The combination of prolonged hot spells with poor air quality greatly compounds the negative effects of each and can pose a major risk to human health, according to new research from the University of California, Irvine.“The weather factors that drive heat waves also contribute to intensified surface ozone and air pollution episodes,” said UCI professor of Earth system science Michael J. Prather, co-author of the study, published this week in Proceedings of the National Academy of Sciences. “These extreme, multiday events tend to cluster and overlap, worsening the health impacts beyond the sum of their individual effects.”