Particulate-phase mercury emissions from biomass burning and impact on resulting deposition: a modelling assessment.

Francesco De Simone,Nicola Pirrone,Francesco Carbone,Noriuki Suzuki,Paulo Artaxo,Christian N Gencarelli,Francesco D'Amore,Xin Bin Feng,Ingvar Wängberg,Mariantonia Bencardino,Matthew S Landis,Aurélien Dommergue,Ian M Hedgecock,Sergio Cinnirella,Francesca Sprovieri

doi:10.5194/acp-17-1881-2017

Abstract

Mercury (Hg) emissions from biomass burning (BB) are an important source of atmospheric Hg and a major factor driving the interannual variation of Hg concentrations in the troposphere. The greatest fraction of Hg from BB is released in the form of elemental . However, little is known about the fraction of Hg bound to particulate matter (HgP) 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 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 involving Hg and the influence of model parametrisations were also investigated, since their interactions with Hg speciation are complex. The comparison with atmospheric HgP concentrations observed at two remote sites, Amsterdam Island (AMD) and Manaus (MAN), in the Amazon showed a significant improvement when considering a fraction of HgP from BB. The set of sensitivity runs also showed how the quantity and geographical distribution of HgP emitted from BB has a limited impact on a global scale, although the inclusion of increasing fractions HgP does limit availability to the global atmospheric pool. This reduces the fraction of Hg from BB which deposits to the world’s oceans from 71 to 62 %. The impact locally is, however, significant on northern boreal and tropical forests, where fires are frequent, uncontrolled and lead to notable Hg inputs to local ecosystems. In the light of ongoing climatic changes this effect could be potentially be exacerbated in the future.

Highlights

Emissions from biomass burning (BB) are an important source of mercury (Hg) to the atmosphere (De Simone et al, 2015; Friedli et al, 2009) and a major factor in determining the interannual variations of its tropospheric concentration (Slemr et al, 2016)
The aim of this study is to investigate the effects on simulated deposition fluxes of Hg resulting from BB when variations in Hg emitted bound to particulates (HgP) fraction and production processes are considered
That a fraction of HgP is present in BB Hg emissions has been confirmed by several field measurements (Obrist et al, 2007; Finley et al, 2009), and this fact has been suggested as an explanation of high HgP observations at a remote site (Angot et al, 2014), but this is the first time it has been included in a model study to assess its effects on a global scale

Summary

Introduction

Emissions from biomass burning (BB) are an important source of mercury (Hg) to the atmosphere (De Simone et al, 2015; Friedli et al, 2009) and a major factor in determining the interannual variations of its tropospheric concentration (Slemr et al, 2016). The deposition flux of Hg from BB has been shown to be more sensitive to certain factors, in particular the chemical mechanism employed in the model and the choice of emission inventory, than to others such as the vertical profiles of emissions (De Simone et al, 2015). In this previous study all Hg emitted from BB was considered to be Hg0(g). The most recent version of the GFED BB emission inventory (van der Werf et al, 2010; Randerson et al, 2012; Mu et al, 2011), has been included in the global online Hg chemical transport model ECHMERIT to simulate Hg deposition from BB for the year 2013 and to quantify the influence of variations in model inputs, assumptions and parametrisations

Objectives

Methods

Results

Conclusion