A novel sampling technique for monitoring atmospheric methane concentrations: A case study with livestock sources.

ABSTRACT

The substantial increase in the presence of greenhouse gases (GHGs) in the atmosphere has led to the development of several sampling techniques to quantify and characterize the sources of high global warming potential gas emissions. In this context, we developed a new method to estimate the time-averaged concentration of atmospheric methane that employs a long hose to collect a sample of gas by diffusion through one of its ends. We performed numerical simulations to illustrate the basis of our method and to determine the numerical factors required to estimate the time-averaged concentration of methane. This novel technique for estimating the mean gas concentration was then validated with two sets of experiments, where the source of methane was ruminant enteric fermentation measured in a respiration chamber. We compared the time-averaged methane concentration obtained with our methodology for periods (T) ranging from 1 to 4 days with those measured using the sensor of a respiration chamber. We found that the accuracy of the estimates improved as T increased from an error of 20 % for T = 1 to an error smaller than 10 % for T ≥ 2 days. In additional tests, and as suggested by numerical simulations, we confirmed that measuring and employing the methane concentration in the furthest half of the collector leads to a more precise estimation of atmospheric concentration than when the concentration of the entire collector is considered. This work demonstrates that the new methodology for air sampling, in conjunction with numerical analysis, is a viable alternative for quantifying atmospheric methane concentrations. In addition, the simple design of the devices showed remarkable benefits in terms of both the cost and simplicity for implementing large-scale individual sampling. We discuss its potential application to other GHGs.