A method for automated analysis of a membrane filter obtained from an air quality monitoring apparatus used for sampling airborne respirable fibres, the method comprising capturing at least one macroscale image of at least a sample portion of a membrane filter supported and fixed on an optically transparent support, wherein the macroscale image is an unmagnified image or low magnification image, wherein low magnification is less than 10 times; analysing the at least one macroscale image using a computer vision method to determine a countable area of the membrane filter and one or more excluded regions within the countable area of the membrane filter, the excluded regions comprising one or more of membrane filter grid lines, air bubbles and large particulate matter, wherein the countable area is a region of the membrane filter within which counting is to be performed; inserting the optically transparent support supporting the sample portion of the membrane 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 magnified phase contrast image at each of N sample locations located across the countable area of the membrane filter using the image sensor of the digital phase contrast microscope, where N is at least 20, and the N sample locations are selected such that a field of view at each sample location does not contain an excluded region; analysing the at least one magnified phase contrast image at each of the N sample locations using a computer vision method to identify and count the number of countable respirable fibres within a counting region of the field of view at each sample location, wherein the counting region of the field of view is defined by a counting graticule, or is a circle or a square with predefined dimensions or area based on the total magnification of the image, or is the entire field of view; and counting and reporting the total number of countable respirable fibres counted in the countable area of the membrane filter. capturing at least one macroscale image of at least a sample portion of a membrane filter supported and fixed on an optically transparent support, wherein the macroscale image is an unmagnified image or low magnification image, wherein low magnification is less than 10 times; analysing the at least one macroscale image using a computer vision method to determine a countable area of the membrane filter and one or more excluded regions within the countable area of the membrane filter, the excluded regions comprising one or more of membrane filter grid lines, air bubbles and large particulate matter, wherein the countable area is a region of the membrane filter within which counting is to be performed; inserting the optically transparent support supporting the sample portion of the membrane 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 magnified phase contrast image at each of N sample locations located across the countable area of the membrane filter using the image sensor of the digital phase contrast microscope, where N is at least 20, and the N sample locations are selected such that a field of view at each sample location does not contain an excluded region; analysing the at least one magnified phase contrast image at each of the N sample locations using a computer vision method to identify and count the number of countable respirable fibres within a counting region of the field of view at each sample location, wherein the counting region of the field of view is defined by a counting graticule, or is a circle or a square with predefined dimensions or area based on the total magnification of the image, or is the entire field of view; and counting and reporting the total number of countable respirable fibres counted in the countable area of the membrane filter.