Effects of Independence Day fireworks on atmospheric concentrations of fine particulate matter in the United States

Previous case studies have documented increases in air pollutants, including particulate matter (PM), during and following fireworks displays associated with various holidays and celebrations around the world. But no study to date has explored fireworks effects on air quality over large regions using systematic observations over multiple years to estimate typical regional PM increases. This study uses observations of fine PM (with particle diameters < 2.5 μm, PM2.5) from 315 air quality monitoring sites across the United States to estimate the effects of Independence Day fireworks on hourly and 24-hr average concentrations. Hourly PM2.5 concentrations during the evening of July 4 and morning of July 5 are higher than on the two preceding and following days in July, considered as control days. On national average, the increases are largest (21 μg/m3) at 9–10 pm on July 4 and drop to zero by noon on July 5. Average concentrations for the 24-hr period beginning 8 pm on July 4 are 5 μg/m3 (42%) greater than on control days, on national average. The magnitude and timing of the Independence Day increases vary from site to site and from year to year, as would be expected given variations in factors such as PM2.5 emissions from fireworks, local meteorological conditions, and distances between fireworks displays and monitoring sites. At one site adjacent to fireworks, hourly PM2.5 levels climb to ∼500 μg/m3, and 24-hr average concentrations increase by 48 μg/m3 (370%). These results have implications for potential improvements in air quality models and their predictions, which currently do not account for this emissions source.