Why group pollutants? 

Because there are many compounds that are used to calculate toxic risk, it is often useful to group them together. Grouping all of the modeled risk components together provides an estimate of the total risk. Because not all sources and compounds are currently included in the risk analysis, this is still a very rough estimate.

The list of compounds, immediately below, shows the three basic subgroupings of compounds that contribute to the current total risk estimates. Currently, the compound list includes many of the important contributors to inhalation cancer risk, but more compounds will be included in the future, as necessary, to improve the risk estimates.

The first compound grouping consists solely of compression ignition diesel, which is the dominant risk producing component included in the current analysis. The risk for this component is unique, in that it is derived by applying a risk factor to the nonspeciated PM10 component of the compression ignition diesel exhaust.

The remaining two groups of compounds, particulate matter less than 10 microns (PM10) derived compounds, and total organic gas (TOG) derived compounds, are placed into those groups based upon whether they normally occur in a solid state (PM10) or a gaseous (TOG) state. For these compounds, risk is determined by applying individual risk factors to each speciated compound (e.g., arsenic).

Partial list of compounds used in risk analysis: 

1. Compression ignition diesel exhaust (nonspeciated particulate matter)

2. Partial list of compounds from particulate matter less than 10 microns (PM10)

• Arsenic
• Cadmium
• Chrome
• Lead
• Nickel

3. Partial list of compounds from total organic gases (TOG):

• 1,3-butadiene
• Acetaldehyde (including secondary)
• Benzene
• Methylene chloride (dichloromethane)
• Ethylene oxide
• Formaldehyde (including secondary)
• Methyl tertiary butyl ether
• Paradichlorobenzene
• Perchloroethylene
• Trichloroethylene

Press Here for Complete List of Compounds

 

Total nondiesel risk: 

Once the PM10 and TOG speciated compound risks were determined, all of the individual compound risks were summed. This risk estimate represents the total risk (for the pollutants and categories included in this modeling run) that is not due to compression ignition diesel. 

Compression ignition diesel risk (nonspeciated diesel PM10): 

Compression ignition diesel cancer inhalation risk is calculated by multiplying the risk factor for this component by the nonspeciated (i.e., not broken down into separate chemical components such as arsenic or benzene) modeled concentration of PM10 for this component. This component dominates the risk picture for many locations throughout the modeled regions. This is due to the combination of a substantial amount of emissions in the inventory and the relatively high unit risk factor assigned to compression ignition diesel, making it a logical component to break out separately into its own group.

Total risk (combined diesel + nondiesel): 

The total risk was calculated by adding the diesel and total nondiesel risk. To avoid double counting of compression ignition diesel risk, the compression ignition diesel component is not speciated, and is, therefore, not included in the nondiesel summed compound totals.