 |
| Titel |
Ozone changes at Jungfraujoch (Switzerland) in 1990-2005: Analysis by backward trajectories |
| VerfasserIn |
J. Cui, J. Staehelin, M. Sprenger, M. Steinbacher |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023950
|
|
|
|
|
|
| Zusammenfassung |
| Surface ozone measurements at Jungfraujoch (JFJ) covering the period 1990-2005 are
investigated in this study. Increasing trends with the maximum +0.63±0.22 ppb/y in winter
and the minimum +0.4±0.35 ppb/y in summer are found. The influences of air masses from
various source regions on ozone trends are examined using 10 days backward trajectory
analysis. Positive trends in ozone are found for both European planetary boundary layer
(PBL) air and background air. The ozone increase in winter in European PBL air is
particularly large, most probably in response to the steady decrease in European NO
emissions leading to less ozone titration. Summer ozone increase in the air masses advected
from the European PBL is small, possibly attributable to the balancing effects of decreasing
European ozone precursor emissions and increasing background ozone concentrations.
A stronger increase of European PBL air advection is found in the most recent
years for all seasons particularly in winter, implying that the exposure time of JFJ
site to the free troposphere is decreasing. A first analysis on the variations of PBL
height suggests that deepening of PBL height might partly be the reason of more
exposure of JFJ to European PBL air. Furthermore, individual source regions of
background air are identified using a series criteria applied to trajectories. Ozone
increase in the stratospheric intruded air and free tropospheric air are larger than
average, indicating their large impact on the overall positive trends. Simple linear trend
analysis is applied to ozone measurement data related to the individual source regions,
respectively. Strikingly, ozone from all source regions shows an increasing trend
throughout 1990-2005 with a similar magnitude. Investigation on the frequency
of air mass from the individual source regions shows that European PBL air and
free tropospheric air are the two dominating air flow regimes, and the increase on
European PBL air is balanced mainly by the free tropospheric air, whose frequency
shows an evident decline from about 60% in the earlier 1990s to about 40% in the
recent years. It is also found that effect of particular years (El Nino, Mount Pinatubo
eruption) do not strongly affect calculated trends. The length of 16 years of ozone
measurements is too short for more in depth analysis of potential causes of the trends. The
most dominant part of ozone in the air at JFJ originates from the free troposphere,
which cannot be traced to any particular origin within the trajectory length of 10
days, therefore changes e.g., in global methane emissions cannot be assessed by
the used method, which is also limited by the lack of description of mixing of air
masses.
The same method of source regions’ classification was applied to ozonesonde
measurements of two European ozonesonde stations (Hohenpeissenberg and Payerne, using
Brewer Mast (BM) sondes). With respect to the dominating air classes, a large discrepancy is
found in the ozone evolution between the two ozonesonde measurements and the surface
ozone measurement at JFJ. This suggest that the data quality problem with respect to ozone
measurements in the troposphere using Brewer Master sondes remains though in the
lowermost stratosphere, the agreement on the ozone anomalies derived from two
ozonesondes stations is convincing. |
|
|
|
|
|
|