Emissions Reductions to Meet a Tighter Ozone Standard in the U.S. through Control Technologies versus Clean Energy Transition Scenarios.

Past studies have found that carbon reduction strategies generally reduce emissions of nitrogen oxides (NOX) and/or volatile organic compounds (VOCs). The reverse is not true, however, as evidenced by over 50 years of air quality improvements in the U.S. with only modest reductions of carbon dioxide (CO2) emissions. This analysis compares energy and emissions pathways to achieve NOX and VOCs targets calculated by the U.S. Environmental Protection Agency (EPA) to meet a hypothetical 65 ppb revision to the National Ambient Air Quality Standard (NAAQS) for ozone. To meet these targets, we model sector-specific reductions over a 15-year horizon with the Multipollutant Emissions Calculator for Air Quality and Climate (MECAQC), considering both conventional emission controls, e.g. technologies, as well as energy system changes, e.g., fuel-switching. Switching away from conventional fuels can achieve the majority of required NOX and VOCs emission reductions, considering maximum decarbonization up to 45% for heavy-duty vehicles, up to 65% for light-duty vehicles, up to 36% for building electrification, and up to 100% for electricity generation. The maximum decarbonization assumptions alone could meet NOX and VOCs targets in the Midwest region and VOCs targets in the Northeast region, reducing NOX emissions in affected areas by 44%, VOCs by 16%, and CO2 by 56%. These carbon-reduction strategies may be supplemented by conventional emission controls to achieve additional VOCs reductions to meet the most targets: reducing NOX emissions in affected areas by 33%, VOCs by 17%, and CO2 by 35%. Conventional controls alone could meet all regional targets except the California NOX target, which cannot be met by any approach evaluated here, reducing NOx emissions in affected areas by 33% and VOCs by 17%, but increasing emissions of CO2 by 1.4%.