couple walking in the city using umbrella in the rain

Can Rain Really Decrease Air Pollution?

Blog written by Veva.

We breathe in and breathe out all the time. But when you have allergies or are sensitive to air pollution, that unconscious activity is something you're constantly aware of, because "as easy as breathing" can be a bit of a challenge when you're coughing and wheezing. Air quality is important, and in the US, the air we breathe is cleaner than it's been in years. But what about Mother Nature's great jokes, otherwise known as pollen, ragweed, and mold? If you have allergies, then you're familiar with scanning the skies for rain, checking the weather for the possibility of a good storm, or just resigning yourself to staying inside until the first frost.

Rain and snow have to be good for clearing out pollen in the air and other pollution, right? Well, maybe. While atmospheric conditions— temperature, air pressure, and humidity—do have an impact on air quality, it's not always positive. While a good rainstorm is wonderful for washing pollen from the air, other pollutants just shift elsewhere. Air is always moving, so the airborne particles that create pollution just move around, meaning that the town next to yours may get dirtier air when you get rain.

Does Rain Decrease Air Pollution?

Studies as far back as the 1980s confirmed that polluted air doesn't just "go away". Coal burning in the Ohio Valley emits sulfur dioxide, which is carried for hundreds of miles on the wind. The result? Acid rainfall as far away as Canada and the eastern United States, where the contaminated rain effectively killed fish in the area lakes—the fish eggs couldn't develop.

So when you look outside after a big rain and see a clear blue sky, it's true that pollen and other pollutants are "washed away" from the skies over your house. Pollen in the air washes away into storm drains and soaks into the ground, but that doesn't mean they've gone—just relocated. If you or any of your family members struggle with allergies or asthma, the truth is that you're generally not that interested in where it all went, just that it's gone and you can breathe when you go outside.

Weather and Pollutants Have a Complicated Relationship

Airborne pollutants are always around, but their visibility is related to atmospheric conditions. The most common example of visible pollution is the pollen in the air that turns everything that yucky yellowish green in the spring—the air is warmer and a little more humid, so the pollen just hangs in the stagnant air.

Cold Weather Pollutants

Here's the question. Is the air dirtier on those cold, crisp, winter days when there's no pollen in the air, but exhaust is visible  from cars, chimneys, and smokestacks? Probably so—carbon monoxide levels from wood-burning smoke and idling cars (the beauty of remote start; the car's warm and toasty when you get in) do cause an increase in pollutants.

The Science Behind How the Atmosphere and Pollution Interact

Particulate matter is the combination of microscopic solid and liquid particles in the atmosphere. It's made from aerosols—smoke, dust, and other minute particles that are naturally suspended in the air. When these particles are unusually large, they cause the atmospheric haze that makes everything look dirty and fuzzy around the edges.

Here are some ways that weather impacts air pollution. We've already touched on rain and air pollution, but sunshine, higher temperatures, air turbulence, and wind speed all affect the concentration of pollen and other pollutants in the air.

  • Direct sunshine and warmer air temperatures can cause chemical reactions that create smog
  • Wind speed and atmospheric turbulence determine how pollutants disperse from an area
  • Stagnant air helps dust particles and pollen create low air quality
  • Wind is a double-edged sword—what it sweeps out, it can also sweep in
  • Coastal cities do get cleaner air from breezes coming off the ocean

Rain clears out pollution from pollen  and other soluble particles, a phenomenon that scientists call "wet" disposition—a natural process (rain, snow, fog) in which droplets are removed from the air by  atmospheric hydrometers and deposited into the soil or water.

Here's how it works.

When rain, snow, or even fog falls through the atmosphere, the droplets attract the tiny aerosol particles before they hit the earth's surface. This process is called coagulation, and is nature's way of clearing the air from soot, sulfates, and organic particles like pollen or mold. Scientists at MIT have even gone so far as to measure how effective this wet disposition is at clearing out the atmosphere—remember that although pollen is more or less at tree level, other pollutants are high up in the atmosphere. They calculate a cloud's altitude, the size of the droplets, and the concentration and diameter of the aerosols to figure out whether a raindrop will clear out a given particulate.

So particulate matter, both natural and man-made, is what causes air pollution. Several respiratory problems are linked to pollution; these are the most common.

  • Coughing and wheezing
  • Asthma
  • Reduced lung function
  • Heart attacks and stroke

Does Rain Make Pollen Better or Worse?

Most of us can accept daily air pollution as part of living in an industrial society, but for some, pollen sensitivity can be a debilitating condition in both spring and fall.

Pollen counts are much higher when trees and shrubbery are dry, and dry pollen travels such more efficiently when the wind blows. A good rain washes all the pollen grains from the leaves and branches, clearing not only the air, but the grass and even streets and houses. In the spring and summer, high humidity usually follows rain, which also helps keep the pollen down.

Does rain make allergies worse?

In general, allergies are better after the rain, when the air is clear and clean.

If you feel like your allergies are worse after a rain, keep in mind that you're probably allergic to more than just pollen. Grass, weed, and mold allergies often go hand in hand with pollen allergies, and a good rain can bring those to the surface. Mold and dust mites in particular thrive in warm and humid conditions, so be sure that you have your air conditioner or a dehumidifier running to keep the air as dry as possible. 

In the fall, ragweed and more pollen make allergies worse for many people, so be sure that you keep leaves under control around the house—they're breeding grounds for both pollen and mold.

Thunderstorm Asthma

For some people with allergies, a thunderstorm can actually make their symptoms worse. There's actually a weather phenomenon called Thunderstorm Asthma, which exacerbates the wheezing, coughing and sneezing that usually go away after a good rain.

Researchers noticed a couple of incidents of increased asthma attacks after violent thunderstorms when the pollen count was high. In Melbourne, AU, in 2008, eight people died from sudden asthma attacks and 8,000 went to the ER. The strange thing was, why do some strong storms result in heightened asthma symptoms, while others have no negative impact? Another oddity is that these cases were prevalent in places with lots of  rye grass pollens, which are typically trapped in the cilia of the nose and sinuses before they get to the lungs.

Scientists at the University of Georgia figured out that a specific airflow pattern, with assists from humidity and electricity, was responsible. Thunderstorms create downdrafts of cold air that build concentrated amounts of pollen, mold spores, and other allergens, and then the particles are swept up into the super humid clouds. Then, wind, humidity, and lightning combine to rupture the allergens and disperse the particles into the atmosphere—small enough for you to inhale.

How You Can Ease the Symptoms of Pollen and Air Pollution

Since you can't count on the weather to wash away pollen and other air pollution, you've got to take control of the air you and your family breathe. When you think about it, you only have total control of your air in one place—your car. There, you can adjust the temperature and humidity, make sure all the air in the cabin is clean and recirculated, and breathe in air that's a lot less irritating than outdoors. Obviously, you can't live in your car, but you can recreate that custom atmosphere—all you need are air purifiers for your home.

How Air Purifiers Work

Veva's HEPA air purifiers are the solution to your air quality concerns. They capture particles as tiny as 0.3 microns—so all the dust, mold, pollen, pet dander, and other microscopic particles that your HVAc and furnace filters can't trap. Our air purifiers also remove odors, so no matter the pet, baby, or teenager scents emanating through the house, you'll never notice them. Veva air purifiers are premium filters that are ozone, UV, and ion free, so there are no traces of ozone in your home. There's also a safety feature that automatically shuts the device off if the curious baby, dog, or even teenager removes the front panel.

There's no need to worry about thunderstorm asthma attacks, learning new rain dances, or other surefire ways to clean your air. Air purifiers are lots more reliable than the weather report.

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