The annoyance of an odor is a function of the FIDOL factors, which are Frequency, Intensity, Duration, Offensiveness and Location. The FIDOL factors can be used as a basic means of assessing the potential odor impact of proposed developments.
Frequency indicates how often a person is exposed to an odor. Even an odor with pleasant hedonic tone can be perceived as a nuisance if exposure is too frequent. At low concentrations a rapidly fluctuating odour is more noticeable than a steady background odour, therefore a high frequency is an aggravating factor.
Intensity indicates the strength of the odor, it is proportional to the log10 of the odor concentration (Steven's law).
Duration indicates the time length of an odor episode, i.e. how long the concentration remains consecutively above the odor threshold.
Offensiveness is a mixture of odor character and hedonic tone at a given odor concentration. Some odors are universally considered offensive, such as decaying animal matter or rotten eggs. Other odors may be offensive only to those who suffer unwanted exposure in the residential intimacy, for example coffee roasting odour.
Location indicates the type of land use and nature of human activities in the vicinity of an odor source. Particular attention must be paid to sensitive receptors, which include housing, schools, hospitals, commercial premises (such as restaurants, offices, shops etc.) and outdoor recreational space.