Terminology

This is a non-exhaustive list of terms and acronyms used in papers [1] [7] [10] on microplastics and nanoplastics (MnP) in the ocean-atmosphere system.

Microplastic / Nanoplastic

• MP: microplastics, particles 1 \(\mu m\) to 5 \(mm\) in diameter.

• NP: nanoplastics, plastic particles smaller than 1 \(\mu m\) in diameter.

• MnP: micro(nano)plastics, collective term for all particles \(\le\) 5 \(mm\), including MPs and NPs.

• Primary MnP: Intentionally manufactured micro/nano-sized plastics.

• Secondary MnP: Plastics formed by degradation of larger items.

Flux

• LOD: Limit of Detection, smallest detectable concentration.

• LOQ: Limit of Quantification, smallest quantifiable concentration.

• SSA: Sea Spray Aerosol, aerosol particles ejected into the atmosphere when air bubbles formed by breaking waves burst at the ocean surface.

• SML: Surface Microlayer, the uppermost ~1000 µm of the ocean surface where floating MNP like PE accumulate.

• MART: Marine Aerosol Reference Tank, to simulate SSA production and measure MNP aerosolization.

• \([\text{MNP}]_{\text{air}}\) or \([\text{MNP}]_{\text{water}}\): Airborne or Waterborne MNP Concentration, number of MNP particles per unit volume of air or water

  • Units: particles \(m^{-3}\) (alternatively particles \(L^{-1}\))

• \(U_{10}\): Wind speed at 10 m height, standard reference wind speed used in ocean-atmosphere modeling

  • Units: \(m \cdot s^{-1}\)

• \(E_f\): Emission Factor, empirical coefficient relating water MNP concentration to emission flux

  • Units: \(m^{3} \cdot m^{-2} \cdot s^{-1}\)

  • Values vary by particle size and type (e.g., \(10^{-9} - 10^{-8}\) for typical MnPs)

• \(Q\): Volumetric flow rate of incoming or outgoing air

  • Units: \(m^3 \cdot s^{-1}\)

• \(\mathcal{C}\): Particle number concentration of MnP

  • Units: particles \(m^{-3}\)

• \(E\): Emission Rate

  • Definition: Total number of MNP particles emitted per second

  • In the MART setup, the change in concentration of particles in the air over time can be written as:

    \[ \frac{d\mathcal{C}}{dt} = Q_{\text{in}} \cdot \mathcal{C}_{\text{in}} - Q_{\text{out}} \cdot \mathcal{C}_{\text{out}} + E - L \]

    Where:

    • \(\mathcal{C}\) = particle concentration in the chamber (air)

    • \(Q_{\text{in}}\) = air inflow rate

    • \(\mathcal{C}_{\text{in}}\) = particle concentration in inflow air

    • \(Q_{\text{out}}\) = air outflow rate

    • \(\mathcal{C}_{\text{out}}\) = particle concentration in outflow air

    • \(L\) = loss of particles (e.g., deposition on walls; often neglected in basic cases)

  • When steady state is reached, i.e., the particle concentration in the chamber becomes constant over time:

    \[ \frac{d\mathcal{C}}{dt} = 0 \]

    Also assume:

    • Clean air inflow: \(\mathcal{C}_{\text{in}} = 0\)

    • Losses are negligible: \(L \approx 0\)

    So the mass balance simplifies to:

    \[ E = Q_{\text{out}} \cdot \mathcal{C}_{\text{out}} \]

  • Units: particles \(s^{-1}\)

• \(F\): Emission Flux

  • Definition: Number of MNP particles emitted per unit area per unit time

  • Formula:

    \[ F(U_{10}, \mathcal{C}) = (3.84 \times 10^{-6} \cdot U_{10}^{-3.41}) \cdot (E_f \cdot \mathcal{C}) \]

  • Units: particles \(m^{-2} \cdot s^{-1}\)

  • Note that \(3.84 \times 10^{-6} \cdot U_{10}^{-3.41}\) is a dimensionless coefficient.

• \(AF\): Aerosolization Factor

  • Definition: Ratio of MNP concentration in air to that in water

  • Formula:

    \[ AF = \frac{[\text{MNP}]_{\text{air}}}{[\text{MNP}]_{\text{water}}} \]

  • Dimensionless (ratio of concentrations)

Aerosol

• Aerosol Size Modes: grouped log-normal size distributions, each has a characteristic size range and composition:

  • Nucleation Mode

    • Diameter < 5 nm

    • Represents the smallest aerosols (e.g., newly formed sulfate particles).

    • No microplastics allowed due to their larger size.

  • Aitken Mode

    • Diameter ~5–50 nm

    • Small particles that can grow via condensation/coagulation.

    • Subdivided into soluble and insoluble.

  • Accumulation Mode

    • Diameter ~50-250/500 nm

    • Intermediate-size aerosols where particles tend to “accumulate.”

    • Important for cloud formation and light scattering.

  • Coarse Mode

    • Diameter >250 nm

    • Larger particles that deposit faster.

    • Includes both soluble and insoluble variants.

  • Super-Coarse Mode

    • Diameter >2500 nm

    • Largest particles (like microplastic fibres).

    • Only insoluble; no soluble version exists in the model.

• MnP Particle Types

  • Fragment:

    • Small broken-down pieces of plastic; emitted across all insoluble modes (except nucleation).

  • Fibre:

    • Thread-like plastic particles (e.g., from textiles); emitted only into the super-coarse insoluble mode.

    • Currently modeled as spheres, which underrepresents their atmospheric behavior.

• CCN: Cloud Condensation Nuclei

  • Particles that can initiate cloud droplet formation when in the soluble mode and in the presence of supersaturation.

• AOD: Aerosol Optical Depth

  • A measure of how much aerosol particles in the atmosphere block or scatter sunlight.

• CDNC: Cloud Droplet Number Concentration

  • The number of cloud droplets per unit volume of air, influenced by aerosol concentration and type.

• Radiative Effects:

  • The influence of particles on Earth’s energy balance via scattering or absorbing radiation.

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