7.2. Fuel Sulfur Content Update

In EMFAC2021, the sulfur content in fuel was assumed to be 15 ppm across all GAIs, based on values last updated in EMFAC2007 to reflect California fuel regulations in effect at that time. The EMFAC2025 update incorporates sulfur content data collected by CARB’s Enforcement Division from service stations between 2008 and 2022. Figures 7.8 and 7.9 present the mean sulfur content measured for gasoline and diesel in each region, respectively. Note that the data are presented by the same control regions used for the Reid Vapor Pressure regulation (see Figure 7.2). For both gasoline and diesel fuels, statewide averages (\(\bar{S}_{\text{statewide}}\)) were calculated as updated fuel sulfur content values using the following equation:

(7.1)\[\bar{S}_{\text{statewide}} = \frac{\sum_{i=1}^{n} (\bar{S}_i \times N_i)}{\sum_{i=1}^{n} N_i}\]

Where \(\bar{S}_i\) is the mean sulfur content in region i and \(N_i\) is the number of samples collected in that region. The updated sulfur content in EMFAC2025 is 6.5 ppm for gasoline and 5.2 ppm for diesel.

Figure 7.8: Gasoline Sulfur Content Across Reid Vapor Pressure (RVP) Control Regions

Figure 7.9: Diesel Sulfur Content Across Reid Vapor Pressure (RVP) Control Regions