This is the time of year when we get a lot of 'pollen alert' from weather channels or websites. Today in our area the alert says "THE POLLEN FORECAST FOR YOUR AREA IS HIGH" (all in capital letters). When clicked, the following page shows that the pollen from grass is high, from tree moderate, from mold low. I am very curious about how they count this pollen level. After searching for info, I found this site the easiest to digest. It's from National Pollen and Aerobiology Research Unit of University of Worcester in UK.
The following pictures were taken last week (May14th) when the pollen forecast was high. Pollen, flowers, blossoms from weeds, mold, grasses, and trees caught on pond surface.
Cottonwood tree's blossoms and pollen on the road.
I copied the page of "Pollen Monitoring" from the site for my education and quick reference.
Recording the Pollen Count
What is the Pollen Count?
The pollen count is a measure of the number of pollen grains of a certain type per cubic metre of air sampled, averaged over 24 hours. The pollen forecasts are produced by the National Pollen and Aerobiology Research Unit using the pollen counts measured each day at the Pollen UK network sites, together with information about the weather, growing seasons and the flowering times of the plants.
How do the grass pollen forecast categories relate to the pollen count?
The pollen forecast is usually given as low, moderate, high or very high.
Low is less than 30 pollen grains per cubic metre of air.
Moderate is 30 to 49 pollen grains per cubic metre of air.
High is 50 to 149 pollen grains per cubic metre of air.
Very High is 150 or more pollen grains per cubic metre of air.
Most sufferers will start to experience symptoms when the count reaches the moderate category, although counts will be higher near to large sources of grass pollen, such as hay meadows.
The categories for tree and weed pollen types are different due to their different sizes and allergenicity.
How is the pollen count measured?
Each of the pollen monitoring sites around the country has a Burkard volumetric spore trap. Traps are located usually on the roof of a suitably accessible building about two or three storeys high. Traps are located at this height to enable the general ambient airflow to be monitored which contains a good mix of the local and further distant pollen sources gathered on the wind. If the trap was at ground level then it would mainly collect pollen from the immediate vicinity and results between sites would not be comparable.
The air is sucked into the trap through a slit at a rate of 10 litres per minute and the pollen and other particles are captured on a prepared adhesive tape passing the slit at a set rate. Some sites have the adhesive tape mounted onto a rotating drum, others use a microscope slide. The tape, after exposure, is put onto a microscope slide and covered with a gel mountant containing a stain to aid identification and the pollen is then counted. Counting is done using a standard sampling procedure.
Twelve transects are counted across the width of the slide representing two hourly intervals. A daily total is obtained by summing the counts found in the twelve transects and these figures are then converted to grains per cubic metre of air using an equation called the correction (or conversion) factor. Counting each slide can take an hour or even longer depending on the amount of pollen on it. Nobody has yet developed a satisfactory automatic method for counting pollen.
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