GRAND TERRACE, Calif. (KABC) -- Southern California recently had 87 consecutive days with unhealthy air quality, the longest stretch in more than 20 years.
It's surprising to some air quality experts, especially after so many years of progress in improving air quality.
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"It's concerning for us because we do show by all our analysis emission levels going down," Dr. Philip Fine with the South Coast Air Quality Management District said. "In general, that should reduce pollutant levels, as well. Although, when you see a blip like this, you want to know why."
Fine said one possibility for the decrease in air quality is the changing weather we've seen over the past three years.
"As everyone has noticed the past three summers have been pretty hot," Fine said. "No storms coming through, so that's really what's been leading to some of our poor air quality over the past few years."
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Other experts say this trend should serve as a warning that improvements still need to be made.
"Really, the emissions of our cars are really clean," Dr. Kelley Barsanti at UC Riverside said. "But if you look at the fleet that's on the road, that fleet is not modern cars."