Particulate matter

Tiny bits float in the air.

They are too small to see. Some come from volcanoes. Others come from dust storms.

People make these bits too. Smoke from fires can make them. Dust from building sites can make them.

These bits can be bad for us. They can get deep into our lungs. They can even travel in our blood.

We must work to keep air clean.

Tiny bits of solid or liquid matter float in the air. We call this particulate matter, or PM for short.

These bits are too small to see with our eyes. Some are called coarse particles. Others are fine particles, known as PM2.5.

Most PM comes from nature. Volcanoes and dust storms send bits into the sky. Sea spray also makes salt particles.

Human activities make the rest. This includes burning fuels for heat or cars. Construction sites and factories also make dust.

PM can be bad for our health. Small particles can go deep into the lungs. They can even travel through the blood. This can cause heart or lung disease. In 2021, PM contributed to many deaths around the world.

Some PM is made of soot, which is mostly carbon. This type of pollution can also affect our climate.

Particulate matter, often called PM, consists of tiny solid or liquid bits floating in the air.

These particles are so small that they are often invisible to our eyes. Scientists group them by how wide they are. Coarse particles, known as PM10, are 10 micrometers or less in diameter.

Fine particles, called PM2.5, are 2.5 micrometers or less. Even smaller are ultrafine particles, which are 100 nanometers or less. These tiny bits are important because they affect our weather and our health.

Particles enter the air in different ways. Some are primary, which means they are breathed out directly from a source. Others are secondary, which form through chemical reactions in the sky.

Natural sources create about 90 percent of the total mass of these particles. Volcanoes, dust storms, and sea spray all send bits into the atmosphere.

Human activities create the other 10 percent. This includes burning fuels, construction work, and even metalworking.

In the United Kingdom, burning things at home is the biggest source of PM. In 2019, wood burning in stoves and open fires caused 38 percent of PM in the UK.

New laws in 2021 helped reduce these levels by limiting certain types of wood and coal. By 2024, wood burning was responsible for 20 percent of PM10 and 11 percent of PM2.5.

In other places, like China, coal is a major cause of PM2.5. In the United States, Egypt, and Russia, oil and natural gas are the main contributors.

These tiny bits can be very dangerous to living things. Because they are so small, they can go deep into the lungs. They can even travel through the bloodstream to reach the brain or other organs.

This can lead to serious health problems like heart disease, stroke, or lung disease. In 2021, PM exposure contributed to 7.8 million deaths worldwide.

Of those, 4.7 million deaths came from outdoor air and 3.1 million from indoor air. There is no known safe level for exposure to these particles.

Particulate matter also changes how our planet works. Some particles, like mineral dust, can travel thousands of kilometers through the air.

Sea salt particles are another big part of the air. These salt bits help tiny water droplets form into clouds.

The shape and size of particles also change how they interact with sunlight. Some particles absorb light, while others scatter it. This process can affect the Earth's climate and temperature.

Particulate matter, often called PM, consists of microscopic particles of solid or liquid matter suspended in the air.

These particles are a major component of atmospheric aerosols, which are mixtures of particulates and air. PM is categorized by its diameter to help scientists understand its behavior and risks. Coarse particles, known as PM10, have a diameter of 10 micrometers (μm) or less. Fine particles, or PM2.5, are 2.5 μm or less in diameter.

Even smaller are ultrafine particles, which are PM1 or less than 100 nanometers (nm) in diameter. One specific type of fine or ultrafine particle is soot, which is primarily made of carbon.

These particles enter the atmosphere through different processes. Some are classified as primary particulates because they are emitted directly from a source. Others are secondary particulates, which form through chemical reactions occurring in the air.

The chemical composition of these particles varies based on their source, geography, and weather. For example, particles from fuel combustion differ from those produced by burning vegetation or construction waste. Some particles, like those from a recycling yard or scrap metal fire, may contain more toxic substances. The composition of these aerosols can even shift between liquid, solid, and semisolid states depending on environmental conditions.

Natural sources are responsible for approximately 90 percent of the total mass of particulate matter in the atmosphere.

Major natural contributors include volcanic ash from volcanoes and desert dust from dust storms. Forest and grassland fires also release significant amounts of particulates. Other sources include living vegetation and sea spray. Sea salt aerosols (SSAs) are a leading global contributor, especially in the Southern Hemisphere where 80 percent of the surface is ocean. These salt particles consist of inorganic salts like sodium chloride, but can also include organic matter like bacteria or proteins.

Human activities, known as anthropogenic sources, account for the remaining 10 percent of the total mass of aerosols.

Human-generated particulates are often smaller, such as PM2.5 or PM1, which poses higher risks. Common sources include the burning of fossil fuels like coal, oil, and natural gas for electricity and transport. Biomass fuels, such as wood or manure, are used for heating and cooking. Construction and renovation activities, including demolition and earthwork, generate significant dust. Industrial processes like mining, smelting, and oil refining also contribute. Other sources include metalworking, woodworking, and even microplastics.

Particulate matter is considered the most dangerous type of air pollution due to its impact on human health.

Because of their small size, these particles can penetrate deep into the lungs. They can then travel through the bloodstream to reach multiple organs, including the brain. This exposure is linked to serious conditions such as stroke, heart disease, lung disease, cancer, and preterm birth. In 2021, worldwide exposure to PM contributed to 7.8 million deaths. Of these, 4.7 million were caused by outdoor air pollution and 3.1 million by household air pollution. Scientists have noted that there is no safe level for exposure to these particulates.

Regional differences determine which fuels or activities contribute most to pollution. In 2021, coal was the highest contributor to PM2.5-related mortality in China. In the United States, Egypt, and Russia, oil and natural gas were the dominant sources. In countries like Pakistan and India, solid biofuels had the highest impact. In the United Kingdom, domestic combustion is the largest single source of PM. In 2019, wood burning in stoves and open fires was responsible for 38 percent of PM in the UK. However, new laws in 2021 restricted wet wood and house coal, causing levels to drop. By 2024, domestic wood burning was responsible for 20 percent of PM10 and 11 percent of PM2.5 in the UK.

Beyond health, particulate matter plays a vital role in the Earth's climate and systems.

The size, shape, and chemical makeup of a particle determine how it interacts with solar radiation. Some particles scatter light, while others absorb it, which changes the Earth's temperature. Mineral dust is light-absorbing and can travel thousands of kilometers from its source.

Additionally, sea salt aerosols are key to cloud formation. They possess hygroscopicity, which is the ability to take up water to become cloud droplets. This connection shows how microscopic particles influence massive global weather patterns.