Didier Davignon

The Arctic: a sink for mercury

Mercury is a persistent, toxic and bio-accumulative pollutant of global interest. Its main mass in the troposphere is in the form of elemental gas-phase mercury. Rapid, near-complete depletion of mercury has been observed during spring in the atmospheric boundary layer of frozen marine areas in Arctic, sub-Arctic and Antarctic locations. It is strongly correlated with ozone depletion. To date, evidence has indicated strongly that chemistry involving halogen gases from surface sea-salt is the mechanism of this destruction. Precisely which halogen gases are the main players has remained unresolved. Our novel kinetic data and multiscale modelling show that Br atoms and BrO radicals are the most effective halogens driving mercury oxidation. The reduction of oxidized mercury deposited in the snow pack back to Hg0 and subsequent diffusion to the atmosphere is observed. However, it cannot compensate for the total deposition, and a net accumulation occurs. We use a unique global atmospheric mercury model to estimate that halogen-driven mercury depletion events result in a 44% increase in the net deposition of mercury to the Arctic. Over a 1-yr cycle, we estimate an accumulation of 325 tons of mercury in the Arctic.

The FireWork air quality forecast system with near-real-time biomass burning emissions: Recent developments and evaluation of performance for the 2015 North American wildfire season

ABSTRACT Environment and Climate Change Canada’s FireWork air quality (AQ) forecast system for North America with near-real-time biomass burning emissions has been running experimentally during the Canadian wildfire season since 2013. The system runs twice per day with model initializations at 00 UTC and 12 UTC, and produces numerical AQ forecast guidance with 48-hr lead time. In this work we describe the FireWork system, which incorporates near-real-time biomass burning emissions based on the Canadian Wildland Fire Information System (CWFIS) as an input to the operational Regional Air Quality Deterministic Prediction System (RAQDPS). To demonstrate the capability of the system we analyzed two forecast periods in 2015 (June 2–July 15, and August 15–31) when fire activity was high, and observed fire-smoke-impacted areas in western Canada and the western United States. Modeled PM2.5 surface concentrations were compared with surface measurements and benchmarked with results from the operational RAQDPS, which did not consider near-real-time biomass burning emissions. Model performance statistics showed that FireWork outperformed RAQDPS with improvements in forecast hourly PM2.5 across the region; the results were especially significant for stations near the path of fire plume trajectories. Although the hourly PM2.5 concentrations predicted by FireWork still displayed bias for areas with active fires for these two periods (mean bias [MB] of –7.3 µg m−3 and 3.1 µg m−3), it showed better forecast skill than the RAQDPS (MB of –11.7 µg m−3 and –5.8 µg m−3) and demonstrated a greater ability to capture temporal variability of episodic PM2.5 events (correlation coefficient values of 0.50 and 0.69 for FireWork compared to 0.03 and 0.11 for RAQDPS). A categorical forecast comparison based on an hourly PM2.5 threshold of 30 µg m−3 also showed improved scores for probability of detection (POD), critical success index (CSI), and false alarm rate (FAR). Implications: Smoke from wildfires can have a large impact on regional air quality (AQ) and can expose populations to elevated pollution levels. Environment and Climate Change Canada has been producing operational air quality forecasts for all of Canada since 2009 and is now working to include near-real-time wildfire emissions (NRTWE) in its operational AQ forecasting system. An experimental forecast system named FireWork, which includes NRTWE, has been undergoing testing and evaluation since 2013. A performance analysis of FireWork forecasts for the 2015 wildfire season shows that FireWork provides significant improvements to surface PM2.5 forecasts and valuable guidance to regional forecasters and first responders.

