Agriculture's Air Pollution: Harmful Emissions And Practices

Agriculture is a major source of air pollution, with emissions from farms outweighing all other human sources of fine-particulate air pollution in much of the United States, Europe, Russia, and China. The use of fertilisers and insecticides, the rearing of livestock, the application of pesticides, and the burning of crop stubble all contribute to poor air quality. These practices release harmful chemicals into the atmosphere, impacting both human and environmental health. Livestock manure, for instance, generates ammonia, which combines with other air pollutants to create solid particles that can cause heart and lung diseases. Furthermore, the combustion of fossil fuels to power farm machinery generates significant carbon emissions, contributing to global warming and climate change. The bidirectional relationship between agriculture and air pollution underscores the importance of adopting sustainable agricultural practices to achieve cleaner air and ensure food security.

Livestock and manure

Livestock and intensive animal farming operations (CAFOs) are a significant contributor to air pollution. Livestock waste is the dominant source of ammonia emissions, which, in turn, are responsible for particulate matter (PM) that affects air quality and leads to respiratory issues and premature deaths.

Ammonia emissions from livestock and manure are a major concern. Ammonia is a harmful pollutant that reduces air quality, destroys the ozone layer, and contributes to climate change. According to a study, emissions from livestock manure and chemicals make up 95% of ammonia emissions, which account for 58% of the particulate matter air pollution in European cities. The high density of animals in CAFOs leads to increased emissions, as these facilities rely more on manure storage and silage.

The impact of ammonia emissions on air quality is evident in agricultural areas with high animal concentrations, where air quality improvement lags. Moreover, the interaction of agricultural emissions with industrial emissions exacerbates the problem. Ammonia from livestock waste combines with nitrogen oxides and sulfates from industrial sources to form solid particles, contributing to disease and death.

The challenge of estimating emissions from livestock waste has been acknowledged by organizations like the EPA since the late 1990s. Factors such as animal type, life stage, population size, geography, environmental conditions, feed additives, and manure management influence emissions. The variability in these factors makes it difficult to accurately quantify emissions and develop effective regulations.

To address the issue of livestock and manure emissions, accurate emission tracking and effective reduction strategies are essential. While some practices, such as sustainable application of livestock waste to fields, can mitigate emissions at farms with lower animal densities, these approaches may be less feasible for large-scale industrial operations.

Burning crop stubble

The burning of crop stubble releases a variety of gaseous pollutants into the atmosphere, including carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), sulfur oxides (SOx), and methane (CH4). These emissions contribute to the formation of particulate matter (PM), which consists of solid or liquid particles found in the air. Some of these particles are large enough to be seen as soot or smoke, while others are so small that they can only be detected with an electron microscope. The release of these pollutants has serious consequences for both human health and the environment.

In South Asia, stubble burning is recognised as a significant contributor to air pollution. The intensive rice-wheat rotation system in this region generates a large amount of stubble, with India alone estimated to produce about 352 Mt of stubble annually. A significant portion of this stubble is burned on fields immediately after harvest, leading to a major deterioration in air quality. For example, in 2019, Delhi recorded a peak Air Quality Index (AQI) of 487, while Greater Noida reported an AQI of 480. These high levels of air pollution have been linked to various health issues, including skin and eye irritation, respiratory diseases, asthma, and even more severe conditions such as cancer.

The practice of burning crop stubble also has negative consequences for soil fertility, as it results in the complete loss of nitrogen and the destruction of other nutrients in the soil. This not only affects crop production but also impacts the economic development and climate of the region. Despite the efforts of governments to impose fines and promote alternatives, stubble burning continues to be a prevalent issue, with farmers in some states finding ways to evade detection by timing their fires strategically.

To address the issue of stubble burning and its impact on air pollution, various alternatives and management practices have been suggested. These include promoting greenery, checking vehicular emissions, and providing farmers with incentives to adopt more sustainable practices. By working together and implementing effective measures, it is possible to mitigate the negative effects of stubble burning and improve air quality, protecting both human health and the environment.

