A method for automated analysis of a filter obtained from an air quality monitoring apparatus used for sampling airborne respirable particles, the method comprising: loading an optically transparent support supporting a sample portion of a filter into a robotic XY stage of a digital phase contrast microscope further comprising an image sensor configured to capture an image of the image plane of the digital phase contrast microscope; capturing at least one image at each of a plurality of sample locations distributed over the sample portion of the filter, wherein the at least one image at each of the sample location comprises at least one magnified phase contrast image, and the robotic XY stage is configured to move the optically transparent support to position the sample location in the field of view of the microscope; performing a quality assessment by analysing one or more images captured at one or more of the plurality of sample locations using a computer vision method to estimate one or more quality criteria and rejecting or terminating further analysis at at least the sample location or the entire filter if the estimated one or more quality criteria fails the quality assessment based upon one or more predefined quality thresholds, wherein estimating the one or more quality criteria comprise estimating one or more of a dust loading, a particle loading, a particle distribution, a pixel colour distribution, a brightness range, or an image property or feature that indicates poor quality or proximity to a boundary, gridline or air bubble; analysing a plurality of the at least one image at each of a plurality of sample locations using a computer vision method to identify and count the number of countable respirable particles wherein the computer vision method is configured to filter out one or more halos and identify the countable respirable particles as those which have a geometry matching a target respirable particle; and reporting either the total number of countable respirable particles counted on the filter, or an estimate of the density of respirable particles on the filter. loading an optically transparent support supporting a sample portion of a filter into a robotic XY stage of a digital phase contrast microscope further comprising an image sensor configured to capture an image of the image plane of the digital phase contrast microscope; capturing at least one image at each of a plurality of sample locations distributed over the sample portion of the filter, wherein the at least one image at each of the sample location comprises at least one magnified phase contrast image, and the robotic XY stage is configured to move the optically transparent support to position the sample location in the field of view of the microscope; performing a quality assessment by analysing one or more images captured at one or more of the plurality of sample locations using a computer vision method to estimate one or more quality criteria and rejecting or terminating further analysis at at least the sample location or the entire filter if the estimated one or more quality criteria fails the quality assessment based upon one or more predefined quality thresholds, wherein estimating the one or more quality criteria comprise estimating one or more of a dust loading, a particle loading, a particle distribution, a pixel colour distribution, a brightness range, or an image property or feature that indicates poor quality or proximity to a boundary, gridline or air bubble; analysing a plurality of the at least one image at each of a plurality of sample locations using a computer vision method to identify and count the number of countable respirable particles wherein the computer vision method is configured to filter out one or more halos and identify the countable respirable particles as those which have a geometry matching a target respirable particle; and reporting either the total number of countable respirable particles counted on the filter, or an estimate of the density of respirable particles on the filter.