I exposed three trials of Spanish moss to one chemical at a time for 10 days. Each trial was observed under the microscope before and after exposure and weighed using the same analytical balance. A damp paper towel was placed at the back of the ESC to keep the humidity constant—around 85 percent. The air pump was kept running constantly in order to circulate the air and pollutants in the closed system. The light and temperature was kept the same as with the controls. I used a three-milliliter syringe to inject the pollutant into the ESC through a stoppered hole daily at 7:30 a.m., including the weekends. I mixed the acid rain solution in a spray bottle and thoroughly sprayed the moss daily. The averages of the data are below:

	Before	After	% Weight Loss	% Dead
Helium	3.2097g	2.1910g	31.71%	100%
Carbon dioxide	3.5943g	3.5825g	0.34%	1.07%
Carbon monoxide	3.7756g	3.3297g	11.79%	37.18%
Sulfur dioxide	3.6988g	3.1689g	14.30%	45.09%
Nitrogen dioxide	3.9122g	3.3371g	14.69%	46.33%
Acid rain	4.0744g	3.1220g	23.39%	71.48%

After all four tests were done, I was surprised with the results. Using the helium control as a standard for 100 percent dead Spanish moss, I was able to get a qualitative number for how "dead" the moss was after being exposed to the four pollutants. Acid rain killed the moss 71 percent. [Moss after acid rain exposure (Click to view)] Acid rain levels are frequently higher in cities than in the country, perhaps explaining why the Spanish moss is disappearing. Also, the Spanish moss that remains in Houston is found on the lower branches of the larger, more densely leafed trees. Perhaps the tree leaves protect the Spanish moss from acid rain; thus it is able to survive in certain protected microclimates.