A224-0014
Smoke plumes, brown carbon and photolysis frequency dynamics
Wednesday, 16 December 2020
Poster
Samuel R Hall1, Kirk Ullmann1, Teresa Lynn Campos2, Yonghoon Choi3, Joshua P DiGangi3, Glenn S Diskin4, Marta A Fenn5, Johnathan W Hair3, Hannah Halliday6, Anthony Notari3, John B Nowak3 and Taylor J Shingler7, (1)National Center for Atmospheric Research (NCAR), Atmospheric Chemistry Observations and Modeling Laboratory, Boulder, CO, United States, (2)Natl Ctr Atmospheric Research, Boulder, CO, United States, (3)NASA Langley Research Center, Hampton, VA, United States, (4)NASA Langley Research Ctr, Hampton, VA, United States, (5)SSAI, Hampton, VA, United States, (6)US Environmental Protection Agency Research Triangle Park, Durham, NC, United States, (7)Science Systems and Applications, Inc., Hampton, VA, United States
Abstract:
Chemistry models often neglect the spectral impacts of smoke on photolysis frequencies. Spectrally resolved actinic flux measurements on the NCAR C-130 and NASA DC-8 aircraft help map the physical and spectral variability in photochemistry during the Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) and Fire Influence on Regional to Global Environments - Air Quality (FIREX-AQ) campaigns. Along the plume, actinic flux is sensitive to changing fire activity, turbulent transport dynamics, diffusion, chemical aging and sun angle. Orthogonal transects reveal expectedly stronger reductions within the plume core under high aerosol loading and lesser reductions along the more diffuse edges.
In addition, spectral absorption from brown carbon (BrC) species produced by the fires strongly perturbs the ultraviolet (UV) where much of the energy for photochemistry is centered. The resulting impacts on photolysis frequencies vary according to the shape of the BrC absorption curve and the spectral response of each molecule. For example, the NO2 absorption cross section spans the UV-A while the ozone cross section spans the UV-B where BrC absorption is the strongest. Thus, the reduction due to BrC is larger for jO3 than jNO2. This effect is not generally taken into account when jNO2 is scaled to calculate additional photolysis frequencies. In one strong plume, the calculated jO3 bias was greater than 80% (jHONO > 20%, jCH2O > 60%, jNO3 > 350%) compared with the measured result. We will also examine the effects in diffuse smoke where the biases are reduced but photolysis rates are higher and the spatial footprint is larger.
