Sources Of Particle Pollution: What's In The Air?

Particle pollution, also known as particulate matter, is a general term for a mixture of solid and liquid droplets suspended in the air. These particles come in many sizes and shapes and can be made up of a number of different components, including acids, inorganic compounds, metals, and biological materials. While particle pollution can occur both indoors and outdoors, what are the primary sources of particle air pollution, particularly outdoors?

Particles from combustion and industry

Combustion sources of primary particles include the burning of carbon-based fuels, such as wood, residential fireplaces, wood stoves, wildfires, agricultural fires, and prescribed fires. The combustion of fossil fuels in factories, power plants, diesel- and gasoline-powered motor vehicles, and equipment also emits a large number of particles. For instance, motor vehicle exhaust contributes about 55% of all carbon monoxide (CO) emissions nationwide, with higher levels of CO occurring in areas with heavy traffic congestion. In cities, up to 95% of CO emissions may come from motor vehicles. Other sources of CO emissions include industrial processes, residential wood burning, and natural sources such as forest fires.

Industrial sources of primary particles include power plants, industrial sites, and automobiles. Particles emitted from these sources include sulfur dioxide and nitrogen oxides, which react with other gases in the atmosphere to form secondary particles. Secondary particles make up most of the fine particle pollution in the United States.

In addition to outdoor sources, particles from combustion and industry can also originate from indoor sources. Indoor activities such as smoking tobacco, cooking, and burning wood, candles, or incense can generate particles. Certain household products, such as cleaning agents and air fresheners, can also release gaseous pollutants that react to form particles indoors.

The health impacts of particle pollution are significant, particularly for vulnerable subpopulations such as people of color and those living near emission sources. Exposure to fine particles, especially those with a diameter of 2.5 microns or less (PM2.5), has been associated with premature mortality, increased hospital admissions for heart or lung causes, acute and chronic bronchitis, asthma attacks, and respiratory symptoms. The World Health Organization's Global Burden of Disease Project has identified PM2.5 as the air pollutant with the greatest proportion of adverse health effects, both in the United States and worldwide.

Natural sources and human activities

Particle pollution, or particulate matter (PM), is a general term for a mixture of solid particles and liquid droplets found in the air. These particles come in many sizes and shapes and can be made up of a number of different components, including acids (such as sulfuric acid), inorganic compounds, organic chemicals, soot, metals, soil or dust particles, and biological materials (such as pollen and mould spores).

Natural Sources

Natural sources of particle pollution include wildfires, sea salt, dust (such as airborne soil), and pollen, but they also include material from volcanic eruptions and particles formed from natural gaseous precursors (e.g. sulphates). Wildfires are growing, particularly in the western United States, due to climate change.

Human Activities

Human activities are also a major source of particle pollution. The combustion of carbon-based fuels, such as wood, diesel, gasoline, and other fossil fuels, generates most of the fine particles in our atmosphere. This includes burning wood in residential fireplaces and wood stoves, as well as agricultural and prescribed fires. The emission of gases from power plants, industrial sites, vehicles, and other sources can also lead to the formation of particles in the atmosphere through chemical reactions.

In addition, human activities such as construction, demolition, metal recycling, smoking, cooking, dusting, and vacuuming can contribute to particle pollution, particularly in indoor settings. Particles produced by these activities can vary in size, with combustion typically resulting in fine particles, and particles of crustal (earth) and biological origin being more likely to be coarse.

Overall, human activities and natural sources both play a significant role in emitting or generating particles that contribute to air pollution.

Indoor sources and activities

Indoor air pollution is a serious threat to human health, causing millions of deaths each year. The air we breathe indoors always contains particle pollution, which can be influenced by outdoor air pollution. Outdoor air pollution can enter indoor spaces through doors, windows, and "leakiness" in building structures. In some cases, indoor levels of particle pollution can exceed outdoor levels.

Indoor sources of particle pollution include building materials, household cleaning products, and biological pollutants such as pollen, mould spores, dust mites, cockroaches, and pet dander. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the area. High temperatures and humidity levels can also increase concentrations of some pollutants.

