Appendix B

Emissions Estimation Methodology for Commercial Harbor Craft 

Operating in California
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Emissions Estimation Methodology for 

Commercial Harbor Craft Operating in California
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Table of Contents

EXECUTIVE SUMMARY.............................................................................................................6

I. INTRODUCTION .................................................................................................................11

A. Background..................................................................................................................11

B. Purpose and Overview ..............................................................................................12

C. Public Process ............................................................................................................13

II. EMISSION ESTIMATION METHODOLOGY...............................................................14

A. Emission Inventory Inputs .........................................................................................14

1. Base Year Vessel Population and Vessel Profiles................................................14

2. Base Year Engine Population and Engine Profiles...............................................18

3. Future Year Vessel and Engine Population...........................................................19

4. Engine Activity.............................................................................................................20

5. Zero-hour Emission Factor........................................................................................21

6. Fuel Correction Factor ...............................................................................................22

7. Engine Deterioration ..................................................................................................23

B. Methodology................................................................................................................24

1. Overview......................................................................................................................24

2. SOx Emission Estimation..........................................................................................25

3. Spatial Allocation........................................................................................................26

4. Additional Considerations and Assumptions..........................................................28

III. EMISSION ESTIMATES..................................................................................................30

REFERENCES............................................................................................................................33

Appendix A Commercial Harbor Craft Emission Factor Table ............................................34
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List of Tables

Table ES-1 Commercial Harbor Craft Emissions in California in 2004 (Tons/day) ..........7

Table ES-2 NOx Emissions By Engine Type and Vessel Type in 2004.............................7

Table ES-3 NOx, PM Emissions By Air District and Air Basin in 2004...............................9

Table I-1 Categories of Commercial Harbor Craft Included in the Emissions Inventory13

Table II-1 California Commercial Harbor Craft Population by Vessel type and by District 

in 2004..........................................................................................................................................17

Table II-2 California Commercial Harbor Craft Engine Profile by Vessel Type...............19

Table II-3 Engine Load Factor by Vessel Type and by Engine Use .................................21

Table II-4 Fuel Correction Factor............................................................................................23

Table II-5 Engine Deterioration Factor...................................................................................24

Table II-6 Statewide Average of Percent of Vessel Activity at Varying Distances from 

Shore ............................................................................................................................................26

Table II-7 Summary of Percent of Time Spent within Land Side Air Basins and Outer 

Continental Shelf Air Basins .....................................................................................................27

Table III-1 Commercial Harbor Craft Emissions in California in 2004 (Tons/day) ..........30

Table III-2 NOx Emissions By Engine Type and Vessel Type in 2004.............................31

Table III-3 NOx, PM Emissions By Air District and Air Basin in 2004...............................31
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List of Figures

Figure ES-1 Illustration of California Air Districts and OCS Air Basins...............................8

Figure ES-2 Estimation of Commercial Harbor Craft NOx, PM Emissions 2004-2025....9

Figure II-1 Illustration of Engine Attrition Curve....................................................................20

Figure II-2 Illustration of the Commercial Harbor Emission Estimation Methodology....25

Figure II-3 The Overlap Between the California Department of Fish and Game’s Fish 

Landings Grid System and the ARB’s “California Coastal Waters”....................................29

Figure III-1 Illustration of California Air Districts and OCS Air Basins...............................32

Figure III-2 Estimation of Commercial Harbor Craft NOx, PM Emissions 2004-2025....33
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EXECUTIVE SUMMARY

Air Resources Board (ARB) staff have developed a consistent methodology to estimate 

emissions from commercial harbor craft in California. This updated inventory will be 

used to support regulatory analysis of statewide regulations to reduce emissions from 

these marine engines. Other goals in undertaking this emissions inventory update were 

to: 

• Update the inventory to reflect the most current harbor craft fleet;

• Accurately reflect adopted regulations and other regulatory programs in the 

baseline inventory and in any forecasts.

• Establish a structure that would allow allocation of the statewide emissions to 

individual air pollution control districts and air basins;

In the Proposed Regulation for Diesel Engines on Commercial Harbor Craft, 

“commercial harbor craft” means any private, commercial, government, or military 

marine vessels including, but not limited to, passenger ferries, tug boats, tow boats, 

push-boats, crew vessels, work boats, pilot vessels, supply boats, research vessels, 

United States Coast Guard vessels, hovercraft, emergency response harbor craft, and 

barge vessels that do not otherwise meet the definition of ocean-going vessels or 

recreational vessels. 

This inventory covers commercial harbor craft that operate within California coastal 

waters and inland waterways, and have a home port located in California. Due to 

limited information currently available about the number of U.S. Navy and/or U.S. Coast 

Guard (USCG) vessels, vessel characteristics, and vessel activity, we decided not to 

include emissions from these vessel types into this inventory.

For this inventory purpose, we grouped commercial harbor craft into nine types of

vessels, including commercial fishing vessels, charter fishing vessels, crew and supply 

boats, ferry and excursion vessels, pilot vessels, tow boats, tug boats, work boats, and

“others”, i.e. other type of vessels that do not fit into the above eight categories. 

To estimate California statewide commercial harbor craft emissions, we first estimated

vessel type and region specific emissions rates, i.e. average emissions per engine per 

year, using an activity-based approach based on engine information collected in the 

2004 ARB’s Commercial Harbor Craft Survey. We then estimated statewide emissions 

by multiplying number of engine in each engine category and in each regionby average 

emissions per engine.

Using the proposed methodology, we estimate statewide emissions from commercial 

harbor craft diesel-fueled engines in 2004 were about 3.3 tons per day of diesel PM,

about 73.2 tons per day of oxides of nitrogen (NOx). Detailed emission estimates are 

presented in Table ES-1. 
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Table ES-1 Commercial Harbor Craft Emissions in California in 2004 (Tons/day)

Vessel Type

Vessel 

Population

Engine 

Population NOx PM ROG CO

Charter Fishing 563 1,419 12.7 0.6 0.9 3.3

Commercial Fishing 2,727 4,309 17.4 0.8 1.3 4.8

Crew and Supply 64 230 1.4 0.1 0.1 0.4

Ferry/Excursion 416 1,348 21.0 0.9 1.4 5.6

Pilot Vessels 27 50 0.4 0.0 0.0 0.1

Tow Boats 35 114 3.0 0.1 0.2 0.7

Tug Boats 128 449 15.3 0.6 1.0 3.8

Work Boats 89 158 0.5 0.0 0.0 0.1

Others 136 214 1.5 0.1 0.1 0.4

Total 4,185 8,291 73.2 3.3 5.0 19.2

Ferry/excursion vessels and tug/tow boats jointly account for about 14% of the 

statewide harbor craft population and 50% of the statewide harbor craft emissions. The 

engines of these vessels are relatively larger and operate more often than other vessel 

categories. Commercial fishing vessels account for 65% of the harbor craft population 

but only emit around 25% of the emissions.

Table ES-2 provides NOx emissions by engine and vessel type. Propulsion engines 

account for 93% of NOx emissions from commercial harbor craft.

Table ES-2 NOx Emissions By Engine Type and Vessel Type in 2004

Main Engine Auxiliary Engine

Vessel Type

Number of 

Engines

Tons/day 

NOx

Number of 

Engines

Tons/day 

NOx

Charter Fishing 997 12.1 422 0.6

Commercial Fishing 3,054 14.8 1,254 2.6

Crew and Supply 160 1.1 70 0.4

Ferry/Excursion 836 20.2 512 0.8

Pilot Vessels 46 0.4 4 0.0

Tow Boats 74 2.8 41 0.2

Tug Boats 246 14.9 204 0.4

Work Boats 130 0.5 28 0.0

Others 151 1.4 63 0.1

Total 5,693 68.1 2,598 5.1

Table ES-3 summarizes NOx and PM emissions by Air Quality Management District 

(AQMD) or Air Pollution Control District (APCD) and Outer Continental Shelf (OCS) air 

basin in calendar year 2004. The AQMDs and APCDs are commonly called air districts. 

