Question

Based on the "national ambient air quality objectives", the acceptable hourly average concentration of carbon monoxide (CO) is 35mg/m^3. Find the acceptable concentration of CO in ppm if the temperature is -30'C and pressure is 0.92 atm. Express the concentration as a percent by volume.

Answer 1

Given :

Concentration : 35 mg / m^3

Pressure in atm = 0.92 atm

T = - 30 deg C

Pressure in mmHg = 760 / 0.92   mmHg

The formula for ppm at NTP

= (mg per m³) (24.46 g per mol)/ MW

Where 24.46 is the molar volume at 25 degree C. and 760 mmHg

MW is the molecular weight of CO

Ppm NTP = ( 35 mg / m^3) ( 24.46 L / mol) / 28.010 g / mol

= 5.57 ppm

At T = -30 deg C

= (ppm at NTP x ( 760 /p ) x ( T / 298)

= 5.57 ppm x ( 760 / (760/0.92 ) ) x ( ((-30 deg C + 273) / 298 )

= 5.20 ppm

Conversion from ppm to volume percent

= 5.20 x 0.0001 %

= 0.000520 %