About Allergen Forecasting

Seasons Vary Year To Year

We have observed that seasons can vary drastically from year to year, especially with the trees. Forecasting is not an exact science and our aim is to try and inform interested individuals as to what is going to happen with the pollen and spores so they are better prepared to deal with their allergies.

The pollen forecast is designed with the primary considerations of allergenicity and the allergy sufferer. The system is designed around a combination of the plants present in any given area and their probable affects in terms of the degree of discomfort they cause people suffering with allergies.

Forecasts combine weather, current pollen levels, historical data, and advanced statistical modelling to project what the concentrations of certain major allergens will be on any one day.

Grasses, Trees and Shrubs

The grasses form an intermediate group both in terms of allergenicity and predictability. The number of species in this group is much higher than the ragweed group and the reactions are more diverse. There is also less cross reactivity than ragweed, hence a person with allergies to one species of grass may not be allergic to other species. One has to remember that we mow grasses before they actually start producing pollen in the air. The antigen is released in the air when one mows the lawn and can create allergic reactions.

Trees and shrubs have a number of species and are usually more diverse. Allergenicity is a level of allergic reaction elicited by the pollen of a particular species. For trees with a high level of allergenicity the amount of pollen in the air may not need to be high to elicit an allergic response in sensitized individuals. Conversely a species of tree with a relatively low level of allergenicity may pollinate in large amounts but may elicit a low allergic response.

Total Pollen and Allergy Sufferer's Sensitivities

A total pollen count, which includes many genera and species, can be confusing especially if what is included in that count is not clearly defined. We believe that a total pollen count should not be indicative of potential allergenicity and needs to be qualified as to what is included or predominant in that count.
An individual’s sensitivity is also specific to that individual, therefore, the level of outdoor allergens may not reflect the potential of allergic reactions. This is due to the predominance of one or more specific species of pollen or spore, the possibility of multiple allergies, cross-reactivity between allergens or any combination of these. Allergies are very individual and reports on outdoor allergens have to be used in conjunction with a person’s reaction and a medical professional.
Because trees display highly individualistic characteristics, both in terms of allergenicity and predictability, predicting on a genus basis is most appropriate both from the standpoint of achieving a realistic prediction and from the actual utility of this information by allergy sufferers.

Predicting Methodology

Parameters Used in Predicting

  • Five years of accurate daily pollen counts at the collection site together with daily parameters for weather factors on a year-round basis.
  • Pollination is a reaction not only to current but also to prior weather conditions.
  • Winter and spring conditions prior to the pollen season and from the previous year are especially important for pollen production.
  • Distribution is influenced by current weather factors and any pollen prediction is tied to the accuracy of the weather forecast parameters in the computer model.
  • Due to biological and weather differences at each location we must have a separate statistical analysis and model for each pollen type predicted.


Dealing with predicting large sites with diversification in distribution of trees

One of the big problems that we are constantly faced with is predicting for certain diverse sites with only one sampling location. Cities such as Halifax and Edmonton, where the distribution of elm populations varies a great deal from one location to another, are excellent examples. Another city is Calgary, where we presently have two locations. The maple tree distributions at each of the Calgary sites are very different, with one site having many and the other site having very few. The pollen levels we forecast for cities such as these are not necessarily representative of the entire city, although the forecasts should provide a good relative indicator: pollen levels will usually increase and decrease at roughly the same time throughout the region.


Interpreting pollen levels using our current scales:

LowModerateHighVery High

A scale of LOW is used to represent the concentration of 20 or less pollen grains per Cubic Meter of Air. This is generally considered a level where most people would not react to a potential allergen.


A scale of MODERATE is used to represent a concentration of greater than 20 but less than 80 grains per Cubic Meter of Air. This is a level where people with allergies may start to react. This depends on an individual’s allergies and the allergenic property of the pollen type.
A scale of HIGH is used to represent a concentration of greater than 80 but less than 200 pollen grains per Cubic Meter of Air. This is a level at which people would be reacting to a certain allergen if it is one they are allergic to. Some people feel there is a difference between the number of pollen in the air even if the level is HIGH. This may be true for certain people and for different allergens.
A scale of VERY HIGH is used to represent a concentration of greater than 200 pollen grains per Cubic Meter of Air. This is a level at which people would very much be reacting to certain allergen if it is one they are allergic to.
Previously we were forecasting numbers for six trees, grasses and ragweed or weeds. These were forecasts based on forecasted weather. We can only be as accurate as the weather and many were using these predicted numbers as actual pollen levels. They we’re not. This is why we chose to go to the new levels we are currently using for all of our reports: LOW, MODERATE, HIGH and VERY HIGH.

Management of allergies

Reactions can be minimized by staying indoors when counts for outdoor allergens are high. Spores, however, are much harder to minimize since they are found in abundance both in the indoor and outdoor environments. The same fungal spores that are found outdoors also exist indoors, however, there are also some differences. Air conditioning, staying indoors when aeroallergens are high, avoiding carpets, vacuuming and air filtration can all help in limiting the amount of allergen one is exposed to. Immunotherapy has also shown to benefit patients with inhalant allergies.

Contact Us

Contact us to set up a network in your community or for more information on predominant pollen and spores for any site collection station.

Email: aerobio@aerobiology.ca
Phone: (613) 226.9820
Fax:(613) 226.9669


Aerobiology Research Laboratories
39-81 Auriga Drive
Ottawa, Ontario
K2E 7Y5