4.7 Wood Products Manufacturing
Categories 35 and 1907
4.7.1 Introduction
Categories 35 and 1907 account for particulate matter (PM, PM10, and PM2.5) emissions from woodworking operations.
Emissions from these categories include generation of small wood waste particles (sawdust) from woodworking operations such as sawing, planing, lathing, and sanding. Industries engaged in these operations include manufacturers of plywood, particleboard, hard board, and furniture.
4.7.2 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 35 is considered a point source category and follows the above methodology for emissions estimates.
Area Sources
Category 1907 is considered an area source category as it covers wood-working 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
Emissions for category 1907 were estimated using the base years of 2011-2015 and applying emissions factors based on data from permitted sources. Detailed background on the determination of throughput, controls, and emission factors is provided in the following sections.
(a) Activity Data / Throughput
Point source throughput is provide by facility operators at the permitted source level as mentioned in the section above.
It was assumed that area sources account for 20% of the total wood production throughput in the Bay Area. Using this estimate and point source throughput (_Category_35_tput), an area source throughput was calculated as follows Category_35_tput / 0.8 * 0.2. For the base years of this inventory, the calculated 2011 throughput was grown using Association of Bay Area Governments (ABAG) 2009 growth profile for Manufacturing and Wholesale Employment51.
(b) County Distribution / Fractions
Point source emissions are distributed to the counties based on the location of the processing facilities. Area source emissions are distributed to match the allocation of point source emissions.
(c) Emission Factors
Point Sources
As mentioned in the Methodology section, point source emissions are calculated based on emission factors either provided by the operator or District permit engineer.
Area Sources
The area source total particulate emission factor is based on the average emission factor (without abatement applied) for point sources. It is estimated to be 20 pounds/ton wood processed.
(d) Control Factors
District Regulation 6, Rule 1 - Particulate Matter - General Requirements implements a restriction on particulate matter emissions on a hourly basis based on the throughput of the process. For this base year, the average effective control for point sources is estimated to be 83%.
(e) Speciation
The PM2.5/PM and the PM10/PM ratios applied to these 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 52. For this category(s), CARB’s speciation profile number is 900; PM2.5 constitutes 42% of total PM and PM10 constitutes 70% of total PM.
4.7.3 Changes in Methodology
No changes in methodology were made in this version of the base year emissions inventory.
4.7.4 Emissions
A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.
4.7.5 Trends
Emissions for both categories have remained somewhat constant since 2001. Prior to this there is a distinct decrease in emissions with the exception of a spike in 1998. The origin of this spike is due to a large increase in throughput at one facility which may or may not be due to an erroneous data entry. This is further explained in the Uncertainties section of this chapter.
(a) Historical Emissions / History
Historical emissions for category 35 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.
Historical emissions for area source category 1907 are based on a combination of prior permit data (back to 1990) and the Association of Bay Area Government’s (ABAG’s) 2009 Manufacturing Employment growth profile.
(b) Future Projections / Growth
Forecasting for both categories 35 and 1907 emissions is done based on calculations as shown in the equation below using recently updated growth profiles. For category 1907, emissions are grown from year 2015 to 2040 using the 2017 ABAG growth profile for Manufacturing and Wholesale Employment. The same growth profile was used to grow emissions for category 35 from year 2020 to 2040.
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 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
4.7.6 Uncertainties
There is some uncertainty in the reported throughput for permitted sources in 1998. The increase in throughput causes emissions to increase by 7 times compared to the prior year but this increase is not seen for the years following. In addition, the assumed 20% split of area source throughput to total throughput is currently based on engineer’s best estimate. These factors create uncertainty in both point and area source emissions that will be further evaluated in future inventories.
4.7.7 Contact
Author: Ariana Husain
Reviewer: Sukarn Claire
Last Update: November 06, 2023
4.7.8 References & Footnotes
ABAG. Association of Bay Area Governments : Forecasts and Projections. [accessed 2023 Feb 22]. https://abag.ca.gov/our-work/land-use/forecasts-projections↩︎
CARB. 2022. PMSIZE. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