A particle detector configured to detect the presence of airborne particles entrained in an air sample, the particle detector including: a detection chamber for receiving a sample flow comprising an air sample for analysis; a radiation source configured to emit a beam of radiation having known polarisation characteristics, said beam propagating across at least part of the detection chamber and being arranged to traverse the sample flow at a region of interest; an arrangement of radiation receiving photodiodes (214, 216, 218, 246, 248, 250), each of the photodiodes configured to receive radiation that is scattered from the beam by interaction with particles entrained in the sample flow and to generate at least one output signal representing the received radiation, the arrangement of radiation receiving photodiodes including a plurality of photodiodes arranged with respect to the beam and region of interest such that the arrangement of radiation receiving photodiodes is configured to receive radiation at a plurality of scattering angles and in a plurality of polarisation angles with respect to a direction of propagation and known polarisation of the beam; a controller configured to analyse the at least one output signal from Z. the arrangement of radiation receiving photodiodes representing the received radiation; and an imaging system including an image capture sensor within the particle detector having a plurality of pixels and being configured to capture images of the region of interest by receiving radiation scattered out of the beam and whereby the controller is configured to analyse the images to determine the presence of particles entrained in the sample flow interacting with the beam in the region of interest based on scattered radiation contained in the captured images wherein the arrangement of radiation receiving photodiodes and the imaging system are arranged to receive radiation from a common region of interest; and wherein the controller correlates the output of the imaging system and the arrangement of radiation receiving photodiodes to determine the presence of airborne particles entrained in the sample flow. a detection chamber for receiving a sample flow comprising an air sample for analysis; a radiation source configured to emit a beam of radiation having known polarisation characteristics, said beam propagating across at least part of the detection chamber and being arranged to traverse the sample flow at a region of interest; an arrangement of radiation receiving photodiodes (214, 216, 218, 246, 248, 250), each of the photodiodes configured to receive radiation that is scattered from the beam by interaction with particles entrained in the sample flow and to generate at least one output signal representing the received radiation, the arrangement of radiation receiving photodiodes including a plurality of photodiodes arranged with respect to the beam and region of interest such that the arrangement of radiation receiving photodiodes is configured to receive radiation at a plurality of scattering angles and in a plurality of polarisation angles with respect to a direction of propagation and known polarisation of the beam; a controller configured to analyse the at least one output signal from Z. the arrangement of radiation receiving photodiodes representing the received radiation; and an imaging system including an image capture sensor within the particle detector having a plurality of pixels and being configured to capture images of the region of interest by receiving radiation scattered out of the beam and whereby the controller is configured to analyse the images to determine the presence of particles entrained in the sample flow interacting with the beam in the region of interest based on scattered radiation contained in the captured images wherein the arrangement of radiation receiving photodiodes and the imaging system are arranged to receive radiation from a common region of interest; and wherein the controller correlates the output of the imaging system and the arrangement of radiation receiving photodiodes to determine the presence of airborne particles entrained in the sample flow.