Abstract
For the identification of regional springtime ozone episodes,
rural European Monitoring and Evaluation Programme (EMEP) ozone measurements
from countries surrounding the western Mediterranean (Spain, France,
Switzerland, Italy, Malta) have been examined with emphasis on periods of
high ozone-mixing ratios, according to the variation of the daily afternoon
(12:00–18:00) ozone values. For two selected high ozone episodes in April
and May 2008, composite NCEP/NCAR reanalysis maps of various meteorological
parameters and/or their anomalies (geopotential height, specific humidity,
vertical wind velocity omega, vector wind speed and temperature) at various
tropospheric pressure levels have been examined together with the
corresponding satellite Infrared Atmospheric Sounding Interferometer (IASI)
ozone measurements (at 3 and 10 km), CHIMERE simulations, vertical
ozone soundings and HYSPLIT back trajectories. The observations show that
high ozone values are detected in several countries simultaneously over
several days. Also, the examined spring ozone episodes over the western
Mediterranean and in central Europe are linked to synoptic meteorological
conditions very similar to those recently observed in summertime ozone
episodes over the eastern Mediterranean (Kalabokas et al., 2013, 2015; Doche
et al., 2014), where the transport of tropospheric ozone-rich air masses
through atmospheric subsidence significantly influences the boundary layer
and surface ozone-mixing ratios. In particular, the geographic areas with
observed tropospheric subsidence seem to be the transition regions between
high-pressure and low-pressure systems. During the surface ozone episodes
IASI satellite measurements show extended areas of high ozone in the lower-
and upper-troposphere over the low-pressure system areas, adjacent to the
anticyclones, which influence significantly the boundary layer and surface
ozone-mixing ratios within the anticyclones by subsidence and advection in
addition to the photochemically produced ozone there, resulting in
exceedances of the 60 ppb standard.
Citation
ID:
25455
Ref Key:
kalabokas2017anatmospheric