Final answer:
Atmospheric pressure decreases with increasing altitude from sea level, not linearly but more rapidly due to exponential air density decrease. Mercury is used in barometers due to practical size and minimal vapor effects. High altitude results in lower pressure and oxygen levels.
Step-by-step explanation:
The question is how atmospheric pressure varies with increasing altitude from sea level. Atmospheric pressure decreases as altitude increases. This decrease is not linear; rather, it decreases more rapidly due to the exponential decrease in air density with altitude. At higher altitudes, there is less air above a given level, resulting in lower atmospheric pressure.
Two main reasons why mercury is used in barometers instead of water are the high density of mercury, which allows the barometer to be of a practical size, and mercury's low vapor pressure, which minimizes the risk of mercury vapor affecting the measurement.
As you ascend through the atmosphere, the number of air molecules above you decreases, leading to a decrease in the pressure exerted by this weight. A high altitude also means that the air is less dense, which contributes to the lower pressure. This is why it can be a challenge for mountain climbers as they experience lower oxygen concentrations and can develop hypoxia.