Passage VI
A study was done in a large city in Asia during the spring to examine the composition of airborne dust particles on 5 days of fair weather and on 5 days of dust storms. There was no precipitation on any of the study days.
Study
A device called an impactor (see Figure 1) was installed on the roof of a 4-story building in the center of the city. To collect airborne, dust particles, the impactor drew in air at a constant rate of 1.1 L/min. A series of 8 filters inside the impactor removed particles from the air. Each filter had openings of a different uniform diameter to allow for the collection of particles belonging to 1 of 8 different size ranges, measured in micrometers (µm).
On each of the selected days, the impactor was operated continuously over a period that began at 9 a.m. At 3 p.m., the impactor was turned off, and the collected particles belonging to each size range were removed and then analyzed for 4 elements: silicon (Si), iron (Fe), sulfur (S), and copper (Cu). The average concentration of each element, in micrograms per cubic meter of air (µg/m3), for the fair weather days and for the dust storm days are shown in Figures 2 and 3, respectively, for each size range.
Figures 2 and 3 adapted from Renjian Zhang et al., “The Elemental Composition of Atmospheric Particles at Beijing during Asian Dust Events in Spring 2004." ©2010 by the Taiwan Association for Aerosol Research.
39. The average concentrations of how many of the elements were generally greater for the dust storm days than for the fair weather days?
Your Answer is
Correct Answer is D
Explanation
Comparing figures 2 & 3, it can be seen that in dust storm weather, the content of the four pollutants will be higher overall, so the four options in D are the correct options