The air quality in Shanghai is getting better overall, but the mix of pollutants like PM2.5, O3, and NO2 is becoming more complex. A new air quality index model (NMAQI) based on four pollutants (PM2.5, SO2, NO2, and O3) shows that considering multiple pollutants together gives a more accurate picture of air quality than just looking at one. This new model can better predict high pollution levels in urban areas, helping to protect people from breathing in harmful pollutants.