1. Figure 2: The caption describes a schematic of “atmospheric aging processes of MNPPs with different size ranges,” but the figure itself is not provided in the manuscript. How can readers evaluate size-dependent aging mechanisms without the visual summary you reference repeatedly in Section 4?
2. You state that terminal settling velocity vTS∝dp3. Stokes’ law gives vTS∝dp2 for spherical particles in the relevant Reynolds number range. The dp3 dependence would only apply at much higher Re (turbulent regime), which is not typical for MNPPs <100 μm. This mathematical error propagates to your lifetime estimates.
3. You cite Busse et al. (2024) as showing MPPs are “non-negligible” INPs, but also state water uptake is “generally ineffective” (Section 2.2). Immersion freezing requires particle immersion in droplets, how can MNPPs act as immersion INPs if they repel water? Please reconcile.
4. Missing additive vs. polymer toxicity distinction: Section 5.2 discusses health impacts but cites studies on PVC workers and flock workers. These occupational diseases are attributed to plasticizers, residual monomers, or processing aids, not the polymer itself. Your call for distinguishing polymer vs. additive effects (Section 6) contradicts your own health impact claims earlier. Which specific studies in your review actually isolate polymer toxicity?
Also:
5. This reads as a review, yet the authors present it as offering “new” perspectives without clearly delineating which arguments are novel versus synthesized from existing literature. The paper fails to establish what specific conceptual advances they contribute beyond summarizing known challenges.
6. The paper defines MPPs as 1 μm to 5 mm and NPPs as <1000 nm, creating an overlap at 1 μm that is never resolved. This ambiguity makes it impossible to compare findings across studies cited in sections 2.1 and 3 where different operational definitions were used.
7. In Section 2.1, the authors state bottom-up estimates are “much lower than top-down estimates” suggesting “incomplete understanding of emission mechanisms.” However, top-down estimates themselves rely on uncertain assumptions about atmospheric transport, deposition velocities, and degradation rates that are not independently constrained for MNPPs. The comparison is not a valid test of either approach.