Natural Air Pollutants: 5 Sources You Should Know About

Air pollution is the presence of harmful substances in the air, which can be gases, small particles, or chemicals. While most air pollution is caused by human activity, natural sources of air pollution include wildfires, dust storms, and volcanic eruptions. Wildfires generate high levels of particle pollution, carbon monoxide, and nitrogen oxides. Volcanoes release ammonia and sulfur dioxide during eruptions, which can form secondary particle pollution when combined with other pollutants in the atmosphere. Dust storms, such as those originating in the Sahara, Gobi, and Taklamakan deserts, are responsible for particle pollution due to the size of the grains spread. Vegetation, such as black gum, poplar, oak, and willow, emit volatile organic compounds (VOCs) on warmer days, which react with human pollution sources to produce a seasonal haze of secondary pollutants. While natural sources of air pollution do not usually create ongoing problems, they can sometimes be significant, and the location and time of year can determine which sources are most important.

Volcanic eruptions

Volcanoes emit various gases and particles during eruptions, including carbon dioxide, sulphur dioxide, and volcanic ash. Carbon dioxide is a lightweight volatile gas that is easily expelled and dispersed during volcanic eruptions. While it is lighter than other expelled gases, carbon dioxide is heavier than air, which causes it to remain close to the Earth's surface. High concentrations of this gas can have detrimental effects on the biosphere and can cause unconsciousness and death in both humans and animals if inhaled in concentrations above 30%.

Sulphur dioxide is another significant pollutant released by volcanic eruptions. In the case of Mount St. Helens' eruption in 1980, up to 3750 tons per day of sulphur dioxide was released into the atmosphere. The eruption also produced a substantial ash cloud that travelled across the United States in three days and reached a global scale in 15 days. Sulphuric acid rain, caused by volcanic emissions of sulphur dioxide, can have persistent health impacts on humans and other terrestrial organisms. The World Health Organization recommends a maximum exposure of 0.5 ppm of sulphuric acid over 24 hours, with higher concentrations causing immediate irritation to the nose, throat, eyes, and skin.

Forest fires

Wildfire smoke is a significant contributor to air pollution and can impact the climate by releasing large quantities of carbon dioxide and other greenhouse gases into the atmosphere. The climate crisis, driven by human activities such as burning fossil fuels and industrial processes, increases the likelihood of wildfires by creating warmer temperatures and drier conditions. This, in turn, prolongs the fire season, making wildfires more frequent and intense.

The impact of wildfires is not limited to the immediate surroundings but can have far-reaching consequences. The smoke and pollutants released can increase background pollution levels for years, even in areas distant from the original source. Additionally, the disruption caused by wildfires can affect transportation, communications, water supply, and power and gas services.

To address the challenges posed by wildfires, policymakers have proposed interventions such as the 'Fire Ready Formula', which allocates two-thirds of spending to planning, prevention, preparedness, and recovery, with one-third dedicated to response. The 'REDD+' framework, established under the Paris Agreement, also aims to protect forests and tackle climate change. However, the complex interplay between wildfires, climate change, and air pollution requires a comprehensive approach that addresses the root causes and acknowledges the interconnectedness of these issues.

Livestock

In addition to methane, livestock farming also produces other hazardous air emissions, such as ammonia. Animal waste is a significant contributor to ammonia emissions, accounting for 50-85% of ammonia emissions in the US, according to EPA estimates. However, despite the significant impact of livestock farming on air quality, farmers and ranchers are currently exempt from reporting air emissions to federal agencies in the US, due to the Fair Agricultural Reporting Method (FARM) Act. This makes it challenging to accurately assess the full extent of air pollution caused by the livestock industry.

The impact of the livestock industry on air quality is not limited to methane and ammonia emissions. A study published in the Proceedings of the National Academy of Sciences found that raising livestock causes poor air quality that leads to about 16,000 deaths per year in the United States. This figure is comparable to the number of deaths caused by other sources of air pollution, such as transportation and electricity generation. The study also revealed that 80% of the 16,000 deaths were linked to animal-based foods, with beef production alone corresponding to 4,000 air pollution-related deaths annually. When pork and dairy production were included, the number rose to 9,100 deaths per year.

The issue of air pollution from livestock farming is not confined to the United States. For example, in the United Kingdom, a study found that emissions from agriculture, including livestock and the crops they require, were associated with increased rates of dementia. The study suggested that individuals can play a role in improving air quality by adopting dietary changes, such as reducing their consumption of red meat or transitioning to vegetarian or vegan diets. These changes could have a significant impact on reducing air pollution and improving public health.

Wind-blown dust

To address the issues caused by wind-blown dust, various dust control methods are employed, depending on local soil properties, topography, and meteorology. In agricultural areas, soil conservation measures are important to prevent wind erosion and minimize wind-blown dust. Public education is also important to advise precautions to avoid exposure to wind-blown dust, just as with any other strong air pollution episode.

Organic compounds from plants

Air pollution is a mix of hazardous substances from both human-made and natural sources. Natural sources of air pollution include organic compounds from plants, sea salt, suspended soils, and dust.

Plants themselves can emit VOCs, known as biogenic VOCs (BVOCs), and these can have complex interactions with urban green spaces, NOx, and O3. Isoprene is one of the major BVOCs, and its emission response to elevated O3 levels has been studied, with varying levels of emission observed between upper and lower leaves.

The effects of VOCs on plants have been studied, and long-term exposure to industrial emissions or acute exposure during accidents is considered the major risk factor for plant damage. VOCs can enrich in leaf organs, causing various synergistic and indirect effects, which tend to be more damaging than direct effects. In badly polluted areas, atmospheric concentrations of VOCs can also cause damage to sensitive tree species.

In summary, organic compounds from plants, particularly VOCs, contribute to air pollution and can have significant effects on both the atmosphere and vegetation. These compounds are released by a variety of sources and can impact the health and growth of plants, as well as influence the air quality and contribute to climate change.

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