4.15 Sand Blasting
Categories 42, 1909
4.15.1 Introduction
Categories 42 and 1909 account for particulate matter (PM, PM10, and PM2.5) emissions from abrasive blasting.
Abrasive blasting (of which sandblasting is a part) is the use of abrasive materials to clean or prepare a surface, such as metal or masonry. Sand is the most commonly used abrasive material. Other abrasives include coal and smelter slags, glass beads, aluminum oxide, steel shot, walnut shells, garnet, etc. Industries that use abrasive blasting include ship building and repair, aircraft manufacturing, fabricated metal manufacturing, oil and gas extraction industries, aluminum and other nonferrous production and processing industries, etc.
There are three types of propelling methods used for abrasive blasting:
- Dry System: where compressed air is used to propel the abrasive using either a suction or pressure type process.
- Wet System: where air or water pressure are used to propel an abrasive slurry to the target surface.
- Centrifugal Wheel System: where centrifugal and inertial forces are used to propel abrasive materials.
In many applications, the abrasive materials can be reused. However, once the abrasive’s particle size gets smaller, its stripping efficiency drops and has to be replaced. On the other hand, sand is commonly used for abrasive operations where recycling is not feasible, such as unconfined sand blasting operations.
4.15.2 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.
For those years where no data is available, emissions data are backcasted to year-1990, as well as forecasted to year-2040 using either interpolation or another mathematical approach (see Trends section). Finally, emissions trends spanning from year 1990-2040 for each category and pollutant are evaluated for anomalies that are then investigated and addressed.
Category 42 is considered a point source category and follows the above methodology for emissions estimates.
Area Sources
Category 1909 is considered an area source category as it covers smaller non-permitted sand blasting operations that are not explicitly permitted or individually cataloged by the District. The general procedure for determining emissions for area source categories is as follows:
- Determine throughput for applicable base year(s) using a top-down approach (i.e. state-, national-level data)
- Backcast and forecast throughput based on growth profiles as outlined in the Trends section of this chapter
- Determine emission factors and control factors for the applicable historical and future years
- Apply these emission and control factors to the backcasted and forecasted throughputs to estimate emissions
Sand is the most commonly used abrasive material, however there are other abrasive materials used in the Bay Area, such as steel shot, glass beads and aluminum oxide. For emission calculation purposes, it is assumed sand is used in both point (Category 42) and area sources (Category 1909). The other abrasive materials’ usages are assumed to be accounted for in the point sources (Category 42).
Emissions for category 1909 were estimated using the base years of 2011-2015 and applying emissions factors based on published literature. Detailed background on the determination of throughput, controls, and emission factors is provided in the following sections.
(a) Activity Data / Throughput
To determine total throughput for the Bay Area and area source throughput (Category 1909) the following was performed:
The sand throughput was estimated using a combination of the previous inventory estimates of throughput and the Association of Bay Area Government’s (ABAG’s) Manufacturing and Wholesale Employment forecast data87. This inventory and prior inventory estimates are based on findings from the U. S. Geological Survey’s (USGS) 2010 Mineral Commodity Summary for Sand and Gravel -Industrial88. According to this summary, abrasive sand consumed approximately 3.7% of the industrial sand production and California received approximately 4.4% of the total sand produced. The BAAQMD’s percentage of California’s total abrasive sand throughput was approximately 12.6%. This was estimated by using the ratio of the number of employees associated with abrasive blasting (by NAICS) in the District versus the California total. The following industries were used for estimation:
- Ship building and repair (NAICS 3366)
- Aircraft manufacturing industry (NAICS 336411)
- Steel product manufacturing industry (NAICS 3312)
- Aluminum production and processing industry (NAICS 3313)
- Nonferrous production and processing industry (NAICS 3314)
- Fabricated metal product manufacturing industry (NAICS 332)
- Oil and gas extraction industry (NAICS 211)
A sample calculation for the 2010 estimated total sand throughput in the Bay Area is shown below:
2010 Sand usage in the United States (from the USGS’s Salient U.S. Silica Statistics):
\[\begin{align} 28,749,347&\ \text{ton/yr} \\ \end{align}\]
2010 Bay Area sand usage for abrasive purposes:
\[\begin{align} 28,749,347&\ \text{ton/yr} \\ \times\ 0.037&\ \text{(for abrasive purposes)} \\ \times\ 0.044&\ \text{(to Calif.)} \\ \times\ 0.126&\ \text{(BAAQMD portion)} \\ \hline = 5,937&\ \text{ton/yr} \end{align}\]
Subtracting out the 2010 point source (category 42) sand throughput of 2,570 tons/year to get the 2010 area source throughput (category 1909) yields:
\[\begin{align} 5,937 & & \text{(total)} \\ – 2,570 & & \text{#42 (point)} \\ \hline = 3,367 &\ \text{ton/yr} & \text{#1909 (area)} \end{align}\]
Subsequent base year throughputs for area source category 1909 were estimated by multiplying the 2010 area source throughput by the Association of Bay Area Government’s (ABAG’s) Manufacturing and Wholesale Employment growth factor.
For all years, Category 1909 throughput was estimated by subtracting the throughput associated with category 42 from the total, as shown above, for each year.
(b) County Distribution / Fractions
For point sources (Category 42), the District’s internal database contains information on the county location of each processing plant; hence, emissions are distributed to the counties accordingly.
