3.8 Metal Recycling & Shredding

Category ID	Description	EIC
2222	Metal Recycling/Shredding Op.	44044070000000, 44044070440000

Introduction

This chapter outlines the methodology used to estimate greenhouse gas (GHG) emissions from fluorinated gas releases associated with metal recycling and shredding operations in the San Francisco Bay Area (SFBA). These emissions primarily originate from the scrapping of end-of-life appliances and equipment that contain refrigerants, such as legacy air conditioners, refrigerators, and used vehicles. These refrigerants include potent fluorinated greenhouse gases such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs).

At a typical metal recycling facility, the primary activities include shredding, sorting, and stockpiling of scrap metal, which is then processed for reuse. These operations can also be a source of particulate matter (PM) emissions, but this chapter focuses specifically on GHG emissions related to refrigerant losses.

Before shredding occurs, California law requires that scrap appliances and equipment be “depolluted”—a process that involves the removal of materials requiring special handling or classified as hazardous wastes (DTSC, 1989). These materials include:

• Combustible fuels such as gasoline and diesel
• Lubricants and fluids such as motor oil, brake fluid, and transmission fluid
• Refrigerants, including CFCs, HCFCs, and other ozone-depleting substances

While the production and import of most CFCs and HCFCs have been phased out due to their ozone-depleting potential, these compounds remain in circulation in older appliances and continue to pose a climate risk due to their long atmospheric lifetimes and very high global warming potentials (GWPs).

If depollution is not properly conducted or if equipment is shredded before refrigerants are fully recovered, uncontrolled releases of CFCs and HCFCs can occur. These releases contribute to GHG emissions and represent a unique emissions source that is often undercounted in regional inventories.

This methodology specifically addresses emissions from Category 2222 – Metal Recycling and Shredding Operations, with a focus on estimating GHG emissions from fugitive refrigerant releases due to incomplete or improper depollution prior to shredding.

Methodology

Point sources are operations that emit air pollution into the atmosphere at a fixed location within a facility, and for which the Bay Area Air Quality Management District (BAAQMD or Air District) has issued a permit to operate (PTO), e.g. refinery cooling towers. These point sources could also be a collection of similar equipment and/or sources located across multiple facilities, e.g. reciprocating engines.

During the PTO issuance process, the Air District collects site-specific information from the operating facility and/or determines from published literature, e.g. U.S. Environmental Protection Agency’s (EPA) AP-42 (EPA, 2024), characteristics of a source including maximum throughput, emission factors for emitted pollutants, and control factors associated with downstream abatement devices. Facilities that hold a PTO are required to renew their permit periodically (this period varies based on facility and source type). Upon renewal, the facilities are requested to provide any updates to source characteristics as well as the source throughput for the past twelve months. This throughput, in combination with the emission factors and controls factors stored in the Air District’s internal database, are used to programmatically estimate annual emissions at the source level. The methodology used to calculate emissions for the base year(s) of a permitted point source is as follows:

Base Year(s) Emissions _{source,pollutant} =

Activity Data _source × Emission Factor_pollutant × Control Factor_pollutant × GWP _pollutant

Base Year(s) Emissions _county = ∑ ^N_i=1 Emissions_i

Where:

• Base Year: is a year for which activity / throughput data is available from permit records.
• Activity Data_source is the throughput or activity data for applicable base year(s) at the source/equipment level. This data is usually available from the internal permit records that are provided annually to the Air District at permit renewal by a source / facility operator.
• Emission Factor_pollutant is a factor that allocates an amount of emissions, in mass, of a particular pollutant by unit of activity data. For example, tons CO₂ per gallons of gasoline burned or pounds of N₂O per million standard cubic feet of natural gas combusted. Criteria pollutants (CAPs) and greenhouse gas (GHG) emissions are calculated by using specific emission factors for every source/operation for which information has been supplied by the facility (and verified/validated through source tests). If no specific emission factors are available, generalized factors developed by Air District staff are used to determine emissions. These default factors typically come from published literature such as USEPA’s AP-42 (USEPA, 2024) or California Air Resource Board’s (CARB) Mandatory Reporting Requirement (CARB, 2019) for Greenhouse Gases.
• Control Factor_pollutant is a fractional ratio (between 0 and 1) that captures the estimated reduction in emissions as a result of District rules and regulations.
• GWP _pollutant is the Global Warming Potential. 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.
• N is the number of permitted and similar sources in a county.

If available, a facility can provide emission factors specific to the source that are verified and validated through source tests to estimate GHG emissions. If no specific emission factors are available, general factors developed by Air District staff are used to estimate emissions. These source level emissions are then sorted and aggregated by year, county, and category.

