Novel source localization method from observed peak emissions in time series using LPDM transfer functions

We developed a novel method to estimate from an observations-time series the upwind distance as well as the emission strength of an unknown source, which releases a gas into the atmosphere (top-down). For this purpose, we used LPDM-modeled particle trajectories to infer the transfer function of the source region. The transfer function that matches the observed enhancement best, identifies the potential source region. In a second step, we infer the source strength using the particle ensemble.

We developed this method with a data set obtained during a six-week campaign in the San Francisco Bay Area. Aim was, to infer greenhouse gas emissions, specifically carbon dioxide and methane, from total column abundances.

At the UC-Berkeley site, one particular instrument recorded a strictly periodic peak-enhancement of approximately 10ppb methane within a consecutive 12-minute interval. Co-emitted species showed no correlation with this pattern. Therefore, we assumed a singular, point, and puff-emitting source of methane.

Due to favorable meteorological conditions, we were able to analyze a total of 14 peaks during a three-hour time-span in the forenoon. We estimated the average emission strength during the emission period to be 1.8+/-0.5 g(CH4)/s (equivalent to 6.48+/-1.80 kg/hr). Although we were unable to identify the source in the field, we concluded that methane ventilation from the natural gas supply, a so-called blow-down, could be a plausible explanation.