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outdoor air quality

How Outdoor Air Quality Affects Indoor Air Quality

 |  Air Purification Systems

Phoenix greeted 2018 with one of the worst air quality days in over a decade, with particulate ratings reaching 283, categorized as Very Unhealthy by the Arizona Department of Environmental Quality (ADEQ).

Outdoor air quality affects indoor air quality. Pollutants find their way in through open doors and windows, as well as gaps throughout the building – within your ductwork and through insulation gaps surrounding windows and doors. You can even carry pollutants in on your person.

In this post, we explain common air pollutants, how weather affects them, and how they impact your health. We also look at how you can protect yourself and improve air quality inside your home.

What Are Common Air Pollutants?

The ADEQ measures a variety of air pollutants to determine air quality.


Ozone is a secondary pollutant, meaning it forms when primary pollutants meet sunlight. It is measured in parts per billion (ppb) and, when high, ADEQ recommends reducing daytime driving and refueling vehicles as late in the day as possible.

The two primary pollutants that cause ozone are volatile organic compounds (VOCs) and Nitrogen Oxides (NOx). Emissions from vehicles, chemical plants, refineries, and other industrial resources cause VOCs and NOx.

Common health effects include:

  • Increased risk of respiratory infection
  • Lung inflammation and decreased function
  • Aggravation of preexisting conditions such as asthma
  • Chest pain

phoenix air pollutantsCarbon Monoxide (CO)

CO is a poisonous gas that forms when the carbon found in fuels doesn’t burn completely. It is measured in parts per million (ppm) and, when high, ADEQ recommends minimizing nighttime driving and proper vehicle maintenance.

In urban areas, around 95 percent of CO pollution comes from motor vehicle emissions. Industrial processes and fuel combustion not related to transportation also cause CO pollution, as does smoke from fires. CO pollution is typically higher during colder weather.

Common health effects include:

  • Reduced oxygen intake and delivery to organs and tissues
  • People with cardiovascular disease suffer the greatest impact

Particulate Matter (PM10 and PM2.5)

Particulate matter measures the diameter of solid or liquid particles in the air. PM10 refers to particles with a diameter 10 micrometers or smaller. PM2.5 refers to particles with a diameter 2.5 micrometers or smaller. Seeing a brown haze in the air indicates high PM2.5 levels.

PM is measured in micrograms per cubic meter and, when levels are high, ADEQ recommends carpooling and using public transit. Also, stabilize loose soil and slow down when driving on dirt roads.

Combustion processes cause high PM2.5 levels. This includes motor vehicles, wood burning, and industrial waste. You see both high PM2.5 and PM10 levels from crushing and grinding operations.

Common health effects include:

  • Aggravation of existing respiratory diseases such as asthma
  • Increased risk of respiratory infection

How Does Weather Affect Air Quality?

phoenix air qualityWeather impacts air quality in a couple of ways. You may expect higher pollution during extremely cold weather, when more people operate wood-burning fireplaces and stoves or allow their vehicles to idle and “warm up” before driving. However, while these activities do lead to higher levels of particulate matter, they don’t represent weather’s main impact on pollution.

During extreme temperatures, air tends to stagnate, causing pollutants to build up nearer ground level. This is especially true during a weather phenomenon known as a temperature inversion.

An inversion is when a layer of warm air forms between two cooler layers. It forms a buffer that traps pollutants below the inversion, raising particulate pollution. When this happens, ADEQ issues poor air quality warnings. These typically include suggestions to reduce driving and limit outdoor activities (especially for children, the elderly, and those who suffer from respiratory issues). These are also usually designated as No Burn days.

How Outdoor Air Quality Affects Indoor Air Quality

As stated earlier, outdoor pollutants make their way into your home in a variety of ways. When pollutant levels are extremely high, people often feel the same effects as they do when outdoors, particularly burning eyes and lungs.

One of the more interesting statistics, though is that, even when pollution levels are high, indoor air quality is typically much worse than outdoor air quality.

What Causes Poor Indoor Air Quality?

Our homes teem with a variety of airborne pollutants, including bacteria and viruses, VOCs, pet dander, secondhand smoke, combustion pollutants, molds, and asthma triggers. When your home doesn’t breathe properly, it fails to clean these items from the air.

Unfortunately, modern homes don’t breathe very well. Today’s builders design homes to be more energy efficient, which is great for your power bill. However, those well-sealed doors, windows, joints, and ductwork keep fresh air from entering and scrubbing away all those airborne pollutants.

In the Phoenix area, we also spend most of the year with our windows closed to keep out the heat. Of course, this also reduces the amount of fresh air that enters your home.

How Poor Indoor Air Quality Affects Your Health

The EPA provides detailed information on the most common indoor air pollutants, as well as how they impact your health. We also touched on them in an earlier blog post about air purification systems. But, the following should give you a general idea about the most common pollutants and potential health issues due to exposure.

  • Radon: The leading cause of lung cancer among nonsmokers, radon gas forms in soil and enters your home through openings in the floors and walls
  • Secondhand smoke: May worsen asthma symptoms and increase risk of ear infections and SIDS
  • Combustion pollutants: Includes space heaters, fireplaces, woodstoves, dryers, and gas stoves; may cause elevated carbon monoxide or nitrogen dioxide levels and increase risk of respiratory infection, headaches, dizziness, nausea, and even death (carbon monoxide)
  • VOCs: Irritate eyes, nose, and throat; cause nausea and headaches; damages central nervous system, kidneys, and liver; may cause cancer
  • Asthma trigger: Includes mold, dust, pet dander, and secondhand smoke; cause coughing and wheezing, chest tightening, and respiratory problems

Improving Indoor Air Quality

The easiest way to improve indoor air quality is through regular admittance of fresh air via open windows and screen doors. However, during extreme weather conditions, this isn’t a viable option.

Of course, when outdoor pollution levels are high, filling your home with “fresh” air doesn’t help improve air quality.

At Isley’s, we recommend air purification systems as the most effective way to improve indoor air quality. They scrub away over 98 percent of the most common pollutants, including bacteria and viruses, VOCs, and asthma triggers. Contact us today to learn more.