Southern Californians who venture outside this week will see excellent air quality, resulting from business closures during the coronavirus pandemic and recent rain.
The area's famous freeways are empty but experts say the lack of cars is contributing only a small amount to the clear skies.
Shipping is down in the ports, meaning fewer trucks and cargo vessels are running.
There are also fewer planes flying and more construction projects on hold.
Emissions from heavy machinery accounts for nearly 80% of all greenhouse gas emissions in LA County.
Researchers are analyzing just how much emissions have dropped. Results are expected in a few weeks.