The U.S. has networks of pollution monitoring sites that use air quality sensors. But the networks have shortcomings such as trouble detecting localized pollution. Technological improvements have led to smaller, more affordable air quality sensors and better satellite-based sensors. These can help close gaps in pollution monitoring and research. For example, through more dense and widespread monitoring, these sensors may help pinpoint air pollution sources and hot spots and improve understanding of community exposure. But these sensors vary in performance, can be hard to interpret, and may not monitor key pollutants such as some air toxics.