"It was a pretty typical Fourth of July. We saw PM spikes in the very unhealthy level, which is about three to four times the acceptable federal limit, and it lasted about two hours," said Heather Heinks with San Joaquin Valley Air Pollution Control District.
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The agency's graph showed the spike, with levels peaking at 10 p.m. on Saturday night.
Officials said poor air quality is typical on Independence Day, and the spikes from this year were similar to those recorded last year.
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Fireworks emit a variety of particulate matter, including ash and metals, which can cause serious health effects.
The medical director of the Chronic Lung Disease Program at UCSF Fresno, Dr. Anil Ghimire, said people with asthma and other respiratory issues are most at risk.
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It's not clear how polluted air may affect COVID-19 patients or if it has any impact on transmitting the virus.
"Irrespective of COVID, I think people need to take precautions based on their chronic condition and the level of the pollution. So far, we don't know whether the increased pollution will increase the risk of COVID or not. We don't know that yet," Dr. Ghimire said.
Dr. Ghimire said while he recommends masks to help prevent the spread of the coronavirus, most do not provide much protection against particulate matter found in fireworks.