OCS air basin covers 3-100 nautical miles from shore. Figure ES-1 illustrates these air 

districts and OCS air basins.
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Figure ES-1 Illustration of California Air Districts and OCS Air Basins

About one third of the state harbor craft are in the Bay Area AQMD. These vessels 

account for about 37% of statewide NOx or PM emissions. South Coast AQMD has 

18% of the statewide harbor craft and account for about 26% of the NOx or PM 

emissions. San Diego County APCD only has 7% of the statewide population but these 

vessels emitted about 12% of statewide harbor craft NOx or PM emissions. These 

three air districts jointly are home to 60% of the statewide harbor craft and these 

vessels are responsible for 75% of statewide NOx or PM emissions.
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Table ES-3 NOx, PM Emissions By Air District and Air Basin in 2004

Air Districts

Number of 

Vessels

NOx 

Tons/year

NOx in 

OCS

PM 

Tons/day

PM in 

OCS

Bay Area AQMD (BA) 1,468 26.9 10.2 1.2 0.5

El Dorado County APCD (ED) 9 0.3 0.0 0.0 0.0

Mendocino County AQMD (MEN) 169 1.3 1.1 0.1 0.0

Monterey Bay Unified APCD (MBU) 379 3.6 2.7 0.2 0.1

North Coast Unified APCD (NCU) 299 2.3 1.9 0.1 0.1

Northern Sonoma County APCD (NS) 145 1.2 1.0 0.1 0.0

Placer County APCD (PLA) 9 0.3 0.0 0.0 0.0

San Diego County APCD (SD) 307 9.2 5.5 0.4 0.2

San Joaquin Valley Unified APCD (SJU) 43 0.8 0.0 0.0 0.0

San Luis Obispo County APCD (SLO) 145 1.4 1.1 0.1 0.1

Santa Barbara County APCD (SB) 193 2.7 2.0 0.1 0.1

South Coast AQMD (SC) 745 18.7 11.7 0.8 0.5

Ventura County APCD (VEN) 194 2.5 1.8 0.1 0.1

Yolo/Solano AQMD (YS) 81 1.9 0.0 0.1 0.0

Total 4,185 73.2 38.9 3.3 1.8

Statewide about 53% of the emissions occur in the Outer Continental Shelf air basin. 

Generally fishing vessels spend the most time in the Outer Continental Shelf, while 

ferries tend to spend the most time closer to shore.

Figure ES-2 Estimation of Commercial Harbor Craft NOx, PM Emissions 2004-

2025

0

10

20

30

40

50

60

70

80

2004 2007 2010 2013 2016 2019 2022 2025

Calendar Year

Tons/day NOx

0

1

1

2

2

3

3

4

Tons/day PM

NOx PM
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Figure ES-2 illustrates the change of commercial harbor craft NOx and PM emissions 

over time from 2004 to 2025. NOx emissions from harbor craft in California will 

decrease from 73 tons per day in 2004 to about 32 tons per day in 2025 and PM 

emissions will decrease from 3.3 tons per day to about 1.2 tons during the same period. 

The decline of emissions between 2004 and 2009 is partially caused by the decline of 

the fishing fleet from 2004 to 2009 as we project based on fish landing data, natural 

engine turnover, and the more stringent EPA marine engine emissions standards. New 

engines need to comply with EPA standards and are cleaner than the old engines which 

are replaced. The decrease in emissions after 2009 reflects the gradual phase in of 

new engines replacing old engines retired from the fleet.
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I. INTRODUCTION

This section provides background on the commercial harbor craft emissions inventory,

the purpose and goals in preparing this emissions inventory, and a general overview of 

the methodology used to estimate emissions from commercial harbor craft. 

A. Background

In the Proposed Regulation for Diesel Engines on Commercial Harbor Craft, 

“commercial harbor craft” means any private, commercial, government, or military 

marine vessels including, but not limited to, passenger ferries, tug boats, tow boats, 

push-boats, crew vessels, work boats, pilot vessels, supply boats, research vessels, 

United States Coast Guard vessels, hovercraft, emergency response vessels, and 

barges that do not otherwise meet the definition of ocean-going vessels or recreational 

vessels. Except for commercial fishing vessels, commercial harbor craft spend most of 

their time within 100 nautical miles from shore.

Most commercial harbor craft are powered by marine diesel engines, including 

propulsion engines and auxiliary engines (1). Propulsion engines are the primary 

engines that move vessels through the water. Auxiliary engines generally provide 

power to vessel electrical systems and may also provide additional power to unique, 

essential vessel equipment (i.e. refrigeration units) during the normal day-to-day 

operation of the vessel.

Marine diesel engines powering commercial harbor craft are usually larger than onroad 

and land based offroad diesel engines. These engines also last longer and have much 

longer operating lifetime. According to the 2004 ARB survey, the average age of 

commercial harbor craft propulsion engines in 2004 is about 18 years old with about 

44% of the them older than twenty years, and about 20% of them older than thirty years

(1). In contrast, the average age of California in-state trucks is about 12 years old.1 

These marine engines are also among the least regulated sources of air pollutants in 

California. The first U.S. EPA rule regulating these engines, “Control of Emissions of Air

Pollution from New CI Marine Engines at or above 37 kW”, was published in 1999. The 

emission standard in this rule only applies to new engines and became mandatory in

2004. Marine engines are less controlled and tend to emit more air pollutants than land 

based engines. Even with a smaller population, commercial harbor craft are important 

sources of air emissions in California especially for coastal areas with heavy marine

activities. It is estimated that emissions from commercial harbor craft in the Bay Area 

Air Quality Management District are equivalent to nearly 60% of the emissions from 

heavy heavy duty diesel trucks in this area.2

 

1

 Based on ARB’s EMFAC2007 model, http://www.arb.ca.gov/msei/onroad/latest_version.htm

2

 Compared to emission estimates for heavy heavy duty diesel truck in the emissions inventory for 

Proposed State Strategy for California's State Implementation Plan (SIP) for the New Federal PM2.5 and 

8-Hour Ozone Standard, http://www.arb.ca.gov/planning/sip/2007sip/2007sip.htm
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B. Purpose and Overview

To avoid inconsistencies in the statewide emissions inventory, ARB staff developed a 

consistent methodology which can be used statewide to estimate emissions from harbor 

craft. This updated inventory will be used to support analysis of statewide regulations to 

reduce emissions from these marine engines. Other goals in undertaking this 

emissions inventory update were to: 

• Update the inventory to reflect the most current harbor craft fleet; 

• Accurately reflect adopted regulations and other regulatory programs in the 

baseline inventory and in any forecasts.

• Establish a structure that would allow allocation of the statewide emissions to 

individual air pollution control districts and air basins;

This inventory covers commercial harbor craft that operate within California coastal 

waters and inland waterways, and have a home port located in California. Due to 

limited information currently available about the number of U.S. Navy and/or U.S. Coast 

Guard (USCG) vessels, vessel characteristics, and vessel activity, we decided not to 

include emissions from these vessel types into this inventory.

For this inventory purpose, we grouped commercial harbor craft into nine types of 

vessels, including commercial fishing vessels, charter fishing vessels, crew and supply 

boats, ferry and excursion vessels, pilot vessels, tow boats, tug boats, work boats, and 

“others”, i.e. other type of vessels that do not fit into the above eight categories. The 

nine categories are described in Table I-1.

This inventory provides estimates of emissions of oxides of nitrogen (NOx), reactive 

organic gas (ROG), carbon monoxide (CO), particulate matter (PM), and sulfur oxides 

(SOx). We chose year 2004 as the base year of this inventory because that’s the end 

of the period when the population data were collected. We forecast emissions for the 

future years (2005-2025) based on projected fleet growth, turnover, engine deterioration, 

and the change of emission rates.
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Table I-1 Categories of Commercial Harbor Craft Included in the Emissions 

Inventory

Vessel Type Description

Commercial Fishing Vessels used in the search and collection of fish for the purpose 

of sale at market.

