Abstract: A particle sensor for measuring size and concentration properties of particles in a gas includes a bipolar diffusion charger configured to charge particles within a received gas sample by the collision of the received particles with and transfer of charge from both positive and negative ions concurrently. At least one electrometer detects the charge of received particles thereby charged. The net, positive, negative or total charge on the bipolarly charged particles has a low sensitivity to variations in the absolute rate of charge generation in the bipolar diffusion charger. A sensor for a ratio of ion charge mobilities in a bipolar diffusion charger employs an ion trap between the bipolar diffusion charger and at least one electrometer.

Abstract: Particle measurement apparatus comprises an inlet for receiving a gas sample for analysis, a photoionisation chamber, at least one light source arranged to illuminate an interior of the photoionisation chamber, first and second electrodes coupled to a power source and configured to provide a DC potential difference across at least a portion of the photoionisation chamber, and an outlet, together defining a gas flow path from the inlet, through the photoionisation chamber, and towards the outlet.

Abstract: Particle measurement apparatus comprises an inlet for receiving a gas sample for analysis, a photoionisation chamber, at least one light source arranged to illuminate an interior of the photoionisation chamber, first and second electrodes coupled to a power source and configured to provide a DC potential difference across at least a portion of the photoionisation chamber, and an outlet, together defining a gas flow path from the inlet, through the photoionisation chamber, and towards the outlet.