Middlesex County Average 1999 NATA Modeled Air Concentrations Compared to Health Benchmarks
Pollutant
Modeled
Air Concentration (ug/m3)
Health
Benchmark (ug/m3)
Risk
Ratio
%
Contribution from
Major Sources
Area
Sources
On-road
Mobile Sources
Nonroad
Mobile Sources
Background
Acetaldehyde
2
0.45
4
3%
4%
55%
9%
28%
Acrolein
0.1
0.020
7
0.2%
23%
58%
19%
0%
Arsenic Compounds
0.00008
0.00023
0.3
10%
90%
0%
0%
0%
Benzene
2
0.13
12
0.9%
10%
47%
14%
28%
Bis(2-ethylhexyl)phthalate
2
0.42
4
0.06%
0.2%
0%
0%
100%
1,3-Butadiene
0.2
0.033
5
0.1%
3%
36%
14%
46%
Cadmium Compounds
0.00008
0.00024
0.3
15%
84%
0%
0.5%
0%
Carbon Tetrachloride
0.3
0.067
4
0.01%
0.4%
0%
0%
100%
Chloroform
0.1
0.043
3
0.4%
61%
0%
0%
39%
Chromium (hexavalent form)
0.0002
0.000083
3
46%
48%
6%
0.2%
0%
1,4-Dichlorobenzene
0.06
0.091
0.7
7%
93%
0%
0%
0%
1,3-Dichloropropene
0.1
0.25
0.5
0%
100%
0%
0%
0%
Diesel Particulate Matter
2
0.0033
568
0%
0%
43%
57%
*
Ethylene Dibromide
0.03
0.0017
19
0.08%
0.007%
0%
0%
100%
Ethylene Dichloride
0.05
0.038
1.2
0.7%
0.1%
0%
0%
99%
Ethylene Oxide
0.008
0.011
0.7
75%
25%
0%
0%
0%
Formaldehyde
2
0.077
26
2%
4%
36%
13%
45%
Methyl Chloride
1
0.56
2
0.04%
0.5%
0%
0%
99%
Naphthalene
0.09
0.029
3
2%
72%
21%
5%
0%
Nickel Compounds
0.002
0.0064
0.3
5%
92%
3%
0.5%
0%
Perchloroethylene
0.3
0.17
1.5
0.7%
48%
0%
0%
51%
1,1,2,2-Tetrachloroethane
0.07
0.017
4
0.5%
0.2%
0%
0%
99%
Chemicals with risk ratios greater than or equal to 1 are
in bold.
Risk Ratios in italics are based on noncarcinogenic effects.
The symbol ug/m3 is micrograms per cubic meter,
the amount (in micrograms) of a chemical in a cubic
meter of air. This is also known as a concentration.
* For diesel particulate matter, onroad and nonroad
concentrations include a model-estimated background
concentration.
