10.1 Construction Operations

Categories 744, 745, 746, 747, and 748

10.1.1 Introduction

Categories 744 through 748 listed below account for fugitive dust emissions (PM) generated from construction activities while building residential, commercial, industrial, and institutional structures, as well as roads. These construction operations include digging, loading, scraping, grading, compacting, light duty vehicle traffic etc.

Category # Description Classification
744 Residential Area
745 Commercial Area
746 Institutional Area
747 Industrial Area
748 Roads Area

10.1.2 Methodology

Categories 744 through 748 are considered an area source category since they cover facilities / emission sources that are not directly permitted by the District, and hence not systematically cataloged. 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

More details on throughput, county distribution, emission factors and controls is provided in the following subsections. The District has estimated PM emissions primarily based on the area source methodologies adopted by the California Air Resource Board (CARB) to estimate emissions from construction and demolition of buildings425 and roads426 when developing a statewide emissions inventory for the 2016 State Implementation Plan (SIP). The District has updated the underlying data when local information is available.

The methodologies estimated the fugitive dust emissions based on the acreage affected by construction. These emissions occur across the acreage of the building activities and are thus considered as an area source.

(a) Activity Data / Throughput

Activity data (throughput) are expressed in terms of acre-months for each category. The method of collecting activity data and calculating throughput varies among the various types of construction sites and are discussed as follows.

Residential Construction (Category 744)

The number of new housing units (single- and multi-family) acquired from Metropolitan Transportation Commission (MTC) were used to calculate the acreage disturbed427. The affected construction area for a single family living unit is estimated at 1/7th of an acre for Alameda, Contra Costa, Marin, San Francisco, San Mateo, and Santa Clara counties; and 1/5th of an acre for Napa, Solano, and Sonoma counties. The affected construction area for multi-family living units is estimated to be 1/20th of an acre1. The construction time for residential units is assumed to be 6 months. For each county, the throughput, is estimated by multiplying the affected construction area, construction time and number of new units of single and multi-family respectively and then lumped together.

Commercial, Industrial, and Institutional Construction (Categories 745 - 747)

The estimated construction acreage for these categories is based on project valuations supplied from the California Department of Finance. The acreage for commercial, industrial, and institutional construction is 3.7, 4.0, and 4.4 acres per million dollars of valuation, respectively. Since these factors are 1977 values, inflationary corrections were made to the project valuations by multiplying the project valuations by the inflationary adjustment factor, which is the ratio of 1977 Consumer Price Index (CPI) value to a particular year’s CPI value428. The construction time for commercial, industrial, institutional buildings is assumed to be 11 months. The throughput for a particular year, expressed in acre-months, is calculated by multiplying that year’s inflationary adjusted project valuation by the construction acreage, and construction time.

Road Construction (Category 748)

The latest road construction for freeways, highways, county and city roads was estimated as the difference in the respective total mileage between a year and its prior year, as reported in the California Statistical Abstract. The affected area per mile of road for freeways, highways, and county and city roads are 12.1, 9.2, and 7.8 acres/mile, respectively. The construction time for roads is assumed to be 18 months for the average project. The throughput, expressed in acre-months, is estimated by multiplying the road construction miles, affected area per mile of new road, and project duration time.

(b) County Distribution / Fractions

For residential buildings construction operations (category 744), the throughput were calculated for each county. For the remaining construction operations, the distribution of emissions into counties was based on construction activity provided by the California Department of Finance.

(c) Emission Factors

Emission factors were derived from CARB’s methodology documents[1,2] which are based on a study done by Midwest Research Institute (MRI)429. For these construction operations, this study produced a site average emission factor of 0.11 ton PM10/acre-month that accounts for the effects of typical control measures, such as watering which is assumed to control dust by 50%. The study also provides an emission factor of 0.42 tons of PM10/acre-month under “worst-case” scenario to account for large-scale construction operations that involved substantial earthmoving activity. In the Bay Area, it was assumed that 20% of construction activity consisted of large-scale construction operations. Therefore, the overall composite emission factor used for all construction activities in the Bay Area was 0.172 ton PM10/acre-month.

(d) Control Factors

The control effectiveness of typical mitigation measures has been taken into consideration in the composite emission factors. No additional control factors were applied.

(e) Speciation

The size fractions in the latest speciation profile for construction dust (PM profile # 420) from CARB were used to estimate PM and fine particulates (PM2.5) emissions430. According to the profile, 48.93% of PM is PM10 while 4.89% of PM is PM2.5.

10.1.3 Changes in Methodology

The following changes have been made since previous base year for residential building construction operations (category 744)

  1. The throughput of base year 2015 were estimated for each county based on the statistics of housing units from MTC3 instead of project valuations supplied from the California Department of Finance.

  2. The emissions of historical years were backcasted based on the annual throughput calculated from MTC’s housing units data as it goes back to year 1967.

10.1.4 Emissions

Construction operations dust is a major source of PM and the contribution to health impact could be amplified due to their proximity to urban population. A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.

10.1.6 Uncertainties

There are known limitations with the current method for estimating emissions from construction operation dust. The methodology is based on the MRI study back in 1996 and has not been evaluated or updated ever since. The emission factors are the same for building and road constructions though the characteristics of the two are quite different. The parameters used are not always based on data specific to Bay Area or up to date. For example, the throughput of road constructions was estimated based on statewide default value of affected area per mile of road constructed. For building constructions, the methodology assumes that valuation is proportional to acreage disturbed, even for high-rise type building construction. With all these assumptions and limitations, it’s difficult to quantify the uncertainties. However, there are ways to improve the emissions estimates, such as conducting well-designed field study to evaluate and update the methodology, identifying and collecting local or more up-to-date activity data from local agencies or private sectors.

10.1.7 Contact

Author: Yuan Du

Reviewer: Abhinav Guha, Tan Dinh

Last Update: November 06, 2023

10.1.8 References & Footnotes

  1. CARB. September 2002. Miscellaneous Process Methodology Section 7.7 Building Construction Dust. https://ww3.arb.ca.gov/ei/areasrc/fullpdf/full7-7.pdf↩︎

  2. CARB. August 1997. Miscellaneous Process Methodology Section 7.8 Road Construction Dust. https://ww3.arb.ca.gov/ei/areasrc/fullpdf/full7-8.pdf↩︎

  3. Metropolitan Transportation Commission (MTC). Dataset on Vital Sign: Housing Permits - by county. [Accessed in January 2020]. ↩︎

  4. Association of Bay Area Government (ABAG). Consumer Price Index. https://abag.ca.gov/tools-resources/data-tools/consumer-price-index↩︎

  5. Muleski, Greg. March 29, 1996. Improvement of Specific Emission Factors (BACM Project No. 1), Final Report. Midwest Research Institute↩︎

  6. CARB. Speciation Profiles Used in CARB Modeling. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