7.1 Domestic Natural Gas

7.1.1 Emissions

Introduction

These categories estimate criteria pollutant (particulate, organic, NOx, SOx, and CO) and GHG emissions (CO2, CH4, and N2O) resulting from the combustion of natural gas in the residential sector. Natural gas consists of a high percentage of methane (generally above 85 percent) and varying amounts of ethane, propane, butane, and inert gases. The combustion of natural gas in the residential sector is broken down into three categories: Space Heating, Water Heating, and Cooking. Categories 283, 284, and 285 account for area source emissions from Space Heating, Water Heating, and Cooking, respectively. Design of residential boilers and furnaces generally resemble fire tube type boilers with flue gas traveling through several channels or tubes with water or air circulated outside the channels or tubes.

Methodologies

Total natural gas usage for these categories was obtained from the California Energy Commission (CEC), the Pacific Gas and Electric Company (PG&E), and the city of Palo Alto. This total natural gas usage was broken down into three categories based on information from CEC and PG&E, and is shown below.

Table 7.1: Apportionment of NG throughput.
Category Percent
#283 Space Heating 57.3%
#284 Water Heating 38.5%
#285 Cooking 4.2%

Emission factor information for natural gas combustion was obtained from the U.S. Environmental Protection Agency’s (EPA’s) document AP-42, the U.S. Department of Energy’s (DOE’s) Energy Information Administration (EIA) and the California Energy Commission (CEC).

The natural gas combustion emission factors for these categories, in pounds per million cubic feet (Lb/MMCF) are shown below in Table 7.2.

Table 7.2: Emission factors (lb/MMCF).
category PM TOG NOx SO2 CO CH4 N2O CO2
#283 Space Heating 7.6 11 94 0.6 40 2.3 2.2 120000
#284 Water Heating 7.6 11 94 0.6 40 2.3 2.2 120000
#285 Cooking 7.6 11 94 0.6 40 2.3 2.2 120000

County Distribution

Natural gas information provided by CEC and PG&E includes residential, commercial, and industrial usage for the Bay Area nine counties by month. Information on Palo Alto’s natural gas usage was obtained separately from the City of Palo Alto and was used together with Santa Clara County natural gas usage values. This was done because the city obtained gas from a supplier other than PG&E. Solano and Sonoma Counties are partially in the San Francisco Bay Area Air District, so data were used for the cities that are in the District. For Solano County, data used were for Benicia, Fairfield, Suisun and Vallejo; for Sonoma County, data used were for Cotati, Petaluma, Rohnert Park, Santa Rosa, Sebastopol and Sonoma.

Table 7.3: County fractions.
category ALA CC MAR NAP SF SM SNC SOL SON
#283 Space Heating 20.4% 15.6% 4.9% 1.9% 13.2% 11.6% 22.9% 3.8% 5.6%
#284 Water Heating 20.4% 15.6% 4.9% 1.9% 13.2% 11.6% 22.9% 3.8% 5.6%
#285 Cooking 20.4% 15.6% 4.9% 1.9% 13.2% 11.6% 22.9% 3.8% 5.6%

Temporal Variation

Space Heating

  • Daily Activity: The maximum activity occurs in the early daylight hours and in the evening hours, with average activity during the day and low activity at night.

  • Weekly Activity Code: The activity is uniform seven days a week.

  • Monthly Activity: The monthly activity was based on monthly residential natural gas sales from the California Energy Commission. Activity occurs from November to June, with the highest months being December through April.

Water Heating

  • Daily Activity: The maximum activity occurs in the early daylight hours and in the evening hours, with average activity during the day and low activity at night.

  • Weekly Activity: The activity is uniform seven days a week.

  • Monthly Activity: The monthly activity is assumed to be uniform throughout the year.

Cooking

  • Daily Activity: The activity occurs during meal time hours.

  • Weekly Activity: The activity is uniform seven days a week.

  • Monthly Activity: The monthly activity is assumed to be uniform throughout the year.