Characterization of microplastics in the atmosphere of megacity Tehran (Iran)

In this study, the characteristics of ambient airborne microplastics were investigated in Tehran to obtain insights into their origins. For this purpose, sampling operations took place at locations with different backgrounds in summer and autumn by using TSP and PM high-volume samplers. As a result of microscopic analysis and Raman spectroscopy, the color, shape, number, size, and type of microplastic particles were investigated. Seven types of chemical structures were identified in the particles, among which polypropylene (18.7%) in summer and polystyrene (20%) in autumn had the dominant share. The average number of particles collected using the TSP and PM samplers were 1165 ± 147.64 and 1006.5 ± 147.64, respectively. The size of microplastic particles in different stations varied between 4 and 3094 μm. In the seasonal examination of the identified colors, black (38-43%), red (17-19%), gold (13-14%), brown (12% in both seasons), blue (7-10%), yellow (3-5%), and green (2-5%) had the largest proportions, respectively. The examined microplastics were in three forms: fiber, bead, and fragment, among which the predominant form was fiber, and the most infrequent particles were fragments. Statistical comparisons showed that the sampling location does not have a significant effect on the number and size of particles (p value > 0.05). The season was not identified as a determining parameter for particle size (p value > 0.05). On the other hand, seasonal changes can have a tremendous effect on the microplastic particle number (p value < 0.05). Lastly, to obtain more detailed information about the origin of these particles, continuous and long-term monitoring near known industries and suspected sources of plastic materials and source apportionment studies were suggested.