Pollen Forecast: Background Information

Since 1993, the Weather Network/MétéoMedia has provided the Pollen Forecast and it is the only nation-wide report on outdoor allergens of its kind in Canada. As part of this program, proprietary to The Weather Network, outdoor air samples are collected every day from early spring to the onset of fall in 27 different sites across Canada. The daily pollen forecast is for personal use only and cannot be redistributed without the consent of The Weather Network/MétéoMedia.

This report is based on scientific research that incorporates the affect of weather on certain aeroallergens. Aeroallergens include pollen and fungal spores that are carried by the wind and have the potential to cause allergic reactions. The forecast models are state of the art and include many years of research to be able to provide as near accurate results as possible.

Generalizations of the pollen and spore season in itself could never be used to accurately predict allergic reactions, for there are far too many local environmental factors that play a role in pollen and spore dispersion. Depending on weather the season starts can vary by almost a month in many locations. For this reason the predictions are based on years of research to better inform the public of current conditions. The daily forecast you see takes into account the current and recent pollen levels, the weather forecast from The Weather Network/MétéoMedia and historical pollen patterns in local areas. The research that has gone into forecasting is important in providing accurate information to the user.

Due to seasonal fluctuation, the graphs posted on our television broadcast and web sites are an attempt to give a time frame of when each tree species pollinates. Our report includes certain trees and weeds but does not give a complete picture of all the pollen and spores that could cause allergic reactions. Each year is different and has to be examined individually when using it as a reference by those who suffer from allergies.

Weather and the Allergy Season

The weather has a profound influence on the type of season we will have. This varies as different trees have adapted to cope with different environmental stresses. For this reason, a particular pollen season can vary from year to year. The weather conditions in the summer have a profound effect on the amount of pollen production for release in the following spring. The weather during the pollen season also influences when the season will begin and the rate of pollen release. A cold spring can delay the pollen season up to several weeks and also affects the length of the season. An early warm spell followed by a prolonged cold, wet spell may trigger the season starting and would probably have an impact on the total pollen levels for that year as a way of responding to environmental stress. Other environmental stresses include ice storms, fires, pollution and floods.

Wind, temperature, rainfall and sunshine also play a vital role in the amount of pollen released. Rain affects the amount of pollen in the air simply by washing it down so it cannot get airborne. Wind, naturally, is the carrier of aeroallergens and plays a significant role in transport of aeroallergens. While the quantities of rainfall vary across the country this also creates a different level of importance to each area. For Vancouver, which receives a lot of rain, the affect on the pollen levels in the air is not the same as it would be in a location like Ottawa, which does not get as much rain. These important relationships are dealt with in the research that occurs for doing forecasting in each region of the Country.

Fungal spores are also influenced by weather patterns. The actual start and severity of the season depends on several factors including temperature, rain, humidity and wind speed/direction. Certain spores prefer cold, moist air, while others prefer hot, humid or drier conditions to release their spores into the air. Certain fungal spores play a vital role in causing human allergic reactions but they are still not as well understood as pollen allergies. There are thousands of different types of spores in the air, especially during the summer and fall months, and only some of them are important in causing allergic reactions. Fungal spores come off of mushrooms and molds and are not well understood or easy to isolate for research.

Allergies and Human Activity

An important factor that has become prevalent is linked to human activity. The introduction of new species in abundance that is not naturally found in certain areas sometimes alters the type of pollen found in the air. The role of climate change will also be a significant factor in the levels and types of aeroallergens found in the air we breathe. Trees are susceptible to the stresses of climate change and the environment and changes in the composition of outdoor aeroallergens will gradually adapt to the stresses of these impacts. . Exposure to these changes is affecting, and in some cases increasing allergies in the population.

Pollen/Spore background

Plants that produce significant amounts of airborne pollen grains are said to be wind pollinated. Plants that produce showy flowers are generally insect- pollinated and are not considered important aeroallergens. People often mistake flowers planted in their garden as being causes of hay fever. Unless you are extremely allergic or handle flowers with bare hands for an extended period of time, flowers are not causing your allergies to airborne allergens.

Some aeroallergens combine or "cross-react" quite easily with other members of the same plant family. Thus, if you are sensitive to alder pollen, there is a good chance that you will also be sensitive to birch pollen, which often cross-reacts with alder. The same problem occurs with weeds. If you have an allergy to one species of ragweed, you are more than likely allergic to all species. Cross-reacting in the grass family, however, is not as prominent. You can be allergic to one species of grass and not to others.

Allergic reactions are not necessarily caused by pollen. In some cases, they are caused by the antigen or protein that pollen carries. This protein, found in all parts of plants, can be carried by the wind. This may explain why allergies can appear before pollen is actually detected in the air. It is important to note that people with strong allergies to trees may develop sensitivities to the skin of certain foods such as fresh fruits, like apples and the plum family, vegetables and nuts. It is thought that the protein, or antigen structure, of the pollen grains and the carbohydrate protein covering the fruit can cross-react.

Mould Spores

Mould allergies are becoming more common and we are simply becoming more aware of their importance in allergic reactions. We know much more about pollen allergies than we do about mould allergies. There are thousands of fungal spores that are airborne and our understanding about them is currently quite small. But the medical community is learning more about the association between mould counts and their relationship with allergic reactions and asthma.

Whereas pollen grains reach counts in the hundreds in any one day, spores can reach over 40,000 in a day. Since moulds are found indoors and outdoors they are a problem all year. The problem for outdoor air, more so than indoor air, is isolating them and knowing which one is causing the allergy. The majority of moulds are ambient and probably do not cause any problems.

Some of the most common and better understood moulds include Cladosporium, Penicillium, Aspergillus, Aternaria and Ganoderma to name a few. These represent only a few of the moulds that we have information about. As more information is available, allergy sufferers and doctors will be better able to understand and deal with the problems caused by aeroallergens.

Having data and information like we have in Canada is a great advantage and this program is hoping to help assist in keeping allergy sufferers and people in the field aware of what is happening.

Data provided by Aerobiology Research Laboratories.