Seasonal variability of measured ozone production efficiencies in the lower free troposphere of Central Europe P. Zanis1,2, A. Ganser3, C. Zellweger4, S. Henne4, M. Steinbacher4, and J. Staehelin3 1Research Centre for Atmospheric Physics and Climatology, Academy of Athens, Athens, Greece 2Department of Meteorology and Climatology, School of Geology, Aristotle University of Thessaloniki, Greece 3Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland 4Swiss Federal Institute for Materials Science and Technology (Empa), Laboratory for Air Pollution/Environmental Technology, 8600 Dübendorf, Switzerland
Abstract. In this study we present the seasonal variability of ozone production
efficiencies (EN), defined as the net number of ozone molecules produced
per molecule of nitrogen oxides (nitrogen oxide (NO) + nitrogen dioxide
(NO2)=NOx) oxidized to NOz (total reactive nitrogen
(NOy)–NOx) determined from field measurements of a seven-year
period (1998–2004) at the Swiss high-alpine research station Jungfraujoch
(JFJ), 3580 m a.s.l. This dataset is a unique long-term data series of
nitrogen levels in the free troposphere over Central Europe and hence it
offers an excellent opportunity to perform such an analysis and provide
further evidence to the photochemical origin of the ozone spring maximum at
locations of the northern hemisphere distant from nearby pollution sources.
Experimentally derived daily EN values have been selected for 571 days
out of the 2557 days from 1998 to 2004, from which an average ozone
production efficiency of 18.8±1.3 molecules of O3 produced per molecule
of NOx oxidized was calculated. This value indicates the great potential
and importance of photochemical ozone production in the free troposphere.
The monthly means of experimentally derived daily EN values show a
seasonal variation with lower values from May to August, which can be
probably attributed to more efficient vertical transport of polluted air
masses from the atmospheric boundary layer up to JFJ. In agreement,
theoretically derived monthly EN values show similar seasonal variation.
The ratio NOy/CO, a parameter to assess the aging process that has
occurred in an air parcel, was used as a criterion to disaggregate the 571
selected days between undisturbed and disturbed free tropospheric (FT). The
monthly means of experimentally derived EN values for the undisturbed FT
conditions show a distinct seasonal cycle with higher values in the cold
season from November to April. The EN values for undisturbed FT
conditions are particularly higher than the respective monthly EN values
for disturbed FT conditions from February to October. It should be noted
that the monthly EN values of March (EN=35.8) and April
(EN=34.9) are among the highest values throughout the year for
undisturbed FT conditions at JFJ. These results highlight the key and
possibly the dominant role for photochemistry in the observed build-up of
tropospheric ozone in the winter-spring transition period.
Citation: Zanis, P., Ganser, A., Zellweger, C., Henne, S., Steinbacher, M., and Staehelin, J.: Seasonal variability of measured ozone production efficiencies in the lower free troposphere of Central Europe, Atmos. Chem. Phys., 7, 223-236, doi:10.5194/acp-7-223-2007, 2007.