treatment of the method has been modified to be suitable for large data series and multimodal size distributions. The limitations of the method have been studied using both laboratory tests and simulations. The lowest mode particle diameter for the density method was found to be 10 nm. For multimodal size distributions, the density results varied approximately by 15 %. The density measurements were performed at the SMEAR II station and the density of boreal forest particles was measured. The ELPI was used to study the physical phase of the fresh SOA particles formed by ozonolysis of pure α-pinene and volatile organic compounds (VOCs) of a living Scots pine in a chamber. The phase of SOA particles formed in the boreal forest was analyzed as well. The particles were found to bounce from smooth impaction plates of ELPI towards lower impactor stages. The behavior was interpreted as an indication of a solid physical phase of the particles. The interpretation was corroborated by SEM (Scanning electron microscope) images. In the TEM (Tunneling electron microscope) analysis, the particles were non-crystalline. Based on these results, the particles were inferred to have adopted an amorphous (glassy) physical state. The α-pinene particles had similar bouncing ability as the Scots pine derived particles indicating similar physical phase behavior. The measured bounce factor did not significantly change during the particle growth for particles larger than 40 nm, indicating no changes in particle solidity. For the smallest particles (below 40 nm), the calculated bounce factor increased as the particles grew, indicating that the smallest particles were less solid than the larger ones. The maximum value of the bounce factor decreased for subsequent impactor stages of ELPI. According to a simplified model, this can be explained as a combined effect of bounce probability and charge transfer between the particles and the impaction surface if at least 60% of the particles bounce. The observed solidity of the SOA particles challenges the traditional views on the kinetics and thermodynamics of SOA formation, their transformation in the atmosphere and their implications on air quality and climate. It can influence the ability of the particles to accommodate water and act as could condensation nuclei or as ice nuclei, reduce the rate of heterogeneous chemical reactions and eventually alter the atmospheric lifetime of the particles.

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