My Grade 9 English teacher Ms. Cairncross used to say, “there are no stupid questions, only stupid answers.” She was right.
To this day, I question things - a lot - and I love to get questions.
This email from Douglas Myra of Halifax came a few days ago.
“Cindy, please explain to me what humidity is. When it is hot and humid, I cannot breathe due to my breathing/health problem. When it rains and is cooler the humidity is 100 per cent yet I have no problem breathing. Are they both humidity? I am really confused.”
That’s a great question, Douglas.
Humidity is defined as “the concentration of water vapour present in the air.” Water vapour, the gaseous state of water, is generally invisible to the human eye.
In order for it to rain, the humidity is usually very close to 100 per cent. The relative humidity doesn’t have to be that high to cause breathing problems in some people.
Breathing in humid air activates nerves in your lungs that narrow and tighten your airways. Humidity also makes the air stagnant enough to trap pollutants and allergens like pollen, dust, mould, dust mites, and smoke. These can set off asthma symptoms.
For example, dust mites live in furniture, carpets, and bedding. They thrive at humidity levels of 70 to 80 per cent. Humidity higher than 60 per cent also encourages the growth of mould. You'll often find mould in damp places like bathroom ceilings and flooded basements. If you're sensitive to mould, breathing it in can flare up your asthma.
Now, back to the question. If the humidity is even higher when it rains, why do some find it easier to breathe?
Grandma used to say that a good rain can clear the air. She was right. As a raindrop falls through the atmosphere, it can attract tens to hundreds of tiny aerosol particles to its surface before hitting the ground. The process by which droplets and aerosols attract is called coagulation, a natural phenomenon that can act to clear the air of pollutants like soot, sulfates, and organic particles.
While fog and rain can clean the air effectively, the chemicals and compounds that pollute the air can fall with rain to pollute soil and surface waters.
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Cindy Day is the chief meteorologist for SaltWire Network
