Vertical Flux - In dry deposition this refers to the rate at which a gas particle is deposited onto another surface without the aid of precipitation. Vertical flux equals concentration of the species multiplied by the deposition velocity.
[International Journal of Heat and Mass Transfer; v31n11; 2291; 1988.]
[Journal of Atmospheric Sciences; v48n11; 1909; 1991.] 
Atmospheric Chemistry Glossary