3.6 Industrial Natural Gas Leakage

    Category ID Description EIC
    48 Oil Production Fields 31099516000000, 31099503240000
    49 Gas Production Fields 41099530000000, 32031600100000
    1575 Oil Production Fields 31031616000000
    1576 Gas Production Fields 31031601000000
    2538 Industrial - Natural Gas 49999500100000

    Introduction

    Natural gas consists of mostly methane (CH4) with small amounts of other hydrocarbons such as ethane, propane, and butane and trace amounts of inert gases such as carbon dioxide (CO2), nitrogen (N2), hydrogen (H2) and helium (He). The emissions reflected in this methodology include methane emissions from the leakage of natural gas (NG) during production of natural gas and petroleum at gas and oil fields in the San Francisco Bay Area (SFBA) and post-consumer meter leakages in the Industrial sector. The following categories account for emissions from the leakage of NG in the Industrial sector:

    • Category 1575 – Fugitive emissions from Oil Production fields
    • Category 1576 – Fugitive emissions from Natural Gas Production fields
    • Category 2538 - Post-Meter Leakage from Industrial Sources

    Since peaking in the mid-1980s, oil production in the SFBA has declined sharply. This trend is due in part to local land use restrictions and environmental regulations, such as San Mateo County’s 1980s ordinance limiting new oil well development (Green Foothills, 2020). The number of actively producing oil wells in the region decreased from 87 in 1986 to approximately 40 in the early 2000s, and today, only a few remain, primarily in Contra Costa and Alameda counties.

    Similarly, very few active natural gas production wells continue to operate in the region. These are also located predominantly in Contra Costa, Alameda, and Solano counties. Given the small number of operational facilities, emissions from Categories 1575 and 1576 represent a diminishing share of regional methane emissions.

    Category 2538 captures post-meter methane emissions from non-permitted industrial users of natural gas. These emissions occur downstream of the utility meter, typically due to leaks in on-site piping, valves, or combustion equipment. Although these leaks are individually small and difficult to monitor, their aggregate impact may be significant due to the large number of facilities involved.

    Methodology

    CARB Sources (Categories 1575 and 1576)

    The methodology for estimating GHG emissions from oil and natural gas (O&G) production activities is derived from the California Air Resources Board’s (CARB) California Emissions Projection Analysis Model (CEPAM) emissions inventory model (CEPAM, 2019). Criteria air pollutant (CAP) emissions data for the SFBA is directly available from the CEPAM model. CARB deploys a general methodology to calculate CAP emissions for the base year(s) for these fugitive O&G sources, which typically involves the following steps to calculate county-level emissions for each pollutant and source category:

    Emissionsstate,pollutant = Activity Data × Emission Factorpollutant

    Base Year(s) Emissions county,pollutant =

    Emissionsstate;national,pollutant × Control Factorpollutant × Fractioncounty × GWPpollutant

    Where:

    • Base Year: is a year for which emissions data is directly reported by CARB and available.
    • Activity Data: is the total statewide (or regional) throughput or activity data for applicable base year(s).
    • Emissionsstate,pollutant: is the amount of emissions from a larger area (e.g. state or national level) to be allocated to a smaller regional area based on a proportional measure, such as allocating based on the ratio of county to state population.
    • Emission Factorpollutant: is a factor that allocates an amount of emissions, in mass, of a particular pollutant by unit of activity data.
    • Control Factorpollutant : is a fractional ratio (between 0 and 1) that captures the estimated reduction in emissions as a result of Air District rules and regulations.
    • Fractioncounty : is the fraction of total regional emissions (between 0 and 1) estimated to be allocated to a particular county.
    • GWPpollutant is the Global Warming Potential of a particular GHG pollutant. The current version of the GHG emissions inventory incorporates the global warming potential (GWP) reported in the Fifth Assessment report of the Intergovernmental Panel for Climate Change (IPCC, 2014). The GWPs for the three principal GHGs are 1 for carbon dioxide (CO2), 34 for methane (CH4), and 298 for nitrous oxide (N2O), when calculated on a 100-year basis with climate-carbon feedback included.

