Volatile Organic Compound (VOC)

Soil Vapor Extraction (SVE) is an in-situ physical remediation technology used for volatile organic compounds (VOCs) and some semi-volatile organic compounds (SVOCs) in unsaturated soil (the vadose zone). The process involves applying a vacuum to the soil through extraction wells, which creates a pressure gradient that induces gas-phase contaminants to move through the soil and be collected for treatment.

The process of capturing carbon dioxide (CO2) from large point sources like power plants and injecting it into deep underground rock formations for long-term storage. Suitable formations include saline aquifers, depleted oil and gas reservoirs, and unmineable coal seams. The CO2 is trapped by an impermeable caprock and through various physical and chemical mechanisms, preventing its atmospheric release.

The Ecological Footprint is a resource accounting metric that measures human demand on nature. It quantifies the amount of biologically productive land and sea area required to produce the resources a population consumes (like food, fiber, and timber), and to absorb its waste, especially carbon emissions. It is the 'demand' side of the Earth Overshoot Day (EOD) calculation.

The Kaya identity is a mathematical formula stating that the total emission level of carbon dioxide can be expressed as the product of four factors: human population, GDP per capita, energy intensity (energy per unit of GDP), and carbon intensity (emissions per unit of energy). The formula is \(F = P \times \frac{G}{P} \times \frac{E}{G} \times \frac{F}{E}\), where F is CO2 emissions, P is population, G is GDP, and E is energy consumption.

Phytoremediation is a bioremediation process that uses various types of plants to remove, transfer, stabilize, or destroy contaminants in soil and groundwater. This low-cost, solar energy-driven technique is effective for cleaning up sites with low to moderate levels of contamination. Different mechanisms are involved, including phytoextraction (uptake into harvestable plant tissues), phytodegradation (breakdown of contaminants), and phytostabilization (reducing mobility).

Biogenic Volatile Organic Compounds (BVOCs) are VOCs produced and emitted by living organisms, predominantly plants. Isoprene (\(C_5H_8\)) and terpenes are the most abundant BVOCs. While natural, their emissions are vast, exceeding anthropogenic VOCs globally. They play critical roles in plant defense, signaling, and are major precursors for atmospheric ozone and secondary organic aerosols, influencing air quality and climate.

In-Situ Chemical Oxidation (ISCO) is an aggressive remediation technology that involves injecting strong chemical oxidants directly into the contaminated subsurface to destroy pollutants. Common oxidants include permanganate, persulfate, hydrogen peroxide (Fenton's reagent), and ozone. These chemicals react with contaminants, converting them into less toxic substances like carbon dioxide, water, and inorganic salts, without requiring excavation of the contaminated material.

Secondary Organic Aerosols (SOAs) are fine airborne particles formed from the atmospheric oxidation of VOCs. Gaseous VOCs react with oxidants like \(O_3\), \(\bullet OH\), or \(NO_3\bullet\) to produce low-volatility products. These products can then undergo gas-to-particle conversion, either by forming new particles (nucleation) or condensing onto pre-existing aerosols. SOAs are a major component of PM2.5, impacting climate and human health.

Involves capturing CO2 and storing it in the deep ocean, which is the planet's largest carbon sink. Methods include direct injection of liquid CO2 into the water column or onto the deep seafloor, and ocean fertilization to stimulate phytoplankton growth, which absorbs CO2 via photosynthesis. Both approaches have significant environmental concerns, primarily ocean acidification and unpredictable impacts on marine ecosystems.

Biocapacity is a metric that represents the biosphere's regenerative capacity in a given year. It measures the amount of biologically productive land and sea area available to provide resources and absorb wastes under current management practices. It is the 'supply' side of the ecological balance sheet used to calculate Earth Overshoot Day, measured in global hectares (gha).