Natural Air Pollution: Forest Fires And Their Impact

Air pollution is a pressing issue that affects people worldwide, causing an estimated seven million premature deaths annually. It is caused by the contamination of the indoor or outdoor environment by any chemical, physical, or biological agent that modifies the natural characteristics of the atmosphere. While human activities such as industrial processes and vehicular emissions significantly contribute to air pollution, natural sources also play a role. An example of natural air pollution is the release of organic compounds from plants, which can include volatile organic compounds (VOCs) and particulate matter. Other natural sources include sea salt, suspended soils, and dust, which can be carried by winds and contribute to reduced air quality in certain regions. Volcanic eruptions are another significant example of natural air pollution, releasing massive amounts of sulphur dioxide and other gases into the atmosphere.

Organic compounds from plants

Natural sources of air pollution include organic compounds from plants, sea salt, suspended soils, and dust. One example of an organic compound from plants that contributes to air pollution is methane, which is released from livestock such as cows and sheep through belching and flatulence. Livestock is the biggest source of methane globally, and it is the second most significant greenhouse gas, contributing to climate change.

Another organic compound from plants that contributes to air pollution is volatile organic compounds (VOCs). While routine measurements of VOCs in the air show that average concentrations are much smaller than those used in laboratory experiments, maximum hourly concentrations of some VOCs can be 100 times larger. VOCs can affect plants by reducing their tolerance to heat and drought stress and reducing antioxidant protection. For example, airborne ethylene can reduce the tolerance of holm oak to heat and drought stress. VOCs can also have indirect effects on plants by reacting with other pollutants. For instance, tropospheric, or ground-level, ozone is formed when VOCs react with oxides of nitrogen (NOx) in the presence of sunlight. Ozone is a secondary pollutant that can enter the leaves of sensitive plants, reducing photosynthesis and plant growth and defence against disease and insects. Over time, this can lead to changes in habitat quality and nutrient and water cycles.

In addition to VOCs, plants can also release toxic air pollutants such as mercury, which can deposit onto soils and be taken up by other plants, ingested by animals, and magnified through the food chain.

Volcanic eruptions

One of the most significant impacts of volcanic eruptions is the release of sulphur dioxide (SO2). During volcanic activity, massive amounts of SO2 are spewed into the atmosphere. For instance, the eruption of Mount St. Helens in 1980 emitted up to 3750 tons of SO2 per day. This gas contributes to the formation of acid rain, which has detrimental effects on both human health and the environment. The United States Geological Survey (USGS) has warned about the persistent health problems caused by acid rain and air pollution downwind from volcanic vents.

Additionally, volcanoes emit carbon dioxide, a lightweight volatile gas that is easily expelled and dispersed during eruptions. While carbon dioxide is lighter than other expelled gases, it is heavier than air, causing it to remain close to the Earth's surface. High concentrations of carbon dioxide can have fatal consequences for humans and other animal species, leading to unconsciousness and death when inhaled in amounts exceeding 30%.

The impact of volcanic eruptions on air pollution is significant, and the resulting pollution can affect populations far beyond the immediate vicinity of the eruption. The potential health and environmental consequences of volcanic activity are carefully monitored by organizations such as the EPA and USGS, which provide expertise and support to ensure the safety and well-being of communities at risk.

Forest fires

The smoke released during forest fires can rise up to 14 miles (23 km) into the stratosphere and spread globally. For example, in 2023, the smoke from Siberian wildfires, fuelled by unusually warm temperatures, travelled across the Pacific Ocean to reach Alaska and Seattle. The specific pollutants released depend on the substances burned. For instance, the 2020 Siberian wildfires, which burned a resinous boreal forest and peat, released record-breaking quantities of pollution, including high levels of mercury.