Further speciation and quality assurance of emissions, including those of GHGs, are performed as a part of the inventory refinement process. A systematic crosswalk was developed between CARB’s California Emissions Projection Analysis Model (CEPAM) source category classification using the primary sector emission inventory codes (EICs) and the Air District’s source category classification (category identification number - cat_ids), which ensures consistency when reporting annual emissions under the California Emissions Inventory Data Analysis and Reporting Systems (CEIDARS) to CARB (CARB, 2022a). This emissions data represents the reported base years emissions for a point source category.

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 x 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 available, and to forecast emissions for future years, using surrogates that are assumed to be representative of activity and/or emissions trends.

For those years where no data is available, emissions data are backcast to year 1990, as well as forecasted to year 2050 using either interpolation or another mathematical approach (see Trends section), or by applying a growth profile based on socioeconomic indicators. GHG emissions data from the years 1990 to 2050 are analyzed for each source category and pollutant, with the trends evaluated for any observed anomalies and modified, if needed.

CFCs and HCFCs are original ozone-depleting substances (ODS) that are emitted and included in point source emissions data for source category 2222. However, ozone-depleting substance substitutes (ODSS), such as hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs), are not included in source category 2222. Instead, ODSS greenhouse gas emissions are accounted for and covered in the High Global Warming Potential (High-GWP) Gases methodology chapter.

Local Controls

District Regulation 6, Rule 4 (Metal Recycling and Shredding Operations; BAAQMD, 2013) requires the development of and compliance with Emissions Minimization Plans (EMPs) designed to minimize the fugitive emissions of PM from metal recycling facilities operating within the Air District. Although the regulation does not directly address GHG emissions reductions, it requires depollution operations prior to metal shredding, including removal of CFCs and HCFCs. The EMPs encourage and recommend the use of best management practices (BMPs) to minimize emissions from depolluting and shredding processes but stop short of requiring the adoption of specific BMPs. Hence, some fugitive losses of CFCs and HCFCs still occur due to incomplete depollution of shredded materials (BAAQMD, 2024) and are accounted for in the reported point source activity data and in-use emissions factors for metal shredding operations. Since the impact of Regulation 6, Rule 4 is already accounted for in the emissions calculations, no separate controls need to be applied to the derived/reported GHG emissions.

Historical Emissions

Historical emissions for point sources are derived from source-specific data provided by the facility on throughputs, compiled or reported emission factors, and regulation-based control factors. This information is archived in the Air District’s internal database and is queried to retrieve the data for historical and current years. Interpolation techniques to account for missing data are used when necessary.

In the case of GHGs, up until the year 2006, the Air District was not engaged in systematic information collection during permit renewal process. This changed when AB32 bill was passed into a statewide law in 2006, and a statewide Cap and Trade system was introduced to reduce GHG emissions from specific facilities. Hence, GHG emissions data for years 1990-2006 are derived from the historical emissions data reported in the base year 2011 GHG inventory (released in year 2012). The historic emissions dataset is scaled to sync with the data in the permit database (which started systematic GHG data accounting from year 2006 onwards), to generate a complete GHG emissions time series for each point source category from 1990 to 2050.

Future Projections

Forecasting of point source emissions is done based on calculations as shown in the equation below using recently updated growth profiles and a base year of 2022. The growth profiles for the current base year inventory have been verified and updated to represent the most likely surrogate for growing emissions for a given category up to the year 2050. Forecasting for point source emissions includes impact of in-place regulations but does not include estimation of controls that will theoretically be implemented as part of future policy emission targets or proposed regulation and legislation.

PE = Gr × C_i × E_i

PE = projected emissions of pollutant i in a future year

Gr = growth rate by economic profile of industry or population

C_i = control factor of pollutant i based on adopted rules and regulations
E_i = base year emissions of pollutant i

Future projection forecasts are determined using the E3 modeling: PATHWAYS Non-Energy GHGs Detailed HFCs BAU Reference scenario from CARB’s 2022 Scoping Plan Update (CARB, 2022b). Since that modeling only goes through the year 2045, the year 2045 data value is held constant for 2045-2050 for all source categories. This statewide forecasting growth profile is based on the regulations and controls applied to bring about the phase-out of hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs), another family of long-lived GHGs with high GWP covered in the High-GWP Gases write-up. These controls and phase-out actions are expected to simultaneously impact all fluorinated gases (including the minor quantities of already phased-out CFCs and HFCs in legacy and old appliances).

Emissions

The detailed breakdown of 2022 ‘Metal Recycling & Shredding’ subsector GHG emissions in units of metric tons of CO₂ equivalents (MTCO₂eq) are provided in the table below.

