Evolution of surface ozone in central Italy based on observations and statistical model

[1] Hourly and daily variations of surface ozone have been analyzed in relation to radon and meteorological parameters to explore its controlling mechanisms. Measurements in central Italy cover the years 2004 and 2005, showing a relevant role of transport in the ozone concentration variability. An analysis based on back trajectories shows that the site is affected by air masses originating from the west to northeast sector in about 74% of the days, suggesting that L'Aquila could be considered a background site. The background hypothesis is also supported by the rather low values of the following ozone quantities: maximum of monthly averages ( 39 ppbv, July), annual median of hourly data ( 29 ppbv), and annual average of hourly maxima recorded daily ( 49 ppbv). Only six hourly data recorded ozone above 90 ppbv in 2 years but never above 100 ppbv. The regression model reproduces measured ozone with accuracy in 67% of hourly observations and 74% of daily mean data. Here the model includes information from the following meteorological parameters: temperature, relative humidity, horizontal wind speed/ direction, sun radiation, and radon concentration. A tracer like radon that tracks the dynamical changes of the lower atmosphere has a significant role in the model ozone prediction improvement, especially for hourly observations and for the synoptic component. In the first case ( hourly observation), inclusion of radon data improves the regression model performance by 5% ( from 62 to 67%); in the last case ( synoptic component), the model accuracy increases by 3% ( from 78 to 81%).