Extreme Nitrogen Oxide and Ozone Concentrations in Athens Atmosphere in Relation to Meteorological Conditions |
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Authors: | Nikolaos Hatzianastassiou Basil D Katsoulis Basil Antakis |
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Institution: | (1) Department of Physics, Laboratory of Meteorology, University of Ioannina, 45110 Ioannina, Greece |
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Abstract: | In the present study, we investigate the variation of NO
x
(NO + NO2) and O3 concentrations and the relation between the extreme events (episodes) of NO
x
and O3 concentrations and the relevant meteorological conditions in the urban atmosphere of the Athens basin. Hourly data of NO,
NO2 and O3 concentrations from 10 representative monitoring sites located in the Athens basin were used, covering the 10-year time period
from 1994 to 2003. The results of our analysis show that the concentrations of air pollutants differ significantly from one
monitoring site to another, due to the location and proximity of each station to the emission sources. For each site, there
are also significant differences in NO
x
and O3 concentrations from day to day, as well as from month to month and/or from season to season. The annual and seasonal variations
show higher NO values in winter and lower in summer. On the contrary, NO2 and O3 values are higher in summer (photochemical production of O3) and lower in winter. These differences are attributed, to a large extent, to the prevailing synoptic and meteorological
conditions, the most important between them being the wind direction and speed as well as the atmospheric pressure. Our analysis
of the identified 179 extreme NO
x
air pollution events shows that most of them took place under anticyclonic conditions, associated with calm or weak winds
(speed <2.5 ms−1) of mostly southern to southwestern directions, as well as with low air temperatures and intense stable surface atmospheric
conditions. There exists a significant decreasing tendency in NO
x
air pollution episodic events over the 10-year study period, resulting in very few to none events in the period from 2000
to 2003. As far as it concerns the extreme O3 concentrations, 34 air pollution events were identified, occurring under high air temperatures, variable weak winds and intense
solar irradiation. The trends of O3 concentrations are stronger in suburban sites than in urban ones. |
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Keywords: | patterns of air pollution meteorological conditions NO x O3 concentrations episodes linear trends |
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