Suspended Particles: Primary Outdoor Air Pollutants?

Total Suspended Particles (TSP) are airborne particles with a diameter of up to 100 micrometres. They are generated by combustion and non-combustion processes, including windblown dust, industrial processes, and vehicle engines. While particles larger than 10 micrometres do not generally pose a risk to human health, smaller particles can penetrate the lower airways of humans and cause adverse health effects. TSP is therefore assessed against health-based criteria, with the Environmental Protection (Air) Policy 2019 (EPP Air) setting an objective of 90 micrograms per cubic metre for an annual exposure period.

This article will explore whether suspended particles are primary outdoor air pollutants, considering the sources and health effects of TSP, as well as the measures in place to protect public health.

Particles smaller than 2.5 micrometres can enter the lower airways of humans and cause adverse health effects

Particles smaller than 2.5 micrometres (known as PM2.5) are inhalable and can enter the lower airways of humans, causing adverse health effects. PM2.5 is a type of fine particulate matter, which is defined as having a diameter of 2.5 micrometres or less. These particles are so small that they can be inhaled deep into the lungs, depositing on the surface of the lung's deeper parts. This can lead to tissue damage, lung inflammation, and a range of adverse health impacts, particularly in infants, children, older adults, and those with pre-existing heart or lung diseases.

The sources of PM2.5 particles include emissions from the combustion of gasoline, oil, diesel fuel, or wood, as well as industrial sources, construction sites, wildfires, and vehicle emissions. These particles can also enter indoor spaces through doors, windows, and leakiness in building structures, leading to elevated indoor particle pollution concentrations. Cooking, smoking, and burning candles or incense can also contribute to indoor PM2.5 levels.

Short-term exposures to PM2.5 (up to 24 hours) have been linked to premature mortality, increased hospital admissions for heart or lung issues, acute and chronic bronchitis, asthma attacks, and respiratory symptoms. Long-term exposure to PM2.5 has been associated with an increased risk of mortality, particularly in individuals with chronic heart or lung diseases, and reduced lung function growth in children.

Research has also found links between PM2.5 exposure and other health issues, such as pregnancy and birth outcomes, including preterm birth, low birth weight, and fetal and infant mortality. Additionally, long-term exposure to particle pollution has been associated with an increased risk of death from cardiovascular disease. While everyone is at risk from the health impacts of outdoor particle pollution, those living near emission sources and vulnerable subpopulations, including people of colour, are at higher risk.

Overall, particles smaller than 2.5 micrometres can have significant adverse health effects on humans, particularly when inhaled over extended periods. These particles contribute to air pollution and can lead to a range of respiratory and cardiovascular issues, making the reduction of PM2.5 concentrations crucial for protecting public health.

Outdoor air pollution can enter homes and buildings, increasing indoor particle pollution concentrations

Outdoor air pollution can enter homes and buildings through open doors and windows, as well as through small cracks and crevices. This can increase indoor particle pollution concentrations, which is a concern as it can have adverse health effects on people, especially those with pre-existing heart or lung diseases, children, and older adults.

Outdoor particle pollution, or particulate matter (PM), is a mixture of solid particles and liquid droplets found in the air. Some particles are large enough to be seen, such as dust, dirt, soot, or smoke, while others are so small they can only be detected with an electron microscope. PM can be directly emitted from sources, such as construction sites, unpaved roads, fields, smokestacks, or fires, and is often a result of the combustion of gasoline, oil, diesel fuel, or wood. These are known as primary particles.

Secondary particles, on the other hand, form in the atmosphere through chemical reactions of gases, such as sulfur dioxide and nitrogen oxides, emitted from power plants, industries, and automobiles. These particles are smaller and can penetrate indoors more easily, especially on calm, stagnant days with little to no wind.

When outdoor particle pollution levels are high, it is recommended to keep windows closed and use portable air cleaners or air conditioners to reduce indoor particle levels. Upgrading to higher-efficiency filters in heating, ventilation, and air conditioning (HVAC) systems can also help mitigate the impact of outdoor air pollution on indoor air quality.

Additionally, indoor activities such as cooking, smoking, burning candles or incense, and even cleaning or vacuuming can generate particles and contribute to increased indoor particle pollution concentrations. Therefore, proper ventilation and regular cleaning are important to maintain good indoor air quality.

Sources of outdoor air pollution include vehicle exhaust, burning wood, gas, and other fuels

Particulate matter (PM) refers to a mixture of solid particles and liquid droplets found in the air. These particles can be large or dark enough to be seen, like dust, dirt, soot, or smoke, or so small that they can only be detected using an electron microscope. The size of these particles is measured in micrometers or microns, with particles under 10 micrometers (PM10) being inhalable and those under 2.5 micrometers (PM2.5) being classified as fine inhalable particles. These smaller particles can be inhaled deep into the lungs and are associated with a range of adverse health effects, including respiratory issues, asthma attacks, and increased hospital admissions for heart or lung causes.