ID	Description	CFC-11	CFC-113	CFC-12	CH2Cl2	HCFC-21	HCFC-22	Total
2222	Metal Recycling/Shredding Op.	60317.8	503.8	9818.3	5.0	7.3	1157.8	71810.0

Summary of Base Year 2022 Emissions

The relative contribution of Metal Recycling & Shredding GHG emissions to region-wide and sector-level GHG emissions totals are highlighted in the tables below.

Contribution of Metal Recycling & Shredding Emissions by Sector

Subsector	Sector	Subsector GHG Emissions (MMTCO2eq)	Sector GHG Emissions (MMTCO2eq)	% of Sector
Metal Recycling & Shredding	Industrial	0.07	17.90	0.40%

Contribution of Metal Recycling & Shredding Emissions to Regional Total

Subsector	Subsector GHG Emissions (MMTCO2eq)	Regional Total GHG Emissions (MMTCO2eq)	% of Regional Total
Metal Recycling & Shredding	0.07	65.68	0.11%

Trends

The time series chart below shows the emission trends for metal recycling and shredding.

Summary of Trends

Prior to year 2019, there was no source test conducted at facilities subject to Reg 6, Rule 4 EMP requirements. Consequently, there were no reported CFC and HCFC emissions under source category 2222. This apparent lack of historical emissions data is an artifact of the calculation approach as emissions factors are set to zero in the internal database prior to the year 2019. It is only from the year 2020 that source tests were conducted to derive emissions factors that take incomplete depollution of shredded materials into account. The forecasted emissions drop steadily as the state’s phase-out of HFCs and PFCs from all appliances and vehicles simultaneously affects the depollution of remainder of minor fraction of ready-to-scrap appliances containing CFC and HCFC compounds.

Uncertainties

GHG emissions estimates for point source categories rely on permitted emission calculations for individual sources, which typically use specific throughputs, emission factors, and control measures. While generally reliable, these calculations vary due to changes in data inputs, regulatory controls, or operational conditions, introducing variability and uncertainty into the emission estimates.

As noted above, point source emission estimates rely on permitted emission calculations, which typically use specific throughputs, emission factors, and control measures. While generally reliable, these calculations vary due to changes in data inputs, regulatory controls, or operational conditions, introducing variability and uncertainty into the emission estimates.

Specifically, the lack of emissions factors in the internal permit database prior to the year 2019 leads to an absence of historical GHG emissions in this subsector. This adds a large degree of uncertainty in the estimates of CFC and HCFC emissions in the SFBA prior to the year 2019, as this subsector is one of only a few subsectors that accounts for such emissions. The next GHG inventory update will seek to rectify this artifact and include the missing historical emissions.

Contact

Author: Abhinav Guha

Reviewer: Ariana Husain

Last Update: 08/20/2025

References

BAAQMD. 2013. Regulation 6 Rule 4 - Metal Recycling and Shredding Operations, Bay Area Air Quality Management District. https://www.baaqmd.gov/rules-and-compliance/rules/reg-6-rule-4--metal-recycling-and-shredding-operations

BAAQMD. 2024. White Paper on Metal Recycling and Shredding Operations, Bay Area Air Quality Management District. https://www.baaqmd.gov/~/media/dotgov/files/rules/reg-6-rule-4--metal-recycling-and-shredding-operations/2025-amendment/documents/20240709_wp_metalrecycling-pdf.pdf?rev=45786b6c52ff4b6cb543946f0bb0d65a&sc_lang=en

CARB. 2019. Regulation for the Mandatory Reporting of Greenhouse Gas Emissions, California Air Resources Board. https://ww2.arb.ca.gov/sites/default/files/classic/cc/reporting/ghg-rep/regulation/mrr-2018-unofficial-2019-4-3.pdf

CARB. 2022a. Emission Inventory Documentation, California Air Resources Board. https://ww2.arb.ca.gov/emission-inventory-documentation. Accessed October 3, 2022. Accessed October 3, 2022.

CARB. 2022b. CARB 2022 Scoping Plan, California Air Resources Board. https://ww2.arb.ca.gov/our-work/programs/ab-32-climate-change-scoping-plan/2022-scoping-plan-documents

DTSC. 1989. California Metallic Discards Act, Department of Toxic Substances Control. https://dtsc.ca.gov/hazardous-waste-management-for-scrap-metal-recyclers-2/#:~:text=The%20Metallic%20Discards%20Act5,baler%20or%20shredder%20for%20recycling.

IPCC. 2014. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II, and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyers (eds.)]. Intergovernmental Panel for Climate Change, Geneva, Switzerland, 151 pp. Available here: https://www.ipcc.ch/site/assets/uploads/2018/02/SYR_AR5_FINAL_full.pdf

USEPA. 2024. AP-42: Compilation of Air Emissions Factors from Stationary Sources, United States Environmental Protection Agency. Available: https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors-stationary-sources. Accessed November, 2024.