Diurnal Concentration of Grass Pollen (IMAGE) Aarhus University Caption Diurnal concentration of grass pollen for periods one-three is shown. The graph shows peak-time distributions for (a) Period 1 (early season), (b) Period 2 (mid-season) and (c) Period 3 (late season). Please note the different scales: Period two has the highest concentrations of pollen. These ideal profiles are based on 37, 58 and 62 basic profiles, respectively. Credit Robert G. Peel Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.