6.19 Solvent Cleaning Operations

Categories 1241, 1243, 1245, 1934, and 1935

6.19.1 Introduction

These categories cover organic emissions (TOG and ROG) resulting from the use of solvent cleaners during Cold Cleaning, Vapor Degreasing, and Other Hand Wiping operations.

Cold Cleaning operations consist of both point (category 1241) and area (category 1934) sources; Vapor Degreasing operations (category 1243) consists only of point sources; and Other Hand Wiping activities consist of both point (category 1245) and area (category 1935) sources.

Cold Cleaners

The two basic types of cold cleaners are maintenance cleaners and manufacturing cleaners. The maintenance cold cleaners are usually simpler, less expensive and smaller. They are designed principally for automotive and general plant maintenance cleaning. Solvents used in maintenance cleaners are mainly aliphatic petroleum solvents such as mineral spirits and Stoddard solvents.

Manufacturing cold cleaners usually perform a higher quality of cleaning than maintenance cleaners and are therefore more specialized. Manufacturing cold cleaning is generally used in metalworking production. A wide variety of solvents are used in this type of cold cleaner. Manufacturing cold cleaners are fewer in number than maintenance cleaners, but tend to emit more solvent per unit because of the larger size and workload.

Cold cleaning operations include spraying, brushing, flushing and immersion. The designs for material handling in cold cleaning systems are generally divided into manual and batch loaded conveyorized systems. Manual loading is used for the simple, small-scale cleaning operations while batch loaded conveyorized systems are used for the more complex, larger-scale cleaning operations.

Vapor Degreasers

Vapor degreasers clean through the condensation of hot solvent vapor on colder parts. Solvent vapors condense on the parts to be cleaned until the temperature of the parts approaches the boiling point of the solvent. The condensing solvent dissolves the oils and provides the washing action. There are two types of vapor degreasers, open top and conveyorized. Open top degreasers are batch loaded (cleaning only one load at a time) and are normally located near the work that is to be cleaned. Conveyorized solvent degreasers generally are located at central cleaning stations, which require transport of parts for cleaning.

A typical vapor degreaser is a tank designed to produce and contain solvent vapor. At least one section of the tank is equipped with a heating element that uses steam, electricity, or fuel combustion to boil the solvent. As the solvent boils, dense solvent vapors displace the air within the equipment. Condenser coils located on the sidewalls of the degreaser control the upper level of this pure vapor. These coils (which are supplied with a coolant such as water) are generally located around the inner surface of the degreaser and must be placed below the top edge of the degreaser. This is to protect the solvent vapor zone from disturbance caused by air movement around the equipment.

The distance from the top of the vapor zone to the top of the degreaser tank is called the freeboard and is generally established by the location of the condenser coils. The freeboard is 50% – 60% of the width of the degreaser for solvents with higher boiling points (perchloroethylene, trichloroethylene, and 1,1,1-trichloroethane). The freeboard is at least 75% of the width of the degreaser for solvents with lower boiling points (trichlorotrifluoroethane and ethylene chloride).

Most degreasers are equipped with a water separator. The condensed solvent and moisture are collected in a trough below the condenser coils and directed to the water separator. The water separator is a simple container, which allows the water to separate and decant from the system while the solvent flows from the bottom of the chamber back into the vapor degreaser.

Hand Wiping

Hand wiping, or wipe cleaning, includes solvent cleaning done by hand or by means of equipment other than cold cleaners or vapor degreasers. Emissions from hand wiping activities are widespread and occur from solvent usage in manufacturing and maintenance activities. Manufacturing usage refers to any activity (other than in cold cleaners or vapor degreasers) where solvent is used to clean products during the manufacturing process. This includes final wipe cleaning prior to packaging and shipping. Maintenance usage refers to any activity (other than in cold cleaners or vapor degreasers) where solvent is used to clean machinery, tools or other equipment not incorporated into the product. To illustrate this, hand wiping may involve wipe-cleaning a small electronic component with alcohol or large manufacturing equipment with a solvent.

