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You may have heard about PM 2.5 mentioned in a recent science or health article, or even on the news as part of coverage of wildfires or other air pollution events. High levels of PM 2.5 can have serious health consequences for you and your family. But what does this term mean, and how is it linked to respiratory disease, heart attack and other health problems? And more importantly, how can you reduce your exposure to it?

What is PM 2.5?

PM 2.5 refers to a category of particulate pollutant that is 2.5 microns or smaller in size. The average cross-section of a human hair is 50 microns. PM stands for “particulate matter.” The EPA and many health organizations categorize particulate matter by size because different size particles have different health effects. For instance, PM 10 particles (particles less than 10 microns in size) can irritate your nose and eyes, but fewer of these particles penetrate deep into your lungs, so they do not cause the same health problems that smaller micron particles can, although they do increase rates of respiratory disease Yu-Fei et al., 2016>.

Particles that are 2.5 microns or smaller are considered especially dangerous to human health because they bypass many of our body’s defenses. Nose hair, mucus, and other defenses work to catch these smaller particles before they enter deeper into our bodies. That said, PM 2.5 particles can get into our lungs, where they can reach the alveoli and eventually enter the bloodstream.

PM 2.5 particles are complex because they can be made up of numerous types of chemicals and particles, and they can be partly liquid, as opposed to solid, like a common dust particle. Particulate pollutants that are entirely or partly made up of liquid droplets are known as an aerosol. Natural kinds of aerosols include dust, sea salt and volcanic ash, whereas man-made sources include factory and auto emissions, coal combustion and biomass burning for clearing land or farming.

Tip: Did you know that PM is not the whole story when it comes to air quality? Learn more about other pollutants beyond PM here and read more about what the air purifier industry isn’t telling you.

What causes PM 2.5 pollution?

PM 2.5 pollutants can come from a variety of sources, making it a very complex type of pollution. Some PM 2.5 sources emit the particles directly. Known as “primary sources,” these include wildfires and some power plants and industrial processes. Secondary PM 2.5 particles, however, are formed when different chemicals combine in the air. Chemicals from coal power plants or automobile exhaust can react with water vapor in the atmosphere and sunlight to form new particles or compounds, and these particles can be under 2.5 microns in size. Because of the myriad of ways in which particles are formed from chemical compounds, as well as the amount of variable factors like region, weather, climate and human activity, it can be nearly impossible to know exactly what chemicals are present in the PM 2.5 particles on a given day.

There are some indoor sources of PM 2.5 which can affect your health even if the outside air is pollution-free, or if you have shut the windows on a poor air quality day. Common indoor sources include wood and coal fires, cooking fumes and even candles.

Why is PM 2.5 harmful?

Numerous health studies have found that higher quantities of PM 2.5 particles in the air may correlate with increased negative health effects, including increased incidence of respiratory disease, worsening of respiratory disease symptoms and cardiovascular effects that can lead to heart attacks and death.

PM 2.5 can have far-reaching and long-term effects because of the ways these particles interact with the body when they get into the lungs, “passing through the filtration of nose hair, reaching the end of the respiratory tract with airflow and accumulating there by diffusion, and damaging other parts of the body through air exchange in the lungs.” Yu-Fei et al., 2016>. What makes PM 2.5 especially dangerous is that it is very difficult to expel from your body, which proves prevention to be the ideal solution. Conversely, PM 10 can be expelled through coughing and sneezing, for example. PM 2.5 cannot.

A 2010 study found that, “Exposure to PM 2.5 … over a few hours to weeks can trigger cardiovascular disease-related mortality and nonfatal events; longer-term exposure (e.g. a few years) increases the risk for cardiovascular mortality to an even greater extent than exposures over a few days and reduces life expectancy … by several months to a few years.” Brook et al., 2010>.

According to the CDC, while particulate pollution is bad for everyone, certain populations are more at risk than others. Anyone with heart or lung disease, the elderly, infants and young children suffer more serious effects from these particles. People with heart disease can experience immediate symptoms when exposed to high concentrations of PM 2.5.

International impact of PM 2.5

The health effects of PM 2.5 have severely impacted the populations of various regions of the world—the WHO estimates that air pollution “kills an estimated seven million people worldwide every year” and their data “shows that 9 out of 10 people breathe air containing high levels of pollutants.”

Asian countries, in particular, have suffered severely from PM 2.5 associated pollution. From 1990 to 2010, the estimated PM 2.5-mortalities in East and South Asia “increased by 21% and 85% respectively.” (Wang et al., 2016).

This dramatic increase has been driven by population growth and migration spurred by economic forces, as well as relatively fewer air pollution controls and lax enforcement.

India has been especially affected. The Financial Times collated NASA satellite data pertaining to PM 2.5 and found that “more than 4 in 10 Indians are exposed to 5 times the safe limit of particulate matter in the air they breathe.” Delhi, in particular, has become notorious for its crop-burning season in November, when “hazy skies are a common occurrence” and winds spread a “river of smoke across much of the Indo-Gangetic Plain.” The resulting haze has “pushed levels of fine particulate matter (PM2.5) to hazardous levels in Delhi, according to data collected at the U.S. Embassy.”

