Seasonal fluctuations of the airborne pollen in Guarda (Portugal)

Pollen grains are biological structures produced as part of the reproductive cycle of plants, vital to the sexual reproduction and to the maintenance of species in nature. As supported in the pollination process, pollen is an important component in the air, much like carbon monoxide, sulphur dioxide, and other gases. The pollens, commonly known as “green pollutants”, could be innocuous if they did not induce allergic reactions. However, when the immune system overreacts and produces antibodies, symptoms like inflammation of the skin and of the sinus airways can appear (Sicard et al. 2011). The severity of allergies depends on a number of variables, such us plant distribution, climatic conditions, or urbanization levels (D’Amato et al. 2007; Peden and Reed 2010). Depending on the sensitivity of each individual, allergenic responses can range from minor irritation to anaphylaxis, a potentially life-threatening emergency (Darrow et al. 2012). The presence of relatively high levels of air pollutants in city centers will modify the properties of the exposed pollen, which may be responsible for the increase of disease-related allergies in highly urbanized regions (Cuinica et al. 2014; Cuinica et al. 2015; Ribeiro et al. 2014; Sousa et al. 2012). 

While allergies cannot be cured, and the treatments can only relieve allergy symptoms, the development of aerobiological studies is important for the elaboration of pollen calendars, which not only indicates the presence and prevalence of allergenic pollen in the atmosphere of a sampling area but also supports the prediction of the flowering season (Scheifinger et al. 2013). This knowledge is useful for clinicians in adjusting treatment procedures and for patients in taking their own prophylactic measures, such as the planning of outdoor activities (Rica, 2003). Airborne pollen monitoring can also support architectural landscape planning, for a more balanced selection of plant species that correspond to the quality of life of the population in urbanized areas (Cariñanos and Casares-Porcel 2011). 

In Portugal, aerobiological studies began with Pinto da Silva in the in the mid-twentieth century (Ribeiro and Abreu 2014) and, since then, some studies have been conducted on the type and concentration of pollen present in the atmosphere of a number of cities (Abreu and Ribeiro 2005; Caeiro et al. 2007; Câmara 2008; Fernandes et al. 2010; Ribeiro et al. 2005). One study also considered the relationship of pollen concentrations with meteorological factors (Ribeiro et al. 2003). 

Since 2003, the Portuguese Aerobiology Network (PANet) has been monitoring the airborne pollen and fungal spores in Portugal, namely in the cities of Oporto, Vila Real, Coimbra, Castelo-Branco, Lisboa, Évora, and Portimão (Caeiro et al. 2007; Nunes et al. 2008) with altitudes between 0 and 425 meters. However, in Guarda, the highest city in Portugal (1056 m), and one of the cities with the greatest temperature range, there are no aerobiological studies. 

The main objective of this work is to eliminate this information gap, evaluate the airborne quality, and compare the results of Guarda with the pollen calendar for the central region of Portugal. Indeed, in terms of chemical air pollutants, Guarda is a city characterized by excellent air quality, and chemical pollutants are not a major problem. Hence, adverse factors in the ambient atmosphere are mainly allergens of biological origin. This study point to the relevance of airborne pollen monitoring as a tool for the measurement of air quality and for the assessment of public health.