Ozone pollution in Handan has been getting worse, especially in the summer of 2018. Scientists used a special indicator called H2O2/HNO3 to study how sensitive Handan is to ozone. They found that this indicator worked better than others and showed that different areas in Handan have different levels of sensitivity to ozone pollution. Some areas are more affected by certain pollutants than others. The study also adjusted the ranges for different indicators to better understand ozone pollution in Handan.