PM2.5 is a common particulate pollutant, widely distributed in the air, after being inhaled, part of it adheres to the airway wall to form carbon end deposits, and part of it floats down to the most distal alveoli to be wrapped up by macrophages or lymphocytes to form substantial nodules of different shapes, the most typical ones are triangular, square, trapezoidal, and round-like nodules located in the lower lobe of both lungs under the pleura, such nodules are harmless nodules for human and animals. They do not turn into lung cancer, do not grow, are carried for life, and are ineffective for any medication. We call them intrapulmonary lymph nodules or sterile chronic granulomas. These nodules are the most common lesions found on CT physical exams, and patients are very anxious because the nodules are only 2-5mm in size and cannot be seen on chest films in previous years, making people believe that they are a recent condition, when in fact they have been there for several years and happen to be detected by CT, inexperienced surgeons may mistake them for lung cancer, and patients may suffer from surgery.