NOx Emission Rate Calculator
Calculate Nitrogen Oxide emissions based on concentration and exhaust flow.
Calculation Results
Understanding NOx Emission Calculations
Nitrogen Oxides (NOx) are a group of highly reactive gases, primarily Nitrogen Dioxide (NO2) and Nitric Oxide (NO). Calculating the emission rate of these pollutants is essential for environmental compliance, air quality permitting, and industrial monitoring. The primary method for calculating mass emission rates from stationary sources involves measuring the concentration of the pollutant and the flow rate of the stack gas.
The Mass Emission Formula
The standard formula used to convert concentration (parts per million by volume) to a mass emission rate (pounds per hour) for NOx is:
E = C × Q × K
- E: Emission rate in pounds per hour (lb/hr).
- C: Pollutant concentration in parts per million (ppm).
- Q: Stack gas flow rate in dry standard cubic feet per minute (dscfm).
- K: Conversion factor. For NOx (calculated as NO2), the factor is 1.194 × 10-7.
The factor 1.194 × 10-7 is derived from the molecular weight of NO2 (46.01 lb/lb-mole) divided by the molar volume of an ideal gas at standard conditions (385.1 scf/lb-mole) and then multiplied by 60 minutes per hour and 10-6 to account for the ppm unit.
Example Calculation
Suppose a natural gas turbine is operating with a stack test showing a NOx concentration of 9 ppm and an exhaust flow rate of 120,000 scfm. If the plant operates 8,000 hours per year, the calculation would be:
- Hourly Rate: 9 ppm × 120,000 scfm × 60 × 0.0000001194 = 7.74 lb/hr.
- Annual Total: (7.74 lb/hr × 8,000 hours) / 2,000 = 30.96 tons per year.
Why Monitoring NOx Matters
NOx emissions contribute significantly to the formation of ground-level ozone and smog. Industrial facilities such as power plants, boilers, and internal combustion engines are required by agencies like the EPA to report these figures accurately. Using a NOx emission rate calculator helps engineers quickly verify if their equipment is meeting the limits set in their Title V or synthetic minor permits.