A method of characterising particles in a sample, comprising: obtaining a scattering measurement (320, 512, 601) comprising a time series of measurements of scattered light from a detector, the scattered light produced by the interaction of an illuminating light beam with the sample; producing a corrected scattering measurement, comprising compensating for scattering contributions from contaminants that can be distinguished from the particles by their larger size by reducing a scattering intensity in at least some time periods of the scattering measurement (320, 512, 601); determining a particle characteristic from the corrected scattering measurement; wherein the scattering measurement comprises a sequence of photon arrival times, and characterised in that reducing the scattering intensity comprises deleting photon arrival times from the sequence by selecting a temporal width for binning and binning the sequence of photon arrival times, each bin corresponding with a time period having the temporal width so that a count of photon arrival times in each bin indicates the scattering intensity over the corresponding time period, and correcting selected bins by deleting a number of photon arrival times from each selected bin to produce a corrected scattering measurement that is a binned time history of scattering intensity with a temporal resolution defined by the temporal width; and reducing the scattering intensity comprises determining a model of scattering contributions from contaminants, the model comprising an estimate of the number of photon arrival times in each bin due to scattering from a contaminant, and correcting the selected bins comprises deleting a number of photon arrival times based on the estimate for each selected bin. obtaining a scattering measurement (320, 512, 601) comprising a time series of measurements of scattered light from a detector, the scattered light produced by the interaction of an illuminating light beam with the sample; producing a corrected scattering measurement, comprising compensating for scattering contributions from contaminants that can be distinguished from the particles by their larger size by reducing a scattering intensity in at least some time periods of the scattering measurement (320, 512, 601); determining a particle characteristic from the corrected scattering measurement; wherein the scattering measurement comprises a sequence of photon arrival times, and characterised in that reducing the scattering intensity comprises deleting photon arrival times from the sequence by selecting a temporal width for binning and binning the sequence of photon arrival times, each bin corresponding with a time period having the temporal width so that a count of photon arrival times in each bin indicates the scattering intensity over the corresponding time period, and correcting selected bins by deleting a number of photon arrival times from each selected bin to produce a corrected scattering measurement that is a binned time history of scattering intensity with a temporal resolution defined by the temporal width; and reducing the scattering intensity comprises determining a model of scattering contributions from contaminants, the model comprising an estimate of the number of photon arrival times in each bin due to scattering from a contaminant, and correcting the selected bins comprises deleting a number of photon arrival times based on the estimate for each selected bin.