Meanwhile, South Korea has also been facing air pollution problems due to its proximity to China, as well as industrial and human activity within its own borders. According to NPR, “Seoul’s air quality index was considered unhealthy for sensitive populations (such as children, the elderly and those with existing respiratory conditions) on 78 days” in 2016—a condition that has been exacerbated by South Korea’s continued reliance on coal-fired power plants.

This situation lies in stark contrast with conditions in Europe and North America, where, over the past two decades, “correlations between population and PM2.5 have become weaker due to air pollution controls but stronger in East Asia due to deteriorating air quality.”

In the wake of these developments, experts have concluded that taking active steps to reduce “primary PM” sources “appears to be the most efficient way for increasing health benefits (i.e., providing the largest mortality reduction per unit emissions)” (Wang et al., 2017).

How to protect yourself from high levels of PM 2.5 outdoors

The first step to protecting yourself from dangerous particulate pollution levels outdoors in knowing when and where dangerous levels of PM 2.5 occur. The EPA collects air quality data from sources across the nation and presents them as an air quality map and air quality forecast at the Air Now website. You can check current and predicted air quality conditions in your area. While the EPA has powerful tools that would allow you to break down the different types of particulate pollutants, the basic map combines particles with gaseous pollutants for a general air quality forecast. This is easier to use and sufficient for most people.

EPA regulations divide air quality into several different categories, based on the number of micrograms of a given type of pollutant per cubic meter of air (ug/m3). Each pollutant category has its own separate “breakpoints” divided by ug/m3, with PM 2.5 and PM 10 getting their own categories. Here are the categories for PM 2.5.

  • Hazardous: 350.4 ug/m3. Air quality this poor almost never happens in the U.S. in a widespread area, although it may occur directly downwind from wildfires or during a major smog event. Everyone needs to take protective measures if the air quality is above “hazardous” levels, especially at-risk groups who are older adults, have children, or suffer from a heart or lung condition. AirNow recommends asking your doctor if leaving the polluted area or moving to another location would be the best course of action.
  • Very Unhealthy: 250.4 ug/m3. Still rare, but may occur during wildfire season or in urban areas on hot, windless days; everyone should avoid outdoor activity at this level.
  • Unhealthy: 150.4 ug/m3. At this level of PM 25 pollutants, time spent outdoors should be limited, outdoor activity restricted, and windows kept shut.
  • Unhealthy for Sensitive Groups: 55.4 ug/m3. Anyone with asthma or other respiratory problems or cardiovascular disease should limit time outdoors and reduce outdoor activity.
  • Moderate: 35.4 ug/m3. This level, activity and outdoor time does not need to be restricted, but for people in sensitive groups, monitor their symptoms and reduce activity if they experience breathing problems.
  • Acceptable/Good: 12 ug/m3. Clean air, no restrictions or limits needed.

If the air quality index in your area shows elevated levels of pollutants, limit your time outdoors and reduce your outdoor activity levels, since higher exertion levels increases your breathing rate and your exposure to pollutants. Be extra cautious if you have asthma or other respiratory problems or cardiovascular disease. You can also check to see if pollution levels are lower during certain times of the day, and plan your activity for those times.

People concerned about outdoor air pollution often turn to face masks for protection. Studies have found that masks can in fact reduce the amount of PM 2.5 you inhale, but the mask must be rated to filter out PM 2.5 and it also has to fit well so there are no air gaps Pacitto et al., 2019>.

A more long-term way to protect yourself against high PM 2.5 levels is to vote for elected officials who are in favor of regulating PM 2.5 pollutants. There is scientific evidence to show that EPA regulations on particulate pollutants result in fewer health problems and reduced overall mortality. In U.S. counties where fine particulate pollutants decreased from 1980 to 2000, life expectancy increased even when controlling for other factors Pope et al., 2009>.

How to protect yourself from PM when indoors

If PM 2.5 levels are high outdoors, staying indoors is an important way to reduce your exposure. You should also keep windows closed (and doors closed as much as possible) and run the air conditioning.

Keeping outdoor particles outside is not enough though, because there are indoor sources of PM 2.5. Limit the use of fans, which can stir up dust and other particles. If you vacuum, use one with a HEPA filter to control how much dust it emits. You should also avoid burning a wood fire or candles inside, and when cooking and using the oven, make sure to allow adequate ventilation.

An air purifier is a good way to remove particulate pollutants from the air in your home. Traditional air filters like HEPA are rated to remove 99.97 percent of particles 0.3 microns in size.

Molekule air purifiers can remove fine particles, as well as destroy airborne chemicals in the air (specifically, volatile organic compounds) using patented Photo Electrochemical Oxidation (PECO) technology.

The primary sources of PM 2.5 in a home mentioned above also release harmful volatile organic compounds (VOCs), which the Molekule PECO-Filter can destroy with a catalytic reaction at the molecular level, converting airborne chemicals into harmless substances of water vapor and carbon dioxide.

PM 2.5 is a potentially dangerous category of air pollutants, and it is important to understand what it is, where it comes from and how to deal with it. By monitoring outdoor air quality and taking a few simple steps in your home, you can limit your exposure to PM 2.5.


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