BOSTON— School districts across New England are now eligible to apply for a portion of $500 million toward the purchase of zero-emissions school buses, which benefit the environment and children’s health, officials said Friday. “These funds will make a real and lasting difference for everyone, especially kids who live in disadvantaged communities who are often the most vulnerable to the impacts of poor air quality and the effects of our changing climate,” Janet McCabe, deputy administrator of the federal Environmental Protection Agency said at a Boston news conference.