Ambient air background levels of gaseous mercury are routinely observed below 150 parts per quadrillion (ppqv), or in typical units, 1.3 ng/m³.  It is now taken for granted that measurements at this level are routine using the automated, continuous, CVAFS-based, Tekran 2537X Gaseous Mercury Air Monitor and associated speciation modules.  At these levels, which are one thousand and one million times lower than typical ambient NO_x and O₃, respectively, it is not surprising that maintaining continuous and accurate automated gaseous air mercury measurements can be more challenging and costly than anticipated.   While high-resolution, automated air mercury speciation measurements have and still are demonstratively valuable for leaps forward in knowledge about air mercury cycling, and the links to wet and dry deposition, the Minimata Convention on Mercury has created an opening for low-tech, lower cost and more widespread ambient air mercury monitoring to compliment the current global instrument-based networks.  At the low ppqv level, a low-tech, low-cost ambient air mercury monitoring method has a number of hurdles to overcome and demands trade-offs in sensitivity and resolution.  Enter the U. of Toronto team of Wania, McLagan and Mitchell who have developed a passive gaseous air mercury method for highly accurate and precise air mercury determinations at the ppqv level.  The science and methodology of MerPAS (Mercury Passive Air Monitor) will be presented, including the key results from calibration and performance studies in comparison to automated electronic monitors.  Additionally, the analysis methodology and unique challenges will be presented in brief.  MerPAS applicability is not confined to ambient air monitoring.   For example MerPAS is useful for source area monitoring studies, which may help with Minimata compliance.  An example of a MerPAS national or global network design will be presented.