2.1. Study design and subject recruitment
In this study, the randomized single-blind crossover intervention design was adopted. 24 SCAD patients were recruited, and the intervention trial was conducted in their residences, with air purifiers placed in their main activity space. Air purifiers equipped with HEPA filter were “real-intervention,” with a clean air delivery rate of 500 mArrangement of the intervention.The subjects were recruited from 3 community-level (or above) general hospitals in Beijing, who were clinically diagnosed with SCAD according to the diagnostic requirements of During the intervention, the individual exposure to PM