Air quality monitoring using mobile low-cost sensors mounted on trash-trucks: Methods development and lessons learned

•From measurements made by mobile low-cost air quality monitors, we develop three techniques to:•Identify and characterize PM2.5 hotspots in cities.•Derive qualitative insights about the relative importance of local versus regional sources of PM2.5.•Estimate PM2.5 source signatures in different parts of cities.•We test these methods using two low-cost optical particle countersdeployed on trash-trucks in the city of Cambridge, MA.•We highlight the lessons we learned during this monitoring experiment.