Indoor activities that generate particle pollution include cooking, fossil fuel combustion activities, smoking tobacco, machine operation, and residential hobbies. Cooking and cigarette smoking are the largest sources of indoor air particle pollution. Smoking is a major source of fine particle pollution, with estimated increases in homes with smokers ranging from 25 to 45 µg/m3, and higher concentrations in winter than in summer.

Particles produced by combustion are more likely to be fine particles, which are more dangerous to human health. Burning wood, gasoline, oil, diesel fuel, or fossil fuels generates much of the fine particle pollution found outdoors, as well as a significant proportion of coarse particle pollution. These particles can enter indoor spaces and contribute to indoor air pollution.

Particles from vehicles

Particle air pollution, also known as particulate matter (PM) or soot, is a mix of solid and liquid droplets suspended in the air. These particles can be emitted directly from sources such as construction sites, unpaved roads, smokestacks, or fires, or they can form in the atmosphere through chemical reactions.

Vehicles are a significant contributor to particle air pollution, particularly in urban areas. Cars, trucks, and buses produce a significant portion of the hydrocarbons and nitrogen oxides present in the air. While individual car emissions are generally small, the large number of vehicles on the road and traffic congestion in urban areas result in substantial air pollution.

The combustion of carbon-based fuels, such as gasoline and diesel, in vehicles generates particulate matter, including soot, and releases volatile organic compounds (VOCs), nitrogen oxides (NOx), and other pollutants. These emissions contribute to the formation of ground-level ozone, a key component of smog, and can have serious health impacts. Fine particles from vehicle emissions can penetrate deep into the lungs, leading to respiratory and cardiovascular issues, and increased risk of cancer.

Older vehicles tend to emit more pollution due to the deterioration of emission control technology and the increasing stringency of emission standards over time. However, newer vehicles may still contribute to particle pollution, especially during fuel production, refining, distribution, and the manufacturing and disposal or recycling of the vehicle.

To mitigate the impact of vehicle emissions, consumers can choose cleaner and more fuel-efficient vehicles. Additionally, carpooling and using high-efficiency filters for passenger cabin air can help reduce exposure to pollutants while driving.

Health effects of particle pollution

Particle pollution, also known as particulate matter (PM) or soot, is a mix of solid and liquid droplets suspended in the air. These particles vary in size and shape and can be composed of various substances, including acids, inorganic compounds, metals, soil, and biological materials. While particle pollution is often associated with haze, smoke, and dust, it can also be present in seemingly clean air.

Particle pollution, especially fine particles (PM2.5), has significant adverse effects on human health. PM2.5 particles are so minuscule that they can penetrate deep into the respiratory tract, reaching the lungs. This can lead to short-term health issues such as eye, nose, throat, and lung irritation, coughing, sneezing, a runny nose, and shortness of breath. Those with pre-existing heart or lung conditions, infants, children, older adults, and people of colour are at a heightened risk of experiencing these adverse effects.

Moreover, particle pollution exacerbates existing medical conditions like heart disease, asthma, and respiratory symptoms, increasing the likelihood of hospitalisations, emergency room visits, and even mortality. Long-term exposure to fine particles has been linked to increased mortality from cardiovascular disease, respiratory disease, lung cancer, and chronic bronchitis. It can also result in reduced lung function and low birth weight.

The size of the particles plays a crucial role in their potential to cause harm. Smaller particles, less than 10 micrometres in diameter (PM10), are more concerning as they can infiltrate the lungs and potentially enter the bloodstream. Coarser particles, on the other hand, are more efficiently expelled from the body through coughing or sneezing.

Particle pollution not only affects human health but also impacts ecosystems, including plants, soil, and water. The deposition of particulate matter on surfaces can lead to soiling and contamination. Certain particulate components, such as metal and organic compounds, can alter plant growth and yield.

To safeguard public health, organisations like the Environmental Protection Agency (EPA) have established National Ambient Air Quality Standards for PM2.5. These standards set limits on the allowable concentration of particulate matter in the air to minimise the adverse health effects on the population.

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