Reference
Jato, V., Rodriguez-Rajo, F.J., Seijo, M.C. and Aira, M.J. 2009. Poaceae pollen in Galicia (N.W. Spain): characterization and recent trends in atmospheric pollen season. International Journal of Biometeorology 53: 333-344.
Background
The Poaceae family (comprised chiefly of herbaceous grasses), in the words of the authors, "is the most diverse and prolific herbaceous plant family in urban areas," and "its pollen is considered a major aeroallergen, causing symptoms in over 80% of pollen allergy sufferers in Europe (D'Amato et al., 2007)."
What was done
Working in four cities in Galicia (Northwest Spain) -- Lugo, Santiago, Vigo and Ourense -- and noting that "the global climate change recorded over recent years may prompt changes in the atmospheric pollen season (APS), Jato et al. collected airborne samples of Poaceae pollen "using Hirst-type volumetric traps," after which the data they obtained "were subjected to Spearman's correlation test and regression models, in order to detect possible correlations between different parameters and trends," while "the APS was calculated using ten different methods, in order to assess the influence of each on survey results."
What was learned
The four researchers report that "all four cities displayed a trend towards lower annual total Poaceae pollen counts, lower peak values and a smaller number of days on which counts exceeded 30, 50 and 100 pollen grains/m3." In fact, the percentage decline in annual pollen grain counts between 1993 and 2007 in Lugo was approximately 75%, while in Santiago the decline was 80%, as best we can determine from the graphs of the researchers' data. In addition, they say that "the survey noted a trend towards delayed onset and shorter duration of the APS."
What it means
In spite of the fact that there was a "significant trend towards increasing temperatures over the months prior to the onset of the pollen season," according the Spanish scientists, the real-world results of their research indicate that Poaceae pollen actually became far less of a negative health factor in the four Galician cities over the decade and a half of their study.
Reference
D'Amato, G., Cecchi, L., Bonini, S., Nunes, C., Annesi-Maesano, I., Behrendt, H., Liccardi, G., Popov, T. and van Cauwenberge, P. 2007. Allergenic pollen and pollen allergy in Europe. Allergy 62: 976-990.