What are ultrafine particles?

The term ultrafine particles (UFPs) refers to airborne particulate matter smaller than 0.1 micron in diameter (sometimes called PM0.1). Some UFPs measure as small as 0.003 microns.

UFPs are considered among the most dangerous particle pollutants due to their small size, which allows them to be breathed into the lungs and pass into the bloodstream through the lungs.

Click here to see why particle size matters.

Their small, nanoscale size and behavior makes UFPs difficult to monitor using current air quality monitoring technology. This size also causes airborne UFPs to move through the air in ways distinct from fine particles like PM2.5 and PM1, moving in random patterns more similar to gases than other particles.

Unlike PM2.5 and other particles, no official standards exist to measure or regulate airborne UFPs, although estimates suggest that over 90% of airborne particles in the air at any given time are UFPs.¹

Despite the lack of regulation, research has increasingly suggested that UFPs often exist at much higher concentrations than other particle pollutants and may be linked to an even wider range of adverse health effects than fine or coarse particles like PM1, PM2.5, or PM10.

What are the sources of ultrafine particles?

Ultrafine particles are most commonly emitted through combustion from natural or human sources. Human activity is believed to be responsible for the largest share of UFPs due to the prevalence of UFPs in cities, where global industrialization and population growth have had the most notable impact on air pollution.²

A 2019 study in Environment International found that UFP concentrations tend to be higher during the day in close correlation with changes in vehicle traffic and near busy roadways, further suggesting the outsized impact of human activity on UFPs.³

Natural sources

Natural sources of UFPs include:

• volcanic lava and ash
• smoke from wildfires
• aerosols in ocean mist

Due to the temporary nature of these sources, UFPs from volcanos and ocean sources aren't considered particularly problematic. Global wind currents quickly disperse these UFPs into low concentrations that pose little threat to human health, with the exception of major volcanic eruptions whose smoke can travel thousands of miles.⁴

UFPs in wildfire smoke, however, have gained attention due to more frequent and severe wildfires in recent years. A 2021 study in Particle and Fibre Toxicology found that even short-term exposure to UFPs in wildfire smoke may significantly increase risks of respiratory and cardiovascular disease.⁵

Human sources

The most common human sources of UFPs include:

• vehicle exhaust
• diesel exhaust
• natural gas and biofuel emissions⁶
• airplane emissions
• factory and industrial emissions
• power plant emissions
• burning of garbage
• cigarettes, cigars, and vaping⁷
• indoor cooking⁸
• controlled burns
• indoor vacuuming⁹
• bacteria
• viruses
• use of office machines like printers and copiers

Human sources of UFPs like vehicles and industry can pose great health risks because they emit new particles over long periods of time, as vehicle traffic and industrial activity occur continuously around the world.

Furthermore, many human sources of UFPs are more prevalent in large urban areas, posing significant dangers to the 4.4 billion people currently living in cities (approximately 55 percent of an estimated 8 billion people).^10,11

How do ultrafine particles affect our health?

The full health impacts of UFPs are still being investigated to differentiate the specific dangers of UFPs in contrast to other types of air pollution.

However, it’s largely undisputed that UFPs cause oxidative stress to tissues throughout your body that can cause systemic harm, penetrating deep into lung tissue, the bloodstream, the brain, and almost every other organ.¹²

A 2020 review article in Experimental and Molecular Medicine found substantial evidence that UFP exposure increases the risk of:¹³

• lung inflammation
• high blood pressure
• ischemic heart disease
• atherosclerosis (plaque buildup or "hardening" of arteries)
• heart attacks
• heart failure
• chronic cough
• nerve damage
• brain damage
• loss of cognitive function
• digestive problems
• diabetes
• increased risk of many cancers
• skin damage

Can ultrafine particles affect indoor air quality?

Like other particle pollutants, UFPs in outdoor air can enter indoor spaces through cracks and leaks in buildings as well as through windows, doors, and other openings in a home or building envelope.

This can be especially problematic for older or poorly built homes during periods of high UFP concentrations, such as wildfires or volcanic eruptions.

