## 2 Soiling-Related Pollen Topics
### Airborne Pollen Monitoring  
For a given location, the \"main pollen season\" refers to the period with significant air pollen concentrations when considering either the pollen from a specific \"pollen type\" or the pollen from the whole set of pollen types [68; 69; 70]. Concerning the aerobiological parameters, the annual pollen integral (_AP_In) and the seasonal pollen integral (SP_In), formerly termed annual pollen index (API) and seasonal pollen index (SPI), respectively, account for the sum of the average daily pollen concentrations over the whole year and over a given period of time, respectively [70]. That is, these parameters denote the relative importance of the different pollen types in relation to the airborne total pollen concentration on a yearly or a seasonal basis [17; 18]. Nowadays, most aerobiological monitoring networks perform pollen sampling by means of Burkard seven-day-recording volumetric traps installed at a certain height above the ground [14]. After automatic sampling, pollen grains are identified and counted by the visual inspection of optical microscope images by an experienced human operator. As the airborne pollen concentrations are not constant through the day (i.e., typically peaking at times of maximum sunlight and temperature) [71], they are reported as \"mean daily values\", their units being the number of pollen grains per cubic meter of air (grain/m\({}^{3}\)) [72]. Although the information about the airborne pollen concentrations is not readily available [14], a live worldwide map of the pollen monitoring stations has been recently published [73].  
Aerobiological studies classify the airborne pollen according to a \"pollen type\" criteria. Through statistical data analysis, they can provide local pollen calendars which show the expected time span for the presence in air of every pollen type. Each pollen type quantifies together the pollen from all the vegetal species whose pollen grains share a distinctive external morphology under light microscopy. Hence, these pollen types may include one species, a genus (i.e., a group of species), a family (i.e., a group of genera) or wider taxonomic groups [18]. For instance, the pollen type \"Cupressaceae\" includes pollen from the whole Cupressaceae family, which share an \"spheroidal, intectate, monoporate, and with a distinct annulus\" appearance [74].  
The Cupressaceae family, which is composed of numerous genera and species concentrated in the temperate world regions, consists of evergreen trees and shrubs which produce abundant anemophilous pollen [75]. The most relevant bioclimatic factor regarding their airborne pollen concentration seems to be the temperature, followed by the relative humidity [76]. In the Mediterranean region, this pollen type reaches record airborne levels during winter or early spring, although the pollen production varies largely from year to year. Concerning Spain, and focusing on the widespread cypresses (i.e., the genus _Cupressus_), blossoming occurs in October-November for _C. macrocarpa_ and January-April  
Figure 3: Gaussian tilted plume model: (**a**) cross-wind integrated pollen deposition at the ground; (**b**) schematic of pollen deposition at the ground. The parameters are: distance from the pollen source, height of pollen release (\(H\)), pollen settling velocity (\(W\)s), and wind mean speed \(\overrightarrow{u}\)). Adapted from [64].  
for _C. arizonica_, _C. sempervirens_, and _C. lusitanica_[77]. Within the genus Cupressus, pollen grains are 29-38 \(\upmu\)m in diameter [78].