Atmospheric Chemistry and Physics Discussions
www.atmos-chem-phys-discuss.net
1680-7367
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6
5
2006
10.5194/acpd-6-9315-2006
http://www.atmos-chem-phys-discuss.net/6/9315/2006/
http://www.atmos-chem-phys-discuss.net/6/9315/2006/acpd-6-9315-2006.html
http://www.atmos-chem-phys-discuss.net/6/9315/2006/acpd-6-9315-2006.pdf
9315
9349
2006-09-26
Seasonal variability of measured Ozone production efficiencies in the lower free troposphere of Central Europe
P. Zanis
A. Ganser
C. Zellweger
S. Henne
M. Steinbacher
J. Staehelin
Research Centre for Atmospheric Physics and Climatology, Academy of Athens, Athens, Greece
Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
Swiss Federal Institute for Materials Science and Technology (Empa), Laboratory for Air Pollution/Environmental Technology, 8600 Dübendorf, Switzerland
In this study we present the seasonal variability of ozone production
efficiencies (<i>E<sub>N</sub></i>), defined as the net number of ozone molecules produced
per molecule of nitrogen oxides (nitrogen oxide (NO) + nitrogen dioxide
(NO<sub>2</sub>)=NO<sub>x</sub>) oxidized to NO<sub>z</sub> (total reactive nitrogen
(NO<sub>y</sub>)-NO<sub>x</sub>) for 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 <i>E<sub>N</sub></i> 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
O<sub>3</sub> produced per molecule of NO<sub>x</sub> 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 <i>E<sub>N</sub></i> 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 <i>E<sub>N</sub></i> values show similar
seasonal variation. The ratio NO<sub>y</sub>/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 <i>E<sub>N</sub></i> values
for the undisturbed FT conditions show a distinct seasonal cycle with higher
values in the cold season from November to April. The <i>E<sub>N</sub></i> values for
undisturbed FT conditions are particularly higher than the respective
monthly <i>E<sub>N</sub></i> values for disturbed FT conditions from February to October.
It should be noted that the monthly <i>E<sub>N</sub></i> values of March (<i>E<sub>N</sub></i>=35.8) and
April (<i>E<sub>N</sub></i>=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.