The South Coast Air Quality District said poor air quality was likely through the afternoon because fireworks emit high levels of particulate matter.
The smell of smoke infused the overnight intrusion of damp marine air over the region.
"June Gloom continues its tight grip on Southern California early this morning despite the turn of the calendar," the National Weather Service said.
July 4 and 5 are typically the worst days of the year for levels of fine particulate matter in the South Coast Air Basin. Breathing particulates can lead to a wide variety of cardiovascular and respiratory health effects.
A smoke advisory was also in effect due to the Tumbleweed Fire burning in mountains near Interstate 5 and the community of Gorman about 60 miles northwest of downtown Los Angeles.
Areas adjacent to the fire were expected to experience the highest concentrations of pollutants.
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