Activity Examples

February 3, 2026 · View on GitHub

This section provides working code examples for computing chemical activity in aerosol particles using Particula's activity strategies. Learn how to use ideal, kappa-Kohler, and BAT (non-ideal) models through practical examples.

Overview

Activity determines how species partition between gas and particle phases and controls water uptake in hygroscopic aerosols. These examples demonstrate:

Computing activity from mass concentrations
Comparing ideal vs. non-ideal activity models
Using the kappa parameter for hygroscopic growth
Integrating activity with equilibria calculations

Example Scripts

Ideal Activity

Basic ideal activity calculation using Raoult's Law with ActivityIdealMolar. Good starting point for understanding the activity API.
BAT Model Activity

Non-ideal activity using the Binary Activity Thermodynamic (BAT) model with ActivityNonIdealBinary. Compares ideal vs. non-ideal activity for organic-water mixtures.
Kappa Parameter Activity

Hygroscopic activity using kappa-Kohler theory with ActivityKappaParameter. Demonstrates water activity at different compositions for inorganic aerosols.
Equilibria Partitioning

Liquid-vapor partitioning using LiquidVaporPartitioningStrategy. Shows how activity integrates with equilibria calculations for gas-particle partitioning.

Interactive Tutorial

For a comprehensive hands-on introduction, see the interactive Jupyter notebook:

:octicons-arrow-right-24: Activity Tutorial

This tutorial covers:

What is activity and why it matters for aerosol modeling
Ideal activity with Raoult's Law
Non-ideal activity with the BAT model
Kappa parameter for hygroscopic growth
Integration with equilibria calculations
Visualization of activity vs. composition

Existing Tutorial: Activity Tutorial (Particle Phase) - Covers Strategy, Builder, and Factory patterns
Feature Guide: Activity System - Comprehensive feature documentation
Theory: Activity Theory - Mathematical foundations

Quick Reference

Available Strategies

Strategy	Import	Description
`ActivityIdealMolar`	`par.particles.ActivityIdealMolar`	Raoult's Law (mole fractions)
`ActivityIdealMass`	`par.particles.ActivityIdealMass`	Ideal (mass fractions)
`ActivityKappaParameter`	`par.particles.ActivityKappaParameter`	Kappa-Kohler model
`ActivityNonIdealBinary`	`par.particles.ActivityNonIdealBinary`	BAT non-ideal model

Basic Usage Pattern

import numpy as np
import particula as par

# 1. Create strategy
strategy = par.particles.ActivityIdealMolar(
    molar_mass=np.array([18.015e-3, 200.0e-3]),  # kg/mol
)

# 2. Define mass concentrations
mass = np.array([0.5e-9, 0.5e-9])  # kg/m^3

# 3. Compute activity
activity = strategy.activity(mass_concentration=mass)