Air Quality & Emissions¶
Duluth-Superior Emissions Analysis¶
The air quality analysis for Duluth-Superior examines emissions from all port-related sources — ocean-going vessels at berth, port equipment, harbor craft, and the MERC coal terminal — and their impact on ambient air quality in surrounding communities.
The 97/3 Insight
The port's Climate Action Plan reveals that Scope 3 vessel emissions account for 97.4% of total port-attributable CO₂. Scope 1+2 (port equipment + electricity) contribute only 1,097 tonnes — less than 3% of the 43,247 tonne total. Shore power deployment is where the real emissions impact lives.
View Live Air Quality Dashboard →
Data Sources¶
| Source | Publisher | Data Provided | Access |
|---|---|---|---|
| AirNow / AQS | EPA | Real-time and historical PM2.5, PM10, ozone, SO₂, NO₂ from regulatory monitors | aqs.epa.gov |
| MPCA Air Monitoring | MN PCA | State-operated monitor data for Duluth-WDSE and West Duluth stations | mpca.state.mn.us |
| National Emissions Inventory | EPA | Port-area emissions from mobile and stationary sources | epa.gov/air-emissions-inventories |
| Toxics Release Inventory (TRI) | EPA | Facility-level chemical releases | epa.gov/toxics-release-inventory-tri-program |
| AIS Vessel Data | MarineCadastre | Vessel position reports for call identification and dwell time | marinecadastre.gov |
| goPEIT | ICCT | Vessel-level emission estimates by port and operating mode | theicct.org |
Monitoring Stations¶
Two air quality monitoring stations provide continuous PM2.5 data for the Duluth-Superior port area:
| Station | Location | Coordinates | Pollutants | Operator |
|---|---|---|---|---|
| Duluth-WDSE | Near port industrial zone | 46.787°N, 92.101°W | PM2.5, O₃ | MPCA |
| West Duluth | Residential area west of terminals | 46.755°N, 92.135°W | PM2.5 | MPCA |
Typical Duluth PM2.5 readings fall in the Good to Moderate AQI range (25–50), with seasonal variation: winter averages ~6.5 µg/m³, shipping season averages ~11.2 µg/m³, with July peak averages reaching ~14.8 µg/m³ — approaching the WHO guideline of 15 µg/m³.
Emissions Inventory¶
Scope 1: Direct Port Operations — 586 tonnes CO₂/yr¶
| Source | Tonnes CO₂/yr | Fuel |
|---|---|---|
| Port equipment (cranes, loaders) | 312 | Diesel |
| Harbor craft | 156 | Diesel |
| On-road vehicles | 78 | Diesel/Gasoline |
| Emergency generators | 40 | Diesel |
| Total Scope 1 | 586 |
Scope 2: Purchased Electricity — 511 tonnes CO₂/yr¶
| Source | Tonnes CO₂/yr | Grid |
|---|---|---|
| Buildings & lighting | 289 | MISO |
| Reefer connections | 122 | MISO |
| Terminal operations | 100 | MISO |
| Total Scope 2 | 511 |
Scope 3: Vessel & Transport Emissions — 42,150 tonnes CO₂/yr¶
| Source | Tonnes CO₂/yr | Notes |
|---|---|---|
| Vessel at-berth emissions | 38,500 | Auxiliary engines running 24–72 hrs during loading |
| Vessel maneuvering | 2,850 | Arrival/departure within harbor |
| Rail transport | 580 | BNSF, CN, CP serving port terminals |
| Truck drayage | 220 | Local freight movements |
| Total Scope 3 | 42,150 |
MERC Coal Terminal — 8,500 tonnes CO₂/yr (until June 30, 2026)¶
The MERC coal-handling facility contributes an additional ~8,500 tonnes CO₂/yr through coal dust emissions, handling operations, and coal carrier vessel emissions. This will be eliminated entirely upon the terminal's closure on June 30, 2026. See MERC Coal Terminal Transition for full analysis.
Analytical Outputs¶
1. Emissions Inventory Reconciliation¶
Cross-referencing ICCT goPEIT vessel-level estimates with EPA NEI facility data and MPCA monitoring to produce a reconciled emissions inventory. Key finding: the port's own Climate Action Plan Scope 1+2 baseline of 1,097 tonnes captures less than 3% of total port-attributable emissions when Scope 3 vessel emissions are included.
2. AQI Trend Analysis¶
30-day and seasonal PM2.5 trend analysis from the Duluth-WDSE and West Duluth monitoring stations. Shipping season (March–January) shows measurable PM2.5 elevation over winter baseline, with the largest spikes correlating with multiple vessels at berth simultaneously during peak iron ore loading months (May–August).
3. Vessel Emissions Modeling¶
Per-vessel emission estimates using EPA AP-42 methodology:
$$E_{berth} = P_{aux} \times LF_{aux} \times T_{berth} \times EF_{fuel} \times \frac{1}{FCR}$$
Where:
- $P_{aux}$ = auxiliary engine power (~750 kW for typical Lakers)
- $LF_{aux}$ = load factor (~0.30 at berth)
- $T_{berth}$ = berth time in hours (24–72 for bulk cargo)
- $EF_{fuel}$ = emission factor for marine diesel (~690 kg CO₂/MWh)
- $FCR$ = fuel consumption rate
This yields approximately 0.155 tonnes CO₂ per hour at berth for a typical Great Lakes bulk carrier — meaning a 48-hour iron ore loading operation produces ~7.4 tonnes CO₂ from auxiliary engines alone.
4. Coal Terminal Transition Impact¶
Pre/post MERC closure emissions comparison. The terminal's June 30, 2026 closure eliminates approximately 19.6% of MERC-attributable emissions from the port total, creating a natural experiment for emissions baseline methodology validation. See MERC analysis →.
5. Comparison Benchmarking¶
Duluth-Superior's emissions profile benchmarked against peer ports:
| Port | Annual Tonnage | Vessel Calls | At-Berth Emissions (t/yr) | Controls |
|---|---|---|---|---|
| Duluth-Superior | 25.3M | 687 | ~190 | None | | Los Angeles/Long Beach | 200M+ | 8,000+ | ~3,200 | CARB regulated | | Houston/Galveston | 280M+ | 8,500+ | ~1,000 | None | | New York/NJ | 175M+ | 5,500+ | ~2,600 | None |
While Duluth-Superior's absolute emissions are smaller, the per-capita exposure is significantly higher due to the compact metro area, and the per-vessel emission intensity is higher due to extended bulk loading berth times.
Last updated: April 2026
Data sources: EPA AirNow/AQS, MPCA, EPA NEI, EPA TRI, ICCT goPEIT, MarineCadastre AIS, Duluth Seaway Port Authority Climate Action Plan