TWENTY-FOUR nations - mostly European - have signed a United Nations protocol to freeze nitrogen oxide emissions at current levels by 1995. Nitrogen oxides are released as fossil fuels, such as coal or gasoline, burn. Like sulfur dioxide, another byproduct of burning fossil fuels, nitrogen oxides mix with moisture in the atmosphere to form acid rain and fog. Nitrogen oxides also contribute directly to smog and indirectly to global warming.
But for the United States and Britain, the protocol could have taken the more meaningful route of reductions. For its part, the US hauled out the dogeared reasons: We don't know enough yet; and we've done a lot already.
Twelve of the signatories took the higher road and pledged a 30 percent cut from current levels over the next 10 years. Still, the protocol, signed this week in Sophia, Bulgaria, is a step forward.
By some estimates more than half the trees in West Germany, Denmark, Britain, Switzerland, the Netherlands, and Czechoslovakia have been damaged by air pollution. In addition, airborne pollution is ravaging many of Europe's most historic buildings and monuments. Deep concern also exists over the adverse effects on people that public-health officials associate with air pollution. Little wonder that European governments are willing to put a lid on nitrogen oxide emissions.
Ideally, the protocol should reduce emissions, but efforts to adopt cuts ran afoul of the United States and Britain. The US noted that its Clean Air Act has already reduced nitrogen oxide emissions. It also contended that acid-rain research was still too incomplete to warrant deeper cuts. The US offered similar reasons for refusing to support a 1985 protocol governing sulfur dioxide.
Unfortunately, both points are weak: The Clean Air Act that the US so proudly touts today was adopted on much shakier scientific ground than exists for acid rain; yet its benefits are little disputed. Moreover, pushing for weaker future goals as ``credit'' for past progress is a hallmark of complacency, not leadership.
That complacency is marginally redeemed by a US willingness to work on follow-up protocols - presumably stricter - if evidence backs the need. US Environmental Protection Agency administrator Lee Thomas followed a similar path with last year's UN protocols to protect the stratospheric ozone layer, which shields Earth from excess ultraviolet radiation. The US ratified the agreement, which calls for a 50 percent cut in global production of several ozone-damaging chemicals by 1998. Last month Mr. Thomas cited new data and called for a phase-out of the chemicals.
Ironically, a nitrogen oxide freeze may force the US to make reductions anyway: Nitrogen oxide emissions in the US are expected to rise about 10 percent over the next 10 years.
Thought now needs to be given to implementation. Amendments to the Clean Air Act, which failed to clear Congress this year, would have required a 25 percent cut in nitrogen oxide emissions over 10 to 12 years. Senate ratification of the latest protocols could provide an extra incentive to reconsider the Clean Air Act amendments when Congress reconvenes.