    The data in the CEPAM model is compiled from data reported by operators of equipment and/or Air Districts reporting as part of the California Emissions Inventory Data Analysis and Reporting System (CEIDARS), which is a database management system developed to track statewide criteria pollutant and air toxic emissions. Emissions from O&G production activities are categorized under ‘Petroleum Production and Marketing’ subsectors in CEPAM, and classified under groups like fugitives, breathing losses, tanks, vapor recovery etc., and identified by unique and standard Emissions Inventory Codes (EICs). The CEPAM data for individual categories is sorted as those resulting from natural gas production and not-gas (crude oil) production, and apportioned to serve as the source data for categories 1575 and 1576, respectively.

    This model provides comprehensive estimates of base year CAP emissions (from years 2000 to 2050) from O&G fugitive losses at the state-level, including projections for future years. It is important to note that the CEPAM model does not directly estimate GHGs but rather accounts for CAP emissions of total organic gases (TOG) and reactive organic gases (ROG). The Air District applies additional methods to estimate CH₄ and CO2 emissions from O&G fugitive sources. A description of the methods used to generate fugitive CH4 and CO2 emissions for O&G production categories is described in the next subsection.

    Once base year emissions are determined, historical backcasting relative to the base year emissions are estimated using a growth profile as follows:

    Current Year Emissions county = Base Year(s) Emission county × Growth Factor

    Where:

    • Growth Factor: is a scaling factor that is used to derive historical emissions estimates for years for which activity data and/or emissions are not reported (or available).

    Emissions Apportionment

    CH4 and CO2 Emissions

    As crude oil and natural gas is brought to the surface from deep wells during extraction, associated gas is released into the air as fugitive emissions (CARB, 2016). CH4 is the principal component of associated gas along with reactive organic gases (ROG), and some relatively inert gases like CO2, N2, H2 and He, and inorganics like hydrogen sulfide (H2S), also known as ‘other gas’. CH4 emissions can be obtained from the total estimated/calculated organic gases as follows:

    TOG Emissionsassociated gas = ROG Emissionsassociated gas + CH4 Emissions + Other Gas emissions

    Where:

    • Associated gas is the co-emitted gas during oil (wet gas) and natural gas (dry gas) production, and,
    • Other gas includes minor fractions of relatively inert gases like CO2, N2, H2 and He, and also H2S.

    Based on CARB’s Greenhouse Gas Emission Inventory Technical Support Document (CARB, 2016), the fraction of ‘other gases’ in wet gas (oil production – category 1575) is assumed to be one-third (33%) of the methane component, while it is assumed to be ~10-11% of the methane component for dry gas (natural gas production, category 1576). Thus, CEPAM emissions data for TOG and ROG can be used to directly derive CH4 emissions. It should be noted that CEPAM dataset cannot be used to generate estimates for CO2 directly.

    GHG emissions from fugitive emissions from the O&G production subsector are also available from the CARB Statewide Greenhouse Gas Inventory Tool (CARB, 2023), which estimates emissions for the entire state. Since CEPAM database does not include CO2 emissions, the Bay Area Air Quality Management District (BAAQMD or Air District) uses the CARB GHG data to obtain the statewide CO2/CH4 ratio for all fugitive categories in the O&G production subsector combined. This ratio is then applied to the CH4 data derived from CEPAM to estimate CO2 emissions for categories 1575 and 1576.

    Once CH4 emissions are determined, the Global Warming Potential (GWP) of a particular GHG pollutant is used to derive emissions on a CO2-equivalent (CO2eq) basis. The current version of the GHG emissions inventory incorporates the GWPs reported in the Fifth Assessment report of the Intergovernmental Panel for Climate Change (IPCC, 2014). The GWPs for the three principal GHGs are 1 for carbon dioxide (CO2), 34 for methane (CH4), and 298 for nitrous oxide (N2O), when calculated on a 100-year basis with climate-carbon feedback included.

