These standards are updated periodically to keep up with the latest scientific research on the health effects of these pollutants. EPA recently tightened the standards on ozone, fine particulates and lead and is working with state partners and others to further reduce emissions. Foreign-flagged ships steam into California ports, creating a major source of air pollution. To control this, EPA and other federal agencies have been working to implement MARPOL Annex VIan international treaty to reduce maritime pollution.