A method and apparatus for enhanced THz radiation coupling to molecules, includes the steps of depositing a test material near the discontinuity edges of a slotted member, and enhancing the THz radiation by transmitting THz radiation through the slots. Sootblowers of the recovery boiler are divided into sootblowing groups, and a sootblowing interval is determined for the sootblowers. 001 to 5 parts by mass of an antioxidant and 0.