For area sources (Category 1909), emissions were distributed to counties by the total employment estimates from those industries listed above by NAICS.
(c) Emission Factors
U.S. EPA recommended particulate emission factors89 for sand blasting were used for emission calculations and are listed below.
- PM: 54 lbs/ton
- PM10: 26 lbs/ton
(d) Control Factors
Larger abrasive blasting operations are subject to District Regulation 6, Rule 1 - Particulate Matter - General Requirements. This regulation places limitations on concentration (in proportion to production and exhaust rate), visible emissions and opacity. Because the regulation sets limitations on concentration (as a result of production rate * exhaust rate), there are no explicit controls enacted to reduce emissions rates and, therefore, no controls are applied herein. However, in many cases, due to the size of the operation or limitation of space, some abrasive blasting operations may choose to use a pollution control device such as dust filters/collectors or bag houses, etc. These non-regulatory controls can allow for abatement up to 99% or higher.
Unconfined and temporary abrasive blasting operations are subject to District Regulation 12, Rule 4-Miscellaneous Standards of Performance, Sandblasting. This rule establishes opacity and abrasives standards.
(e) Speciation
All emissions are categorized as particulate matter (PM). Particle size distribution is shown below:
| Size | Fraction of Total Particulate (TSP) |
|---|---|
| 10 micron | 0.48 |
| 2.5 micron | 0.05 |
The PM2.5/PM and the PM10/PM ratios applied to this category or 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, PM speciation ratios used by other regional air quality agencies, and other relevant literature. These ratios are not necessarily consistent with the latest speciation profiles developed by CARB90 or the US Environmental Protection Agency91. The Air District staff routinely review speciation profiles and may update ratios as needed for improving emissions estimates.
(f) Sample Calculations
The 2015 Area Source Sand Blasting emissions (Category 1909) for total particulates (PM) and PM10 in the BAAQMD are calculated as follows:
\[ \begin{eqnarray} \text{PM} &=& 3,491\ \text{ton/yr} \times 54\ \text{lb/ton} \div 2000\ \text{lb/ton} \\ &=& 94.26\ \text{ton/yr (or 0.26 ton/day)} \end{eqnarray} \]
\[ \begin{eqnarray} \text{PM}_{10} &=& 3,491\ \text{ton/yr} \times 26\ \text{lb/ton} \div 2000\ \text{lb/ton} \\ &=& 44.45\ \text{ton/yr (or 0.12 ton/day)} \end{eqnarray} \]
4.15.3 Changes in Methodology
There are no changes in methodology for this base year inventory.
4.15.4 Emissions
A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.
4.15.5 Trends
(a) Historical Emissions / History
Historical emissions for point source emissions, category 42, are derived from source-specific throughputs provided by the permitted facility, compiled/reported emission factors, and regulation-based control factors. This information is archived in the BAAQMD’s internal database which is queried to retrieve the data for historical and current years. Interpolation techniques to account for missing data are used when necessary, this is the case for years 1991-1992.
The historical growth profile (back to 1991) for area sources (Category 1909) was based on sand production data from the USGS 92.
The construction industry hit a sharp decline in 2008 due to the economic crisis which in turned caused a sharp decrease in demand for sand and sand blasting operations.
(b) Future Projections / Growth
Forecasting of categories 42 and 1909 is done based on calculations as shown in the equation below using recently updated growth profiles. For category 42, emissions are grown from year 2020 to 2040 using the 2017 ABAG growth profile for Manufacturing and Wholesale Employment. The same growth profile was used to grow emissions for category 1909 from year 2015 to 2040.
The growth profiles have been verified and updated to represent the most likely surrogate for growing emissions for a given category up to year 2040. 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.
\[ \text{PE} = \text{Gr} * \text{Ci} * \text{Ei} \] \(PE\) = projected emissions of pollutant i in a future year
\(Gr\) = growth rate by economic profile of industry or population
\(Ci\) = control factor of pollutant i based on adopted rules and regulations
\(Ei\) = base year emissions of pollutant i
4.15.6 Uncertainties
The AP-42 factors used for area source emissions calculations (category 1909) are rated E, Poor, due to the determination being made based on one study. To lower the uncertainty for the emissions calculated using these factors, further studies should be done and results collected to derive a more representative sample set and emission factors.
4.15.7 Contact
Author: Ariana Husain
Reviewer: Sukarn Claire
Last Update: November 06, 2023
4.15.8 References & Footnotes
Association of Bay Area Governments (ABAG). Forecasts and Projections. [accessed 2023 Feb 22]. https://abag.ca.gov/our-work/land-use/forecasts-projections↩︎
United States Geological Survey (USGS). Crushed Stone Statistics and Information.[accessed 2023 Mar 14].https://www.usgs.gov/centers/national-minerals-information-center/crushed-stone-statistics-and-information↩︎
U.S. Environmental Protection Agency (EPA). 1998. AP-42 Compilation of Air Emission Factors. Ch.13.2.6↩︎
CARB. 2022. PMSIZE. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎
U.S. Environmental Protection Agency (EPA). 2022. SPECIATE. https://www.epa.gov/air-emissions-modeling/speciate↩︎
United States Geological Survey (USGS). USGS Sand Production Historical Data. [accessed 2023 Mar 16]. https://www.usgs.gov/media/files/construction-sand-and-gravel-historical-statistics-data-series-140↩︎