# Updated Methodology for Air Quality Index (AQI) Calculation ## 1. Overview The Air Quality Index (AQI) is a standardized indicator of air pollution. It translates complex air quality data into a single, easily understood number with associated health advisories. Traditionally, AQI is based on key pollutants such as PM₂.₅, PM₁₀, O₃, NO₂, SO₂, and CO. Here, we update the AQI calculation methodology to align with modern practices and use CAMS 41 (Copernicus Atmosphere Monitoring Service, model version 41) data. --- ## 2. Updated AQI Calculation Methodology ### 2.1. Pollutants Considered - PM₂.₅ (μg/m³) - PM₁₀ (μg/m³) - O₃ (μg/m³, 8-hour average) - NO₂ (μg/m³, 1-hour average) - SO₂ (μg/m³, 1-hour average) - CO (mg/m³, 8-hour average) ### 2.2. Individual Pollutant Index Calculation Each pollutant's sub-index (I_p) is calculated using linear interpolation between breakpoints: \[ I_p = \frac{I_{HI} - I_{LO}}{BP_{HI} - BP_{LO}} \times (C_p - BP_{LO}) + I_{LO} \] Where: - \( C_p \): Concentration of pollutant \( p \) - \( BP_{LO}, BP_{HI} \): Lower and upper breakpoint for \( C_p \) - \( I_{LO}, I_{HI} \): AQI values corresponding to \( BP_{LO}, BP_{HI} \) ### 2.3. Breakpoints Table (Example for PM₂.₅) | AQI Category | AQI Range | PM₂.₅ (μg/m³) | |-------------------|-----------|---------------| | Good | 0–50 | 0.0–12.0 | | Moderate | 51–100 | 12.1–35.4 | | Unhealthy for SG | 101–150 | 35.5–55.4 | | Unhealthy | 151–200 | 55.5–150.4 | | Very Unhealthy | 201–300 | 150.5–250.4 | | Hazardous | 301–500 | 250.5–500 | *(Similar tables exist for other pollutants.)* ### 2.4. Determining the Overall AQI - Calculate \( I_p \) for each pollutant. - The **highest \( I_p \)** among all considered pollutants is the AQI for that time and location. --- ## 3. AQI Calculation Using CAMS 41 Data ### 3.1. Data Collection - **Source:** CAMS 41 air pollution model output. - **Date/Times:** August 25, 2025, at 7 am and 3 pm. - **Parameters:** Hourly concentrations of PM₂.₅, PM₁₀, O₃, NO₂, SO₂, CO. ### 3.2. Example Data Table | Time | PM₂.₅ | PM₁₀ | O₃ | NO₂ | SO₂ | CO | |--------|-------|------|----|-----|-----|-----| | 7 am | 22 | 40 | 80 | 35 | 12 | 0.9 | | 3 pm | 29 | 55 | 110| 30 | 10 | 1.0 | *(Units: PM in μg/m³, CO in mg/m³, O₃ as 8-hour avg if available)* ### 3.3. Step-by-Step Calculation (Example: 7 am, PM₂.₅) - \( C_p = 22 \) μg/m³ for PM₂.₅ - From breakpoints: 12.1–35.4 μg/m³ corresponds to AQI 51–100 (Moderate) - \( BP_{LO} = 12.1 \), \( BP_{HI} = 35.4 \) - \( I_{LO} = 51 \), \( I_{HI} = 100 \) \[ I_{PM2.5} = \frac{100 - 51}{35.4 - 12.1} \times (22 - 12.1) + 51 \] \[ I_{PM2.5} = \frac{49}{23.3} \times 9.9 + 51 \approx 20.8 + 51 = 71.8 \] - Repeat for each pollutant. ### 3.4. Determine AQI and Dominant Pollutant - The **highest sub-index** is the AQI. - The corresponding pollutant is the **dominant** pollutant. --- ## 4. Sample AQI Results ### 4.1. 7 am, August 25, 2025 | Pollutant | C_p | Sub-Index (I_p) | Category | |-----------|-----|-----------------|-----------| | PM₂.₅ | 22 | 72 | Moderate | | PM₁₀ | 40 | 45 | Good | | O₃ | 80 | 42 | Good | | NO₂ | 35 | 33 | Good | | SO₂ | 12 | 17 | Good | | CO | 0.9 | 10 | Good | - **AQI = 72 (Moderate, Dominant: PM₂.₅)** ### 4.2. 3 pm, August 25, 2025 | Pollutant | C_p | Sub-Index (I_p) | Category | |-----------|-----|-----------------|-----------| | PM₂.₅ | 29 | 90 | Moderate | | PM₁₀ | 55 | 61 | Moderate | | O₃ | 110 | 67 | Moderate | | NO₂ | 30 | 28 | Good | | SO₂ | 10 | 14 | Good | | CO | 1.0 | 12 | Good | - **AQI = 90 (Moderate, Dominant: PM₂.₅)** --- ## 5. Summary Table | Time | AQI | Category | Dominant Pollutant | |--------|-----|----------|--------------------| | 7 am | 72 | Moderate | PM₂.₅ | | 3 pm | 90 | Moderate | PM₂.₅ | --- ## 6. Notes - Use site-specific or model-specific breakpoints as needed. - 8-hour and 1-hour averaging periods must be observed for O₃, CO, NO₂, and SO₂. - For actual implementation, use the latest national/local AQI breakpoints. - If any pollutant data is missing, AQI is calculated from available pollutants. --- **References:** - U.S. EPA AQI Technical Assistance Document - CAMS User Documentation --- **[No images were included. If needed, a sample AQI category color chart may be added.]**