We provide the first evidence that short-term exposure to air pollution affects the work performance of a group of highly skilled, quality-focused employees. We repeatedly observe the decision making of individual professional baseball umpires, quasi-randomly assigned to varying air quality across time and space. Unique characteristics of this setting combined with high-frequency data disentangle effects of multiple pollutants and identify previously underexplored acute effects. We find that a 1 ppm increase in 3-hour CO causes an 11.5% increase in the propensity of umpires to make incorrect calls and a 10 μg/m3 increase in 12-hour PM2.5 causes a 2.6% increase. We control carefully for a variety of potential confounders, and results are supported by robustness and falsification checks. Our estimates imply that a 3% reduction in productive output is associated with a change in CO concentrations equivalent to moving from the 25th to the 95th percentile of the CO distribution in many of the largest US cities.