It is reported that tropical atmospheric carbon dioxide sequestration is 50 pounds per tree per year. It can be roughly calculated by measuring the tree's diameter, the weight of the tree above ground, the height of the tree.
Using some computation method and some given constants, it is reported that "a newly-planted Acacia angustissima, 2.5 years old, 15 feet tall with a trunk 3 inches in diameter gave 21.5 lbs. of CO2 sequestered per year". (Reference)