9.7 Ships - Mobile Marine Ship
Categories 2041 - 2220
9.7.1 Introduction
Categories 2041 through 2220 account for emissions from combustion of fuel from engines of commercial ocean-going vessels (OGVs).
The emission estimates for OGVs are developed by the California Air Resources Board (CARB) and are based on numerous sources that include data from CARB OGV surveys, vessels population data from governmental agencies such as State Land Commissions, and engine characteristic data from various OGV studies and manufacturer reports. The inventory accounts for commercial OGVs greater than or equal to 400 feet in length, or 10,000 gross tons in weight, or propelled by a marine compression ignition engine with a displacement equal to or greater than 30 liters per cylinder. The emission inventory includes all ocean-going vessels emissions occurring within 3, 24, and 100 nautical miles from the coastline of the San Francisco Bay Area region. The emissions reflected herein include all five criteria pollutants (PM, VOC, NOx, SOx, CO).
Ship emissions occur during three distinct operating modes: transit (emissions from vessels operations between ports), maneuvering (slow speed vessels operations while in-port areas), and hoteling (also known as berthing; in-port emissions while moored to a dock). The emissions occur from ship engines: main engines, which are used to propel the vessels at sea; and auxiliary engines, which are used to provide power to ships for uses other than propulsion. Additionally, most ships have auxiliary boilers to provide steam heat for uses including fuel heating and hot water. Emissions also result from the operation of ship boilers. The emissions are calculated by CARB and are based primarily on a ship by ship and a port call by port call basis. Ship emissions are then categorized by vessels type. For the inventory, the vessels types are classified into 8 categories. They include auto, bulk cargo, container, general cargo, passenger, reefers, Ro-Ro, and tankers.
For a more detailed description of ships, more information can be found at CARB’s website, CARB Appendix D - Emissions Estimation Methodology for Ocean-Going Vessels. 353.
9.7.2 Methodology
Ship emissions data are derived by inventory staff of the state’s chief air quality regulatory agency, the California Air Resources Board (CARB). 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) inventory354. For related sets of categories, such as airport ground support equipment (GSE), ships, structures coatings etc., where independent data collection and derivation of emissions are both cost- and time-prohibitive and likely a redundant effort, BAAQMD staff export the emissions data directly from CEPAM into the District’s Base Year inventory package. This calculation approach and collection of categories is internally termed as “CARB Source Categories”.
The CEPAM provides historical emissions as well as forecasts emissions for major emission source classifications including – a) on-road mobile sources [from Emissions Factor (EMFAC) model], b) off-road mobile sources (OFFROAD model), and, c) stationary and areawide sources - For these major source classifications, CEPAM combines facility level /area source emissions data reported to the California Emissions Inventory Development and Reporting System (CEIDARS) for multiple years by various regional air quality agencies (including the BAAQMD).
The current base year inventory uses the 2016 CEPAMv1.05 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.
In the QA process, BAAQMD staff perform a systematic crosswalk between CEPAM’s source category classification (Emission Inventory Code - EICs) and the District’s source category classification (category identification number - cat_ids). Based on the scope of emissions covered, individual EIC or a group of EICs are mapped to a single cat_id. This process also addresses issues when cat_ids have no matching EICs or there are discontinued EICs that need to be investigated. Following this, emissions data are backcasted to year-1990, as well as forecasted to year-2040 using certain mathematical methods, as described in the Trends section. Finally, the emissions trends spanning from year 1990-2040 for each category and pollutant are evaluated, and CARB staff are consulted for explanation of any observed anomalies in trends.
9.7.3 Changes in Methodology
The methodology used to estimate OGV emissions is based on the above mentioned CARB’s 2005 draft report1. Although the report is in draft form, the emission data is derived based on methodology and findings given in this report. The methodology is similar to that of previous Base Year (BY2011) methodology.
9.7.4 Emissions
A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.
9.7.5 Trends
The emissions data from CARB CEPAM inventory only covers year 2000 to 2035. Different approaches were applied to estimate emissions for years 1990 to 1999 and 2036 to 2040 as described below. Please refer to CARB’s CEPAM Inventory Documentation 1 for more information.
(a) Historical Emissions / History
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 ships, the BY2011 scaling method is used to derive emissions for years 1990 through 1999.
(b) Future Projections / Growth
For ship categories processed as CARB Sources, emissions are forecasted to year 2035 by CARB staff by applying growth profiles to the base year-2012 inventory data (see above in ‘Methodology’ section). Further emissions forecasting was done by holding the year-2035 emissions data constant through and up to year-2040.
(c) Controls
The United States Environmental Protection Agency (USEPA) currently regulates ocean-going ships engine types355. The EPA rules are designed to decrease air pollutants via requirements of new ships to have more efficient fuel burning engines (category 3 engines) installed and old ships retrofitted with new engines. The current rules apply only to U.S. ships. In mid-2009 via rule enactment, ARB has begun to regulate the types of fuel use for all ocean going vessels traveling within 24 nautical miles from the California coast line356. All ocean going vessels are required to use low sulfur fuel within this 24 nautical mile zone of the California coastline. Since the enactment of this rule, there has been a significant decrease in SOx and PM emissions from ocean going vessels. Additionally, to comply with CARB Ships At-Berth Regulation357, shore power installation is currently being installed by various Bay Area Ports as a mean to further reduce ship emissions. Shore power regulation mainly affects container, passenger, and refrigerated cargo vessels. It is anticipated that the usage of electric power will significantly reduce hoteling emissions from ocean going vessels. Other regulations include the MARPOL ANNEX VI regulation which regulates certain fuel type for all ocean going vessels358.
9.7.6 Uncertainties
Please refer to CARB’s CEPAM Inventory documentation2 for more information.
9.7.7 Contact
Author: Tan Dinh
Reviewer: Abhinav Guha, Yuan Du
Last Update: November 06, 2023
9.7.8 References & Footnotes
CARB. 2008. https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2008/fuelogv08/appdfuel.pdf↩︎
CARB. Criteria Pollutant Emission Inventory Information (CEPAM) . [accessed 2023 Mar 13]. https://ww2.arb.ca.gov/criteria-pollutant-emission-inventory-data↩︎
USEPA. 2021. https://www.epa.gov/vessels-marinas-and-ports↩︎
CARB. 2008. https://ww2.arb.ca.gov/our-work/programs/ocean-going-vessel-fuel-regulation↩︎
CARB. 2021. https://ww2.arb.ca.gov/our-work/programs/ocean-going-vessels-berth-regulation↩︎
USEPA. 2011. https://www.epa.gov/enforcement/marpol-annex-vi-and-act-prevent-pollution-ships-apps↩︎