    County Fractions

    The CEPAM tool provides county-specific TOG and ROG emissions data for the SFBA. CH4 and CO2 emissions are derived directly and indirectly from the overall TOG emissions in CEPAM, respectively, and hence the county distribution of emissions is the same as that for the TOG emissions within each of the Air District’s counties. For counties like Sonoma and Solano, which partially fall within the SFBA, CEPAM provides county-specific emissions that are already apportioned to Air District’s jurisdiction.

    ID Description ALA CC MAR NAP SF SM SNC SOL SON
    1575 Oil Production Fields 0.21 0.01 0.0 0.0 0.26 0.05 0.47 0.00 0.00
    1576 Gas Production Fields 0.00 0.56 0.0 0.0 0.11 0.00 0.00 0.33 0.00
    2538 Industrial - Natural Gas 0.02 0.87 0.0 0.0 0.00 0.00 0.02 0.07 0.01

    Emission Control

    The Air District adopted Regulation 8, Rule 37 in 1985 to control emissions at crude oil and natural gas production facilities (BAAQMD, 1990). This rule originally required a control of 80% on ROG, with a rule effectiveness of 90% reached by 1989. Since ROG is co-emitted with CH4, this rule is assumed to have decreased fugitive emissions of CH4 in similar proportions as ROG. All impacts of this rule are assumed to be fully accounted for in the reported/estimated CEPAM emissions, and no further controls are required to be applied to the GHG emissions calculations.

    CARB adopted a landmark Oil and Gas Regulation in 2017 that required O&G production facilities to set up leak detection and repair programs (LDAR) and conduct frequent (e.g. quarterly) surveys of all equipment in oil and gas fields (CARB, 2017). The impact of this rule on SFBA O&G infrastructure is expected to be minimal because of exemptions for small facilities and equipment that generally operate across the limited O&G production infrastructure in the SFBA.

    Historical Emissions

    Historical emissions data for categories 1575 and 1576 for the years 2000 to 2022 are derived from the current CEPAM inventory model (CEPAM, 2019). For category 1575 and 1576, the Air District staff uses available regional oil and gas historical production data for the SFBA that shows activity varied non-linearly during that period. Therefore, emissions from 1990 to 1999 were backcasted based on the gas production data from the California’s Department of Conservation-Division of Oil, Gas, and Geothermal Resources (DOGGR, 2000) for category 1575 and 1576.

    Future Projections

    Future projections are obtained directly from the CEPAM data which provides emissions projections from the year 2023 to 2050. These emissions projections indicate a slow declining growth rate into the future. This trend is aligned with the extrapolation of California Annual Operable Atmospheric Crude Oil Distillation Capacity trend from 2010 to 2020, which indicates a 0.67% annually decreasing growth rate. as projected by the Energy Information Administration (EIA, 2023).

    Assessment of Methodology

    The general methodology for determining GHG emissions for these categories has changed as the GHG emissions are now derived from the criteria pollutant estimates in the CEPAM inventory and the statewide GHG emissions inventory. This is different from the previous iteration of the GHG inventory when a forecast profile was used to grow base year 2011 GHG emissions that were derived using a different and undocumented method. This has made an impact on the accuracy of emissions accounted for under the Industrial sector.

