If you’re sitting in a Bexar County parking lot in the cab of your semi-truck with the engine running, don’t be surprised if a county official pays you a cordial visit.

County commissioners passed an order May 3 banning any vehicles of more than 14,000 pounds from idling more than five minutes, with several exceptions. The San Antonio City Council is expected to pass a similar ordinance in June. The city manager’s office also is preparing an “administrative directive” telling most city employees not to idle, sustainability director Doug Melnick said.

Local officials are hoping that the measures can reduce tailpipe emissions that help form ground-level ozone, a key component of smog. By October 2017, the San Antonio metro area will almost certainly be in violation of the Environmental Protection Agency’s ozone standard, which will likely trigger increased federal oversight.

The higher the ozone level, the more potential consequences, so the Alamo Area Council of Governments is leading an effort to keep ozone levels as low as possible.

Across Texas, 44 communities have already adopted anti-idling ordinances, including Houston, Dallas, Fort Worth and Austin. Dallas-Fort Worth and Houston have long had ozone levels above federal standards. Austin’s level is barely below the threshold.

No one believes that anti-idling policies alone will rein in San Antonio’s ozone levels back below the federal standard.

“It’s part of a puzzle,” Melnick said. “There’s no one measure we can point to that can solve the problem.”

Still, many see unneeded idling trucks as a clear, easy target to cut air pollution. According to the EPA, a heavy-duty diesel engine idling for an hour emits an average of 33 grams of nitrogen oxides, which form ozone when exposed to sunlight. That’s the weight of a pudgy adult mouse.

About 44 percent of the ozone-forming emissions from San Antonio roads come from heavy-duty vehicles, Melnick said at a May 10 City Council subcommittee meeting.

At the meeting, District 8 Councilman Ron Nirenberg compared anti-idling ordinances to laws that ban littering. Nirenberg also is chairman of an AACOG committee focused on air quality.

“We’re looking at this as sort of our opening salvo to our air quality strategies,” Nirenberg said, adding that these policies are expected to cut nitrogen oxide emissions by 500 tons per year.

Drivers who spew pollutants needlessly from their tailpipes can be as tough to catch as those who hurl plastic bottles out their windows, Nirenberg said.

“We don’t often observe people littering, but it’s unlawful,” Nirenberg said. Without enforcement, “the law’s only as good as an honor code.”

At a joint meeting last month between the AACOG committee and its Austin-area counterpart, Bexar County environmental engineer Andrew Winter discussed the difficulty of enforcing the order.

No one wants to tie up sheriff’s deputies or the courts with idling scofflaws, so the county is taking an approach of educate first, civil penalties later, if necessary, Winter said.

On May 17, Winter assembled a team of six code enforcers, environmental law enforcement and animal control officers to visit several machine shops and gas stations along Interstate 10 to educate drivers about the new county order. Their goal was simply to tell drivers about the ordinance and pass out fliers.

“Instead of writing these people a $200 ticket, we’re educating people,” Winter said. “We’re all in this together. We’re breathing the same air.”

Education is the plan now, but Winter’s team has more leverage at its disposal if necessary: first a formal notice of violation, then a Class C misdemeanor citation that carries a $200 fine.

In the field, they met drivers with trucks of many different model years and emissions levels. Many qualified as exempt from the order. The exemptions include any 2008 or later EPA-certified, clean-idling diesel or natural gas engines.

At a Texaco station along Interstate 10, Winter and animal control officer Javier Flores approached truck drivers Robert Delgado and Jesus Delgado. The latter shared a cab with his son Jesus Delgado Jr. They had stopped for fuel while hauling loads of pipe from El Paso in trucks too old to meet the clean-idling standard.

“It’s good,” Robert Delgado said of the order. “We need to clean the air.”

Next to the Delgados, Greg Sutler of Florence, Arizona, parked his 2009 International Harvester, a certified clean-idling truck. He seemed familiar with trucking regulations across the country, explaining the intricacies of California’s regulations on refrigerated trailers, known in the industry as “reefers.”

“So many new laws,” Sutler said.

In the same parking lot, a white Ford F-250’s engine chugged in front of an empty driver’s seat. That vehicle would be too small to violate the order.

There are still more exemptions. The order does not apply to military, National Guard, emergency, law enforcement or airport ground-support vehicles. Armored trucks can idle while the driver sits inside to guard its contents and while loading or unloading.

Vehicles idling to operate machinery or for maintenance are also exempt, as are those stuck in traffic, idling to defrost a windshield, or supplying heating and cooling during road maintenance. For buses or other public transportation, idling for passenger comfort and health is allowed for up to 30 minutes.

A driver can also idle his or her truck when snoozing in “the vehicle’s sleeper berth for a government-mandated rest period” if not within 2 miles of a facility offering electrical connections.

Winter’s team’s last stop that day was a Flying J, where a parking lot in the rear held dozens of trucks. Environmental law enforcement officer Stan Jordan counted 24 idlers, many driving for big corporations such as Tyson, True Value and Knight Transportation. Most had stickers proclaiming them as clean-idling, in need of a special fuel additive stored in a tank near the diesel pumps.

That was a new lesson for Flores, the animal control officer. Some drivers told him their companies install automatic shutoffs that kill the engine after four or five minutes.

“That’s one of the things I learned today,” he said. “It’s the older trucks we have to continue to worry about.”

Out of the dozens of drivers they spoke to that day, only two were idling when they were not supposed to, Winter said. One driver made his feelings about the order known, but nothing more, he said.

“I think he begrudgingly accepted that that’s the way it is,” Winter said. “And that’s all we can hope for.”

In a few months, similar tasks could fall to the city’s sustainability staff, downtown operations, parking enforcement, code inspectors and metro health inspectors, Melnick said.

Winter said he would repeat his educational efforts at truck stops and garages on Interstates 35 and 37. His team will return in six months, count the idlers again and see if the strategy is working.

bgibbons@express-news.net, Twitter: @bgibbs