treasure valley road dust study: final report - ResearchGate

5. EMISSIONS INVENTORIES FOR THE TREASURE VALLEY
In this chapter, we summarize the steps taken to calculate the road dust emissions
inventories for the year 2000. Specific inventories for two episodes that correspond to periods of
air quality concern are also presented. Those episodes are January 1 – 9, 1991 and December 20
– 26, 1999.
We begin with a discussion of the methodology for calculating paved road emissions in
section 5.1. Section 5.2 addresses unpaved road emissions calculations. The results of the
emissions inventories for the Treasure Valley are summarized in 5.3 and compared to the
emissions inventory prepared by SAI (1997) as well as emissions based on siltsamples that were
obtained as part of this study. Complete listings of the emissions inventories for year 2000,
future years, and episodic periods are provided in electronic format as an appendix to this report
(See Appendix C for a description of file contents).
5.1 Emissions inventory for paved roads
Emissions inventories for paved roads were carried out in several steps. First, link-level
emissions potentials were calculated based on roadway characteristics that were available from
the Traffic Demand Model as well as road location and setting. Next, emissions were calculated
for paved roads under dry conditions, i.e. in the absence of precipitation. Results from the
TRAKER portion of the study were used to estimate both PM 10 and PM 2.5 emissions. Finally, a
correction was applied to account for the effect of precipitation on the emissions of road dust.
Meteorological information cited here is only intended for road dust emissions calculation
purposes. For a more thorough review of historical precipitation and wind conditions in the
Treasure Valley, please see the document attached as Appendix B to this report.
5.1.1 Year 2000 Paved roads
5.1.1.1 Emissions potentials
For a given length of road, the emissions factor, EF, in grams per vehicle kilometer
traveled ([g/vkt]) can be expressed as:
EF ? bs
Eq (5-1)
where b is the emissions potential in grams per vehicle kilometer traveled per meter per second
[g/vkt/mps] and s is the speed of the vehicles traveling on the length of road in meters per second
([mps]) and can be expressed as:
b
? x
? C C , S , T
? s
Eq (5-2)
where C C,S,T is a constant that depends on the county the road is in (Ada or Canyon), the setting
of the road (rural or urban), and time of year (season), s is the vehicle speed, and x is an
empirically-derived exponent. The emissions potential is a measure of the road “dirtiness” while
the emissions factor is a measure of how much dust is emitted from a road when vehicles travel
the road at a certain speed. Emissions potentials,emissions factors, and Equations 5-1 and 5-2
were discussed in Section 4; the results of that work are recapped as part of the two subsections
that follow.
5-1