Charter Fishing Vessels available for hire by the general public and used for the 

search and collection of fish for the purpose of personal 

consumption.

Crew and Supply Vessels used for carrying personnel and supplies to and from offshore and in-harbor locations, including vessels at anchorage, 

construction sites, and off-shore platforms.

Ferry/Excursion

Vessels used for public use in the transportation of persons or 

property as a part of the public transport systems and 

commercial vessels used for sightseeing, whale watching, and 

dinner cruising, etc.

Pilot Vessel Vessels used to carry pilots to and from ships to provide pilot 

service into and out of a port or harbor.

Towboat/Pushboat

Vessels used to push barges and pontoons. Towboats are 

characterized by a square bow with steel knees for pushing, a 

shallow draft, and powerful engines. They are most often seen on 

inland waterways since their hull designs (like little freeboard) 

would make open ocean operations dangerous.

Tug Boat

Vessels primarily used to assist other vessels maneuvering in 

harbors, over the open sea or through rivers and canals by 

pushing and towing. They are also used to tow barges, or other 

floating structures.

Work boat Vessels used to perform duties such as fire/rescue, law 

enforcement, hydrographic surveys, spill/response research, 

training, and construction.

Other Vessels used in various commercial operations that do not fit into 

any other category such as vessels used to dispose of cremated 

remains.

C. Public Process

Allowing stakeholders and the general public to review and comment on a product 

associated with a rulemaking process is a critical element of that rulemaking process. 

The following steps were taken to ensure interested parties could provide input.
B - 14

Comments on impacts were solicited from the Commercial Harbor Craft Working Group. 

Members of the working group include representatives of the groups and agencies that 

would be impacted by any rulemaking undertaken by the ARB. Representatives include 

diesel-fueled compression ignition engine manufacturers, environmental groups, ferry 

operators, local air pollution control and air quality management districts, and control 

technology manufacturers.

We provided local air districts and the public the opportunity to review, comment on the 

methodology and the inventory by conducting working group meetings/teleconferences, 

and public workshops. The inventory was presented to six public workshops and 

several teleconferences with air districts. Comments obtained through these meetings, 

teleconferences and workshops were used to assess and modify the inventory.

II. EMISSION ESTIMATION METHODOLOGY

To estimate California statewide commercial harbor craft emissions, we first estimated 

vessel type and region specific emissions rates, i.e. average emissions per engine per 

year, using an activity-based approach based on engine information collected in the 

2004 ARB’s Commercial Harbor Craft Survey (1). We then estimated statewide 

emissions by multiplying number of engine in each engine category and in each region 

by average emissions per engine.

A. Emission Inventory Inputs

Data needed for estimating harbor craft emissions include:

• Base year vessel and engine population

• Future fleet growth and engine turn over

• Engine hours of operation and engine load

• Zero-hour (new engine) emission factor

• Engine deterioration and other adjustments

• Spatial allocation surrogate

Engine population for a given year was estimated using base year vessel population,

vessel profiles information collected from various sources, engine and vessel 

information collected in the ARB’s Commercial Harbor Craft Survey (1), fleet growth 

rates provided by air districts, and engine attrition rates based on the ARB’s OFFROAD 

model.

1. Base Year Vessel Population and Vessel Profiles

Since there is no one available data set that covers all commercial harbor craft 

operating in California, vessel population data were collected from various sources, 

including the U.S. Coast Guard documentation data, the California Department of Fish 

and Game registration data, the ARB Harbor Craft Survey (1), and information from 

recent emission inventory estimates generated for the Port of Los Angeles. Each of 
B - 15

these sources of commercial harbor craft information is described in greater depth 

below. In addition, the specific steps taken to develop estimates of numbers of specific 

vessel types and spatially allocate those populations are also described below.3 Based 

on available information, we estimate that there were approximately 4,185 harbor craft 

vessels operating in California in year 2004.

United States Coast Guard Vessel Data:

The United States Coast Guard (USCG) administers a vessel documentation program. 

The USCG vessel documentation program is a national form of registration. The ARB 

purchased the U.S. Coast Guard documentation data through the National Technical 

Information Service.

Types of vessels that are documented in the data set include:

• vessels that measure at least five net tons (a measure of the vessel’s volume, 

most vessels more than 25 feet in length will measure five net tons or more)

• vessels wholly owned by a citizen of the United States (with the exception of 

certain oil spill response vessels)

• vessels of five net tons or more used in fishing activities on navigable waters of 

the United States or in the Exclusive Economic Zone (EEZ)

• vessels used in coastwise trade (transportation of merchandize or passengers 

between points in the United States)

• towboats operating between points and dredges operating in United States or the 

EEZ must be documented.

The information provided represents nation-wide vessel documentation information for 

the years 1985 through June 2001. ARB staff sorted the data by state and removed all 

non-California documented vessels. The majority of the vessels that are California 

documented vessels fall into one of five categories of vessels. Those categories are 

commercial boats, fishing, offshore supply, passenger, tow/tugboats, and unclassified. 

California Department of Fish and Game Data:

The California Department of Fish and Game (DFG) registers all commercial fishing 

vessels, passenger fishing boats, and fish businesses in California. We obtained their 

file of the commercial fishing permits registrations issued for 2004. That information 

was used to augment the USCG documentation and ARB Survey data when evaluating 

the commercial and charter fishing categories of commercial harbor craft.

 

3

In early 2004, ARB staff contacted approximately 60 of California’s harbormasters and port and marina 

administrators. Using a brief two-page survey, ARB staff collected estimates of the current commercial harbor craft 

populations for the nine vessel types described earlier in this document. ARB staff was able to obtain numbers of 

commercial harbor craft at all but one of the harbors, ports, and marinas contacted. This information was used as a 

reality check of the estimates using the four population data sources listed above. 
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Port of Los Angeles Fishing Vessel Data:

During the course of the development of a port-wide emissions inventory, the Port of 

Los Angeles collected information about the commercial fishing vessels that operate out 

of the Port. The Port provided the ARB with vessel names and owner/operator contact 

information for approximately 250 commercial fishing vessels.

ARB’s Commercial Harbor Craft Survey (March 2004):

In 2004, ARB staff conducted a survey of commercial harbor craft owner/operators in an 

effort to collect information about where the different types of harbor craft in the State 

operate, vessel activity, and engine-specific information (ARB’s Statewide Commercial 

Harbor Craft Survey, or ARB Survey) (1). Owners/operators of commercial fishing 

vessels, tugs, ferries and excursion vessels, work and tow boats, and crew and supply 

boats were sent a copy of the ARB’s survey in late 2002. The survey requested 

information about the home port, the type of vessel, if the vessel was used for 

commercial fishing, the type of fishery targeted, annual fuel use, information about 

where the vessel generally operated, and engine information (make and model of the 

engine, is it a propulsion or auxiliary engine, horsepower, was it a repower, annual 

hours of use, etc.). The survey was sent to more than 5,000 owner/operators statewide 

and the ARB received more than 700 responses representing approximately 850 

vessels.

Estimating Vessel Population:

To establish a data base from which to estimate the statewide commercial harbor craft 

vessel population, we first segregated the information from the USCG, the California 

Department of Fish and Game (DFG), the Port of Los Angeles (POLA), and the ARB 

commercial harbor craft survey into four major groups: Ferry/excursion vessels, fishing

vessels, work boats, and other types of vessels. We chose these four groupings 

because they are the four primary groups the USGC uses to classify commercial harbor 

craft. We grouped the information from the DFG, the POLA and the USCG fishing with 

the information from the ARB’s commercial harbor craft survey for commercial fishing 

and charter vessel data to develop the statewide population estimate for commercial 

fishing vessels. Ferry, crew and supply, and pilot vessel information from the ARB 

commercial harbor craft survey were grouped with the USCG ferry/excursion vessel 

data to develop statewide population estimates for ferry/excursion vessels. We added 

the ARB commercial harbor craft survey data for tugs, tow boats and work boats to the 

USCG work group data to develop statewide population estimates for work boats. 

