Comparison between the counting methods used by two aerobiology networks in southern Europe (Spain and Italy)

Aerobiology studies the biological particles suspended in the atmosphere in order to know what types are present in the air and how their concentrations vary spatially or seasonally. The measurement of airborne pollen concentration requires a standardized methodology. Normally, the analysis of the slides obtained after samplings is carried out according to national network procedures. Different networks use different slide counting methods (longitudinal sweeps, transverse sweeps or random fields), and a different number of lines/fields are routinely read. In this study, we compared two slide counting methods adopted by two monitoring centres belonging to different aerobiology networks that operate in southern Europe, the University of Malaga (Spanish Aerobiology Network, the REA) and the University of Roma Tor Vergata (Rete Italiana di Monitoraggio in Aerobiologia, the RIMA). For that, the same samples were counted following the two methodologies consisting on the reading of four (REA) and six (RIMA), respectively, longitudinal sweeps at a magnification of 400X (REA). Statistical analysis was performed in order to search the degree of association between the two series of data obtained, as well as whether or not there were significant differences between them. The results showed highly significant correlation and regression coefficients. On the other hand, Wilcoxon tests, in general, did not showed significant differences between the series for the total pollen as well as for the major pollen types. This confirms that the two methods can be used indistinctly although it would be convenient for the different networks to standardize and unify methodologies in order to follow the same operating procedures.