The bulk of the atmospheric aerosol mass is present in the lower troposphere, reflecting the short residence time of aerosols against deposition (~1-2 weeks; see problem 8. 1). Aerosol concentrations in the upper troposphere are typically 1-2 orders of magnitude lower than in the lower troposphere. The stratosphere contains however an ubiquitous H2SO4-H2O aerosol layer at 15-25 km altitude, which plays an important role for stratospheric ozone chemistry (chapter 10). This layer arises from ... A differential equation called the Aerosol General Dynamic Equation (GDE) characterizes the evolution of the number density of particles in an aerosol due to these processes. Aerosols are small particles in the air that can either cool or warm the climate, depending on the type and color of the particle. In short, the aerosol meaning in a simple way is an aerosol is a collection of solid particles or liquid droplets dispersed in the air . Examples include smoke, fog, sea spray and pollution particles of the atmosphere.