Evidence of mixing between polluted convective outflow and stratospheric air in the upper troposphere during DC3

Authors

Jason R. Schroeder, University of California-IrvineFollow
Laura L. Pan, National Center for Atmospheric Research, Boulder, Colorado
Tom Ryerson, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado
Glenn Diskin, NASA Langley Research Center, Hampton, Virginia
Johnathan Hair, NASA Langley Research Center, Hampton, Virginia,
Simone Meinardi, University of California-Irvine
Isobel Simpson, University of California-Irvine
Barbara Barletta, University of California-Irvine
Nicola Blake, University of California-Irvine
Donald R. Blake, University of California-IrvineFollow

Date of this Version

2014

Citation

Schroeder, J. R., L. L. Pan, T. Ryerson, G. Diskin, J. Hair, S. Meinardi, I. Simpson, B. Barletta, N. Blake, and D. R. Blake (2014), Evidence of mixing between polluted convective outflow and stratospheric air in the upper troposphere during DC3, J. Geophys. Res. Atmos., 119, 11,477–11,491

Comments

U.S. Government Work

Abstract

Aircraft measurements, including non-methane hydrocarbons (NMHCs), long-lived halocarbons, carbonmonoxide (CO), and ozone (O₃) collected on board the NASA DC-8 during the Deep Convection, Clouds, and Chemistry (DC3) field campaign (May – June 2012), were used to investigate interactions and mixing between stratospheric intrusions and polluted air masses. Stratospherically influenced air masses were detected using a suite of long-lived halocarbons, including chlorofluorocarbons (CFCs) and HCFCs, as a tracer for stratospheric air. A large number of stratospherically influenced samples were found to have reduced levels of O₃ and elevated levels of CO (both relative to background stratospheric air), indicative of mixing with anthropogenically influenced air. Using n-butane and propane as further tracers of anthropogenically influenced air, we show that this type of mixing was present both at low altitudes and in the upper troposphere (UT). At low altitudes, this mixing resulted in O₃ enhancements consistent with those reported at surface sites during deep stratospheric intrusions, while in the UT, two case studies were performed to identify the process by which this mixing occurs. In the first case study, stratospheric air was found to be mixed with aged outflow from a convective storm, while in the second case study, stratospheric air was found to have mixed with outflow from an active storm occurring in the vicinity of a stratospheric intrusion. From these analyses, we conclude that deep convective events may facilitate the mixing between stratospheric air and polluted boundary layer air in the UT. Throughout the entire DC3 study region, this mixing was found to be prevalent: 72% of all samples that involve stratosphere-troposphere mixing show influence of polluted air. Applying a simple chemical kinetics analysis to these data, we show that during DC3, the instantaneous production of hydroxyl radical (OH) in these mixed stratospheric-polluted air masses was 11 ± 8 times higher than that of stratospheric air, and 4.2 ± 1.8 times higher than that of background upper tropospheric air.