Preprints
https://doi.org/10.5194/egusphere-2024-1460
https://doi.org/10.5194/egusphere-2024-1460
27 Aug 2024
 | 27 Aug 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Measurement Report: Diurnal Variability of NO2 and HCHO Lower Tropospheric Vertical Profiles in Southeastern Los Angeles

Peter Peterson, Lisa Hernandez, Leslie Tanaka, and Alejandro Dunnick

Abstract. Ground level ozone in excess of United States ambient air quality standards remains a prevalent issue across Southern California, particularly in the summer months. To improve our understanding of the vertical distribution of ozone precursors in southern California, we used ground-based MAX-DOAS measurements in Whittier CA to simultaneously retrieve both near-surface mole fractions and vertical column densities of both NO2 and HCHO. While vertical column densities of NO2 are well correlated with TROPOMI observations over the study period (R=0.77), HCHO VCDs and FNRs derived from MAX-DOAS observations are less well correlated (R=0.44 and 0.35, respectively). These observations also show differing diurnal cycles between near surface mixing ratios and vertical column densities due to variability in the vertical profile that will be increasingly critical to understand given the ongoing shift from sun synchronous to geostationary satellite observations. Ratios of HCHO to NO2, commonly referred to as FNR, derived from satellite-based measurements are used to diagnose ozone production chemistry over regions without consistent surface based measurements. Using ground-based measurements, we determine FNRs using both surface mole fractions and vertical column densities, finding FNRs derived from surface mole fractions are generally lower than those derived from column based measurements. Evaluating ozone exceedance probability as a function of FNR for both quantities suggests the transition between a VOC limited and NOx limited regimes may begin at lower FNR values than those derived from satellite based measurements in East LA. We find these differences in FNR derived form ground based and satellite based measurements are driven by variability in the vertical distribution of HCHO. These impacts are most pronounced in late afternoon, when ozone exceedances are most prevalent.

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Peter Peterson, Lisa Hernandez, Leslie Tanaka, and Alejandro Dunnick

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1460', Anonymous Referee #2, 05 Nov 2024 reply
Peter Peterson, Lisa Hernandez, Leslie Tanaka, and Alejandro Dunnick

Data sets

Whittier_CH2O_NO2_MAXDOAS_20200326 Peter Peterson https://doi.org/10.5281/zenodo.11117573

Peter Peterson, Lisa Hernandez, Leslie Tanaka, and Alejandro Dunnick

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Short summary
This work uses spectroscopy to examine the vertical distribution of nitrogen dioxide and formaldehyde in southeastern Los Angeles, USA, a region heavily impacted by ozone pollution. We examine how both the amount and vertical profile of the two species varies throughout the day, finding that differences between the two species impact the utilization of satellite-based measurements to diagnose ozone production chemistry and these impacts are variable depending on the time of day.