The Chicago Department of Public Health (CDPH) and the University of Illinois Chicago (UIC) School of Public Health publicly released data from Open Air Chicago, the largest community air monitoring network in the country and second largest in the world. Over six weeks in summer 2025, a total of 277 Clarity Node-S sensors that measure levels of fine particulate matter (PM2.5) and nitrogen dioxide (NO2) were installed using a scientific, grid-based approach across the City with input from community members participating on the Advisory Board. This network supplements the local air quality data currently available on AirNow.gov, which includes data from federal-grade monitoring systems, to provide air pollutant estimates at the hyperlocal level. The network name, Open Air Chicago, comes out of multiple discussions with the Advisory Board and underscores the openness and transparency of the process, project, and data. By sharing clear, accessible air quality data, the project helps Chicagoans understand the air they breathe and make informed choices to protect their health and communities.