Remaining vessels from the ARB commercial harbor craft survey were added to the 

USCG’s “other” group data to develop statewide population estimates for other types of 

commercial harbor craft.
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Table II-1 California Commercial Harbor Craft Population by Vessel type and by District in 2004

District

Charter 

Fishing

Commercial 

Fishing

Crew and 

Supply

Ferry/

Excursion Others

Pilot 

Vessels

Tow 

Boats

Tug 

Boats

Work 

Boats

Total by 

District

Bay Area 164 972 9 140 64 4 23 57 34 1,468

El Dorado County 6 0 0 3 0 0 0 0 0 9

Mendocino County 5 158 0 3 1 0 0 0 1 169

Monterey Bay Unified 18 336 0 17 7 0 0 1 0 379

North Coast Unified 6 285 2 1 0 0 2 2 299

Northern Sonoma County 9 132 0 4 0 0 0 0 0 145

Placer County 5 0 0 4 0 0 0 0 0 9

San Diego County 84 106 0 76 15 0 8 16 2 307

San Joaquin Valley Unified 9 23 1 5 1 1 0 1 1 43

San Luis Obispo County 8 131 1 3 0 0 0 2 1 145

Santa Barbara County 31 119 23 11 4 0 0 1 3 193

South Coast 191 274 15 134 37 21 1 38 33 745

Ventura County 16 148 12 11 4 1 0 3 0 194

Yolo/Solano 11 43 0 3 2 0 3 8 11 81

Total by Vessel Type 563 2,727 64 416 136 27 35 128 89 4,185
B - 18

Each population was then assigned to a county and a district based on their reported 

home port.4 The distribution of vessels into the nine inventory categories was 

determined based on district-specific vessel distribution ratios developed using 

information from the ARB commercial harbor craft survey. As shown in Table II-1, 

fishing vessels account for the largest percentage of vessels at 77% of the total 

commercial harbor craft population. Table II-1 also shows the summary of the 

commercial harbor craft vessel population by AQMD or APCD.

2. Base Year Engine Population and Engine Profiles

As described previously, the ARB’s Statewide Commercial Harbor Craft Survey 

collected information about the various commercial harbor craft and associated engines 

operating in California's coastal waters and inland waterways, harbors, and ports during 

2002-2004. The vessel information included vessel home port, vessel use and age, 

annual fuel use, and percent of time operated at various distances off the California 

coast. In addition, the Survey collected information about the engines powering those 

vessels. The engine information included number of engines per vessel, engine make 

and model, engine age, engine horsepower, annual hours of operation, and other 

information. Detailed information for about 850 vessels with about 400 auxiliary engines 

and about 1000 propulsion engines were collected during the survey. 

Based on the Survey, individual engine profiles were developed by combining specific 

information about an engine. That information includes engine use (propulsion or 

auxiliary), type of vessel the engine is associated with, model year of the engine, engine 

horsepower, annual hours of operation, etc. These data were used to estimate 

emissions from individual engines.

Table II-2 summarizes the statewide commercial harbor craft engine profiles developed 

using the vessel and engine data collected in the ARB Survey. Since most commercial 

harbor craft are doing routine work, the operation profile remains relatively stable. 

Because the information needed to project harbor craft engine profiles in the future was 

not available, we assumed the engine profiles developed from the ARB survey hold 

throughout the future years for which we estimated emissions. Number of engines per 

vessel by vessel type was used to estimate statewide engine population and engine 

useful life was used to account for engine attrition and engine deterioration described in 

the following sections. Total life is defined as the age when 90% of engines retire and 

useful life (UL) is defined as half of total life.

 

4

 Those vessels with home ports far from navigable waters were assigned to the closest ports. Those 

vessels that did not have a “home port” listed (11 percent of the vessels) were assigned one based on the 

address of the owner/operator. Those vessels that reported a “home port” outside of California (4 percent 

of the vessels) were assigned to the ports, harbors, and marinas in counties and districts where they 

“landed” their catch. 
B - 19

Table II-2 California Commercial Harbor Craft Engine Profile by Vessel Type

Propulsion Engine Auxiliary Engine

Vessel Type

# of 

Engines 

per Vessel

Average 

Annual 

Operating Hrs

Useful 

Life

# of 

Engines 

per Vessel

Average 

Annual 

Operating Hrs

Useful 

Life

Commercial Fishing 1.12 1,250 21 0.46 1,633 15

Charter Fishing 1.77 1,622 16 0.75 2,077 15

Ferry/excursion

Vessels 2.01 1,843 20 1.23 1,254 20

Crew and Supply 2.5 788 22 1.1 3,036 22

Pilot Vessels 1.7 1,031 19 0.14 994 25

Tug Boats 1.92 2,274 21 1.59 2,486 23

Tow Boats 2.1 1,993 26 1.17 2,965 25

Work Boats 1.46 675 17 0.32 750 23

Others 1.11 779 23 0.46 805 22

3. Future Year Vessel and Engine Population

We estimated future year vessel and engine population based on fleet growth rates and 

engine turnover rates. 

We used air districts’ fleet growth rates to project commercial harbor craft population in 

the future years. We adjusted these growth rates based on available information. 

Since tug boats are generally over-powered and are capable of handling larger vessels, 

we assumed tug boats fleet growth is flat throughout the future years we projected. We 

adjusted growth rate for California’s commercial fishing fleet to reflect the most recent 

fish landings (tons per year) data available. The data indicate that there has been a six 

percent per year decline in fish landings over the last decade. Since there is no way to 

accurately predict whether or not that trend continues indefinitely, an annual decline of 

six percent in the numbers of vessels in California’s waters is continued through 2009. 

From 2010 on, the growth is flat.

We assumed vessels in the future years have the same number of engines and same 

engine profile as the vessels in the base year. Future year engine population was 

estimated using vessel population and number of engines by vessel type as shown in 

Table II-2.

We estimated engine turnover using attrition curve of ARB’s OFFROAD model. Figure 

II-1 illustrates the engine attrition curve we applied to commercial harbor craft engines. 

Age/UL represents the ratio between engine age and useful life. The basic assumption 

of the attrition curve is that 50% of the engines of certain model year retire before they 

reach their useful life (when age/UL = 1), and 100% of the engines of certain model year 

retire when they reach their total life (when age/ UL = 2). Vessel and engine use specific 

useful life are presented in Table II-2.
B - 20

Figure II-1 Illustration of Engine Attrition Curve

0

20

40

60

80

100

0 0.5 1 1.5 2

Age/UL

Cumulative % Scrapped

We estimated number of new engines in each future calendar year using the difference 

between the population estimated based on growth rates and the population estimated 

based on engine turnover. The calendar year was used as engine model year of the 

new engines. Vessel type and horsepower range specific average horsepower and 

average hours of operation were estimated using engine information collected in the 

2004 ARB’s Commercial Harbor Craft Survey (1) and were assigned to these new 

engines.

4. Engine Activity 

Two of the key inputs of the emission estimation methodology include the engine’s 

annual hours of operation and the typical engine load. Annual hours of operation for 

each individual engines collected in the ARB survey were used to estimate emissions 

from these engines.

We chose the marine engine load factor (43%) in the U.S. EPA’s Nonroad model for 

commercial harbor craft auxiliary engines. We adjusted tug boats auxiliary engine load 

factor to 31% following the Port of Los Angeles’ emission inventory developed by the 

Starcrest Consulting Group, LLC based on more detailed data.