    Year

    Revision

    Reference

    2022

    1. Used CARB’s CEPAM inventory to generate CH4 emissions using available TOG and ROG emissions data.
    2. Used CARB’s statewide GHG inventory to derive CO2 emissions from CO2/CH4 ratio.
    3. Made assumptions for composition of associated gas for oil and gas production
    4. Used DOGGR’s regional production data to backcast and derive emissions for years 1990-99
    5. Used CEPAM inventory forecasts for TOG to project and derive CH4 and CO2 emissions forecast
    1. CEPAM, 2019
    2. CARB, 2023
    3. CARB, 2023
    4. DOGGR, 2000
    5. CEPAM, 2019; CARB, 2023

    2015

    1. Used single base year of 2010, 1990-2010 consistent with Air District’s BY 2011 estimates
    2. GHG emissions derivation method is undocumented and/or unknown
    3. Forecast based on Greenblatt analysis; includes unpassed policy and goals
    1. BAAQMD, 2015; BAAQMD, 2017
    2. Greenblatt, 2013

    Area Sources (Category 2538)

    Category 2538 is considered an area source category as it accounts for emissions from industrial leakage sources that are not directly permitted by the Air District, and thus not routinely or annually reported. The data used to estimate emissions for these sources must be extracted from either CARB or California Energy Commission (CEC) databases. The methodology used to calculate emissions for the reported base years for this source category is as follows:

    Base Year(s) Emissions county,pollutant =

    Activity Data × Emission Factorpollutant × Control Factorpollutant × Fractioncounty × Fractionin District× GWP pollutant

    Where:

    • Base Year: is a year for which activity / throughput data is reported by CEC and/or CARB, and available.
    • Activity Data: is the throughput or activity data for applicable reported base years. This data may be determined in one or two ways:
      • Apportioning Larger-Scale Data: Throughput data from a larger domain, such as state or national level, is scaled using the proportion of a representative metric in the regional domain relative to the larger domain. For example, the ratio of a county’s population to the state population can be used as a scaling factor to determine the county throughput from state-level throughput.
      • Using Local Sources: Alternatively, data from a locally published and verifiable source may be used, such as the county-level natural gas usage data provided by the CEC.
    • Emission Factorpollutant: is a factor that allocates an amount of emissions, in mass, of a particular pollutant by unit of activity data. For example, tons of CO2 per gallon of gasoline burned or pounds of N2O per million standard cubic feet (MMSCF) of natural gas combusted. This factor generally comes from a published literature source such as USEPA AP-42 (USEPA, 1998) or CARB’s Mandatory Reporting Requirement (MRR) for Greenhouse Gases (CARB, 2019).
    • Control Factorpollutant : is a fractional ratio (between 0 and 1) that captures the estimated reduction in emissions as a result of Air District rules and regulations.
    • Fractioncounty : is the fraction of total regional emissions (between 0 and 1) estimated to be allocated to a particular county. It is typically derived from regional socioeconomic metrics and/or actual county-level throughput data.
    • Fractionin District : The Air District jurisdiction covers only a portion of Solano and Sonoma County. For this reason, additional allocation must be made for these counties to determine the proportion of the county’s emissions occurring within the Air District’s jurisdiction.
    • GWPpollutant is the Global Warming Potential of a particular greenhouse gas (GHG) pollutant. The current version of the GHG emissions inventory incorporates the global warming potential (GWP) reported in the Fifth Assessment report of the Intergovernmental Panel for Climate Change (IPCC, 2014). The GWPs for the three principal GHGs are 1 for carbon dioxide (CO2), 34 for methane (CH4), and 298 for nitrous oxide (N2O), when calculated on a 100-year basis with climate-carbon feedback included.

    Once base year emissions are determined, historical backcasting and forecasting of emissions relative to the base year emissions are estimated using growth profiles as follows:

    Current Year Emissions county = Base Year(s) Emission county × Growth Factor

    More details on the inputs and variables used above are provided in the following subsections:

    Throughput

    The reported base years for source category 1591 are the years 2011 – 2019. The datasets used to determine throughputs for the reported base years for the Commercial sector are listed below:

    • CEC Natural Gas Usage in Therms by County and by Residential and Non-Residential sectors, years 1990 – 2022 (CEC, 2023a),
    • CEC Natural Gas Usage in Therms by County and by Economic sector, years 1990 – 2022 (CEC, 2023b), and,
    • Reported natural gas throughputs by permitted industrial and commercial facilities to the Air District for years 2011-2019.

