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Vertical concentrations gradients and transport of airborne microplastics in wind tunnel experiments

Title data

Esders, Eike M. ; Georgi, Christoph ; Babel, Wolfgang ; Held, Andreas ; Thomas, Christoph:
Vertical concentrations gradients and transport of airborne microplastics in wind tunnel experiments.
In: Aerosol Research. Vol. 2 (2024) Issue 2 . - pp. 235-243.
ISSN 2940-3391
DOI: https://doi.org/10.5194/ar-2-235-2024

Official URL: Volltext

Project information

Project title:
Project's official title
Project's id
SFB 1357 Mikroplastik
391977956

Abstract in another language

Microplastics are an ubiquitous anthropogenic material in the environment, including the atmosphere.
Little work has focused on the atmospheric transport mechanisms of microplastic nor its dispersion, despite it being a potential pollutant. We study the vertical transport of airborne microplastics in a wind tunnel, a controllable environment with neutral stability, to identify the necessary conditions for the long-range atmospheric transport of microplastics. An ultrasonic disperser generated airborne water droplets from a suspension of polystyrene microsphere microplastics (MPs) with a diameter of 0.51 μm. The water droplets were injected into the airflow, evaporating and releasing single airborne MPs. The disperser allowed for time-invariant and user-controlled
concentrations of MPs in the wind tunnel. MPs were injected at 27, 57, and 255 mm above the ground. A single GRIMM R11 optical particle counter (OPC) and three Alphasense OPCs measured time-averaged MP concentration profiles (27, 57, and 157 mm above the ground). These were combined with turbulent airflow characteristics measured by a hotwire probe to estimate vertical particle fluxes using the flux-gradient similarity theory. The GRIMM R11 OPC measured vertical concentration profiles by moving its sampling tube vertically. The three Alphasense OPCs measured particle concentrations simultaneously at three distinct heights. Results show that maximum concentrations are not measured at the injection height but are rather shifted to the surface by gravitational settling. The MPs experience higher gravitational settling while they are part of the larger water droplets.
For the lowest injection at 27 mm, the settling leads to smaller MP concentrations in the wind tunnel, as MPs are lost to deposition. Increasing the wind speed decreases the loss of MPs by settling, but settling is present until our maximum friction velocity of 0.14 m s−1. For the highest injection at 255 mm and laminar flow, the settling resulted in a net MP emission, challenging the expectation of a net MP deposition for high injection.
Turbulent flows reverse the MP concentration profile giving a net MP deposition with deposition velocities of
3.7 ± 1.9 cm s−1. Recognizing that microplastics share deposition velocities with mineral particles bridges the gap in understanding their environmental behavior. The result supports the use of existing models to evaluate the transport of microplastics in the accumulation mode. The similar deposition velocities suggest that microplastics transported in the atmosphere can be found in the same places as mineral particles.

Further data

Item Type: Article in a journal
Refereed: Yes
Keywords: Microplastics; particulate matter; atmospheric turbulence; dispersion; deposition
Institutions of the University: Faculties
Faculties > Faculty of Biology, Chemistry and Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Professor Micrometeorology
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Professor Micrometeorology > Professor Micrometeorology - Univ.-Prof. Dr. Christoph K. Thomas
Profile Fields
Profile Fields > Advanced Fields
Profile Fields > Advanced Fields > Ecology and the Environmental Sciences
Profile Fields > Advanced Fields > Nonlinear Dynamics
Research Institutions
Research Institutions > Central research institutes
Research Institutions > Central research institutes > Bayreuth Center of Ecology and Environmental Research- BayCEER
Research Institutions > Collaborative Research Centers, Research Unit
Research Institutions > Collaborative Research Centers, Research Unit > SFB 1357 - MIKROPLASTIK
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 500 Natural sciences
500 Science > 530 Physics
500 Science > 540 Chemistry
500 Science > 550 Earth sciences, geology
500 Science > 570 Life sciences, biology
Date Deposited: 03 Aug 2024 21:00
Last Modified: 05 Aug 2024 08:03
URI: https://eref.uni-bayreuth.de/id/eprint/90147