In comparison with stated normal amounts of aluminum found in the air.
(Quote) “…..Levels of aluminum in the air generally range from 0.005 to 0.18 micrograms (1 microgram, ?g, equals a millionth of a gram, 1 gram equals 0.0022 pound) of aluminum per cubic meter of air (0.005–0.18 ?g/m3 or 0.00018 mg/L) , depending on location, weather conditions, and level of industrial activity in the area. Most of the aluminum in the air is in the form of small suspended particles of soil (dust). Aluminum levels in urban and industrial areas may be higher and can range from 0.4 to 8.0 ?g/m3 ….” http://www.eoearth.org/view/article/155461/
