Emissions Inventory
A comprehensive accounting of air pollutant emissions from all sources in a geographic area, used for regulation and planning.
Detailed Explanation
An emissions inventory is a database that lists, by source, the amount of air pollutants discharged into the atmosphere in a given time period (typically annually). The EPA maintains the National Emissions Inventory (NEI), which is updated every three years and covers all criteria pollutants, hazardous air pollutants (air toxics), and greenhouse gases from all source categories. Sources are categorized as point sources (large stationary facilities like power plants and factories), area sources (smaller stationary sources aggregated by category, such as dry cleaners or residential heating), mobile sources (on-road vehicles, aircraft, locomotives, marine vessels), and natural sources (wildfires, biogenic emissions from vegetation, windblown dust). Emissions inventories are essential tools for air quality management — they help regulators identify the largest pollution sources, design effective control strategies, and track progress toward air quality goals. They also serve as inputs to air quality models that predict how emission changes will affect pollutant concentrations. For cities tracked by AirHistory, the local emissions inventory explains why certain pollutants dominate. A city dominated by PM2.5 likely has significant combustion sources or is downwind of wildfire-prone areas. A city dominated by ozone likely has a combination of vehicle traffic and industrial VOC sources in a climate favorable to photochemical reactions. Understanding the emissions inventory provides the "why" behind AirHistory's trend data.
Related Terms
Criteria Pollutants
The six common air pollutants regulated by the EPA under the Clean Air Act: ozone, PM2.5, PM10, CO, NO2, and SO2.
EPA Air Quality System (AQS)
The EPA's national database of ambient air quality data collected from monitoring stations across the United States.
National Ambient Air Quality Standards (NAAQS)
EPA-established limits on concentrations of six criteria pollutants that must be met nationwide to protect public health and the environment.
Volatile Organic Compounds (VOCs)
Carbon-containing chemicals that easily evaporate at room temperature and contribute to ozone formation and direct health effects.
Frequently Asked Questions
A comprehensive accounting of air pollutant emissions from all sources in a geographic area, used for regulation and planning.
An emissions inventory is a database that lists, by source, the amount of air pollutants discharged into the atmosphere in a given time period (typically annually). The EPA maintains the National Emissions Inventory (NEI), which is updated every three years and covers all criteria pollutants, hazardous air pollutants (air toxics), and greenhouse gases from all source categories. Sources are categorized as point sources (large stationary facilities like power plants and factories), area sources (smaller stationary sources aggregated by category, such as dry cleaners or residential heating), mobile sources (on-road vehicles, aircraft, locomotives, marine vessels), and natural sources (wildfires, biogenic emissions from vegetation, windblown dust).