Stationary Source Control Techniques Document for Fine Particulate ...

2.4 CHARACTERIZATION OF PM 2.5 CONCENTRATIONS
Ambient samples of PM 2.5 from eight research studies are summarized in Figures 1 and 2. 4,5
The PM 2.5 samples were chemically analyzed to determine the amounts of ammonium sulfate,
ammonium nitrate, carbon, and soil present. Ammonium sulfate and ammonium nitrate are secondary
particles formed in the atmosphere from the reaction of ammonia with sulfur dioxide (SO 2) and nitrogen
oxides (NO X), respectively. Carbon and soil are primary particles. These are generally emitted
directly into the atmosphere, or generated by processes such as wind erosion, construction, or traffic on
paved or unpaved roads. The results of these analyses for eastern states are shown in Figure 1. Figure
2 summarizes the results for western states.
Figure 1 indicates that in the eastern states, PM 2.5 was dominated by ammonium sulfate
particles which accounted for 40 to 60 percent of the total mass. Ammonium nitrate particles
contributed another 5 to 15 percent. Carbon particles, from sources such as incomplete combustion,
accounted for 30 to 40 percent of the PM 2.5 mass. The fraction of soil in the eastern samples ranged
from 5 to 10 percent. 5
Figure 2 shows that only 5 to 15 percent of the PM 2.5 was ammonium sulfate, and ammonium
nitrate accounted for 1 to 35 percent of the total mass. The percentage of carbon from incomplete
combustion ranged from 35 to 65 percent of the western samples. Soil content in the western samples
contributed 5 to 15 percent of the total mass of PM 2.5. 5
The following sections of this document address techniques for reducing primary particulate
emissions from stationary combustion sources and industrial processes. As illustrated above,
secondary particles (ammonium sulfate and ammonium nitrate) comprise a large percentage of the
PM 2.5 samples in both the Eastern and Western United States. This is indicative of the need to address
emissions of sulfur dioxide, nitrogen oxides, and ammonia when considering means of reducing PM 2.5
concentrations in the future.
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