Pima County appears to be on the edge of meeting — or exceeding — the new federal standard setting limits for ozone, the basic ingredient in airborne smog.
The new nationwide limit on ground-level ozone, set Thursday by the Environmental Protection Agency, is 70 parts per billion, down from a previous standard of 75.
The stricter smog limit will force states to reduce emissions over the next decade.
Over the past three summer ozone seasons in Pima County, including the May-September 2015 period, the highest reading at any of eight ozone monitors was 69, a notch below the standard, says the Pima County Department of Environmental Quality. That highest reading was taken from a monitor at Saguaro National Park East. A 71 would be out of compliance.
When EPA determines whether Pima County actually meets the standard, it will look at the summers of 2014, 2015 and 2016, and each year thereafter. That means we don’t know yet if the county will meet the new standard, said Ursula Nelson, the county department’s director.
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“At 69 we are fine. We have to be below 71 to meet the standard,†she said. “We’re very much on the edge.â€
If the air quality values continue to be the same next year, the county can meet the standard without taking any additional cleanup measures, she said. But as a community, “we need to be aware of our status and do anything that we can to reduce air pollution,†she said.
The longer-term picture for Pima County looks good, although some forecasters have said population growth and climate change could induce more air pollution, Nelson said.
Primarily due to a continued cleanup in vehicle emissions from tighter standards and less polluting fuels, EPA predicts most regions of the U.S. will meet the new standard by 2025, Nelson said.
“It’s a wonderful thing that Pima County’s air is good. But it’s something we need to take care of. The most important thing is for us to drive less and choose alternative modes of transportation,†Nelson said. “We don’t want to look at this and say, ‘We’re good, we’re done.’â€
The EPA chose the weakest of three new standards it was studying. It considered going as low as 60 parts per billion. Its Science Advisory Panel had recommended 65.
Many environmental groups blasted the new standard as inadequate while business groups said it was too strict and would cost jobs. EPA’s view was that the economic benefits gained by a reduction in asthma and other respiratory problems from the new standard would outweigh economic costs.