206094 Southern Hemisphere In Situ Observations of OH, HO_, CIO and BrO from the ER-2 Aircraft for the 1994 ASHOE Mission Final Technical Report NASA-Langley Agreement No. NAG-l-1609 April 11, 1994-April 10, 1995 Submitted to National Aeronautics and Space Administration from The President and Fellows of Harvard College c/o Office for Sponsored Research Holyoke Center, Room 458 1350 Massachusetts Avenue Cambridge, Massachusetts 02138 James G. Anderson, Principal Investigator Department of Chemistry Harvard University 12 Oxford Street Cambridge, Massachusetts 02138 January 30, 1996 Note: Fundingfor this researchwassplit betweentwo grantsfrom NASA Langley: NAG-l-1617 (for field research)and NAG-l-1609 (development/analysiswork in supportof the field mission). This report is submitted as the Final Technical Report for both grants. The NASA Arctic Southern Hemisphere Ozone Experiment (ASHOE) campaign involved forty flights of the ER-2 from Ames Research Center, Moffett Field, CA; Barbers Point Naval Air Station, Hawaii; Nadi Field, Fiji; and Christchurch, New Zealand. The responsibility of the Harvard research team was the in situ observation of the radicals OH, HO2, CIO and BrO, with corollary observations of ozone and water vapor. These radicals constitute the reactants in the rate limiting steps of the catalytic cycles that control the destruction rate of ozone in the lower stratosphere. The instruments performed very well throughout the course of the ER-2 flights for the ASHOE campaign. The data analysis is complete for that mission and the data have been submitted to the mission data network for open access by the scientific community. Key results prepared for publication are attached as appendices to this report. A summary of the first order scientific conclusions that emerged from the research done under this grant are as follows: 1. For the first time, the concentration of the key hydrogen and halogen radicals OH, HO2, C10 and BrO were determined on a global scale extending from the arctic circle to the antarctic circle, over the altitude domain of the ER-2. That domain extends from 15-20 km altitude, covering a critical part of the lower stratosphere. 2. Simultaneous, in situ measurements of the concentrations of OH, HO2, (210, BrO, NO and NO2 demonstrate the predominance of odd-hydrogen and halogen free radical catalysis in determining the rate of removal of ozone in the lower stratosphere over the complete ASHOE mission. This extends to the global scale the "first look" data obtained during the NASA Stratospheric Photochemistry and Dynamics Experiment (SPADE), executed out of Ames Research Center in June 1993. This represents a major rearrangement of our understanding with respect to the hierarchy of dominant catalytic cycles controlling ozone loss in the lower stratosphere. For the past twenty years,it hasbeenassumedthatnitrogenradicalsdominatethe destructionrateof ozoneinthelowerstratosphere. 3. Throughoutthealtitudeandlatituderangecoveredby ASHOE,it wasdeterminedthat asinglecatalyticcycle,HO2+03--_OH+202,accountedfor onehalf ofthetotal03 removalinthis regionoftheatmosphereH.alogenradicalcatalyticcycleswerefound toaccountfor onethirdoftheozoneloss,andnitrogenradicalswerefoundtoaccount for20%oftheloss. 4. Simultaneousobservationsof the full complementof radicals,tracers,ozone,and water vapor during ASHOE demonstratedquantitativelythe coupling that exists betweenthe rate limiting radicalsandotherreactivespeciesin the photochemical reactionnetwork. Specifically,the concentrationsof CIO and HO2 are inversely correlatedwith the concentrationof NO×.This carriesthe implicationthattheNO× effluentfrom the proposedHigh SpeedCivil Transportmay be lessdestructiveto stratosphericozone than had previously been thought. ASHOE brought this conclusionforwardforthefirsttimeonaglobalbasis. 5. The densityof BrO wasmeasuredon a globalscaleduring ASHOE in the lower stratosphereI.t wasfoundthatbromineisresponsiblefor 55-65% ofthelocalrateof catalytic destruction of ozone by reactions involving bromine and chlorine. Normalizing calculatedlossratestototal availableinorganicbromineandchlorine explicitly demonstratesthatbromineis 60-80 timesmoreefficient thanchlorinein removing ozone in the lower stratosphereA. n inferred value of total inorganic bromineisin excellentagreemenwt ithmeasurementosftheirsourcespecies,organic brominecompoundsin thetroposphere. Publications 1. Stimpfle, R. M., D. W. Kohn, P. O. Wennberg, R. C. Cohen, T. Hanisco, J. G. Anderson, R. J. Salawitch, J. W. Elkins, G. S. Dutton, M. Volk, R. S. Gao, D. W. Fahey, "Bromine in the lower stratosphere: In situ measurements of BrO from the NASA ER-2 aircraft," Science, submitted, January 1996. 