Introduction

Simple package to help with calculation of aerosol optical properties and derived parameters. Currently two size distrubtions are supported:

Monodisperse

A 'distribution' with particles of a single radii. Can be convenient for derived classes.

Lognormal

The equation describing the distribution is:

\frac{dn}{dr} = \frac{n}{\sqrt{2\pi}r\ln\sigma_g}\exp\left(-\frac{(\ln(r)-\ln(r_g))^2}{2\ln^2\sigma_g}\right)

where $r_g$ is the median radius, and $\sigma_g$ is the width.

Installation

You can dowload the package from pypi using

pip install aerosol_optprop

Or, if you'll be developing, then clone the repository and use

pip install -e .

Example Usage

Cross section Calculations

from aerosol_optprop import Lognormal

# create a lognormal distribution and compute the cross section
aerosol = Lognormal(median_radius=0.1, width=1.5)
print(aerosol.cross_section(wavelength=0.525))

Calculation of derived properties

aerosol = Lognormal(median_radius=0.1, width=1.5, n=10)
print('extinction =', aerosol.extinction(wavelength=0.525), 'km^-1')
print('surface area density =', aerosol.surface_area_density, 'microns^2/cm^3')
print('volume density =', aerosol.volume_density, 'microns^3/cm^3')

Internally consistent parameters

aerosol = Lognormal(median_radius=0.1, width=1.5, n=10)
aerosol.mode_radius = 0.1  # update the mode radius of the distribution
print('median radius is now =', aerosol.median_radius, 'microns')

Extinction can be kept constant if desired

aerosol = Lognormal(median_radius=0.1, width=1.5)
aerosol.set_n_from_extinction(extinction=1e-3, wavelength=0.525, persistant=True)
print('old n =', aerosol.n, 'cm^-3')
aerosol.median_radius = 0.12
print('new n = ', aerosol.n, 'cm^-3')

Phase function calculations (these are a bit slow)

import matplotlib.pyplot as plt

aerosol = Lognormal(median_radius=0.1, width=1.5, n=10)
theta = np.arange(0, 181)
p = aerosol.phase_function(wavelength=0.525, scattering_angles=theta)
plt.plot(theta, p)
plt.xlabel('scattering angle (deg)')
plt.ylabel('P')

Details

The code uses the miepython implementation of the Wiscombe code developed by Scott Prahl for the Mie calculations.

Optical properties are from Palmer and Williams between 0.36-25 microns and Beyer et al. between 0.214 and 0.36 microns, assuming 75% H2SO4 and 25% H2O. If you prefer to use your own refractive index data then this can be changed using the refractive_index_file variable. Files should have three columns in the format

1. Optical Constants of Sulfuric Acid; Application to the Clouds of Venus? Kent F. Palmer and Dudley Williams Appl. Opt. 14, 208-219 (1975)

2. Measurements of UV refractive indices and densities of H2SO4/H2O and H2SO4/HNO3/2:O solutions Keith D. Beyer, A. R. Ravishankara, and Edward R. Lovejoy J. Geophys. Res., 101, D9, 2156-2202, 1996 http://dx.doi.org/10.1029/96JD00937