The Maine environment loses a strong voice and devoted advocate this week with the departure of Ned Sullivan, commissioner of the Department of Environmental Protection.

Mr. Sullivan is returning to New York, his home state, for family reasons, just four years after he left a position there as deputy commissioner of the state’s Department of Environmental Conservation. His tenure as Maine’s chief environmental officer was as lively and, occasionally, as contentious, as any time in the department’s recent history, but with a distinct difference over previous years.

Instead of allowing his department to become mired in the procedural swamp of stalled permits, protest appeals and a general lack of direction, as occurred in the 1980s and early ’90s, Mr. Sullivan stirred up the various environmental constituencies exactly as he should have, by proposing substantive advances in Maine’s environmental laws and policies. More so, Mr. Sullivan’s broad understanding of federal trends made Maine once again a national influence on environmental issues.

Nowhere was this more evident than in his work for cleaner air. Maine had known for years that much of the air pollution here arrived from the south and west of the state, but could do little about it and faced penalties from the federal government for pollution over which it had no control. By keeping Maine in a coalition of Northeastern states, whose influence was greater than any single state’s, and making Maine’s case to Congress, the EPA and anyone else who would listen, Mr. Sullivan got the feds to approve rules that cleaned up the source of the problem without dunning Maine. It was a win for the state and, more to the point, for cleaner air.

The debate was just as intense inside the state on issues such as dioxin, mercury and the gasoline additive MTBE. The DEP made progress in each of these areas during the last four years, besides tackling dozens of problems that did not receive a lot of public attention.

This isn’t to suggest the job of improving Maine’s environment has been completed — the number of bills in the Legislature this session affecting air, woods and water attest to that. But in four years of hard work, Mr. Sullivan leaves Maine this legacy: The state now has a DEP that has a clear sense of where it is going; though underfunded, has developed the support needed to achieve its goals; and, most importantly, treats residents of this state as partners instead of adversaries.

That is a legacy to be proud of, built by a job well done.