As they have for several years, both Salt Lake City and Provo-Orem turned up this week on the Environmental Protection Agency's list of cities in violation of clean air standards for carbon monoxide last year. Salt Lake City also was on the two-year list of ozone violators in 1985-87.

Yet before Utahns run gasping for an oxygen tent, it might help to understand what it means for a community to be in "violation" of federal air quality regulations.The standard for ozone is 0.12 parts per million, a maximum "one-hour" average "not to be exceeded more than once a year" in a two-year measurement. That is tight indeed.

For Salt Lake City, where ozone measurements hit 0.15 for an average 3.8 days each year, it means the city was meeting air quality standards for ozone nearly 99 percent of the time. But it was still in violation.

The standard for carbon monoxide is 9.0 parts per million for an eight-hour average, not to be exceeded more than once per year. Salt Lake City was up to 9.8 for two days in 1987 - in violation of the law. Even Provo-Orem, which has special industrial problems, averaged 13.3 for 20 days. That means that the area was meeting EPA standards for 345 days of the year.

Certainly, Utah and the nation need to keep pushing for cleaner air. In fact, the figures for both Salt Lake City and Provo-Orem showed a decline in the amount and length of air quality violations compared to the previous year.

However, there comes a time when the push for cleaner air becomes so costly that that what little more is gained isn't worth the cost. For example, if a community reaches 99 percent compliance by spending $50 million, it hardly makes sense to spend $50 million more to raise compliance to 99.5 percent. There is a law of diminishing returns.

A bill currently in Congress seeks to do just that. It would set even more stringent standards and raise the punishment for failure, so that even a place like Salt Lake City - out of compliance only two days, but still technically in violation - could face severe penalties.

Let's continue to seek to improve the air quality, but let's keep some sensible balance between cost and results in mind.