9.9 Recreational Boats

Categories 1676, 1677, 1678, 1679, and 1680

9.9.1 Introduction

Categories 1676 through 1680 account for fuel combustion emissions (NO_x, CO, PM, PM₁₀, PM_2.5, ROG, SO₂, and TOG) from pleasure boats with inboard or outboard engines, and personal watercraft, etc. in the Bay Area. Nearly all outboard and personal watercraft motors utilized two-stroke engines. These engines burn gasoline inefficiently and discharge as much as 30% unburned fuel into water and subsequently into the air. Spark-ignition outboard engines are available in power ratings from 2 to 300 horsepower. They are used in a wide variety of applications including fishing, water skiing and water-borne transportation.

Spark-ignition outboard engines include carbureted, fuel injected and direct-injected two-stroke, and carbureted and fuel injected four-stroke configurations. Personal watercraft are defined by U.S. EPA as marine vessels that are not outboards, inboards, or sterndrive, but they can more accurately be defined as small craft on which the rider sits or stands during operation. Personal watercraft are primarily used for recreation, including touring, and water skiing.

9.9.2 Methodology

The Recreational Boats emissions are derived by California Air Resources Board (CARB) inventory staff. This significant emissions dataset, sorted by county, is published every few years and is a product of the State Implementation Plan (SIP) emissions document formally known as the California Emissions Projection Analysis Model (CEPAM) inventory. BAAQMD staff export the emissions data directly from CEPAM into the District’s Base Year inventory package. This calculation approach and collection of categories are internally termed as “CARB Source Categories”.

This base year inventory uses the 2016 CEPAMv1.05³⁶⁶ to estimate emissions from “CARB Source Categories”. This version of the CEPAM derives emissions from a 2012 base year inventory and contains backcasts and forecasts from year-2000 to year-2035. All applicable regulatory and technological controls are assumed to be built into the CEPAM dataset during CARB staff’s inventory computation work. After the emissions data are exported, the inventory for CARB Source categories is taken through a quality assurance (QA) process.

9.9.3 Changes in Methodology

Emissions data were obtained from the CARB’s 2016 CEPAMv1.05¹. In comparison, the BY2011 methodology involved area source categories were derived from the CARB’s OFFROAD2007 model.

9.9.4 Emissions

A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.

9.9.5 Trends

(a) Historical Emissions / History

Base year 1999 emissions, the methodology was based upon a study by System Applications International (SAI) entitled “Development of an Improved Inventory of Emissions from Pleasure Craft in California”. The study was carried out for the California Air Resources Board and was completed in June 1995. California Department of Motor Vehicles (DMV) Vessel Registration showed that over 98% of the boats registered were pleasure craft. The registration figures were sub-divided into 6 unique length groups and various methods of propulsion, such as inboard, outboard, jet powered and others. For each group, fuel usage was determined from a survey of 10,000 registered boat owners. The survey showed that inboard, inboard/outboard and jet powered craft were the biggest consumers of fuel. Outboard craft were found to be medium gasoline users. Others include sailboats and auxiliary sailboats and were found to have very low average annual consumption. Emission factors were obtained from National Marine Manufacturers Association. These emission factors were also used by Environmental Protection Agency (EPA) in their Non-road Engine and Vehicle Emissions Study. These were given for outboard 2 stroke gasoline engines and inboard 4 stroke gasoline and diesel engines from several engine manufacturers including Honda, Mercury Marine, Outboard Marine Corporation, Volvo and Yamaha. The SAI Report contained average monthly, weekly and diurnal profiles for northern, southern and central California. The figures for northern California were used to develop the annual average inventory.

California Air Resources Board (CARB) developed the Off-road vehicle emission inventory (OFFROAD2007) model to estimate emissions from off-road motor vehicles for all counties and air basins in California. The previous inventory’s criteria air pollutants and GHG emissions data for recreational boat categories in the Bay Area were obtained from the CARB’s OFFROAD2007 model.

Three different methods are used for backcasting to project historical emissions prior to year-2000 going back to year-1990, which is the starting year of the current base year inventory (referred to as BY2015). Following preliminary evaluation of the data available for initial years (post-year 2000) in the CEPAM inventory, BAAQMD staff recommends a backcasting approach. The default backcasting approach is defined by a formula here –

\[ \begin{eqnarray} \text{BY2015 emissions for year X for county Y} = \text{BY2011 total emissions for year X} \\ \\ \times \dfrac{\text{BY2015 year-2000 emissions}}{\text{ BY2011 year-2000 emissions}} \\ \\ \times \dfrac{\text{county Y fraction}}{\text{ fractional total}} \end{eqnarray} \]

This calculation is referred to as the BY2011 scaling method (based on the previous base year inventory). The second calculation approach is to derive the linear regression best fit of the year 2000-2008 CARB Sources emissions data for a category, species, and county, and extrapolate that data back in time. If this backcasting results in negative emissions prior to a certain year, the lowest positive emission value is held constant from that particular year back to year-1990. The third possible calculation approach is to use a specific growth profile for the category, provided by the in-house staff expert. These custom growth profiles are often derived from surrogate data provided by another agency or resource, or available activity data that is assumed to scale with the emissions for that specific CARB Source category.

For the recreational boats categories, the BY2011 scaling method is used to derive emissions for years 1990 through 1999.

(b) Future Projections / Growth

Emissions forecasting was done by holding the year-2035 emissions data constant through and up to year-2040. For CARB Sources, emissions are forecasted by CARB staff by applying growth profiles to the base year-2012 inventory data (see above in ‘Methodology’ section).

(c) Control

Recreational Boats emissions were reduced by following actions:

• In 1998, the U.S. EPA began regulating exhaust emissions from marine engines (outboard motors and personal watercraft) to reduce 75% emissions by 2025.
• In December of 1998, the CARB adopted standards to require cleaner engines. Beginning with 2001 models, new outboard engines, personal watercraft and jet boats must be 75% cleaner and 90% cleaner by 2008.

9.9.6 Uncertainties

The estimated Recreational Boats emissions for Solano and Sonoma counties under District’s jurisdiction may contribute to an increased uncertainty of the Bay Area Off-road emissions.

9.9.7 Contact

Author: Michael Nguyen

Reviewer: Sukarn Claire

Last Update: November 06, 2023

9.9.8 References & Footnotes

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366. CARB. 2016. California Emissions Projection Analysis Model (CEPAM) inventory, https://www.arb.ca.gov/app/emsinv/2016ozsip/2016ozsip/fcemssumcat_2016o3sip105.php↩︎