Environmental Chemistry

The pathways by which chemical elements and compounds move through the biotic (living) and abiotic (non-living) compartments of Earth, including the carbon, nitrogen, phosphorus, and sulfur cycles. These cycles are driven by biological, geological, and chemical processes.

Organic compounds that resist environmental degradation through chemical, biological, and photolytic processes. They bioaccumulate in food chains, are transported across international boundaries by air and water, and pose serious health risks to humans and wildlife.

Precipitation with a pH below 5.6, caused primarily by emissions of sulfur dioxide ($\text{SO}_2$) and nitrogen oxides ($\text{NO}_x$) from fossil fuel combustion. These gases react with water vapor in the atmosphere to form sulfuric acid and nitric acid.

The excessive enrichment of a body of water with nutrients, particularly nitrogen and phosphorus, leading to dense algal blooms. When the algae die and decompose, dissolved oxygen is depleted, creating hypoxic or anoxic conditions that kill aquatic organisms.

The thinning of the stratospheric ozone layer caused by catalytic destruction of ozone molecules ($\text{O}_3$) by halogenated compounds, primarily chlorofluorocarbons (CFCs). Each chlorine atom released from a CFC molecule can destroy tens of thousands of ozone molecules.

The process by which greenhouse gases ($\text{CO}_2$, $\text{CH}_4$, $\text{N}_2\text{O}$, water vapor, and fluorinated gases) in the atmosphere absorb and re-emit infrared radiation, warming Earth's surface. Human activities have intensified this natural effect, driving global climate change.

The introduction of toxic metallic elements such as lead, mercury, cadmium, arsenic, and chromium into the environment through mining, industrial discharge, and improper waste disposal. Heavy metals do not degrade and can bioaccumulate in organisms.

The chemical processes used to make water safe for drinking or to treat wastewater before discharge. Key processes include coagulation, flocculation, sedimentation, filtration, and disinfection using chlorine, ozone, or ultraviolet light.

The use of living organisms, primarily microorganisms, to degrade or transform environmental contaminants into less toxic or non-toxic forms. This approach leverages natural metabolic pathways and can be enhanced through bioaugmentation or biostimulation.

A type of air pollution formed when sunlight drives chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the atmosphere, producing ground-level ozone, peroxyacetyl nitrate (PAN), and other secondary pollutants.