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Theoretical Background

This section introduces the aerosol science theories and calculation methods used in AeroViz.

Optical Properties

Mie Scattering Theory

Mie theory describes the scattering and absorption of electromagnetic waves by spherical particles and is the foundation for calculating aerosol optical properties.

  • Extinction, scattering, and absorption efficiency factors
  • Internal mixing vs external mixing vs core-shell structure
  • Effects of refractive index and particle size

IMPROVE Extinction Equation

The IMPROVE (Interagency Monitoring of Protected Visual Environments) equation is used to estimate extinction coefficients from chemical composition.

  • Original version vs revised version
  • Hygroscopic growth factor f(RH)
  • Mass extinction efficiency of each component

Size Distribution

Log-normal Distribution

Aerosol size distributions typically follow log-normal distributions and can be characterized by geometric mean diameter (GMD) and geometric standard deviation (GSD).

  • Number/surface area/volume distribution conversion
  • Modal analysis (Nucleation, Aitken, Accumulation, Coarse)
  • Size distribution statistics

ICRP 66 Lung Deposition Model

The International Commission on Radiological Protection (ICRP) human respiratory tract model is used to calculate regional deposition of inhaled aerosols.

  • Head airways (HA), tracheobronchial (TB), and alveolar (AL) regions
  • Activity intensity and breathing patterns
  • Deposition fraction calculation

Chemical Properties

kappa-Kohler Theory

kappa-Kohler theory describes the hygroscopicity of aerosol particles, where the kappa value reflects the particle's ability to act as cloud condensation nuclei.

  • Single-parameter kappa definition
  • Relationship between chemical composition and kappa
  • Hygroscopic growth factor calculation

Mass Reconstruction

Reconstructing PM2.5 mass from chemical composition to verify analytical completeness.

  • Major components: SIA, OM, EC, Soil, SS
  • Ammonium status determination
  • OM/OC ratio selection

VOC Analysis

Ozone Formation Potential (OFP)

Assessment of volatile organic compounds (VOC) contribution to ozone formation.

  • Maximum Incremental Reactivity (MIR)
  • Species-specific OFP calculation
  • Secondary Organic Aerosol Potential (SOAP)