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# Calculating Residence Time of Atmospheric SO2

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Natural sources add sulfur dioxide (SO2) to the atmosphere at a rate of about 1E8 tonnes (S)/yr. The background concentration of atmospheric SO2, measured in remote areas where anthropogenic sources are not likely to have much influence, is about 0.4 parts per billion, by volume. What is the residence time of  atmospheric SO2 in the remote regions (in days)?

Proposed method:
Calculate mass of atmosphere, number of moles of air , moles of SO2, mass SO2 and residence time.

https://brainmass.com/chemistry/chemical-kinetics/calculating-residence-time-atmospheric-so2-542847

#### Solution Preview

0.4 ppb means

(0.4 mol SO2 / 10^9 mol of air) x (1. 8 x 10^20 mol air) = 7.2 x 10^10 mol SO2

[Assuming the mass of air = 5.14 x 10^18 kg and that air is 78% N2 and ...

#### Solution Summary

The mass of atmosphere, number of moles of air, moles of SO2, mass SO2 and residence time are calculated from the given information.

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