SAN DIEGO — The San Diego County Air Pollution Control District will be expanding its role in addressing the foul odors affecting communities near where sewage spills over the U.S.-Mexico border, following conflicting reports earlier this week about whether the stinky air people breathe is dangerous.

On Thursday, the district’s governing board unanimously agreed to have the agency develop an alert system that would issue warnings whenever certain levels of toxic gases, such as hydrogen sulfide, are detected in the Tijuana River Valley. It would be a more official system with guidelines than the initial advisory the agency issued on Sunday, which recommended that people limit outdoor physical activity if they noticed strong odors.

Nora Vargas, chair of the county Board of Supervisors who also serves on the air agency, suggested the idea. The tool, she said, could model smog alerts, which advise limiting outdoor activity during specific hours when ozone levels are highest. Or it could model the beach water quality alerts seen across Southern California, including in San Diego County, where yellow and red signs warn of contaminated water and exposure to illnesses. The system could be offered via a dashboard or mobile app and emergency alerts issued by the county’s Office of Emergency Services.

With such a system in place, “the school boards, the businesses in our communities know when the red flag comes up … they understand what they need to do,” Vargas said.

The air district will also deploy air purifiers to impacted households in South County using at least $100,000 in grant funding from the U.S. Environmental Protection Agency. Plans also include searching for additional money for purifiers or other personal protective equipment. Last month, the county gave away about 400 purifiers.

Additionally, the agency announced that it enlisted the help of the South Coast Air Quality Management District to “expand its monitoring efforts.” A mobile air monitoring van was deployed in the river valley Thursday, officials said.

The San Diego County air district has had six air monitoring sensors running at a San Ysidro fire station over the last 11 months, though plans are to have them spread out and fully activated in South County. Paperwork issues have delayed those efforts, though. Since collecting data in mid-October, the highest levels of hydrogen sulfide were detected over the weekend when the county experienced a heat wave, district staff said Thursday. Preliminary data showed levels peaked at around 110 parts per billion.

California’s standard for hydrogen sulfide levels outdoors is 30 parts per billion averaged over one hour, which can cause headaches and nausea.

Thursday’s board efforts follow back-to-back news conferences held by the county and university researchers regarding reports of toxic gases.

On Monday, research teams studying polluted air and water announced that air monitors detected hydrogen cyanide levels at 50 parts per million (the federal threshold for an exposure considered dangerous to life) near the border and within proximity to schools.

Then on Tuesday, the county said its monitoring presented no elevated levels of hydrogen cyanide. A county report released later that day stated levels detected ranged from zero to 25 parts per million, which “is below any immediate life and safety threshold.”

Many criticized Vargas, who held the county news conference with public health experts, for saying the air “smells horrible, but it’s safe.”

University researchers have yet to disclose their data fully. Kim Prather, a UC San Diego atmospheric chemist, took to social media to say their “validated preliminary results” will be shared “when we publish it. This is how the science process works.”

Over at the Tijuana River, polluted flows have stopped, the U.S. International Boundary and Water Commission announced Wednesday. A key sewage pump in Mexico, known as PBCILA, that’s supposed to divert wastewater from the river and clean it at treatment plants is back online.

That’s good news because fixing the pump was the most immediate way to reduce flows in the seasonal river, which has been flowing nonstop for at least one year even though it should be dry during the dry season.

Through the Tijuana River Valley, the river was running with an average of 40 million gallons of polluted water per day. But after repairs, flows have reduced significantly. So have levels of hydrogen sulfide, one of the main chemical components of sewer gas, according to university teams studying the impacts of the cross-border pollution crisis.

“We’ve been consistently seeing hydrogen sulfide concentrations in the 1,000s (parts per billion) for anywhere from 1 to 4,000 parts per billion,” Ben Rico, a graduate student working with UC San Diego’s Prather, said Thursday morning at a news conference in the river valley. “And last night, now that the river flow has dropped considerably, we’ve seen the peak (hydrogen sulfide) concentration was below 100 parts per billion.”

It’s going to take a very long time for the river valley to clean itself up from sewage and toxic chemicals pollution, said Chris Helmer, director of Environmental and Natural Resources for the city of Imperial Beach. But, he added, fewer flows could mean less pollution in the atmosphere, meaning fewer odors.

“What all of this is showing us right now is that with the right political pressure in Mexico, they’ll start turning on their pipes,” said Helmer. “There’s a way to stop the flow from coming across the border. That’s the lesson here. What’s the difference between today and yesterday? Well, there’s millions of gallons of less flow coming across the river.”

Parents dropping off their children at Nestor and Berry elementary schools noticed a difference overnight, they said.

“You know, actually, last night was better,” said Josie Hoffos, a mother of three. “I used to run in the estuary all the time, but I stopped because of the odors.”

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