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Six years ago, Andy Darrell and Isabelle Silverman were glancing aimlessly out the window of their office near Gramercy Park and noticed a black plume of smoke rising from the heating system of a building across the street. “That’s pretty disgusting,” Silverman said. “Somebody should do something about it.” Then they looked at one another. “Well,” Darrell said, “we do work for the Environmental Defense Fund.” He was also part of an advisory panel for the mayor’s PlaNYC, which seized on the disgusting numbers: About 10,000 buildings burned heating oil so dirty that it produced more soot than all the city’s cars and trucks combined. The administration crafted new regulations mandating the noxious heating fuels be phased out … by 2030. Fortunately, EDF and City Hall didn’t leave things there. In a rare, unsexy instance of politicians, nonprofits, and private finance coming together to do something hard but important, a $100 million financing program was created to help building owners pay the capital expense of replacing outdated parts and shifting to cleaner, cheaper fuels. By this year, about 3,000 buildings have been converted, cutting sulfur-dioxide levels by a whopping 69 percent. The initiative is both a public-health and a climate-change boon, and it cuts across those two cities we’ve been hearing about. Now the challenge is to keep the momentum going. “We’ve begun to crack the code on how New York buildings can be turned into environmental winners,” Darrell says. “Is there a way to carry this private-­public coalition forward with geothermal or solar power?” Sounds like the kind of idea a real progressive should love.