Greta Jimenez
Particulate matter (PM) is a mixture of solid particles and liquid droplets found in the air. These particles vary in size, shape, and chemical composition and can be emitted directly from a source or formed in the atmosphere as a result of chemical reactions. PM is the most harmful form of air pollution as it can penetrate deep into the lungs and brain, causing serious health issues such as stroke, heart disease, lung disease, cancer, and preterm birth. PM2.5, fine particles with a diameter of 2.5 micrometers or less, are of particular concern as they contributed to millions of deaths worldwide in 2021. These particles can remain in the atmosphere for extended periods and travel long distances, affecting air quality far from their source. While regulations and measures aim to reduce PM emissions and protect public health, understanding the charge distribution of atmospheric aerosols is crucial for comprehending their environmental and health impacts.
| Characteristics | Values |
|---|---|
| Definition | Particulate Matter (PM) is a mixture of solid particles and liquid droplets found in the air. |
| Types | Suspended particulate matter, thoracic and respirable particles, coarse particles (PM10), fine particles (PM2.5), ultrafine particles, and soot. |
| Size | Coarse particles have a diameter of 10 micrometers or less, while fine particles have a diameter of 2.5 micrometers or less, and ultrafine particles have a diameter of 100 nm or less. |
| Health Effects | Particulate matter is the most harmful form of air pollution as it can penetrate the lungs and brain, causing stroke, heart disease, lung disease, cancer, and preterm birth. |
| Sources | Primary particles are emitted directly from sources such as construction sites, unpaved roads, smokestacks, fires, and indoor activities like cooking and smoking. Secondary particles form in the atmosphere from chemical reactions involving sulfur dioxides, nitrogen oxides, and organic compounds emitted from power plants, industries, and automobiles. |
| Measurement | Modern methods of measuring particulates include optical photodetectors, tapered element oscillating microbalances, and Aethalometers. Techniques like X-ray spectrometry can be used to determine atomic composition. |
| Regulation | The EPA regulates inhalable particles and has implemented rules to reduce emissions of pollutants that form PM, helping improve air quality. |
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What You'll Learn
Particulate matter (PM) basics
Particulate Matter (PM) refers to a mixture of solid particles and liquid droplets found in the air. Some particulate matter, such as dust, dirt, soot, or smoke, is large or dark enough to be seen with the naked eye. Other particulate matter is so small that it can only be detected using an electron microscope.
PM2.5 refers to fine inhalable particles with diameters that are generally 2.5 micrometers and smaller. The average human hair is about 70 micrometers in diameter, making it 30 times larger than the largest fine particle. These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. Some are emitted directly from sources such as construction sites, unpaved roads, fields, smokestacks, or fires. Most particles form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from human-triggered or natural fire activity.
PM10 refers to inhalable coarse particles with a diameter of 10 micrometers or less. These particles are also referred to as thoracic and respirable particles. Particles larger than 10 micrometers, such as sand and large dust, are not regulated by the EPA.
Fine particles are the main cause of reduced visibility (haze) in parts of the United States, including national parks and wilderness areas. They can also cause serious health problems as they can get deep into the lungs and even into the bloodstream. According to the EPA, particles less than 2.5 micrometers in diameter pose the greatest risk to health.
To protect yourself from harmful levels of particulate matter, you can refer to daily air quality alerts such as the Air Quality Index (AQI). The AQI translates air quality data into numbers and colours that help people understand when to take action to protect their health.
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Primary and secondary particles
Air pollution is a pressing issue that poses significant risks to human health and the environment. Among the various types of air pollutants, particulate matter (PM) stands out as a critical concern due to its ubiquitous presence and detrimental health impacts. PM refers to a mixture of solid particles and liquid droplets suspended in the air, ranging from large particles visible to the naked eye, such as dust and soot, to ultrafine particles that can only be detected using advanced microscopes. These particles come in different sizes, commonly categorized as PM10 and PM2.5, indicating their aerodynamic diameters.
