Air Pollution's Agricultural Sources: A Comprehensive Overview

Farming is a major source of air pollution, with agricultural emissions including odours, chemical discharges, particulates, and greenhouse gases such as carbon dioxide, nitrous oxide, and methane. In the US, agriculture accounts for about 11% of emissions, with 36% of that coming from the raising, feeding, and management of livestock. In addition, ammonia from animal waste and fertilizer combines with other air pollutants to create fine particulate matter, which has been linked to heart and lung diseases and is said to cause millions of deaths each year.

Animal waste and livestock facilities

Ammonia (NH3) emissions from livestock waste

Fertilizer use and runoff

Fertilizers are essential for crop growth, providing nitrogen and phosphorus to the soil. However, the overuse and mismanagement of fertilizers have significant environmental implications, contributing to air pollution and negatively impacting air quality.

When fertilizers are over-applied or mismanaged, excess nitrogen and phosphorus can be lost from farm fields. This can occur through various pathways, including runoff during rain or snow melt events, leaching through the soil into groundwater, and erosion, where fine particles of nutrient-enriched soil are carried away by wind or water. This process leads to nutrient pollution, as the excess nutrients reach nearby waterways, including rivers, streams, wetlands, and lakes. The excess nutrients cause eutrophication, leading to hypoxic "dead zones" where fish and other aquatic life cannot survive. Additionally, the increased nutrient levels can stimulate harmful algal blooms, further disrupting aquatic ecosystems and potentially producing toxins harmful to wildlife and humans.

Ammonia, a common component of fertilizers, is particularly harmful to aquatic life. When ammonia is deposited from the atmosphere into surface waters, it can directly impair the health of fish and other aquatic organisms, even leading to mortality at high concentrations. Additionally, ammonia in the air can combine with other pollutants, forming solid particles that contribute to air pollution and pose risks to human health when inhaled.

To mitigate the environmental impact of fertilizer use, farmers can adopt best management practices and regenerative agriculture strategies. This includes improving nutrient management by applying the right amount of fertilizer at the appropriate time of year and using conservation tillage practices to reduce soil erosion and runoff. Implementing buffer zones, such as planting streamside buffer crops, can also help capture and filter excess nutrients before they reach waterways.

By following these practices, farmers can play a crucial role in reducing nutrient losses, protecting water and air quality, and minimizing the environmental footprint of agricultural activities.

Pesticides and herbicides

Agricultural practices that involve the use of pesticides contribute to air pollution. During spraying in fields, about 30–50% of pesticides are dispersed into the air and subsequently vaporized from the soil and plants before entering the atmosphere. Pesticides have been detected in the outdoor air of various countries, demonstrating their widespread presence. The mobility of pesticides through wind erosion has serious implications, as they can contaminate not only the soil and water sources but also the atmosphere, leading to long-distance transport.

The impact of pesticides on the environment and human health is a critical concern. Pesticides can remain in the environment for extended periods due to their persistence and bioaccumulative properties, threatening global human, animal, and ecological health. The human toxicity potential of detected pesticides is significant, with acute toxicity, reproduction toxicity, carcinogenic effects, and endocrine disruption reported. The widespread presence of pesticides in the air indicates that current environmental risk assessments, field application techniques, and regulations may not be sufficient to protect human and ecological health.

Additionally, the use of herbicides, a subset of pesticides, contributes to air pollution from farming. Herbicides are designed to control or eliminate unwanted plants or weeds and are commonly used in agricultural settings. While they serve a purpose in weed management, herbicides can also have negative impacts on the environment and human health when released into the air. The use of herbicides in agriculture can result in chemical drift, where these chemicals reach nearby lands or neighbourhoods, affecting air quality in surrounding areas.

To mitigate the impact of pesticides and herbicides on air pollution, sustainable agricultural practices and integrated pest management techniques are recommended. By adopting cover crops, utilizing integrated pest management strategies, and reducing the reliance on chemical pesticides and herbicides, it is possible to minimize their release into the atmosphere and subsequent negative consequences. Regulatory measures, such as the Clean Air Act and state implementation plans in the United States, also play a crucial role in controlling and reducing emissions from agricultural practices, including the use of pesticides and herbicides.

Diesel emissions from farm vehicles

Diesel has been the primary fuel for the agricultural industry for generations. However, with the industry moving towards net-zero GHG emissions, diesel and other fossil-derived fuels are being phased out in favour of more sustainable alternatives.

Diesel-powered farm vehicles, such as tractors, contribute significantly to air pollution. These vehicles emit nitrogen-oxide, which combines with ammonia from fertilizers and livestock waste to form solid particles, or aerosols, that are harmful to human health and the environment. In addition, diesel engines are often left idling, consuming fuel and producing emissions without any useful output, further contributing to air pollution.

To address this issue, the US Environmental Protection Agency (EPA) offers funding for projects that aim to reduce emissions from existing diesel engines. Strategies such as idle-reduction practices and engine efficiency improvements can help decrease diesel emissions from farm vehicles. The EPA also provides information and guidance to farmers through its Clean Agriculture program, assisting them in reducing emissions from older diesel engines.

Several alternatives to diesel fuel for farm vehicles are being explored. One option is electricity generated using renewable resources, such as solar panels, wind turbines, or biogas combustion. While this approach can work for smaller vehicles or automatic machines, the weight of batteries required for larger agricultural tractors limits their engine efficiency and damages the soil. Another alternative is compressed biomethane (bioCNG), which is already being used in the UK and can be distributed to farms through biomethane trucks. Biomethane can also be produced on-farm through biogas plants, making it a readily available diesel replacement. Hydrogen, produced through electrolysis powered by renewable energy, is also proposed as a long-term diesel replacement for heavy vehicles, offering a significant reduction in GHG emissions.

Air pollution from burning

One of the main causes of agricultural burning is the practice of clearing land, fertilizing soil, and preparing it for new plantations. While many farmers consider it the most cost-efficient method, it comes at a heavy cost to the environment and human health. The smoke and flames from these fires pose risks to neighbouring communities, buildings, and fields. Additionally, the repeated burning of fields destroys organic matter, reduces water retention and soil fertility, and increases the need for expensive fertilizers.

Backyard burning, or the burning of household waste, is another source of air pollution. This practice is common in many areas, but people often do not realize its harmful effects. It releases pollutants at ground level, making them more easily inhaled and incorporated into the food chain. Backyard burning produces toxic dioxins and is linked to increased health risks, including heart and lung disease, stroke, and certain cancers.

To address the issue of agricultural burning, organizations like the Climate and Clean Air Coalition are working with farmers to promote alternatives. This includes providing information, assistance, and subsidies to help farmers access alternative methods to clear land and dispose of crop residues. For example, in Punjab, the coalition is working with the UN Food and Agriculture Organization (FAO) to turn crop residues into a renewable fuel source, creating a circular economy that benefits both the environment and farmers' incomes.

The EPA in the United States is also taking steps to reduce air pollution from agricultural burning. They are working to refine the distinction between wildland fires and agricultural burning in their policies and providing resources to help farmers reduce diesel emissions from farm equipment. Additionally, the EPA has developed a voluntary consent agreement with the AFO industry to monitor emissions and reduce air pollutant emissions from agricultural land management and cropping operations.

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