AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Particle Rebound and Phase State in Amazonia
ADAM BATEMAN, Zhaoheng Gong, Antonio O. Manzi, Paulo Artaxo, Rodrigo A. F. Souza, Scot Martin, Harvard University
Abstract Number: 453 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The effect of relative humidity (RH) on the extent of semisolidity of particulate matter during GoAmazon 2014/15 was investigated through the use of particle rebound (or lack thereof) during impaction. The physics governing particle rebound has been previously modeled and can be attributed to the surface and material properties. The phase state of secondary organic material is regulated by the local relative humidity (RH), the recent history of RH in the case of hysteresis, and chemical composition, among other factors. Across the range of atmospheric RH, hygroscopic water uptake can occur and transitions from higher to lower viscosity phases are possible.
By varying the particulate matter water content and observing particle rebound as a function of RH, the hygroscopic response and phase state of the organic material under investigation can be determined. Custom made impactors were employed to study the effects of RH (up to 95%) on the particle phase. Results inferred from the particle rebound measurements indicate that under ambient conditions (RH > 70%) particles in Amazonia can be considered in a liquid phase state. However, during certain time periods, a fraction (10 - 30%) of the particles is found to rebound during the highest RH conditions, an indication of hydrophobic particles in a semi-solid or solid phase state. The origin and chemical composition of this particle subset is further investigated.