Volcanoes are recognized contributors of mercury (Hg) emissions to the atmosphere; however, the amount of Hg released globally from these natural sources remains poorly constrained. To improve this understanding, a multi-year suite of atmospheric, water, and ash samples were collected from Poás and Turrialba volcanoes, Costa Rica. Atmospheric sampling at Poás was conducted over two stages of volcanic activity (passive degassing and active eruption) using continuous monitoring near the crater in addition to passive and active sampling techniques within the crater. Results corroborate earlier assessments that Poás is a low Hg emitting volcano compared to Turrialba, even during active phases. A novel model of crustal Hg incorporation is proposed to explain the large global variance in volcanic plume Hg concentrations in relationship to eruption frequency. Based on the model, a new global volcanic Hg flux is estimated to be 30 ± 39 t/a for 2006‒2015.