# Appendix C

Mobile Source Precursor Discussion

## PM 2.5 

## Precursors to Consider

40 CFR 93.119(f)(7) through (10) identifies the pollutants for PM 2.5 for which regional emissions analysis needs to be performed for transportation conformity purposes. These parts of the rule are listed below: §119(f)(7) – PM 2.5

in PM 2.5 areas; §119(f)(8) – Reentrained road dust in PM 2.5

areas only if the EPA [Environmental Protection Agency] Regional Administrator or the director of the State air agency has made a finding that emissions from reentrained road dust within the area are a significant contributor to the PM 2.5

nonattainment problem and has so notified the MPO and DOT [Department of Transportation]; §119(f)(9) – NO X

[nitrogen oxides] in PM 2.5

areas, unless the EPA Regional Administrator and the director of the State air agency have made a finding that emissions of NO X

from within the area are not a significant contributor to the PM 2.5

nonattainment problem and has so notified the MPO and DOT; and §119(f)(10) – VOC [volatile organic compounds], SO 2 [sulfur dioxide] and/or ammonia in PM 2.5

areas if the EPA Regional Administrator or the director of the State air agency has made a finding that any of such precursor emissions from within the area are a significant contributor to the PM 2.5

nonattainment problem and has so notified the MPO and DOT. Primary, or direct, PM 2.5 tailpipe emissions must be considered for the transportation conformity regional em issions analysis. The other precursor pollutants and re-entrained road dust only need to be considered if the State air agency and/or the EPA have deemed the pollut ant as a significant contributor to the PM 2.5 nonattainment problem. The following sections discuss the significance of the precursor pollutants and re-entrained road dust to the PM 2.5 nonattainment problem. The discussion of the significance of these precursors for the attainment demonstration is located in Section 7.2.

Nitrogen Oxides (NO X

) As EPA has not made a finding that emissions of NO X are not a significant contributor to the PM 2.5 nonattainment problem in the Birmingham area, a mobile source budget will be established. Please see Section 7.2 for a discussion of NO X as a precursor in the development of the control strategy.

Sulfur Oxides (SO X

)

The PM 2.5 precursor SO 2 could not be deemed insignificant to the overall PM 2.5 nonattainment problem since sulfate is such a large fraction of the PM 2.5 composition. However, ADEM determined that SO 2 emitted by the mobile source sector is insignificant. EPA in it s Federal Register notice for PM 2.5 does not address the mobile sector in its listing of significant sources of SO 2 emissions. ADEM agrees with the following statements addressing SO 2 from onroad mobile emissions as published in the May 6, 2005, Federal Register, 70 FR 24283:“While speciated air quality data show th at sulfate is a relatively significant component (e.g., ranging from nine to 40 percent) of PM 2.5

mass in all regions of the country, emissions inventory data and projections show that onroad emissions of SO X

constitute a ‘‘de minimis’’ (i .e., extremely small) portion of total SO X

emissions. Emissions inventory data for 1999 for the 372 potential PM 2.5

nonattainment counties for PM 2.5

(based on 1999–2001 air quality data) show that onroad sources were responsible for only two percent of total SO X emissions. Furthermore, EPA has already adopted two regulations that will greatly reduce emissions of SO X

from onroad sources by the time such regulations are both in full effect in 2009. First, in 2004 the low sulfur gasoline program began to be phased in and will be fully effective in 2007 (February 10, 2000, 65 FR 6697). This regulation will reduc e the sulfur content of gasoline by approximately 90 percent when fully effective. Second, in 2006 the low sulfur diesel program will begin to be phased in and will be fully effective by 2009 (January 18, 2001, 66 FR 5001). This regulation will reduce the sulfur content of diesel fuel by approximately 97 percent nationally when fully effective. Projections of onroad emissions of SO 2 in 2020 indicate that onroad sources will be responsible for less th an one percent of the total SO 2 emissions in 2020 in the 372 potential PM 2.5

nonattainment counties (based on 1999 – 2001 air quality data). These projections confirm that the implementation of the fuel regulations discussed above will ensure that as a general matter of SO 2 emissions from onroad sources remain at insignificant levels in all areas.” Although SO 2 is a significant component of the PM 2.5 nonattainment problem in Birmingham, the majority of the SO 2 emissions in 2009 came from the stationary point source sector. The mobile source se ctor only contributed 0.1% of the 2009 or 2012 statewide SO 2 emissions. This finding is consistent with what was stated above.

Since the mobile source SO 2 contribution is insignificant, ADEM is not establishing MVEBs for this precursor. An affirmative insignificance finding from EPA only relieves the transportation partners from a regional emissions analysis for SO 2 emissions for these areas, but does not relieve them of the other transportation conformity requirements. The transportati on partners will need to note the SO 2 insignificance finding (if found adequate and approved by EPA) in future conformity determinations.

Volatile Organic Compounds (VOC) and Ammonia (NH 3 ) The two remaining species that comprise PM 2.5 , ammonia (NH 3 ) and volatile organic carbons (VOCs), have been deemed as insign ificant contributors to the total mass of PM 2.5 by EPA. With regards to NH 3 , 72 FR 20586 states NH 3 “is presumed not to be a PM 2.5 attainment plan precursor, meaning that the State is not required to address [NH 3 ] in its attainment plan or evaluate sources of [NH 3 ] emissions for reduction measures.” Likewise, the final rule for VOCs states that “States are not required to address VOC in PM 2.5 implementation plans and evaluate control measures for such pollutants unless the State or EPA makes a technical demonstration that emissionsof VOCs from sources in the State significantly contribute to PM 2.5 concentrations in a given NAA.” ADEM agrees with EPA’s pr esumptive exclusion of NH 3 and VOCs with regards to this PM 2.5 implementation plan. Therefore, ADEM did not set MVEBs for NH 3 and VOCs in the Birmingham PM 2.5 NAA.

Road and Construction Dust The majority of the roads in the Birmingham area are paved, so there is minimal road dust due to the paved roads. The factor used to calculate re-entrained road dust on paved roads is very small. What dust is generated, has been shown in the literature, Methodology to Estimate the Transportable Fraction (TF) of Fugitive Dust Emissions for Regional and Urban Scale Air Quality Analyses, US EPA, August 3, 2005 , to be inconsequential. This fact is affirmed by the small crustal component in the PM 2.5 speciated data which measures only 7% at the North Birmingham monitoring site and only 6% at the Wylam monitoring site in 2002.

Since re-entrained road dust is no t a significant contributor to the PM 2.5 nonattainment problem, ADEM did not est ablish MVEBs for this source category.