Particulate-Phase Mercury Emissions during Biomass Burning and Impact on Resulting Deposition: a Modelling Assessment

Mercury (Hg) emissions from Biomass Burning (BB) are an important source of atmospheric Hg and is a major factor driving the inter-annual variation of Hg concentrations in the troposphere. Little is known about the fraction of Hg bound to particulate matter (Hg P ) released from BB, and the factors controlling this fraction are also uncertain. In light of the aims of the Minamata Convention to reduce intentional Hg use and emissions from anthropogenic activities, the relative 5 importance of Hg emissions from BB will have an increasing impact on Hg deposition fluxes. Hg speciation is one of the most important factors determining the redistribution of Hg in the atmosphere and the geographical distribution of Hg deposition. Using the latest version of the Global Fire Emissions Database (GFEDv4.1s) and the global Hg chemistry transport model, ECHMERIT, the impact of Hg speciation in BB emissions, and the factors which influence speciation, on Hg deposition have been investigated for the year 2013. The role of other uncertainties related to physical and chemical atmospheric processes 10 involving Hg, and the influence of model parametrisations were also investigated, since their interactions with Hg speciation are complex. The quantity and geographical distribution of Hg P emitted from BB has a limited impact on a global scale, although the inclusion of increasing fractions Hg P does limit Hg0 (g) availability to the global atmospheric pool. This reduces Hg deposition from BB to the world's oceans from 71% to 62%. The impact locally is however significant, northern boreal and tropical forests where fires are frequent and uncontrolled leads to notable Hg inputs to local ecosystems. Under water-stressed 15 conditions in tropical forests and warming temperatures in northern forests this effect may be exacerbated in the future.