Multi-pollutant air pollution is a common issue in China, where multiple pollutants reach high levels at the same time. The current air quality index (AQI) used in China only considers the highest pollutant level, not the combined effects of multiple pollutants. A new study compared three air quality indices in six Chinese cities and found that the current AQI underestimates health risks from multi-pollutant exposure. The new indices, AAQI and HAQI, show higher risk levels on days when multiple pollutants exceed safety standards. This suggests that stricter actions should be taken during high pollution events, especially for vulnerable groups like children and the elderly. The study also found that the new indices are sensitive to certain factors, such as pollutant constants and threshold values.