Measurement of Water Vapor Sorption by Single Biological Aerosols

Single particle levitation (SPL) is used to measure water vapor sorption and desorption from micrometer-sized particles comprised of Bacillus spores and yellow pine pollen. Water gain--loss is determined from increasesdecreases in the weight-balancing levitation voltages. BET (Brunauer, Emmett, and Teller) surface area analysis of the spore water isotherms are performed and compared to values previously reported using bulk gravimetric methods. Two salient differences are found between the SPL and bulk data: (1) greater osmotic swelling is observed in the SPL data and (2) the SPL data exhibits open loop hysteresis while bulk data exhibits closed loop hysteresis. Yellow pine pollen exhibits a distinct water isotherm when compared to that of Bacillus spores.