Air Quality & Pollution Control – Key Vocabulary

REHS Study

Donora, Pennsylvania Smog (1948)

A five-day industrial smog event that killed 20 people and sickened 6,000 of the town’s 14,000 residents, highlighting the dangers of air pollution.

London “Killer Fog” (1952)

Severe smog episode that caused more than 3,000 deaths; buses required lantern-carrying guides due to diminished visibility.

Air Pollution Control Act (1955)

First U.S. federal law to address air pollution; provided funds for research but set no enforceable standards.

Federal Clean Air Act (1963)

Established federal authority to tackle interstate air pollution and set the stage for later, stricter amendments.

U.S. Environmental Protection Agency (EPA)

Federal agency created in 1970 to enforce environmental laws, including air quality regulations.

National Ambient Air Quality Standards (NAAQS)

EPA limits (1975) on six criteria pollutants to protect public health and welfare.

State Implementation Plan (SIP)

State-level strategy for attaining and maintaining NAAQS, approved by the EPA.

Clean Air Act Amendments (1990)

Major update that tightened limits on pollutants, addressed acid rain, toxic air emissions, and ozone depletion.

California Air Pollution Act (1947)

Authorized creation of local air pollution control districts (APCDs) in California.

Air Pollution Control District (APCD)

Local California agency responsible for regulating stationary sources of air pollution.

California Air Resources Board (CARB)

State agency (1967) that sets vehicle emissions standards and oversees California’s air quality programs.

California Clean Air Act (1988)

Requires California to achieve and maintain state ambient air quality standards that are often stricter than federal limits.

Criteria Air Pollutants

Six common pollutants regulated under NAAQS: CO, SO2, NO2, O3, Pb, and particulate matter (PM10 & PM2.5).

Primary Pollutant

Contaminant emitted directly from a source in its original form (e.g., CO from vehicle exhaust).

Secondary Pollutant

Pollutant formed in the atmosphere through chemical reactions of primary pollutants (e.g., ozone).

Carbon Monoxide (CO)

Colorless, odorless gas; 95 % comes from motor‐vehicle exhaust; reduces oxygen delivery in the body.

Sulfur Dioxide (SO2)

Gas mainly from coal-fired power plants and refineries; precursor to acid rain.

Nitrogen Dioxide (NO2)

Reddish-brown gas from vehicles and power plants; key ingredient in ozone formation.

Hydrocarbons

Organic compounds of hydrogen and carbon; react with NOx to form photochemical smog.

Volatile Organic Compounds (VOCs)

Carbon-based chemicals that easily vaporize and contribute to ozone and PAN formation.

Carbon Dioxide (CO2)

Natural atmospheric gas; leading greenhouse pollutant from fossil fuel combustion.

Chlorofluorocarbons (CFCs)

Stable compounds once used as refrigerants and propellants; deplete stratospheric ozone.

Particulate Matter (PM)

Mixture of solid particles and liquid droplets suspended in air; classified by size as PM10 or PM2.5.

PM10

Inhalable particles ≤10 µm; can penetrate the respiratory tract and cause damage.

PM2.5

Fine particles ≤2.5 µm; linked to premature death, heart and lung disease, asthma.

Photochemical Smog

Brownish haze produced when sunlight acts on NOx and VOCs; typical of urban areas.

Ground-Level Ozone (O3)

Secondary pollutant formed from NOx + VOCs + sunlight; irritates lungs and damages plants.

Acid Rain

Precipitation containing sulfuric and nitric acids formed from SO2 and NOx emissions.

Peroxyacyl Nitrates (PAN)

Secondary pollutants (from hydrocarbons + O2 + NO2 + UV) causing eye and respiratory irritation and plant damage.

Fugitive Pollutant

Dust, gas, or vapor that escapes to outdoor air without passing through a stack (e.g., construction dust).

Thermal Inversion

Atmospheric condition where a warm layer overlays cooler air, trapping pollutants near the ground.

Hazardous Air Pollutants (HAPs)

Toxic substances regulated for their carcinogenic, mutagenic, or reproductive effects; many are VOCs.

Primary Air Quality Standard

NAAQS level set to protect sensitive human populations such as children and the elderly.

Secondary Air Quality Standard

NAAQS level aimed at protecting vegetation, buildings, and visibility.

Chronic Obstructive Pulmonary Disease (COPD)

Long-term lung disease exacerbated by air pollution exposure.

Ringelmann Smoke Chart

Visual tool with 4 rectangular shades used to estimate smoke opacity from stacks.

Electrostatic Precipitator

Device that removes particulates by applying an electric charge and collecting them on plates.

Cyclone Separator

Mechanical collector that uses centrifugal force to remove large particles from gas streams.

Baghouse Filter

Fabric filter system that captures fine particulates as gas passes through filter bags.

Air Scrubber

Equipment that cleans gas streams by contacting them with a liquid to remove pollutants.

Catalytic Converter

Automotive exhaust device that converts CO, NOx, and hydrocarbons into less harmful gases.

Settling Chamber

Large chamber where gas velocity is reduced, allowing heavy particles to settle out.

Adsorption/Absorption

Gas control methods that capture pollutants on solid surfaces (adsorption) or dissolve them in liquids (absorption).

Indoor Air Pollutants

Contaminants such as asbestos, radon, formaldehyde, VOCs, mold, and tobacco smoke found inside buildings.

Radon

Radioactive gas originating from soil; significant cause of lung cancer in indoor environments.

Formaldehyde

Irritating VOC emitted from pressed-wood products and some building materials.

Environmental Tobacco Smoke (ETS)

Mixture of mainstream and sidestream smoke that contributes to indoor air pollution.

Vector-Borne Disease Risk

Potential increase in diseases transmitted by insects (e.g., mosquitoes) due to climate-related changes in air quality and weather.