a high volume virtual impactor for sampling atmospheric aerosols has a plurality of inlet nozzles and associated receiving tubes mounted in a common frame or housing having passageways which divide the airflow through the inlet nozzles into a major flow and a minor flow . the minor flow , or the smaller volume flow , passes through the respective receiving tube into a common chamber , while the major flow is caused to turn 180 ° between flow exit of the inlet nozzle and its associated receiving tubes and pass as through a small particle filter . the impactors are arranged in oppositely facing and aligned pairs . the exhaust ends of the receiving tubes in a part face each other , so that the flows from the receiving tubes will intermix in the center of a chamber , to prevent substantial particle impingement against the housing surfaces . the filters are located at the bottom of the housing to minimize losses . use of several parallel vertical impactor inlet nozzles and receiving tubes permits a high total flow rate while keeping the flow rate through any individual tube at a reasonable value and thus within good operating parameters . because the input nozzles and receiving tubes are mounted in a single frame , the mounting holes for them can be machined precisely to insure near perfect alignment and thus enhance operation .