Grasses are the most cosmopolitan allergophytes. A large part of aerobiological researches have been devoted to produce forecasts using regression analyses between daily airborne pollen counts and meteorological factors. However, in these studies, the bioclimatology and eco-physiology of grass pollination were forgotten. By studying the aerobiology of grass pollen in Montreal for the past 19 years we were able to show that both seasonal total and maximum daily value (/m³) presented a decreasing trend, which could be correlated to a similar trend for rain fall, putting some doubt to the popular belief that global change will induce more allergy symptoms.
By drawing frequencies curves of pollen abundance for different meteorological condition categories, we were able to visualize grass pollen behavior: with temperature, the profile was negatively asymmetrical, meaning that, in Montreal, there is always a deficit of temperature for grass pollen; for relative humidity and wind speed, the profile was symmetrical, meaning that both have specific optimum; while for rain, it was parabolic, both arms representing rainout and washout processes.
These results allow us to better understand the eco-physiology of grasses and could show potential sources of error when particular climatological factors are considered for forecasting.