Southern California ozone exposure disparities under different emissions control strategies in a low-carbon future

Environmental justice (EJ) has emerged as a critical consideration when planning new air pollution control strategies. In this study we analyze how traditional ozone (O₃) control strategies for the year 2050 will affect exposure disparities, defined as departures from the population average exposure, for O₃ and oxides of nitrogen (NOx) in Southern California. Future air quality fields were simulated using a chemical transport model under five emission scenarios that explore a range of traditional controls that target the largest sources of precursor emissions using a novel O₃ source apportionment technique but without considering exposure disparities. We find that traditional O₃ control strategies reduce O₃ exposure disparities by <1.6 % and reduce NO₂ exposure disparities by <9 % in Southern California. For the Black and African residents living in the urban core of Los Angeles, the relative NO₂ exposure disparities increase from +23.1 % to +66.2 % and O₃ exposure disparities increase from -3.3 % to +0.1 % due to NOx emissions reductions mainly in outlying regions and the NOx-rich environment in the urban core. Additional analysis shows that complete elimination of NOx emissions from Los Angeles International Airport (LAX) would reduce the NO₂ exposure disparities by up to 50 %, but there is currently no practical method to achieve this goal. The results of the current study highlight the challenge of simultaneously attaining O₃ standards and reducing exposure disparities for O₃ and NO₂ in cities with NOx-rich urban cores. Reducing emissions by region may be a solution to this challenge.