In 2014, Chengdu experienced significant air quality challenges, recording 125 days of pollution according to the Air Quality Index (AQI) standards. This total included 93 days of light pollution, 22 days of moderate pollution, and 10 days of heavy pollution. Despite these figures, the city also saw 148 days with good air quality and 16 days classified as excellent. The persistent haze was largely attributed to the city's location in the Sichuan Basin, where bowl-shaped topography traps industrial emissions and vehicle exhaust, particularly during the winter months. During a severe episode in late January 2014, the city faced a ten-day period of continuous heavy pollution, with PM10 concentrations reaching as high as 562 micrograms per cubic meter. Progress has been noted since then, as Chengdu was ranked the 15th most polluted city in China that year, leading to increased local and national efforts to monitor and reduce particulate matter levels.