2. Hanisco, T. F., P. O. Wennberg, R. C. Cohen, J. G. Anderson, D. W. Fahey, E. R. Keim, R. S. Gao, R. C. Wamsley, S. G. Donnelly, L. A. Del Negro, R. J. Salawiteh, K. K. Kelly, and M. H. Proffitt, "In situ measurements of HO× for super- and subsonic aircraft exhaust plumes," Science, in preparation, 1996. Kotm, D. W., R. M. Stimpfle, P. O. Wennberg, T. F. Hanisco, and J. G. Anderson, ° "Constraints on sulfate aerosol reactions along back trajectories imposed by HO× and CIOx in situ measurements," J. Geophys. Res., in preparation, 1996. Submitted to Science, January ]_996 Bromine Catalyzed Removal of Ozone: In Situ Measurements of BrO in the Lower Stratosphere R. M. Stimpfle', D. W. Kohn, P. O. Wennberg, R. C. Cohen, T. F. Hanisco, J. G. Anderson, R. J. Salawitch, J. W. Elkins, R. S. Gao, D. W. Fahey, M. H. Proffitt, M. Loewenstein and K. R. Chan Abstract: Observations of the BrO radical in the lower stratosphere obtained simultaneously with measurements of short-lived hydrogen, nitrogen and chlorine radicals and long-lived radical precursors demonstrate that reactions involving bromine account for more than half of the catalytic destruction of ozone by halogens at -20 km. In the air masses sampled, using the NASA ER-2 aircraft, bromine is 60 to 80 times more efficient on a per atom basis than chlorine at ozone removal. An inferred value for total stratospheric bromine agrees within error with measurements of the bromine source species, the organic bromine compounds that enter the stratosphere from the troposphere. R. M. Stimpfle, D. W. Kohn, P. O. Wennberg, R. C. Cohen, T. F. Hanisco, J. G. Anderson, Department of Chemistry, Harvard University, Cambridge, MA 02138, USA. R. J. Salawitch, Jet Propulsion Laboratory, Pasadena, CA 91109, USA J. W. Elkins, Climate Monitoring and Diagnostics Laboratory, National Oceanic and Atmospheric Administration (NOAA), Boulder, CO 80303, USA. D. W. Fahey, NOAA Aeronomy Laboratory, Boulder, CO 80303, USA. R. S. Gao, M. H. Proffitt, NOAA Aeronomy Laboratory, Boulder, CO 80303 and CIRES, University of Colorado, Boulder, CO 80309, USA. M. Loewenstein, K. R. Chan, National Aeronautics and Space Adminstration (NASA) Ames Research Center, Moffett Field, CA 94035, USA. *To whom correspondence should be addresssed R. M. Stimpfle et al., Bromine Catalyzed Removal of Ozone 1 Introduction Bromine compounds contribute to halogen catalyzed ozone loss in the lower stratosphere with remarkable potency relative to more abundant chlorine compounds on a per atom basis (1, 2). This increased efficiency arises from three causes. First, the organic source molecules (often referred to as CBry) that transport bromine from the troposphere to the stratosphere are relatively short-lived compared with chlorinated source gases (3). Thus in the stratosphere bromine is converted into forms capable of destroying ozone more rapidly than chlorine. Second, once bromine has been released from its source molecules, more than half is present during daylight in radical forms (BrO, Br) capable of efficient O3 removal, whereas only a few percent of chlorine is present as radicals (4). Finally, the rates for two limiting reactions for catalytic 03 loss involving bromine, BrO + HO2 and BrO + CIO, are very rapid compared to rates for analogous reactions involving chlorine, CIO + HO2 and C10 + CIO. In 1987 the Montreal Protocol introduced provisions, further amended in London and Copenhagen, to regulate future emission of CBrF3, CBrCIF2 and C2Br2F4 (Halons 1301,1211 and 2402), the industrially produced bromine compounds that posed the most substantial threat to the ozone layer. Approximately half of CBry is comprised of CH3Br (methyl bromide) which has both natural and anthropogenic sources. Knowledge of the relative contribution of these two sources of CH3Br is important to future regulatory decisions and is the subject of much controversy and uncertainty (5). Thus, while there is clear evidence from measurements of organic chlorine compounds in the troposphere that future 03 loss by chlorine will likely decrease if the Protocol and its amendments are followed (6), the future course for bromine induced 03 loss is unclear. Measurements in the stratosphere are required to test hypotheses concerning the abundance and speciation of bromine compounds (7). Previous efforts have been hampered compared with similar work for chlorine compounds because atmospheric concentrations of bromine species are very low. Mixing R. M. Stimpfle et al., Bromine Catalyzed Removal ofOzone 2