Maritime shipping emits as much fine particulate matter as half of global road traffic. We are the first to measure the consequences of US maritime emissions standards on air quality, human health, racial exposure disparities, and behavior. The introduction of US maritime emissions control areas significantly decreased fine particulate matter, low birth weight, and infant mortality. Yet, only about half of the forecasted fine particulate matter abatement was achieved by the policy. We show evidence consistent with behavioral responses among ship operators, other polluters, and individuals that muted the policy’s impact, but were not incorporated in ex-ante models.