SME
Environmental Engineering · Problem type
Parts per million to micrograms per cubic meter
Use this for “The SO₂ standard is 0.075 ppm. What is it in μg/m³ at 25 °C and 1 atm?”
This is an example. Type your own values to start a new problem.
Cₘ (μg/m³)
=
Cᵥ (ppm)
×
M (g/mol)
×
1000
24.45
Formulas
Cₘ
=
Cᵥ
×
M
×
1,000
24.45
196.5031
=
0.075
×
64.06
×
1,000
24.45
Assumptions
•
ppm here is by volume (ppmv): moles of the gas per million moles of air.
•
Air at 25 °C and 1 atm, where 1 mol of an ideal gas fills 24.45 L.
•
M is the gas’s own molar mass (SO₂ 64.06, NO₂ 46.01, CO 28.01 g/mol).
Step-by-step
WE KNOW
Cᵥ = 0.075 ppm, M = 64.06 g/mol
FIND
mass concentration (Cₘ)
Step 1 · Find mass concentration (Cₘ)
Use Cₘ = Cᵥ × M × 1,000 ÷ 24.45
Cᵥ
×
M
gives
the
micrograms
of
gas
in
1
mol
of
air,
which
fills
24.45
L;
1
m³
holds
1000
L.
Cₘ
=
0.075
×
64.06
×
1,000
24.45
Cₘ
=
4.8045
×
1,000
24.45
Cₘ
=
4,804.5
24.45
Cₘ
=
196.5031
μg/
m
3
Check
Put the numbers back in. Both sides should match.
196.5031
=
0.075
×
64.06
×
1,000
24.45
✓
Topic check
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