Is Air Pollution Worse in Winter? The Impact of Cold Weather on Air Quality

Fact checked by Olga Sadouskaya, MD
Clinical Pharmacologist, Chief Medical Officer

Air quality plays a crucial role in our health and well-being. In winter, we spend more time indoors, so we tend to focus on improving the air quality in our homes. But what about outdoor pollution? Does it get better or worse in winter? Let’s find out!

What makes air quality bad?

Various air pollutants, both natural and man-made, can affect air quality. When we think of air pollution, we usually imagine a busy city with heavy traffic and factory fumes. While these industrial pollutants have an undeniable impact on air quality, let’s not forget that natural contaminants like mold, dust, and pollen can also make air quality bad. Pollutants can come in the form of gasses, solid particles, or liquid droplets — think of volcanic ash, carbon monoxide from car exhaust, and acid rain.

The growing population and increasing industrial development have made air pollution a major concern worldwide.

Regardless of their origins, air pollutants can cause various respiratory problems. In fact, in recent years, allergies have become more common due to climate change. Rising temperatures make the pollen season longer, and more frequent flooding encourages mold growth. All this results in a higher concentration of airborne allergens that can trigger an asthma attack or allergic reaction in anyone who inhales them.

The impact of weather on air quality

So what does the weather have to do with the quality of the air we breathe? In fact, anything from strong wind to low barometric pressure can affect air pollution. On windy days, for example, you may notice the air quality decline. The reason for this is simple: wind picks up and spreads pollen and mold particles, as well as other allergens, making it easier for you to breathe them in. Powerful winds can even transport industrial pollutants and dust particles across country borders!

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Warm, dry weather also increases your exposure to airborne allergens, especially pollen. An extended period of hot, sunny weather can create drought conditions and increase ozone pollution. Forest fires are also not uncommon during heat waves — they release carbon monoxide and particulate matter into the air.

Rainy days and air quality

Rainy weather can bring relief to people with seasonal allergies. It helps to push common air pollutants like dust and pollen particles to the ground, giving you a much-needed breath of fresh air.

Unfortunately, though, it’s not that simple. Sometimes, heavy rain can have the opposite effect on the air quality: it can split pollen particles and release more allergens into the air. This usually happens during thunderstorms.

Another common culprit of bad air quality in humid weather is mold.

It grows quicker in damp conditions, and mold spores can be spread by wind and even travel through fog or dew.

Does snow clean the air?

If you think the air feels cleaner after a snowstorm, you may be onto something. Like rain, snow can be excellent at reducing air pollution. Researchers from Canada discovered that snow can absorb pollutants coming from car exhaust and remove dust and smoke particles from the air. Unfortunately, this effect is temporary. The air pollution will build up again after the snowfall. But don’t let it stop you from enjoying a day out in the snow when the air is fairly clean!

Cars as one of the sources of smog in urban areas

Winter smog: is it worse in urban areas?

When the temperature drops, we start turning up the heating in our cars and homes. Whether you use wood, gas, or electricity to keep your home toasty, it still has a significant effect on air quality. A 2015 study attributed a whopping 20 percent of air pollution in cities to domestic fuel burning. So, it’s not surprising that the winter air can become loaded with these pollutants, and their build-up can then result in winter smog. Unsurprisingly, it’s more common in cities where the population is denser and traffic is heavier, making winter smog a serious issue in urban areas. The high concentration of air pollution in winter can weaken the immune system, and trigger respiratory problems.

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3 reasons air pollution can be worse in winter

As we’ve already discovered, wind, rain, and snow can have a big impact on air quality. But what can make air pollution worse during the winter months?

1. Cold air is more dense

Have you noticed a slight chill on your feet when you walk around your home? This happens because cold air is more dense and usually sinks, while warm air rises. So, in winter, the dense cold air traps air pollutants and acts as a lid, pushing them closer to the earth’s surface. As a result, their concentration in the air is higher, which means you probably end up breathing in more pollutants during winter.

2. Dry air holds more pollution

As we mentioned before, humid weather pushes dust and other air-soluble pollutants closer to the ground making the air cleaner. But the cold air is dry, so it holds more pollution, which can trigger respiratory problems.

Smoke coming out of the chimney as a source of winter air pollution

3. Our winter habits increase pollution

The way we behave during colder months also contributes to higher levels of air pollution. In winter, we use more energy to keep our homes warm, which means we create more pollution from burning fossil fuels. Also, when the weather gets cold, we are more likely to cozy up in front of a fireplace and keep the windows closed. This lack of ventilation and the increase in levels of particulate matter makes indoor air quality worse in winter.

What can you do to improve air quality in winter?

You can do a few things to reduce air pollution during the winter months. Try to avoid burning wood for warmth and reduce energy use whenever possible — this can help lower levels of particulate matter and carbon monoxide. Make sure to open your windows every once in a while and get an air purifier with HEPA filters to keep the air in your home clean. To reduce emissions from your car’s exhaust, limit the time you leave it idling, or better still, opt to carpool or use public transportation if possible.

Final thoughts

There are several reasons why air pollution can be worse in winter. When the weather gets colder, we use up more energy to stay warm. This increase in energy consumption releases more pollutants into the atmosphere. Because the cold air is more dense, it traps all this pollution build-up, creating winter smog. Snow, however, can temporarily make the air cleaner by removing dust particles and some air pollutants. Still, keep an eye on the air quality levels and stay indoors when it’s declining. An air purifier with HEPA filters can ensure the air in your home is clean and keep allergies under control.

November 17, 2022