## 1 Introduction  
The expansion of residential centers has led to some problems of coexistence between the population and the production activities located in the same area [1]. Livestock activities or husbandries, in particular swine, dairy and poultry farms, are sources of odorant compounds that cause conflicts with the neighboring population [2, 3]. The most common problem caused by odor issues is nuisance [4]. Moreover, extended exposure to malodors leads to a reduced quality of life and health [5]. In the agricultural sector, offensive odors are mainly generated by the incomplete anaerobic decomposition of manure and by manure management (storage, handling and land application) [6]. Ammonia (NH\({}_{3}\)), hydrogen sulphide (H\({}_{2}\)S) and volatile organic compounds (VOCs) are the principal odorous substances emitted by pig farms [7]. The compounds emitted from fattening swine houses vary, are complex and may result in odors nuisance. Representative VOCs emitted from swine facilities are mainly amines, sulfuric compounds, volatile fatty acids, phenolic compounds, carboxylic acids, esters, ketones, terpenes and aromatic compounds [8]. Few specific VOCs have been identified to be the dominant odorants on swine farms such as sulfuric compounds and ammonia, which are often identified as the predominant components of all odor compounds [9, 10]. Beside the effects on the neighborhood, excessive odor from swine facilities can cause discomfort to workers, leading to low labor efficiency [11] and reduced well-being [12]. In air, odors are usually transported by dust particles [13], so they can travel for long distances before being deposited to the ground surface. The numerous complaints from people working and living nearby farms made it necessary to adopt strategies to reduce odor nuisance. As an example, Germany, The Netherlands, Austria and other countries have established guidelines based on separation distances between livestock units and residential areas, for determination of odor-annoyance-free level [14; 15]. Alternatively, strategies for reducing odor emissions from livestock activities can be implemented in farms and can be divided into two main lines of action: (i) \"upstream\", aimed at reducing emissions before they are emitted; and (ii) \"downstream\", aimed at containing emissions, once produced. As an example, nutritional strategies [16] and building design [17; 18] fall into \"upstream\" category, whereas the application of covering systems [19], manure treatments [20; 21] or air treatment technologies [22] fall under \"downstream\". In particular, for what concerns air cleaning technologies, acid scrubbers, bio-scrubbers and biotrichling filters are considered effective techniques for odor removal in pig farms [23; 24; 25]. Biofilters, biotrickling filters, acid scrubbers and multi-stage air cleaning systems are also reported by [PERSON] et al. [13] in the JRC report entitled \"Best Available Techniques (BAT) Reference Document for the Intensive Rearing of Poultry or Pigs\". In particular, for pig farms with a forced ventilation system, odor removal is reported to be, on average, 30% for acid scrubbers, 45% for biotrickling filters and 60% for bioscrubber. The adoption of measures for the reduction and mitigation of odor emissions not only allows conflicts between the residents of the neighboring areas and farmers to be reduced [6], but it also allows the air quality inside sheds to be improved, with positive effects on animal and workers [11]. The chemical-analytical techniques allow the identification and quantification of the odorous compounds, but to quantify the response (the perception of odor), sensory techniques are required [26]. Dynamic olfactometry, a sensorial technique, is the only internationally accepted method for measuring odor concentration [27]. It is regulated by the European standard EN 13725 [28] and it is based on the use of human panelists and an olfactometer. It is commonly used to assess the abatement efficiency of air treatment technologies [29; 30].