Patent ID: 8607616

Claim:
A sensor ( 100 ) for sensing airborne particles larger than 10 nm, comprising a passage ( 110 , 112 , 114 ) with open ends, the passage having disposed in it: a discharge electrode ( 120 ) for generating airborne unipolar ions in the passage; an air-pervious counter electrode ( 124 , 324 ) adapted to attract said airborne ions; an air-pervious screening electrode ( 128 ; 372 , 374 ) located downstream of the discharge electrode; and a particle sensing section ( 114 ) for sensing electrically charged airborne particles in the passage, the particle sensing section being located downstream of the screening electrode, wherein: the counter electrode is located downstream of the discharge electrode and upstream of the screening electrode in the passage, thereby being adapted to cause a downstream net flow of airborne ions for thereby generating a downstream airflow; and the screening electrode is adapted to subject airborne ions to an electrostatic force in a second direction, distinct from the downstream direction, for separating airborne ions from the airflow.