Meteorology of air pollution in Los Angeles

The meteorology of air pollution in Los Angeles (LA) is studied via daily near-surface air chemistry, aerosol and weather data assimilated from insitu and satellite measurements in the period 2005-2016. Atmospheric fields are regressed onto seasonal air pollution indices and reveal that a ridge of high pressure north of California weakens the longshore circulation and reduces dispersion. A 10-case composite of atmospheric anomalies during winter air pollution episodes was analyzed. Periods of high nitrogen dioxide and carbon monoxide show increasing temperature gradients that induce the converging of land-seabreezes beneath a strengthened thermal inversion. The atmospheric environment of an air pollution episode in December 2005 reveals recirculating trajectories. Efforts to limit emissions have contributed to reductions of nitrogen dioxide, but other constituents remain a public health concern. Knowledge of weather conditions underlying air pollution episodes will improve warnings and the effectiveness of mitigating actions.