Abstract View
The Effect of Aerosol Acidity on the Volatility of Isoprene and Monoterpene-derived Secondary Organic Aerosol (SOA)
ALLA ZELENYUK, David Bell, Matthieu Riva, Dan Imre, Marianne Glasius, ManishKumar Shrivastava, John Shilling, Jason Surratt, Joel A. Thornton, Emma D'Ambro, Rahul Zaveri, Pacific Northwest National Laboratory
Abstract Number: 452
Working Group: Aerosol Chemistry
Abstract
Reactive uptake of isoprene and monoterpene-oxidation products by acidic sulfate particles has been identified as an important source of SOA that leads to the formation of low-volatility products, i.e. oligomers and organosulfates (OS).
We have previously investigated the reactive uptake of isomeric isoprene epoxydiols (IEPOX) by acidic ammonium bisulfate (ABS) and non-acidic deliquesced ammonium sulfate (AS) particles. Using single particle mass spectrometry, we demonstrated that IEPOX uptake by pure ABS and AS particles is a volume-controlled process, which results in particles with uniform composition across a wide range of sizes. In contrast, IEPOX uptake by ABS particles coated with α-pinene SOA is lower compared to that of pure ABS particles and is strongly dependent on particle size.
The measurements of room-temperature evaporation kinetics of size-selected particles indicate that nearly 90% of IEPOX-SOA formed on ABS seeds is non-volatile. IEPOX-SOA formed on ABS at low RH and evaporated at high RH exhibit slightly higher evaporative loses, retaining 75% of their volume after 24 hours of evaporation. In comparison, IEPOX-SOA particles formed on AS seeds retain only 50% of their volume after 24 hours, at which point the particles composition is dominated by OS. In all cases the volatility of IEPOX-SOA is ~3 orders of magnitude lower than that of SOA formed by gas-phase isoprene photooxidation.
To better understand the observed size-dependent IEPOX uptake by α-pinene SOA-coated ABS particles we examined the chemical interactions between ABS seeds and α-pinene oxidation products. We will present the results of experiments, in which we observed size-dependent reactive uptake of gas-phase monoterpene ozonolysis products, size-independent reactive uptake of α-pinene oxide, and quantified volatility of α-pinene SOA coatings as a function of coating thickness.