Question

Dust falls on Chicago at a rate of 65.0 mg m^-2 day^-1. Major metallic elements in the dust include Al, Mg, Cu, Zn, Mn, Pb. Pb accumulates at a rate of .0300 mg m^-2 day^-1. How many metric tons (1metric ton=1000kg) of Pb fall on the 535 square kilometers of Chicago in 20. years?

Answer 1

metric ton = 1000 kg = 1 x 10^9 mg

Km^2 = 10^6 m^2

year = 365 days

20 years = 20 x 365 = 7300 days

535 km^2 = 535 x 10^6 m^2

rate of Pb accumulates = 0.0300 mg m^-2 day^-1

metric tons of lead = ( 0.03 mg / m^2 . day) x 7300 days x 535 x 10^6 m^2

                               = 1.17165 x 10^11 mg

1 metric ton --------- 1 x 10^9 mg

??       ------ 1.17165 x 10^11 mg

metric tons of Pb = 117 metric tons