Modelling of Mercury Hemispheric Transport and Depositions

MSC-E Technical Report 6/2002

O.Travnikov, A.Ryaboshapko

ABSTRACT

This report describes the progress in the model elaboration and preliminary results of mercury transport modelling over the Northern Hemisphere.

Motivation of the hemispheric modelling activity is given in Introduction of the report. It is pointed out that the model is to be used for multi-year computations of mercury cycling in the environment in order to evaluate its accumulation in the compartments and inter-compartmental fluxes, for the evaluation of the correct boundary conditions for the regional modelling (for the EMEP region), for the contamination assessment of remote regions (e.g. the Arctic), and finally, for the evaluation of future mercury contamination levels.

Literature survey of physical and chemical properties of mercury in the atmosphere is presented in Chapter 1. New scientific researches devoted to mercury atmospheric speciation and its transformations both in the gaseous and aqueous phase are considered in order to bring the model chemical scheme into conformity with contemporary knowledge of mercury behaviour in the atmosphere.

Description of the developed atmospheric module of the hemispheric model is presented in Chapter 2. It describes mercury emissions from anthropogenic and natural sources, transport in the atmosphere, chemical transformations both in gaseous and aqueous phase, and deposition to the surface. The model domain covers the whole Northern Hemisphere with resolution 2.5°x2.5°. The three-dimensional atmospheric transport is based on the flux-form Bott advection scheme.

Input information collected and adjusted to the hemispheric modeling is described in Chapter 3. It includes mercury emission data, meteorological and geophysical information, data on the atmospheric content of chemical reactants. Peculiar attention is paid to natural emission of mercury to the atmosphere. According to expert estimates up to 70% of the entire mercury input to the atmosphere can be contributed by natural sources.

Preliminary results of mercury transport and depositions modelling over the Northern Hemisphere are presented and described in Chapter 4. Mercury concentration levels in the ambient air and deposition fluxes over the Northern Hemisphere are assessed. The modelling results are verified against available monitoring data and calculated values obtained by the regional mercury transport model (MSCE-HM). The inter-continental transport of mercury in the Northern Hemisphere is estimated. According to the preliminary results more than 40% of mercury deposition to Europe is from external anthropogenic and global natural sources. The influence of different regions and continents on the Arctic mercury contamination is also investigated.

Basic principles of the multi-compartment model of mercury cycling in the environment are formulated in Chapter 5 basing on the literature survey. The main environmental compartments are distinguished and qualified according to their capacity and mercury residence time. The most important inter-compartmental fluxes are pointed out. General steps of future model development are outlined.