Nitrogen Dioxide (NO2) AQI Calculator

These examples show typical NO2 values and resulting AQI ranges using this method.

This calculator converts your NO2 concentration into an Air Quality Index value using linear interpolation between concentration breakpoints:

• C_p is the (truncated) NO2 concentration in ppb.
• C_Lo, C_Hi are the bounding breakpoints that bracket C_p.
• I_Lo, I_Hi are the AQI values at those breakpoints.

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If you enter µg/m³, the calculator converts to ppb using an ideal-gas scaling based on temperature and pressure:

ppb = (µg/m³) × (24.45 / MW) × (T(K) / 298.15) × (101.325 / P(kPa))   where MW = 46.01 g/mol for NO2.

1. Enter your measured NO2 concentration and choose its unit.
2. If using µg/m³, set temperature and pressure for conversion accuracy.
3. Select your preferred rounding method for the final AQI.
4. Click Calculate AQI to show results above the form.
5. Use the CSV or PDF buttons to export the result block.

• This tool estimates a NO2 sub-index. Overall AQI is typically the maximum across pollutants.
• Use the daily maximum 1-hour NO2 concentration for daily reporting workflows.
• Conversion between µg/m³ and ppb depends on temperature and pressure.
• Regulatory reporting rules can vary by jurisdiction and agency.

1) Why NO2 matters in air quality reporting

Nitrogen dioxide (NO2) is a reactive gas strongly linked to combustion. Road traffic, diesel equipment, power generation, and industrial boilers are common contributors. Short-term NO2 peaks often occur during rush hours or under stable night-time conditions. Because the AQI communicates health risk clearly, converting measured NO2 to an index helps translate sensor numbers into actionable guidance.

2) Typical concentration ranges you may see

In many urban areas, hourly NO2 can range from 10–50 ppb on cleaner days and 50–100 ppb near busy corridors. During strong inversions or heavy congestion, 100–200 ppb is possible, especially close to traffic. Values above 300 ppb usually indicate severe local emissions, meteorological trapping, or an episodic event.

3) How the AQI is computed from breakpoints

This calculator uses linear interpolation between concentration breakpoints for the NO2 1‑hour sub-index. The method maps a truncated concentration (C_p) to an AQI value (I) within the corresponding band. For example, 0–53 ppb maps to AQI 0–50, and 54–100 ppb maps to AQI 51–100. The full set of bands extends up to 2049 ppb for AQI 500.

4) Why truncation and rounding options are provided

Many AQI workflows truncate pollutant concentrations to match how breakpoint tables are applied and to reduce false precision. After interpolation, the AQI is reported as an integer. The calculator offers nearest, floor, and ceil rounding so you can align outputs with internal reporting rules or conservative safety messaging.

5) Unit conversion and the role of temperature and pressure

Monitoring networks may report NO2 as ppb (volume mixing ratio) or µg/m³ (mass concentration). Converting between them depends on the ideal-gas relationship. At 25°C and 101.325 kPa, 1 ppb NO2 is about 1.88 µg/m³. Adjusting temperature and pressure refines the conversion, which matters for high-altitude sites and heat waves.

6) Interpreting categories for different audiences

“Good” and “Moderate” typically indicate low risk for the general population, while “Unhealthy for Sensitive Groups” highlights increased risk for asthma, COPD, and people with cardiovascular concerns. Higher categories suggest broader impacts and justify reducing outdoor exertion, minimizing roadside exposure, and improving indoor filtration where possible.

7) Data quality checks before you publish an AQI value

Use an hourly value that represents the daily maximum 1‑hour NO2 concentration for daily reporting. Confirm instrument calibration, check for negative or missing values, and compare nearby stations to identify outliers. For low-cost sensors, apply validation factors and note uncertainty in public dashboards.

8) Practical mitigation steps when NO2 is elevated

When NO2 AQI rises, reduce high‑intensity outdoor activity near traffic, shift exercise to midday when mixing is stronger, and choose routes away from major roads. Indoors, close windows facing busy streets and use high‑efficiency filtration. Communities can reduce spikes by managing diesel idling and improving traffic flow.

1) Is this the overall AQI for my area?

No. This tool estimates the NO2 sub-index. Many public AQI reports use the highest sub-index among multiple pollutants to represent overall conditions for the day.

2) Which NO2 value should I enter for daily reporting?

Use the daily maximum 1-hour NO2 concentration. That value best matches common daily AQI workflows and highlights short-term peak exposure risk.

3) Why do ppb and µg/m³ conversions change with weather?

They change because air density changes with temperature and pressure. Warmer air or lower pressure reduces density, shifting the relationship between mass concentration and mixing ratio.

4) What does “Unhealthy for Sensitive Groups” mean?

It means people with asthma, COPD, heart disease, older adults, and children may experience effects sooner. They should limit prolonged exertion, especially near roadways and busy intersections.

5) Why does the calculator truncate concentration before computing AQI?

Truncation aligns the concentration with how breakpoint tables are applied in many AQI methods and avoids overstating precision. The final AQI is still interpolated within the selected band.

6) Can I use this for minute-by-minute sensor data?

You can, but interpret results carefully. AQI is typically based on an hourly value. For real-time sensors, average to one hour to reduce noise and improve comparability to reference monitors.

7) Does this include indoor NO2 impacts?

The AQI method is designed for ambient outdoor reporting. Indoor NO2 can be influenced by gas cooking and ventilation. Use indoor measurements and health guidance separately, especially in poorly ventilated spaces.