For decades, Southern California has waged a slow but successful war on smog.
Through vehicle emissions rules, clean-fuel standards and other tough measures, officials have lifted the choking pall of air pollution that once shrouded Los Angeles, bringing clearer skies and healthier lungs.
But now, progress appears to be faltering. Smog has gotten worse for the second straight year, even though emissions are on the decline.
That apparent disconnect is forcing regulators to explain why air quality in the nation’s worst-polluted region is dipping.
Their solution, blame climate change and President Trump.