6.19.2 Methodology

Point Sources

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

During the permit to operate (PTO) issuance process, the BAAQMD collects information from the operating facility and/or determines from published literature, e.g. EPA’s AP-42, characteristics of a source including maximum throughput, emission factors for emitted pollutants, and control factors associated with downstream abatement devices. These characteristics are then stored for future use in the BAAQMD’s internal database. Facilities that hold a permit to operate are required to renew this 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 last 12 months. This throughput, in combination with the emission factors and controls factors stored in the internal database, are used to estimate annual emissions at the source level. These source level emissions are then sorted and aggregated into categories.

Categories 1241, 1243, 1245 are considered point source categories and follow the above methodology for emissions estimates.

Area Sources

Categories 1934 and 1935 are considered area source categories as they cover sources that are not explicitly permitted or individually cataloged by the District. Emissions for area source categories are determined using the formula:

Current Year Emissions = Base Year Emission X Growth Profile, and,

Base Year Emission = Throughput X Control Factor X Emission Factor

where,

  • throughput or activity data for applicable base year(s) is determined using a top-down approach (e.g. state-, national-level data);
  • emission factor is derived from general literature, specific literature and reports, and/or source testing results provided by Air District staff;
  • control factor (if applicable) is determined by District and state rules and regulations in effect;
  • and, historical backcasting and forecasting of emissions is based on growth profiles as outlined in the Trends section of this chapter

Emissions for these categories do not follow the above procedure but instead forecast and backcast emissions as determined for base years 2011-2015. Organic emissions for category 1934 (area source) were determined by subtracting point source organic emissions (category 1241) from the total organic emissions allocated to these processes for the Bay Area. The same approach is used for estimating emissions for area source category 1935, Other Hand wiping.

(a) Activity Data / Throughput

Point Sources

Throughput for point sources are provided by individual source operators and collected as referenced in the Methodologies section of this chapter.

Area Sources

Area source emissions are not calculated using a throughput. Instead emissions are estimated using a top down approach starting with state level factors as outlined below:

  1. Cold Cleaners

Emissions from cold cleaning categories (categories 1241 and 1934) were estimated using data from the a 2002 BAAQMD Staff report231. Per this report, the total number of cold cleaners in use in the Bay Area was estimated to be 7,900 in the year 2002. Using census bureau information232 for the year 2002, the total businesses that may use cold cleaners (assumed to be mostly auto-body shops) was determined to be 3,060. Dividing total cleaners by total businesses, an average of 2.58 cold cleaners per business was estimated. The 2002 staff report also determined an emission factor of 0.6 lbs of organics per day per cold cleaner. Using this emission factor and census bureau data for total businesses for the base year(s), emissions from all cold cleaners within the Bay Area were estimated by multiplying the number of cold cleaners per business by total business count for that year.

  1. Other Hand Wiping

Total organic emissions from hand-wiping operations within the Bay Area are based a report published by the University of California, Riverside233. In this report, an updated inventory of organic emissions by solvent cleaning equipment type for the state was estimated for year 2008. Per the report, these emissions were estimated using total employment numbers for California. By applying the percentage of employment in the Bay Area for 2008 (as determined by census bureau data), emissions specific to the Bay Area were determined. These emissions were then forecasted, based on employment growth in the Bay Area, to estimate organic emissions for all hand wiping operations (category 1245 and 1935) for the base year(s).

There are hand wiping emissions that can be found in other District categories (both point and area sources). Since these sources are subject to various other rules (i.e. graphic printing operations, polyester resin operations, various industrial/commercial coatings rules, etc.), the emissions will remain in these specific categories. To prevent “double-counting”, the organic emissions from these categories are subtracted from the total hand wiping value.

(b) County Distribution / Fractions

For point sources, the District’s internal database system contains information on the county location of each facility; hence, emissions are distributed to the counties accordingly. For area sources, emissions distributed into the nine Bay Area counties are based on the county fractions based on employment numbers in each county.

(c) Emission Factors

As mentioned in the throughput section of this chapter, emissions for area source categories are estimated by applying regional percentages to state level factors such as total emissions (category 1935) or total businesses (category 1934).

