10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

Abstract View


Use of Continuous Measurements of the Growth Rate of Particles Inside Captive Aerosol Chambers to Study the Properties and Sources of the Species Responsible for Their Growth

DON COLLINS, Cassandra Milan, Jordan McCormick, Sean Kinahan, Joshua Santarpia, James Flynn, Matthew H. Erickson, Robert Griffin, Henry Wallace, Alexander Bui, Texas A&M University

     Abstract Number: 885
     Working Group: Aerosol Chemistry

Abstract
Two Captive Aerosol Growth and Evolution (CAGE) chambers were operated in a clearing in a state forest north of Houston, TX to study the condensational growth rate of particles exposed to ambient levels of trace gases and solar radiation. The site is impacted by pollution from Houston and the surrounding region and by isoprene and monoterpene emissions from the surrounding forest. The chambers are roughly cubic meter cylinders constructed mostly of highly light transmitting FEP Teflon and surrounded by UV transmitting acrylic such that the solar spectral intensity inside approaches that outside. Efficient exchange of water vapor and trace gases across a sheet of gas-permeable expanded PTFE membrane that seals one end of the chamber maintains near-ambient gas composition inside. Monodisperse ammonium sulfate particles were intermittently injected and their size tracked over periods of several hours. By staggering the size of the injected particles new modes were added as soon as the existing mode(s) became difficult to track. The result is an almost continuous dataset of particle growth rate recorded over a two-month period in late summer and early fall. Complementary measurements of spectral solar intensity and of the concentrations of organic and inorganic trace gases were used with a simple box model to attribute observed particle growth to responsible precursor and oxidant gases. Among the salient findings from the study are i) growth rate was only weakly dependent upon particle size and ii) only minimal particle shrinkage or evaporation was observed. Nitrate radical chemistry was active in the early evening, resulting in a study average growth rate from 8:00 – 9:00 p.m. of 5.8 nm/hr that was comparable to the peak daytime growth rate of 6.1 nm/hr from 9:00 – 10:00 a.m.