## 4 Discussion  
At present, there are few industrial activities in Europe that have regulated odor emissions. The Joint Research Centre (JRC) published a Reference Document for Waste Treatment where it describes different emission levels and emission factors for different waste treatment activities [21]. In Italy, there is also a lack of well-defined legislation for different industrial activities. In the Testo Unico Ambientale (TUA) (Legislative Decree n. 152 of 2006) odor pollution is generically referred to as air pollution, and there are no specific limits for odor emissions, other than those defined for specific substances for stack emissions. Authorizations of atmospheric emissions are the responsibility of the regions. Regional competences also include the definitions of the best available technologies (BAT), available for the specific treatment of odorous emissions. This is done in order to improve the control of odorous emissions and thus guarantee a higher quality and health of the environment. Those responsible for the assessment and management of air quality are the regions and autonomous provinces that (according to Legislative Decree 351/99) have to carry out an assessment of air quality, either through direct measurements of pollutant levels or through the use of diffusion models. In this context, in Italy, the regions can issue guidelines on odor emissions, while also specifying values for emissions. The Lombardy Region (Giunta Regionale LOMBARDIA: 16 April 2003 n. 7/12764) has published guidelines on the construction and operation of compost production plants, setting emissions to 300 \(\mathrm{ou_{E}/m^{3}}\), and the Emilia Romagna Region (Giunta Regionale EMILIA ROMAGNA: 24 October 2011 n.1495) has technical criteria for the mitigation of environmental impacts in the design and management of biogas plants, setting odor emissions to 400 \(\mathrm{ou_{E}/m^{3}}\). Data available from odor stack emissions from bitumen-related production sites plants are very limited and, to the best of our knowledge, are only available for Italian plants [14]. In Italy, guidelines for \"Olfactometric characterization and possible mitigation of asphalt plants\" [22] have been recently prepared by ARPA, the regional agency for environmental protection, and are now used only for ARPA's internal purposes in the Lombardy Region. In these guidelines two examples of odor emissions are presented, acquired by ARPA technicians, equal to 16,000 \(\mathrm{ou_{E}/m^{3}}\) and 1750 \(\mathrm{ou_{E}/m^{3}}\) with emission rates of 113,527 and 21,390 \(\mathrm{ou_{E}/s}\) equal to 1.14 \(\times\) 10\({}^{5}\) and 2.14 \(\times\) 10\({}^{4}\)\(\mathrm{ou_{E}/s}\) respectively, in line with data reported in this study (see Tables 1 and 2). The data we present here seem to have a large variability, up to two orders of magnitude, being from 200 to 37,000 \(\mathrm{ou_{E}/m^{3}}\). In order to have data that were all-inclusive, all available data were used, even when samples were collected by plant managers. Still, data have a normal distribution. Considering data from 47 plants, and analyzing log-transformed data, the arithmetic mean and median of odor concentration in stack fumes, \(\mathrm{log(C_{od})}\), are similar, 3.38 and 3.36, respectively. The null hypothesis of normality cannot be rejected and data used are normally distributed with a mean value (the inverse logarithm) of \(\mathrm{C_{od}=2424\leavevmode\
obreak\ \mathrm{ou_{E}/m^{3}}}\). This could be assumed as an immediate starting point for a reference emission value for Italian HMA plants. To estimate OER and OEF values emission data, production and conveyed air flow data are all necessary [23]. Despite the fact that we have data from 47 plants in Italy, we were only able to use data acquired by us, coming from eight plants, to estimate emission