Sources Of Particulates: What You Need To Know

Particulate matter (PM) is a complex mixture of solid particles and liquid droplets suspended in the air. These particles vary in size, shape, and chemical composition. Some particles are emitted directly into the air from sources such as cars, trucks, construction sites, and natural sources like dust storms and wildfires. Other particles are formed in the air through chemical reactions. PM can have significant health impacts, especially smaller particles that can be inhaled deep into the lungs, potentially leading to respiratory and cardiovascular issues, reduced lung function, and even premature death. The sources and composition of particulates play a crucial role in understanding their effects.

Outdoor sources

Outdoor particulate matter, also known as particle pollution, can enter buildings through windows, doors, ventilation systems, and small cracks and crevices. Outdoor PM can be high at any time of year and is higher near busy roads and where people burn wood.

• Traffic and transportation
• Industrial activities
• Power plants
• Construction sites
• Waste burning
• Fields
• Mining operations
• Agricultural activities
• Factory emissions

Outdoor air pollution can be caused by high-temperature combustion in vehicles, industries, and power-generating facilities. The predominant source of carbon monoxide in ambient air is from motor vehicles. Carbon monoxide can cause difficulties in breathing, exhaustion, dizziness, and other flu-like symptoms. Exposure to high levels of carbon monoxide can be deadly. Sulfur dioxide is predominantly derived from the combustion of fossil fuels for domestic heating, industries, and power generation. Exposure to sulfur dioxide is associated with asthma hospital admissions and emergency room visits.

Natural sources

Particulate matter (PM) is a mixture of solid particles and liquid droplets found in the air. It can be emitted naturally or through human activity. Natural sources of PM include:

Volcanic Eruptions

Volcanic eruptions emit particulates such as volcanic ash, which is classed as PM2.5 due to its fine particle size.

Dust Storms

Dust storms, common in arid regions such as the Sahara Desert, are a source of PM. Wind-blown dust from open lands and construction sites is included in PM10.

Forest and Grassland Fires

Fires emit particulates such as soot, which is classed as PM2.5. Natural fires, such as those caused by lightning, are a source of smaller aerosols.

Living Vegetation

Trees and vegetation emit organic compounds, which can form secondary particles through chemical reactions with other gases in the atmosphere.

Sea Spray

Sea spray, particularly from dried sea salt, is a natural source of PM. This is more common in the Southern Hemisphere, where there is a higher proportion of ocean compared to land.

Pollen

Pollen is a natural particulate that can be found both outdoors and indoors, as it can enter indoor spaces through doors, windows, and leaks in building structures.

Human-made sources

Human activities are responsible for a significant proportion of particulate matter (PM) in the atmosphere. These particles are a mixture of solid and liquid droplets suspended in the air, and they can have adverse effects on human health and the environment.

Transportation

Vehicles, including cars, trucks, and buses, emit particulate matter directly from their exhausts. This is particularly problematic near busy roads, where the concentration of these particles can be high.

Industrial Processes

Factories and industrial processes, such as power plants, release particles into the air through fuel combustion and other activities. This includes pollutants such as sulfur dioxide and nitrogen oxides, which can react in the atmosphere to form secondary particles.

Construction and Agriculture

Construction sites, unpaved roads, and tilled fields are significant sources of particulate matter. Activities such as stone crushing and soil disturbance can generate and disperse particles into the air.

Residential Activities

Residential heating and cooking contribute to indoor and outdoor particulate matter. The burning of wood, especially in closed stoves and open fires, is a major source of PM2.5 and PM10. In some regions, wood smoke can account for a substantial percentage of fine particle air pollution during winter. Additionally, activities such as smoking tobacco, burning candles or incense, and using certain cleaning products can generate particles indoors.

Waste Management

The combustion of waste, such as in recycling yards or scrap metal fires, can release particulate matter into the air. These particles may contain toxic substances, posing additional health risks.

Indoor sources

Indoor particulate matter (PM) is a mixture of many chemical species and is composed of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. It is important to note that indoor PM levels are dependent on several factors, including outdoor levels, infiltration, types of ventilation and filtration systems used, indoor sources, and personal activities of occupants.

Additionally, household products like cleaning solutions, air fresheners, oil diffusers, and aerosol sprays can contribute to indoor PM levels. Certain hobbies, such as woodworking, metalworking, 3D printing, and activities involving glues and adhesives, can also produce PM.

Biological sources, including mold spores, dust mites, and cockroaches, are another important source of indoor PM. These biological sources are known allergens that can impact indoor air quality and human health.

It is worth mentioning that outdoor PM can also infiltrate indoor spaces through open doors and windows, as well as small cracks and crevices in building structures. Therefore, a combination of indoor and outdoor sources contributes to the overall indoor PM levels.

Chemical reactions

Particulate matter (PM) is a mixture of solid particles and liquid droplets found in the air. It comes in various sizes and shapes and can be made up of hundreds of different chemicals. Some particles are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks, or fires, while others form in the atmosphere through chemical reactions.

Secondary particles, which make up most of the fine particle pollution in the United States, are formed through chemical and physical reactions with compounds such as sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3), and volatile organic compounds (VOCs). These reactions occur through a process called nucleation, where the gaseous molecules of ammonia condense to form either liquid or solid particles suspended in the atmosphere.

Sulfate aerosols, for example, are inorganic sulfur compounds like SO2− 4, HSO− 4, and H2SO− 4, which are produced when sulfur dioxide reacts with water vapour to form gaseous sulfuric acid and various salts. These salts then undergo hygroscopic growth and coagulation before shrinking through evaporation. Some sulfate aerosols are biogenic, produced via atmospheric chemical reactions with dimethyl sulfide from marine plankton, while others are geological, originating from volcanoes, wildfires, and other natural combustion events. However, in recent decades, anthropogenic sulfate aerosols produced by burning fossil fuels with high sulfur content, such as coal and certain less-refined fuels, have dominated.

Organic matter (OM) found in aerosols can also be either primary or secondary. Secondary organic matter derives from the oxidation of volatile organic compounds (VOCs), which can be biogenic or anthropogenic. These organic compounds influence the atmospheric radiation field by scattering and absorbing radiation. Some aerosols are believed to contain strongly light-absorbing materials, resulting in large positive radiative forcing.

Additionally, some secondary organic aerosols (SOAs) formed from the combustion products of internal combustion engines have been identified as hazardous to health. Particulate matter has been linked to cardiovascular and respiratory diseases, including asthma, bronchitis, emphysema, and even cancer. Smaller particles, such as PM2.5, can penetrate deeper into the respiratory and circulatory systems, causing damage to the lungs, heart, and brain.

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