POLLUTANTS WITH SIGNIFICANT BACKGROUND CONCENTRATIONS
For six of the 1999 air toxics of concern in New Jersey,
NATA predicts air concentrations that are higher than
their respective health
benchmarks even without local emissions from within
New Jersey. These six pollutants are:
Benzene
|
Ethylene
dibromide
|
|
Carbon
tetrachloride
|
Ethylene
dichloride
|
|
Chloroform
|
Formaldehyde
|
For these pollutants, USEPA assumed a constant background
concentration for the whole country. For the purposes
of the NATA study, "background" represents air
toxic concentrations resulting from emissions from past
years (persistence), and long-range transport from distant
sources.
Comparing the background concentrations of these pollutants
to their health benchmarks results in risk
ratios greater than one. This is shown graphically
in Figure 1.
Figure 1: Risk Ratios of Background
Concentration Over Health Benchmark
To gain a better understanding of the significance of
these background concentrations, we have compared the
percent contribution to total air concentration from background
to the percent contribution from New Jersey major
point, area,
on-road
mobile and non-road
mobile sources. This distribution is shown in Figure
2.
Figure 2: Source Category Contributions
to Overall Concentrations
From Figure 2, you can see that background is responsible
for 100% of the predicted concentrations of carbon tetrachloride
and ethylene dibromide, and over 90% of the predicted
concentration of ethylene dichloride. For the other three
pollutants, there are also significant contributions from
other source categories. The biggest contribution to the
total benzene concentration comes from the on-road mobile
source category, with smaller contributions from all of
the other source categories. Chloroform comes mainly from
background, but about 10% of the predicted air concentration
comes from major point sources and 10% from area sources.
For formaldehyde, the biggest contribution is from non-road
sources, followed closely by on-road sources. Area sources
and background contribute smaller amounts.
Figure 3 again shows the risk ratios for these six pollutants,
but also shows the amounts attributed to different sources.
Figure 3: Source Category Contributions
to Risk Ratios
Comparing this graph to Figure 1, we can see that the
total risk ratios for carbon tetrachloride, ethylene dibromide
and ethylene dichloride do not change much when other
sources are added to Background. However, the benzene
and formaldehyde risk ratios do increase substantially.
The emissions from these two pollutants will require multiple
control stategies if the risk ratios in the state are
to be reduces. For the other four Background pollutants,
there is little that New Jersey can do locally to reduce
the general exposures experienced in this state.
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