Standard atmosphere (unit)
| Atmosphere | |
|---|---|
| Unit of | Pressure |
| Symbol | atm |
| Conversions | |
| 1 atm in ... | ... is equal to ... |
| SI units | 101.325 kPa |
| US customary units | 14.69595 psi |
| other metric units | 1.013250 bar |
The standard atmosphere (symbol: atm) is a
History
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of
In chemistry and in various industries, the reference pressure referred to in standard temperature and pressure was commonly 1 atm (101.325 kPa) prior to 1982, but standards have since diverged; in 1982, the International Union of Pure and Applied Chemistry recommended that for the purposes of specifying the physical properties of substances, standard pressure should be precisely 100 kPa (1 bar).[4]
Pressure units and equivalencies
| Pascal | Bar | Technical atmosphere
|
Standard atmosphere | Torr | Pound per square inch
| |
|---|---|---|---|---|---|---|
| (Pa) | (bar) | (at) | (atm) | (Torr) | (lbf/in2) | |
| 1 Pa | — | 1 Pa = 10−5 bar | 1 Pa = 1.0197×10−5 at | 1 Pa = 9.8692×10−6 atm | 1 Pa = 7.5006×10−3 Torr | 1 Pa = 0.000145037737730 lbf/in2 |
| 1 bar | 105 | — | = 1.0197 | = 0.98692 | = 750.06 | = 14.503773773022 |
| 1 at | 98066.5 | 0.980665 | — | 0.9678411053541 | 735.5592401 | 14.2233433071203 |
| 1 atm | ≡ 101325 | ≡ 1.01325 | 1.0332 | — | 760 | 14.6959487755142 |
| 1 Torr | 133.322368421 | 0.001333224 | 0.00135951 | 1/760 ≈ 0.001315789 | — | 0.019336775 |
| 1 lbf/in2 | 6894.757293168 | 0.068947573 | 0.070306958 | 0.068045964 | 51.714932572 | — |
A pressure of 1 atm can also be stated as:
- ≡ 101325 pascals (Pa)
- ≡ 1.01325 bar
- ≈ 1.033 kgf/cm2
- ≈ 1.033 technical atmosphere
- ≈ 10.33 m H2O, 4 °C[n 1]
- ≈ 760 mmHg, 0 °C, subject to revision as more precise measurements of mercury's density become available[n 1][n 2]
- ≡ 760 torr (Torr)[n 3]
- ≈ 29.92 inHg, 0 °C, subject to revision as more precise measurements of mercury's density become available[n 2]
- ≈ 406.782 in H2O, 4 °C[n 1]
- ≈ 14.6959 pounds-force per square inch(lbf/in2)
- ≈ 2116.22 pounds-force per square foot(lbf/ft2)
- = 1 ata (atmosphere absolute).
The ata unit is used in place of atm to indicate the total pressure of the system, compared to a vacuum.[5] For example, an underwater pressure of 3 ata would mean that this pressure includes 1 atm of air pressure and thus 2 atm due to the water.[citation needed]
Notes
- ^ a b c This is the customarily accepted value for cm–H2O, 4 °C. It is precisely the product of 1 kg-force per square centimeter (one technical atmosphere) times 1.013 25 (bar/atmosphere) divided by 0.980 665 (one gram-force). It is not accepted practice to define the value for water column based on a true physical realization of water (which would be 99.997 495% of this value because the true maximum density of Vienna Standard Mean Ocean Water is 0.999 974 95 kg/L at 3.984 °C). Also, this "physical realization" would still ignore the 8.285 cm–H2O reduction that would actually occur in a true physical realization due to the vapor pressure over water at 3.984 °C.
- ^ NISTvalue of 13.595 078(5) g/mL assumed for the density of Hg at 0 °C
- ^ Torr and mm-Hg, 0°C are often taken to be identical. For most practical purposes (to 5 significant digits), they are interchangeable.
See also
References
- ^ "Water Pressures at Ocean Depths". NOAA Pacific Marine Environmental Laboratory. Retrieved 11 October 2022.
- ^ Resnick, Robert; Halliday, David (1960). Physics for Students of Science and Engineering Part 1. New York: Wiley. p. 364.
- ^ a b "BIPM - Resolution 4 of the 10th CGPM". www.bipm.org.
- ^ IUPAC.org, Gold Book, Standard Pressure
- ^ "The Difference Between An ATM & An ATA". Scuba Diving & Other Fun Activities. March 2, 2008.