6.18 Asphalt Roofing

Category 1618

6.18.1 Introduction

Category 1618 covers organic gas emissions (TOG and ROG) from roofing operations involving asphalt. It does not include emissions resulting from the manufacture of roofing materials or from associated fuel combustion processes.

Asphalt is a dark brown to black cementitious material (solid or liquid) of which the main constituents are bitumens which occur naturally or as a residue of petroleum refining224. This composite material is used to adhere, repair, and/or create a smooth finish over manufactured roofing materials (i.e. cap sheets, felt sheets and flashing squares) on commercial, industrial, and multiple unit dwelling buildings.

6.18.2 Methodology

Category 1618 is considered an area source category as it covers sources 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

Emissions for category 1618 were estimated using the base years of 2011-2015.The procedure is based on The California Air Resources Board’s (CARB) methodology 225. CARB uses a top-down, emission factor based approach starting with regional sales of asphalt and deriving state and county throughputs by applying estimated proportions based on population and employment data. Emissions are then estimated by applying a general emission factor.

(a) Activity Data / Throughput

Activity data in units of thousand barrels of asphalt and road oil supplied to the West Coast was collected from the Energy Information Administration (EIA) Office of Oil and Gas 226. It was assumed 80% of the asphalt is used for road paving and 20% is used for roofing.

(b) County Distribution / Fractions

County distribution is based on employee count for the non-residential and residential construction sectors as estimated using information from the United States Census Bureau227 and sorting by NAICS code.

(c) Emission Factors

An organic emission factor of 6.2 lb/ton of roofing material was used to estimate emissions for this category228.

(d) Control Factors

There are no District or Federal rules covering asphalt roofing, therefore no control or regulatory factors apply to this category.

(e) Speciation

The speciation applied to TOG to determine ROG is consistent with the size fractions of speciation profiles developed by the California Air Resources Board (CARB) and published on their emissions inventory web-page 229. All organic emissions are assumed to be reactive, therefore reactive organics is equal total organics.

(f) Sample Calculations

In 2015, 3,814,000 barrels of asphalt were used in the Bay Area for paving and roofing purposes. Of that amount, it is assumed that 20% (~ 762,800 barrels/year) was used for roofing. Using a density of 8.34 lb/gal, throughput for the BAAQMD for 2015 is estimated to be 95,423 tons of asphalt. An example calculation of TOG emissions for 2015 is shown below.

\[ 762,800\ \tfrac{bbl}{yr} \times 42\ \tfrac{gal}{bbl} \times 8.34\ \tfrac{lb}{gal} \text{ (density factor)} \times \tfrac{1\ ton}{2000\ lb} \times 6.2 \tfrac{lb}{ton} \text{ (emission factor)} \times \tfrac{1\ ton}{2000\ lb} = 414 \tfrac{ton}{year} \]

6.18.3 Changes in Methodology

For the previous base year, information for county apportionment was provided by CARB. For base year publication, county apportionment is based on U.S. Census Bureau employment data for the construction sector.

6.18.4 Emissions

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

6.18.6 Uncertainties

An 80/20 split between paving and roofing is assumed to apply to total asphalt used in the state. This was determined by Sonoma Technology Institute (STI) in 2003. However, going forward, actual throughput numbers for paving and roofing would help improve the accuracy of emission estimates for this category.

6.18.7 Contact

Author: Ariana Husain

Reviewer: Sukarn Claire

Last Update: November 06, 2023

6.18.8 References & Footnotes

  1. BAAQMD. 1987. Regulation 8, Rule 15 - Emulsified and Liquid Asphalts↩︎

  2. CARB. 2003. Attachment C: Asphalt Paving and Roofing, from STI’s Area Source Emissions Updates↩︎

  3. EIA. 2021. West Coast (PADD 5) Product Supplied of Asphalt and Road Oil (Thousand Barrels). https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=MAPUPP51&f=A↩︎

  4. U.S. Census Bureau. Data. [accessed 2023 Jan 30]. https://www.census.gov/data.html↩︎

  5. EPA. 2000. Emissions Inventory Improvement Program (EIIP), Volume 3b - Area Source Method Abstracts - Asphalt Roofing Kettles. https://www.epa.gov/air-emissions-inventories/volume-3b-area-source-method-abstracts↩︎

  6. CARB. 2022. ORGPROF. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎

  7. ABAG. Association of Bay Area Governments : Open Data Catalog. [accessed 2023 Jan 30]; https://abag.ca.gov/tools-resources/data-tools/open-data-catalog↩︎