Burning wood and other fuels, such as petrol, charcoal, natural gas, and kerosene, can release harmful pollutants into the air. Carbon monoxide (CO), a colourless, odourless, and toxic gas, is produced by the incomplete combustion of these carbonaceous fuels. CO interferes with the body's ability to absorb oxygen, causing symptoms like difficulty breathing, exhaustion, and dizziness, and can even be deadly at high levels. Additionally, the combustion of fossil fuels like coal and oil releases sulfur dioxide (SO2), a colourless gas with a sharp odour that can cause respiratory problems, including increased asthma symptoms.

Outdoor burning and wood smoke are significant contributors to air pollution, particularly in mountainous areas during winter when wood is burned for heat. Particle pollution levels can be exceptionally high during wintertime inversions, where a layer of cooler air is trapped near the ground, allowing smoke and pollution to accumulate. Gas and diesel-powered equipment, certain industries, and wildfires also add to air pollution. Wildfires, for instance, release smoke and ozone, which can travel many miles and impact air quality in surrounding areas.

To address outdoor air pollution, various strategies can be implemented. These include adopting clean technologies, improving waste management practices, promoting access to clean household energy solutions, prioritizing clean modes of power generation and transportation, improving energy efficiency in urban planning, and increasing the use of low-emissions fuels and renewable power sources. By implementing these measures, communities can work towards reducing the harmful impacts of air pollution on human health and the environment.

Outdoor air pollution can be caused by natural sources such as wildfires and human activities such as industrial processes

Outdoor air pollution is a serious issue that affects people in low-, middle-, and high-income countries alike. It is caused by a variety of natural and human-induced sources, including wildfires and industrial processes.

Natural sources of outdoor air pollution include wildfires and other forest fires. These fires release particulate matter (PM) into the atmosphere, which can include dust, dirt, soot, and smoke. PM with a diameter of 10 microns or less (PM10) can be inhaled into the lungs and cause adverse health effects, including respiratory issues and lung inflammation. Finer PM, with a diameter of 2.5 microns or less (PM2.5), can have even more severe health impacts, including premature mortality, increased hospital admissions for heart or lung-related issues, and adverse effects on children's lung development.

Human activities, such as industrial processes, also contribute significantly to outdoor air pollution. Industrial facilities, power generation, and the combustion of fuels in the transportation sector release various pollutants, including nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). NO2 is commonly released during fuel combustion in transportation and industrial activities. SO2, a colourless gas with a sharp odour, is produced from burning fossil fuels like coal and oil, as well as smelting mineral ores containing sulfur. Carbon monoxide, another harmful gas, is released during the incomplete combustion of carbonaceous fuels, such as wood, petrol, charcoal, natural gas, and kerosene.

In addition to wildfires and industrial processes, other human activities that contribute to outdoor air pollution include residential energy use for cooking and heating, agricultural and waste incineration practices, and vehicle emissions. The impact of these sources can vary based on spatial and temporal factors, with pollution concentrations often being higher near major sources, such as oil refineries, and in high-traffic areas.

Addressing outdoor air pollution requires concerted action from policymakers and individuals alike. Policy interventions, such as promoting clean technologies, improving waste management, and transitioning to cleaner transport and energy sources, can significantly reduce pollution levels. Individuals can also play a role by adopting cleaner household energy solutions for cooking, heating, and lighting, as well as staying informed about air quality through resources like the Air Quality Index (AQI).

Outdoor air pollution is higher near busy roads and where people burn wood for heat

Outdoor air pollution is a serious issue, with vulnerable groups like pregnant people, children, the elderly, and those with pre-existing health conditions being particularly at risk. It is well-established that outdoor air pollution is higher near busy roads and highways due to vehicle emissions. The type and age of vehicles, their operating conditions, fuel type, and engine lubricants all contribute to the emission of pollutants like ultrafine particles, black carbon, nitric oxide, NO2, carbon monoxide, and volatile organic compounds. People living closest to these busy roads are at a higher risk of developing asthma, respiratory infections, and other serious health issues.

Additionally, the combustion of fossil fuels, such as oil and gas extraction, negatively impacts air quality over large areas. However, those residing closer to these operations are more susceptible to the harmful effects, including exposure to VOCs, which can worsen asthma, damage the nervous system, and cause developmental issues.

The burning of wood for heat is another significant contributor to outdoor air pollution. Wood smoke contains toxic air pollutants, including particulate matter (PM), carbon monoxide, nitrogen oxides, and volatile organic compounds. These microscopic particles can enter the respiratory system, causing coughing, wheezing, asthma attacks, and even heart attacks. EPA estimates suggest that many wood stoves in the US are older, inefficient models that significantly contribute to pollution.

Residential areas that use wood-burning appliances, such as stoves and hydronic heaters, can experience substantially worsened outdoor air quality. This is especially true during the winter when wood smoke is a primary source of fine particle pollution, leading to poor air quality days across the United States. Children, teenagers, older adults, and those with pre-existing health conditions are at a heightened risk from wood smoke exposure.

To mitigate the impact of wood-burning on outdoor air pollution, some communities have implemented woodstove change-out programs to promote the use of cleaner and more efficient heating alternatives, especially among low-income families.

Frequently asked questions