Long-range transport of ozone from the Los Angeles Basin: A case study

Abstract

Airborne lidar measurements of ozone above the Los Angeles Basin on 17 July 2009 show orographic lifting of ozone from the surface to the free troposphere by the San Gabriel Mountains. Mixing ratios in excess of 100 parts-per-billion-by-volume (ppbv) were measured ∼4 km above mean sea level (ASL). These observations are in excellent agreement with published model studies, confirming that topographic venting by the so called “mountain chimney effect” is a potentially important pathway for removal of pollutants from the Los Angeles Basin. The lofting of ozone and other pollutants into the free troposphere also greatly increases the potential for long-range transport from the Basin, and trajectory calculations suggest that some of this ozone may have been transported ∼1000 km to eastern Utah and western Colorado.