Recent studies have highlighted the importance of the atmosphere in the long-range transport of microplastic fibers (MPFs). However, both dry deposition processes and sources of MPFs are poorly understood due to their complexity in size and shape, which can be 100s $\mu m$ long, possessing round or flat cross-sections with dimensions of $O(1)\,\mu m$ thickness, and $O(10)\,\mu m$ width. Here, we develop a theory-based settling velocity model for MPFs in the atmosphere, predicting a much smaller aerodynamic size than a volumetrically equivalent spherical particle. Incorrect identification of flat fibers as cylindrical ones due to uncertainty in the thickness of sampled MPFs overestimates their dry deposition rate. Accounting for fiber thickness in sampled MPFs leads to a mean residence-time enhancement above $450\%$ compared to spherical-shaped particles, suggesting a much more efficient long-range transport of flat fibers than previously thought and that the ocean might be a major source of atmospheric plastics.
The spatiotemporal characteristics of air temperature and humidity mediated by urban bluespace are investigated using a combination of dense network of climatological observations in a medium-sized US city, computational fluid dynamics and analytical modeling approaches. Both numerical simulation and observational results show that the rate of change of hourly averaged air temperature and humidity at 3.5 m over urban areas peaks two hours after sunset, while it decreases with time monotonically over greenspace, indicating different impacts due to presence of urban lakes. The apparent temperature decreases with distance to lakes in urban area due to higher near-shore humidity. This highlights that urban lakes located near city center can deteriorate the nighttime cooling effects due to elevated humidity. Finally, two analytical models are presented to explain the connection between the surface and air temperature as well as the spatial variation of air temperature and humidity adjacent to the urban lakes. These simplified models with parameters being inferred from the network of measurements have reasonably good performance compared to the observations. Compared to other sophisticated numerical simulations, these analytical models offer an alternative means that is easily accessible for evaluating the efficacy of bluespace on urban nocturnal cooling.
The spatiotemporal characteristics of air temperature and humidity mediated by urban bluespace are investigated using a combination of dense network of climatological observations in a medium-sized US city, computational fluid dynamics and analytical modeling approaches. Both numerical simulation and observational results show that the rate of change of hourly averaged air temperature and humidity at 3.5 m over urban areas peaks two hours after sunset, while it decreases with time monotonically over greenspace, indicating different impacts due to presence of urban lakes. The apparent temperature decreases with distance to lakes in urban area due to higher near-shore humidity. This highlights that urban lakes located near city center can deteriorate the nighttime cooling effects due to elevated humidity. Finally, two analytical models are presented to explain the connection between the surface and air temperature as well as the spatial variation of air temperature and humidity adjacent to the urban lakes. These simplified models with parameters being inferred from the network of measurements have reasonably good performance compared to the observations. Compared to other sophisticated numerical simulations, these analytical models offer an alternative means that is easily accessible for evaluating the efficacy of bluespace on urban nocturnal cooling.
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