Application of CMAQ at a hemispheric scale for atmospheric mercury simulations

Abstract

Application of a regional model to study of fate and transport of a global pollutant such as mercury in the atmosphere can be challenging and improper usage of models may lead to questionable results. The difficulties in such application stem from the fact that regional models are usually used in relatively small domains and rely heavily on initial and boundary conditions (IC/BC) provided by global models where atmospheric physics and chemical mechanisms are generally diverse. This problem is particularly apparent for a persistent air pollutant such as mercury. In this study, a conventional application of the CMAQ (Community Multi-scale Air Quality) modeling system on regional scale was extended towards a hemispheric scale. Two simulations were performed using different IC/BC obtained from two global models. In terms of model evaluation, aircraft measurements of total gaseous mercury (TGM) concentration as well as mercury concentration and deposition data from ground-based measurements were used altogether in comparisons with the model simulations. The model results suggested an improvement in performance, as evidenced by a better circulation of the pollutant in Northern hemisphere relative to regional-scale simulations performed in our previous work. In this study, the simulation results using the two different inputs were found to be convergent as the simulation time progressed. The model results also suggested that BC has much weaker influence on the simulation results in a hemispheric domain than that on our previous regional assessment where BC was found to be one of the most important factors. In addition, mitigations of influences from IC/BC on model results in a hemispheric domain and implication of peaks of TGM concentration evident in aircraft measurement are also discussed

Multi-model study of mercury dispersion in the atmosphere: Vertical distribution of mercury species

“…The observed TM profiles are often similar to GEM profiles. Inside the PBL, oxidized mercury (OM) (here, OM is defined as the sum of all oxidized forms of mercury including model species GOM, PBM, and any mercury in the aqueous phase) concentrations are very low and mostly between 20 and 100 pg m −3 in Europe and North America, even in source regions with high anthropogenic emissions (e.g., coal-fired power plants) (Xu et al, 2016;Gay et al, 2013;Tørseth et al, 2012;Prestbo and Gay, 2009;Weiss-Penzias et al, 2015). In China, PBM concentrations up to 1000 pg m 3 and GOM concentrations up to 100 pg m 3 have been observed, but no aircraft observations in the PBL and the LFT are available for this region : (Fu et al, 2015(Fu et al, , 2016Sprovieri et al, 2016).…”

Top-down constraints on atmospheric mercury emissions and implications for global biogeochemical cycling

“…Tropospheric Br fields are archived from a full chemistry GEOS-Chem simulation (Parrella et al, 2012). Models also hypothesize gas-and/or aqueousphase reductions of oxidized Hg and scale their kinetics to match atmospheric observations (Holmes et al, 2010;Pongprueksa et al, 2011;Selin et al, 2007). However, an accurate determination of potential pathways is lacking (Subir et al, 2011(Subir et al, , 2012, and their atmospheric relevance is unknown (Gårdfeldt and Jonsson, 2003).…”

Multi-model study of mercury dispersion in the atmosphere: vertical and interhemispheric distribution of mercury species

“…A spin-up period of 10 days is used to eliminate the impact of initial conditions for atmospheric oxidants (O 3 and OH) that react with mercury. As for mercury species, global models were simulated for several years prior to the study period (2005) in order to provide the initial and boundary conditions for this study (Pongprueksa et al, 2011). A hemispheric model domain with a polar stereographic projection at 108 km spatial resolution and 187 × 187 grid cells was used for this experiment with 13 hybrid sigma layers up to 50 hPa.…”