Tropospheric HONO Distribution and Chemistry in the Southeastern U.S.

Wednesday, 17 December 2014: 9:45 AM
Xianliang Zhou1, Chunxiang Ye1, Dennis Pu2, Jochen Stutz3, James Festa3, Max Spolaor3, Andrew John Weinheimer4, Teresa Lynn Campos5, Julie Anne Haggerty6, Christopher A Cantrell7, Lee Mauldin7, Alex B Guenther8, Rebecca S Hornbrook4, Eric C Apel5 and Jorgen B Jensen9, (1)Wadsworth Center, Albany, NY, United States, (2)SUNY at Albany, Albany, NY, United States, (3)University of California Los Angeles, Los Angeles, CA, United States, (4)NCAR, Boulder, CO, United States, (5)National Center for Atmospheric Research, Boulder, CO, United States, (6)Natl Ctr Atmospheric Res, Boulder, CO, United States, (7)Univ of Colorado, Boulder, CO, United States, (8)Pacific Northwest National Laboratory, Richland, WA, United States, (9)NCAR Researc Aviation Facility, Broomfield, CO, United States
During the NOMADSS field campaign, nitrous acid (HONO) and particulate nitrate (pNO3) was measured on NCAR C-130 research aircraft during five research flights over the Southeast U.S. Aerosol samples were also collected on Teflon filters for the determination of pNO3 photolysis rate constants in the laboratory. Daytime HONO concentrations range from low ppt in free troposphere to 10-20 ppt in the boundary layer in the background air masses, to up to 40 ppt in the industrial and urban plumes. While daytime HONO sink is well defined, dominated by its photolysis, daytime sources vary in different types of air masses: pNO3 photolysis appears to be the major HONO source in the background terrestrial air masses in both the boundary layer and the free troposphere. With an average pNO3 photolysis rate constant of (2.8±1.7)×10-4 s-1, p-NO3 photolysis becomes to be an effective pathway to recycle HNO3 to NOx in the troposphere, with HONO as a dominant intermediate product. Within the high-NOx industrial plumes encountered, HONO is predominantly produced by secondary formation processes involving NOx as the precursor. Away from ground surface, no significant nighttime HONO accumulation exists in the background terrestrial air mass.