The ability of an atmospheric aerosol to take up water or to participate in heterogeneous reactions is highly influenced by its phase state – solid, semi-solid, or liquid. These changes in phase state can be predicted by glass transition temperature (Tg), as particles at temperatures below their Tg will show solid properties, while increasing the temperature above their Tg will allow for semi-solid and eventually liquid properties. Historically, measurements of the Tg of bulk materials have been studied in order to model the phase states of aerosols in the atmosphere; however, these methods only permit an estimation of aerosol Tg based on their bulk chemical composition. Determining the Tg of individual particles will allow for more accurate model predictions of aerosol phase state. Herein, we apply a recently developed method utilizing a nano-thermal analysis (nanoTA) module coupled to an atomic force microscope (AFM), to determine the Tg of individual secondary organic aerosol (SOA) particles generated from the reactive uptake of isoprene epoxydiol (IEPOX) onto acidic ammonium sulfate aerosol particles. NanoTA works by using a specialized AFM probe which can be heated while in contact with a particle of interest. As the temperature increases, the probe deflection will first increase due to thermal expansion of the particle followed by a decrease at its melting temperature (Tm). The Tg of the particle can then be determined from Tm using the Boyer–Beaman rule. We compared the Tg of IEPOX-derived SOA particles generated at relative humidity (RH) of 30, 65, and 80%, and found that increasing RH from 30 to 80% led to a decrease in average Tg of 22 K, indicating less viscous particles at higher RH conditions. Our measurements with this technique will allow for more accurate representations of the phase state of aerosols in the atmosphere.
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This content will become publicly available on October 2, 2024
Direct Determination of Melting Temperatures for Individual, Sub-Micron Isoprene Epoxydiol-Derived Secondary Organic Aerosol Particles
The phase state of atmospheric aerosol particles – solid, semi-solid, or liquid – influences their ability to take up water and participate in heterogeneous chemical reactions. Changes in phase state have been predicted by glass transition temperature (Tg) and viscosity; however, direct measurements of these properties is challenging for sub-micron particles. Historically, bulk measurements have been used, but this does not account for particle-to-particle variation or the impacts of particle size. Melting temperature (Tm) is the most significant predictor of Tg, and the two properties can be related through the Boyer-Beaman rule. Herein, we apply a recently developed method utilizing a nano-thermal analysis (nanoTA) module coupled to an atomic force microscope (AFM), to determine the Tm of individual secondary organic aerosol (SOA) particles generated from the reactive uptake of isoprene-derived epoxydiols (IEPOX) onto acidic ammonium sulfate aerosol particles. NanoTA works by using a specialized AFM probe which can be heated while in contact with a particle of interest. As the temperature increases, the probe deflection will first increase due to thermal expansion of the particle followed by a decrease at its Tm. The direct measurements are compared with model predictions based on molecular composition from hydrophilic interaction liquid chromatography coupled to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOF-MS) analysis. We compared the Tm of the SOA particles formed from IEPOX uptake onto acidic ammonium sulfate particles created at 30, 65, and 80% relative humidity (RH), and found that increasing RH from 30 to 80% led to an overall decrease in average Tm, indicating less viscous particles at higher RH conditions. Our measurements with this technique will allow for more accurate representations of the phase state of aerosols in the atmosphere.
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- Award ID(s):
- 2001027
- NSF-PAR ID:
- 10486830
- Publisher / Repository:
- AAAR
- Date Published:
- Journal Name:
- 41st Meeting AAAR
- Format(s):
- Medium: X
- Location:
- Portland, OR
- Sponsoring Org:
- National Science Foundation
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The ability of an atmospheric aerosol particle to take up water or to participate in heterogeneous reactions is highly influenced by its phase state – solid, semi-solid, or liquid. The changes in phase state can be predicted by glass transition temperature (Tg), as particles at temperatures below their Tg will show solid properties, while increasing the temperature above their Tg will allow for semi-solid and eventually liquid properties. Historically, measurements of the Tg of bulk materials have been studied in order to model the phase states of aerosols in the atmosphere; however, these methods only permit an estimation of aerosol Tg based on their bulk chemical composition. Determining the Tg of individual particles will allow for more accurate model predictions of aerosol phase state. Herein, we apply a recently developed method utilizing a nano-thermal analysis (nanoTA) module coupled to an atomic force microscope (AFM), to determine the Tg of individual secondary organic aerosol (SOA) particles generated from the reactive uptake of isoprene-derived epoxydiols (IEPOX) onto acidic ammonium sulfate aerosol particles. NanoTA works by using a specialized AFM probe which can be heated while in contact with a particle of interest. As the temperature increases, the probe deflection will first increase due to thermal expansion of the particle followed by a decrease at its melting temperature (Tm). The Tg of the particle can then be determined from Tm using the Boyer–Beaman rule. We compare the Tg of the SOA particles formed from IEPOX uptake onto ammonium sulfate particles with different initial aerosol pH values, as well as under a range of oxidant exposure conditions. Our measurements will allow for more accurate representations of the phase state of aerosols under a range of atmospheric conditions.more » « less
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