Weather and Air Quality: How Air Quality Compares in Winter vs. Summer

Trees in Summer and Winter

Have you noticed that the air quality seems to worsen in the summer months? That is due, in part, to an increase in wildfires that negatively impact the air quality. But just because we can see the impact of forest fires...

Does that mean the air quality is worse overall during summer than in winter?

Weather and air quality are definitely related, but today we’re diving into what that actually means for the quality of our air. In this blog, we'll discuss the weather and air quality, as well as how things such as temperature, humidity and air pressure impact air quality.

How Does Weather Affect Air Quality?

The weather can significantly impact air quality since different aspects of the weather affect the amount of particulate matter present in the air. Sunshine, temperatures, rain, wind speed, air turbulence, and more affect pollutant concentrations and the overall air quality.

  • Higher temperatures can speed up chemical reactions in the air.
  • Sunshine can cause pollutants to undergo chemical reactions that result in the development of weather phenomena like smog.
  • Rain washes away the particulate matter (PM) and can also wash out dissolvable pollutants.
  • Wind, air turbulence, and mixing depth all affect how contaminants are spread out in an area.

How Winter Affects Air Quality

The air quality in winter is impacted by the increased time spent driving and idle time for vehicles when defrosting. Additionally, there is an increased use of fireplaces and wood-burning stoves to heat homes. When we use these methods to heat our homes, it can triple the amount of particulate matter. Lastly, the colder, drier air traps more pollution.

Most of the time, temperature decreases with elevation, which makes it easy for polluted air near the surface of the Earth to rise and lift away. However, temperature inversions are more likely to occur during colder winter months. Temperature inversions are when the temperature in relation to elevation is inverted from what is typical.

During the colder months, the sun is weaker, and the warmer upper layer of the atmosphere acts as a "lid" that traps the cooler, more polluted air below. To the average person, this phenomenon looks like winter smog.

Cold air molecules also naturally hold less moisture. When it comes to air quality, this isn’t ideal because rain helps to wash away pollutants and stop temperature inversions from happening by mixing up layers of air.

How Summer Affects Air Quality

Wildfires are a significant contributor to poor air quality in summer, as fires add carbon monoxide and particle matter to the atmosphere. A 2021 study, published in Nature, showed respiratory hospitalizations could increase by up to 10% with just a 10 μg m−3 increase in the daily average PM2.5 from wildfire smoke.

High temperatures not only increase the likelihood of wildfires but increase ground-level ozone. Ground-level ozone health effects range from respiratory infections to triggering asthma attacks and lung scarring.

Learn more about air quality illnesses and how they impact the respiratory system.

Dry conditions associated with the heat also increase dust particles in the air, and dust can travel significant distances to impact larger areas and areas away from storm activity. In one study, researchers in India found that dry and dusty weather, combined with increased temperatures, significantly increased the presence of airborne PM10 pollution.

In particular, they estimated that dust accounted for up to 40% of the total particulate matter during the summer due to loose soil, airborne ash, and stirred-up road dust. In this study, they also found that during a single summer dust storm, PM10 levels rose by 248%, and PM2.5 increased by 110%.

Next, hot, dry, windy, and stormy conditions significantly increase the amount of pollen circulating. This collision of environmental factors causes pollen grains to burst into smaller pieces, making it easier for the particles to be blown around and inhaled.

Climate change is also impacting general pollen concentration levels. Over the past twenty years, annual pollen seasons in North America have increased by more than 20 days, and overall pollen concentrations have increased by over 21%. Pollen is a significant contributor to respiratory illness.

How Air Quality Changes in Summer vs Winter

It’s impossible to state conclusively whether air quality is worse during the summer or winter months. Some pollutants are particularly harmful on warm days, while others are active mainly in colder temperatures. As air temperature impacts the movement of air, it can also affect the movement of pollution. This means that when the temperature is high, pollutants are generally in higher altitudes.

Additionally, when there is more air movement, pollutants are moved from one area to another. This doesn’t necessarily mean air quality is improved; it simply means one area is impacted over another.

While car exhaust fumes and other pollutants are more visible when it’s cold outside, and air quality appears to be impacted during wildfires, it doesn’t necessarily mean this is where air quality is the worst. Understanding weather and air quality, specifically how weather impacts air quality, can help us to make decisions during the summer and winter.

Worried About Your Air Quality?

Monitor the Particulate Matter levels around the world with our free, real-time PurpleAir Map or join PurpleAir's mission to make air quality data accessible to everyone by investing in an air quality monitor for your home.

Together, we can be informed and make changes in our daily habits and the community to improve air quality.