4.12 Concrete Batching
Categories 39 and 1908
4.12.1 Introduction
Categories 39 and 1908 account for particulate emissions (PM, PM10, and PM2.5) from concrete batching plants.
Concrete is composed of water, cement, sand, gravel and crushed stone. Concrete batching is prepared either at a building construction site or for the manufacture of concrete products such as pipes and prefabricated construction parts. Sources of emissions include fugitive losses from the loading and unloading of cement, handling of sand and the mixing of cement, sand, and aggregate. There are two types of concrete batch facilities: truck mix and central mix. Truck mix facilities load materials into trucks and then mix to form the final product. Central mix facilities load all materials into a central stationary mixer and, from there, the final product is loaded into trucks.
4.12.2 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.
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 39 is considered a point source category and follows the above methodology for emissions estimates.
Area Sources
Category 1908 is considered an area source category as it covers smaller, retail bakeries 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
For Category 1908 (area source operations), emissions are estimated by taking the Bay Area subset of the national throughput data for base years 2011-2015, negating the throughput allocated to Category 39, and applying emission factors as specified in EPA’s AP-42 document75.Detailed background on the determination of throughput, controls, and emission factors is provided in the following sections.
(a) Activity Data / Throughput
Point source throughputs were provided by individual plant operators as described in the Methodology section of this chapter.
Area source throughputs for years 2012 to 2015 are estimated using the calculated 2011 area production and growing this production according to the Association of Bay Area Government’s (ABAG) 2013 Projection data for Construction Employment 76.
Cement production for California in 2011 was estimated at 8,833,000 short tons. This was calculated by taking the U.S. production, as provided by the Department of Conservation, Bureau of Mines, and then multiplying this figure by the California fraction of the U.S. total population. By using the fraction of Bay Area population to that of California, the 2011 cement production in the BAAQMD was estimated at 1,627,190 short tons. The Bay Area’s 2011 concrete production from both point and area sources was estimated at 13,335,670 tons/year (using mixing ratios found in AP-42, Section 11.12). The 2011 area source throughput (category 1908) of 3,435,624 tons/year was calculated by subtracting the total point source throughput (category 39) from the BAAQMD’s total concrete production throughput.
The 2015 area source throughput (category 1908) is estimated to be 3,920,000 tons/year.
(b) County Distribution / Fractions
For point sources, the District’s internal database contains information on the county location of each processing plant; hence, emissions are distributed to the counties accordingly. Emissions from area sources are distributed to the Bay Area counties by the number of employees estimated in the Ready-Mix Concrete Manufacturing sector (NAICS 327320) as determined by the US Department of Commerce’s 2009 County Business Patterns 77.
(c) Emission Factors
Emission factors for point source concrete batching operations (category 39) are provided by the individual facilities.
For area source concrete batching operations, the emission factor for particulate (PM, PM10, PM2.5) is based on truck mix operations1 as the majority of concert batch plants fall under this operation type. The emission factor accounts for particulate emissions that occur from the transfer and loading of materials, wind erosion from sand and aggregate storage piles, and vehicular travel on unpaved roads. The composite particulate emission factor was estimated to be 0.16 lbs/ton of concrete produced.
(d) Control Factors
There are no applicable regulatory controls for these categories.
(e) Speciation
All emissions are categorized as particulate matter (PM). Particle size distribution is shown below:
| Size | Fraction of Total Particulate (TSP) |
|---|---|
| 10 micron | 0.3 |
| 2.5 micron | 0.2 |
The PM2.5/PM and the PM10/PM ratios applied to this category or this group of related categories are consistent with size fractions of speciation profiles developed by the California Air Resources Board (CARB) and published on their emissions inventory web-page 78.
(f) Sample Calculations
For both point and area source categories the calculation is emission factor based. Below is an example of how emissions are estimated for year 2015 for Category 1908 (area source).
4.12.3 Changes in Methodology
No major changes in methodology were made in this version of the base year emissions inventory as compared to the previous version with base year of 2011.
Updates to base year data from the previous version include the following:
- Employment projection data from Plan Bay Area 2040, a publication by ABAG and the Metropolitan Transportation Commission (MTC), is used for emissions forecasting2
4.12.4 Emissions
Concrete batching accounts for less than 1% of total particulate emissions for the Bay Area. Since 1990, emissions have dramatically decreased due to increased use of process controls such as baghouses/dust collectors and water sprays to keep particulate dispersion down. These controls have been implemented to protect both workers and nearby residential and commercial receptors and are a regular practice for many sites.
4.12.5 Trends
(a) Historical Emissions / History
Historical emissions for category 39 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.
A historical growth profile from 1987 to 2005 based on a combination of prior emissions data and the Association of Bay Area Government’s (ABAG’s) 2009 Construction Employment projections is used for category 1908. From 2005 to 2015, the profile is based on ABAG’s 2013 Construction Employment projections2. Since 1990, emissions from concrete batching have dramatically decreased due to the increased use of process controls and improvements in equipment.
(b) Future Projections / Growth
Forecasting of point source emissions (category 39) 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
Forecasting for area source emissions (category 1908) applies a similar procedure to above but starting with a base year of 2015.
Projections of emissions to 2040 for both categories are based on ABAG’s 2017 Construction Employment projections2.
4.12.6 Uncertainties
As there is no source from which to obtain total concrete production for the Bay Area or total count of concrete batch sites in operation in a given time period, the throughput for the Bay Area was estimated based on the ratio of the Bay Area population to total California population. This assumption, that population is directly correlated to production, brings some uncertainty to the final throughput estimate. The emission factors are based on EPA’s AP-42 documentation1 which rates the factors at a level B indicating tests were performed by a generally sound methodology, but lacked enough detail for adequate validation.
4.12.7 Contact
Author: Ariana Husain
Reviewer: Sukarn Claire
Last Update: November 06, 2023
4.12.8 References & Footnotes
U.S. Environmental Protection Agency. AP-42, Fifth Edition, Compilation of Air Pollutant Emissions Factors, Volume I : Stationary Point and Area Sources, Section 11.12. 2006. https://www.epa.gov/sites/default/files/2020-10/documents/c11s12.pdf↩︎
ABAG. Association of Bay Area Governments: Forecasts and Projections. https://abag.ca.gov/our-work/land-use/forecasts-projections↩︎
United States Census Bureau. County Business Patterns. 2009. https://www.census.gov/data/datasets/2009/econ/cbp/2009-cbp.html↩︎
PMSIZE. CARB 2022. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