The International System of Units (SI) is founded, according to the National Institute of Standards and Technology (NIST) on the 7 Base Units. Quoting directly from NIST: The SI is founded on seven SI base units for seven base quantities assumed to be mutually independent, as given in Table 1. With the exception of electric current, amount of substance and luminous intensity, the other four are frequently mentioned in relationship to the measurement of airflow rate. However, the amount of substance is also present. Because it is referred to as, the mole it is frequently overlooked as something only related to Chemistry.

The US EPA requires that the concentration of airborne particulate matter referred to as PM10 be reported at EPA Standard Conditions, which is a temperature of 25°C (298.15°K) and a Barometric Pressure of 760 mm of Hg (Sea Level). The official EPA flow rate is 16.67 lpm. This odd flow rate is derived from 1 m3/hr. Here are all the elements of an “amount of substance.” Since it is a flow rate, time is involved as well as Temperature.

A Qs (Q standard) flow rate of 16.67 lpm may be converted to Moles per min.

Using the ideal Gas Law one can calculate the volume of a mole of air at STP.

PV = nRT

Where:
P = Pressure in Atmospheres
V = Volume in Liters
n = Number of Moles of gas
R = Gas Constant =0.0821 L atm K-1 mol-1
T= Temperature in degrees Kelvin

Rearranging terms:

V=nRT/P

V=1*0.0821*298.15 = 24.48 liters per mole of air at STP 760/25 (EPA)

The EPA flow rate for PM10 sampling is 16.67 lpm at 760/25 (1 m3/hr). Therefore, this value may be expressed in moles/min:

(Liters/min)/(Liters/Mole) = 16.67/24.48 = 0.681 Moles/min as the EPA flow rate for PM10 sampling.

Therefore, any calibrator which measures air flow plus atmospheric temperature and pressure and goes on to express the flow rate as Q standard (Qs), could be set to read in Moles/second, two of the SI Base units.