We estimated main engine load factor based on fuel consumption data, engine 

horsepower, and annual hours of operation data collected in the ARB Survey. The ARB 

Survey provided engine-specific annual use values. We assumed that all of an engine’s 

hours of operation occurred within the California Coastal Waters. Vessel type specific 

propulsion engine load factor was estimated using the following equation.
B - 21

LF = BSFC * HP* Hr /TF 

Where:

LF is the vessel type specific propulsion engine load factor;

BSFC is brake specific fuel consumption rate; we used 0.078 gal/kW-hr or 0.058 

gal/hp-hr estimated from manufacturers’ marine engine data;

HP is rated horsepower of the engine;

Hr is the number of annual operating hours of the engine;

TF is total fuel consumption per engine per year.

Table II-3 summarizes the engine load factors used to estimate commercial harbor craft 

emissions.

Table II-3 Engine Load Factor by Vessel Type and by Engine Use

Vessel Type Propulsion Engine Load Auxiliary Engine Load

Commercial Fishing 0.27 0.43

Charter Fishing 0.52 0.43

Ferry/Excursion 0.42 0.43

Crew and Supply 0.45 0.43

Pilot Vessels 0.51 0.43

Tug Boats 0.50 0.31

Tow Boats 0.68 0.43

Work Boats 0.45 0.43

Others 0.52 0.43

5. Zero-hour Emission Factor 

ARB staff collected potential commercial harbor craft emission factors from a broad 

range of sources. Those sources included the U.S. EPA’s Compilation of Air Pollutant 

Emission Factors (AP-42), Lloyd's Register of Ships, U.S. EPA Category 1 marine 

engine emission factors, U.S. EPA Marine Engine Certification data, ARB OFFROAD 

Model, and actual emission testing results from a variety of vessels.

.

ARB staff reviewed the emission factors from all of these sources in an effort to select 

those that would be the most applicable to the development of a commercial harbor 

craft emission inventory. Applicability was based on a number key engine-related of 

factors to make that determination. Those factors included the horsepower of the 

engine, the model year, whether there were emission factors for the pollutants of 

interest (NOx, PM, HC, and CO), and the engine test cycle associated with the emission 

factor.

ARB’s OFFROAD Model emission factors have been used in the past to estimate 

emissions from off-road equipment and those emission factors met the criteria set forth 
B - 22

by the ARB’s emission inventory staff, the balance of the potential emission factor sets 

were compared to those emission factors. 

After evaluation of the available data, we chose the emission factors in the ARB’s 

OFFROAD Model with the following adjustments:

• for 1996 through 1999 model year engines, use the Tier Zero (1996) emission 

factors;

• for 2000 and beyond model year engines, use the U.S. EPA emission standards for 

marine engines or the NOx limits of the IMO MARPOL Annex VI whichever is lower;

5

and 

• adjust the OFFROAD Model emission factors to reflect an “E3” test cycle for 

propulsion engines and “D2” test cycle for auxiliary engines.

6

No changes were made to the OFFROAD emission factors to differentiate between 

“wet” and “dry” exhaust from marine engines. This decision was made based on a lack 

of information definitively supporting any difference between the characteristics of the 

two methods of exhausting marine engine combustion gases.

No changes were made to the OFFROAD emission factors to differentiate between 

emissions from 2 stroke and 4 stroke engines. This decision was also based on a lack 

of information on the differences in emissions between the two types of engines that 

would allow ARB staff to make that distinction at this time.

The harbor craft emission factors are shown in Appendix A.

6. Fuel Correction Factor

ARB OFFROAD model’s fuel correction factors are used to account for the benefits of 

cleaner diesel fuel (2). Engines certified using federal on- and off-road diesel fuel 

receive NOx and PM benefit of 7% and 20% respectively, due to the lower aromatic 

content of California diesel fuel. Engines certified using federal off-road diesel fuel 

receive an additional 5% PM benefit due to the lower sulfur content of California diesel 

fuel. A fuel correction factor of 0.72 for hydrocarbon emissions will be applied to all 

diesel-powered engines beginning with the 1994 calendar year. Starting in 2007, 

California will requires the use of ultra low sulfur diesel fuel (ULSD -15 ppmw sulfur). 

An additional 4% PM benefit is assumed for all engines not certified on this fuel (2). 

Table II-4 summarizes the fuel correction factors.

 

5

 We compared OFFROAD emissions factors, U.S. EPA Tier I, II and proposed Tier III and Tier IV 

standards, and the NOx limits of the Annex VI of the International Convention for the Prevention of 

Pollution from Ships (MARPOL). We chose the lowest of these emission factors.

6

Because the OFFROAD Model emission factors are based on a “C1” engine test cycle, ARB staff 

compared emission results from similar engines testing for both the “C1” and “E3” test cycles. Based on 

this evaluation, we recommended that the OFFROAD Model emission factors be adjusted to better reflect 

the “E3” test cycle. The adjustment factors for propulsion engines are 1.19 for NOx, 0.73 for CO, and 

0.94 for PM. The same evaluation was conducted to compare “C1” and “D2” testing cycles for auxiliary 

engines are 1.19 for HC, 1.03 for CO, and 0.84 for PM. 
B - 23

Table II-4 Fuel Correction Factor

Calendar Years Horsepower Range Model Years NOx PM

<25 Pre-1995

25-50 Pre-1999

51-100 Pre-1998

101-175 Pre-1997

176+ Pre-1996

0.930 0.750

<25 1995+

25-50 1999-2010

51-100 1998-2010

101-175 1997-2010

1994-2006

176+ 1996-2010

0.948 0.822

<25 Pre-1995

25-50 Pre-1999

51-100 Pre-1998

101-175 Pre-1997

176+ Pre-1996

0.930 0.720

<25 1995+

25-50 1999-2010

51-100 1998-2010

101-175 1997-2010

176+ 1996-2010

0.948 0.800

2007+

All 2011+ 0.948 0.852

Source: Off-road Exhaust Emissions Inventory Fuel Correction Factors (2)

7. Engine Deterioration 

As an engine ages, the pollutant-specific emission factors slowly increase with age. 

This phenomenon is described as “deterioration” which is primarily due to the wear on 

the various parts of an engine associated with its day-to-day activities and is a result of 

malfunction of emissions related components. Deterioration occurs at different rates for 

each pollutant. When developing emission estimates, it is essential that deterioration 

be taken into account and factored in the emission estimation methodology. 

We adopted engine deterioration factors from ARB’s OFFROAD model (3). Table II-5

summarizes the deterioration factor we used for estimating emissions from commercial 

harbor craft operating in California. The values represent the increase of emission 

factors at the end of the useful life of engines. For example, for an engine larger than 

250 horsepower, the NOx, PM, HC, and CO emission factors will increase 21%, 67%, 

44% and 25%, respectively, at the end of its useful life.
B - 24

Table II-5 Engine Deterioration Factor

Horsepower Range NOx PM HC CO

25-50 0.06 0.31 0.51 0.41

51-250 0.14 0.44 0.28 0.16

>251 0.21 0.67 0.44 0.25

B. Methodology

1. Overview

The basic equation for the estimating emissions from a commercial harbor craft engine 

is:

HP LF Hr

UL

A

E = EF0 × F ×(1+ D× ) × × × 

 

Where:

E is the amount of emissions of a pollutant (ROG, CO, NOx, or PM) emitted 

during one period; 7

EF0 is the model year, horsepower and engine use (propulsion or auxiliary) 

specific zero hour emission factor (when engine is new); 

F is the fuel correction factor which accounts for emission reduction benefits from 

burning cleaner fuel; 

D is the horsepower and pollutant specific engine deterioration factor, which is 

the percentage increase of emission factors at the end of the useful life of 

the engine; 

A is the age of the engine when the emissions are estimated; 

UL is the vessel type and engine use specific engine useful life;

HP is rated horsepower of the engine;

LF is the vessel type and engine use specific engine load factor; 

Hr is the number of annual operating hours of the engine. 

Total emissions from the California statewide commercial harbor craft fleet can be 

estimated by summing up the emissions from individual engines or by multiplying the 

emissions rates, average emissions per engine per year, with the engine population.

