Emissions from New England’s 14 oldest power plants have increased for the third consecutive year, according to a report by environmental groups. The old plants aren’t held to the same standards as new ones because of a loophole in the Clean Air Act. In other dirty power plant news, the six New England states and New York sent a petition to the EPA on Tuesday asking for stricter limits on emissions that cause acid rain. And more than a dozen environmental groups yesterday said they plan to sue American Electric Power Co., one of the largest U.S. utilities, for failing to install better pollution control technology in coal-burning plants when those plants were upgraded.