What is PM2.5?

Particulate matter, or PM, refers to particles found in the air, including dust, soot, dirt, smoke, and liquid droplets.

PM2.5 particles measure 2.5 microns or less in diameter. PM2.5 particles are so small they can only be seen with an electron microscope.

Of all air pollution measures, PM2.5 pollution poses the greatest health threat (1). Due to its small size, PM2.5 can remain suspended in the air for long periods of time and can be absorbed deep into the bloodstream upon inhalation.

What are the sources of PM2.5 pollution?

Particulate matter can be either emitted directly from manmade or natural sources, with manmade sources generally resulting in greater amount of PM2.5 (2).

Some of the most common manmade sources of pollutant PM2.5 are (3) (4) (5):

• motor combustion
• power plant combustion
• industrial processes
• stoves, fireplaces, and home wood burning
• smoke from fireworks
• smoking

Natural sources of PM2.5 can include:

• dust
• soot
• dirt
• windblown salt
• plant spores
• pollen
• smoke from wildfires

The dominant sources of PM2.5 air quality can vary depending on the season, weather, climate, level of urbanization, country, and region.

A 1994 study in Atmospheric Environment looked at PM2.5 sources in the United States, determining that biomass burnings were the highest contributors to PM2.5 pollution in the Northwest, while residual oil combustion was the dominant source in the Northeast and in major seaport cities (6).

Sources of pollutants can include emissions from neighboring countries. A 2019 study of source contributions in Canada published in Environmental Science and Technology found that 33 percent of Central Canada’s pollutant PM2.5 originated in the U.S. (7).

The same study uncovered that residential combustion was the primary source of PM2.5 in Central Canada, while wildfires were the responsible sources for PM2.5 pollution in Northern, Atlantic, and Western Canada.

What are the chemical components of PM2.5?

PM2.5 can be created by other pollutants chemically reacting in the atmosphere.

Chemical reaction between gases can be sources of PM2.5 pollutants, including reactions between (8):

• sulfur dioxide
• nitrogen oxides
• ammonia
• black carbon
• mineral dust
• water
• volatile organic compounds

How does PM2.5 pollution affect our health?

PM 2.5’s microscopic size increases its potential to be lodged deep into the respiratory tracts. At 2.5 microns, PM2.5 is capable of entering the circulatory system and even the brain (9). Short term symptoms of exposure to high levels of particulate matter include irritation of the throat and airways, coughing, and difficulty breathing (10).

More serious, long-term complications can include:

• heart and lung disease
• bronchitis
• emphysema
• nonfatal heart attacks
• irregular heartbeat
• asthma and more intense flareups
• decreased lung function
• early death

People with heart or lung diseases, children, and older adults are most likely to be affected by particle pollution exposure.

Numerous studies have confirmed a multitude of serious health complications caused by exposure to pollutant PM2.5.

For example, a 2011 study published in The American Journal of Respiratory and Critical Care Medicine tracked 1.2 million Americans from 1982 until 2008 (11). Each 10 microgram per cubic meter increase in PM2.5 concentrations was associated with a 15-27% increase in lung cancer mortality.

PM2.5 pollution has been tied to increased risk of asthma in young children in Denmark, according to a 2020 study published in the British Medical Journal(12). All children born between 1997 and 2014 were followed for asthma onset and persistent wheezing from age 1 to 15. The study found that children exposed to higher levels of PM2.5 were more likely to develop asthma and persistent wheezing than children who weren’t exposed.

Is there a difference between PM2.5 and PM10?

PM10 and PM2.5 are both forms of pollutants that are different sizes. PM2.5 particles are considered to be fine and PM10 is larger and more coarse. PM10 particles are between 2.5 and 10 micrograms.

Our bodies can more easily defend against PM10 by sneezing or coughing. Those defenses don’t work with smaller particles (13).

PM10 can embed within the lungs where they are associated with adverse health impacts, such as lung tissue damage and asthma. However, PM10 it isn’t as likely to enter the blood stream as PM2.5 due to its size (14).

What are the environmental effects of PM2.5 air quality?

PM2.5 causes environmental harm in several ways, such as (15):

• damage of materials and buildings
• acid deposition
• increased ozone levels

PM2.5 pollution can travel long distances through strong winds, up to hundreds of thousands of miles from their source (16). PM2.5 can be carried to coastal waters and river basins, where they change the nutrient balance. When particle pollution settles on crops and forests, it can damage the vegetation.

What can be done about PM2.5 pollution?

People with concerns about PM2.5 in their environment can advocate for clean air legislation and for low-emission zones.

Reducing PM2.5 and PM10 air pollution is a priority for most countries. India joined the United Nation’s Climate and Clean Air Coalition in 2019 with the goal of reducing national particulate pollution by 20 to 30 percent by 2024. In 2019, India launched the National Clean Air Programme in order to meet those goals (17).

People can help limit particulate matter emissions in their own lives. Actions that can be taken include (18):

• drive less frequently
• slow mold growth by controlling humidity
• use a mop, damp cloth, and HEPA vacuum for cleaning
• never smoke indoors
• burn candles and incense less often
• improve electricity and fuel efficiency
• limit wood or trash burning
• don’t use outdoor wood boilers
• your vehicle should never idle in attached garages or near doors and windows
• generators and barbecues should never be run indoors or inside attached garages
• run a room air purifier to clean the air and remove PM2.5
• install a whole-house air purifier to eliminate PM2.5 from your home
• facilities can install high-efficiency HVAC unit air filters in schools and commercial buildings
• monitor your indoor and outdoor air quality

Can PM2.5 affect indoor air quality?

Outdoor sources of pollutant PM2.5 can impact indoor environments by entering through leaks in windows and doors as well as spaces within generally “leaky” buildings (19).

An airtight home can’t protect against indoor sources of PM2.5, such as (20):

• cooking with wood
• candles
• incense burners
• fireplaces
• stoves
• smoking

Even household cleaners and air fresheners can create gaseous pollutants through chemical reactions, resulting in PM2.5 pollution indoors.

What other air pollutants threaten your air quality?

There are many forms of pollutants apart from PM10 and PM2.5. Common pollutants across the globe include:

• ammonia
• asbestos
• benzene
• black carbon
• carbon dioxide
• carbon monoxide
• lead
• nitrogen dioxide
• ozone
• sulfur dioxide
• volatile organic compounds (VOCs)

There are six criteria air pollutants regulated in the United States (21):

• carbon monoxide
• lead
• nitrogen oxides
• ground-level ozone
• particulate matter (including PM10 and PM2.5)
• sulfur dioxides

The criteria were set by the Clean Air Act, and the U.S. Environmental Protection Agency determines standards for the criteria. The listed pollutants were selected in part because they’re commonly found across the U.S.

There are two types of criteria:

• primary: standards focused on human health and safety
• secondary: standards focused on indirect harm to the environment and human well-being

Though regulations have helped keep air pollution in check and improve quality of life, there are still significant pollutants harming humanity’s health and financial well-being. Look at our Cost of Air Pollution counter to see how clean air can improve quality of life and limit the economic burden of pollution.