4.14 Stone, Sand, and Gravel
Category 41
4.14.1 Introduction
Category 41 accounts for dust (PM, PM10, and PM2.5) emissions generated from stone, sand, and gravel processing (i.e. crushing, quarrying, screening, handling, etc.). Fugitive sources include the transfer of stone, sand, and gravel, truck loading, mixer loading, vehicle traffic, and wind erosion from sand.
4.14.2 Methodology
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.
Further speciation and quality assurance of emissions are performed as a part of the inventory process. The BAAQMD staff also perform a systematic crosswalk between CEPAM’s source category classification (Emission Inventory Code - EICs) and the District’s source category classification (category identification number - cat_ids), which ensures consistency in the annual emissions reporting process (CEIDARS) to California Air Resources Board. The last part of the inventory development process includes forecasting and back casting, and aggregation into sub-sectors and sectors for documentation purposes. 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 41 is considered a point source category and follows the above methodology for emissions estimates.
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 CARB83 or the US Environmental Protection Agency84. For this category or group of categories, PM2.5 constitutes 7% of total PM and PM10 constitutes 50% of total PM. The Air District staff routinely review speciation profiles and may update ratios as needed for improving emissions estimates.
The ROG/TOG 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, TOG speciation ratios used by other regional air quality agencies, and relevant literature including latest speciation profiles developed by CARB85 and the US Environmental Protection Agency. For this category or group of categories, ROG constitutes 70% of TOG.
4.14.3 Changes in Methodology
There are no changes to methodology for Stone, Sand, and Gravel (Category 41).
4.14.4 Emissions
A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.
4.14.5 Trends
In 2018, a reduction of particulates can be attributed to the amendment of District’s Regulation 6, Rule 1 86.
(a) Historical Emissions / History
Historical emissions for point source emissions 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.
In 1963, there was at least 50% reduction of particulate emissions from equipment brought about by the District’s [Regulation 6] on visible emissions from the Ringlemann 2 standard. In 1970, there was at least an additional 25% reduction in particulates from the Ringlemann 1 standard.
(b) Future Projections / Growth
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 2020. 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 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 past or 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
Projections of emissions to 2040 were also based on ABAG’s 2017 Construction Employment growth profile.
4.14.6 Uncertainties
The major pollutant of concern for this category is particulate matter and the major contributor of PM for this category can be attributed to one major facility still in operation. For this facility, the emission factors and throughputs are specific to the sources on site. For this reason, the uncertainty in this category is dictated by the margin of error in the emission factors as determined by the site operator which is unknown at this time.
4.14.7 Contact
Author: Michael Nguyen
Reviewer: Ariana Husain
Last Update: November 06, 2023
4.14.8 References & Footnotes
CARB. 2022.PMSIZE https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎
EPA. 2022. SPECIATE https://www.epa.gov/air-emissions-modeling/speciate↩︎
CARB. 2022.ORGPROF https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎
BAAQMD. 2018. Regulations 6, Rule 1 - Particulate Matter General Requirements, https://www.baaqmd.gov/~/media/dotgov/files/rules/archive-2018-regulation-6-rule-1/documents/rg0601-pdf.pdf?la=en↩︎