It’s Alabama’s uncharacteristic September heat, not lack of rain, that’s caused recent air quality ozone alerts in numbers unheard of this late in the summer. That’s the word from the Jefferson County Department of Health expert Corey Masuca.

Masuca, who is the county’s air quality control engineer, is one of six experts who the U.S. Environmental Protection Agency is required to depend on for recommendations on air quality standards for ozone and particulate matter, among other air pollutants, to protect public health and safety.

Ozone alerts have occurred nine days since May, according to the health department. Six of those have occurred in September. Check here for daily information on air quality in Jefferson County.

Ninety-degree Fahrenheit temperatures are expected to persist for the next several days in a “heat dome” effect that occurs only once every 10 to 30 years, according to an analysis by the joint national weather services of the U.S., Canada and Mexico.

And the National Oceanic Atmospheric Agency predicts a 40 percent probability of the next three months producing above average temperatures in Alabama.

Ground level ozone, the main component of smog, is a human lung irritant and results primarily from the exhaust from gas and diesel combustion engines, Masuca said. It also can damage other animals and plants. Ultrafine particulate matter, or soot, can enter the bloodstream when inhaled and is largely caused by smokestack industry. People with poor lung health, including asthma and chronic obstructive pulmonary disease, are especially affected by abnormally high levels of these pollutants and advised to avoid outdoor activity during air quality alert days.

Ozone is formed secondarily in the air, rather than directly from a source. It occurs when pollutants from cars, power plants, refineries and other sources chemically react in sunlight, a reaction made worse by high temperatures.

Masuca said the air quality alerts this summer are due primarily to transportation sources exacerbated by the weather’s stagnant air, with smokestack industry playing only a minor role. Effects are worse near congested roadways, particularly interstate highways, he said. Natural, nonhuman, contributions to ozone concentrations are minor in comparison but are commonly overlooked, he added. Wildfires, vegetation and lightning are among the causes of this background level of ozone.

Drought conditions in the state do not play a direct part in the formation of ozone.

“Rain would scrub the air of particulate matter, but the weather pattern of high temperatures and high humidity, coupled with lack of air movement, are the main drivers of the ozone alerts,” Masuca said.

Air quality in Birmingham has improved greatly over the years, Masuca noted, due primarily to better regulation of emissions from industry and transportation. This has occurred “even though we’ve had increased population, increased industrial output and increased vehicular traffic,” he said.