Pan-Arctic seasonal cycles and long-term trends of aerosol properties from 10 observatories

Journal Article · Tue Mar 08 00:00:00 EST 2022 · Atmospheric Chemistry and Physics (Online)

DOI:https://doi.org/10.5194/acp-22-3067-2022· OSTI ID:1860628

Schmale, Julia  ^[1]; Sharma, Sangeeta ^[2]; Decesari, Stefano ^[3]; Pernov, Jakob  ^[4]; Massling, Andreas ^[5]; Hansson, Hans-Christen ^[6]; von Salzen, Knut ^[7]; Skov, Henrik  ^[5]; Andrews, Elisabeth  ^[8]; Quinn, Patricia K. ^[9]; Upchurch, Lucia M. ^[10]; Eleftheriadis, Konstantinos  ^[11]; Traversi, Rita  ^[12]; Gilardoni, Stefania  ^[13]; Mazzola, Mauro  ^[13]; Laing, James ^[14]; Hopke, Philip  ^[15]

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1. Ecole Polytechnique Federale Lausanne (Switzerland)
2. Environment and Climate Change Canada, Toronto, ON (Canada)
3. Italian National Research Council (INRC), Bologna (Italy)
4. Ecole Polytechnique Federale Lausanne (Switzerland); Aarhus Univ. (Denmark)
5. Aarhus Univ. (Denmark)
6. Stockholm Univ. (Sweden)
7. Environment and Climate Change Canada, Victoria, BC (Canada)
8. Univ. of Colorado, Boulder, CO (United States)
9. National Oceanic and Atmospheric Administration (NOAA), Seattle, WA (United States). Pacific Marine Environmental Laboratory
10. National Oceanic and Atmospheric Administration (NOAA), Seattle, WA (United States). Pacific Marine Environmental Laboratory; Univ. of Washington, Seattle, WA (United States)
11. National Centre of Scientific Research (NCSR) "Demokritos", Athens (Greece)
12. Univ. of Florence (Italy); National Research Council (CNR), Venice (Italy)
13. National Research Council (CNR), Venice (Italy)
14. Washington State Department of Ecology, Shoreline, WA (United States)
15. Clarkson Univ., Potsdam, NY (United States)

Even though the Arctic is remote, aerosol properties observed there are strongly influenced by anthropogenic emissions from outside the Arctic. This is particularly true for the so-called Arctic haze season (January through April). In summer (June through September), when atmospheric transport patterns change, and precipitation is more frequent, local Arctic sources, i.e., natural sources of aerosols and precursors, play an important role. Over the last few decades, significant reductions in anthropogenic emissions have taken place. At the same time a large body of literature shows evidence that the Arctic is undergoing fundamental environmental changes due to climate forcing, leading to enhanced emissions by natural processes that may impact aerosol properties. In this study, we analyze 9 aerosol chemical species and 4 particle optical properties from 10 Arctic observatories (Alert, Kevo, Pallas, Summit, Thule, Tiksi, Barrow/Utgiavik, Villum, and Gruvebadet and Zeppelin Observatory – both at Ny-Ålesund Research Station) to understand changes in anthropogenic and natural aerosol contributions. Variables include equivalent black carbon, particulate sulfate, nitrate, ammonium, methanesulfonic acid, sodium, iron, calcium and potassium, as well as scattering and absorption coefficients, single scattering albedo and scattering Ångström exponent. First, annual cycles are investigated, which despite anthropogenic emission reductions still show the Arctic haze phenomenon. Second, long-term trends are studied using the Mann–Kendall Theil–Sen slope method. We find in total 41 significant trends over full station records, i.e., spanning more than a decade, compared to 26 significant decadal trends. The majority of significantly declining trends is from anthropogenic tracers and occurred during the haze period, driven by emission changes between 1990 and 2000. For the summer period, no uniform picture of trends has emerged. Twenty-six percent of trends, i.e., 19 out of 73, are significant, and of those 5 are positive and 14 are negative. Negative trends include not only anthropogenic tracers such as equivalent black carbon at Kevo, but also natural indicators such as methanesulfonic acid and non-sea-salt calcium at Alert. Positive trends are observed for sulfate at Gruvebadet. No clear evidence of a significant change in the natural aerosol contribution can be observed yet. However, testing the sensitivity of the Mann–Kendall Theil–Sen method, we find that monotonic changes of around 5 % yr^–1 in an aerosol property are needed to detect a significant trend within one decade. This highlights that long-term efforts well beyond a decade are needed to capture smaller changes. It is particularly important to understand the ongoing natural changes in the Arctic, where interannual variability can be high, such as with forest fire emissions and their influence on the aerosol population. To investigate the climate-change-induced influence on the aerosol population and the resulting climate feedback, long-term observations of tracers more specific to natural sources are needed, as well as of particle microphysical properties such as size distributions, which can be used to identify changes in particle populations which are not well captured by mass-oriented methods such as bulk chemical composition.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Atmospheric Radiation Measurement (ARM) Data Center
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Contributing Organization: Pacific Northwest National Laboratory (PNNL); Brookhaven National Laboratory (BNL); Argonne National Laboratory (ANL); Oak Ridge National Laboratory (ORNL)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1860628
• Journal Information: Atmospheric Chemistry and Physics (Online), Vol. 22, Issue 5; ISSN 1680-7324
• Publisher: Copernicus Publications, EGU
• Country of Publication: United States
• Language: English

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54 ENVIRONMENTAL SCIENCES