Diesel Emissions
Diesel engines emit a complex mixture of air pollutants, composed of both solid and gaseous material. The visible emissions you can see in diesel exhaust are known as particulate matter. These include many carbon particles (also called soot), as well as gases that become visible as they cool. Diesel particulate matter (diesel PM) has been identified as having the potential to cause cancer, as well as many other adverse health effects. In addition to particulate matter, emissions from diesel-fueled engines include over 40 other cancer-causing substances.
The major sources of diesel PM are on-road and off-road vehicles powered by diesel engines. In addition to cars, trucks, and buses, diesel engines are used in construction vehicles, agricultural equipment, trains, and marine vessels. Diesel engines are also used to generate electricity on both an emergency and routine basis, and are also found on cranes, drilling equipment, and portable pumps.
There are hundreds of diesel engines in New Jersey (and many more around the country) that are used to produce power for small-scale operations or are kept to generate electricity in an emergency. Emissions from these diesel engines are not accounted for in USEPA’s diesel PM inventory, but these numerous small sources can contribute significant amounts of pollutants to the air that we breathe. As the larger non-emergency engines apply for or renew New Jersey Air Pollution Control Permits, they are being required to include particulate control measures and/or cleaner fuel in their operations.
DIESEL PM HEALTH RISK AND THE 2020 AirToxScreen RESULTS
NJDEP evaluated the health risk from diesel PM in ambient air based on concentrations that were estimated by USEPA for the AirToxScreen. Throughout the state, the cancer risk from exposure to diesel PM exceeds the one in a million risk level. Average estimated risk ranged from a high of 174 in a million in Hudson County, to a low of 27 in a million in Sussex County. The statewide average risk is 72 in a million.
| 2020 Air ToxScreen Diesel Particulate Risk | |||||
|---|---|---|---|---|---|
| Modeled Mean Air Concentration (µg/m3) | Cancer Risk Ratio | Cancer Risk Ratio Range | % Contribution by Source Category | ||
| Mobile On-Road Sources | Mobile Non-Road Sources | ||||
| Statewide | 0.24 | 72 | 18 - 767 | 41 | 58 |
| Atlantic | 0.10 | 30 | 22 - 245 | 37 | 63 |
| Bergen | 0.39 | 119 | 43 - 260 | 36 | 64 |
| Burlington | 0.19 | 56 | 21 - 96 | 47 | 52 |
| Camden | 0.26 | 79 | 29 - 678 | 40 | 57 |
| Cape May | 0.10 | 32 | 22 - 171 | 19 | 81 |
| Cumberland | 0.11 | 32 | 22 - 78 | 37 | 63 |
| Essex | 0.39 | 119 | 76 - 262 | 41 | 58 |
| Gloucester | 0.19 | 58 | 30 - 111 | 39 | 60 |
| Hudson | 0.57 | 174 | 125 - 767 | 35 | 62 |
| Hunterdon | 0.16 | 49 | 32 - 89 | 60 | 39 |
| Mercer | 0.22 | 67 | 42 - 80 | 53 | 46 |
| Middlesex | 0.27 | 82 | 48 - 550 | 49 | 50 |
| Monmouth | 0.18 | 53 | 34 - 140 | 33 | 67 |
| Morris | 0.18 | 54 | 26 - 88 | 46 | 54 |
| Ocean | 0.13 | 38 | 21 - 55 | 33 | 67 |
| Passaic | 0.31 | 94 | 26 - 137 | 35 | 65 |
| Salem | 0.15 | 45 | 29 - 73 | 36 | 64 |
| Somerset | 0.23 | 69 | 36 - 113 | 51 | 49 |
| Sussex | 0.09 | 27 | 18 - 50 | 50 | 50 |
| Union | 0.33 | 101 | 65 - 207 | 45 | 54 |
| Warren | 0.15 | 46 | 23 - 79 | 70 | 30 |
| Cancer health benchmark = 0.0033 µg/m3 | |||||
| Note: In some counties, on-road and nonroad source contributions do not add up to 100% because of point source contributions. | |||||
For the 2020 AirToxScreen, the maximum cancer risk caused by diesel particulate matter is 759 in a million. In 2019, the maximum risk was 339 in a million. However, in 2020 there are only 10 census blocks with cancer risks greater than 339 in a million. The highest risk driver is nonroad (point) railyards in all census blocks with high diesel PM risk.
CARCINOGENICITY OF DIESEL PM
The International Agency for Research on Cancer (IARC) considers diesel engine exhaust to be “carcinogenic to humans.”
For more diesel information from IARC click here.
USEPA did not present quantified diesel cancer risk with any of the AirToxScreen results because in their “Health Assessment Document for Diesel Engine Exhaust” (May 2002; EPA/600/8-90/057F) they concluded that the available data were not sufficient to develop a confident estimate of cancer potency (i.e., unit risk estimate or URE). However, USEPA acknowledges that: diesel particulate matter is likely to be carcinogenic to humans through inhalation; several human epidemiology studies link increased lung cancer to diesel exhaust; and exposures in several of these epidemiology studies are in the same range as ambient exposures throughout the United States. USEPA also states that “an exploratory risk analysis shows that environmental cancer risks possibly range from 10-5 to nearly 10-3.” If diesel emissions had been factored into USEPA’s latest AirToxScreen cancer risk assessment, they would have contributed the greatest relative cancer risk.
For more diesel information from USEPA, see Diesel Fuel Standards.
In 1990, California identified diesel exhaust as a chemical known to cause cancer under its Proposition 65. In 1998, particulate emissions from diesel-fueled engines was added to the California Air Resources Board list of Toxic Air Contaminants. California’s Office of Environmental Health Hazard Assessment (OEHHA) subsequently developed a unit risk factor for use in quantifying cancer risk for its Air Toxics Hot Spots Program. The OEHHA “Technical Support Document for Describing Available Cancer Potency Factors” (see below), gives an estimated range of lung cancer risk of 1.3 x 10-4 to 1.5 x 10-3 per ug/m3, with a “reasonable estimate” of 3 x 10-4.” This “reasonable estimate” unit risk factor is used by NJDEP to estimate cancer risk for diesel PM from the AirToxScreen. In the table above, it has been converted to a “Cancer Health Benchmark” that is equal to the air concentration that gives a one in a million cancer risk (0.0033 ug/m3).
For more diesel information from California, see: California’s Diesel web page