Smoke's Nature: Gaseous Air Pollutant?

Air pollution is a pressing issue that poses a significant threat to both human health and the environment. It refers to the release of harmful substances into the atmosphere, which can have detrimental effects on people, animals, and the planet. Smoke, a common byproduct of combustion, is a significant contributor to air pollution. But is smoke itself a gaseous air pollutant? This question delves into the complex nature of smoke and its impact on the air we breathe.

Smoke composition

Smoke is an aerosol, or mist, of solid particles and liquid droplets that are close to the ideal range of sizes for Mie scattering of visible light. The composition of smoke depends on the nature of the burning fuel and the conditions of combustion.

Fires with a high availability of oxygen burn at a high temperature and produce a small amount of smoke. The particles are mostly composed of ash or, with large temperature differences, of condensed aerosol water. High temperatures also lead to the production of nitrogen oxides. Sulfur content yields sulfur dioxide, or, in the case of incomplete combustion, hydrogen sulfide. Carbon and hydrogen are almost completely oxidized to carbon dioxide and water.

Fires burning with a lack of oxygen produce a significantly wider palette of compounds, many of which are toxic. Partial oxidation of carbon produces carbon monoxide, while nitrogen-containing materials can yield hydrogen cyanide, ammonia, and nitrogen oxides. The presence of sulfur can lead to the formation of gases like hydrogen sulfide, carbonyl sulfide, sulfur dioxide, carbon disulfide, and thiols. The latter tend to get adsorbed on surfaces and produce a lingering odor even long after the fire.

Pyrolysis of burning material, especially incomplete combustion or smoldering without adequate oxygen supply, also results in the production of a large amount of hydrocarbons, both aliphatic and aromatic. It also results in the emission of a range of smaller oxygenated volatile organic compounds which are formed as combustion by-products, as well as less volatile oxygenated organic species such as phenolics, furans, and furanones. Heterocyclic compounds may also be present. Heavier hydrocarbons may condense as tar; smoke with significant tar content is yellow to brown.

The combustion of solid fuels can result in the emission of many hundreds to thousands of lower-volatility organic compounds in the aerosol phase. The presence of metals in the fuel yields particles of metal oxides. Particles of inorganic salts may also be formed, e.g. ammonium sulfate, ammonium nitrate, or sodium chloride. Inorganic salts present on the surface of the soot particles may make them hydrophilic. Many organic compounds, typically aromatic hydrocarbons, may also be adsorbed on the surface of the solid particles. Metal oxides can be present when metal-containing fuels are burned, e.g. solid rocket fuels containing aluminium.

Smoke can be used for various purposes, including weather modification, cloud seeding, pest control, communication, defensive and offensive capabilities in the military, cooking, smoking, and rituals. In agriculture, smoke compositions are used to disperse insecticides and fungicides. In the military, smoke compositions are used as payloads of smoke bombs and smoke grenades, and for creating obscurant smoke.

Health effects

Smoke is a mixture of particles and gaseous air pollutants, including nitrogen oxides, carbon monoxide, and hydrocarbons, which can be toxic. It is a significant health concern, especially for those with pre-existing health conditions. The health effects of smoke inhalation range from minor to severe, and even healthy individuals can experience symptoms.

Smoke can irritate the eyes, nose, throat, and skin, causing coughing, phlegm, chest tightness, and shortness of breath. These symptoms are temporary and usually resolve within a couple of days after exposure stops. However, smoke exposure can also have more severe acute and chronic effects, especially for sensitive groups such as children, older adults, and people with cardiovascular or respiratory conditions.

The fine particles in smoke can penetrate deep into the respiratory tract, reaching the lungs. This can cause respiratory irritation, exacerbate asthma, and worsen medical conditions such as heart and lung disease. Prolonged exposure to fine particles has been linked to an increased risk of cardiovascular disease and mortality. Studies have also found a correlation between long-term exposure to air pollution and higher COVID-19 mortality rates.

Smoke from fires, including wildfires and the burning of trash, furniture, and wood, releases hazardous chemicals and pollutants into the air. The release of these particles and chemicals can have both immediate and long-term health consequences. Wildfire smoke, in particular, has been associated with eye and respiratory tract irritation, exacerbation of asthma and heart failure, and even premature death.

Additionally, smoke can affect the body's ability to remove foreign materials, such as viruses and bacteria, from the lungs. It can also cause changes in lung and heart function, with carbon monoxide reducing the body's oxygen supply and aggravating heart conditions. Prolonged exposure to smoke, especially in occupational settings, may have cumulative effects on lung function, as seen in studies of wildland firefighters.

Wildfires and smoke

Wildfires are a significant contributor to air pollution, and the smoke they produce can have detrimental effects on human health and the environment. Wildfire smoke is a complex mixture of gaseous and particulate pollutants, including hazardous substances that can have both short-term and long-term impacts on human health.

Smoke from wildfires contains a range of harmful substances, including carbon monoxide, nitrogen oxides, hydrocarbons, and particulate matter. These pollutants can have immediate and severe effects on people's health, particularly those with pre-existing respiratory or cardiovascular conditions. The fine particles in wildfire smoke, known as PM2.5, are of particular concern as they can penetrate deep into the lungs and even enter the bloodstream. This can lead to a range of health issues, including coughing, chest tightness, and increased risk of heart attack and stroke. Even short-term exposure to elevated levels of PM2.5 has been associated with adverse health outcomes.