    For this category, facilities subject to the registration requirements in Regulation 9, Rule 7 (BAAQMD, 2011) reported their annual throughput to the Air District from 2011 to 2019. In 2011, the Air District’s registration program for industrial process boilers and heaters came into full effect, but prior to 2011 the throughput for these devices was not reported to the Air District. Therefore, the year 2011 is considered to be a representative year for historical backcasting, as it is the first year where throughput from these registered boiler/heaters were recorded.

    In a similar manner, the year 2019 is chosen to be a representative year for estimating future trends as it is the last year where natural gas throughput data was collected from these registered sources.

    Prior to collecting direct natural gas usage from registered facilities (in the 1990s and 2000s), the CEC Natural Gas Usage by Residential and Non-Residential sectors was used to estimate emissions. To remain consistent with historical calculations, the same data set is used but the Air District now uses a refined approach for proportioning natural gas usage to the non-permitted area source in the Industrial and Commercial sectors using an additional CEC Natural Gas Usage by Economic sector data set. After determining the amount of natural gas used for the Industrial sector and natural gas usage from Hydrogen (H2) production for the SFBA using the two datasets, the natural gas usage of industrial point sources, based on the Air District’s registered dataset (category 307_ind), are subtracted from CEC’s natural gas usage for the Commercial sector to avoid double counting.

    The leakage rate of 0.28% for industrial sources (CEC, 2020) is applied to natural gas usage to calculate the amount lost to leakage.

    County Distribution

    County distribution is determined by using base year data for 2022 for Industrial sector natural gas usage from the CEC.

    BAAQMD Jurisdiction Fraction

    The BAAQMD jurisdiction only accounts for a part of Solano and Sonoma counties. The remaining area is covered by other Air Districts. For category 1590, the percentage of Solano and Sonoma County populations within the Air District boundary (or jurisdiction) are estimated using the Association of Bay Area Government’s (ABAG) Plan Bay Area 2050 dataset (ABAG, 2021). The dataset summarizes population by Travel Analysis Zones (TAZs). The population for each TAZ within Air District’s jurisdictional boundaries is summed and divided by the total county-wide population to estimate the percentage of population within the SFBA for Solano and Sonoma counties. These proportions are shown below:

    County

    % of Population within the District’s jurisdiction

    Solano

    0.70

    Sonoma

    0.86

    Emission Factors

    The natural gas leakage methane emission factor is based on the methane content in natural gas and the density of methane (in units of lb/standard cubic feet (scf)). Emission factors are calculated using the values shown below:

    Category(ies)

    Characteristic

    Value

    Source

    All

    % Methane

    97.3%

    PG&E, 2023. Concentration varies but typically between 95% – 98%; historically the Air District has used 97.3%.

    All

    Methane Density

    0.044 lb/scf

    Engineering Toolbox, 2023

    The calculation of the natural gas leakage emission factor using million standard cubic feet (MMSCF) as the basis follows as:

    CH4 emission factor = 0.973 × 0.044 lb/scf × 106 scf/MMSCF = 42,812 lb/MMSCF

    Local Controls

    GHG emissions from category 2538 are fugitive in nature, and there are no current emissions controls or regulations that apply on these sources. Since the throughput for category 2538 (post-meter leakage) is a fixed leak percentage of industrial NG throughput for category 1590, in theory, the throughput and subsequently emissions of category 2538 would be impacted if there was a regulation that impacted the throughput of category 1590.

    The GHG emissions calculated for the Industrial Fuel Combustion area source category 1590 are not currently regulated under District Regulation 9, Rule 7 (BAAQMD, 2011) or Regulation 9, Rule 6 (BAAQMD. 2021). These rules are designed to control air pollution by setting limits on emissions of NOx and CO. It specifically applies to regulated and permitted industrial, institutional, steam generators, and process heaters. However, sources in category 1590 are not subject to the same emission limits or compliance requirements.

