10.16 Ozone Depleting Substance Substitutes (ODSS)
Categories 2289 - 2332, 2531, 2532, 2533, 2534, 2556, 2557, and 2558
10.16.1 Introduction
This chapter accounts for organic (TOG) emissions from various ozone depleting substance substitutes (ODSS). Ozone-depleting substances (ODS) are those that are known to deplete the stratospheric ozone layer and have been majorly phased out under the terms of the 1987 Montreal Protocol and the 1990 Clean Air Act Amendments. ODS include chlorofluorocarbons (CFCs; Class I), hydrochlorofluorocarbons (HCFCs; Class II), halons and other Class I compounds like methyl bromide (CH3Br), carbon tetrachloride (CCl4), methyl chloroform (CH3CCl3), etc. These ODS have been traditionally used in refrigeration and air conditioning equipment, solvent cleaning, foam production, sterilization, aerosol and fire extinguishing applications.
The substitutes approved to replace the ODS include hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) and are collectively known as ODSS. They emit total organic gases (TOGs) that are also greenhouse gases (GHGs), with many of them having a high global warming potentials (GWPs485).
For this emissions inventory, the District’s inventory is directly derived from California Air Resources Board’s (CARB) statewide GHG emissions inventory486. The statewide GHG inventory uses an economic sector-specific classification system that results in a total of 49 ODSS categories (Categories 2289 - 2332, 2531-2534, and 2556-2558), each of which covers a specific sub-type of ODSS sources (e.g. Category 2291 represents emissions of the gas CF4 from Fire Protection usage in the Commercial sector487).
Emissions from ODSS categories typically occur from diffused leaks from thousands of pieces of equipment and machinery. These emissions may occur from permitted sources but the methodology to calculate them is similar to that of aggregated non-point sources, and hence these emissions are considered as area source emissions. All ODSS emissions are considered total organic gas (TOG) emissions. All of the ODSS are non-reactive, so there are no reactive organic gas (ROG) emissions.
Emissions are classified under the following category numbers:
| Category # | Description |
|---|---|
| 2289 | Commercial Aerosols HFC-134a |
| 2290 | Commercial Aerosols HFC-152a |
| 2556 | Commercial Aerosols HFC-43-10mee |
| 2291 | Commercial Fire Protection CF4 |
| 2292 | Commercial Fire Protection HFC-125 |
| 2293 | Commercial Fire Protection HFC-236fa |
| 2294 | Commercial Fire Protection HFC-227ea |
| 2295 | Commercial Foams HFC-134a" = 2295 |
| 2296 | Commercial Foams HFC-245fa" = 2296 |
| 2297 | Commercial Refrigeration and Air Conditioning HFC-125 |
| 2298 | Commercial Refrigeration and Air Conditioning HFC-134a |
| 2299 | Commercial Refrigeration and Air Conditioning HFC-143a |
| 2300 | Commercial Refrigeration and Air Conditioning HFC-236fa |
| 2301 | Commercial Refrigeration and Air Conditioning HFC-32 |
| 2302 | Commercial Refrigeration and Air Conditioning HFC-152a |
| 2303 | Industrial Aerosols HFC-134a |
| 2304 | Industrial Aerosols HFC-152a |
| 2557 | Industrial Aerosols HFC-43-10mee |
| 2305 | Industrial Fire Protection CF4 |
| 2306 | Industrial Fire Protection HFC-125 |
| 2307 | Industrial Fire Protection HFC-236fa |
| 2308 | Industrial Fire Protection HFC-227ea |
| 2309 | Industrial Foams HFC-134a, |
| 2310 | Industrial Foams HFC-245fa |
| 2311 | Industrial Refrigeration and Air Conditioning HFC-125 |
| 2312 | Industrial Refrigeration and Air Conditioning HFC-134a |
| 2313 | Industrial Refrigeration and Air Conditioning HFC-143a |
| 2314 | Industrial Refrigeration and Air Conditioning HFC-236fa |
| 2315 | Industrial Refrigeration and Air Conditioning HFC-32 |
| 2316 | Industrial Refrigeration and Air Conditioning HFC-152a |
| 2317 | Industrial Solvents CF4 |
| 2318 | Industrial Solvents HFC-245fa |
| 2531 | Industrial Solvents HFC-365mfc |
| 2532 | Industrial Solvents HFC-43-10mee |
| 2533 | Industrial Solvents Other PFC and PFE |
| 2319 | Residential Aerosols HFC-134a |
| 2320 | Residential Aerosols HFC-152a |
| 2534 | Residential Aerosols HFC-227ea |
| 2558 | Residential Aerosols HFC-43-10mee |
| 2321 | Residential Foams HFC-134a |
| 2322 | Residential Foams HFC-245fa |
| 2323 | Residential Refrigeration and Air Conditioning HFC-125 |
| 2324 | Residential Refrigeration and Air Conditioning HFC-134a |
