engleski

Atmospheric dynamics and the elevated ozone concentrations in the northern Adriatic

We examined the influence of mesoscale flow on the elevated O3 concentrations recorded during 13-19 August 2000 in the coastal town of Rijeka (45.33°N, 14.45°E). Although high levels of ozone concentration are often observed there, this episode was unique due to hourly afternoon concentrations persistently higher than 180 μg m-3 and nocturnal levels above 100 μg m-3. To study this episode, available meteorological and ozone measurements were analyzed along with supplemental numerical simulations and trajectories. The measurements revealed favorable atmospheric conditions for the production of ozone, i.e., high air temperatures associated with (i) the exchange of two dominant (although relatively weak) large-scale flows: southwesterly versus northeasterly bora winds, and (ii) local thermal circulation. The bora wind was relatively weak and short lasting. Although the bora transported away the polluted air mass along the western Adriatic coast, the southwesterly flow returned ozone rich air toward the Alps, thus contributing to the overall pollution over the northern Adriatic Sea. Models revealed the superposition of the southwesterly wind and local, thermally induced winds that caused the regional transport of ozone toward the Alps and the eastern Adriatic coast. However, while the regional transport of ozone from the northern Adriatic was found to somewhat enhance the ozone concentrations in Rijeka (at the end of period studied), its surrounding local emission sources, uniform local thermal circulation systems, and recirculation of pollutants were crucial factors in the formation of the large daytime and nighttime ozone levels observed in Rijeka.

air quality; pollution episode; sea/land breeze circulation; bora; WRF model; EMEP model

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