A large fraction of fine particulate matter (aerosol) in the atmosphere is secondary in nature, formed from the atmospheric oxidation of gas-phase compounds. This oxidation chemistry can govern the amount and properties of aerosol particles, and hence their impacts on climate and health. Much of our understanding of aerosol formation derives from laboratory studies, which to be most useful for atmospheric modeling should cover the range of atmospheric oxidation conditions as well as possible. One particular challenge is matching the chemistry of organic peroxy (RO2) radicals; these key intermediates can react via a number of channels – bimolecular reactions with different radical species (NO, HO2, RO2…) as well as unimolecular (isomerization) reactions – each of which may have its own reaction product distribution and aerosol yields. This talk will describe our group’s efforts to measure aerosol formation in an environmental (“smog”) chamber, across the full range of RO2 conditions found in the atmosphere. For the oxidation of a given aerosol precursor, we vary RO2 chemistry in the chamber by changing concentrations of various reactants, and estimate RO2 fate using chemical ionization mass spectrometry (CIMS) of gas-phase products as well as mechanistic modeling of the oxidation chemistry. Chemical systems examined include the oxidation of dimethyl sulfide (CH3SCH3, emitted to the atmosphere by phytoplankton) to form sulfate aerosol, and the oxidation of isoprene and alpha-pinene (C5H8 and C10H16, emitted by plants) to form organic aerosol.
About the Speaker:
Jesse Kroll is a professor at MIT’s Departments of Civil and Environmental Engineering and Chemical Engineering, and is the Director of MIT’s Ralph M. Parsons Laboratory for Environmental Science and Engineering. He received his Ph.D. in Chemistry from Harvard University in 2003, and was a postdoc at Caltech and then a Research Scientist at Aerodyne Research, Inc. Jesse’s research group studies atmospheric organic chemistry, focusing on laboratory studies of oxidation reactions, organic aerosol formation and evolution, and the use of low-cost sensors to measure gas-phase and particulate pollutants.