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  16 Dec 2020

16 Dec 2020

Review status: this preprint is currently under review for the journal ACP.

The impact of Los Angeles basin pollution and stratospheric intrusions on the surrounding San Gabriel Mountains as seen by surface measurements, lidar, and numerical models

Fernando Chouza1, Thierry Leblanc1, Mark Brewer1, Patrick Wang1, Sabino Piazzolla2, Gabriele Pfister3, Rajesh Kumar3, Carl Drews3, Simone Tilmes3, and Louisa Emmons3 Fernando Chouza et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Wrightwood, CA, USA
  • 2Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA
  • 3National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA

Abstract. In this work, the impact of Los Angeles basin pollution transport and stratospheric intrusions on the surface ozone levels observed in the San Gabriel Mountains is investigated based on a combination of surface and lidar measurements as well as WRF-Chem (Weather Research and Forecasting with Chemistry) and WACCM (Whole Atmosphere Community Climate Model) model runs. The number of days with observed surface ozone levels exceeding the National Ambient Air Quality Standards exhibit a clear seasonal pattern, with a maximum during summer, when models suggest a minimum influence of stratospheric intrusions and the largest impact from Los Angeles basin pollution transport. Additionally, measured and modeled surface ozone and PM10 were analyzed as a function of season, time of the day and wind direction. Measurements and models are in good qualitative agreement, with maximum surface ozone observed for south-west and west winds. For the prevailing summer wind direction, slightly south of the ozone maximum and corresponding to south south-west winds, lower ozone levels were observed. Back-trajectories suggest that this is associated with transport from the central Los Angeles basin, where titration limits the amount of surface ozone. A quantitative comparison of the lidar profiles with WRF-Chem and WACCM models revealed good agreement near the surface, with models showing an increasing positive bias as function of altitude, reaching 75 % at 15 km above sea level. Finally, three selected case studies covering the different mechanisms affecting the near-surface ozone concentration over the San Gabriel mountains, namely stratospheric intrusions and pollution transport, are analyzed based on surface and ozone lidar measurements, as well as co-located ceilometer measurements and models.

Fernando Chouza et al.

Status: open (until 10 Feb 2021)
Status: open (until 10 Feb 2021)
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Fernando Chouza et al.

Fernando Chouza et al.


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