AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Experimental Studies of Particle Bounce: Comparison of Secondary Organic Material (SOM) from Harvard Environmental Chamber and Field Studies in Amazonia
ADAM BATEMAN, Pengfei Liu, Scot Martin, Harvard University
Abstract Number: 524 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The effect of relative humidity (RH) on the extent of semisolidity was investigated through the use of particle bounce (or lack thereof) during impaction. The physics governing particle bounce can be attributed to particle surface properties, specifically the coefficient of restitution and surface adhesion forces. It has been suggested that aerosols can form disordered amorphous solids (glasses) due to the complex organic composition, with larger and more hydrophobic organic molecules more likely to form glasses. The amorphous organic phases can form from a variety of organic compounds upon drying of an aqueous solution and can undergo transitions during the course of hydration and dehydration. By varying the particulate matter water content and observing particle bounce as a function of RH, the phase state of the organic material under investigation can be determined. Custom made impactors were employed to study the effects of RH on the phase state of organic particles, up to an RH of 99%. Particles were produced in the Harvard environmental chamber from a variety of precursors and oxidants, including isoprene, alpha-pinene, and toluene. In addition, two field campaigns were conducted in the wet and dry season in Amazonia using the custom impactors. Comparison with the particle bounce experiments from the laboratory give insights into the phase state of atmospheric SOM as a function of RH.