3.0 Affected Environment - Knik Arm Bridge and Toll Authority

Knik Arm Crossing DraftFinal EIS
Affected Environment
3.5.1 Air Quality
The Anchorage area is currently designated as meeting the National Ambient Air Quality
Standards (NAAQS) for four of the six criteria pollutants. The NAAQS are summarized in
Table 3-13. Note that two forms of particulate matter are regulated: particles less than or
equal to 10 microns in diameter (PM 10 ) and particles less than or equal to 2.5 microns in
diameter (PM 2.5 ). The only “nonattainment” area with respect to the NAAQS in the
Anchorage vicinity is in Eagle River, located approximately 10 miles northeast of
Anchorage. Airborne concentrations of lead (Pb), sulfur dioxide (SO 2 ), ozone (O 3 ), and
nitrogen dioxide (NO 2 ) are currently below the established NAAQS for each of these
pollutants. The Anchorage area is designated a maintenance area for carbon monoxide (CO).
While concern over CO emissions has generally decreased nationwide, there has been a
greater concern over so-called mobile source air toxics (MSATs) on some large highway
projects in recent years. MSATs of greatest concern from motor vehicles include benzene,
toluene, and other organic compounds that are emitted from vehicle exhausts when there is
incomplete combustion of all fuel components. While concern over MSATs has been rising,
emissions of these compounds have probably fallen substantially over the past several
decades, as CO emissions have fallen. There are no good long-term measurements to
demonstrate this, but the same techniques of more complete combustion and catalytic
oxidation that are being used to reduce CO emissions would also tend to reduce MSAT
emissions.
The EPA is the lead Federal Agency for administering the Clean Air Act and has certain
responsibilities regarding the health effects of MSATs. The EPA issued a Final Rule for the
Control of Hazardous Air Pollutants from Mobile Sources (Source: Federal Register,
February 26, 2007). This rule was issued under the authority in Section 202 of the Clean Air
Act. In its rule, EPA examined the impacts of existing and newly promulgated mobile source
emission control and fuel quality programs on emissions of MSATs, including the final rule
referenced above. Between 1999 and 2030, EPA projects that even with an 88 percent
increase in VMT, these control programs will reduce on-highway emissions MSATs (not
including diesel PM) by approximately 60 percent
3.5.1.1 Climatic conditions
The winter climate of Anchorage with its relative lack of sunshine and its cold climate,
promotes surface temperature inversions. These inversions tend to limit vertical mixing of
the atmosphere near the ground and, because of the higher terrain surrounding most of
Anchorage, keep emissions trapped near the ground. Also, during periods of cool
temperatures and light winds, cold air tends to drain like a fluid into lower areas. Given these
forcing factors, air quality impact analysis of CO emissions from vehicles and other nearsurface
sources is generally focused on wintertime conditions.
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