Gaseous Air Pollutants: Understanding Harmful Invisible Threats

Gaseous air pollutants are uncondensed or volatile gases, usually comprised of chemical compounds, that are discharged into the Earth's atmosphere. They are one of the major causes of air pollution, which is defined as the release of various gases, finely divided solids, or finely dispersed liquid aerosols into the atmosphere at rates that exceed the natural capacity of the environment to dissipate and dilute or absorb them. Gaseous air pollutants are primarily released into the air through the burning of fossil fuels, such as fuel oil, gasoline, and natural gas, and they can have detrimental effects on both human health and the planet.

Characteristics and Values of Gaseous Air Pollutants

Nitrogen Dioxide (NO2) is a reddish-brown gas that can cause respiratory distress and lung disease

Gaseous air pollutants are gases that are released into the atmosphere at rates that exceed the natural capacity of the environment to dissipate and dilute or absorb them. They are one of the major contributors to air pollution, which is now the world's fourth-largest risk factor for early death.

Nitrogen Dioxide (NO2) is a reddish-brown gas and is one of the six widespread gaseous air pollutants. It is composed of nitrogen and oxygen and is a member of a group of highly reactive gases known as nitrogen oxides or NOx. NO2 is formed when fossil fuels such as coal, oil, methane gas (natural gas), or diesel are burned at high temperatures. The primary sources of NO2 emissions are cars, trucks, and buses, followed by power plants, industrial processes, and coal-fired power plants.

NO2 is harmful to both human health and the environment. It can irritate the airways in the human respiratory system, aggravate respiratory diseases, and potentially cause asthma in children and adults. Scientific evidence suggests that elevated levels of NO2 exposure during childhood can lead to smaller lungs at maturity. In addition, NO2 can also cause visible injury to vegetation, including trees, forests, and crops.

To address the harmful effects of NO2, the U.S. Environmental Protection Agency (EPA) has established the Clean Air Act to regulate and reduce nitrogen dioxide emissions. As a result, power plants, industrial sites, and on-road vehicles have become cleaner, improving air quality nationwide. However, it is important to note that many people still breathe unhealthy levels of nitrogen dioxide, particularly those living near emission sources or in large urban regions.

Individuals can take steps to protect themselves, such as advocating for the cleanup of air pollution and reducing their exposure to unhealthy levels of air pollutants.

Sulphur Dioxide (SO2) is a toxic gas released during the combustion of sulphur-containing ores and fossil fuels

Gaseous air pollutants are gases that are released into the atmosphere at rates that exceed the natural capacity of the environment to disperse or absorb them. They are one of the major causes of air pollution, which is the fourth-largest risk factor for early death worldwide. Sulphur dioxide (SO2) is one such gaseous air pollutant. It is a colourless gas with a pungent smell, often described as the odour of burnt matches.

SO2 is a toxic gas that is released during the combustion of sulphur-containing ores and fossil fuels. It is also produced during the industrial processing of sulphur-containing ores and industrial energy production. The largest sources of SO2 emissions are fossil fuel combustion at power plants and other industrial facilities. The burning of fossil fuels, especially coal, at these industrial facilities, is the primary source of SO2.

SO2 is harmful to both human health and the environment. Short-term exposure to SO2 can irritate the human respiratory system and make breathing difficult. People with asthma, particularly children, are more vulnerable to these effects. SO2 can also combine with particles and moisture in the air, creating an even greater health risk. Furthermore, SO2 contributes to the formation of acid rain by transforming into sulfuric acid in the atmosphere.

In plants, SO2 enters through stomata and affects the levels of various secondary metabolites. It can also alter the levels of specific PSMs and reduce the content of certain compounds in plants. While low levels of SO2 are beneficial for plant growth, increased air pollution by SO2 is a significant concern for plant growth and overall ecosystem health.

To reduce SO2 emissions, individuals can limit their electricity usage and use more efficient electric devices. Additionally, governments and industries have implemented various methods to control and reduce SO2 emissions, such as "scrubbing" gas leaving power plants or removing sulfur from fuel before combustion.

Hydrogen Sulfide (H2S) is a gaseous air pollutant present at high levels in various regions

Gaseous air pollutants are harmful chemicals and gases released into the atmosphere at rates that exceed the environment's capacity to absorb or dilute them. These pollutants can have detrimental effects on human health and the planet. While most gaseous air pollutants are invisible, nitrogen dioxide, a common gaseous air pollutant, is identifiable by its distinct brown colour.

