Hydroxyl radicals in the tropical troposphere over the Suriname rainforest: airborne measurements M. Martinez1, H. Harder1, D. Kubistin1, M. Rudolf1, H. Bozem1, G. Eerdekens1,*, H. Fischer1, T. Klüpfel1, C. Gurk1, R. Königstedt1, U. Parchatka1, C. L. Schiller2, A. Stickler1,**, J. Williams1, and J. Lelieveld1 1Department of Atmospheric Chemistry, Max Planck Institute for Chemistry, Mainz, Germany 2Department of Chemistry, York University, Toronto, Canada *now at: Department of Biology, University of Antwerp, Belgium **now at: Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland
Abstract. Direct measurements of OH and HO2 over a tropical rainforest were made
for the first time during the GABRIEL campaign in October 2005, deploying
the custom-built HORUS instrument (HydrOxyl Radical measurement Unit based
on fluorescence Spectroscopy), adapted to fly in a Learjet wingpod. Biogenic
hydrocarbon emissions were expected to strongly reduce the OH and HO2
mixing ratios as the air is transported from the ocean over the forest.
However, surprisingly high mixing ratios of both OH and HO2 were
encountered in the boundary layer over the rainforest.
The HORUS instrumentation and calibration methods are described in detail
and the measurement results obtained are discussed. The extensive dataset
collected during GABRIEL, including measurements of many other trace gases
and photolysis frequencies, has been used to quantify the main sources and
sinks of OH. Comparison of these measurement-derived formation and loss
rates of OH indicates strong previously overlooked recycling of OH in the
boundary layer over the tropical rainforest, occurring in chorus with
Citation: Martinez, M., Harder, H., Kubistin, D., Rudolf, M., Bozem, H., Eerdekens, G., Fischer, H., Klüpfel, T., Gurk, C., Königstedt, R., Parchatka, U., Schiller, C. L., Stickler, A., Williams, J., and Lelieveld, J.: Hydroxyl radicals in the tropical troposphere over the Suriname rainforest: airborne measurements, Atmos. Chem. Phys., 10, 3759-3773, doi:10.5194/acp-10-3759-2010, 2010.