Optical light microscopy in the determination of small fractions of suspended particles in the air of the urban environment

Abstract

Small fractions of particulate matter are a common air pollutant in the urban environment. To analyze the amount and size of solid particles, various modifications of optical microscopy and laser detection methods are used. The aim of the work is to evaluate the possibility of the usage of light microscopy to determine the quantitative and granulometric composition of particulate matter in the air of the urban environment. The article presents the results of gravimetric analysis of particulate matter, followed by examination by light microscopy of clarified filters. It is shown that using light microscopy makes it possible to estimate the number of particle size fractions of particulate matter larger than 0.3 µm in atmospheric air. It has been established that the number of particles in the atmospheric air in certain districts of Grodno varied by more than 15 times. The change in the mass concentrations of dust and the number of dispersed particles in the atmospheric air of individual points in the urban environment can be reversed, which indicates the difference in the sources of solid particles and their different chemical nature. The diameter of suspended particles in the atmospheric air of the urban environment is characterized by very high variability (80–157 %). The distribution of frequencies of occurrence of particles of different sizes in the air does not correspond to the normal law and right-sided asymmetry and positive kurtosis were observed in the variational histograms. A significant inverse connection was found between the particle size and their proportion in the samples. The most common fraction in the atmospheric air of Grodno was particles with a diameter of 0.5–1 µm (41.5–61.3 %). At the same time, a statistically significant association of points of the urban environment into clusters was determined primarily by the proportions of particles with a diameter of more than 5 microns.