In this paper, I analyze the effects of changes in day-to-day air pollution levels on daily absences for New York City schools from 2006 to 2019. I combine EPA air quality data with absences for more than 1600 schools. To alleviate endogeneity concerns I use wind as an instrument for transport of air pollution. I estimate that an additional 1 μg/m3 of PM2.5 pollution increases absences across all schools by 0.044 percentage points (pp), and an extra part-per-billion (PPB) of Ozone increases it by 0.029pp. PM2.5 pollution has the largest effects on elementary and middle schools, and on schools with more impoverished students. Examining trends across 14 years of pollution and absences, my results suggest that the decrease in average daily PM2.5 pollution of 5 μg/m3 from 2006 to 2019 led to at least 0.2pp fewer absences across NYC schools every day. In contrast, Ozone concentrations did not decline over time, and I find that Ozone affects high school absences more than it affects elementary or middle school absences. This work shows the improvements over time in air quality in New York City but also highlights the disparate impacts of air pollution.