The particulate matter in wildfire smoke can be classified into two main categories: coarse particles (PM10-2.5) and fine particles (PM2.5). Coarse particles are generally larger than 2.5 micrometres and smaller than or equal to 10 micrometres in diameter. While coarse particles are present in wildfire smoke, they are also commonly generated from mechanical operations such as construction and agriculture. On the other hand, fine particles are those with diameters of 2.5 micrometres or smaller, and they represent the main pollutant emitted from wildfire smoke, comprising approximately 90% of the total particle mass. These fine particles are of the greatest health concern due to their ability to penetrate deep into the respiratory system.

The health effects of wildfire smoke exposure can vary depending on several factors, including the length and level of exposure, individual health risks, and the presence of multiple pollutants. Certain sensitive groups, such as children, the elderly, and people with pre-existing health conditions, are more vulnerable to the harmful effects of wildfire smoke. It is crucial for individuals in wildfire-prone areas to take precautions and reduce their exposure to smoke to minimize potential health risks.

Additionally, the impact of wildfires and smoke extends beyond immediate health concerns. Wildfire smoke can linger in the atmosphere for extended periods, polluting the air with particulate matter and gaseous pollutants over vast distances. This can have long-term effects on the environment, contributing to climate change and further exacerbating the air quality issues associated with it. Climate change-fuelled droughts and dry conditions create a feedback loop, increasing the frequency and intensity of wildfires and, consequently, the release of pollutants into the atmosphere.

Indoor air pollution

Smoke is a gaseous air pollutant that can have detrimental effects on human health. It is primarily composed of particles, with other gaseous pollutants like nitrogen oxides, carbon monoxide, and hydrocarbons, which may be toxic. These gaseous pollutants are released during combustion, such as the burning of wood, natural gas, or tobacco.

One of the main concerns with indoor air pollution is the release of particulate matter and hazardous air pollutants (HAPs). These fine particles, often present in smoke, can be inhaled and cause respiratory and cardiovascular issues. They can enter the bloodstream, leading to an increased risk of heart attack and stroke, especially for individuals with pre-existing heart and lung conditions. Additionally, indoor air pollution can aggravate respiratory illnesses such as asthma, bronchitis, and emphysema.

Certain groups, such as children, the elderly, and those with existing health conditions, are more vulnerable to the effects of indoor air pollution. For instance, studies have shown that overweight or obese children with asthma may be more susceptible to indoor PM2.5 and NO2 exposure, experiencing symptoms like cough, wheeze, and chest tightness. Similarly, secondhand smoke exposure has been linked to adverse health effects in children, with a significant proportion of children in the United States exposed to it.

To mitigate indoor air pollution, it is essential to minimise the use of solid fuels and avoid burning wood, gas logs, or incense indoors. Regularly opening windows and doors to improve ventilation and investing in air cleaners with HEPA filters can also help reduce indoor particle pollutants. Additionally, specific measures such as installing carbon monoxide detectors and following local guidelines for fireplace burning can further enhance indoor air quality.

Mitigating air pollution

Smoke is a gaseous air pollutant that consists of particles and gaseous air pollutants, including nitrogen oxides, carbon monoxide, and hydrocarbons that may be toxic. Exposure to smoke can irritate the eyes, nose, throat, and skin, and can cause coughing, phlegm, chest tightness, and shortness of breath. Prolonged exposure to smoke has been linked to reduced lung function, increased risk of heart attack and stroke, and chronic respiratory diseases.

To mitigate the effects of air pollution from smoke, individuals can take several measures to protect themselves and their communities. Here are some strategies for mitigating air pollution:

Reducing Emissions and Improving Air Quality

• Slashing carbon emissions and reducing the use of toxic chemicals are crucial steps in improving outdoor air quality. This includes reducing emissions from vehicles, factories, power plants, and other sources that combust fossil fuels.
• Promoting the use of clean energy sources, such as solar, wind, and hydroelectric power, can help reduce the combustion of fossil fuels and decrease air pollution.
• Implementing regulations and policies, such as the Clean Air Act in the United States, can help control and reduce emissions of harmful air pollutants.

Protecting Indoor Air Quality

• Avoid adding particle pollutants to your home by burning wood, gas logs, candles, or incense. Limit the amount of ash brought inside and wipe off your shoes and pets' paws to reduce tracked-in pollutants.
• Consider investing in a high-quality air purifier for your home, specifically one with a high-efficiency (HEPA) mechanical filter or an electrostatic precipitator. Avoid air purifiers that generate ozone, as they can increase indoor pollution.
• When outdoor air quality improves, open windows and doors to allow for a clean exchange of air inside your home.
• Turn on fans to improve air circulation, but ensure they don't overheat and only run them when necessary to conserve energy.

Community-Level Mitigation

• Stay informed about public health and safety guidelines, especially during periods of high air pollution or wildfire smoke. Follow the recommendations of local health authorities and take precautions such as staying indoors or in locations with cleaner indoor air.
• If you live in a Smoke Control Area, adhere to the regulations regarding the types of fuels or appliances permitted for heating your home. These areas are designated to maintain good air quality and limit smoke pollution.
• Participate in community efforts to plant and protect trees. Trees act as natural air purifiers, absorbing air pollution and producing oxygen.

Personal Protection

• When exposed to smoke or air pollution, wear a particulate respirator mask, such as an N95 or P100 mask, to protect your lungs from particulate matter. However, masks do not provide protection against harmful gases.
• Stay hydrated, especially when exposed to polluted air, as it can help flush out toxins and keep your body functioning optimally.
• Pay attention to your health and the health of those around you. If you experience any symptoms or health concerns, contact your doctor. Sensitive populations, including people with heart and lung disease, are particularly vulnerable to the effects of air pollution.

Frequently asked questions