Abstract View
Changes in Light Absorption Driven by Two Different Oxidation Processes on Atmospheric Tar Balls from Wildfires in Western United States
BENJAMIN SUMLIN, Nishit Shetty, Andrew Lambe, Edward Fortner, Andrew Lambe, Rajan K. Chakrabarty, Washington University in St. Louis
Abstract Number: 65
Working Group: Carbonaceous Aerosol
Abstract
Carbonaceous aerosol interacts with sunlight to drive radiative forcing by scattering and absorbing incoming sunlight. Carbonaceous aerosol is broadly categorized as either black carbon (BC), otherwise known as soot or elemental carbon, and organic carbon (OC). Organic carbon aerosol was once thought to be purely scattering; however, we now understand that a class of organic carbon aerosol known as tar balls strongly absorbs sunlight, particularly in the short visible and near-UV wavelengths, contributing positively to Earth’s radiation balance. Furthermore, there is a growing body of evidence that the light absorption characteristics of these aerosol are impacted by atmospheric processing, including oxidation reactions. A new multiwavelength photoacoustic spectrometer, developed in the Complex Aerosol Systems Research Laboratory at Washington University in St. Louis, was installed on board the Aerodyne Mobile Laboratory during FIREX-AQ. It measured light scattering and absorption by aerosol at four wavelengths (405, 488, 561, and 637 nm) from several wildfires in the western United States, both from ambient air and after these aerosols were subjected to two different oxidation processes using an Aerodyne Potential Aerosol Mass oxidation flow reactor. Daylight-driven oxidation was mimicked by exposing tar balls to varying quantities of OH radical, while nighttime processes were mimicked using NO3. We present a comparison of the effects on light absorption of these two processes in context of previous laboratory findings.