Abstract
Abstract. In this study, the WRF-Chem regional model is updated to improve simulated short-lived pollutants (e.g., aerosols, ozone) in the Arctic. Specifically, we include in WRF-Chem 3.5.1 (with SAPRC-99 gas-phase chemistry and MOSAIC aerosols) (1) a correction to the sedimentation of aerosols, (2) dimethyl sulfide (DMS) oceanic emissions and gas-phase chemistry, (3) an improved representation of the dry deposition of trace gases over seasonal snow, and (4) an UV-albedo dependence on snow and ice cover for photolysis calculations. We also (5) correct the representation of surface temperatures over melting ice in the Noah Land Surface Model and (6) couple and further test the recent KF-CuP (Kain–Fritsch + Cumulus Potential) cumulus parameterization that includes the effect of cumulus clouds on aerosols and trace gases. The updated model is used to perform quasi-hemispheric simulations of aerosols and ozone, which are evaluated against surface measurements of black carbon (BC), sulfate, and ozone as well as airborne measurements of BC in the Arctic. The updated model shows significant improvements in terms of seasonal aerosol cycles at the surface and root mean square errors (RMSEs) for surface ozone, aerosols, and BC aloft, compared to the base version of the model and to previous large-scale evaluations of WRF-Chem in the Arctic. These improvements are mostly due to the inclusion of cumulus effects on aerosols and trace gases in KF-CuP (improved RMSE for surface BC and BC profiles, surface sulfate, and surface ozone), the improved surface temperatures over sea ice (surface ozone, BC, and sulfate), and the updated trace gas deposition and UV albedo over snow and ice (improved RMSE and correlation for surface ozone). DMS emissions and chemistry improve surface sulfate at all Arctic sites except Zeppelin, and correcting aerosol sedimentation has little influence on aerosols except in the upper troposphere.
Highlights
The Arctic is one of the fastest warming regions on Earth (IPCC, 2013)
It is difficult to attribute precisely the improvement to each of these changes, the change in fire emissions likely had a strong effect on modeled black carbon (BC), since we find that GFEDv3.1 BC emissions north of 60◦ N used in earlier WRF-Chem simulations were 1.5 and 3.9 times higher in June and July than FINNv1.5 BC emissions used here, a point discussed in AMAP (2015)
Simulated airborne and surface BC in the Arctic is sensitive to the effect of cumulus clouds on aerosols and trace gases and to the representation of skin temperatures over sea ice, affecting stability, in the Noah land surface model
Summary
The Arctic is one of the fastest warming regions on Earth (IPCC, 2013). Early studies have shown that 20th century Arctic warming was mostly a consequence of the increased concentration of well-mixed greenhouse gases (e.g., CO2 and CH4), associated with the effect of shorter-lived climate forcers, especially aerosols and ozone (Shindell et al, 2006). AMAP (2015) showed that WRF-Chem performs reasonably well for ozone, but other research (Ahmadov et al, 2015) indicates that the version of WRF-Chem used in AMAP (2015) can be strongly biased low for ozone over snow-covered ground due to overestimated dry deposition and underestimated photolysis rates In this context, the main objectives of this study are to improve WRF-Chem results for Arctic aerosols and ozone compared to the previous large-scale model intercomparisons of Eckhardt et al (2015) and AMAP (2015), to identify potential areas of further improvements in the WRF-Chem model, and to define a model setup that can be used in future work to study aerosol and ozone pollution on continental scales in the Arctic, defined in this study as the region north of 60◦ N.
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