7.12 Other External Combustion - All Other Fuels

Categories 308, 309, 310, 311, and 312

7.12.1 Introduction

Categories 308, 309, 310, 311, and 312 account for emissions of criteria pollutants (particulate, organic, NO_x, SO_x, and CO) from external combustion of fuels, such as, liquefied petroleum gas (LPG), distillate oil, residual oil, coke & coal, and other fuels at industrial facilities in the Bay Area.

7.12.2 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.

Categories 308, 309, 310, 311, and 312 are point source categories and follow the above methodology for emissions estimates.

The Bay Area Air District’s Regulation 9, Rule 7 controls NO_x emissions from external combustion of fuels.

The PM_2.5/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-page³²⁶.

For category 308, CARB PM speciation profile number is 120; PM_2.5 and PM₁₀ constitutes 100.0% of total PM.

For category 309, CARB PM speciation profile number is 112; PM_2.5 and PM₁₀ constitutes 96.8% of total PM.

For category 310, CARB PM speciation profile number is 111; (NA - There were negligible or no emissions for category 310 for year 2015).

For category 311, CARB PM speciation profile number is 131; PM_2.5 and PM₁₀ constitutes 33.3% of total PM.

For category 312, CARB PM speciation profile number is 134; PM_2.5 constitutes 92.9% and PM₁₀ constitutes 99.6% of total PM.

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 CARB³²⁷ and the US Environmental Protection Agency³²⁸.

For categories 308, 309, 310, 311, and 312, ROG to TOG ratios are 0.66, 0.83, NA, 0.06, and 0.70, respectively. Further assessment and improvement of ROG / TOG speciation profiles has been planned in future inventory updates.

7.12.3 Changes in Methodology

No changes to methodology were made in this version of the base year emissions inventory.

7.12.4 Emissions

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

7.12.5 Trends

(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.

Emissions prior to 1987 were derived from Base Year 1983 trend values. Category 309 had been grouped as four categories before Base Year 1987 and Category 311 had been grouped as two categories. The historical trend values for categories 309 and 311 were summed, respectively, to build the historical emissions data.

(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 BY2015 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 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

For these categories, it was felt that annual emissions would tend to follow the industrial employment activity in the Bay Area.

The employment data were obtained from the Association of Bay Area Government’s (ABAG) 2017 “Projections” report³²⁹.

7.12.6 Uncertainties

Uncertainties may result from some inaccuracies in data reporting by the facilities.

7.12.7 Contact

Author: Sukarn Claire

Reviewer: Ariana Husain

Last Update: November 06, 2023

7.12.8 References & Footnotes