Direct measurements improve estimates of dairy greenhouse-gas emissions

California is the leading dairy state in the United States, producing 21 % of the nation's milk supply. The state's highest concentration of dairies is in the San Joaquin Valley, a region that violates federal limits for ozone and particulate matter in the air. Volatile organic compounds and greenhouse-gas emissions from dairies contribute to regional air-quality challenges and also play a role in climate change. We used an environmentally controlled chamber to monitor greenhouse-gas emissions from dairy cattle over a 24-hour period, and we measured the emissions from waste slurry using a simulated dairy waste lagoon. This research helps to quantify emissions from dairies in California and suggests possible approaches for their mitigation.