| 2325 | Residential Refrigeration and Air Conditioning HFC-32 |
| 2326 | Transportation Aerosols HFC-134a |
| 2329 | Transportation Refrigeration and Air Conditioning HFC-125 |
| 2330 | Transportation Refrigeration and Air Conditioning HFC-134a |
| 2331 | Transportation Refrigeration and Air Conditioning HFC-143a |
| 2332 | Transportation Refrigeration and Air Conditioning HFC-32 |
10.16.2 Methodology
The ODSS category emissions are estimated from CARB’s Documentation of California’s Greenhouse Gas Inventory (CARB2, accessed May 12, 2020). The CARB inventory is developed using the CARB ODSS Emissions Model488. The emissions values in the CARB inventory are statewide totals and divided into four sectors (commercial, industrial, residential and transportation). Within each sector, the ODSS emissions are further divided by usage (i.e. Aerosols, Fire Protection, Foams, Refrigeration and Air Conditioning, and Solvents, if applicable).
The District’s portion of the State’s total is estimated for each sector based on the 2015 socioeconomic metrics from the following sources:
Industrial Sector - Total industrial employment from California Employment Development Department489
Commercial Sector - Total commercial (Service + Government) employment from California Employment Development Department5
Residential Sector - Total Bay Area residential population as per California Association of Bay Area Governments490
Transportation Sector - Total number of vehicle registrations (year 2019) from California Department of Motor Vehicles.
It should be noted that the ABAG population data is derived from State of California’s Department of Finance reports491
In 2015, the fraction of Bay Area TOG emissions to that of the State for the ODSS categories are estimated to be 0.2220, 0.2265, 0.1899, and 0.1846 for commercial, industrial, residential, and transportation sectors, respectively. The Bay Area portion of emissions for each ODSS category was derived by multiplying the state totals from CARB by the fractions noted above.
(a) Activity Data / Throughput
The District does not have access or exposure to the activity data used in the ODSS model4 and directly uses the statewide emissions for further processing.
(b) County Distribution / Fractions
The county-specific socioeconomic metrics in Bay Area (employment for commercial and industrial sectors, population for residential sector, and vehicle registrations for transportation sector) are used to derive the county fractions, which further split the emissions of Bay Area into each county.
(c) Emission Factors
Since emissions are derived directly from State emissions inventory which is based on the ODSS emission model4, the District does not have information on category-specific emission factors.
(d) Control Factors
Presently, no known District regulations or controls have been instituted to prevent emissions of ODSS from individual facilities. The District has the jurisdiction and reserves the right to enforce existing State laws regarding use of or ban on use of ODSS within the Bay Area.
(e) Speciation
All ODSS emissions are considered total organic gas (TOG) emissions. All ODSS gases are non-reactive in the lower troposphere, so there are no reactive organic gas (ROG) emissions. Hence the ROG to TOG ratio is equal to zero.
10.16.3 Changes in Methodology
In District’s prior inventories (e.g. base year 2011 inventory), the emissions of ODSS were classified into eight categories (1751 through 1758) based on the type of ODSS emitted (e.g., Category 1752 for HFC-125) across all sectors. In the current base year inventory, the District’s efforts have been aligned with the state’s ODSS emission inventory, in which a sector-specific classification system has been adopted with an additional level of hierarchy included to represent the ‘use class’ within each sector2. This results in a total of 49 ODSS categories (Categories 2289 - 2332, 2531 - 2534, and, 2556 - 2558) with a narrow scope of emissions for each category (e.g., Category 2291 represents emissions on CF4 from Fire Protection in the Commercial sector).
In addition, the data sources of the proxy activity data (or socioeconomic metrics, see Methodology) used to apportion the statewide ODSS emissions to county level across the four economic sectors have been updated.
10.16.4 Emissions
A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.
