Multi-model study of chemical and physical controls on transport of anthropogenic and biomass burning pollution to the Arctic

• Published in: Atmospheric Chemistry and Physics
• Other Authors: Monks, S. (author), Arnold, S. (author), Emmons, Louisa (author), Law, K. (author), Turquety, S. (author), Duncan, B. (author), Flemming, J. (author), Huijnen, V. (author), Tilmes, Simone (author), Langner, J. (author), Mao, J. (author), Long, Y. (author), Thomas, J. (author), Steenrod, S. (author), Raut, J. (author), Wilson, C. (author), Chipperfield, M. (author), Diskin, G. (author), Weinheimer, Andrew (author), Schlager, H. (author), Ancellet, G. (author)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2015
• Subjects: Arctic
• Online Access: http://nldr.library.ucar.edu/repository/collections/OSGC-000-000-021-577; https://doi.org/10.5194/acp-15-3575-2015

Using observations from aircraft, surface stations and a satellite instrument, we comprehensively evaluate multi-model simulations of carbon monoxide (CO) and ozone (O₃) in the Arctic and over lower latitude emission regions, as part of the POLARCAT Model Inter-comparison Project (POLMIP). Evaluation of 11- atmospheric models with chemistry shows that they generally underestimate CO throughout the Arctic troposphere, with the largest biases found during winter and spring. Negative CO biases are also found throughout the Northern Hemisphere, with multi-model mean gross errors (9-12%) suggesting models perform similarly over Asia, North America and Europe. A multi-model annual mean tropospheric OH (10.8 ± 0.6 × 105 molec cm⁻³) is found to be slightly higher than previous estimates of OH constrained by methyl chloroform, suggesting negative CO biases in models may be improved through better constraints on OH. Models that have lower Arctic OH do not always show a substantial improvement in their negative CO biases, suggesting that Arctic OH is not the dominant factor controlling the Arctic CO burden in these models. In addition to these general biases, models do not capture the magnitude of CO enhancements observed in the Arctic free troposphere in summer, suggesting model errors in the simulation of plumes that are transported from anthropogenic and biomass burning sources at lower latitudes. O₃ in the Arctic is also generally underestimated, particularly at the surface and in the upper troposphere. Summer O₃ comparisons over lower latitudes show several models overestimate upper tropospheric concentrations. Simulated CO, O₃ and OH all demonstrate a substantial degree of inter-model variability. Idealised CO-like tracers are used to quantitatively compare the impact of inter-model differences in transport and OH on CO in the Arctic troposphere. The tracers show that model differences in transport from Europe in winter and from Asia throughout the year are important sources of model variability at Barrow. Unlike ...