What type of atmospheric dispersion models were based on visual observations?

Passive models are designed to simulate atmospheric dispersion based on visual observations and empirical data rather than complex computations. These models rely on simpler methods to approximate how pollutants disperse in the atmosphere, often using graphical techniques or observational data to inform predictions about the spread of airborne substances. Passive models tend to incorporate real-world measurements, such as the behavior of smoke plumes or other discernible markers of dispersion, which make them particularly useful in scenarios where detailed meteorological data or sophisticated computational resources might not be available.

Numerical models typically use mathematical equations to simulate the physics of dispersion and require extensive environmental data for their calculations. Dynamic models focus on the time-dependent behavior of dispersing substances, considering factors like wind speed and direction in a more complex manner than passive models do. Exponential models, on the other hand, are more often employed in pollutant concentration decay over distance without incorporating real-time observational data as a basis for modeling dispersion.