It’s not just you. ‘Cold, dry, stagnant’ conditions causing poor air quality in Modesto area
The mornings are foggy, the nights are smoky and the air quality is poor. For folks living in Modesto, this week has been hard to breathe in.
Downtown Modesto reached a new 90-day high in particulate matter Dec. 5. Air quality is expected to remain poor at least until Sunday. At around 10:30 a.m. Dec. 5, the small particulate matter in the air reached unsafe levels for sensitive groups and for everyone doing strenuous outdoor activities.
The San Joaquin Valley Air Pollution Control District issued an Air Quality Advisory listing “stagnant conditions” as the main thing contributing to deteriorating air quality.
The process is called “radiative inversion” said Noah Hughes, a meteorology instructor at Modesto Junior College.
“The valley is like a bowl surrounded by mountains on all sides,” Hughes said. “So this cold air gets trapped in the valley until some wind comes along and scours it out or the sun is strong enough to heat the ground, to get the air to rise and mix with the rest of the atmosphere.”
This type of air quality issue is common in Modesto around this time of year.
“We have this wintertime pattern,” said Jaime Holt, spokesperson for the San Joaquin Valley Air Pollution Control District. “That high-pressure system brings a lot of stability to the area, and what it means is that we have a tight lid that’s basically trapping the pollution in the valley.”
The biggest pollutant showing up in Modesto’s air supply is something called PM2.5, basically small particulate matter that can come from smoke, dust, smog and even pesticides that mix in high-pressure environments. And this pollution gets condensed overnight.
“All of that pollution gets kind of squeezed tighter and becomes more dense,” Holt said. “And that’s what we see, especially overnight.”
When air quality gets bad, people can experience itchy, watery eyes or a sore throat with some coughing and sneezing mixed in.
“If you’re going to go out and exercise, you should check the air quality first,” Hughes said. “If it’s over 150 on the air quality index, consider not exercising outside. Exercise inside or consider changing it up.”
For people with health issues, Hughes recommends the same once it reaches 100.
Holt said to help keep good air quality indoors, it’s best to have what she calls a “clean room,” where you don’t cook anything and maybe have an air filter. To that end, Stanislaus County still has funds available for its Clean Air Room program, which offers free air filters for people in low-income areas.
Another contributor to the bad air is wood smoke. Because of this, a residential wood-smoke reduction program has been in effect since Nov. 1 and runs through February. Currently, no one in Stanislaus should be burning wood without being registered.
Dekari Anderson, a meteorologist with the National Weather Service, said low stratus clouds are in Modesto but the weekend should have some breeze.
“It looks like we will be stuck in this pattern at least until Sunday, but there is more wind in the forecast next week, so that will hopefully improve our air quality,” Hughes said.
This story was originally published December 5, 2024 at 5:30 PM.