    Historical Emissions

    For historical backcast of natural gas throughput, the CEC natural gas usage by county for the Residential and Commercial sectors for 1990 to 2011 is used to produce a backcast profile. This profile is normalized to the year 2011 and applied to the year 2011 throughput obtained from the latest CEC publication (CEC, 2023a) to determine throughput for years 1990-2011.

    Future Projections

    The CEC publishes an Integrated Energy Policy Report (IERP) every 2 years in which they forecast natural gas usage by an energy provider that accounts for achievable fuel substitution (AAFS) and achievable energy efficiency (AAEE). For all forecasting, a scenario based on a combination of AAFS and AAEE factors that best represents business-as-usual scenario is chosen. Business-as-usual is defined as existing conditions that include impacts from state and federal regulation adopted as of year 2022. To portray business-as-usual forecasting of emissions, the CEC recommends the use of Scenario 3 Programmatic AAFS and AAEE for the Pacific Gas & Electricity (PG&E) regional service area (CEC, 2023b).

    Sample Calculations

    An example calculation for year 2022 for Contra Costa County, CH4 emissions for category 2538 (Industrial Natural Gas Leakage) is shown below:

    Step 1

    Convert 2019 natural gas usage for Non-Residential sector, obtained from the CEC for Contra Costa County, from MMTherms million therms) to MMSCF (million standard cubic feet)

    1028.69 MMTherms

    × 100,000 MMBtu/MMTherms

    ÷ 0.001026 MMBtu/scf

    × 1E-06 MMSCF/scf

    = 100,262.6 MMSCF

    Step 2

    Estimate the amount of non-residential natural gas used in the Industrial sector for Contra Costa using industrial usage percentage

    100,262.6 MMSCF

    x 95.0%

    = 95,249 MMSCF

    Step 3

    Gather 2019 natural gas usage data from permitted/registered sources located in Contra Costa County in the Industrial sector in MMSCF (category 307_ind)

    31,756 MMSCF

    Step 4

    Derive 2019 natural gas usage for area sources in the Industrial sector

    by subtracting 2019 natural gas usage activity data for category 307_ind

    95,249 MMSCF

    – 31,756 MMSCF

    = 63,493 MMSCF

    Step 5

    Calculate loss of natural gas through leakage

    63,493 MMSCF

    x 0.0028

    = 177.8 MSCF

    Step 6

    Grow natural gas emissions from 2019 to 2022 using growth projections from ABAG Plan Bay Area 2050 datasets

    177.8 MMSCF

    x 0.711

    = 126.4 MMSCF

    Step 7

    Natural gas leakage methane emission factor

    42,812 lb/MMSCF

    Step 8

    Convert emissions to million metric tons of CO2 equivalents (MMTCO2eq/year) by applying the GWP of 34 for methane

    42,812 lb/MMSCF

    × 126.4 MMSCF

    × 1/2000 ton/lb

    × 0.907185 MT/ton

    × 34

    × 10-6 MMT/MT

    = 0.083 MMTCO2eq

    Assessment of Methodology

    The general methodology for determining emissions in category 2538 has not changed. However, the determination of natural gas throughput allocated to the category has been significantly improved upon by the inclusion of post-meter leakage and a refined sector split of industrial area and point source contributions that significantly improves the accuracy of the resulting emissions.