Global mercury modelling at Environment Canada

We describe the recent developments of Environment Canadas atmospheric mercury model (GRAHM) and its application to the intercontinental source-receptor relationships of mercury. The model includes 2188 Mg yr-1 global anthropogenic emissions, 1600 Mg yr-1 terrestrial emissions and 2600 Mg yr-1 oceanic emissions). Transport, chemical transformation and deposition of Hg0, Hg(II) and Hg(p) are simulated in GRAHM within a meteorological assimilation and forecasting system. Current version of the GRAHM includes GEM oxidation by ozone in the troposphere and halogen oxidation in the Polar and the marine boundary layers. It also includes dynamic exchange of mercury fluxes at air-snow/ice interface. The model simulates springtime atmospheric mercury depletion events (AMDEs) and the net accumulation of mercury in snow in the Polar Regions. We performed one reference simulation with emissions as above and four perturbation simulations with 20% reduced anthropogenic emissions over East Asia, South Asia, Europe and North Africa and North America. 20% reduction in anthropogenic emissions of mercury over East Asia, South Asia, Europe and North Africa and North America represent 7.7%, 1.6%, 2.5% and 1.3% reduction in global anthropogenic emissions respectively. The deposition over East Asia, South Asia, Europe and North America are reduced by 13.5%, 7.9%, 8.3% and 4.3% due to the emission reductions within the same regions. Deposition in North America is found to be most affected by the emission reductions in other regions and the deposition in East Asia is least affected by outside reductions. The deposition in the Arctic is nearly equally sensitive to the unit emission reductions in Europe and East Asia and is most sensitive in springtime due to the high deposition related to AMDEs.

Human health impacts of biodiesel use in on-road heavy duty diesel vehicles in Canada.

Regulatory requirements for renewable content in diesel fuel have been adopted in Canada. Fatty acid alkyl esters, that is, biodiesel, will likely be used to meet the regulations. However, the impacts on ambient atmospheric pollutant concentrations and human health outcomes associated with the use of biodiesel fuel blends in heavy duty diesel vehicles across Canada have not been evaluated. The objective of this study was to assess the potential human health implications of the widespread use of biodiesel in Canada compared to those from ultralow sulfur diesel (ULSD). The health impacts/benefits resulting from biodiesel use were determined with the Air Quality Benefits Assessment Tool, based on output from the AURAMS air quality modeling system and the MOBILE6.2C on-road vehicle emissions model. Scenarios included runs for ULSD and biodiesel blends with 5 and 20% of biodiesel by volume, and compared their use in 2006 and 2020. Although modeling and data limitations exist, the results of this study suggested that the use of biodiesel fuel blends compared to ULSD was expected to result in very minimal changes in air quality and health benefits/costs across Canada, and these were likely to diminish over time.

A New Canadian Modeling Platform for Policy Emission Reduction Scenarios: Year 2006 Configuration

The Air Quality Modeling and Application Section of Environment Canada (EC) is transitioning its policy modeling platform from base year 2002 to base year 2006. The motivation behind this transition is to take into account the latest technological and scientific information upon which sound advice can be given to policy management. The latest data available at the beginning of the transition process includes 2006 emission inventories, 2006 meteorology inputs, and latest tools such as the meteorological and chemical transport models, interpolators, etc. The development of such a modeling platform encompasses the meteorology generation and interpolation, the emissions inventory and processing tools, post-processing of the modeling outputs, preparation of inputs for health and environmental benefits valuation models as well as the performance verification. The new system also addresses some of the technical weaknesses of the previous platform such as portability for different users, domain nesting capabilities, flexibility in emissions scenarios, more robust post-processing tools and better system diagnostic tools (reporting, error traceability). These changes will facilitate easier exchange of scenario configurations, data and results, allowing for improved coordination and collaboration between EC modelers. This paper provides an overview of the new policy modeling platform. It first outlines the general model configuration follow by preliminary results of the 2006 annual base case evaluation.

Poster 21 The North American mercury model inter-comparison Study (NAMMIS)

Abstract NAMMIS is an intercomparison of atmospheric Hg models with a focus on North America. Three regional-scale atmospheric Hg models are the prime subjects of the study: the Community Multi-scale Air Quality model (CMAQ) developed by NOAA and EPA, the Regional Modeling System for Aerosols and Deposition (REMSAD) developed by ICFI, and the Trace Element Analysis Model (TEAM) developed by AER. The models were run for the entire year of 2001 using the same initial and boundary condition data.