A13E-0378
Total OH reactivity measurements aboard the Zeppelin NT during the PEGASOS campaigns 2012 and 2013: Spatial and vertical distribution and contribution of substance classes

Monday, 14 December 2015
Poster Hall (Moscone South)
Robert Wegener1, Julia Jäger2, Andreas Hofzumahaus1, Hendrik Fuchs1, Sebastian Gomm3, Sebastian Broch3, Rolf Häseler4, Frank Holland1, Ralf Tillmann4, Thomas F Mentel5, Astrid Kiendler-Scharr6, Andreas Wahner7, Jennifer Kaiser8, Keding Lu9, Glenn Wolfe10, Frank N Keutsch11 and Mitchell P Thayer12, (1)Forschungszentrum Jülich GmbH, Jülich 52428, Germany, (2)Scientific Analysis Laboratories Limited, Manchester, United Kingdom, (3)Forschungszentrum Jülich, Institute of Energy and Climate Research, IEK-8: Troposphere, Jülich, Germany, (4)Forschungszentrum Jülich, Institute of Energy and Climate Research, IEK-8, Jülich, Germany, (5)IEK-8-Troposphere, Juelich, Germany, (6)Forschungszentrum Jülich, Institute for Energy and Climate Research: Troposphere (IEK-8), Jülich, Germany, (7)Forschungszentrum Jülich, Jülich, Germany, (8)University of Wisconsin- Madison, Madison, WI, United States, (9)Forschungszentrum Juelich(FZJ), Beijing, China, (10)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (11)Harvard University, Cambridge, MA, United States, (12)University of Wisconsin Madison, Madison, WI, United States
Abstract:
Hydroxyl (OH) radicals are the main oxidants of atmospheric pollutants. The quantification of their sources and sinks is necessary to fully comprehend the measured OH concentration. Due to difficulties quantifying all the individual compounds contributing to the OH loss, the direct quantification of the OH loss is a crucial means to have predictive capability of atmospheric OH concentrations and thus oxidation rates. Especially in forested areas, where OH reactivity is dominated by highly reactive organic compounds, the directly measured OH loss rate often exceeds the calculated total OH reactivity.

Here we present the total OH loss data and data for the individual sinks of OH measured on board of the Zeppelin NT in summer 2012 and 2013. The campaigns were part of the Pan-European Gas AeroSOls-climate interaction Study (PEGASOS) and were performed from May – July 2012 in the area of Rotterdam (the Netherlands) and Bologna (Italy) and from April – July 2013 over Finland. Total OH reactivity was measured monitoring the decay of photolytically produced OH with laser induced fluorescence (LIF). OH, HO2, Volatile Organic Compounds (VOC), CO, formaldehyde, NOx, HONO and ozone were analyzed online together with photolysis frequencies, particle number concentrations and meteorological parameters. The Zeppelin NT was flying at low speed at altitudes of up to 900 m which provided insight into the vertical structure of the lower troposphere.

On average, the total OH reactivity was 6.1 ± 1.2 s-1 over the area of Rotterdam, 3.8 ± 1.4 s-1 over the region of Bologna and only 2.1 ± 1.1 s-1 over Finland.

During almost the entire campaigns, the measured total OH reactivity could be explained by the contributions of measured species.

Oxygenated volatile organic compounds (OVOC) contributed the major part of the total OH reactivity measured with a percentage share of 30% over the Rotterdam area and 40% over the area of Bologna. In the morning hours when layered structures had been built up over night, large gradients of the total OH reactivity were observed. The contribution of OVOC was especially large in the residual layer, which was decoupled from emissions from the ground.

Acknowledgement: PEGASOS project funded by the European Commission und the Framework Program 7 (FP7-ENV-2010-265148) and NSF-AGS (1051338).

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