The value of B dependents on the tolerance for false positives. In practice, sporadic spikes may correspond to sensor malfunctions or error from raw data processing rather than actual emissions. We need a metric to evaluate the persistence of the high values defined using the amplitude threshold A. In this study, we use an amplitude threshold of A = 0.5 ppm and B = 20% for the main analysis. An example of a successful detection is illustrated in Section S3 of the SI. We also analyzed how different sensor types may affect the detection efficiency by using A = 5.0 ppm and B = 20% to generate results corresponding to a lower quality sensor. There are various ways to define detection which can be easily accommodated within our framework, and we included a brief analysis of different choices in Section S4 of the SI.