Environmental Chemistry

1.0What is Environmental Chemistry? 

Environmental Chemistry is the branch of Chemistry that focuses on understanding the chemical processes occurring in the environment, including air, water, soil, and living organisms. Introduction to environmental Chemistry involves studying the sources, reactions, transport, effects, and fate of chemical species in natural and polluted environments. 

Pollution is the introduction of contaminants into the natural environment, causing adverse changes. Here we will learn some major types of Pollution under topics of environmental Chemistry.

2.0Atmospheric Pollution 

Atmospheric pollution in the troposphere, the lowest layer of Earth's atmosphere, consists of undesirable solid and gaseous particles that adversely affect air quality, health, and the environment. Here's a concise summary of the major pollutants found in the troposphere:

Gaseous Air Pollutants

1. Oxides of Sulfur (e.g., SO₂): Produced from burning sulfur-containing fuels, leading to respiratory issues and environmental damage.
2. Oxides of Nitrogen (e.g., NO, NO₂): Formed during high-temperature combustion processes, contributing to smog, respiratory issues, and ecosystem damage.
3. Hydrocarbons: Result from incomplete combustion in vehicles, associated with cancer risks and environmental stress.
4. Carbon Monoxide (CO): A colorless, odorless gas from incomplete combustion, highly toxic due to its ability to impair oxygen transport in the bloodstream.
5. Carbon Dioxide (CO₂): Emitted from burning fossil fuels and other organic materials, a key greenhouse gas contributing to global warming.

Global Warming and Greenhouse Effect

Solar energy absorbed by the Earth's surface increases its temperature, with some heat trapped by greenhouse gases in the atmosphere, leading to global warming. Human activities, such as burning fossil fuels and deforestation, increase greenhouse gas concentrations, disrupting the Earth's natural greenhouse effect. This can result in rising global temperatures, melting polar ice caps, and increased risks of infectious diseases. Efforts to reduce greenhouse gas emissions are essential to mitigate these effects and preserve the planet's climate balance.

Acid Rain

Acid rain is a type of precipitation that occurs when acidic pollutants, primarily sulfur dioxide (SO₂) and nitrogen oxides (NO_x), react with water vapor in the atmosphere to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃). These acids then mix with rain, snow, fog, or dew, resulting in precipitation with a lower pH than normal rainwater.

Particulate Pollutants: Include dust, mist, fumes, smoke, and smog, which can penetrate respiratory systems, causing various health problems.

Smog- Smog, a blend of smoke and fog, is a prevalent form of urban air pollution. There are two types:

1. Classical Smog: A mix of smoke, fog, and sulfur dioxide, acting as a reducing agent.

2. Photochemical Smog: Results from sunlight reacting with vehicle and industrial emissions, containing harmful substances like ozone and nitrogen dioxide, causing respiratory and environmental issues.

Control Measures:

• Use catalytic converters in vehicles.
• Plant certain trees that can absorb pollutants.

3.0Stratospheric Pollution

Stratospheric pollution refers to the presence of pollutants in the Earth's stratosphere, the layer of the atmosphere located above the troposphere. One of the most significant concerns regarding stratospheric pollution is the depletion of the ozone layer, which plays a crucial role in protecting life on Earth from harmful ultraviolet (UV) radiation from the sun.

Formation and Breakdown of Ozone

• Formation: Ozone (O₃) is formed naturally in the stratosphere through the absorption of UV radiation by oxygen molecules (O₂). This process leads to the dissociation of oxygen molecules into oxygen atoms (O), which can then react with other oxygen molecules to form ozone.

${\mathrm{O}}_2(\mathrm{g})\stackrel{\mathrm{UV}}{\to }\mathrm{O}(\mathrm{g})+\mathrm{O}(\mathrm{g})$

$\mathrm{O}(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})\stackrel{\mathrm{UV}}{\rightleftharpoons }{\mathrm{O}}_3(\mathrm{g})$

• Breakdown: Ozone molecules can be broken down by various natural and human-made substances, including chlorofluorocarbons (CFCs), halons, hydrochlorofluorocarbons (HCFCs), and other ozone-depleting substances (ODS). When these substances are released into the atmosphere, they rise to the stratosphere, where they undergo chemical reactions facilitated by UV radiation. These reactions release chlorine and bromine atoms, which catalytically destroy ozone molecules.

Effects of depletion of Ozone Hole: With the depletion of ozone layer, more UV radiation filters into the troposphere. UV radiation lead to (i) Ageing of skin (ii) Cataract (iii) Sunburn (iv) Skin cancer (v) Killing of many phytoplankton, damage to fish productivity etc.

