Particulate Matter: Where It's Hiding And How To Avoid It

Particulate matter (PM) is a mixture of solid and liquid particles suspended in the air. It can be emitted directly from sources such as construction sites, unpaved roads, and smokestacks, or formed when pollutants from various sources react in the atmosphere. PM comes in different sizes, with particles smaller than 10 micrometres (PM10) able to enter our lungs and cause serious health issues. Even more concerning are particles smaller than 2.5 micrometres (PM2.5), known as fine particles, which can penetrate deeper into the lungs and have been linked to illnesses and deaths from heart and lung diseases. People can be exposed to PM both outdoors and indoors, with sources including car exhaust, smoke, road dust, pollen, factory emissions, and wildfires.

Outdoor air pollution

Particulate matter, a complex mixture of small solid particles and liquid droplets, is of particular concern due to its health risks. PM is categorized based on particle size, with PM10 referring to particles with a diameter of 10 micrometers or less, and PM2.5 referring to particles with a diameter of 2.5 micrometers or less. These particles are so small that they can be inhaled into the lungs, causing adverse health effects. PM2.5 is of greater concern as it can penetrate deeper into the lungs and is more likely to cause serious health problems. Exposure to PM2.5 has been linked to an increased risk of heart disease, asthma, low birth weight, and lung cancer.

To reduce exposure to outdoor air pollution, individuals can take several measures. Staying indoors when outdoor pollution levels are high, especially for sensitive groups such as children, the elderly, and people with heart or lung conditions, is recommended. When outdoors, wearing a well-fitting face mask, such as an N95 or KN95 mask, can help reduce the inhalation of particulate matter. Avoiding areas close to busy roads or industrial sites is also advisable.

On a larger scale, addressing outdoor air pollution requires concerted action by policymakers and industries. Implementing cleaner technologies, improving waste management practices, transitioning to cleaner modes of power generation and transportation, and promoting energy efficiency in buildings are all effective strategies to reduce outdoor air pollution.

Indoor air pollution

Sources of Indoor Air Pollution

There are numerous sources of indoor air pollution, some of which may be surprising:

• Tobacco smoke: Secondhand smoke exposure is estimated to cause about 7,300 lung cancer deaths in non-smoking adults in the United States annually, and tobacco smoke is a major source of indoor air pollution, containing over 7,000 chemicals.
• Cooking stoves: In developing countries, the burning of solid fuels for cooking and heating releases particulate matter and toxins, contributing to approximately 3.1 million premature deaths each year, primarily among women and children.
• Cleaning products: Many cleaning products contain toxic chemicals and volatile organic compounds (VOCs) that can be harmful when inhaled, causing respiratory infections, asthma, and even cancer.
• Mould: Mould grows in damp and humid environments and can cause respiratory infections, asthma, and allergies. It can be especially dangerous for those with weakened immune systems or pre-existing conditions.
• Pet dander: Dander from pets can be inhaled, triggering asthma attacks, hay fever, and other allergies.
• Dust: Indoor dust can contain heavy metals, allergens, and pollutants, negatively impacting health, especially for those with respiratory conditions.
• Building materials and furnishings: Some building materials and furnishings emit volatile organic compounds (VOCs) and other harmful chemicals, contributing to indoor air pollution.
• Candles and incense: Burning candles and incense can produce particulate matter and other pollutants, especially if not properly ventilated.
• Unvented heaters and fireplaces: The use of unvented space heaters, kerosene heaters, and wood-burning stoves or fireplaces can release pollutants and toxins, including carbon monoxide, into indoor spaces.

Reducing Indoor Air Pollution

It is important to take steps to reduce indoor air pollution to protect your health. Here are some ways to do so:

• Ensure proper ventilation: Open windows or doors, use exhaust fans, and maintain a well-functioning ventilation system to bring in fresh outdoor air and remove indoor pollutants.
• Choose low-emission products: Opt for green cleaning products made with natural ingredients, and select building materials and furnishings that emit lower levels of VOCs.
• Use air purifiers: High-efficiency particulate air (HEPA) filters can effectively remove pollutants like mould spores, pet dander, and tobacco smoke from indoor air.
• Keep indoor spaces clean and dry: Regular cleaning and maintaining a dry environment can help reduce the presence of mould, dust mites, and other allergens.
• Monitor air quality: Stay informed about outdoor air quality and keep windows closed when pollutant levels are high. Utilize air quality alerts and notifications to protect yourself and your family.
• No smoking indoors: Do not allow smoking inside your home, as secondhand smoke is a significant source of indoor air pollution.

Wildfires and other natural sources

Wildfires are a growing concern due to their frequency, intensity, and speed of spreading, which are anticipated to increase due to climate change. They can dramatically increase levels of toxic air pollutants, such as fine particles (PM2.5), which can be inhaled deep into the lungs and may even enter the bloodstream, impairing vital organs.

Wildfire smoke is a complex mixture of gaseous pollutants, hazardous air pollutants, water vapour, and particle pollution. Particle pollution, or particulate matter, refers to a mixture of solid and liquid droplets suspended in the air, with sizes ranging from coarse particles (PM10-2.5) to fine particles (PM2.5). Coarse particles are generally generated from mechanical operations, while fine particles are primarily emitted from wildfire smoke and account for approximately 90% of total particle mass.

The health impacts of wildfire smoke are not yet fully understood and may differ from those of PM2.5 from other sources due to differences in concentrations and chemical composition. However, studies have linked exposure to wildfire smoke with various health effects, particularly respiratory and cardiovascular issues.

