Assessment of co-exposure to allergenic pollen and air pollution in Copenhagen

Background .Co-exposure to air pollutants and allergenic pollen can elicit or exacerbate a number of conditions in susceptible individuals, including allergic airway diseases. Both concentrations and diurnal patterns are relevant when assessing potential health effects. Methods. To assess which pollutants may be of particular relevance when investigating co-exposure with pollen, we examined yearly variation and diurnal patterns of pollutants on days with high pollen levels, and also for the remaining part of the pollen season. This analysis included measurements of grass and birch pollen, sulphur dioxide (SO 2 ), ozone (O 3 ), nitrogen dioxide (NO 2 ) and particulate matter (PM) in the period 1997-2012. Results. O 3 concentrations were found to be higher on peak pollen days and high O 3 concentrations coincide both seasonally and diurnally with high pollen counts, potentially leading to clinically relevant simultaneous co-exposure. NO 2 and SO 2 did not appear to coincide in concentration peaks with pollen counts, and concentrations were well below potential thresholds for adjuvant effects to the allergic reaction. Neither diurnal nor seasonal concentration peaks in PM were found to coincide with peaks in pollen concentrations, however daily average PM concentrations were higher on peak pollen days than on non-peak days. Conclusion. This study indicates that when considering co-exposure effects from pollen and pollutants, O 3 appears to be the most relevant pollutant to further examine for clinical effects of simultaneous co-exposures.