Predicted Levels Compared to Monitoring Data

NJDEP measures outdoor concentrations of air toxics at four monitoring sites in New Jersey. They are located in Camden, Elizabeth, New Brunswick, and Chester. The Camden site has been measuring several toxic volatile organic compounds (VOCs) since 1989. The Elizabeth site began measuring VOCs in 2000, and the New Brunswick and Chester sites became operational in July 2001.  Also in July 2001, analysis for toxic metals began at all four sites.  Air toxics monitoring data summaries can be found in the annual NJDEP Air Quality Report, under “Air Toxics Summary” and “Appendix B – Fine Particulate speciation Summary.”   Some results are discussed below.

NJDEP Air Toxics Monitoring Sites


One way to determine whether the air toxics concentrations predicted by USEPA’s National-Scale Air Toxics Assessment (NATA) are reasonable is to compare them with actual monitoring data. For a number of chemicals of concern, data from the four NJDEP monitoring sites were compared with the modeled concentrations predicted by the 2017 AirToxScreen at the corresponding census tracts. The comparisons are shown in the graph below.  It appears from this analysis that the agreement between the predicted and monitored concentrations is remarkably good for most of the chemicals.  Modeling predictions are dependent on many variables, any of which can vary from the actual conditions, and many of which can not be accounted for.  The results produced by the modeling depend on emission estimates for stationary, area, and mobile sources, meteorological conditions, and how well the dispersion model represents what happens in reality.


The graphs below show the ambient air concentrations for five air toxics that have been monitored in New Jersey over the years. Benzene, 1,3-butadiene, formaldehyde and acetaldehyde are pollutants of concern in New Jersey, meaning that their air concentrations exceed their health benchmarks.

Benzene is emitted from many different types of sources, but primarily from mobile sources. It is a major component of gasoline. It is widely used as a solvent, and as a starting material in the production of numerous other chemicals. It ranks in the top 20 in production volume for chemicals produced in the U.S., although its use in consumer products (glues, paints, furniture wax, detergents) has been decreasing significantly. It is a known human carcinogen.
1,3-Butadiene primarily comes from on-road mobile sources (cars, trucks), so it is not surprising to see higher levels at the Elizabeth monitoring site, which is located next to the New Jersey Turnpike. Other uses include the production of rubber and plastics. Although the overall trend in the air concentration from 1994 has been downward, levels measured at every site except Chester (in rural Morris County) still tend to be above the health benchmark. 1,3-butadiene is classified as probably causing cancer in humans.
Formaldehyde air concentrations are affected by direct emissions, and by formation from the interaction of other pollutants. Formaldehyde is emitted during the production and use of household goods (such as cosmetics, cleaning products, and manufactured wood products) and industrial chemicals, and sources of combustion (such as cigarette smoke, gas cookers, fireplaces, and of course, automobile exhaust). The graph shows that formaldehyde concentrations haven’t changed much in the recent past, and aren’t even very different in urban and rural areas. Levels are above the health benchmark. Formaldehyde is classified as a probable human carcinogen. (Note that there is no data point for 2003 in Camden because of a monitoring instrument malfunction.)
Acetaldehyde is emitted from mobile sources and other combustion sources, but much of the ambient concentration comes from atmospheric transformation, by which a pollutant is formed secondarily from other pollutants in the air. Although levels have been decreasing in New Jersey, they are still above the health benchmark.