What is atmospheric pressure and how it is measured

Atmospheric pressure is Force that exerts the air on the surface of the Earth. Although we do not notice, we are surrounded by a layer of gases, mainly oxygen and nitrogen, which form the atmosphere. The severity of the Earth maintains this layer of “stuck” air to its surface, and the weight of that air presses everything that is in contact with it.

We recommend reading this article about the composition of the atmosphere.

Atmospheric pressure can be measured in several units, and the choice of one or the other depends on the context or the region:

• Hectopascal (HPA): This is the most used unit in meteorology to measure atmospheric pressure. A hectopascal is equivalent to 100 pascals, which is the basic pressure unit in the International Units System (SI). At sea level, atmospheric pressure is usually around 1013 HPA.
• Mercury millimeters (mmhg): Also known as Torr, this unit comes from the old mercury barometers. In this type of barometers, atmospheric pressure pushes mercury inside a tube, and the height of the mercury column is a pressure measure. At sea level, typical atmospheric pressure is approximately 760 mmHg.
• ATMOSFERAS (ATM): Although it is used less frequently, the atmosphere (ATM) is another pressure unit. An atmosphere is equivalent to the pressure exerted by air at sea level, that is, approximately 1013 HPA or 760 mmHg. This unit is useful in fields such as physics and chemistry.
• Bar: The bar is another pressure unit, more common in industrial applications. A bar is approximately 1000 HPA or 100,000 Pa. Like the atmosphere, it is close to the value of the pressure at sea level.

Atmospheric pressure is measured with an instrument called barometer. There are different types of barometers, and each one works differently, but they all have the same goal: to measure the force exerted by air on the earth. The types of barometers are:

• Mercury barometer: It works using a closed glass tube at the top and full of mercury. The base of the tube is submerged in a container also full of mercury. As the atmospheric pressure pushes mercury in the container, it rises or low inside the tube. The height of the Mercury column, which is measured in millimeters of Mercury (MMHG), indicates atmospheric pressure.
• Aneroid barometer: This type of barometer does not use liquids, which makes it more practical and portable. Instead, it contains a sealed metal capsule with a partial vacuum inside. As the atmospheric pressure changes, the capsule is compressed or expands.
• Digital barometers: Modern barometers use electronic sensors to measure atmospheric pressure. These sensors, called pressure transducers, detect air pressure changes and turn that information into a digital reading.

Atmospheric pressure is not constant, but varies by different factors:

• Altitude: Atmospheric pressure decreases as we rise in height. This happens because the higher we are, the less air there is on us, which means less weight and, therefore, lower pressure. In places at sea level, like the coasts, the pressure is higher because the air is more “stacked.”
• Temperature: When the air heats up, the molecules expand and become less dense, which causes a decrease in pressure. This occurs because hot air tends to rise, leaving less air on the surface.
• Meteorological systems: Variations in atmospheric pressure are key to understanding the weather. Meteorologists observe high and low pressure areas to predict time.
• Wind effect: The air tends to move from high pressure areas to low pressure, creating air currents. The greater the pressure difference between two places, the stronger the wind will be.

Atmospheric stability and instability refer to the trend of air to remain in position or move vertically:

• Atmospheric stability: The atmosphere is considered stable when the air tends to remain in place and does not rise easily. This occurs when the air layers closest to the ground are colder or equal to cold than the upper layers.
• Atmospheric instability: The atmosphere is unstable when the air closest to the surface is much warmer than the air in the upper layers. In this case, hot air, which is less dense, tends to rise quickly. When ascending, the air cools and can reach its condensation point, forming clouds. If instability is intense enough, these clouds can develop vertically, which gives rise to storms.

Atmospheric pressure has a direct impact on our lives, both in physical aspects and how we perceive the environment:

• Changes in blood pressure: Some people are sensitive to changes in atmospheric pressure, especially those with hypertension or hypotension problems.
• Headaches and migraines: Changes in atmospheric pressure, especially when there are low pressures associated with bad weather systems, can trigger migraines or headaches in predisposed people.
• Joint pains: Some people with arthritis or other joint problems report an increase in pain or rigidity when atmospheric pressure drops.
• Respiratory problems: In high altitude areas, where atmospheric pressure is lower, some people may experience difficulty breathing.
• Height evil: When we travel to large altitudes, as in high mountains or plateaus, atmospheric pressure decreases significantly, which reduces the amount of oxygen in the air.
• Effects on flights and aviation: As a plane rises to higher altitudes, air pressure decreases, which can affect the way humans breathe. That is why the cabins of the airplanes are pressurized, to maintain a comfortable pressure level for passengers and crew.

Now that you know what atmospheric pressure is, do not miss these articles on the atmospheric river: what it is, how it is formed and consequences and how the atmosphere influences time.

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