Variability of Ozone over California during CABOTS 2016: Assessing the Role of Long-Range Transport and Local Emission Using Airborne Measurements and Models

Different sources of ozone (O₃) were investigated during the California Baseline Ozone Transport Study (CABOTS) from May to June 2016 using airborne Alpha Jet Atmospheric eXperiment (AJAX) trace gas measurements, MERRA2 reanalysis data, and trajectory models. To assess the roles of local emission and long-range transport, synoptic conditions during the campaign were also analyzed.

Back-trajectory model simulations demonstrate how often the air masses come from local or long-distance transport, and thus how much they contribute to O₃ transport over California (CA). The impact of the high O₃ transported aloft on the surface O₃ concentration through vertical and horizontal transport within a few days is substantiated by influence maps determined from the Weather Research and Forecasting Stochastic Time Inverted Lagrangian Transport (WRF-STILT) model. The Q diagnostic, which is a measure of the mixing of the air masses, is another tool used to indicate when O₃ from the different origins is mixed and transported to the western U.S. NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite, and TROPOspheric Monitoring Instrument (TROPOMI) data is also used to identify the transport pathways of O₃.

KORUS-AQ aerosol and O₃ data measured over the Koran peninsula during April – June 2016 are also investigated as upwind information regarding aerosol and ozone transport. It is expected that transport will have the greatest impact in April and May, and local impact is expected to dominate in June due to synoptic weather conditions. Integrated data analysis using trajectory models, in-situ airborne and surface measurements, satellite, reanalysis products, and diagnostic tools allows various ozone distributions over CA to be attributed to multiple source processes.