Persistence and Temporally Ordered Prediction of High-Concentration TMA and DMS Episodes in Incomplete Continuous Monitoring Data

This study quantified the persistence of high-concentration odor episodes in incomplete long-term continuous monitoring data and evaluated, in temporal order, the predictive value of information available at episode onset for subsequent persistence probability. Trimethylamine (TMA) and dimethyl sulfide (DMS), measured at 20 min intervals at three odor-emitting facilities from August 2022 to June 2023, were analyzed. Episodes with confirmed starts were constructed using facility- and compound-specific 90th percentile (q90) thresholds, and right censoring was applied when observations were interrupted. A total of 1991 episodes were included in the primary analysis, and the Kaplan–Meier median duration was 20 min for all six facility–compound combinations. However, S(60) ranged from 15.1% to 25.5%, S(120) from 8.4% to 17.9%, and RMST120 from 38.8 to 49.0 min, indicating that short episodes coexisted with longer-lasting events. When two consecutive non-exceedances were required to confirm episode termination, restricted mean survival time up to 120 min (RMST120) increased to 63.0–71.4 min, demonstrating the influence of episode definition on persistence estimates. In the temporally ordered predictive evaluation, 921 test episodes were used to assess the additional value of onset concentration and meteorological information, and the predictive effects varied by facility, compound, and evaluation horizon. These results demonstrate that the persistence of high-concentration odor episodes can be quantified at the event level even under incomplete continuous monitoring and provide an analytical framework integrating persistence probability estimation with temporally ordered predictive evaluation.