Appendix O: 

Insignificance of 

NH3 and VOCs to 

PM2.5 Attainment in North Carolina 
Insignificance of NH3 and VOCs to PM2.5 Attainment in North Carolina 

The Hickory And Greensboro-Winston Salem-High Point, NC PM2.5 Appendix O 

North Carolina Attainment Demonstration August 21, 2009 

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Insignificance of NH3 and VOCs to PM2.5 Attainment in North Carolina 

The Hickory And Greensboro-Winston Salem-High Point, NC PM2.5 Appendix O 

North Carolina Attainment Demonstration August 21, 2009 

1

1 Significance of Precursors Contributing to Fine Particulate Formation 

The United States Environmental Protection Agency (USEPA) revised the National Ambient Air 

Quality Standards (NAAQS) for particulate matter in 1997 establishing fine particulates 

(particulate matter with aerodynamic diameter ≤ 2.5 micrometers or PM2.5) as a benchmark. 

The revised NAAQS for particulate matter set a daily standard of 65 μg/m3

 and an annual 

standard of 15.0 μg/m3

. The daily PM2.5 standard was more recently revised in 2006 by 

lowering it to 35 μg/m3 based on a review of the air quality criteria and the NAAQS, but the 

annual PM2.5 standard was retained at 15.0 μg/m3. Both of these revisions to the NAAQS for 

particulate matter are published in 40 CFR 50.7 and 40 CFR 50, Appendix N. 

Areas designated as “nonattainment” for fine particulates by the USEPA must submit formal 

implementation plans detailing how attainment will be met as outlined in the Clean Air Act 

(CAA). These implementation plans must outline the measures that will be taken to curtail the 

concentrations of various pollutants that are assumed to have significant contributions to fine 

particulate nonattainment, including sulfur dioxide (SO2), nitrogen oxides (NOx), and PM2.5. 

The USEPA, in 72 FR 20586, requires states to “evaluate and consider control strategies for 

sources of SO2, direct PM2.5, and NOx emissions in all nonattainment areas.” However, the rule 

does allow states to make technical demonstrations to reverse the inclusion of NOx as precursor 

of PM2.5, or deem the precursor insignificant, based on geographical regions, emissions, etc. 

This then eliminates the need to examine NOx control measures for purposes of reducing PM2.5 

concentrations. Although NOx is a relatively minor precursor of PM2.5 in North Carolina, the 

State of North Carolina is foregoing a technical demonstration of NOx insignificance and will 

follow the requirements in 72 FR 20586 to include NOx as a precursor for addressing attainment 

of the 1997 and 2006 revisions of the PM2.5 NAAQS. 

The two remaining species that comprise PM2.5, ammonia (NH3) and volatile organic carbons 

(VOCs) have been deemed as insignificant contributors to the total mass of PM2.5 by the 

USEPA. With regards to NH3, 72 FR 20586 states NH3 “is presumed not to be a PM2.5 

attainment plan precursor, meaning that the State is not required to address [NH3] in its 

attainment plan or evaluate sources of [NH3] emissions for reduction measures.” Likewise, the 

final rule for VOCs states that “States are not required to address VOC in PM2.5 implementation 

plans and evaluate control measures for such pollutants unless the State or EPA makes a 

technical demonstration that emissions of VOCs from sources in the State significantly 

contribute to PM2.5 concentrations in a given nonattainment area.” 

2 NH3 and VOC Insignificance 

The State of North Carolina agrees with the USEPA’s presumptive exclusion of NH3 and VOCs 

with regards to the PM2.5 implementation plan. Therefore, emission controls for NH3 and 

VOCs are not considered as a part of the North Carolina Division of Air Quality’s (NCDAQ’s) 

PM2.5 attainment demonstration plan.