Air Quality Indoors Can Be the Worst in the Winter

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Surprisingly, it can be. Outdoor pollutant levels can skyrocket in the winter because of increased burning of fossil fuels and vehicle use. Air quality indoors also decreases because houses are tightly sealed to keep heat inside, which also traps pollutants. This, in turn, can aggravate breathing problems and other health issues.

What gets worse when it is cold?

The air in your car. Poor outdoor air can actually have the most impact when you are driving in traffic. This is already a bad situation, with lots of pollutants from exhaust and brake dust, and now the combustion gasses are staying low to the ground and in your car. This happens because overcast weather traps pollution beneath the cloud, and the cold winter air traps pollutants close to the ground, in a process called “temperature inversion”. Some cars offer filtered air, which will help some, but the best solution is the hardest: commute a little less!

The smoke coming from your fireplace. Wood fireplaces are often used to offset cold temps indoors without raising the heating bill. But a winter fire could mean more fireplace smoke inside than usual. Cold Science is behind this. Fireplace chimneys work best when the fireplace flue is warm. And when the air is cold and dense the smoke has more resistance and can struggle to exhaust to the outdoors, leaving more smoke inside your home.

The dense air combined with a cold vent (flue) can cause your natural draft hot water heater orp furnace to back-draft. Causing combustion gasses, carbon monoxide, and nitrogen dioxide to come back into the house. For these reasons we recommend, homes have at least one low-level carbon monoxide detector.

A low-level carbon monoxide detector will alarm at a lower level (typically around 10 PPM) and commonly displays the results. It actually does not comply with the new Underwriters Laboratory (UL) 2034 requirements because it detects at lower levels. The exiting UL requirement requires the unit to alarm when the levels are at 70 PPM for 60-240 minutes. If the reading goes below 70 PPM the time starts over. This is why we recommend a low-level carbon monoxide alarm. These units are intended to be near sleeping areas.

What is Happening Outdoors?

Air Quality Indoors Can Be the Worst in the Winter

So what is Temperature Inversion?

Temperature inversion occurs when warm air is pushed above cooler air. The most common kind is a surface inversion, which occurs during cold and windless nights. During those chilly winter nights, the earth surface loses temperature very fast. The air close to the surface gets cooler faster than the air above it, forming a warmer layer of air above the colder one.

Air Quality Indoors Can Be the Worst in the Winter

That’s the reason behind air inversion: but why is this a problem? Because the warm layer prevents the air below from passing through, as demonstrated in the image above. Pollutants from burning fossil fuels for household heating, vehicle exhaust fumes, and other industrial pollutants circulate near the surface of the earth, causing an increased concentration of toxins in the air we breathe.

A city located in a valley and close to a mountain is more likely to experience temperature inversion, as the dense cold air slides down the mountain to the valley, leaving the warmer air above. This is one of the fascinating reasons that the San Francisco Bay remains hazy even during the summer months. The trapped nitrogen oxides and other volatile organic compounds (VOCs) in the air appear gray at the start of a hot day, when it’s cooler. If the temperature rises, a chemical reaction is set off and they turn yellowish-brown, forming smog (smoke+fog).  

What about Indoor Pollution?

Air quality indoors can be the worst in the winter. As we close up our homes to keep the cold out, we keep the chemicals, moisture, and pollutants inside with the heat! That one of the reasons your house can start to feel “stuffy” on a stormy day. If at all possible, crack open a window for at least a few minutes each day. You’ll let in a blast of chilly air, but you’ll let out at least a little of the accumulated pollutants!

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Dana Sundblad
Dana Sundblad
Dana is a seasoned marketing and communications professional with over 20 years experience helping companies achieve awareness and financial goals in consumer, technology, and non-profit industries. Most recently she was Director of Communications at Castilleja School and began her career in brand marketing with Clorox. She received her MBA from Harvard University and BA from Wellesley College.
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