3.1.3. Dust

The concentration of MPs in ambient dust is very high, both in deposited dust and in suspended dust. In terms of deposited MP particles, the distribution of MPs of different shapes and sizes is very uneven under the influence of external forces (natural or human activities), and they are easily suspended in the atmospheric environment due to external forces. However, the form of MPs in floating dust is mainly fine fibers. Compared with other types of plastics, the lower-density characteristics of MPs facilitate their suspension in air [40]. Liu et al. studied and analyzed indoor and outdoor dust samples from 39 cities in China and found that PET majorly contributes to the content of MPs in indoor dust. This may be because indoor MPs are mainly derived from synthetic fabrics and PET is the main component of polyester in commonly used synthetic fabrics, which are easy to use, wash, and dry. Secondly, polycarbonate (PC), which is widely used in electronic equipment, hardware, and food packaging, can also easily fall off and enter the atmosphere [62,63].

## 3.1.4. Other Small Sources

Atmospheric MPs are also likely to come from the degradation of large plastics, such as building materials and synthetic furniture; landfills; synthetic particles from gardening; and industrial and other emissions-related activities. However, compared with the major sources of MPs such as synthetic textiles, transportation, and dust, the actual contribution of these sources to atmospheric MPs may be very small and remains in the stage of idea and speculation, without the availability of data [32,33,38].

### 3.1.5. Gaps in and Prospective Research on the Sources of Atmospheric MPs

From the above series of articles, it is found that the current articles on the sources of atmospheric MPs are mostly focused on synthetic textiles, transportation, dust deposition, and resuscitation, while other sources are often ignored, and the contribution of these sources to atmospheric MPs cannot be quantified. Detailed data on their pollution concentrations, types, and occurrence are scarce. In the analysis of the sources of atmospheric MPs in many pieces of literature, the proportion of unknown sources in the experimental results is relatively high, indicating that there is still a considerable part of atmospheric MP sources that is unclear. In addition, many research methods to identify the origin remain in the characterization and chemical composition analysis. To this end, we propose the following for future research:


### *3.2. Transportation and Fate of Atmospheric MPs*
