LOS ANGELES (CBSLA) — Air quality following Fourth of July weekend was the worst in the region since the Bobcat Fire last September, the South Coast Air Quality Management District said Tuesday.

The group also said the air quality showed the second-highest pollution levels for the holiday in the last decade.

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The level of fine particulate matter remained higher than normal Fourth of July celebrations, but was 14% lower than last year’s historic pollution levels, according to the SCAQMD.

SCAQMD said personal “backyard” fireworks and commercial fireworks displays in the region contributed to the poor air quality.

Officials warned that high levels of fine particulate matter can have negative health effects and lead to cardiovascular and respiratory health problems.

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The group found “unhealthy” to “hazardous” air in the valley and inland areas, with the highest concentration recorded in the San Bernardino County city of Ontario.

Concentrations of PM2.5 were 70% higher than previous years between 7 p.m. on July 4, 2021 and 7 a.m. the next day in the South Coast Air Basin, which includes Orange County and parts of Los Angeles, Riverside and San Bernardino counties, according to the AQMD.

The 14% drop over last year’s pollution level was attributed to the amount of emissions from fireworks, as well as weather conditions.

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(© Copyright 2020 CBS Broadcasting Inc. All Rights Reserved. City News Service contributed to this report.)