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.