LADCO Ozone Precursor Emissions Review Task Force Project

LADCO Ozone Precursor Emissions Review Task Force Project

Background

Starting in June 2026 LADCO launched a structured technical effort to support member state decisions on nitrogen oxide (NOx) and volatile organic compound (VOC) emissions controls for key source sectors. Ground-level ozone remains the most challenging air quality standard for LADCO member states. Several nonattainment areas in the region face a deadline to demonstrate attainment with the 2015 ozone National Ambient Air Quality Standard (NAAQS). Meeting that standard will require additional NOx and VOC reductions beyond what currently adopted measures will deliver.

LADCO’s Technical Oversight Committee (TOC) has identified a set of priority emissions sectors where controls may offer meaningful reductions. To evaluate those options rigorously, LADCO is establishing sector-specific task forces composed of agency staff from the Ozone Technical Workgroup (O3TWG). The task forces will assess emissions data, review available control measures, and develop recommendations for state consideration.

Each task force will complete four interconnected tasks on the selected emissions sectors:

  • Emissions inventory review. Assess the reliability and magnitude of National Emissions Inventory (NEI) data for the sector in the LADCO region.
  • Control options review. Catalogue available control measures from the U.S. Environmental Protection Agency (EPA), California Air Resources Board (CARB), Ozone Transport Commission (OTC), and peer states.
  • State applicability analysis. Identify which control options are most applicable to LADCO member states, considering regulatory feasibility, adoption status, emissions reduction potential, and control costs.
  • Recommendations. Synthesize findings into a tiered set of recommendations for state consideration, noting confidence levels and data gaps.

This page documents the work of the task forces and centralizes the materials used and created by the task forces in their review of the emissions sectors.

Phase 1: June – September 2026

Sectors

Task Force Membership

Medium and Heavy Duty Diesel Vehicles (MHDV)

MD/HD diesel vehicles are the single largest anthropogenic nitrogen oxide (NOx) source in the LADCO region, accounting for 14.5% of regional anthropogenic NOx from long-haul combination trucks alone and roughly 40% of on-road NOx when all diesel MD/HD truck types are combined. In every nonattainment area designated under the 2015 O3 NAAQS, diesel highway vehicles rank first or among the top NOx sources. Achieving further regional NOx reductions will require controls on this sector.

The task force has four specific objectives:

  • Assess the reliability of the 2022 National Emissions Inventory (NEI) for MD/HD diesel trucks in the LADCO region, including known methodological limitations and comparison to EMFAC-based estimates.
  • Catalogue available control measures for this sector, drawing on EPA, California Air Resources Board (CARB), Ozone Transport Commission (OTC), and peer state programs. Characterize achievable emission reductions, cost-effectiveness, and implementation mechanisms.
  • Evaluate the applicability of control measures to LADCO member states, considering current adoption status, legal and regulatory feasibility, magnitude of potential NOx and VOC reductions, and interaction with federal programs.
  • Develop tiered control measure recommendations with supporting rationale and confidence assessment, suitable for use by member state agencies in SIP planning and regulatory development.

MHDV Resources

Meetings

DateDescriptionResources
June 25, 2026Kickoff CallSlides

Natural Gas Internal Combustion Engines (NG ICE)

The NG ICE sector covers three distinct equipment categories: (1) reciprocating internal combustion engines (RICE), both lean-burn and rich-burn types, used in industrial, commercial/institutional, and electric generation applications (3,047 t/yr NOx from 20xxxxxx SCCs, 2022v1 NEI); (2) gas turbines used for electric generation and industrial drives; and (3) natural gas pipeline compressor stations, the largest sub-sector at 20,135 t/yr NOx (NAICS 486210, 2022v1 NEI). Combined, these categories total approximately 23,182 t/yr NOx LADCO-wide. When pipeline compressors are included, Ohio becomes the largest state contributor (7,638 t/yr pipeline + 367 t/yr ICE = 8,005 t/yr), followed by Michigan (5,251 t/yr), Illinois (5,219 t/yr), and Minnesota (2,646 t/yr). Key within-NAA concentrations include Chicago, IL (592 t/yr pipeline + 520 t/yr ICE = 1,112 t/yr combined), Detroit, MI (421 + 254 = 675 t/yr), and Ohio NAAs combined (~1,349 t/yr pipeline + ~90 t/yr ICE).

Achieving further regional NOx reductions from this sector requires understanding the federal regulatory floor established by RICE MACT (40 CFR Part 63 Subpart ZZZZ) and NSPS (40 CFR Parts 60 GGGa and OOOOb), characterizing the sources and facilities that remain above that floor, and evaluating which additional controls are technically, economically, and legally achievable for LADCO member states to require.

