WHAT ARE POINT, AREA, AND MOBILE SOURCES?
Air toxics are emitted from many types of sources. These sources of air pollution are generally categorized as point, area, and mobile (on-road and non-road) sources.
Point Sources: A point source is a stationary facility or process that emits a significant amount of air pollution during manufacturing, power generation, heating, incineration, or other such activity. For the National-Scale Air Toxics Assessment (NATA), USEPA calls this category "Major Sources," and included in it are just those sources which emit at least 10 tons per year of any one hazardous air pollutant (HAP), or at least 25 tons per year total of any HAPs. Major point sources include power plants; refineries; municipal waste incinerators; toxic waste transfer, storage and disposal facilities (TSDFs); large TRI sources (facilities that are required to report their emissions under the Toxic Release Inventory program); and other sources that must report emissions under other state and federal programs.
Area Sources: These are small sources of air pollution which by themselves may not emit very much, but when their emissions are added together, they account for a significant portion of the total emissions of air toxics. In NATA, USEPA refers to this category as "Area and Other Sources," and includes small industrial sources that fall below the "major source" threshold (meaning that annually they emit less than 10 tons of any one HAP or 25 tons of a combination of HAPs). Area sources are often too small or too numerous to be inventoried individually. The following are grouped under area sources in NATA:
- Industrial processes such as chromium electroplating, surface coating of cans and paper, metal parts cleaning, metal recycling, small chemical manufacturing plants, and bakeries
- Consumer products, including personal care products, household products, adhesives and sealants, automotive products, and coatings such as paints
- Residential heating and fuel use
- Pesticide use
- Gasoline stations
- Dry cleaners
- Institutional and commercial heating
Mobile Sources are divided into two categories:
- On-road mobile sources are vehicles found on roads and highways, including cars, trucks, buses, and motorcycles.
- Non-road mobile sources include aircraft, trains, lawnmowers, boats, dirt bikes, construction vehicles, farm equipment, leaf blowers, and more.
THE NATIONAL AIR TOXICS EMISSIONS INVENTORY
As part of NATA, USEPA prepares a comprehensive list of air toxics emissions for the entire country. This emissions inventory is briefly reviewed and revised by each state before being finalized by USEPA. Although there are bound to be some errors in the details of such a massive undertaking, the inventory does give us a good indication of which are the most important sources of air toxic emissions in our state. As can be seen from the pie chart below, mobile sources are the largest contributors of air toxics emissions in New Jersey, with on-road mobile sources accounting for 34%, and non-road mobile sources contributing 28%. Area sources represent 28% of the inventory. The remaining 5% of the inventory is attributable to major point sources.
Note that this pie chart does not include emissions of diesel particulate matter. For a discussion of diesel emissions, click here. The 1996 and 1999 NATA results were discussed on this website previously, and can still be accessed by clicking 1996 or 1999. However, USEPA emphasizes that the methods used to conduct emissions inventories vary somewhat from year to year, so the results are not exactly comparable.
COMPARISON OF EMISSIONS BY COUNTY
When the New Jersey emissions estimates are broken down by county, it is evident that the areas with the largest air toxic emissions are generally those with the largest population. This is directly related to high levels of vehicle use, residential fuel burning, solvent use, and other population-related types of activities in those counties.
Charts for 1996 and 1999 are available for viewing. However, USEPA emphasizes that the methods used to conduct emissions inventories vary somewhat from year to year, so the results are not exactly comparable.
POLLUTANTS WITH SIGNIFICANT BACKGROUND CONCENTRATIONS
Concentrations of some air toxics are dominated not by local emissions, but by what USEPA refers to as "background." These concentrations can be attributed to long-range pollutant transport, unidentified emission sources and past emissions. A detailed description of how USEPA came up with these "background concentrations" can be found on USEPA's NATA web site.
For eight air toxics that are of concern in New Jersey in the 2002 NATA, USEPA estimated background concentrations that are higher than their respective health benchmarks. These pollutants are:
Acetaldehyde
Arsenic compounds
Benzene
1,3-Butadiene
Carbon tetrachloride
Chloroform
Formaldehyde
Methyl chloride
To gain a better understanding of the significance of these background concentrations, we have compared the percent contribution of each source category (major, area, on-road mobile and non-road mobile, plus background) to the total statewide average risk ratio. In the table below, you can see that background contributes 100% of the predicted risk from carbon tetrachloride, which is no longer in use and therefore no longer emitted in the state. Concentrations of methyl chloride and arsenic compounds are also primarily background, and not emissions.
Source Category Contribution to Statewide Risk Ratios (Based on 2002 NATA)
1999 Emissions Inventory Information
1996 Emissions Inventory Information
back
to top
|