Let’s get a few things out of the way: Yes, there are always tons of illegal fireworks being shot off across Los Angeles on the Fourth of July. And yes, you’ll often still hear plenty of booms in the weeks before and after Independence Day. But this year was different—even with a countywide fireworks ban—and the data proves it.
We combed through the Environmental Protection Agency’s archive of air pollution data, and the air following this year’s fireworks was the unhealthiest post-Fourth of July air in the greater L.A. area in at least a decade, and among the worst since the 1990s.
The EPA’s AirNow archive displays records of the daily Air Quality Index value (AQI)—essentially an average rating of how clean or polluted the air is in a given date—dating back to 1980. Since fireworks activity ramps up as the night goes on and pollution tends to linger into the next day, the AQI is almost always higher on July 5 than July 4. With that in mind, the AQI of 186 on July 5, 2020 (which puts the day’s air into the red color-coded “unhealthy” rating) is the worst since 2008.
The air was so bad this year that L.A. briefly held the title of worst air in the world on Sunday morning, as We Like L.A. noted. A particulate advisory issued by the South Coast Air Quality Management District said the AQI reached the “hazardous” category (the worst possible rating of air pollution) during the overnight and early morning hours in parts of Los Angeles and Orange counties.
You can see an hour-by-hour map of the pollution on AirNow, with maps available dating back to 2015, and this year was the only one to cross into the purple “very healthy” category. By 10pm, the air in most of Central and Northeast L.A. was considered “very unhealthy.” At its peak the next morning, that dubious distinction was true in much of the Valley and into the Westside, as well. Looking at conditions just past midnight, here’s how that compares to previous years (2020 is in the bottom right—you know, the one with the big purple blob).
One other thing: The daily AQI values include both ozone and fine particulates like dust and smoke. Ozone pollution levels in L.A. were awful in the ’80s and ’90s and have vastly improved since then. And IQAir cites multiple studies that show a surge specifically in fine particulates during and after fireworks shows. So if we look at just particulate matter (dubbed PM2.5 and PM10 based on their size), 2020’s fireworks pollution is even more remarkably bad. The finer PM2.5, which comes from the combustion of fuel and wood, is the worst since 2005. And PM10, which includes dust from things like construction sites and wildfires, was at its highest level since 2007 and one of the three worst days dating back to 1990, the earliest for which data is available.
UPDATE: The South Coast Air Quality Management District has confirmed that the air pollution during the Fourth of July weekend was the worst in the last decade due to a combination of personal fireworks and dry, stagnant air. Overnight PM2.5 levels were 70% higher than previous years, with particularly high concentrations in Central L.A., North Hollywood and Anaheim (some of AQMD’s instruments were caked in so much particulate matter residue that the readings couldn’t even be properly validated).
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