The data described in the previous section were feed into a database driven harbor craft 

emissions estimation model. The model estimates vessel type specific emission rates 

 

7

SO2 will be estimated using the percent sulfur found in the different types of diesel fuel used statewide

and estimated fuel consumption. This methodology is described in section B.2.
B - 25

based on survey data and scales up to the statewide population. The model is able to 

project future year emissions by taking into account fleet growth, engine deterioration, 

the change of emission standards, and other factors.

Figure II-2 shows the relationship among the elements of the model. Emissions are 

estimated based on engine population and emission rates. Engine population is 

estimated based on vessel population and the average number of engines per vessel.

Vessel population is estimated based on base year fleet population and growth rates. 

Figure II-2 Illustration of the Commercial Harbor Emission Estimation 

Methodology

Future engine data are based on the base year engine data collected in the ARB survey, 

the growth rates, and attrition rates. The methodology also accounts for the impacts of 

regulations on engine emission factors and engine turnover rates. These projections 

reflect expected growth rates in the commercial harbor craft populations , changes in 

emission factors over time as the new engine standards are implemented, and the fleet 

turnover, and proposed regulations. 

2. SOx Emission Estimation

We used a fuel-based methodology to estimate SOx emissions from commercial harbor 

craft. We first estimated annual fuel consumption of individual engines based on the 

following equation.

FC = HP× LF × Hr × BSFC

Where 

Fc is fuel consumed per engine per year;

HP is rated horsepower of the engine;

Hr is the number of annual operating hours of the engine;

ARB Survey Data

Emission Rates

Statewide Population

Statewide Emissions

Vessel Population Spatial 

Distribution

Emissions Allocated to 

Regions
B - 26

LF is the load factor; 

LF is the vessel type specific engine load factor;

BSFC is brake specific fuel consumption rate; we used 0.078 gal/kW-hr or 184 

g/hp-hr estimated from manufacturers’ marine engine data.

We then converted fuel consumption to SOx emissions based on mass based sulfur 

content of fuels. We assumed that 1) fuel consumption rate is constant over time; 2) all 

(100%) sulfur is emitted as SO2; 3) SO2 emission rate is a function of fuel consumption 

and sulfur content only; and 4) SO2 emission rate is not subject to engine deterioration.

Sulfur content will be vessel type and air district specific before calendar year 2007, 

when all California commercial harbor craft are required to use ultra low sulfur fuel with 

15 ppm sulfur. We assumed all commercial craft use EPA on-road diesel with 330 ppm 

sulfur content before year 2007, except:

• In calendar years 2002-2007, ferries were required to use CARB diesel with 140 

ppm sulfur. All commercial harbor craft fueling in the following districts receive 

CARB diesel: Mendocino, North Coast Unified, Northern Sonoma, and Tehama; 

• From 2006, all south coast commercial harbor craft use ultra low sulfur fuel with 

15 ppm sulfur.

3. Spatial Allocation

We allocated emissions to counties, air districts, and air basins based on where the 

home ports of the vessels are and/or where the activities occur using our best 

engineering judgment. We also split emissions between land side air basins and Outer 

Continental Shelf (OCS) air basins based on the ARB’s Commercial Harbor Craft 

Survey which collected the percent of time vessels spend at varying distances from 

shore, including percent of time spent in harbor, within 0-25, 25-50, 50-75, 75-100, and 

beyond 100 nautical miles. The land side air basins cover the areas 3 nautical miles 

from shore and the Outer Continental Shelf air basin cover the areas 3-100 nautical 

miles from shore. Table II-6 summarizes the statewide average of percent of vessel 

activity at varying distances from shore by ship type. 

Table II-6 Statewide Average of Percent of Vessel Activity at Varying Distances 

from Shore

Vessel Type Harbor 0-25nm 25-50nm 50-75nm 75-100 nm >100nm

Commercial Fishing 6% 37% 16% 11% 8% 22%

Charter Fishing 8% 40% 20% 19% 12% 0%

Ferries 51% 40% 6% 2% 1% 0%

Tow Boats 40% 22% 14% 9% 8% 7%

Tug Boats 34% 15% 12% 13% 20% 6%

Pilot Vessels 33% 30% 13% 10% 12% 1%

Work Boats 35% 32% 5% 10% 9% 8%

Crew and Supply 29% 27% 13% 11% 13% 8%

Others 30% 30% 12% 11% 10% 7%
B - 27

Source: ARB Commercial Harbor Craft 2002 survey

Table II-7 summarizes the percent of time commercial harbor craft spend within land 

side air basins or the Outer Continental Shelf air basins based on the information 

collected in the ARB’s Commercial Harbor Craft Survey.

Table II-7 Summary of Percent of Time Spent within Land Side Air Basins and 

Outer Continental Shelf Air Basins

Vessel Type Land side Air Basin Outer Continental Shelf Air Basin

Commercial Fishing 12% 88%

Charter Fishing 15% 85%

Ferries 59% 41%

Tow Boats 43% 57%

Tug Boats 36% 64%

Pilot Vessels 39% 61%

Work Boats 42% 58%

Crew and Supply 33% 67%

Others 35% 65%

We received several comments and suggestions to improve the spatial allocation. 

These comments reflected regional specific differences in vessel operations. According 

to Ventura County APCD, tug boats meet vessels one nautical mile from port and most 

emissions should be allocated to the land air basin. We believe there are tugs pushing 

barges transiting along the coast and these activities account for the emissions we 

allocated to the Outer Continental Shelf air basin. Ventura APCD suggests 36% of Crew 

& Supply vessel emissions occur within the South Central Coast air basin while 64% 

occur in the Outer Continental Shelf air basin. These numbers agree well with the 

statewide allocation in Table II-7.

Santa Barbara APCD suggests emissions from commercial boats are split evenly 

between the South Central Coast air basin and the Outer Continental Shelf air basin. 

We believe that this allocation sounds reasonable for commercial boats other than 

fishing vessels. This also agrees with the statewide allocation within acceptable range. 

Because we understand that most fishing activities occur beyond the 3 nautical mile 

zone, we assign more than 85% of fishing vessel emissions to the Outer Continental 

Shelf.

Considering the heavy marine traffic in the San Francisco air basin, we conducted 

additional analysis to allocate emissions within the Bay Area Air Quality Management 

District (BAAQMD). We allocate 84% of commercial fishing and charter fishing vessel 

emissions to the OCS air basin, and allocate the remaining 16% to the San Francisco 

air basin; we allocate tow boat emissions following the statewide default to reflect the 

inter-port long haul activity; we allocate 5% of emissions from all the other type of 

vessels to the OCS air basin, and allocate the remaining 95% to the San Francisco air 

basin.
B - 28

4. Additional Considerations and Assumptions

a. Operation in California Coastal Waters

The emission estimation methodology assumes all of the hours of operation occur 

within the boundaries defined by the California Coastal Waters. The two vessel types 

that might deviate from this assumption would be commercial fishing and charter fishing 

vessels. In an effort to address the issue as it pertains to those two types of commercial 

harbor craft, the ARB staff contacted the California Department of Fish and Game (DFG) 

and requested information about the region off California where fishing primarily occurs. 

The DFG segregates the waters off the coast of California into 10 minute by 10 minute 

grid system in an effort to track the types and quantities of marine resources taken off 

the California coast and landed at California’s ports and harbors. Comparison of the 

DFG grid system with the ARB’s definition of “California Coastal Waters” reveals that for 

the majority of the coastline, the DGF Fisheries Charts were within California Coastal 

Water boundaries. The results of that comparison are illustrated in Figure II-3.

