Air Pollution's Wildfire Risk: Understanding The Connection

Wildfires are a pressing global issue that has affected the lives of millions of people, animals, and the environment. They release harmful fine particulates known as PM2.5, which spread across large distances and negatively impact air quality. The particles are small enough to penetrate deep into the lungs and enter the bloodstream, causing serious health issues such as eye and respiratory tract irritation, aggravating asthma, triggering lung disease, and even leading to premature death. With climate change expected to increase the frequency and intensity of wildfires, it is crucial to understand the relationship between air pollution and wildfires. This includes examining how air pollution caused by wildfires affects human health and the environment, as well as exploring the role of air pollution in contributing to the ignition and spread of wildfires.

Wildfires release harmful fine particulates known as PM2.5

PM2.5 is released into the air during combustion-related activities, such as wildfires, and can be composed of various components, including acids (e.g. sulfuric acid), inorganic compounds (e.g. ammonium sulfate), organic chemicals, soot, metals, and soil or dust particles. The small size of these particles allows them to easily penetrate homes and buildings, increasing indoor particle concentrations. During wildfires, the concentration of PM2.5 in the air can increase significantly, becoming visible to the naked eye.

The health effects of exposure to wildfire-specific PM2.5 are not yet fully understood, but recent studies suggest that it may be more toxic than PM2.5 from other sources. For example, a study in Southern California found that a 10 μg m−3 increase in wildfire-specific PM2.5 was associated with a 10% increase in respiratory hospitalizations, compared to a 1.3% increase associated with non-wildfire PM2.5. Another study in the Western US found a 7.2% increase in the risk of respiratory admissions during smoke wave days with high wildfire-specific PM2.5.

The toxicity of wildfire-specific PM2.5 may be due to its chemical composition and the different stages of biomass combustion. Animal toxicological studies have shown that particulate matter from wildfires can cause more inflammation, oxidative stress, and respiratory infection than PM2.5 from other sources. Additionally, the types of trees and the temperature at which combustion occurs may also play a role in the differential toxicity of wildfire-specific PM2.5.

As climate change is expected to increase the frequency and intensity of wildfires, it is crucial to address the health impacts of wildfire-specific PM2.5 and develop intervention-focused policies to protect public health.

Wildfire smoke contains hazardous air pollutants

Wildfire smoke is a complex mixture of gaseous pollutants, hazardous air pollutants (HAPs), water vapour, and particle pollution. The particle pollution from wildfire smoke is the principal public health threat. These particles are a mixture of solid and liquid droplets suspended in the air. They come in many sizes and shapes, and some are so small that they are only visible using an electron microscope. These particles can be made up of different components, including acids, inorganic compounds, organic chemicals, soot, metals, soil or dust particles, and biological materials.

The particles in wildfire smoke that are of greatest concern are those that are 10 micrometers (µm) in diameter or smaller. These particles can pass through the nose and throat and enter the lungs, with the smallest particles ( < 2.5 µm) possibly even entering the bloodstream. Once inhaled, these particles can affect the lungs and heart and cause serious health effects. These health effects include an increased risk of both cardiovascular and respiratory issues, as well as eye and respiratory tract irritation, and the worsening of heart and lung disease, including asthma.

The hazardous air pollutants found in wildfire smoke include polycyclic aromatic hydrocarbons (PAHs), particulate matter, nitrogen dioxide, ozone, and lead. The particulate matter in wildfire smoke, known as PM2.5, is of particular concern as it can travel deep into the lungs and may enter the bloodstream. It has been linked to a range of negative health outcomes, including asthma, lung disease, heart attacks, and premature death. The concentration of PM2.5 in Siberia hit a record high during the 2021 wildfires, and in several North American cases, the particles reached excessive levels hundreds of kilometres from the source of the fires.

The health effects of wildfire smoke exposure are well documented in scientific literature, with a growing body of evidence linking it to various negative outcomes. These effects are particularly pronounced in individuals with cardiovascular or respiratory disease, older adults, children under 18, pregnant women, outdoor workers, and those of lower socioeconomic status. It is important for these sensitive groups to limit outdoor activities, especially when the Air Quality Index (AQI) reaches levels considered unhealthy. Even healthy individuals may experience symptoms after exposure to wildfire smoke.

Wildfire smoke can affect people and animals across large areas

Wildfire smoke can have detrimental effects on the health of both people and animals across large areas. The smoke is made up of gaseous pollutants, hazardous air pollutants, water vapour, and particle pollution. It is the particle pollution that is the main concern for human health. These particles are a mixture of solid and liquid droplets suspended in the air, and they can be made up of acids, inorganic compounds, organic chemicals, soot, metals, soil or dust particles, and biological materials.

