Efficient Environmental Impact Evaluation of Biomass Deployment Strategies in Central California Using CMAQ Adjoint Sensitivity Analysis

Landfill diversion mandates and energy incentive policies support the rapid development of organic waste recycling infrastructure in California. Though these policies are largely driven by the potential greenhouse gas benefits of organic waste diversion, there are potential negative impacts from these facilities to the local ecosystem, such as increasing ozone exceedances. Both global and local impacts must be modeled, and the specifics of how this biomass distributed generation (BDG) system will be developed - and how policy incentives impact this - must be understood. This study evaluates the pollution impacts of 32 alternative organic waste BDG scenarios for California based on a previously developed investment model that defines the size, location, feedstock, and conversion and utilization technologies of facilities built for a given waste and energy incentive scenario. We quantify each scenario's spatially distributed life-cycle emissions of greenhouse gases, PM 2.5, nitrogen oxides, and volatile organic compounds with emission factors generated in previous analyses informed by onsite measurements at operational facilities in California. Emissions considered include trucking, waste processing, energy conversion, and digestate management, as well as the emission offsets from reduced biomass burning and fossil fuel powered electricity generation. An advanced analytical tool CMAQ adjoint model, is used to efficiently link the high-resolution emission scenarios to their ozone air quality impact in the central California region, home to more than half of the disadvantaged communities in California. This efficient impact evaluation approach is generalizable for other cases and particularly suitable for policy-oriented users. Results indicate that net ozone impacts of the 32 scenarios are largely driven by onsite NOx emissions at BDG facilities, highlighting the importance of facility siting. Lowest ozone impacts of the BDG system occur with high biomethane price, low electricity price, and commingled waste stream due to the favoring of anaerobic digestion facilities over gasification. Further comparison between scenarios provides more insights about how energy prices and waste commingling influence BDG system development, and how that translates to local air quality impacts.