Nitrogen-based fertilisers

Excess nitrogen from fertilised fields can be lost to the air in the form of gaseous, nitrogen-based compounds. This excess nitrogen can contribute to increased formation of ground-level ozone, higher amounts of climate-changing greenhouse gases, and the thinning of the protective ozone layer. It has also been linked to acid rain and the creation of "'dead zones'" in water bodies, which cause serious harm to aquatic wildlife.

To reduce the environmental impact of nitrogen-based fertilisers, farmers can adopt nutrient management techniques. This involves applying the right amount of nutrients, at the right time of year, using the appropriate method and placement. Additionally, conservation drainage practices, such as subsurface tile drainage, can help manage water movement and reduce nutrient losses.

While nitrogen-based fertilisers have benefits for crop production, it is crucial to address their environmental and health impacts through careful application and the adoption of sustainable agricultural practices.

Insecticides and pesticides

Pesticides can be detected in the air in the form of solids, gases, and liquids. During spraying in agricultural areas, about 30–50% of pesticides are dispersed into the air through drift (by the wind) and evaporation. Pesticide drift occurs when pesticides are carried by wind or other factors away from the intended target area during application, resulting in the unintended release of pesticides into the surrounding air, soil, and water bodies. This can lead to chemical drift, where pesticides reach nearby lands or neighbourhoods and contribute to poor air quality elsewhere. The specific effects of pesticides on air quality can vary depending on the type of pesticide used, application methods, weather conditions, and local environmental factors.

The use of pesticides has been linked to negative health outcomes, particularly for farmworkers who are exposed during spraying and their families, who may be exposed through contamination on clothing. Rural residents are also at risk of exposure to contaminated water, air, and food. Pesticides have been associated with increased blood pressure and the occurrence of asthma and rhinitis in children. They have also been implicated in the decline of pollinator populations, such as the monarch butterfly and native bees.

To reduce the impact of pesticides on air quality, it is essential to implement air quality monitoring systems on farms. By regularly monitoring air quality, farmers can make informed decisions about pesticide application and take steps to minimize drift and reduce air pollution in their communities. Implementing Integrated Pest Management (IPM) can help manage pests more sustainably and reduce pesticide use. Additionally, adopting regenerative agriculture practices, such as improving soil health through planting cover crops, can help mitigate the effects of pesticides on the environment.

The complex shifts in agricultural practices due to a growing global population and climate change may lead to increased pesticide use. Elevated carbon dioxide levels, for example, may disrupt crop-pest interactions, influencing the types and quantities of pesticides required. To ensure the safe and sustainable use of pesticides, robust policies, and regulations supported by education, training, and research are crucial.

Fossil fuel combustion

The combustion of fossil fuels is not limited to machinery and vehicles; it also extends to the production of artificial fertilizers, which have seen a rapid increase in production since 1950, with about a third of them being nitrogen-based. The production and application of fertilizers contribute to air pollution by releasing nitrogen-rich compounds into the atmosphere. Nitrogen oxides, a product of fossil fuel combustion, are among the most widely emitted pollutants and can directly damage crop cells. They also play a role in forming ground-level ozone, which is known to reduce crop yields.

Additionally, the use of fossil fuels in agricultural practices can lead to the release of fine particulate matter, which can create a haze and reduce visibility. This particulate matter, when inhaled, poses serious health risks to humans and has been associated with heart and lung diseases. According to a study, exposure to particulate pollution has been linked to up to 10 million deaths worldwide.

Moreover, the combustion of fossil fuels in agriculture contributes to climate change. Short-lived air pollutants, including those from fossil fuel combustion, are responsible for 30-40% of the atmospheric warming happening today. This rise in temperature significantly damages crop production, with each degree Celsius of global warming potentially decreasing crop yields of staples like rice, maize, and wheat by up to 10%.

To address the issue of fossil fuel combustion in agriculture, there have been efforts to improve engine efficiency and adopt cleaner diesel technologies. The US EPA, for example, has initiatives such as the National Clean Diesel Campaign, which aims to reduce diesel emissions and nitrogen oxide levels. By focusing on reducing emissions and adopting sustainable practices, the agricultural sector can play a crucial role in mitigating air pollution and its subsequent impact on the environment and human health.

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