Fireworks bring very unhealthy air to an already problematic issue for the San Joaquin and Sacramento Valleys. Air quality is typically the worst between 4 and 6p.m. during the summer. This is due to the heating of gases creating higher ozone.
Fireworks on the Fourth of July can present health hazards later in the day. Many times, the worst air quality on the holiday is later in the evening around 11 p.m.
The issue isn’t ozone, it is particulate matter (PM) from fireworks. In large quantities, this can be harmful, especially to those with existing respiratory problems.
Air quality usually spikes in the very unhealthy range around peak firework activity around 11 p.m. The good news is it falls within about an hour but is still in the unhealthy range.
Air quality tends to be the best in the early morning hours for ozone. The pattern for smoke around any active wildfires though is opposite, peaking in the morning and improving in the afternoon.
