Southern California ozone pollution declining in recent decades

Many studies have documented the decline in ozone pollution and its precursors in the Los Angeles air basin over the past several decades.

Now Pollack et al. have analyzed new data from research aircraft, along with archived data from roadside monitors and ground-based instruments, to provide a synthesis of concentrations and emissions ratios of ozone, other secondary pollutants, and their precursors from 1960 to 2010.

The data shows that photochemical processing rates have increased and that reaction pathways have changed, reducing not only ozone but also the organic nitrate compounds associated with eye irritation.

According to the authors' analysis, these reductions are the direct result of changes in emissions standards for precursors, indicating that emission control measures in Southern California have been effective.

While emissions of precursors have declined, motor vehicles remain the dominant source of emissions in Los Angeles.