The toxicity of wildfire particulate matter may be higher than that of ambient particulate matter from other sources. This is attributed to the presence of more polar organic compounds, which generate more free radicals and cause greater inflammation and oxidative stress in the lungs.

Wildfire-specific PM2.5 has been found to be up to 10 times more harmful to human health than PM2.5 from other sources. It can particularly affect vulnerable populations, such as children, the elderly, and those with pre-existing cardiovascular or respiratory diseases.

The understanding of the health impact of wildfire-related air pollution is challenging due to the episodic nature of wildfires, making it difficult to link wildfire-specific air pollution with health outcomes. Additionally, ambient monitors cannot distinguish the proportion of PM2.5 directly attributable to wildfires.

To address these challenges, studies have utilised chemical transport models, such as the GEOS-Chem model, to estimate daily wildfire-specific PM2.5 levels over large geographical areas and extended periods. These models improve the spatial and temporal resolution of exposure estimates.

In conclusion, wildfires and their resulting particulate matter pose a significant health risk, particularly to vulnerable populations. The toxicity of wildfire-specific particulate matter and its impact on respiratory health are areas of ongoing research, with a growing body of evidence suggesting that it may be more harmful than particulate matter from other sources.

Vehicle emissions

There are two types of vehicle emissions that contribute to PM: exhaust emissions and non-exhaust emissions. Exhaust emissions refer to the gases and particles released from the tailpipes of vehicles, while non-exhaust emissions include particles generated from tyre wear, brake wear, and road dust resuspension.

Diesel vehicles, particularly heavy-duty diesel vehicles, are a significant source of exhaust emissions. The combustion of gasoline and diesel fuel in vehicle engines emits large amounts of particles, including PM10 and PM2.5. PM10 particles are inhalable particles with diameters of 10 micrometers or smaller, while PM2.5 particles are fine inhalable particles with diameters of 2.5 micrometers or smaller. These fine particles can penetrate deeper into the lungs and pose a more significant risk to human health.

Non-exhaust emissions from vehicles also contribute significantly to PM levels. For example, tyre wear, brake wear, and road dust resuspension can generate PM10 and PM2.5 particles. The abrasion of brake pads and tyres can release particles containing heavy metals and other toxic substances into the air.

The impact of vehicle emissions on PM levels and human health is particularly notable in urban areas with dense and busy roads. In these areas, vehicles are a major source of air pollution, and the proximity to emission sources increases the exposure to particles.

To reduce exposure to vehicle emissions, individuals can take several measures. These include buying electric or hybrid vehicles, maintaining proper vehicle tuning and maintenance, and avoiding unnecessary idling, especially near schools and hospitals. Additionally, governments and policymakers can implement strategies such as encouraging the use of public transportation, promoting the adoption of electric vehicles, and enforcing stricter emission standards for older vehicles.

Industrial processes

Sources of Particulate Matter in Industries:

• Construction and Roadwork: Construction sites, roadwork, and maintenance activities can release PM into the air. This includes dust from excavation, drilling, concreting, moving construction materials, and roadwork operations.
• Industrial Emissions: Industrial facilities, such as power plants and factories, emit PM directly into the atmosphere. This includes emissions from smokestacks, boilers, cement kilns, and other industrial processes.
• Chemical Reactions: PM can also be formed indirectly through chemical reactions in the atmosphere. Certain gases, such as sulfur dioxide (SO2) and nitrogen oxides (NOx), emitted from industrial processes, can react and form secondary particles that contribute to PM pollution.

Control and Reduction of Particulate Matter:

• Electrostatic Precipitators (ESPs): ESPs use static electricity to remove soot and ash from exhaust gases. Charged electrodes attract and collect solid particles, which are then removed through mechanical vibration or by spraying the collecting electrodes with water.
• Wet Scrubbers: Wet scrubbers use liquid droplets to capture pollutants through impaction, diffusion, interception, or absorption. The liquid containing the captured pollutants is then collected for disposal.
• Venturi Scrubbers: This type of wet scrubber uses high-velocity exhaust gas and water streams to atomize the liquid into fine droplets, capturing small particulate matter. The solid pollutants are collected along with the liquid, while cleaned gas escapes.
• Cyclones: Cyclone separators create a spiraling vortex of dirty gas, forcing solid particles outward through centrifugal force. The particles are collected at the bottom of the chamber, while cleaned gas exits from the top.
• Fabric Filter Baghouses: These systems use woven cloth material to capture particulate matter as gas flows through it.

Health and Environmental Impacts:

• Respiratory and Cardiovascular Diseases: Exposure to PM, especially PM2.5 and PM10, has been linked to respiratory and cardiovascular health issues. Short-term exposures can lead to increased hospital admissions for heart or lung causes, asthma attacks, respiratory symptoms, and restricted activity days. Long-term exposure to PM2.5 has been associated with premature death, particularly in individuals with chronic heart or lung diseases.
• Reduced Visibility: PM, especially PM2.5, can reduce visibility by altering how light is absorbed and scattered in the atmosphere. This is particularly noticeable in national parks and wilderness areas.
• Climate Change: Some constituents of PM, such as black carbon, promote climate warming, while others, like nitrate and sulfate, have a cooling influence. Thus, ambient PM has both warming and cooling properties, impacting the climate.
• Ecosystem and Material Damage: PM deposition can adversely affect ecosystems, including plants, soil, and water quality. Additionally, PM deposition on surfaces can lead to soiling and material degradation.

Frequently asked questions