The Influence of Absolute Mass Loading of Secondary Organic Aerosols on Their Phase State

Abstract

Absolute secondary organic aerosol (SOA) mass loading (C SOA ) is a key parameter in determining partitioning of semi-and intermediate volatility compounds to the particle phase. Its impact on the phase state of SOA, however, has remained largely unexplored. In this study, systematic laboratory chamber measurements were performed to elucidate the influence of C SOA , ranging from 0.2 to 160 µg m −3 , on the phase state of SOA formed by ozonolysis of various precursors, including α-pinene, limonene, cis-3-hexenyl acetate (CHA) and cis-3-hexen-1-ol (HXL). A previously established method to estimate SOA bounce factor (BF, a surrogate for particle viscosity) was utilized to infer particle viscosity as a function of C SOA . Results show that under nominally identical conditions, the maximum BF decreases by approximately 30% at higher C SOA , suggesting a more liquid phase state. With the exception of HXL-SOA (which acted as the negative control), the phase state for all studied SOA precursors varied as a function of C SOA . Furthermore, the BF was found to be the maximum when SOA particle distributions reached a geometric mean particle diameter of 50-60 nm. Experimental results indicate that C SOA is an important parameter impacting the phase state of SOA, reinforcing recent findings that extrapolation of experiments not conducted at atmospherically relevant SOA levels may not yield results that are relevant to the natural environment.

Predicting the glass transition temperature and viscosity of secondary organic material using molecular composition

“…For instance, Grayson et al (2016) used mass loadings of 121 to 14 000 µg m −3 and observed that viscosity decreased as mass loading increased. Higher mass loadings would lead to greater partitioning of semi-volatile and lower-molar-mass compounds into the particle phase, which would lead to the decrease in T g and the viscosity of the resulting SOA mixture, as very recently demonstrated experimentally by Jain et al (2018). Grayson et al (2016) concluded that their results should be considered a lower limit for the viscosity of α-pinene SOA in the atmosphere.…”

“…The sensitivity calculations showed that T g,org contributed the most to the uncertainty in the viscosity estimates. Previous studies have shown that the experimental conditions such as particle mass concentrations Jain et al, 2018) and RH upon SOA formation (Kidd et al, 2014;Hinks et al, 2018) can impact the chemical composition of SOA and hence the phase state and viscosity. Further efforts to constrain the uncertainties are needed both in experiments and parameterizations.…”

“…Regarding the applications to air quality and climate models, Eq. (1) can be applied in the volatility basis set (VBS; Donahue et al, 2006Donahue et al, , 2011 and the molecular corridor approach to predict the T g of SOA particles , while the new parameterization may be suitable for coupling with the statistical oxidation model, which characterizes the SOA evolution as a function of n C and n O (Cappa and Wilson, 2012;Jathar et al, 2015).…”

Supplementary material to "Predicting the glass transition temperature and viscosity of secondary organic material using molecular composition"

“…Regarding the applications to air quality and climate models, Eq. (1) can be applied in the volatility basis set (VBS; Donahue et al, 2006Donahue et al, , 2011 and the molecular corridor approach (Shiraiwa et al, 2014; to predict the T g of SOA particles (Shiraiwa et al, 2017), while the new parameterization may be suitable for coupling with the statistical oxidation model, which characterizes the SOA evolution as a function of n C and n O (Cappa and Wilson, 2012;Jathar et al, 2015).…”

Correction: Jain, S., et al. The Influence of Absolute Mass Loading of Secondary Organic Aerosols on Their Phase State. Atmosphere, 2018, 9, 131

“…The authors would like to correct the published article [1] concerning the acknowledgments, as follows: This material is based upon work supported by the National Science Foundation under Grant No. CHE-1709751.…”