The particulate matter (PM2.5) in wildfire smoke is a primary public health concern. It is associated with premature deaths and can cause or exacerbate various diseases, including respiratory conditions, and issues affecting the lungs, heart, brain/nervous system, skin, gut, kidneys, eyes, nose, and liver. Additionally, it has been linked to cognitive impairment and memory loss. The toxicity of wildfire smoke is more pronounced than that of other types of pollution and increases over time. Studies have shown that smoke toxicity can double or even quadruple in the hours after emission.

To mitigate the impacts of forest fires, it is essential to focus on prevention and reducing the underlying causes of air pollution. This includes lowering emissions in cities, transitioning to cleaner cooking methods, and rapidly reducing the use of fossil fuels. By addressing these issues, we can minimize the occurrence and severity of forest fires and their associated air pollution.

Nitrogen and sulphur dioxide from trains

Natural sources of air pollution include organic compounds from plants, sea salt, suspended soils, and dust. Volcanic eruptions, for example, can spew massive amounts of sulphur dioxide into the air.

One example of natural air pollution is the emission of nitrogen and sulphur dioxide from trains, particularly those powered by diesel engines. Diesel locomotive engines are a major contributor to air pollution, producing nitrogen oxide (NOx) and sulphur dioxide (SO2). Nitrogen dioxide (NO2), a type of NOx, is of particular concern as it is 240 times more destructive to the ozone layer than carbon dioxide, making it a primary contributor to climate change. It also has adverse effects on human health.

Diesel trains emit harmful pollutants, including nitrogen oxides, sulphur dioxide, and particulate matter, into the air. In London's Paddington Station, for example, emissions of nitrogen dioxide were found to far exceed European recommendations, with levels higher than those on a busy nearby road. This is particularly concerning given that up to 70% of trains passing through the station are powered by diesel engines, and many of these older trains are exempt from modern diesel locomotive regulations.

The issue of diesel train emissions is not limited to Paddington Station. In Europe, about 20% of rail traffic is hauled by diesel locomotives, with countries like the UK, Greece, Estonia, Latvia, and Lithuania highly dependent on diesel traction. While electrification of train lines has made progress, approximately half of Europe's train lines remain non-electrified. This has significant implications for air quality, especially in train stations where passengers may be exposed to poor air quality.

To address this issue, the EU-funded ENSPIRIT project aims to develop an innovative emission abatement system capable of reducing nitrogen oxide and sulphur dioxide pollution levels. This system seeks to meet stringent new regulations and ensure that both new and old locomotives can comply with emission standards. The ultimate goal is to integrate ENSPIRIT into a combined system that addresses heat, moisture, sulphur oxides, particulate matter, and nitrogen oxides.

Methane from livestock

Livestock, particularly cattle, are a significant source of methane emissions, a potent greenhouse gas contributing to climate change. Cattle have specialised stomachs that can digest grasses and hays that humans cannot. During digestion, bacteria break down the food, producing methane, which is released through belching. This process, known as enteric fermentation, is the largest source of livestock methane emissions, accounting for over 90% of methane from cattle.

The impact of methane emissions from livestock on global warming is significant. Methane has accounted for approximately 30% of global warming since pre-industrial times, and its atmospheric concentration is increasing faster than at any other time since record-keeping began in the 1980s. Reducing methane emissions from livestock is crucial in mitigating climate change. Strategies such as modifying diets, selective breeding, and adopting new technologies in agricultural practices are being explored to reduce methane production without compromising animal health and productivity.

While livestock methane emissions are a concern, it's important to note that agricultural methane emissions also arise from other sources, such as manure management and paddy rice cultivation. Together, these sources contribute to the overall environmental impact of the agricultural sector. Addressing these emissions through initiatives like the United Nations' Koronivia Joint Work on Agriculture and the Paris Agreement demonstrates a global commitment to tackling climate change and improving air quality.

In conclusion, methane from livestock is a significant contributor to natural air pollution, and efforts are being made to reduce these emissions while balancing the needs of animal agriculture. By lowering methane emissions from livestock and other agricultural sources, we can help mitigate climate change and work towards achieving global climate targets.

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