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An Introduction to Aeroallergens

Pollen is a microscopic grain discharged from the male part of a flower or from a male cone that can fertilize the female ovule.

Plants have evolved to have their pollen be transported either by the wind, or by insects or other animals. Insect and animal pollinated plants are not considered to be aeroallergens, not because people aren’t allergic to them, but because the pollen from those plants are not designed to be distributed in the air – any exposure to the pollen from these flowering plants is localized to within a few meters, while wind-borne pollen is designed to travel very long distances. We study the wind pollinated pollen of trees, grasses and weeds.


Fungal spores are also microscopic particles, and are discharged from a fungus or mold, such as mushrooms or Penicillin. These are the reproductive parts of the fungus. Like wind-borne pollinators, fungi have also evolved to distribute their spores through the air. We study these airborne particles.


The reproductive phases of plants and fungi are one of the most important parts of their life cycle, and just as each have their growing seasons, so too do they have a reproductive season. In the case of wind-borne pollinators such as trees, the timing of this reproductive season is very important, because each type of tree needs to release pollen at the same point in time as other trees of that type are ready to receive it – otherwise they may fail to reproduce. The reproductive seasons vary a great deal from year to year, due primarily to environmental factors. Weather conditions have an effect in the short-term and long-term on when pollen release begins, as well as an immediate effect on pollen release itself. For trees in particular, this goes even further as weather conditions and other environmental factors during the previous year influence the production of pollen on trees. Fungi have a different life cycle from plants and the release of fungal spores are more affected by daily weather fluctuations. By way of example, the start and duration of birch pollen release at a particular geographical location both vary on the order of weeks from year to year.


Additionally, the volume of pollen released overall as well as on a day-to-day basis varies significantly.


And this variation isn’t only shared by trees – plants such as grasses and weeds can have a vast difference in amount of pollen released and when the season starts.


The reproductive seasons at each geographical location across the country are also very different and unique. Obviously due to climate differences, Vancouver is very different from Montreal. But there are differences between Toronto and Montreal, too. These differences stem not only from their weather but also from the particular species of plants that are prominent at each site and the populations of those plants. As can be inferred from all of this variability, the study of aeroallergens depends highly on having data. Continuous ongoing monitoring of particle concentrations in outdoor air, over many years and in many different geographical locations, has allowed us to learn these differences, and also lets us keep tabs on how they change as the environment, both weather and otherwise, continues to evolve.

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