The assorting images, classification and measurement of PM2.5 in atmosphere

It is very important to understand size and shape of PM2.5 (particulate matter smaller than 2.5 mu m in aerodynamic diameter) for further studying composition and characteristics of particulate matter in atmosphere. The PM2.5 was collected using no-filter membrane method. The PM2.5 images were observed by Differential Interference Contrast (DIC) Microscopy with 12 million pixels digital static camera, and the images with fine resolution 300nm were obtained. Some images of particles assorted by physical method were presented. In order to count and measure the particles, these images were processed by a series of methods, such as color channel extracting, contrast enhancing, background flattening, Gauss filtering, and scaling with standard objective micrometer, on the Image-Pro Plus (IPP) software platform. The design considerations of parameters in analyzing process were also discussed in detail. The statistical data of particle size and number of PM2.5 were obtained. Results show that the total number of particles < 2.5 mu m in this measurement is made up of 97%, and 29.13% is the particles < 1 mu m.