Primary particles are those emitted directly from specific sources. They include pollutants like carbon monoxide, nitrogen oxide, sulfur oxide, and particulate matter itself. Sources of primary particles vary, encompassing construction sites, unpaved roads, smokestacks from industrial processes, and fires, including wildfires and combustion activities like motor vehicles and wood-burning. Primary particles contribute significantly to air pollution, particularly in urban and industrial areas.
Secondary particles, on the other hand, are formed through complex atmospheric reactions involving chemicals. They arise from the interaction of pollutants, such as sulfur dioxide and nitrogen oxides, emitted from power plants, industries, and automobiles. These reactions occur in the lower atmosphere, leading to the synthesis of secondary pollutants like ozone and secondary organic aerosols (haze). Secondary particles are more challenging to control because their formation is not fully understood, and they occur naturally in the environment, causing issues like photochemical smog.
The distinction between primary and secondary particles is essential in understanding the sources and behaviour of air pollutants. Primary particles are released directly into the atmosphere from identifiable sources, while secondary particles result from chemical transformations and reactions in the atmosphere. This distinction guides the development of strategies to mitigate air pollution. For example, reducing emissions of primary pollutants from vehicles and industries can directly impact the levels of secondary particles formed from those precursors.
Moreover, the size of particles plays a crucial role in their impact on air quality and human health. Finer particles, such as PM2.5, can penetrate deeper into the respiratory system, reaching the lungs and even the brain through bloodstreams. This characteristic makes them extremely harmful, contributing to various health issues, including stroke, heart disease, lung disease, cancer, and preterm birth. With no safe level of exposure, fine particles have been associated with millions of deaths worldwide, highlighting the urgency of addressing particle pollution, especially in densely populated urban areas.
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Health effects of PM2.5
PM2.5 refers to fine inhalable particles with diameters of 2.5 micrometres or smaller. These particles are a form of air pollution and can be made up of hundreds of different chemicals. They are so small that they can penetrate deeply into the lungs, irritating and corroding the alveolar wall and impairing lung function. This can lead to respiratory diseases such as chronic obstructive pulmonary disease (COPD) and lower-respiratory infections such as pneumonia. Long-term exposure to PM2.5 has also been linked to ischemic heart disease, lung cancer, stroke, type 2 diabetes, and adverse birth outcomes.
The health effects of PM2.5 are a growing concern, especially in countries with high death rates and large populations such as China and India, which together account for 58% of the total global mortality burden from PM2.5. In 2019, there were an estimated 1.42 million deaths attributable to PM2.5 in China and 980,000 in India. The burden of disease from PM2.5 is influenced by various factors, including changes in population size and age structure, with older people being more vulnerable to diseases linked to air pollution.
The impact of PM2.5 on human health has become a major research topic in recent years, particularly in China, where urban development and modernisation have worsened air pollution. Less than 1% of the 500 largest cities in China meet the air quality guidelines recommended by the World Health Organization. High levels of pollution can greatly limit visibility and have severe health consequences. China's government and its population have expressed mounting concern over the health effects of air pollution, and controlling it is a challenging long-term task.
PM2.5 particles are formed through complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are released from sources like construction sites, unpaved roads, fields, smokestacks, and fires. The pathogenicity of PM2.5 is determined by its size, composition, origin, solubility, and ability to produce reactive oxygen. PM2.5 particles have large surface areas relative to their volume, allowing them to carry various toxic substances. They can pass through the filtration of nose hair and reach the end of the respiratory tract, accumulating there and causing damage.
To protect public health, it is crucial to limit exposure to air pollution. Governments and authorities play a vital role in implementing effective measures to reduce emissions and improve air quality. Individuals can also take precautions, such as using air quality alerts like the Air Quality Index (AQI), to understand when to take action to protect their health.
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Sources of particle pollution
Particle pollution, or particulate matter (PM), is a mix of solid and liquid particles that vary in size and shape and are suspended in the air. These particles are often so small that they can only be detected using an electron microscope. PM is composed of a variety of substances, including acids, inorganic compounds, organic chemicals, soot, metals, soil, and dust particles. The sources of particle pollution can be both natural and human-induced. Here are some of the primary sources:
- Combustion and Industrial Activities: The combustion of fossil fuels, such as gasoline, diesel, and oil, is a major contributor to particle pollution. This includes emissions from vehicles, power plants, factories, and industrial processes. The burning of wood, especially in residential areas for heating and cooking, is another significant source, with domestic combustion being the largest single source of PM2.5 and PM10 in the United Kingdom.
