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  4. Smog in Winter Air: What To Know and Do
  • What You Need To Know about Smog in Winter Air

    Outdoor air pollution can sometimes be a bigger threat during the wintertime.

    A man looking at his phone outside in the winter

    • Colder temperatures aren’t the only thing that change our air during winter. When the season changes, shifts in things like barometric pressure, vehicle use and more can increase the amount of smog in the air we breathe. Understanding the basics of winter air pollution can help you protect yourself—and decrease the amount you’re adding to the atmosphere.

      What is smog?

      Smog is air pollution that spreads over a large distance. The word “smog” is a combination of “smoke” and “fog,” referring to the gray, hazy look the air can have when it’s especially polluted. There are a few different types of smog, but all of it is usually caused by vehicle exhaust emissions and burning fossil fuels like coal.

      Causes of smog: The science, simplified

      Things like barometric pressure can make the science of air quality sound confusing, but it’s actually quite simple—when air pressure decreases, it tends to get more wet and windy in that area. More wind means more pollution blown in from other areas, while snow and rain can harbor all sorts of pollutants, too. If air pressure increases, the air stops moving, so pollution tends to stay where it is.¹ Additionally, wintertime air tends to be colder near the surface of the Earth than it is farther up. That warm air locks in the colder stuff underneath, giving pollution less room to disperse.¹

      Winter airtime pollutants to watch for

      While the weather has a big effect on smog in winter air, human actions contribute to the seasonal increase, too. In the winter, large-scale industrial operations that contribute to emissions stay the same, but things like wood-burning fireplaces and cars running while they warm up are more frequent in the wintertime.¹ Pollutants like carbon monoxide, vehicle exhaust and smog are some of the common culprits of wintertime pollution.

      How you can take care of air quality—indoors and out

      Winter weather may be out of your control, but the steps you take to care for the air are not! Start by familiarizing yourself with the Air Quality Index (AQI) and monitoring it in your area. If it rises above healthy levels, consider delaying outdoor activities for another time. No matter what the AQI measures, avoid idling your car outside—modern vehicles don’t actually require “warming up,” so you don’t have to start it in advance, anyway.²

      Smog can make a difference indoors, too. When smog in winter air is at higher levels, avoid opening windows and ensure there are no drafts near entrances and exits to your home. Make sure you’re using a fresh HVAC filter and running your HVAC system on high AQI days—the longer the system is on, the more air it can filter. If you’re concerned about particulate matter 2.5 (PM2.5) like smog, opt for a Filtrete™ Smart Filter that can help catch the tiny particles from air passing through the filter you don’t want hanging out in your air.


      1. https://scied.ucar.edu/learning-zone/air-quality/how-weather-affects-air-quality

      2. https://www.epa.gov/transportation-air-pollution-and-climate-change/what-you-can-do-reduce-pollution-vehicles-and-engines

      Related reads

      1. https://www.filtrete.com/3M/en_US/filtrete/home-tips/full-story/~smart-strategies-for-cooking-at-home-to-help-improve-indoor-air-quality/?storyid=0f217e40-1168-4e7b-9e65-6690242afee3

      2. https://www.filtrete.com/3M/en_US/filtrete/home-tips/full-story/~key-findings-from-the-2020-ala-state-of-the-air-report/?storyid=43abe694-f9fe-4887-902a-3a565fec59a8