State officials have notified the Environmental Protection Agency that Utah is likely to miss yet another air-quality deadline, leading some clean-air advocates to criticize regulators for a lack of action.

Utah’s latest plan for reducing spikes of small-particulate pollution over the Wasatch Front was due to the EPA in December. But at this point, state officials say it’s unlikely they can meet that deadline and still provide adequate opportunity for public comment.

Because it has missed prior air-quality deadlines, the state is required to draft a new plan for dealing with particulate pollution, known as PM 2.5 which builds up during temperature inversions in the winter. Utah was classified as a “serious” nonattainment area earlier this year because the state did not meet a 2015 deadline for reaching federal pollution standards.

But the state Division of Air Quality’s efforts to draft the new plan is now behind schedule, said division director Bryce Bird.

The draft was supposed to be sent to the states’ Air Quality Board for review in September, but it won’t be ready for that meeting, Bird said. Missing that milestone will delay the rest of the process, lessening the state’s chances of meeting the final Dec. 31 deadline.

Bird said his staff is still working on technical details and computer modeling associated with the plan. He also attributed the delay to the EPA’s failure to declare the state’s “serious” air-quality status in a timely manner, although state regulators began work on the new plan well before that, when it became apparent in late 2015 the EPA would probably change that status.

Once the draft plan for tackling particulates is complete, it still needs approval from the Air Quality Board and public review.

News of the looming missed deadline is fraying the patience of some Utah air-quality advocates. Ashley Soltysiak, policy director for clean-air advocacy group HEAL Utah, expressed frustration on Friday over what she called “the delay and lack of rigor going into the process so far.”

HEAL, alongside other advocacy groups, holds monthly work sessions with state officials on the plan’s development. But Soltysiak said the state hasn’t taken advocates’ ideas seriously and has instead chosen mostly to revise existing air-quality rules rather than adopting new, more progressive initiatives.

As a result, Soltysiak said she worried that the state’s plan “may not be robust enough to get to where our air quality complies with the [EPA] standard.”

For example, HEAL is urging the state to impose tougher vehicle emissions standards above and beyond what the federal government requires. But Bird said Utah doesn’t have the authority to create such rules on its own — though it could adopt the more stringent emissions standards used in California, which he said were nearly the same as EPA rules and wouldn’t have a large impact on Utah’s air quality.

“What this really shows is that there aren’t a lot of new and innovative options to improve air quality here,” Bird said. “We are having a difficult time finding new big, bold strategies that really move the needle.”

So far, new rules with the largest potential to improve Utah’s air quality, Bird said, including reducing emissions of chemicals called volatile organic compounds from paints, cleaners and other such products. New technologies that will reduce emissions from industry and from cars will also help, he said, as will adoption in Utah of cleaner Tier 3 fuels for vehicles.

Soltysiak also fretted about the lack of public participation so far as the state drafts its pollution plan. In the past, she said, state officials have held county-by-county meetings to collect input on air-quality regulations.

But Bird said the state hasn’t had as much time to draft this plan as it had with previous plans, which has cut back on the amount of time state regulators have to meet with residents face-to-face. Instead, he said, they have invited the public to engage online and on Facebook