Stack Emission Rate Calculator
Mass emission rate from stack testing data.
About this calculator
This calculator converts raw stack testing data — flow rate and pollutant concentration — into the mass emission rates that permits and regulatory thresholds are actually written in terms of. It first converts your stack flow (entered in dry standard cubic feet per minute) to metric units, then multiplies by the measured concentration to get an uncontrolled emission rate in grams per second: E = Q × C. That uncontrolled rate is then reduced by whatever control device efficiency you specify (a scrubber, baghouse, or similar), giving the net emission rate actually leaving the stack, E_net = E × (1 − η). The calculator reports this net rate in both g/s and lb/hr (using the 7.937 lb/hr per g/s conversion), then extrapolates to tons per year using your specified annual operating hours — useful because most air permit thresholds are annual, not instantaneous.
It also back-calculates the uncontrolled annual total and the difference between the two, showing how many tons per year the control device is actually capturing. Two threshold flags are included as quick reference points: 10 tons/yr is a common major-source cutoff for a single hazardous air pollutant (HAP), and 25 tons/yr for total HAPs or many criteria pollutants — but these are typical figures, not universal; actual applicability depends on your specific permit, pollutant, and jurisdiction, so treat the flags as a screening signal rather than a permitting determination. Also note the calculator assumes your input concentration is already the representative, time-averaged value from valid stack testing — it does nothing to account for test method uncertainty or non-steady-state operating conditions.
Inputs
Results
Net emission rate (g/s)
0.01
How to Use This Calculator
- Enter Stack flow rate (dscfm), Pollutant concentration (mg/m³), and Control device efficiency (%).
- Set Annual operating hours.
- Review the Net emission rate (g/s) result.
- Use Net emission rate (lb/hr) and Annual emissions (tons/yr) to inform your decision.
How the result changes with Control device efficiency (%)
| Control device efficiency (%) | Net emission rate (g/s) |
|---|---|
| 45 | 0.06 |
| 68 | 0.04 |
| 100 | 0 |
What each input means
- Stack flow rate (dscfm)
- Dry standard cubic feet per minute of exhaust gas at standard conditions.
- Pollutant concentration (mg/m³)
- Measured pollutant concentration at the stack in mg per cubic meter.
- Control device efficiency (%)
- Removal efficiency of scrubber, baghouse, or other control device.
- Annual operating hours
- Hours per year the source operates. 8760 = continuous.
What each result means
- Net emission rate (g/s)
- Pollutant emission rate after control device, in grams per second.
- Net emission rate (lb/hr)
- Same emission rate expressed in pounds per hour.
- Annual emissions (tons/yr)
- Total controlled emissions over operating hours per year.
- Uncontrolled rate (g/s)
- Emission rate before control device.
- Uncontrolled annual (tons/yr)
- What annual emissions would be without the control device.
- Pollutant removed (tons/yr)
- Amount of pollutant captured by the control device annually.
- Exceeds HAP major threshold?
- 1 if annual emissions ≥ 10 tons/yr (major source for hazardous air pollutants).
- Exceeds criteria major threshold?
- 1 if annual emissions ≥ 25 tons/yr (major source for criteria pollutants).
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersStack flow rate (dscfm) = 5000, Pollutant concentration (mg/m³) = 50, Control device efficiency (%) = 90, Annual operating hours = 8000 = 4 input(s) provided
- Calculate Net emission rateNet emission rate = uncontrolledGS * (1 - eta)0.0118 = 0.0118
- Calculate Net emission rateNet emission rate = netEmissionGS * 7.9370.094 = 0.094
- Calculate Annual emissionsAnnual emissions = (netEmissionLbHr * operatingHoursPerYear) / 20000.37 = 0.37
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why do I need to enter both control device efficiency and concentration — isn't the measured concentration already the net emission?
It depends on where in the stack you measured. This calculator treats your entered concentration as the uncontrolled (pre-control) value and multiplies flow rate by that concentration to get the uncontrolled rate, then applies your control efficiency percentage to derive the net rate actually leaving the stack (E_net = E × (1 − η)). If your concentration reading was actually taken downstream of the control device, set control efficiency to 0 so the calculator doesn't apply a second reduction.
Why does annual operating hours matter so much for the tons/yr figures?
The instantaneous rates (g/s, lb/hr) only describe emissions while the source is running, but permit thresholds like the 10 and 25 tons/yr flags are annual totals. The calculator multiplies your net lb/hr rate by operating hours per year and divides by 2,000 to get tons/yr, so a source running 4,000 hours/yr instead of the continuous 8,760-hour maximum will show roughly half the annual emissions at the same instantaneous rate.
Are the 10 and 25 tons/yr threshold flags a guarantee of my permit status?
No — these are commonly cited reference points (10 tons/yr for a single hazardous air pollutant, 25 tons/yr for total HAPs or many criteria pollutants) but actual major-source applicability depends on your specific pollutant, permit type, and jurisdiction. Treat the flags as a screening signal that tells you when to look more closely at your permit obligations, not as the regulatory determination itself.
What does the 'pollutant removed' output represent, and where does it come from?
It's the difference between the uncontrolled annual tons/yr (what emissions would be with no control device at all) and the net annual tons/yr (what's actually being emitted after control), both computed from the same measured concentration and flow rate. This figure shows how many tons per year your scrubber, baghouse, or other control device is actually capturing, which is useful for demonstrating control device performance separately from the raw emission numbers.
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