The TOG emissions for base year 2015 from the 49 ODSS categories in the SFBA total to 2504 tons/year, of which 34% are from Commercial, 15% from Industrial, 25% from Residential, and about 26% from Transportation sectors. This makes the group of ODSS sources a mid-tier contributor to TOG emissions in the SFBA.
10.16.5 Trends
The use of ODSS has steadily increased since 1990. The TOG emissions for most major-emitting categories in the Commercial sector increased significantly from the 1990s through 2010s and beyond. In some cases, emissions decreased after peak emissions occurred (around year 2010) like Category 2330 (Transportation) or stabilized/slightly decrease like Category 2312 (Industrial). This could be related to federal mandates and regulations on vehicle and industrial refrigeration and air conditioning substances. Emission increases stabilized in the case of major-emitting Industrial categories after year 2020.
(a) Historical Emissions / History
The CARB GHG inventory2 estimates emissions from year 2000 to 2017. In order to estimate historical emissions for the full time span of the current base year inventory (year 1990 to 2040), a linear regression approach is applied. For each category, the slope and intercept of emission trend line is derived using emissions data from year 2000-2003. These parameters are used to extrapolate the emissions back to year 1990 for each of the 49 categories. In case the extrapolated trend line intercepts the x-axis (leading to negative numbers), the TOG emissions are set to zero from that point going back to year 1990.
(b) Future Projections / Growth
The CARB GHG inventory2 estimates emissions from year 2000 to 2017. In order to make future projections for the full time span of this base year inventory (year 1990 to 2040), a linear regression approach is applied. For each category, the slope and intercept of emission trend line is derived using emissions data from year 2014-2017. These parameters are used to extrapolate the emissions to year 2040 for each of the 49 categories. In case the extrapolated trend line intercepts the x-axis (leading to negative numbers), the TOG emissions are set to zero from that point going forward to year 2040.
10.16.6 Uncertainties
The main sources of uncertainties in this calculation approach arises from the accuracy of the throughput data collected across the state and the leakage rates / emissions factors assumed. More details on the uncertainties for individual ODSS gases can be found in Gallagher et al.3. Uncertainty levels for inventory-based emission estimates vary from 15% to 25% for the major ODSS compounds. Since there is some uncertainty involved in scaling a state-level inventory to produce Bay Area specific estimates, mainly arising from the scaling parameters used for the four sectors, the above uncertainty estimate should be considered to be a lower threshold.
10.16.7 Contact
Author: Abhinav Guha
Reviewers: Tan M. Dinh and Yuan Du
Last Update: November 06, 2023
10.16.8 References & Footnotes
IPCC. 2000. Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories. Intergovernmental Panel on Climate Change. https://www.ipcc-nggip.iges.or.jp/public/gp/bgp/3_7_Substitutes_Ozone-Depleting_Substances.pdf↩︎
CARB. 2020a. California’s GHG Inventory by Sector and Activity. California Air Resources Board. Twelfth Edition - 2000 to 2017. https://ww2.arb.ca.gov/ghg-inventory-archive↩︎
CARB. 2020b. https://ww2.arb.ca.gov/applications/california-ghg-inventory-documentation↩︎
Gallagher, G. et al. 2014. High-global Warming Potential F-gas Emissions in California: Comparison of Ambient-based versus Inventory-based Emission Estimates, and Implications of Refined Estimates. Gallagher, G.; Zhan, T.; Hsu, Y-K.; Gupta, P.; Pederson, J.; Croes, B.; Blake, D. R.; Barletta, B.; Meinardi, S.; Ashford, P.; Vetter, A.; Saba, S.; Slim, R.; Palandre, L.; Clodic, D.; Mathis, P.; Wagner, M.; Forgie, J.; Dwyer, H.; Wolf, K. Environ Sci. Technol. 2014, 48, 1084-1093. (See Supporting Information). http://pubs.acs.org/doi/suppl/10.1021/es403447v↩︎
EDD. 2020. California Employment Development Department. https://data.edd.ca.gov/↩︎
ABAG. 2019. Plan Bay Area 2040. Association of Bay Area Government (ABAG). http://2040.planbayarea.org/reports↩︎
CDF. 2021. State of California. Department of Finance. E-5 Population and Housing Estimates for Cities. Counties and the State — January 1, 2011-2021. May 2021. https://www.dof.ca.gov/Forecasting/Demographics/Estimates/e-5/↩︎