 
the idefics pages
drop size definitions
Several special drop sizes are defined to characterize a spray from a nozzle. The most important in spray drift research are listed below:
 VMD: Volume Median Diameter (also noted as D_{V50}): this may be the most used sizing parameter for a spray; half the spray volume consists of drops smaller than this diameter, the other half consists of larger drops.
 D_{V10}: defined in a similar way as VMD, but in this case 10% of spray volume consists of drops smaller than D_{V10}, obviously the other 90% consists of larger drops.
 D_{V90}: for this third median diameter, 90% of spray volume consists of drops smaller than D_{V90}, and the other 10% consists of larger drops.
 SMD: Sauter Mean Diameter (also: D_{32}): equivalent to the ratio of total spray volume and total surface area of all drops:
(i sums over all drops in the spray; D_{i} is the diameter of the ith drop). SMD is useful e.g. to calculate the fraction of wetted surface area after deposition of drops; this fraction is also noted as 'coverage'.
 D_{30}: Volume Mean Diameter (note that this one is a mean diameter, not a median); it is the average drop size, taking account of the total spray volume. If one would catch the whole spray, divide it into small equal pieces, the number of which would be equal to the number of drops in that spray, then the volume of one piece would be the average volume of a single drop. Its diameter would be D_{30}. Or defined by an equation:
(N is the total number of drops)