We noticed an area of the DFG Fisheries Charts associated with the waters west of the 

Catalina Islands that lie outside California’s Coastal Waters. ARB staff evaluated the 

DFG 2002 landings data and found that the resources caught in that area amounted to 

less than one percent of the total 2002 landings for the counties associated with those 

waters (Santa Cruz, Monterey, San Luis Obispo, Santa Barbara, Ventura, Los Angeles, 

Orange, and San Diego). With that being the case, the ARB determined that it would 

make little or no difference in the emission estimates to continue to include emissions 

from commercial fishing vessels and charter fishing vessels associated with that area. 
B - 29

Figure II-3 The Overlap Between the California Department of Fish and Game’s

Fish Landings Grid System and the ARB’s “California Coastal Waters”
B - 30

b. Fuel Type

The emission estimation methodology assumes all commercial harbor craft engines are 

powered by diesel fuel. During the course of reviewing and collating the responses to 

the ARB’s Commercial Harbor Craft Survey, the ARB staff noticed that the percentage 

of vessel owner/operators that indicated they use gasoline as the primary fuel for their 

propulsion or auxiliary engines was less than five percent of all engines reported. When 

preparing the Survey data for use to typify commercial harbor craft engines, the ARB 

staff removed any engines that were clearly powered by gasoline.

c. Vessel Profile and Future Improvements

The ARB’s Commercial Harbor Craft Survey collected information for about 850 vessels 

which represent about 20% of the statewide population. The emission methodology 

assumes the results of the Survey are representative of California’s commercial harbor 

craft and used these profiles to scale up to statewide population. 

ARB’s proposed commercial harbor craft regulation will require vessel owners and 

operators to report more detailed information of the vessels and the engines. We will 

build a more complete and more reliable California commercial harbor craft data set 

which will provide a foundation for us to improve the emissions estimation in the future.

III. EMISSION ESTIMATES

Using the proposed methodology, we estimate statewide emissions from commercial 

harbor craft diesel-fueled engines in 2004 were about 3.3 tons per day of diesel PM, 

about 73.2 tons per day of oxides of nitrogen (NOx). Detailed emission estimates are 

presented in Table III-1. 

Table III-1 Commercial Harbor Craft Emissions in California in 2004 (Tons/day)

Vessel Type

Vessel 

Population NOx PM ROG CO

Charter Fishing 563 12.7 0.6 0.9 3.3

Commercial Fishing 2,727 17.4 0.8 1.3 4.8

Crew and Supply 64 1.4 0.1 0.1 0.4

Ferry/Excursion 416 21.0 0.9 1.4 5.6

Pilot Vessels 27 0.4 0.0 0.0 0.1

Tow Boats 35 3.0 0.1 0.2 0.7

Tug Boats 128 15.3 0.6 1.0 3.8

Work Boats 89 0.5 0.0 0.0 0.1

Others 136 1.5 0.1 0.1 0.4

Total 4,185 73.2 3.3 5.0 19.2

Ferry/excursion vessels and tug/tow boats jointly account for about 14% of the 

statewide harbor craft population and 50% of the statewide harbor craft emissions. The 

engines of these vessels are relatively larger and operate more often than other vessel 
B - 31

categories. Commercial fishing vessels account for 65% of the harbor craft population 

but only emit around 25% of the emissions.

Table III-2 provides NOx emissions by engine and vessel type. Propulsion engines 

account for 93% of NOx emissions from commercial harbor craft.

Table III-2 NOx Emissions By Engine Type and Vessel Type in 2004

Main Engine Auxiliary Engine

Vessel Type

Number of 

Engines

Tons/day 

NOx

Number of 

Engines

Tons/day 

NOx

Charter Fishing 997 12.1 422 0.6

Commercial Fishing 3,054 14.8 1,254 2.6

Crew and Supply 160 1.1 70 0.4

Ferry/Excursion 836 20.2 512 0.8

Pilot Vessels 46 0.4 4 0.0

Tow Boats 74 2.8 41 0.2

Tug Boats 246 14.9 204 0.4

Work Boats 130 0.5 28 0.0

Others 151 1.4 63 0.1

Total 5,693 68.1 2,598 5.1

Table III-3 summarizes NOx and PM emissions by Air Quality Management District 

(AQMD) or Air Pollution Control District (APCD) and Outer Continental Shelf (OCS) air 

basin in calendar year 2004. The AQMDs and APCDs are commonly called air districts. 

OCS air basin covers 3-100 nautical miles from shore. Figure III-1 illustrates these air 

districts and OCS air basins.

Table III-3 NOx, PM Emissions By Air District and Air Basin in 2004

Air Districts

Number of 

Vessels

NOx 

Tons/year

NOx in 

OCS

PM 

Tons/day

PM in

OCS

Bay Area AQMD (BA) 1,468 26.9 10.2 1.2 0.5

El Dorado County APCD (ED) 9 0.3 0.0 0.0 0.0

Mendocino County AQMD (MEN) 169 1.3 1.1 0.1 0.0

Monterey Bay Unified APCD (MBU) 379 3.6 2.7 0.2 0.1

North Coast Unified APCD (NCU) 299 2.3 1.9 0.1 0.1

Northern Sonoma County APCD (NS) 145 1.2 1.0 0.1 0.0

Placer County APCD (PLA) 9 0.3 0.0 0.0 0.0

San Diego County APCD (SD) 307 9.2 5.5 0.4 0.2

San Joaquin Valley Unified APCD (SJU) 43 0.8 0.0 0.0 0.0

San Luis Obispo County APCD (SLO) 145 1.4 1.1 0.1 0.1

Santa Barbara County APCD (SB) 193 2.7 2.0 0.1 0.1

South Coast AQMD (SC) 745 18.7 11.7 0.8 0.5

Ventura County APCD (VEN) 194 2.5 1.8 0.1 0.1

Yolo/Solano AQMD (YS) 81 1.9 0.0 0.1 0.0

Total 4,185 73.2 38.9 3.3 1.8
B - 32

Figure III-1 Illustration of California Air Districts and OCS Air Basins

About one third of the state harbor craft are in the Bay Area AQMD. These vessels 

account for about 37% of statewide NOx or PM emissions. South Coast AQMD has 

18% of the statewide harbor craft and account for about 26% of the NOx or PM 

emissions. San Diego County APCD only has 7% of the statewide population but these 

vessels emitted about 12% of statewide harbor craft NOx or PM emissions. These 

three air districts jointly are home to 60% of the statewide harbor craft and these 

vessels are responsible for 75% of statewide NOx or PM emissions.

Statewide about 53% of the emissions occur in the Outer Continental Shelf air basin. 

Generally fishing vessels spend the most time in the Outer Continental Shelf, while 

ferries tend to spend the most time closer to shore.
B - 33

Figure III-2 illustrates the change of commercial harbor craft NOx and PM emissions 

over time from 2004 to 2025. NOx emissions from harbor craft in California will 

decrease from 73 tons per day in 2004 to about 32 tons per day in 2025 and PM 

emissions will decrease from 3.3 tons per day to about 1.2 tons during the same period. 

The decline of emissions between 2004 and 2009 is partially caused by the decline of 

the fishing fleet from 2004 to 2009 as we project based on fish landing data, natural 

engine turnover, and the more stringent EPA marine engine emissions standards. New 

engines need to comply with EPA standards and are cleaner than the old engines which 

are replaced. The decrease in emissions after 2009 reflects the gradual phase in of 

new engines replacing old engines retired from the fleet.

Figure III-2 Estimation of Commercial Harbor Craft NOx, PM Emissions 2004-2025

0

10

20

30

40

50

60

70

80

2004 2007 2010 2013 2016 2019 2022 2025

Calendar Year

Tons/day NOx

0

1

1

2

2

3

3

4

Tons/day PM

NOx PM

REFERENCES

1. California Air Resources Board, Statewide Commercial Harbor Craft Survey. 

2004. Available at 

http://www.arb.ca.gov/ports/marinevess/documents/hcsurveyrep0304.pdf

2. California Air Resources Board, Off-road Exhaust Emissions Inventory Fuel 

Correction Factors. 2005. Available at 

http://www.arb.ca.gov/msei/offroad/techmemo/arb_offroad_fuels.pdf.