4.0Water Pollution

Water pollution occurs when harmful substances—such as chemicals, waste, or contaminants—enter water bodies, significantly altering the water's quality and making it toxic to humans and the environment. Here's a brief overview of its causes:

Causes of Water Pollution:

• Industrial Discharge: Factories release pollutants directly into water bodies without treatment, including heavy metals, chemicals, and other toxic substances.
• Agricultural Runoff: Pesticides and fertilizers used in agriculture can wash into rivers and lakes, leading to nutrient pollution, which in turn can cause excessive algae growth and harm aquatic life.
• Pathogens:
• Disease-causing agents like bacteria and other microorganisms contaminate water through sewage and animal waste.
• Organic Wastes:
• Leaves, grass, and trash pollute water through runoff, with bacteria decomposing organic matter and depleting dissolved oxygen levels.
• Chemical Pollutants:
• Water-soluble inorganic chemicals, including heavy metals like cadmium, mercury, and nickel, are significant pollutants.

Biochemical Oxygen Demand (BOD):

• BOD measures the oxygen needed by bacteria to degrade organic matter in water.
• It indicates the level of organic material present, with clean water having a BOD value of less than 5 ppm.

Eutrophication:

• Nutrient-rich water bodies support dense plant growth, leading to oxygen depletion and loss of animal life and biodiversity.

5.0Soil Pollution

Soil pollution is the contamination of soil by harmful substances, impacting soil quality and posing risks to health and the environment. Key causes include:

Chemical Pesticides and Fertilizers: Overuse can lead to toxic residues in the soil and groundwater contamination.

Industrial Waste: Introduces pollutants like heavy metals and chemicals into the soil.

Solid Waste: Landfills and improper disposal contribute to soil contamination with non-biodegradable materials.

Oil Spills: Affect soil structure and fertility, harming living organisms.

Sewage Sludge: Can contaminate soil with pathogens and toxins.

Mining Activities: Cause soil erosion, contamination, and land degradation.

Pesticides- Pesticides are chemicals used to eliminate or control a variety of agricultural and household pests that can damage crops and spread disease. They include herbicides for weeds, insecticides for insects, fungicides for fungi, and rodenticides for rodents. 

Industrial Waste

(1) Biodegradable Waste-

1. Cotton mills 
2. Food processing units 
3. Paper mills 
4. Textile factories. 

(2) Non-Biodegradable Waste-

1. Thermal power plants which produce fly ash.
2. Integrated iron and steel plants which produce blast furnace slag and steel melting slag. 
3. Industries manufacturing Aluminium, Zinc and Copper produce mud and tailings. 
4. Fertilizer industries produce gypsum.

Waste management- Waste management involves the collection, transportation, treatment, and disposal of waste materials to minimize their adverse effects on human health and the environment. 

The Swachh Bharat Mission, divided into urban (SBM-U) and rural (SBM-G) components, aims to enhance India's cleanliness and sanitation:

The Swachh Bharat Mission (SBM), launched by the Government of India, is a nationwide campaign aiming to clean up the streets, roads, and infrastructure of India's cities, towns, and rural areas. It's divided into two sub-missions: Swachh Bharat Mission–Urban (SBM-U) and Swachh Bharat Mission–Gramin (SBM-G).

• SBM-U: Focuses on eliminating open defecation in urban areas and ensuring scientific solid waste management.
• SBM-G: Aims to improve rural life quality by promoting hygiene and eliminating open defecation, with efforts toward community-managed waste systems.

6.0Green Chemistry

Green Chemistry aims to minimize pollution and waste generation, making processes both environmentally friendly and cost-effective. By optimizing reaction conditions and using environmentally friendly mediums, such as water, chemical hazards can be reduced.

Careful selection of starting materials and synthesis conditions can ensure high yields of environmentally friendly products. Utilizing aqueous mediums for synthesis is advantageous due to water's properties, including high specific heat and low volatility, making it cost-effective, nonflammable, and free of carcinogenic effects.

Green Chemistry in Everyday Life

(i) Dry Cleaning: Tetra chloroethene replaced with liquid carbon dioxide, reducing groundwater contamination.

(ii) Paper Bleaching: Hydrogen peroxide replaces chlorine gas, minimizing environmental impact.

(iii) Chemical Synthesis: Ethanal synthesized with 90% efficiency using ionic catalysts in aqueous medium.

(iv) Water Treatment: Tamarind seed powder cleans wastewater, offering a cost-effective, eco-friendly solution.

7.0Environmental Chemistry Applications

1. Monitoring Environmental Quality: Assessing air, water, and soil conditions to identify and quantify pollutants.
2. Pollution Remediation: Developing methods to clean contaminated air, water, and soil, including bioremediation and phytoremediation.
3. Public Health Protection: Evaluating chemical exposure risks to safeguard human health.
4. Informing Policy and Regulation: Providing scientific data to shape environmental laws and standards.
5. Advancing Sustainable Practices: Promoting green Chemistry and resource recovery to minimize environmental impact.
6. Addressing Climate Change: Investigating and mitigating the effects of greenhouse gases.

The Concept and scope of environmental Chemistry is continually evolving as new environmental challenges emerge and our understanding of chemical processes in the environment deepens. This field is pivotal in advancing our ability to live sustainably on Earth, ensuring the well-being of future generations.