    Year

    Revision

    Reference

    2022

    1. Used reported base years throughputs for 2011 to 2019.
    2. Updated base year, backcast and forecast natural gas usage based on CEC data normalized to 2011 and 2019, respectively . Use CEC data based on the business-as-usual model forecast.
    3. Updated Sonoma/Solano County proportions in the SFBA using ABAG’s Plan Bay Area 2050 projections for 2022.
    4. Reduced potential double counting errors by subtracting the point source contributions (Category 307_ind) from the industrial sector for area sources.
    5. Updated emission factors based on USEPA AP-42 and Title 40 values
    6. Updated control factors to reflect latest applicable local regulatory requirements
    7. Used the latest GWP from the Fifth Assessment report of the IPCC.
    1. BAAQMD permitted inventory for base years
    2. CEC, 2023c
    3. ABAG, 2021
    4. BAAQMD, internal
    5. USEPA,1998; USEPA, 2016
    6. BAAQMD, 2023
    7. IPCC, 2014

    2015

    1. Used single base year of 2010, 1990-2010 data is same as Air District’s BY 2011 estimates
    2. The forecast includes projected reductions based on nonmandated policies and goals.
    3. No controls accounted for in the emissions from adopted Air District regulations
    1. BAAQMD, 2015
    2. Greenblatt, 2013
    3. Greenblatt, 2013

    Emissions

    The table below summarizes GHG emissions for the base year 2022 in metric tons of CO2 equivalents (MTCO2eq).

    ID Description CH4 CO2 Total
    2538 Industrial - Natural Gas 153711.4 0.0 153711.4
    1576 Gas Production Fields 3885.4 1159.2 5044.6
    1575 Oil Production Fields 202.4 60.5 262.9

    Summary of Base Year 2022 Emissions

    GHG emissions resulting from Industrial post-meter leakage category is around 0.15 MMTCO2eq for year 2022. The Oil and NG production-related leakage losses (category 1575 and 1576) and CH4 emissions are negligible given the limited presence of these operations in the SFBA.

    Contribution of Industrial Natural Gas Leakage Emissions by Sector
    Subsector Sector Subsector GHG Emissions (MMTCO2eq) Sector GHG Emissions (MMTCO2eq) % of Sector
    Industrial Natural Gas Leakage Industrial 0.16 17.90 0.89%

    Contribution of Industrial Natural Gas Leakage Emissions to Regional Total
    Subsector Subsector GHG Emissions (MMTCO2eq) Regional Total GHG Emissions (MMTCO2eq) % of Regional Total
    Industrial Natural Gas Leakage 0.16 65.68 0.24%

    Trends

    The time series chart below shows the emission trends for the applicable categories.

    Summary of Trends

    Historical and future trends follow historical NG consumption data for the SFBA and predicted future NG consumption for the region. California’s LDAR rule (CARB, 2017) is expected to impact overall leak rates observed across the state’s O&G infrastructure. The impact of these regulations leads to a further decrease in the downward trend in emissions in addition to the CEPAM forecasts.

    Uncertainties

    The range for natural gas leakage factors varies from 0.3 – 0.5% (95% confidence interval; Fischer et al., 2018) across studies that have been conducted in the state. This is due to the varying post-meter equipment, and that might affect the leakage rate. The industrial leakage rate is not determined from direct and representative information in the literature. It is generated from the average observed residential leakage factor derived from measurements done for 75 California homes (CEC,2018), and the commercial leakage rate derived from studies with a sample size of close to 100 commercial buildings (CEC, 2020). Due to these relatively low sample rates, the uncertainty for both studies can be considered very high. Other regional measurement-based studies in the Los Angeles region have suggested much higher leakage rates ranging from 1.6 to 2.7% of NG usage (CEC, 2018).

    Contact

    Author: Abhinav Guha

    Reviewer: Ariana Husain

    Last Update: 08/11/2025

    References

    ABAG. 2021. Plan Bay Area 2050, Association of Bay Area Governments. https://planbayarea.org/finalplan2050

    BAAQMD. 1990. Regulation 8, Rule 37 – Natural Gas and Crude Oil Production Facilities, Bay Area Air Quality Management District. https://www.baaqmd.gov/~/media/dotgov/files/rules/reg-8-rule-37-natural-gas-and-crude-oil-production-facilities/documents/rg0837.pdf?rev=08b4199b2bdb4f94a62f67ebe9ae22e2&sc_lang=en

