Interstitial aerosol

Gillani, N. V., S. E. Schwartz, W. R. Leaitch, J. W. Strapp, and G. A. Isaac, Field Observations in Continental Stratiform Clouds Partitioning of Cloud Particles between Droplets and Unactivated Interstitial Aerosols, J. Geophys. Res., 100, 18687-18706 (1995). 

The maximum supersaturation reached inside a cloud/fog is an important parameter. Particles with critical supersaturations lower than this value will become activated and become cloud droplets. The rest remain close to equilibrium but never grow enough to be considered droplets and are called interstitial aerosol. The aerosol population inside a cloud is therefore separated into two groups interstitial aerosols that contain significant amounts of water but are not activated (their sizes are usually smaller than 2 pm) and cloud droplets, with size increases corresponding to mass changes of three orders of magnitude. 

If C/fl is the concentration (in mass per volume of air) of an aerosol species in clear air before cloud formation (e.g., at the cloud base), and Qdoud and C)jnl are its concentrations again in mass per volume of air in the aqueous phase and in the interstitial aerosol,... 

Interstitial aerosol particles collide with cloud droplets and are removed from cloud interstitial air. The coagulation theory of Chapter 13 can be used to quantify the rate and effects of such removal. If n(Dp,t) is the aerosol number distribution and nd(Dp,t) the droplet number distribution at time r, the loss rate of aerosol particles per unit volume of air due to scavenging by cloud drops is governed by... 

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