An Air Quality and Boundary Layer Dynamics Analysis of the Los Angeles Basin Area During the Southwest Urban NOx and VOCs Experiment (SUNVEx)

The NOAA Chemical Sciences Laboratory (CSL) conducted the Southwest Urban NOx and VOCs Experiment (SUNVEx) to study emissions and the role of boundary layer (BL) dynamics and seabreeze (SB) transitions on the time evolution of coastal air quality. The study presented focuses utilizes remote sensing and in situ observations in Pasadena, California. Investigations of the synoptic conditions during days when O3 was greater than 70 ppb led to the identification of high pressure conditions and an overall reduction in BL height throughout the day as being primary dynamical factors responsible for enhanced ozone. Enhanced trapping of pollutants at night resulted in reduced O3 and increased NOx (titration), while trapping during the day coincided with a simultaneous decrease in NOx and increase in VOCs that promoted favorable O3 conditions. To evaluate micrometeorological impacts, we selected a day when O3 exceeded 70 ppb during a SB, used empirical mode decomposition to isolate higher frequency variations (micrometeorology), and developed a multivariate spectral coherence mapping (MSCM) technique using the Ricker wavelet to study the role of BL growth and SB transitions on the evolution of air quality measurements. The extraction of time-scales from chemistry and dynamics scaleograms led to a quantitative evaluation of dynamical contributions from BL growth and a SB transition. A statistical evaluation of chemistry data during August 2021 during BL growth supported findings from the case study, but with the caveat of SB interactions with land BL and complex chemical reactions contributing to the scatter distribution caused by day-to-day variation.