Temporal Variations and Characteristics of Microplastics in Indoor and Outdoor Air

Abstract Introduction Microplastics (MPs) are emerging particulate air pollution in indoor air. However, studies on their characteristics, temporal variations, and influencing factors using active sampling methods in houses are limited. Study objectives In this study, an active sampling method was employed to collect indoor and outdoor airborne MP samples in different seasons and examine the differences between weekdays and weekends. Results The average MP concentrations were 1.80 ± 1.93 and 2.66 ± 1.76 particles m −3 in indoor and outdoor air, respectively. No significant differences were observed between indoor and outdoor MP concentrations, similar results were found in the cold season, warm season, and on weekdays. However, the concentrations of outdoor MP were significantly higher than the indoor levels on the weekends. Additionally, no significant differences were found between MP concentrations in warm versus cold seasons or between weekdays and weekends for either indoor or outdoor air. The predominant sizes and shapes of MPs were 3–50 μm and fragments in indoor air, respectively, accounting for 77% and 88%; corresponding values were 3–100 μm and fragments for outdoor air, accounting for 84% and 93%. The majority of polymer compositions were polyethylene terephthalate (PET) in indoor air and a combination of PET and polypropylene (PP) in outdoor air. High indoor MP concentrations may be attributed to increased ventilation rates during the warm season and the number of occupants. Conclusion In summary, MP concentrations in residential houses showed no significant temporal variations, with turbulent airflow and occupant activities were the major influencing factors. Graphical abstract