There is no general emission factor that is applicable for vapor degreasing as this is a point source category and emission factors are facility and source specific as provided by the operator or determined by a permit engineer.

(d) Control Factors

District Rule 8-16234 set operating and equipment standards for cold cleaners and vapor degreasers. In Rule 8-16, hand wiping activity was only subject to the Monitoring and Records section. (However, hand wiping may be subjected to other Regulation 8 rules.) Originally adopted in 1979, there have been several amendments to this rule, with the latest being October 2002. It is estimated the current overall control efficiency for cold cleaners is approximately 68%. For vapor degreasers, the overall control efficiency is currently estimated at 83%.

An amendment to Rule 8-4235 adopted October 16, 2002 and effective June 1, 2003) placed VOC limits on solvent usage in surface preparation (hand wiping) activities to 50 g/l unless controlled by an approved abatement device with an overall control efficiency of at least 85%. (There was a limited exemption which delayed these surface preparation standards in production machinery until June 1, 2004.)

(e) Speciation

The ROG/TOG ratios applied to this group of related categories are based on an Air District internal speciation profile. Multiple data sources have been used for developing speciation profiles, such as Air District-approved source tests, TOG speciation ratios used by other regional air quality agencies, and relevant literature including latest speciation profiles developed by CARB236 and the US Environmental Protection Agency237.

For categories 1241 (cold cleaning - point) and 1934 (cold cleaning - area), ROG constitutes 89% of TOG. For category 1243 (vapor degreaser - point), ROG constitutes 1% of TOG. For categories 1245 (other hand wiping- point) and 1935 (other hand wiping-area), ROG constitutes 60% of TOG.

Further assessment and improvement of ROG/ TOG speciation profiles has been planned in future inventory updates.

6.19.3 Changes in Methodology

Changes in methodology for area source emissions estimations (category 1934 and 1935) include the following:

  • Use of University of Riverside’s updated CARB inventory from 2002 to 2008 for solvent cleaning emissions

  • Use of U.S. Census Bureau data on employment and businesses to estimate regional level total emissions

There are no changes in methodology for point source categories.

6.19.4 Emissions

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

6.19.6 Uncertainties

There are some uncertainties brought in by the assumptions made in calculating emissions for area source categories. These assumptions include the following:

  • The number of cold cleaners per business
  • The assumption that business with smaller, non-permitted cold cleaners consist only of auto-body shops
  • The correlation between employment in the manufacturing sector and the use of solvent cleaning

6.19.7 Contact

Author: Ariana Husain

Reviewer: Sukarn Claire

Last Update: November 06, 2023

6.19.8 References & Footnotes

  1. BAAQMD. 2002. Staff Report on Proposed Amendments to BAAQMD Regulation 8, Rule 16: Solvent Cleaning Operations↩︎

  2. U.S. Census Bureau. Explore Census Data. [accessed 2023 Mar 16]. https://data.census.gov/cedsci/↩︎

  3. University of California, Riverside. 2011. Development of Updated ARB Solvent Cleaning Emissions, Final Report, Agreement No. 06-322. https://ww2.arb.ca.gov/sites/default/files/classic/research/apr/past/06-322.pdf↩︎

  4. BAAQMD. 2002. Regulation 8, Rule 16 - Solvent Cleaning Operations. https://www.baaqmd.gov/rules-and-compliance/rules/reg-8-rule-16-solvent-cleaning-operations↩︎

  5. BAAQMD. 2002. Regulation 8, Rule 4 - General Solvent and Surface Coating Operations. https://www.baaqmd.gov/rules-and-compliance/rules/reg-8-rule-4-general-solvent-and-surface-coating-operations↩︎

  6. CARB. 2022.ORGPROF. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎

  7. U.S. Environmental Protection Agency (EPA). 2022. SPECIATE.https://www.epa.gov/air-emissions-modeling/speciate↩︎

  8. Association of Bay Area Governments (ABAG). Forecasts and Projections. [accessed 2023 Feb 22]. https://abag.ca.gov/our-work/land-use/forecasts-projections↩︎