Practitioner tool
ppm to lb/hr Converter (Stack Concentration to Mass Rate)
Convert a stack gas concentration in ppmv to a mass emission rate in lb/hr, or back, using stack flow and molecular weight. Shows every step.
Stack tests and CEMS report concentrations in parts per million by volume; permits usually limit pounds per hour. This converter uses the ideal gas law at the standard conditions you choose.
ppm to lb/hr calculator
Same basis as the concentration (dry or wet).
- Mass rate
- 1.7908 lb/hr
- At 8,760 hr/yr
- 7.8439 tons/yr
Steps
- Molar volume = 10.7316 × (68 + 459.67) ÷ (29.92 × 0.4911541) = 385.34 scf/lb-mol
- lb/hr = ppm × 10⁻⁶ × MW × flow × 60 ÷ molar volume = 50 × 10⁻⁶ × 46.006 × 5,000 × 60 ÷ 385.34 = 1.7908 lb/hr
Questions engineers ask
Why does the standard temperature change the answer?
A pound-mole of gas occupies more volume at a higher temperature, so the same ppm in the same standard flow represents a slightly different mass. Use the standard conditions your rule or test method defines, and keep the flow on the same standard.
Can I use actual (acfm) flow?
Not directly. Convert actual flow to standard flow with the stack temperature, pressure, and (for a dry basis) moisture first. The concentration and flow must share the same basis.
What molecular weight do I use for VOC?
It depends on how the rule expresses VOC, for example as carbon, as propane, or as the compound measured. Check the rule and the test method.
More converters: O2 correction, ppm to lb/MMBtu, lb/MMBtu to lb/hr, g/hp-hr to lb/hr, lb/hr to tons/yr, ppm to mg/m³, Wet to dry basis.
How this works
Formula
- lb/hr = ppmv × 10⁻⁶ × MW × Q(scfm) × 60 ÷ V̂
- V̂ (scf/lb-mol) = R × T(°R) ÷ P(psia), with R = 10.7316 psia·ft³/(lb-mol·°R)
Before you rely on the number
- Concentration and flow must be on the same basis. Dry concentrations (ppmvd) go with dry standard flow (dscfm); wet with wet.
- Standard conditions differ between rules and programs. Use the temperature and pressure your permit, rule, or test method defines.
- Many rules express NOx as NO2 when converting to mass. Check the rule that applies.
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