AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
A New Method to Measure Aerosol Particle Bounce and Estimating the Phase State of Atmospheric Aerosols
SHASHANK JAIN, Giuseppe Petrucci, University of Vermont
Abstract Number: 103 Working Group: Instrumentation and Methods
Abstract Organic aerosol (OA) is a ubiquitous component of atmospheric particulate that influences both human health and global climate. A large fraction of OA is secondary in nature (SOA), being produced by oxidation of volatile organic compounds (VOCs) emitted by biogenic and anthropogenic sources. Recent studies have shown that atmospheric SOA could be liquid or solid in phase and can affect the global climate in multiple and complex ways through its interactions with radiation and clouds. SOA can either scatter or absorb solar radiation, thereby modifying the Earth’s radiative balance. Such scattering or absorbing largely depends on aerosol physical properties and environmental conditions. Moreover, the physical state of particles can affect particulate phase chemical reactions, and thus the growth rates of newly formed atmospheric particles. Hence understanding the phase state of aerosol is a key to understanding the global climate change.
In the present work, we describe a simplified method to measure the phase state (liquid or non-liquid) of organic aerosol by estimating the bounce factor of polydisperse SOA using only a multi-stage cascade electrical low pressure impactor (ELPI). The method eliminates the need for an independent measure of the particle size distribution (for example, as with an SMPS) and relies on comparison of absolute ion currents at each impactor stage under conditions that favor or reduce particle bounce. We validated the proposed method with solid, liquid and non-liquid aerosols, namely ammonium sulfate (AS), dioctyl sebacate (DOS), oleic acid (OA) and ozonized OA, and present bounce factor evolution of aging alpha-pinene-derived SOA.
This simplified method helps us to determine the real-time SOA phase state for polydisperse aerosols and establish a relationship between SOA phase, oxidative formation and chemical aging. This method will also helps us to understand the impact that various parameters, such as SOA precursor, oxidation type and mixing ratio, can have on the phase of atmospheric organic particulate.