Secondary organic aerosol (SOA) formed from the atmospheric processing of Volatile Organic Components (VOCs) can account for a substantial fraction of the total aerosol mass. Quantifying the impact of SOA on climate, air quality and health requires an understanding of how the fundamental physicochemical properties of SOA influence their ability to interact with solar radiation, act as cloud condensation nuclei and ice nuclei, and determine the gas-particle partitioning of semi-volatile organic compounds (SVOC). In this work we will present a single particle approach to simultaneously characterise: the equilibrium hygroscopic response of SOA; the relative humidity (RH) dependence of the optical properties (refractive index, RI); the volatility distribution of SVOCs; the existence of liquid-liquid phase separation; and the kinetic factors regulating gas-particle partitioning of water and SVOCs. We will demonstrate that such a combined approach can provide unique insights into how the various properties of the SOA are linked, evolve with time and depend on environmental conditions.<br/><br/>More specifically, we will present measurements of the properties for a-pinene, limonene and b- caryophyllene SOA extending over wide ranges in RH (&lt;10 % to &gt;99.5%) and temperature (-25 to 50 °C). SOA samples are generated in a photo-chemical flow reactor from the oxidation of different VOCs precursors. Known variable VOC, NOx and ozone concentrations are introduced into the chamber and UV irradiation is provided by an Hg pen-ray. SOA samples are collected with an electrical low pressure impactor. Single charged SOA solution droplets generated from the sample are confined within an Electrodynamic Balance (EDB) in a gas flow of controlled temperature and RH. The evolving light scattering pattern is collected and fitted with a library of Mie-Theory simulations to monitor variations in the radius, morphology and the refractive index of the droplet with time. We will show how these measurements can be used to examine the physicochemical properties of SOA surrogates, their dependence on reaction conditions and the influence of environmental factors.

Single particle measurements of the physicochemical properties of secondary organic aerosol surrogates

254th National Meeting (2017)

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