Passage II

Substances in the atmosphere, such as Cu²⁺ , Zn²⁺ , Cl^- , and SO₄²⁻ ions, are carried down to Earth's surface by precipitation. This process is known as wet deposition. Cu²⁺ and Zn²⁺ ions are put into the atmosphere by high-temperature combustion processes. The presence of Cl⁻ and SO₄²⁻ ions in the atmosphere can be attributed to road-salt dust and electrical power generation, respectively.

Study 1

A rain gauge, placed on the roof of a 1-story building, at a specific urban site was used to collect precipitation over a 12-month period. At the same time each evening, the amount of precipitation in the rain gauge was recorded, after which the collected precipitation was emptied from the gauge and stored. (Assume no measurable evaporation occurred during any day.) Figure 1 shows the measured monthly precipitation in centimeters.

At the end of each month, all the samples collected during that month were mixed, and some of this combined sample was analyzed for the concentrations of Cu²⁺ and Zn²⁺ ions. Using these data, the monthly wet deposition of each substance, in micrograms (μg) per meter² , was calculated (see Figure 2).

Study 2

Another portion of the combined sample for each month was analyzed for the concentrations of Cl⁻ and SO₄²⁻ ions. Using these data, the monthly wet deposition of each substance, in milliequivalents (meq) per m² , was calculated (see Figure 3).

Study 3

The annual wet deposition of Cu²⁺ and of Zn²⁺ for the 12-month period, in μg/m², was calculated for the urban site (the source of the Cu²⁺ and Zn²⁺) and also for Rural Sites 1 and 2, located 50 km and 100 km east, respectively, of the urban site (see Figure 4).