Submitted:
18 December 2025
Posted:
18 December 2025
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Abstract
Keywords:
1. Introduction
2. Materials and Methods
2.1. Composition of Smog
2.2. Role of Temperature Inversion
2.3. Experimental Set-up
3. Results and Discussion
3.1. Influence of Weather and Emissions on AQI
3.2. Effect of Emission Composition
4. Mitigation Strategies and Solutions
5. Conclusions
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
| ANN | Artificial Neural Network |
| AQI | Air Quality Index |
| AR | Additive Regression |
| AURI | Acute Upper Respiratory Infections |
| BRT | Boosted Regression Trees |
| GAM | Generalized Additive Model |
| GBR | Gradient Boosting Regression |
| GRU | Gated Recurrent Unit Network |
| GWO | Grey Wolf Optimizer |
| LSTM | Long Short-Term Memory Network |
| REPT | Reduced Error Pruning Tree, |
| RF | Random Forest |
| RNN | Recurrent Neural Network |
| RT | Random Tree |
| RSS | Random Subspace |
| SVM | Support Vector Machine |
| SVR | Support Vector Regression |
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| Reference | Location | Scope | ML Model used | Findings |
|---|---|---|---|---|
| [22] | Delhi, India | Air quality monitoring using temp, humidity , wind for PM only | RF and Adaboost Models | Accuracy for Adaboost reaches 98.24% which is highest among all the models |
| [23] |
Lahore, Pakistan | Analyze pollutants to determine main cause for respiratory diseases | RF, XGBoost, Logistic Regression Models | The models had been identified to be very accurate, F1-score, and ROC-AUC measures. PM 2.5 and PM 1.0 found to be main cause of respiratory and other health problems |
| [24] | Punjab, Pakistan | Predictive model to forecast PM 2.5 and PM10 | ANN Model | Model’s high accuracy (> 90%) in predicting air quality indices and identifying critical thresholds for smog |
| [25] | Delhi, India | Predictive model for PM 2.5 forecast | RF, ANN, SVM Models | RF gave the best results for both training and testing. Testing accuracy (R2 = 0.842, RMSE = 0.06, and MAE = 0.045) |
| [26] | Delhi, India | Predictive method to examine and measure how stubble burning affects air pollution | Gradient Boosting Regression Model | AQI change per 1% fire count increase varies between 0.08% and 0.38%, showing a consistent but varying impact. |
| [27] | Hong Kong | Develop machine learning-based models for predicting hourly street-level PM2.5 and NOx concentrations | RF, BRT, SVM, XGBoost, GAM, and Cubist Models | RF outperformed other MLAs with ten-fold cross validation (CV) R2 values higher than 0.81 and 0.62 for PM2.5 and NOx predictions, respectively. |
| [28] | Macau | Develop a dependable air pollution prediction model for Macau | RF, SVR, ANN, RNN, LSTM, GRU Models | The RF model best predicted PM10, PM2.5, NO2, and CO concentrations with the highest PCC and KTC in a daily air pollution prediction |
| [29] | Eastern China | Predictive model for daily NO2 concentrations | XGBoost Model | R2 of 0.75 and root-mean-square error (RMSE) of 9.11 μg/m3 |
| [30] | Lahore, Pakistan | Predictive model for Aerosol optical depth (AOD) used to estimate the extent of air pollution | SVR and SVR-GWO Models | SVR-GWO model (RMSE = 0.07, MAE = 0.06, R2=0.6) performed better than others |
| [31] | Dhaka, Bangladesh | Prediction model for the ground-level PM2.5 concentrations | RT, AR, REPT, RSS Models | The RSS model is the most suitable model for PM2.5 prediction, as shown by the lower MAE and RMSE values and a higher R2 value |
| [32] | Almaty, Kazakhstan | Prediction model for the ground-level PM2.5 concentrations | RNN, LSTM Models | LSTM is better at forecasting for 90 days (MAE = 2.0,MAPE = 11.57, RMSE = 2.18) |
| [33] | Visakhapatnam, India, | Prediction model for AQI | RF, Catboost, Adaboost, and XGBoost Models | Catboost and RF models performed best, howing maximum correlations of 0.9998 and 0.9936 |
| Pollutant | Primary Sources | Contribution to Smog |
|---|---|---|
| Nitrogen Oxides (NOx) | - Vehicle exhaust (cars, trucks, buses) - Power plants and thermal electricity generation - Industrial combustion processes |
NOx reacts with volatile organic compounds (VOCs) under sunlight to form ozone and secondary PM. Major contributor to photochemical smog. |
| Particulate Matter (PM2.5, PM10) | - Vehicle exhaust (especially diesel) - Industrial emissions (cement, brick kilns, steel) - Construction dust and road dust - Biomass burning (wood, crop residue) |
Causes haze, reduced visibility, and respiratory diseases. PM2.5 penetrates deep into the lungs. |
| Volatile Organic Compounds (VOCs) | - Fuel evaporation and incomplete combustion from vehicles - Industrial solvents and chemical processes - Biomass burning |
VOCs react with NOx in sunlight to produce ozone and secondary organic aerosols, contributing to photochemical smog. |
| Sulfur Oxides (SO₂, SOₓ) |
- Coal and oil combustion in power plants - Industrial furnaces - Refineries |
Reacts in the atmosphere to form sulphate aerosols, contributing to acid smog and haze. |
| Ozone (O₃) | - Secondary pollutant formed by NOx + VOCs under sunlight | Not emitted directly, forms in the troposphere during photochemical reactions. High ozone concentrations irritate eyes, lungs, and worsen respiratory diseases. |
| Carbon Monoxide (CO) | - Incomplete combustion from vehicles, industries, and biomass burning | Reduces oxygen delivery in the body; indirectly contributes to photochemical smog formation. |
| Carbon Dioxide (CO₂) | - Fossil fuel combustion - Industrial processes |
Weak direct contribution to smog, but important greenhouse gas; acts as a tracer for emissions. |
| Model | Key Hyperparameters / Architecture | Values / Settings |
|---|---|---|
| Random Forest Regressor | Number of Trees (n_estimators) | 100 |
| Minimum Samples per Leaf (min_samples_leaf) | 1 | |
| Splitting Criterion | Mean Squared Error | |
| Random Seed | 42 | |
| XGBoost Regressor | Number of Trees (n_estimators) | 100 |
| Learning Rate (eta) | 0.1 | |
| Maximum Depth (max_depth) | 3 | |
| Subsample Fraction (subsample) | 1 | |
| Random Seed | 42 |
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