A 2019 study conducted in the U.S. state of Colorado found that indoor concentrations of particulate matter could be up to 4.6 times higher than outdoor concentrations in the absence of natural ventilation sources like wind.¹⁴

UFPs from indoor sources, such as kitchens or biomass fuel burning, can also build up to dangerously high concentrations, especially in airtight energy-efficient homes, and carry a risk of additional health effects.

A 2007 review article in Indoor Air found that exposure to high levels of indoor UFPs during childhood can cause lung damage and inflammation that increases a child’s risk of developing lifelong asthma.¹⁵

Tips to reduce ultrafine particles

Here are some actions that individuals and organizations can take to help reduce UFPs:

• Choose commuting options that help reduce vehicle traffic, such as walking, cycling, public transportation, or ridesharing.
• Purchase an electric or hydrogen-powered vehicle to replace personal vehicles that have combustion engines.
• Install solar energy systems in homes or workplaces to help reduce strain on the electrical grid.
• Replace diesel-powered fleets with fuel-efficient or electric transportation vehicles.
• Reduce or avoid any type of indoor burning, including scented candles and wood in fireplaces.
• Use a kitchen range hood to help reduce particulate pollutants as well as other smoke and gas pollutants after you cook.
• Limit indoor vacuuming to once a week or as needed, or use a vacuum with a HEPA filter.
• Reduce or quit smoking cigarettes, cigars, or vaping products.

Should ultrafine particles be regulated?

Until UFPs are subject to new standards and regulations, little can be done to enforce control of UFP emissions by major contributors like factories, manufacturing facilities, and automobile manufacturers whose vehicles produce exhaust filled with UFPs.

Some organizations have conducted independent studies of regional UFP emissions in order to better understand the sources, patterns, and health effects of UFPs and contribute to future monitoring technology and regulation.

In 2014, the Bay Area Air Quality Management District (BAAQMD) completed a study of UFPs in the U.S. San Francisco Bay Area, home to nearly 8 million people.¹⁶

The report indicates that even a small rise in UFPs could increase hospitalizations from heart and lung conditions by nearly 20% and increase the risk of death from these conditions by over 2%. This report suggests the high stakes involved in regulating and reducing UFPs.

A 2016 report published by the American Academy of Allergy, Asthma, and Immunology also concluded that the notable harm that UFPs cause to the body, including damage to DNA and increased risk of allergy sensitization, warranted special regulatory attention.¹⁷

A 2016 U.S. Environmental Protection Agency (EPA) workshop also concluded that investment by U.S. automobile manufacturers in UFP monitoring could help better isolate combustion engine mechanisms that lead to UFP emissions, paving the way for more efficient technologies that reduce UFP emissions altogether.¹⁸

Some progress has been made on the ability to monitor UFPs.

A 2021 study in Science of the Total Environment suggests the use of cyclone sampling for measuring UFPs.¹⁹Using centrifugal forces to separate UFPs from other airborne matter, cyclone sampling has been successful in measuring bioaerosols containing viral particles like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

But with improvements in efficacy, cyclone sampling may be able to measure other UFPs quickly and accurately while uncovering the nuances of exposure.

A 2020 study involving high school students in urban China used this cyclone sampling technique to suggest two key patterns in personal UFP exposure:²⁰

• Exposure to UFPs can vary widely throughout the day from 0.13 micrograms per cubic meter (μg/m3) to 240.8 μg/m3. The highest UFP concentrations were mostly found indoors, especially in hospitals, household kitchens, or bedrooms less than 10 meters (32.8 feet) from a roadway.
• UFP exposure is highest during commutes. Student participants faced much higher UFP concentrations traveling between home to school or when leaving school facilities for meals than during any other time of the day.

More studies like this can help target regulation towards the most significant UFP sources indoors and out, such as cooking areas or busy roadways, and help protect those who frequently travel between indoor and outdoor spaces affected by UFPs.

Takeaway

UFPs are among the most dangerous and prevalent airborne pollutants, with a wide variety of noted health effects. However, no regulatory standards exist to control UFP emissions.

Many science and health organizations are increasingly calling for investment into research that will improve understanding of how to measure, regulate, and reduce UFPs to prevent their sinister health effects.²¹

Individuals and organizations alike can take measures to help reduce and prevent UFP emissions entirely by changing behaviors related to transportation, energy usage, and daily lifestyle habits.