Factors Controlling Liquid Particulate Matter in Amazonia

Abstract:

The hygroscopic response of particulate matter (PM) during GoAmazon 2014/5 was investigated through the use of particle rebound (or lack thereof) during impaction. The hygroscopic response was measured online and in real-time using a custom designed impaction apparatus. The impaction apparatus was calibrated with respect to particle viscosity indicating a liquid state (viscosity <10² Pa s) for complete adherence (no particle rebound). By varying the PM water content and observing particle rebound as a function of RH (up to 98%), the hygroscopic response and phase state of the PM under investigation was determined.

The hygroscopic response curves were categorized according to the rebound fraction at high RH (80 – 98%) bounded by two extremes. 1) Time periods that resemble pure SOM generated under controlled chamber conditions, where no particle rebound is observed above 80% RH. 2) Time periods that a large fraction (10 – 40%) of particles rebound at RH values >95%, an indication of hydrophobic particles. The role of anthropogenic and biogenic factors in controlling the hygroscopic response of PM in Amazonia is investigated through meteorological conditions and particle chemical composition.