Conversion of CO Concentration from ppm to μg/m³ and mg/m³

Question

A sample of air analyzed at 0°C and 1 atm pressure is reported to contain 15 ppm of Carbon Monoxide (CO). Determine the equivalent CO concentration in:

• Micrograms per cubic meter (μg/m³)
• Milligrams per cubic meter (mg/m³)

Given Data

Parameter	Value
CO Concentration	15 ppm
Molecular Weight of CO	28 g/mol
Temperature	0°C
Pressure	1 atm
Molar Volume at STP	22.4 L/mol

Formula Used

μg/m³ = (ppm × Molecular Weight × 10³) / 22.4

Step 1: Calculate Concentration in μg/m³

μg/m³ = (15 × 28 × 10³) / 22.4

μg/m³ = 420000 / 22.4

μg/m³ = 18,750

Step 2: Convert μg/m³ to mg/m³

Since:

1 mg = 1000 μg

mg/m³ = 18,750 / 1000

mg/m³ = 18.75

Final Answer

CO Concentration = 18,750 μg/m³

CO Concentration = 18.75 mg/m³

Shortcut Formula for Examinations

mg/m³ = (ppm × Molecular Weight) / 22.4

mg/m³ = (15 × 28) / 22.4

mg/m³ = 18.75 mg/m³

Exam Tip: At STP (0°C and 1 atm), remember:

mg/m³ = (ppm × Molecular Weight) / 22.4

Author: Mohan Dangi

Prepared for Environmental Engineering, Air Pollution Control, GATE, SSC JE, State Engineering Services and Civil Engineering Students.