Atmospheric Pressure Conversions - Outgassing Rates

Atmospheric pressure, also known as air pressure, is the force exerted on a surface by the weight of the air above it. It is measured in units of force per unit area, such as Pascals (Pa) or pounds per square inch (psi). At sea level, the average atmospheric pressure is about 1013 millibars (mb) or 101.3 kilopascals (kPa), which is equivalent to 14.7 psi. The atmospheric pressure decreases with increasing altitude, so it is less at the top of a mountain than at sea level. The atmospheric pressure also varies with weather systems, and can change rapidly with changes in temperature, humidity, and wind.*

The table below provides conversion factors between common units of force.

Standard units = pascal (Pa)

The standard atmosphere is a model of the Earth's atmosphere that is used as a reference for measuring and reporting atmospheric pressure, density, and temperature. It is defined by the International Civil Aviation Organization (ICAO) and the International Standards Organization (ISO). The standard atmosphere defines a pressure of 1013.25 hPa (hectopascals) at sea level, a temperature of 15 degrees Celsius (59 degrees Fahrenheit), and a relative humidity of 0%. As altitude increases, the temperature, pressure and density of air decrease in a standard way .It is also defined as a temperature gradient of -6.5°C per 1000m of altitude increase. It's used in many fields, such as aeronautics, meteorology, and atmospheric science, as a reference for the calculation of performance and safety of aircrafts, weather forecasting and atmospheric pollution.*

Outgassing refers to the release of gases, usually in the form of volatile compounds, from a material or substance. This can occur due to a variety of reasons such as heating, pressure changes, or the presence of a vacuum. Outgassing can be a problem in many different fields, such as materials science, construction, packaging, and space travel. In space applications, outgassing can cause problems such as instrument malfunctions or the adhesion of materials. To prevent these issues, materials used in space-related applications are often specially treated to reduce or eliminate the release of gases.*

* Outgassing properties of a few materials (after 1 hour):      Source: Leybold

Outgassing is the phenomenon of embedded gasses escaping from materials, akin to paint drying. Higher ambient temperature and/or lower ambient atmospheric pressure usually increases the rate at which the gases escape. Testing of assemblies destined for high altitude and/or space is performed in vacuum chambers which often include control of temperature, acceleration and impact, and irradiation.

* Generated by Chat GPT AI