One such gaseous air pollutant is Hydrogen Sulfide (H2S). H2S is a toxic gas that can be found at high levels in various regions of the atmosphere. It is often associated with industrial activities, such as the processing of sulfur-containing ores and industrial energy production. H2S has been linked to adverse effects on plant cell physiology and ecosystems.

A study conducted in Reykjavik, Iceland, between 2003 and 2009, found a correlation between ambient H2S air pollution and increased mortality rates. The results suggested that exposure to H2S may contribute to premature deaths, although further research is needed to confirm this relationship.

The presence of H2S in the atmosphere can also impact plant life. While sulfur is an essential nutrient for plant growth, high levels of atmospheric H2S can be detrimental. H2S interacts with atmospheric water vapour to form sulfurous and sulfuric acid, which reach the Earth's surface through acid rain, affecting ecosystems and plant health.

Overall, Hydrogen Sulfide (H2S) is a gaseous air pollutant of significant concern due to its potential impacts on human health and the environment. Its presence in high levels in various regions underscores the importance of monitoring and mitigating its release into the atmosphere.

Ozone (O3) is a key component of smog, which irritates the eyes and throat and damages the lungs

Ozone (O3) is a gas molecule composed of three oxygen atoms. It exists in two layers of the atmosphere: the stratosphere (upper layer) and the troposphere (ground level up to 10km).

In the stratosphere, ozone is beneficial as it protects life on Earth from the sun's ultraviolet radiation. However, ozone in the troposphere is a powerful greenhouse gas and air pollutant that harms human health and ecosystems. It is a major component of smog, which irritates the eyes and throat and damages the lungs.

Tropospheric ozone is formed by the interaction of sunlight with volatile organic compounds (VOCs) and nitrogen oxides (NOx) emitted largely by human activities. These precursor pollutants come from sources such as cars, vehicles, fossil fuel power plants, oil refineries, and other industries.

The health risks of ozone exposure are greater when ozone levels are higher, and when individuals have pre-existing medical conditions, such as lung diseases like asthma, or metabolic disorders like obesity. Studies have also shown that women may face higher respiratory health risks from ozone exposure. The impact of ozone pollution is not limited to humans; it also affects sensitive vegetation and ecosystems, including forests, parks, and agricultural crops.

Ozone pollution, also known as smog, is dangerous and widespread. Strategies to prevent the formation of tropospheric ozone focus on reducing methane emissions and cutting levels of atmospheric pollution from vehicles, power plants, and other sources.

Gaseous air pollutants can induce visible injury in sensitive forest species and affect tree growth

Gaseous air pollutants are harmful chemicals and gases released into the atmosphere by the burning of fossil fuels. These include sulfur dioxide (SO2), hydrogen sulfide (H2S), nitrogen oxides (NO and NO2), carbon monoxide (CO), and ozone (O3). While most gaseous air pollutants are invisible, nitrogen dioxide has a distinct brown colour.

Gaseous air pollutants can have a significant impact on forest ecosystems. They can induce visible injury in sensitive forest species and affect tree growth, health, and species composition. Lichen and soil fungi are particularly vulnerable to gaseous air pollution. In a scientific study of over one million U.S. trees of 71 different species, nitrogen and sulfur deposition significantly affected most of them, decreasing their growth and chance of survival. This leads to a decline in the number and size of trees in a forest.

Trees play a crucial role in absorbing gaseous molecules in the air through tiny pores on their leaf surfaces called stomata. However, ground-level ozone has been found to significantly reduce tree growth, injure foliage, and make trees more susceptible to insect and disease attacks. Similarly, high levels of SO2 in the atmosphere, primarily from industrial activities, are a major concern for plant growth. SO2 can enter plants through stomata and alter the levels of secondary metabolites, affecting the biosynthesis of important amino acids.

The impact of gaseous air pollutants on forest ecosystems can be assessed through various methods, with passive (diffusive) samplers being widely used due to their simplicity and cost-effectiveness. By understanding the critical loads of sulfur and nitrogen and identifying vulnerable species, park managers can prioritise remediation efforts in sensitive park ecosystems.

Frequently asked questions