An air quality monitoring system comprising: a plurality of particulate matter, PM, sensors, the plurality of PM sensors positioned at a corresponding plurality of positions in a monitoring area; and an air quality processing device coupled to each of the plurality of PM sensors via a communications network, the air quality processing device configured to: receive a particulate level signal from at least two of the plurality of PM sensors; and determine particulate matter flow between the at least two PM sensors based on the corresponding particulate level signals.