EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Wintertime Arctic Air Pollution over Alaska

Eleftherios Ioannidis1, Kathy Law1, Jean-Christophe Raut1, Tatsuo Onishi1, William R. Simpson2, Rachel M. Kirpes3, and Karri A. Pratt3
Eleftherios Ioannidis et al.
  • 1LATMOS, Sorbonne Université, 4, place Jussieu, 75252, Paris, France (
  • 2Department of Chemistry and Biochemistry & Geophysical Institute, University of Alaska, Fairbanks, AK, USA
  • 3Department of Chemistry & Department of Earth & Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA

The Arctic is influenced by long-range transport of aerosols, for example, sulphate, black carbon, and dust from mid-latitude emissions, especially in winter and spring, leading to the formation of Arctic Haze with enhanced aerosol concentrations. However, more recently, local sources of aerosols, such as wood-burning or resource extraction, are highlighted as already being important, but many uncertainties about sources and aerosol processes still remain. For example, the formation of secondary aerosols, such as sulphate, in winter despite very low temperatures and the absence of sunlight.

In this study, which contributes to the international PACES-ALPACA initiative, the Weather Research Forecasting (WRF) and WRF-Chem models are used to investigate wintertime pollution over Alaska with a focus on regions influenced by local pollution, such as Fairbanks and by Arctic Haze, such as Utqiagvik (formerly known as Barrow). Fairbanks is the most polluted city in the United States during wintertime due to high emissions and the occurrence of strong surface temperature inversions.

As a first step, background aerosols originating from remote sources were evaluated in large- scale quasi-hemispheric WRF-Chem runs using ECLIPSE anthropogenic emissions. The model performs quite well over Alaska at background sites (e.g. Denali Park) compared to observations from the US Environmental Protection Agency (EPA). Discrepancies in modelled aerosols due to formation mechanisms and aerosol acidity are being investigated.

Secondly, in order to better simulate Arctic aerosols and local pollution episodes, different schemes in WRF were tested over Alaska with a particular focus on improving simulations of the Arctic boundary layer structure and, in particular, wintertime temperature inversions which trap pollution at the ground. In order to simulate these extreme/cold meteorological conditions, different schemes linked to boundary layer physics, surface layer dynamics and the land surface have been tested and evaluated against Integrated Global Radiosonde Archive (IGRA2) and Integrated Surface Database (ISD). The model captures the cold meteorological conditions over Alaska, for example, capturing strong temperature inversions over Utqiagvik and Fairbanks in winter 2012.

Thirdly, WRF-Chem is used to simulate background and local Arctic air pollution, using the improved WRF setup for meteorology over Alaska for winter 2013-2014. The model is being run with Hemispheric Transport of Air Pollution version 2 (HTAP v2) and other high-resolution emission inventories and evaluated against available aerosol data (PM2.5, black carbon, sulphate) over Alaska including data on aerosol chemical properties. The model is used to examine aerosol composition in locally produced and remote aerosols and to identify the origins contributing to aerosol distributions. The sensitivity of modelled aerosols to, for example, meteorological factors, such as humidity, is examined.

How to cite: Ioannidis, E., Law, K., Raut, J.-C., Onishi, T., Simpson, W. R., Kirpes, R. M., and Pratt, K. A.: Wintertime Arctic Air Pollution over Alaska, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7849,, 2020.


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displays version 1 – uploaded on 03 May 2020
  • CC1: Comment on EGU2020-7849, Gudrun Nina Petersen, 04 May 2020

    Dear Eleftherios,

    I was wondering how many vertical layers you had in you simulations and how they were distributed. Do you find the model to manage to simulate the strong temperature inversions? I can see from the slides that the average profile is fine but I'm interested solely in the low-level inversions.

    Kind regards,

    G. Nína Petersen

    • AC1: Reply to CC1, Eleftherios Ioannidis, 09 May 2020

      Dear Nina,

      Thank you for your comment. In my simulations I used 50 vertical layers - it is the number of vertical levels we are using for all the WRF/WRF-Chem simulations at my laboratory. As you can see from the slides, during the avergaed period was not observed a strong temperature inversion in Utqiagvik. I have been testing WRF for another study concerning Fairbanks in Alaska (which is located in a valley) and during wintertime strong inversion profiles are observed. The model - at 20km resolution and with a different physics parametrization than the one I presented on my slides - the model was simulating quite well strong inversions. The differences from the observed profiles were up to 3 degrees, between the surface and 500m altitude. Are you running WRF simulations over the Arctic? What setup are you using?

      Best regards,

      Eleftherios Ioannidis