California's goal to reduce greenhouse gas (GHG) emissions to a level that is 80?% below 1990 levels by the year 2050 will require adoption of low-carbon energy sources across all economic sectors. In addition to reducing GHG emissions, shifting to fuels with lower carbon intensity will change concentrations of short-lived conventional air pollutants, including airborne particles with a diameter of less than 2.5?μm (PM2.5) and ozone (O3). Here we evaluate how business-as-usual (BAU) air pollution and public health in California will be transformed in the year 2050 through the adoption of low-carbon technologies, expanded electrification, and modified activity patterns within a low-carbon energy scenario (GHG-Step). Both the BAU and GHG-Step statewide emission scenarios were constructed using the energy–economic optimization model, CA-TIMES, that calculates the multi-sector energy portfolio that meets projected energy supply and demand at the lowest cost, while also satisfying scenario-specific GHG emissions constraints. Corresponding criteria pollutant emissions for each scenario were then spatially allocated at 4?km resolution to support air quality analysis in different regions of the state. Meteorological inputs for the year 2054 were generated under a Representative Concentration Pathway (RCP) 8.5 future climate. Annual-average PM2.5 and O3 concentrations were predicted using the modified emissions and meteorology inputs with a regional chemical transport model. In the final phase of the analysis, mortality (total deaths) and mortality rate (deaths per 100?000) were calculated using established exposure-response relationships from air pollution epidemiology combined with simulated annual-average PM2.5 and O3 exposure. Net emissions reductions across all sectors are ?36?% for PM0.1 mass, ?3.6?% for PM2.5 mass, ?10.6?% for PM2.5 elemental carbon, ?13.3?% for PM2.5 organic carbon, ?13.7?% for NOx, and ?27.5?% for NH3. Predicted deaths associated with air pollution in 2050 dropped by 24–26?% in California (1537–2758 avoided deaths yr?1) in the climate-friendly 2050 GHG-Step scenario, which is equivalent to a 54–56?% reduction in the air pollution mortality rate (deaths per 100?000) relative to 2010 levels. These avoided deaths have an estimated value of USD?11.4–20.4?billion?yr?1 based on the present-day value of a statistical life (VSL) equal to USD?7.6?million. The costs for reducing California GHG emissions 80?% below 1990 levels by the year 2050 depend strongly on numerous external factors such as the global price of oil. Best estimates suggest that meeting an intermediate target (40?% reduction in GHG emissions by the year 2030) using a non-optimized scenario would reduce personal income by USD?4.95?billion?yr?1 (?0.15?%) and lower overall state gross domestic product by USD?16.1?billion?yr?1 (?0.45?%). The public health benefits described here are comparable to these cost estimates, making a compelling argument for the adoption of low-carbon energy in California, with implications for other regions in the United States and across the world.
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