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| Titel |
Large-scale distribution of surface ozone mixing ratio in southern Mongolia: A survey |
| VerfasserIn |
F. X. Meixner, T. Behrendt, M. Ermel, N. Hempelmann, M. O. Andreae, P. Jöckel |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068375
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| Zusammenfassung |
| For the first time, measurements of surface ozone mixing ratio have been performed from
semi-arid steppe to arid/hyper-arid southern Mongolian Gobi desert. During 12-29 August
2009, ozone mixing ratio was continuously measured from a mobile platform (4x4
Furgon SUV). The survey (3060 km / 229171km2) started at the Mongolian capital
Ulaan-Baatar (47.9582Ë N, 107.0190Ë E ), heading to south-west (Echin Gol, 43.2586Ë N,
99.0255Ë E), eastward to Dalanzadgad (43.6061Ë N, 104.4445Ë E), and finally back to
Ulaan-Baatar.
Ambient air was sampled (approx. 1 l/min) through a 4 m long PTFE-intake line along a
forward facing boom mounted on the roof of a 4x4 Furgon SUV. Ozone mixing ratio has been
measured by UV-spectroscopy using a mobile dual-cell ozone analyzer (model 205,
2BTechnologies, Boulder, U.S.A.). While ozone signals were measured every 5 seconds, 1
minute averages and standard deviations have been calculated on-line and stored into the data
logger. The latter are used to identify and to discriminate against unrealistic low or
high ozone mixing ratios which have been due to occasionally passing plumes of
vehicle exhaust and/or biomass burning gases, as well as gasoline (at gas filling
stations).
Even under desert conditions, the temporal behaviour of ozone mixing ratio was
characterized by considerable and regular diel variations. Minimum mixing ratios
(15-25 ppb) occurred early in the morning (approx. 06:00 local), when surface
depletion of ozone (by dry deposition) can not be compensated by supply from the free
troposphere due to thermodynamic stability of the nocturnal boundary layer. Late in
the afternoon (approx. 17:00 local), under conditions of a turbulently well mixed
convective boundary layer, maximum ozone mixing ratios (45-55 ppb) were reached.
Daily amplitudes of the diel cycle of ozone mixing ratio were in the order of 30 ppb
(steppe), 20 ppb (arid desert), to approx. 5 ppb (hyper-arid Gobi desert (Shargyn
Gobi)).
Ozone surface measurements were compared to gridded ozone mixing ratios
calculated by the global ECHAMMESSy model. Despite the model data’s nature and
the rather coarse spatial resolution (approx. 220 km) of the MESSy model, the
agreement between (late afternoon) measured data and modelled data is surprisingly
good.
The attempt is made to estimate the (night-time) dry deposition of ozone to steppe and
desert soils from the observed diel cycles of ozone mixing ratio by application of the
“Nocturnal Boundary Layer Mass Balance Technique”. |
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