Search results
Results from the WOW.Com Content Network
Atmospheric pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m 3, μg/m 3, etc.) at sea level will decrease with increasing altitude because the atmospheric pressure decreases with increasing altitude. The change of atmospheric pressure with altitude can be obtained from this equation: [2]
mg/m 3 = milligrams of pollutant per cubic meter of air at sea level atmospheric pressure and T: ppmv = air pollutant concentration, in parts per million by volume T = ambient temperature in K = 273. + °C 0.082057338 = Universal gas constant in L atm mol −1 K −1: M = molecular mass (or molecular weight) of the air pollutant
As chloride mg/m2 As sodium chloride μg/cm2 As sodium chloride mg/m2 As mixed salts μg/cm2 As mixed salts mg/m2 1 0.1 0.36 3.6 0.6 6 0.5 5 5 0.5 1.8 18 3 30 2.5 25 10 1 3.6 36 6 60 5 50 20 2 7.2 72 12 120 10 100
To calculate the density of air as a function of altitude, one requires additional parameters. For the troposphere, the lowest part (~10 km) of the atmosphere, they are listed below, along with their values according to the International Standard Atmosphere , using for calculation the universal gas constant instead of the air specific constant:
The most common international unit for the MVTR is g/m 2 /day, or "metric perm". In the USA, g/100in 2 /day is also in use, which is 0.064516 (approximately 1/15) of the value of g/m 2 /day units. Typical rates in aluminium foil laminates may be as low as 0.001 g/m 2 /day, whereas the rate in fabrics can measure up to several thousand g/m 2 /day.
Get AOL Mail for FREE! Manage your email like never before with travel, photo & document views. Personalize your inbox with themes & tabs. You've Got Mail!
A variant of the metric perm is used in DIN Standard 53122, where permeance is also expressed in grams per square meter per day, but at a fixed, "standard" vapor-pressure difference of 17.918 mmHg. This unit is thus 17.918 times smaller than a metric perm, corresponding to about 0.084683 of a U.S. perm.
(mol/s)/(m 2 ·mol/m 3) = m/s; Note, the units will vary based upon which units the driving force is expressed in. The driving force shown here as ' ' is expressed in units of moles per unit of volume, but in some cases the driving force is represented by other measures of concentration with different units.