Bounce behavior of freshly nucleated biogenic secondary organic aerosol particles

Abstract

Abstract. The assessment of the climatic impacts and adverse health effects of atmospheric aerosol particles requires detailed information on particle properties. However, very limited information is available on the morphology and phase state of secondary organic aerosol (SOA) particles. The physical state of particles greatly affects particulatephase chemical reactions, and thus the growth rates of newly formed atmospheric aerosol. Thus verifying the physical phase state of SOA particles gives new and important insight into their formation, subsequent growth, and consequently potential atmospheric impacts. According to our recent study, biogenic SOA particles produced in laboratory chambers from the oxidation of real plant emissions as well as in ambient boreal forest atmospheres can exist in a solid phase in size range >30 nm. In this paper, we extend previously published results to diameters in the range of 17-30 nm. The physical phase of the particles is studied by investigating particle bounce properties utilizing electrical low pressure impactor (ELPI). We also investigate the effect of estimates of particle density on the interpretation of our bounce observations. According to the results presented in this paper, particle bounce clearly decreases with decreasing particle size in sub 30 nm size range. The comparison measurements by ammonium sulphate and investigation of the particle impaction velocities strongly suggest that the deCorrespondence to: A. Virtanen (annele.virtanen@tut.fi) creasing bounce is caused by the differences in composition and phase of large (diameters greater than 30 nm) and smaller (diameters between 17 and 30 nm) particles.

Humidity-dependent phase state of SOA particles from biogenic and anthropogenic precursors

“…These SOA particles can undergo phase transitions as a result of changes in relative humidity, and/or O / C level. Addition of hygroscopic sulphuric acid to the SOA liquefied the mixed particles at low RH I , which is consistent with aerosol bounce observations from Virtanen et al (2011) and T g measurements from Koop et al (2011). The phase of the SOA affects corresponding timescales for mass transfer and heterogeneous reactions within the particles (Cappa and Wilson, 2011;Vaden et al, 2011;Shiraiwa et al, 2011), and may influence their ability to serve as cloud condensation nuclei or ice nuclei in the atmosphere.…”

“…The discussion above indicates that this might be true independently of whether the sulphate and organic fraction are phase-separated or not. As the particles grow via condensation of oxygenated organic species, the mass fraction and, hence, the effective T g might increase and the particles may solidify (Virtanen et al, 2010(Virtanen et al, , 2011.…”

Relating hygroscopicity and optical properties to chemical composition and structure of secondary organic aerosol particles generated from the ozonolysis of α-pinene

“…Virtanen et al (2011) reported that α-pinene-O 3 SOA bounces off impactor plates as if particles were glassy. Other studies reported that the evaporation kinetics of α-pinene-O 3 SOA was lower than expected by models for liquid droplets, indicating a non-liquid-like state Vaden et al, 2011).…”

Kinetic modeling studies of SOA formation from <i>α</i>-pinene ozonolysis

“…The phase states of SOA particles have been investigated in more detail by a wide variety of measurement techniques recently. The first indications of an amorphous (semi-)solid state for biogenic SOA particles were deduced by Virtanen et al (2010) and were established in subsequent studies (Virtanen et al, 2011;Cappa and Wilson, 2011;Vaden et al, 2011;Saukko et al, 2012;. These studies have provided a first qualitative estimate of the particle-phase state; however, quantitative values such as the particle-phase bulk diffusion coefficients are essential for model description.…”