Increasing Pollen Trends in Atlanta, GA Over a 20-Year Period

The inhalation of outdoor allergenic pollen and mold spores is a primary cause for allergic rhinitis (Grammer and Greenberger 2009), or hayfever, which is a significant burden to public health. In the US, annual treatment costs were estimated at $11.2B (Blaiss 2010), in addition to annual economic costs of $5.4B, due to lost productivity (Kessler, Almeida et al. 2001). Pollen seasons for certain allergenic plants have lengthened (Garcia-Mozo, Galan et al. 2006) and pollen concentrations have increased over time (Corden and Millington 1999, Emberlin, Smith et al. 2007, Frei and Gassner 2008), according to studies conducted in Europe. In the US, the season for ragweed pollen has been lengthening, especially in the northern latitudes of the country (Ziska, Knowlton et al. 2011). Additionally, changes in pollen production have been attributed to warming temperatures in Europe (Garcia-Mozo, Galan et al. 2006, Sofiev and Bergmann 2013). More specifically, the timing of pollen release for certain species such as birch and alder are affected by winter temperatures, either due to the chilling requirement needed for bud formation, or the warm temperatures needed for pollen flowering and pollen release. (Sofiev and Bergmann 2013). Previous research suggests that as pollen increases, allergic rhinitis and other allergic-related illnesses and symptoms (e.g., asthma, wheezing) also increase (Heguy, Garneau et al. 2008, Darrow, Hess et al. 2011, Sheffield, Weinberger et al. 2011). We investigated the long-term trends in pollen production for 18 different allergenic taxa from one pollen station in the metropolitan Atlanta area from 1992 to 2011. We performed a time-series analysis on a 20–year pollen dataset to determine trends: pollen count, pollen season onset day (1% of annual cumulative pollen count), peak day (day of maximum pollen count per year), end day (99% of annual cumulative pollen count), and season length (onset day minus end day). Additionally, we performed an exploratory analysis to evaluate if shifts in pollen production were related to winter Celsius temperatures, which we found to be cooling over the same time period. Ten of the eighteen plants in this analysis exhibited an increasing pollen count over the 20-year period. We found several trees exhibited lengthier pollen seasons each year: ash, beech, sycamore, and willow, but no plants exhibited an earlier season onset. This may be due to the methodology we used to define seasonal onset and end (i.e. 1% and 99% of cumulative pollen to define seasonality), because this approach excluded low pollen concentration at the beginning and end of the season (Emberlin, Smith et al. 2007). We found that winter cooling, as measured separately by the number of freezing days and minimum temperatures, was not a significant predictor for pollen production for the plants in this analysis. To our knowledge, this is the first time that a recent medium-term (20 years) assessment has been conducted in North America for multiple allergenic taxa. Our findings suggest that pollen counts have increased over the last 20 years in Atlanta, GA, and the pollen season for certain allergenic plants have lengthened. Further research is needed to determine how year-to-year variations in climate affect allergenic pollen production in North America, which would aid in the development of predictive risk models for pollinosis.