    BAAQMD. 2011. Regulation 9- Inorganic Gaseous Pollutants, Rule 7 – Nitrogen Oxides and Carbon Monoxide Industrial, Institutional, and Commercial Boilers, Steam Generators, and Process Heaters, Bay Area Air Quality Management District. Available at: https://www.baaqmd.gov/~/media/dotgov/files/rules/reg-9-rule-7-nitrogen-oxides-and-carbon-monoxide-from-industrial-institutional-and-commercial-boiler/documents/rg0907.pdf?rev=ab95f36c2dd146528f1cf3c10596bce3&sc_lang=en

    BAAQMD. 2015. Bay Area Emissions Inventory Summary Report: Greenhouse Gases, Base Year 2011, Bay Area Air Quality Management District. http://www.baaqmd.gov/~/media/Files/Planning%20and%20Research/Emission%20In ventory/BY2011_GHGSummary.ashx?la=en

    BAAQMD. 2017. Greenhouse Gas Emission Estimates and Draft Forecasts, Bay Area Air Quality Management District. . Available: https://www.baaqmd.gov/~/media/files/planning-and-research/plans/2017-clean-air-plan/ghg_emissions_and_forecasts_draft.pdf

    CARB. 2017. Oil and Gas Methane Regulation, California Air Resources Board. https://ww2.arb.ca.gov/resources/fact-sheets/oil-and-gas-methane-regulation

    CARB. 2016. 2000-2014 Greenhouse Gas Emission Inventory Technical Support Document 2016 Edition, Section 1.E. – Energy: Oil and Gas Production, California Air Resources Board. https://ww2.arb.ca.gov/sites/default/files/classic/cc/inventory/ghg_inventory_tsd_00-14.pdf

    CARB. 2023. GHG Query Tool for the years 2000-2021, California Air Resources Board. https://ww2.arb.ca.gov/applications/greenhouse-gas-emission-inventory-0

    CEC. 2018. Natural Gas Methane Emissions from California Homes. Marc L. Fischer, Wanyu R. Chan, Seonguen Jeong, Zhimin Zhu. Publication Number: CEC-500-2018-021, California Energy Commission. https://www.energy.ca.gov/sites/default/files/2021-06/CEC-500-2018-021.pdf

    CEC. 2020. Characterization of Fugitive Methane Emissions from Commercial Buildings in California, Johnston, E., Bluestein, J., Liu, J., Kanaan, J., Cohen, J., Cooper, W.,2020, Characterization of Fugitive Methane Emissions from Commercial Buildings in California. Publication Number: CEC-500-2020-048, California Energy Commission. https://www.energy.ca.gov/sites/default/files/2021-05/CEC-500-2020-048.pdf

    CEC. 2023a. Natural Gas Usage in MMTherms by County and by Residential and Non-Residential sectors, 1990 – 2022, California Energy Commission. Downloaded September 23, 2023. Available at: http://www.ecdms.energy.ca.gov/gasbycounty.aspx

    CEC. 2023b. 2023 Integrated Energy Policy Report (IERP). Bailey, Stephanie, Jennifer Campagna, Mathew Cooper, Quentin Gee, Heidi Javanbakht, and Ben Wender. Publication Number: CEC-100-2023-001-CMF, California Energy Commission. https://www.energy.ca.gov/data-reports/reports/integrated-energy-policy-report/2023-integrated-energy-policy-report.

    CEPAM. 2019. California Emissions Projection Analysis Model (CEPAM), 2019 v1.0.4, California Air Resources Board. https://ww2.arb.ca.gov/emission-inventory-landing

    DODGR. 2000. Annual Reports of the State Supervisor of Oil and Gas, 1990-2000, California’s Department of Conservation- Division of Oil, Gas, and Geothermal Resources. https://www.conservation.ca.gov/calgem/pubs_stats/annual_reports/Pages/annual_reports.aspx

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