The task force has five specific objectives:

  • Assess the reliability of the 2022 NEI for NG ICE in the LADCO region, including known data gaps (particularly pipeline compressor stations), sub-sector characterization, and the relationship between the NEI point source inventory and RICE MACT/NSPS compliance baselines.
  • Catalogue available control measures for this sector, for both NOx (DLN combustion modification, SCR, NSCR, ULNB, water injection) and VOC/formaldehyde (oxidation catalysts, combustion efficiency improvements), characterizing achievable reductions, cost-effectiveness, applicable engine types, and implementation mechanisms.
  • Quantify formaldehyde (HCHO) and reactive VOC emissions from NG ICE sources using two complementary methods: (1) EPA SPECIATE database speciation profiles applied to inventoried VOC by source classification code; and (2) HCHO-to-CO mass emission ratios applied to CO inventory data (Olaguer et al. 2023, Atmosphere 14:461). Mass ratios by source category: landfill gas ICE  at 15%, industrial engines at permitted facilities at 10%, flares at 5%, other combustion at 2%. These two methods provide complementary estimates, the VOC-based approach draws on the HCHO fraction of the speciated VOC inventory; the CO-based approach is applicable where CO is inventoried separately and can serve as an independent check or fill gap where VOC is unreliable.
  • Evaluate the applicability of control measures to LADCO member states, considering the existing federal regulatory baseline, source mix by state, APTE threshold screening, magnitude of achievable surplus reductions, and legal/regulatory feasibility for state SIP programs.
  • Develop tiered control measure recommendations with supporting rationale and confidence assessment, suitable for use by member state agencies in SIP planning and regulatory development.

NG ICE Resources

Meetings

DateDescriptionResources
July 2, 2026Kickoff CallSlides | Inventory Spreadsheet

Gasoline Small Offroad Engines (SORE)

SORE is the largest single source of volatile organic compound (VOC) emissions in the LADCO nonroad sector. The 2022v1 LADCO emissions inventory shows a LADCO-wide baseline of 73,714 t/yr VOC and 14,434 t/yr NOx from this sector, with an estimated reduction potential of 54,548 t/yr VOC (−74%) and 8,949 t/yr NOx (−62%) if LADCO states were to adopt California Air Resources Board (CARB) SORE regulations. In every LADCO-region nonattainment area designated under the 2015 O3 NAAQS, SORE is a top-two VOC source, and VOC reductions from this sector matter for ozone attainment in most member state SIPs.

The task force’s first obligation is to establish whether the underlying inventory and control estimates are reliable enough to serve as a SIP planning basis. SORE emissions are modeled entirely from equipment population estimates, and the 2022v1 baseline uses MOVES3 national default values that have not been updated with state-specific data. The CARB regulation itself has evolved since Ramboll completed its Phase I analysis: the rule was finalized in 2021, and the battery-electric outdoor power equipment market has expanded substantially. The task force must validate both the inventory and the control estimates before any state can use them in a SIP submission.

The task force has four specific objectives:

  • Assess the reliability of the 2022 NEI for SORE in the LADCO region, including the adequacy of MOVES3 national default equipment populations, identification of any state-specific data that could improve county-level estimates, and explicit uncertainty characterization for the planning baseline.
  • Catalogue available control measures for this sector, including the CARB SORE regulation (Phase 1 ICE standards and Phase 2 zero-emission mandate), fleet modernization and electrification programs, green procurement policies, and local ordinances. Evaluate achievable emission reductions, cost-effectiveness, and implementation pathways against the current (finalized 2021) CARB rule text.
  • Evaluate the applicability of control measures to LADCO member states, considering CARB opt-in legislative feasibility, current fleet characteristics, NAA-specific VOC and NOx needs, SIP credit timeline under different adoption scenarios, and voluntary measures independent of CARB adoption.
  • Develop tiered control measure recommendations with supporting rationale and confidence assessment, suitable for use by member state agencies in SIP planning and regulatory development.

SORE Resources

Meetings

DateDescriptionResources
July 1, 2026Kickoff CallSlides | Questionnaire | Profile Dashboard

Metallurgic Sources (Metals)

The Metals task force addresses NOx emissions from metallurgical coke manufacturing and integrated iron and steel manufacturing, which together account for approximately 10,739 t/yr NOx in the LADCO 2022v1 inventory, the largest non-EGU stationary source sector in the region. Unlike the other task force sectors, metallurgic sources face a threshold data quality challenge: 93 of 108 emission units show CE=0% with no existing controls listed in the 2022v1 inventory, representing 8,696 t/yr — 81% of the LADCO metallurgical total. The Ramboll (2022) Non-EGU NOx White Paper explicitly flagged this as a controls data reliability concern. Before feasibility analysis can proceed with confidence, states must verify current permit conditions at priority facilities.

The objectives of this task force are:

  • Controls Data Verification: Conduct permit record review at major metallurgical facilities to determine which CE=0% units have no controls versus those with controls not captured in the 2022v1 inventory.
  • Inventory Correction: Update the LADCO NOx controls analysis with verified CE values and recalculate surplus reduction estimates.
  • State Applicability and Regulatory Pathways: Assess the regulatory pathway (RACT rulemaking, permit revision, consent order, voluntary agreement) and timeline feasibility for requiring new NOx controls at priority facilities in each state relative to the 2029 attainment date.
  • Finalized Control Feasibility Assessment: Compile confirmed control feasibility and cost-effectiveness findings and prepare the deliverable for presentation to the O3TWG committee.

Metals Resources

Meetings

DateDescriptionResources
June 29, 2026Kickoff CallSlides | Inventory Spreadsheet

Other Applicable Resources