- Agriculture and Wildfires: Agricultural practices, such as wildfires, brush burning, and waste burning, release particulate matter into the atmosphere. Wildfires, particularly in regions like the western United States, have been increasing due to climate change, contributing significantly to particle pollution.
- Construction and Unpaved Roads: Construction sites and unpaved roads generate dust and debris, which contribute to particle pollution. Fine particles from these sources can carry over long distances, affecting air quality in regions far from the original source.
- Natural Sources: Natural sources of particle pollution include wind-blown mineral dust, pollen, and fragments of bacteria. In areas with frequent natural fires, such as the Amazon during land-clearing fires, smaller aerosols dominate the particle pollution.
- Indoor Sources: Indoor sources of particle pollution include smoking tobacco, cooking, burning wood or incense, and using household cleaning products and air fresheners. These activities release particles and gaseous pollutants that contribute to indoor air pollution.
- Vehicular Emissions: Diesel- and gasoline-powered vehicles, including cars, trucks, and buses, emit particle pollutants. Diesel particles, in particular, have been associated with various health risks.
It is important to note that particle pollution is not limited to a single pollutant but is a complex mixture of many chemical species. The available evidence suggests that overall, particle pollution components are linked to adverse health effects, with fine particles being of greater concern due to their ability to penetrate deep into the respiratory system.
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Air quality standards
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, or "criteria pollutants", that are common in outdoor air, harmful to public health and the environment, and that come from numerous and diverse sources. These pollutants are regulated by the Clean Air Act, which was last amended in 1990. The EPA is required to periodically review these standards and the science behind them to determine whether changes are warranted.
The six criteria pollutants are:
- Particulate Matter (PM): A mixture of solid particles and liquid droplets found in the air. Some particles such as dust, dirt, soot, or smoke are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.
- PM2.5: Fine inhalable particles with diameters that are generally 2.5 micrometers and smaller. These particles are about 30 times smaller than the average human hair and can be made up of hundreds of different chemicals.
- PM10: Inhalable coarse particles with a diameter of 10 micrometers or less.
- Ultrafine particles: Particles with a diameter of 100 nm or less.
- Nitrogen Oxides: Pollutants emitted from complex reactions of chemicals.
- Sulfur Dioxide: A pollutant that contributes to the formation of PM2.5.
The NAAQS are designed to protect public health and welfare. The primary standards aim to protect public health, including sensitive populations such as asthmatics, children, and the elderly. The secondary standards aim to protect public welfare, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.
The EPA also establishes an Air Quality Index (AQI) for the five major air pollutants regulated by the Clean Air Act. The AQI is a yardstick that runs from 0 to 500, with higher values indicating greater levels of air pollution and health concerns. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. The AQI is a useful tool for the public to understand when to take action to protect their health.
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Frequently asked questions
PM stands for Particulate Matter, also known as Particle Pollution.
Particulate Matter is a mixture of solid particles and liquid droplets found in the air. These particles can be made up of hundreds of different chemicals, including inorganic ions, metallic compounds, elemental carbon, organic compounds, and compounds from the Earth's crust.
PM10 refers to inhalable coarse particles with a diameter of 10 micrometres or less. PM2.5 refers to fine particles with a diameter of 2.5 micrometres or less. PM2.5 is more harmful as it can penetrate deep into the lungs and brain, causing serious health issues such as stroke, heart disease, and cancer.
Particulate Matter can be emitted directly from sources such as construction sites, unpaved roads, fields, smokestacks, fires, and vehicles. These are known as primary particles. Particulate Matter can also form in the atmosphere through complex chemical reactions, creating secondary particles.
Charged particles can be collected using electrostatic plates, helping to clean the air. However, charged particles can also have environmental effects, influencing the evolution of charge distribution in the atmosphere.
