Open-path sensors are critical for expanding methane (CH4) 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 (\({\chi }_{p})\) method. In a zero-flux experiment, this method yielded near-zero fluxes with a random error of 0.057 mg·m−2·hr−1 (\(1\sigma\)), 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 \({\chi }_{p}\) 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 \({\chi }_{p}\) method offer a reliable solution for expanding flux networks in remote regions critical to the global CH4 budget.
