A monitoring device, comprising: a plurality of radiation sources (30, 32) that respectively emit a different type of radiation; at least one radiation detector (34, 54) situated to detect radiation emitted by the radiation sources and reflected off airborne particles (26, 28), the at least one radiation detector having a first sensitivity configured for detecting a concentration of the particles within a first range and a second sensitivity configured for detecting a concentration of the particles within a second, different range; and a processor that is configured to determine a ratio of the types of radiation in the detected radiation based on an indication from the radiation detector, a type of the particles reflecting the detected radiation based on the ratio, and the concentration of the particles reflecting the detected radiation based on the first or second sensitivity; characterised in that the monitoring device is configured to: selectively control use of the first sensitivity or the second sensitivity; detect the radiation reflected off the airborne particles (26, 28) at the first sensitivity; determine whether a detector (34, 54) is saturated at the first sensitivity by the detecting; when the detector is saturated at the first sensitivity, detect the radiation reflected off the airborne particles at the second sensitivity, wherein the second sensitivity is lower than the first sensitivity; determine whether the detector is saturated at the second sensitivity by the detecting; and provide an indication when the detector is saturated at the second sensitivity. a plurality of radiation sources (30, 32) that respectively emit a different type of radiation; at least one radiation detector (34, 54) situated to detect radiation emitted by the radiation sources and reflected off airborne particles (26, 28), the at least one radiation detector having a first sensitivity configured for detecting a concentration of the particles within a first range and a second sensitivity configured for detecting a concentration of the particles within a second, different range; and a processor that is configured to determine a ratio of the types of radiation in the detected radiation based on an indication from the radiation detector, a type of the particles reflecting the detected radiation based on the ratio, and the concentration of the particles reflecting the detected radiation based on the first or second sensitivity; a ratio of the types of radiation in the detected radiation based on an indication from the radiation detector, a type of the particles reflecting the detected radiation based on the ratio, and the concentration of the particles reflecting the detected radiation based on the first or second sensitivity; characterised in that the monitoring device is configured to: selectively control use of the first sensitivity or the second sensitivity; detect the radiation reflected off the airborne particles (26, 28) at the first sensitivity; determine whether a detector (34, 54) is saturated at the first sensitivity by the detecting; when the detector is saturated at the first sensitivity, detect the radiation reflected off the airborne particles at the second sensitivity, wherein the second sensitivity is lower than the first sensitivity; determine whether the detector is saturated at the second sensitivity by the detecting; and provide an indication when the detector is saturated at the second sensitivity. selectively control use of the first sensitivity or the second sensitivity; detect the radiation reflected off the airborne particles (26, 28) at the first sensitivity; determine whether a detector (34, 54) is saturated at the first sensitivity by the detecting; when the detector is saturated at the first sensitivity, detect the radiation reflected off the airborne particles at the second sensitivity, wherein the second sensitivity is lower than the first sensitivity; determine whether the detector is saturated at the second sensitivity by the detecting; and provide an indication when the detector is saturated at the second sensitivity.