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

Abstract

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.

The Unmanned Systems Research Laboratory (USRL): A New Facility for UAV-Based Atmospheric Observations

“…Up to an altitude of about 20 km, ozonesondes constitute the most important data source with long-term coverage for the derivation of ozone trends. UAV-borne ozone observations have been reported in the literature for close-to-the-ground (boundary layer) deployment using Electrochemical Concentration Cell (ECC) ozonesondes (by Illingworth et al [7]; Chouza et al [82]). Gronoff et al [83] reported UAV-ozone measurements from ship plume emissions using an octocopter with a 2B-Technologies POM ozone sensor, which calculates ozone concentration from optical absorption of UV light generated from a low-pressure mercury lamp.…”

Description and Evaluation of the Fine Particulate Matter Forecasts in the NCAR Regional Air Quality Forecasting System

“…Recently, we supported the NASA Fire Influence on Regional to Global Environments Experiment-Air Quality (FIREX-AQ) campaign in the summer of 2019. Third, we generated the vertical distributions of ozone and aerosol information at NASA Tropospheric Ozone Lidar Network (TOLNET) sites so that transient events, e.g., stratospheric intrusions and transport of polluted air from the urban area to the nearby mountains (e.g., from the Los Angeles basin to the San Gabriel mountains [6]), could be captured. Fourth, the NCAR system was aimed at providing long-term air quality simulations for use in health impact studies.…”