Calculator
Enter a measured value, pick its unit, then set temperature and pressure. Optional fields help estimate mass in a room or sample.
Formula used
This tool treats nitrogen dioxide as an ideal gas and uses the ideal gas law to switch between volume fraction and mass concentration.
| Molar density | n/V = P / (R·T) |
|---|---|
| From ppm to µg/m³ | µg/m³ = ppm · (P / (R·T)) · MW |
| From µg/m³ to ppm | ppm = (µg/m³) · (R·T) / (P · MW) |
| From ppm to mol/m³ | mol/m³ = (ppm · 10⁻⁶) · (P / (R·T)) |
Where P is pressure in Pa, T is temperature in Kelvin, R is 8.314462618 Pa·m³/(mol·K), and MW is molecular weight in g/mol.
How to use this calculator
- Enter the measured nitrogen dioxide value and select its unit.
- Set the temperature and pressure from the sampling environment.
- Keep molecular weight at default unless using a different gas.
- Optional: add a limit to get a pass/fail comparison.
- Optional: add room or sample volume to estimate total mass.
- Press Calculate to view results, then export CSV or PDF.
Example data table
These rows use 25°C and 101.325 kPa with NO₂ molecular weight. Values are approximate and for demonstration only.
| Scenario | Value | Unit | Temp (°C) | Pressure (kPa) | Approx µg/m³ |
|---|---|---|---|---|---|
| Urban roadside | 60 | ppb | 25 | 101.325 | 112.83 |
| City background | 30 | ppb | 25 | 101.325 | 56.41 |
| Suburban | 15 | ppb | 25 | 101.325 | 28.21 |
| Near ventilation exhaust | 150 | ppb | 25 | 101.325 | 282.06 |
| Indoor cooking peak | 200 | ppb | 25 | 101.325 | 376.09 |
Why unit conversion matters in NO₂ work
Field monitors, passive badges, and lab methods report nitrogen dioxide in different units. You may receive ppb from ambient sensors, ppm from industrial logs, or µg/m³ from reports. Urban background values are often single‑digit to tens of ppb, while roadside peaks may exceed 50–100 ppb near traffic. A consistent unit set prevents transcription errors, supports trend charts, and keeps exposure summaries comparable across sites and seasons. A quick check is ppb ÷ 1000 = ppm.
Temperature and pressure sensitivity
Mass concentration depends on air density. This calculator uses the ideal gas relationship P/(R·T) to adjust for sampling conditions. At 25°C and 101.325 kPa, 1 ppm NO₂ is about 1.88 mg/m³ (≈1880 µg/m³), so 10 ppb is roughly 18.8 µg/m³. At 25°C, the standard molar volume is about 24.45 L/mol, which explains the common ppm‑to‑mg/m³ shortcut. Lower temperatures raise µg/m³ for the same ppm, while lower pressure reduces it proportionally.
Interpreting results against limits
Limits are commonly expressed as µg/m³ or ppm. Enter your target value and unit to receive a direct pass/fail check using the same temperature and pressure assumptions. For audits, record the limit unit, conversion settings, and the calculated ppm and µg/m³ so reviewers can replicate the comparison. If your policy uses averaging periods, document whether the input is a peak, hourly mean, or shift mean.
Estimating mass in rooms and samples
Concentration describes “per volume,” but many workflows need total mass. Room mass is estimated as mg/m³ × room volume (m³), useful for ventilation planning or emission screening. Sample mass is estimated as µg/m³ × sampled volume (m³), supporting sorbent capacity checks and gravimetric expectations. A 20 L grab sample is 0.020 m³; multiply by µg/m³ to estimate total micrograms captured.
Reporting and quality checks
Use the exported CSV for spreadsheets and the PDF for sign‑off packages. Verify inputs: sensor value, unit, temperature, pressure, and molecular weight (NO₂ default 46.0055 g/mol). If results look unusual, recheck unit selection, confirm pressure units, and compare with a second measurement or blank‑corrected lab result.
FAQs
1) Which unit should I enter if my instrument reports NO₂ in ppb?
Select ppb and enter the displayed value. The tool will convert to ppm, µg/m³, mg/m³, and mol/m³ using your temperature and pressure.
2) Why does the same ppm become different µg/m³ values?
µg/m³ depends on air density. Higher pressure increases mass per cubic meter, and higher temperature decreases it. ppm is a volume fraction, so the conversion must use P and T.
3) Is the molecular weight fixed for nitrogen dioxide?
For NO₂, the molecular weight is 46.0055 g/mol. Only change it if you are intentionally converting a different gas with the same workflow.
4) How accurate is the ideal gas approach?
For typical air-monitoring ranges and near-ambient conditions, the ideal gas assumption is a practical approximation. At very high pressures, unusual temperatures, or reactive mixtures, consult a detailed gas model or method guidance.
5) Can I use this to check compliance with a standard?
You can compare against any limit you enter. Ensure the averaging time and measurement method match the limit definition, and keep the same temperature and pressure assumptions used for your official reporting.
6) What do the room and sample volume options represent?
They estimate total NO₂ mass in a space or captured air volume. Room mass uses mg/m³ × m³, and sample mass uses µg/m³ × sampled m³, helping you connect concentration to total loading.
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