The particles are so small that they can easily penetrate homes and buildings, increasing indoor particle concentrations. These fine particles (known as PM2.5) are the main pollutant emitted from wildfire smoke and comprise around 90% of the total particle mass. They can travel deep into the lungs and may even enter the bloodstream. This can cause serious health effects, particularly for those with existing respiratory or cardiovascular conditions, older adults, children, pregnant women, outdoor workers, and those of lower socioeconomic status.

The health effects of wildfire smoke exposure include an increased risk of cardiovascular and respiratory issues, as well as potential damage to neural connections in the brain. It can also affect mental health, with links to impaired judgment, poorer school performance, and higher levels of crime.

Wildfire smoke also has significant impacts on wildlife. Birds, for example, have highly efficient respiratory systems, which make them more sensitive to air pollution. Whales and dolphins are also vulnerable to smoke due to the large amount of air they exchange with each breath and their lack of protective structures like sinuses and mucus.

Smoke can cause symptoms such as labored or rapid breathing, wheezing, panting, coughing, and foaming of the nostrils in animals. It can trigger long-lasting immune responses, harm respiratory and cardiovascular health, and suppress the immune system. Studies have shown that exposure to wildfire smoke can have long-term effects on the respiratory and immune systems of infant rhesus macaques and captive bottlenose dolphins.

Overall, wildfire smoke can have far-reaching consequences for both human and animal health, affecting large areas due to the spread of smoke across the globe.

Wildfire smoke can cause serious health issues

Wildfire smoke is a complex mixture of gaseous pollutants, hazardous air pollutants (HAPs), water vapour, and particle pollution. Particle pollution is the main component of wildfire smoke and the principal public health threat. These particles are so small that they can enter and lodge deep in the lungs and may even enter the bloodstream. They can also affect the body's ability to remove inhaled foreign materials, such as viruses and bacteria, from the lungs.

The health effects of particle pollution exposure can range from relatively minor issues, such as eye and respiratory tract irritation, to more serious health effects, including exacerbation of asthma and heart failure, and premature death. Fine particles are respiratory irritants, and exposure to high concentrations can cause persistent coughing, phlegm, wheezing, and difficulty breathing. Even in healthy individuals, exposure to fine particles can lead to transient reductions in lung function and pulmonary inflammation.

Studies have shown that children who breathed smoky air during wildfires experienced increased coughing, wheezing, bronchitis, colds, and hospital visits for respiratory causes, especially asthma. Particle pollution triggers asthma attacks, heart attacks, and strokes and can be fatal.

Wildfire smoke also contains carbon monoxide, a colourless and odourless gas most common during the smouldering stages of a fire. Inhaling carbon monoxide reduces oxygen delivery to the body's organs and tissues and can lead to headaches, nausea, dizziness, and even death in high concentrations.

The potential health implications of wildfire smoke are a significant concern, and with climate change expected to spark a surge in wildfires, the focus on mitigating these health risks becomes even more crucial.

Wildfire smoke can worsen urban air pollution

Wildfire smoke is a complex mixture of gaseous pollutants, hazardous air pollutants, water vapour, and particle pollution. Particle pollution is the main component of wildfire smoke and the principal public health threat. These particles are a mixture of solid and liquid droplets suspended in the air. They can be made up of different components, including acids, inorganic compounds, organic chemicals, soot, metals, soil or dust particles, and biological materials.

The particles are so small that they can easily penetrate homes and buildings, increasing indoor particle concentrations. During a wildfire, concentrations of particles can increase substantially in the air to the point that particle pollution is visible to the naked eye. Fine, inhalable particulate matter (PM2.5) is the air pollutant of greatest concern from wildfire smoke because it can travel deep into the lungs and may even enter the bloodstream.

Individuals at greater risk of health effects from wildfire smoke include those with cardiovascular or respiratory disease, older adults, children, pregnant women, outdoor workers, and those of lower socioeconomic status. These fine particles have been linked to inflammation, which may cause damage to neural connections in the brain. They can also trigger respiratory conditions such as asthma and worsen heart and lung disease.

Wildfire smoke has been found to be particularly harmful to certain immune cells in the lungs, with a toxicity four times greater than particulates from other types of pollution. As smoke ages, its toxicity increases. This was demonstrated in a study that found the toxicity of smoke doubled in the hours after it was first emitted, reaching a peak of four times its initial toxicity.

The impact of wildfire smoke on air quality is significant enough to offset recent public health gains achieved through pollution reductions in cars and factories. For example, in 2023, smoke from Canadian wildfires caused a significant decline in air quality in New York and other areas. Furthermore, a 2022 study found that a quarter of the US's PM2.5 pollution was caused by wildfire smoke, with western regions showing that up to half was due to smoke.

Frequently asked questions