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Dynamic flux chambers (DFCs) and micrometeorological (MM) methods areextensively deployed for gauging air–surface Hg0 gas exchange. However,a systematic evaluation of the precision of the contemporary Hg0 fluxquantification methods is not available. In this study, the uncertainty inHg0 flux measured by the relaxed eddy accumulation (REA) method, theaerodynamic gradient method (AGM), the modified Bowen ratio (MBR) method, aswell as DFC of traditional (TDFC) and novel (NDFC) designs, are assessedusing a robust data set from two field intercomparison campaigns. The absolute precision in Hg0 concentration difference (ΔC) measurements is estimated at 0.064 ng m−3 for the gradient-basedMBR and AGM systems. For the REA system, the parameter is Hg0concentration (C) dependent at 0.069 + 0.022C. During the campaigns, 57 and62 % of the individual vertical gradient measurements are found to besignificantly different from 0, while for the REA technique, the percentageof significant observations is lower. For the chambers, non-significantfluxes are confined to a few night-time periods with varying ambient Hg$^{0}$concentrations. Relative bias for DFC-derived fluxes is estimated to be~ ±10, and ~ 85% of the flux bias is within±2 ng m−2 h−1 in absolute terms. The DFC flux bias follows adiurnal cycle, which is largely affected by the forced temperature andirradiation bias in the chambers. Due to contrasting prevailingmicrometeorological conditions, the relative uncertainty (median) inturbulent exchange parameters differs by nearly a factor of 2 between thecampaigns, while that in ΔC measurement is fairly consistent.The estimated flux uncertainties for the triad of MM techniques are 16–27,12–23 and 19–31% (interquartile range) for the AGM, MBR and REA methods,respectively. This study indicates that flux-gradient-based techniques (MBRand AGM) are preferable to REA in quantifying Hg0 flux over ecosystemswith low vegetation height. A limitation of all Hg0 flux measurementsystems investigated is their inability to obtain synchronous samples for thecalculation of ΔC. This reduces the precision of fluxquantification, particularly in the MM systems under non-stationarity ofambient Hg0 concentration. For future applications, it is recommended toaccomplish ΔC derivation from simultaneous collected samples

Mercury vapor air–surface exchange measured by collocated micrometeorological and enclosure methods – Part II: Bias and uncertainty analysis