Textbook Notes (363,143)
Chemistry (161)
CHEM 302 (14)
Chapter 8

# Chapter 8 Problems.pdf

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School
University of British Columbia
Department
Chemistry
Course
CHEM 302
Professor
Michael Wheeler
Semester
Fall

Description
153 PROBLEMS 8. 1 Residence times of aerosols 210 7 The radioisotopes Pb and Be are often used to determine the atmospheric residence times of aerosols. 222 1. Lead-210 is produced by radioactive decay of Rn emitted from soils, and condenses immediately on preexisting aerosol particles. The 222Rn emission flux is 1.0 atoms cm s from land (30% of Earth’s surface) and zero from the oceans. The only sink of 222Rn is radioactive decay (half-life 3.8 days), producing 210Pb. Removal of 210Pb is by radioactive decay (half-life 23 years) and by aerosol 210 deposition. The total mass of Pb in the troposphere is estimated from observations to be 380 g. Derive the residence time against deposition of 210Pb-carrying aerosols in the troposphere. You should find a value of 8 days. 2. Beryllium-7 is produced by cosmic rays in the stratosphere and upper troposphere. Similarly to 210Pb, it condenses immediately on preexisting aerosol particles. The global source of 7Be is 150 g yr ; 70% of that source is in the stratosphere and 30% is in the troposphere. Removal of Be is by radioactive decay (half-life of 53 days) and by aerosol deposition (in the troposphere only). We assume that the troposphere and stratosphere are well-mixed reservoirs, that 7 Be is at steady state in each of these reservoirs, and that the transfer rate constant from the stratosphere to the troposphere is k = 0.8 yr-1The total mass ST of Be in the troposphere is estimated from observations to be about 3 g. Derive 7 the residence time against deposition of Be-carrying aerosols in the troposphere. You should find a value of 24 days. 210 7 3. Why are the lifetimes of Pb-carrying aerosols and Be-carrying aerosols in the troposphere so different? 222 4. Since most of the Rn emitted at the surface decays in the troposphere, one might expect 21
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