Air Pollutants: Crops And Soil Adversely Affected

Air pollution is a pressing issue that affects all living organisms, including plants and crops. The main air pollutants are gases, particles in suspension, ionising radiation, and noise. These pollutants can have a detrimental impact on crops and soil, with plants acting as a source of fibre, fuel, shelter, and nutrition for humans and other animals.

Plants are sensitive to different forms of pollution, and their vulnerability depends on factors such as soil type, pollutant concentration, plant age, temperature, and season. The effects of air pollution on plants can be direct or indirect. Direct effects occur when toxins like ozone and nitrogen oxides deposit on plants, disrupting leaf metabolism and carbon uptake. Indirect effects happen via the soil, where air pollutants like heavy metals change the soil chemistry and pH, making it difficult for plants to obtain necessary nutrients.

Particulate matter, composed of fine particles from industries and agriculture, can cause mechanical harm to plants by reducing light penetration and blocking stomata openings, hindering their function. Additionally, photochemical smog, resulting from chemical reactions between nitrous oxides and volatile organic compounds, leads to the formation of ground-level ozone, which has detrimental effects on vegetation and agricultural crops.

Agricultural operations, particularly animal-raising operations, are significant contributors to air pollution. Cattle, pig, and chicken farms release methane, nitrous oxide, and ammonia into the air, accelerating climate change and posing risks to human health.

Water pollution, caused by sewage leakage, industrial spills, and agricultural runoff, also affects plants by disrupting their water intake and causing nutrient imbalances. Soil pollution, either directly from toxic chemical dumping or indirectly from air pollution, can alter soil chemistry and prevent plants from obtaining essential nutrients.

Addressing air pollution and its impact on crops and soil requires a comprehensive approach that includes reducing greenhouse gas emissions, improving air quality monitoring, and implementing sustainable agricultural practices that protect the environment while maintaining productivity.

Ozone pollution

Ozone affects plants and crops by entering leaf openings called stomata and oxidising (burning) plant tissue during respiration, damaging leaves and reducing survival rates. It can also reduce photosynthesis, slow plant growth, and increase plants' susceptibility to other pollutants and severe weather.

Some plants are more sensitive to ground-level ozone than others. In general, broad-leaved plants, middle-aged leaves, and young plants are more vulnerable. Sensitive plant species include trees found in many areas of the US, such as tulip trees, as well as cucumber, grape, green bean, lettuce, onion, potato, radish, tobacco, and tomato.

Ozone injury to plants can manifest in several ways, including necrotic lesions (dead tissue), yellowing or chlorosis of leaves, and reduced growth. It can also cause flecking, bronzing, or bleaching of leaf tissues. These symptoms typically occur on the upper surface of affected leaves. While yield reductions often coincide with visible foliar injury, crop loss can also occur without any apparent signs of stress. Conversely, some crops can sustain visible foliar injury without any adverse effects on yield.

Particulate matter

Plants that are affected by this pollution could lose the most affected leaves or fade due to the inability to photosynthesize. Leaves can also sustain chemical injuries, lesions, if the deposited dust reacts with water from the environment. Alkaline dust turns toxic for plants when reacting with water.

During long-term exposure, plants are under stress. Some fruit trees like peaches and cherries, for example, experience shorter flowering periods and drop fruits too soon. Their overall productivity is reduced.

• PM10 (generally defined as all particles equal to and less than 10 microns in aerodynamic diameter; particles larger than 10 microns are not generally deposited in the lung)
• PM2.5, also known as fine fraction particles (generally defined as those particles with an aerodynamic diameter of 2.5 microns or less)
• PM10-2.5, also known as coarse fraction particles (generally defined as those particles with an aerodynamic diameter greater than 2.5 microns, but equal to or less than a nominal 10 microns)
• Ultrafine particles generally defined as the particles less than 0.1 microns

The sources of air pollution as it relates to particulate matter can be classed as either local or widespread. Local pollutants are those emitted from a specific stationary source and result in a well-defined zone of vegetation injury or contamination. Most common among the local pollutants are sulfur dioxide, fluorides, ammonia, and particulate matter. Widespread pollutants consist primarily of "oxidants". Ozone, the major component of oxidants, is produced in the atmosphere during a complex reaction involving nitrogen oxides and reactive hydrocarbons, components of automobile exhausts and fossil fuel combustion.

Photochemical smog

The major undesirable components of photochemical smog are nitrogen dioxide, ozone, peroxyacetyl nitrate (PAN), and chemical compounds that contain the –CHO group (aldehydes). PAN and aldehydes can cause eye irritation and plant damage if their concentrations are sufficiently high. Ozone is the most toxic component of photochemical smog and has caused considerable damage to agricultural and native plants in many locations.

Acid rain

Impact on Soil

Impact on Crops

Impact on Overall Ecosystem

The effects of acid rain extend beyond crops and soil, affecting the entire ecosystem. It can contaminate water bodies, making them more acidic and harmful to aquatic life. Acid rain also contributes to the corrosion of infrastructure and buildings. Additionally, the pollutants that cause acid rain, such as sulphur dioxide and nitrogen oxides, can have adverse effects on human health when inhaled.

Preventative Measures

To mitigate the impacts of acid rain, several measures have been implemented. The Clean Air Act, passed in 1970 and amended in 1990, has helped reduce the levels of sulphur dioxide and nitrogen oxides in the atmosphere, making rainwater less acidic. Additionally, the Agriculture Air Quality Task Force, established by the USDA, works to address agriculture-related air quality issues and promote cooperative efforts between agricultural communities and environmental protection agencies.

Soil pollution

One of the primary ways in which air pollution affects soil is by altering its chemistry, particularly through acid precipitation. As soils become more acidic, their ability to retain essential nutrients, minerals, and elements decreases. This leads to a decline in calcium (Ca), magnesium (Mg), and potassium (K) levels, which are crucial for plant growth and the health of land organisms. The increased acidity also mobilizes heavy metals within the soil, such as aluminum (Al). These heavy metals can then flow into nearby water bodies, posing a threat to aquatic life. For instance, aluminum is poisonous to fish and other wildlife.

Soils vary in their vulnerability to acid precipitation. Soils with higher concentrations of calcium carbonate, such as those found in limestone and dolomite, are more resistant to acid rain due to their ability to chemically neutralize acids. On the other hand, soils with lower levels of calcium carbonate, such as those on quartzite, gneiss, and granite, are more susceptible to the damaging effects of acid rain.

Additionally, air pollution contributes to the movement of persistent organic pollutants (POPs) through the grasshopper effect. This is of particular concern in Arctic regions, where these pollutants tend to concentrate. Air pollution can also lead to eutrophication, where excessive nutrients, elements, and heavy metals leach from soils and become suspended in water bodies. This can result in rapid and significant increases in plant and algal growth, which can deplete oxygen resources needed by other organisms.

Moreover, air pollution can affect the pH of the soil through the deposition of nitrogen compounds, particularly in forest ecosystems. This alteration in pH can impact the availability of essential nutrients and the solubility of toxic salts of metals like aluminum.

The effects of air pollution on soil are far-reaching and have significant implications for the health of ecosystems and human well-being. It is crucial to address and mitigate these impacts to ensure the sustainability and resilience of our environment.

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