Meteorological Influences on Surface Ozone in the Los Angeles Basin
Abstract: Ozone levels in the Los Angeles Basin have improved over the last twenty years due to reductions in pollutants responsible for ozone formation. Still, meteorological effects can increase or decrease ozone levels. This study was an attempt to identify weather patterns that contribute to elevated or depressed ozone levels at four sites in the South Coast Air Quality Management District in California. Hourly surface ozone and meteorological measurements were compared at sites in Santa Clarita, Los Angeles (North Main Street), Costa Mesa, and San Bernardino. Comparisons were made on sixty-two days with good air quality and sixty-five days with unhealthy air quality between the years 2008 and 2012. Days were selected between April and September based on the Los Angeles area Air Quality Index. Ozone concentrations were shown to be positively correlated with temperature and negatively correlated with absolute humidity. While temperature and humidity do not cause changes in ozone production, they are indicators of weather parameters that do. Days with warmer temperatures have less clouds and more solar radiation. Results show that unhealthy ozone levels occur on days when solar radiation exceeds 800 W/m2. Absolute humidity is related to ozone because it distinguishes between marine and continental airmass source regions. Low ozone levels were consistently observed near the coast in Costa Mesa. The highest ozone levels were found at the receptor sites, San Bernardino and Santa Clarita, downwind of Los Angeles. Finally, wind speed was found to limit ozone in Los Angeles, but no relation between wind speed and ozone was found at the receptor sites. The meteorological conditions that resulted in changes in solar radiation and air mass source region had the largest impact on ozone levels in the Los Angeles Basin.