Ammonia from vehicle exhaust. Three-way catalytic converters have been installed in new vehicles in order to reduce pollutants from motor vehicle exhaust emissions. However, these converters unintentionally increase the level of ammonia in the air. Environmental Science and Technology (September 1, 2000) published a study on the ammonia levels near the exit ramp of a San Francisco highway tunnel. The data in the next table represent daily ammonia concentrations (parts per million) on eight randomly selected days during afternoon drive-time in the summer of 1999.
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AMMONIA
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1.53
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1.50
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1.37
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1.51
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1.55
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1.42
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1.41
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1.48
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(a) Find and interpret the mean daily ammonia level in air in the tunnel.
(b) Find the standard deviation of the daily ammonia levels. Interpret the result.
(c) Suppose the standard deviation of the ammonia levels during morning drive-time at the exit ramp is 1.45 ppm. Which time, morning or afternoon drive-time, has more variable ammonia levels?