Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 1: Deployment of the Indiana University laser-induced fluorescence instrument S. Dusanter1, D. Vimal1,*, P. S. Stevens1, R. Volkamer2,3,4, and L. T. Molina2,5 1Center for Research in Environmental Science, School of Public and Environmental Affairs, and Department of Chemistry, Indiana University, Bloomington, IN 47405, USA 2Massachusetts Institute of Technology, Cambridge MA, USA 3University of California at San Diego, La Jolla CA, USA 4University of Colorado at Boulder and CIRES, Boulder CO, USA 5Molina Center for Energy & the Environment, La Jolla CA, USA *now at: Molecular Physics Laboratory, SRI International, Menlo Park, CA, USA
Abstract. Measurements of tropospheric hydroxyl (OH) and hydroperoxy (HO2)
radicals were made during the MCMA (Mexico City Metropolitan Area) field
campaign as part of the MILAGRO (Megacity Initiative: Local and Global
Research Observations) project during March 2006. These radicals were
measured using a laser-induced fluorescence instrument developed at Indiana
University. This new instrument takes advantage of the Fluorescence Assay by
Gas Expansion technique (FAGE) together with direct excitation and detection
of OH at 308 nm. HO2 is indirectly measured as OH by titration with NO
inside the fluorescence cell. At this stage of development, IU-FAGE is
capable of detecting 3.9×105 molecule/cm3 of both OH and
HO2, with a signal to noise ratio of 1, an averaged laser power of
10-mW and an averaging time of 5-min. The calibration accuracies (1σ) are ±17% for OH and ±18% for HO2 using the
water-vapor photolysis/O2 actinometry calibration technique.
OH and HO2 concentrations were successfully measured at an urban site
in Mexico City, with observed concentrations comparable to those measured in
other polluted environments. Enhanced levels of OH and HO2 radicals
were observed on several days between 09:30–11:00 a.m. and suggest an intense
photochemistry during morning hours that may be due to elevated sources of
HOx (OH+HO2) and a fast cycling between the radicals under the
high NOx (NO+NO2) conditions of the MCMA.
Citation: Dusanter, S., Vimal, D., Stevens, P. S., Volkamer, R., and Molina, L. T.: Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 1: Deployment of the Indiana University laser-induced fluorescence instrument, Atmos. Chem. Phys., 9, 1665-1685, doi:10.5194/acp-9-1665-2009, 2009.