Regional and climatic variations in atmospheric microplastic deposition: A study throughout Iran

The atmosphere is a critical reservoir for and transporter of microplastics (MPs) but little is known about the nature and drivers of their regional and climatic variability. In this study, dry deposition of MPs is quantified simultaneously over a seven-day period in nine Iranian cities encompassing different populations and climates and relationships with meteorological conditions and gaseous and particulate air quality parameters investigated. Overall, mean deposition ranged from 5.2 + 1.9 to 112.9 + 27 MP m -2 h -1 and was dominated by fibres of various sizes and constructed of different polymers (mainly polyethylene, polyethylene terephthalate, polypropylene, polystyrene and nylon), and there were clear and significant differences in mean values between the different cities that were not a simple function of climate or population. On a local scale, both positive and negative relationships between MP deposition and various meteorological and air quality parameters were observed among the cities. However, the pooled depositional data for MPs and various shapes and sizes thereof exhibited significant inverse relationships with wind speed and specific measures of airborne particulate matter (e.g., dust, PM 2.5 , PM 10 ). The results suggest that there is a broadly consistent, fibre-dominated regional population of MPs whose deposition (and presumably resuspension) is influenced by variations in wind speed, but additional location-specific factors and sources contribute to temporal variations within the different cities. Despite relationships between deposition and certain gaseous and particulate air quality parameters identified at specific locations, there is no general parameter that can be used as a regional proxy for MP deposition. • Dry deposition of microplastics (MPs) over 7 d determined in nine Iranian cities • Measured and modelled meteorological and air quality parameters also considered • Different MP deposition by city but overall population of MPs by shape-size similar • Regional inverse relationships between MP deposition and wind speed observed • Additional location-specific environmental factors are important at the city scale