**3. Data description**

Air micro-pollution-analyzed data come from an air monitoring network, working since 1975, covering an industrial area of 500 km2 , including the towns of Priolo–Melilli–Siracusa, situated in the province of Siracusa, in the region of Sicily. This industrial area was declared 'a high environmental risk rate place' by the Law 349/86 and covers six surrounding towns (Augusta, Priolo, Melilli, Siracusa, Floridia, Solarino); the landscape is very varied and is formed by sandy hills, mountains, and plains near the coast [37, 38].

In this territory, a lot of chemical plants, energy production industries, and oil refineries are found, as well as members of a private organization, the industrial trust for environmental safety (CIPA, Consorzio Industriale Protezione Ambiente–Environmental Protection Industrial Consortium). In its operative center, CIPA assembles and works out different micro-pollution parameters and various meteorological variables, measured by 12 different monitoring stations. Data collection and processing is useful in statistical analysis and in upgrading air pollution management in order to avoid the air-tested-exceeding threshold qualities, previously established [38–42].

This chapter studies monitoring station in Melilli only, because in this place, data concerning air micro-pollution quantities and weather conditions, present at the moment of pollution sample construction, are thoroughly collected. In fact, in Melilli, monitoring station hourly quantities of some micro-pollutants, such as sulfur oxide, nitric oxide, non-methanic hydrocarbon, ozone, sulfonyl hydrogen, and different meteorological conditions present at the moment of their observations, such as air temperature, relative humidity index, wind direction, and speed are observed and stored. Some previous studies show the evident correlation between these environmental variables and the quantity of air micro-pollution found in the samples. Because of the complete data present in the samples studied, levels of four micropollutants (SOx, CH<sup>4</sup> , NMHC, NOx) in correlation with the meteorological variables previously mentioned [42, 43] are analyzed in this chapter.

Data recovered from the Melilli monitoring station during 2 weeks, more precisely 1 week in January and 1 in August 2010, have been studied, in order to observe differences of analysis results also on the basis of the different seasons of the year. Daily available recorded 'objects' described both by meteorological variables (condition attributes) and by micro-pollution quantity (decision attribute) have been considered. More than 1000 data records have been analyzed, as an example to which the RSA could be applied.

The selected condition attributes/criteria (descriptors) considered in this analysis are the hour of observation (attribute), wind speed (criterion) and wind direction (attribute), air temperature (criterion), and the relative humidity index (criterion), whereas the levels of the aforementioned micro-pollutants are the decision classes. The descriptors have been chosen because in previous studies [36, 42] they looked like some very important factors, at a local level, influencing air micro-pollution quantity.