3. California Air Resources Board, Mail-Out #: MSC 99-32: Notice of Public Meeting 

to Consider Approval of California's Emissions Inventory for Off-Road Large 

Compression Ignited Engines (>25HP) Using the New OFFROAD Emissions 

Model. 1999: Sacramento. Available at 

http://www.arb.ca.gov/msei/offroad/pubs/mo9932.zip.
B - 34

APPENDIX A COMMERCIAL HARBOR CRAFT EMISSION FACTOR TABLE

HP Range Model Year ME 

NOx

ME 

PM

ME 

ROG

ME 

CO

AE 

NOx

AE 

PM

AE 

ROG

AE 

CO

pre-1998 8.14 0.72 1.84 3.65 6.90 0.64 2.19 5.15

1998-1999 8.14 0.72 1.80 3.65 6.90 0.64 2.14 5.15

2000-2004 7.31 0.72 1.80 3.65 6.90 0.64 2.14 5.15

2005-2008 5.32 0.30 1.80 3.73 5.32 0.30 2.14 3.73

25-50 hp

2009-2020 5.32 0.22 1.80 3.73 5.32 0.22 2.14 3.73

pre-1997 15.34 0.80 1.44 3.50 13.00 0.71 1.71 4.94

1997-1999 10.33 0.66 0.99 2.55 8.75 0.58 1.18 3.59

2000-2004 7.31 0.66 0.99 2.55 7.31 0.58 1.18 3.59

2005-2008 5.32 0.30 0.99 3.73 5.32 0.30 1.18 3.73

51-120 hp

2009-2020 5.32 0.22 0.99 3.73 5.32 0.22 1.18 3.73

pre-1971 16.52 0.73 1.32 3.21 14.00 0.65 1.57 4.53

1971-1978 15.34 0.63 1.10 3.21 13.00 0.55 1.31 4.53

1979-1983 14.16 0.52 1.00 3.21 12.00 0.46 1.19 4.53

1984-1986 12.98 0.52 0.94 3.14 11.00 0.46 1.12 4.43

1987-1995 12.98 0.52 0.88 3.07 11.00 0.46 1.05 4.33

1996-1999 9.64 0.36 0.68 1.97 8.17 0.32 0.81 2.78

2000-2003 7.31 0.36 0.68 1.97 7.31 0.32 0.81 2.78

2004-2012 5.10 0.22 0.68 3.73 5.10 0.22 0.81 3.73

121-175 hp

2013-2020 3.80 0.09 0.68 3.73 3.80 0.09 0.81 3.73

pre-1971 16.52 0.73 1.32 3.21 14.00 0.65 1.57 4.53

1971-1978 15.34 0.63 1.10 3.21 13.00 0.55 1.31 4.53

1979-1983 14.16 0.52 1.00 3.21 12.00 0.46 1.19 4.53

1984-1986 12.98 0.52 0.94 3.14 11.00 0.46 1.12 4.43

1987-1994 12.98 0.52 0.88 3.07 11.00 0.46 1.05 4.33

1995-1999 9.64 0.36 0.68 1.97 8.17 0.32 0.81 2.78

2000-2003 7.31 0.36 0.68 1.97 7.31 0.32 0.81 2.78

2004-2013 5.10 0.15 0.68 3.73 5.10 0.15 0.81 3.73

176-250 hp

2014-2020 3.99 0.08 0.68 3.73 3.99 0.08 0.81 3.73

pre-1971 16.52 0.70 1.26 3.07 14.00 0.62 1.50 4.33

1971-1978 15.34 0.60 1.05 3.07 13.00 0.53 1.25 4.33

1979-1983 14.16 0.50 0.95 3.07 12.00 0.45 1.13 4.33

1984-1986 12.98 0.50 0.90 3.07 11.00 0.45 1.07 4.33

1987-1994 12.98 0.50 0.84 2.99 11.00 0.45 1.00 4.22

1995-1999 9.64 0.36 0.68 1.97 8.17 0.32 0.81 2.78

2000-2003 7.31 0.36 0.68 1.97 7.31 0.32 0.81 2.78

2004-2013 5.10 0.15 0.68 3.73 5.10 0.15 0.81 3.73

251-500 hp

2014-2020 3.99 0.08 0.68 3.73 3.99 0.08 0.81 3.73
B - 35

Continued from previous page

HP Range Model Year ME 

NOx

ME 

PM

ME 

ROG

ME 

CO

AE 

NOx

AE 

PM

AE 

ROG

AE 

CO

pre-1971 16.52 0.70 1.26 3.07 14.00 0.62 1.50 4.33

1971-1978 15.34 0.60 1.05 3.07 13.00 0.53 1.25 4.33

1979-1983 14.16 0.50 0.95 3.07 12.00 0.45 1.13 4.33

1984-1986 12.98 0.50 0.90 3.07 11.00 0.45 1.07 4.33

1987-1994 12.98 0.50 0.84 2.99 11.00 0.45 1.00 4.22

1995-1999 9.64 0.36 0.68 1.97 8.17 0.32 0.81 2.78

2000-2006 7.31 0.36 0.68 1.97 7.31 0.32 0.81 2.78

2007-2012 5.10 0.15 0.68 3.73 5.10 0.15 0.81 3.73

501-750 hp

2013-2020 3.99 0.08 0.68 3.73 3.99 0.08 0.81 3.73

pre-1971 16.52 0.70 1.26 3.07 14.00 0.62 1.50 4.33

1971-1978 15.34 0.60 1.05 3.07 13.00 0.53 1.25 4.33

1979-1983 14.16 0.50 0.95 3.07 12.00 0.45 1.13 4.33

1984-1986 12.98 0.50 0.90 3.07 11.00 0.45 1.07 4.33

1987-1998 12.98 0.50 0.84 2.99 11.00 0.45 1.00 4.22

1999 9.64 0.36 0.68 1.97 8.17 0.32 0.81 2.78

2000-2006 7.31 0.36 0.68 1.97 7.31 0.32 0.81 2.78

2007-2011 5.53 0.20 0.68 3.73 5.53 0.20 0.81 3.73

2012-2016 4.09 0.08 0.68 3.73 4.09 0.08 0.81 3.73

751-1900 hp

2017-2020 1.30 0.03 0.18 3.73 1.30 0.03 0.18 3.73

pre-1971 16.52 0.70 1.26 3.07 14.00 0.62 1.50 4.33

1971-1978 15.34 0.60 1.05 3.07 13.00 0.53 1.25 4.33

1979-1983 14.16 0.50 0.95 3.07 12.00 0.45 1.13 4.33

1984-1986 12.98 0.50 0.90 3.07 11.00 0.45 1.07 4.33

1987-1998 12.98 0.50 0.84 2.99 11.00 0.45 1.00 4.22

1999 9.64 0.36 0.68 1.97 8.17 0.32 0.81 2.78

2000-2006 7.31 0.36 0.68 1.97 7.31 0.32 0.81 2.78

2007-2012 5.53 0.20 0.68 3.73 5.53 0.20 0.81 3.73

2013-2015 4.37 0.10 0.68 3.73 4.37 0.10 0.81 3.73

1901-3300 hp

2016-2020 1.30 0.03 0.18 3.73 1.30 0.03 0.18 3.73

pre-1971 16.52 0.70 1.26 3.07 14.00 0.62 1.50 4.33

1971-1978 15.34 0.60 1.05 3.07 13.00 0.53 1.25 4.33

1979-1983 14.16 0.50 0.95 3.07 12.00 0.45 1.13 4.33

1984-1986 12.98 0.50 0.90 3.07 11.00 0.45 1.07 4.33

1987-1998 12.98 0.50 0.84 2.99 11.00 0.45 1.00 4.22

1999 9.64 0.36 0.68 1.97 8.17 0.32 0.81 2.78

2000-2006 7.31 0.36 0.68 1.97 7.31 0.32 0.81 2.78

2007-2013 5.53 0.20 0.68 3.73 5.53 0.20 0.81 3.73

2014-2015 4.94 0.25 0.68 3.73 4.94 0.25 0.81 3.75

3301-5000 hp

2016-2020 1.30 0.03 0.18 3.73 1.30 0.03 0.18 3.75