Towards correction free open-path eddy covariance flux measurements for methane

Open-path sensors are critical for expanding methane (CH 4 ) eddy covariance flux observations in power-constrained environments but are traditionally hindered by density and spectroscopic artifacts that reduce measurement confidence. This study introduces the HT8600P, an open-path analyzer enabling a novel pseudo dry mixing ratio ( \({χ }ₚ)\) method. In a zero-flux experiment, this method yielded near-zero fluxes with a random error of 0.057 mg·m −2 ·hr −1 ( \(1σ\) ), and a net correction 10 times smaller than a co-located commercial analyzer. We further identify “phantom” errors, artifacts from density and spectroscopic effects, that inflate random error estimates in conventional density-based open-path flux measurements. The \({χ }ₚ\) method reduced these apparent errors by 60–70%, yielding uncertainty consistent with the empirically determined random error (0.063 mg·m −2 ·hr −1 ) using paired flux measurements. By minimizing corrections and enabling robust uncertainty quantification, the HT8600P and \({χ }ₚ\) method offer a reliable solution for expanding flux networks in remote regions critical to the global CH 4 budget.