Air emission inventory
An air air emission inventory is an accounting of the amount of pollutants discharged into the atmosphere. An air air emission inventory usually contains the total emissions for one or more specific greenhouse gases or air pollutants, originating from all source categories in a certain geographical area and within a specified time span, usually a specific year.
An air air emission inventory is generally characterized by the following aspects:
Why: The types of activities that cause emissions
- What: The chemical or physical identity of the pollutants included, and the quantity thereof
- Where: The geographic area covered
- When: The time period over which emissions are estimated
- How: The methodology to use
Air emission inventories are compiled for both scientific applications and for use in policy processes
Emissions and releases to the environment are the starting point of every environmental pollution problem. Information on emissions therefore is an absolute requirement in understanding environmental problems and in monitoring progress towards solving these. Air emission inventories provide this type of information.
Air emission inventories are developed for a variety of purposes:
- Policy use: by policy makers to track progress towards emission reduction targets develop strategies and policies or
- Scientific use: Inventories of natural and anthropogenic emissions are used by scientists as inputs to air quality models
For each of the pollutants in the inventory emissions are typically estimated by multiplying the intensity of each relevant activity (‘activity rate’) in the geographical area and time span with a pollutant dependent proportionality constant (’emission factor’).
Why: the source categories
To compile an air air emission inventory, all sources of the pollutants must be identified and quantified. Both source categorisations make a clear distinction between sources related to the combustion of (fossil) fuels and those that are not caused by combustion. In most cases the specific fuel combusted in the former is added to the source definition.
Source categories include:
- Energy
- Fuel combustion
- Stationary combustion
- Industrial combustion
- Residential heating
- Mobile combustion (transport)
- Fugitive emissions from (fossil) fuel use
- Industrial Processes
- Solvent and other product use
- Agriculture
- LULUCF (Land Use, Land Use Change and Forestry)
- Waste
What: the pollutants
Air emission inventories have been developed and still are being developed for two major groups of pollutants:
- Greenhouse gases:
- Carbon dioxide (CO2),
- Methane (CH4),
- Nitrous oxide (N2O) and
- A number of fluorinated gaseous compounds (HFCs, PFCs, SF6)
Air pollutants:
- Acidifying pollutants: sulphur dioxide (SO2), nitrogen oxides (NOx, a combination of nitrogen monoxide, NO and nitrogen dioxide, NO2) and ammonia (NH3),
- Photochemical smog precursors: again nitrogen oxides and non-methane volatile organic compounds (NMVOCs)
- Particulates and particulate precursors
- Toxic pollutants like heavy metals and persistent organic pollutants Carbon monoxide (CO)
Where: geographical resolution
Typically national inventories provide data summed at the national territory only. In some cases additional information on major industrial stacks (‘point sources’) is available. Stacks are also called release points, because not all emissions come from stacks. Other industrial sources include fugitive emissions, which cannot be attributed to any single release point.
Some inventories are compiled from sub-national entities such as states and counties, which can provide additional spatial resolution.
In scientific applications, where higher resolutions are needed, geographical information such as population densities, land use or other data can provide tools to disaggregate the national level emissions to the required resolution, matching the geographical resolution of the model.
When: temporal resolution
Similarly, national air emission inventories provide total emissions in a specific year, based on national statistics. In some model applications higher temporal resolutions are needed, for instance when modelling air quality problems related to road transport.
In such cases data on time dependent traffic intensities (rush hours, weekends and working days, summer and winter driving patterns, etc.) can be used to establish the required higher temporal resolution.
Inventories compiled from Continuous Emissions Monitors (CEMs) can provide hourly emissions data.