Fig 1.
The air pollution implications of electric vehicle rebates were modeled according to this schematic.
Blue boxes represent data inputs and model parameters, including the current Clean Vehicle Rebate Project rebate distribution, the EMFAC (Emission Factors) model, and the Clean Vehicle Rebate Project consumer survey [20,33,34]. Yellow boxes represent calculated values, with the calculations described correspondingly in the methods section. Italicized text summarizes the calculations performed to convert blue inputs into yellow calculated values. The model was used to evaluate emissions changes under 4 scenarios (Table 1).
Table 1.
The clean vehicle rebate project was evaluated under four scenarios, including one current and three possible future scenarios.
Fig 2.
More disadvantaged communities have received fewer clean vehicle rebates.
Based on (a) CalEnviroScreen 4.0, (b) Hispanic population, (c) less than high school education, and (d) poverty indicators, communities of greater disadvantage have received fewer Clean Vehicle Rebate Project rebates from 3/18/2010 to 1/31/2021. Boxes show the median and extend to the 25th and 75th percentiles; whiskers span 1.5 Interquartile Range (IQR). Notches approximate a 95% confidence interval for the median, extending to ± 1.58 * IQR / sqrt(n). Disadvantaged Communities are highlighted in red. Census tracts are grouped into 20 quantile groups based on CalEnviroScreen 4.0 or sub-indicator percentile.
Fig 3.
In California, electricity generating units (EGUs) are disproportionately located in disadvantaged communities.
Panel (a) presents statewide data and panel (b) presents a regional example, centered on the city of Los Angeles in Southern California. Black circles represent the 231 EGUs in the state of California catalogued by the 2020 AVERT (Avoided Emissions and Generation Tool) model. Census tracts are divided into 4 quartiles based on CalEnviroScreen 4.0 (CES 4.0) percentile score, with higher CES 4.0 percentile scores corresponding to a darker background. Disadvantaged Communities (DACs) are defined as having CES 4.0 scores in the highest quartile for the state, while we define Least Disadvantaged Communities (LDACs) as having CES 4.0 scores in the lowest quartile. This map was produced in R using United States Census Bureau 2010 TIGER/Line Shapefiles [46], available from https://www.census.gov/cgi-bin/geo/shapefiles/index.php?year=2010&layergroup=Census+Tracts.
Fig 4.
As a result of the clean vehicle rebate project, net local primary PM2.5 emissions decrease more for least disadvantaged communities than for disadvantaged communities, as modeled under the present-day scenario.
Based on (a) CalEnviroScreen 4.0, (b) Hispanic population, (c) less than high school education, and (d) poverty indicators, as the level of community disadvantage increases moving to the right, the modeled change in annual primary PM2.5 emissions per census tract increases, moving from more negative to less negative median values. Boxes show the median and extend to the 25th and 75th percentiles; whiskers span 1.5 Interquartile Range (IQR). Notches approximate a 95% confidence interval for the median, extending to ± 1.58 * IQR / sqrt(n). The red horizontal line marks a net local emissions change of zero. Disadvantaged Communities are highlighted in red. Census tracts are grouped into 20 quantile groups based on CalEnviroScreen 4.0 or sub-indicator percentile.
Fig 5.
As a result of the clean vehicle rebate project, net local SO2 and NOX emissions decrease more for least disadvantaged communities than for disadvantaged communities, as modeled under the present-day scenario.
Based on the CalEnviroScreen 4.0 indicator, as the level of community disadvantage increases moving to the right, the modeled change in annual (a) SO2 or (b) NOX emissions per census tract increases, moving from more negative to less negative median values. Boxes show the median and extend to the 25th and 75th percentiles; whiskers span 1.5 Interquartile Range (IQR). Notches approximate a 95% confidence interval for the median, extending to ± 1.58 * IQR / sqrt(n). The red horizontal line marks a net local emissions change of zero. Disadvantaged Communities are highlighted in red. Census tracts are grouped into 20 quantile groups based on CalEnviroScreen 4.0 percentile.
Fig 6.
Future scenarios with an unchanged rebate distribution maintain distributional inequities.
Under future model scenarios, net local primary PM2.5 emissions reductions are disproportionately concentrated among Least Disadvantaged Communities, but increased utilization of renewable sources to supply electricity for new electric vehicles lowers the total net change in primary PM2.5 emissions resulting from the Clean Vehicle Rebate Project. Based on the CalEnviroScreen 4.0 indicator, as the level of community disadvantage increases moving to the right, the modeled change in annual primary PM2.5 emissions moves from more negative to less negative median values. Increasing the Electric Demand Reduction Factor from 0.5 (black, future scenario 1) to 0.7 (dark green, future scenario 2) to 0.9 (light green, future scenario 3) lowers total primary PM2.5 emissions but leaves the distributional trend largely unchanged. The red horizontal line marks a net local emissions change of zero. Disadvantaged Communities are highlighted in red. Census tracts are grouped into 20 quantile groups based on CalEnviroScreen 4.0 percentile, with points representing the median for each quantile group.
Fig 7.
Despite impacting modeled aggregate primary PM2.5 emissions changes as a result of the current clean vehicle rebate project scenario, different temporal charging distributions do not substantially alter the heterogenous distribution of net emissions changes.
Models were run according to (a) 24-hour charging distribution, (b) daytime charging from 7am to 7pm, and (c) nighttime charging from 7pm to 7am. Boxes show the median and extend to the 25th and 75th percentiles; whiskers span 1.5 Interquartile Range (IQR). Notches approximate a 95% confidence interval for the median, extending to ± 1.58 * IQR / sqrt(n). The red horizontal line marks a net local emissions change of zero. Disadvantaged Communities are highlighted in red. Census tracts are grouped into 20 quantile groups based on CalEnviroScreen 4.0 percentile.