SACRAMENTO, Calif. — After a week of new fires capped off with more than a few illegal fireworks displays, ozone levels will be higher Friday in the valley. Because of this, it's the first Spare the Air Day of the year for Sacramento.
Air quality values will be in the 126-140 range in the valley, which is considered unhealthy for sensitive groups. This means if you have preexisting breathing issues such as asthma, you are more prone to being affected by the increased ozone in the air. A vast majority of the public won't notice a difference.
Ozone — composed of 3 oxygen molecules — is beneficial when high up in the atmosphere because it helps protect Earth by absorbing some of the sun's ultraviolet light. Near-surface or low-level ozone is a very harmful pollutant.
Ozone can come from the upper atmosphere, but it can also form near the surface. In Friday's case, ozone is forming near the surface due to a combination of factors.
Little to no onshore wind will limit the dispersal of pollutants from industrial facilities, car exhaust, gas station pumps, and other emissions sources producing volatile organic compounds (VOCs) and nitrous oxides (NOx).
Intense sunlight and very hot temperatures cause chemical reactions between NOx and VOCs, creating near-surface ozone. This is what we're dealing with Friday. Air Quality Index values are expected to be above 126 (on a scale of 500), which puts us in the Unhealthy for Sensitive Groups category.
If we had less stagnant air or even a delta breeze, these pollutants would get mixed into the air and cause less of a problem.
Because the forecast doesn't change much over the next few days — very hot temperatures, abundant sunshine and stagnant air — near-surface ozone formation and pollution are expected to continue, keeping the AQI around 120. If you have trouble breathing on days with high ozone, make it a point to spend plenty of time indoors in air conditioned areas the next few days.
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