Concentrations and size-distributions of water-soluble inorganic and organic species on aerosols over the Arctic Ocean observed during the US GEOTRACES Western Arctic Cruise GN01
Introduction
The Arctic region has witnessed intense warming, at a rate almost twice the global average rate over the last 20–30 years; an effect known as Arctic amplification (Serreze and Barry, 2011; Flato et al., 2013; van Wijngaarden, 2015). Presumably related to this warming, the average annual sea-ice extent decreased by 3.6% per decade between 1976 and 2007 (Meier et al., 2007). Results from satellite observations reveal a ~77% decrease in the Arctic planetary albedo over the past 40 years (Pistone et al., 2014). Although model studies claim that cloudiness has a small effect on Arctic amplification (Screen and Simmonds, 2010; Ghatak and Miller, 2013), it is a major source of uncertainty in understanding recent trends and predicting the future pattern of climate change in the Arctic (Vavrus, 2004; Künzli et al., 2005; Inoue et al., 2006; Walsh et al., 2009; Kay et al., 2016).
Certain aerosol particles can serve as cloud condensation nuclei (CCN), influencing the radiative properties of clouds. Aerosol particle size and the solubility of aerosol species control the activation of CCN at different levels of supersaturation, but the effects of aerosols on cloud dynamics and climate change in the Arctic have not yet been thoroughly examined in climate models due to limited aerosol data from observations over the Arctic (Walsh et al., 2005; Chang et al., 2011; Carslaw et al., 2013).
Over the open ocean, sulfate and ammonium aerosols in particular play important roles as CCN (Galloway et al., 1982; Quinn et al., 1987; Vong et al., 1988) and are crucial for altering the absorption properties of aerosols (Lim et al., 2018). Non-sea-salt-sulfate (NSS-sulfate) particles from natural and anthropogenic sources primarily exist in the fine mode and are generally produced by gas-to-particle conversion (Murphy et al., 1998). Dimethyl sulfide (DMS), produced by phytoplankton through the enzymatic cleavage of dimethyl sulfonio-propionate (DMSP), is a major oceanic source of sulfur to the atmosphere (Prospero and Savoie, 1991; Bates et al., 1992). Alongside this biogenic production of NSS-sulfate, methanesulfonate (MSA) is also produced by the oxidation of DMS derived from phytoplankton, and the ratio of MSA/NSS-sulfate is used as a metric for determining the biogenic contribution to NSS-sulfate (Savoie and Prospero, 1989; Li et al., 1993b; Gondwe et al., 2003; Chen et al., 2012). Several marine sources, such as zooplankton metabolism and the decay of organic material, contribute to gas-phase ammonia (Quinn et al., 1988; Galloway et al., 1995; Bouwman et al., 1997; Adams et al., 1999; Wentworth et al., 2016), which in turn leads to the formation of fine-mode aerosol ammonium (Du et al., 2010).
Water-soluble organic species (WSOS) on aerosols are also potential CCN (Novakov and Penner, 1993; Yu, 2000; Sun and Ariya, 2006). Previous work shows that WSOS can account for a significant fraction (~20–50%) of the total organic mass in aerosols (Cadle and Groblicki, 1982; Yu and Schauer, 2002; Liya et al., 2005), mostly on fine-mode particles (Zappoli et al., 1999). Previous results from both polar regions show that water-soluble low molecular weight carboxylic acids (such as acetic, formic, and oxalic acids) constitute a significant fraction (~20–70%) of the total organic carbon in aerosol (Kawamura et al., 1995; Saxena and Hildemann, 1996; Decesari et al., 2000; Xu et al., 2013). Several primary sources, including vegetation and biomass burning, directly emit organics into the air (Kawamura et al., 1985), whereas oxidation of biogenic olefins, hydrocarbons, and isoprene can act as potential secondary sources (Chebbi and Carlier, 1996).
Although many previous studies on Arctic aerosols focused on inorganic species (Barrie and Hoff, 1985; Li et al., 1993b; Suzuki et al., 1995; Norman et al., 1999; Quinn et al., 2009; Frossard et al., 2011; Zhan et al., 2014, 2017), there are comparatively few reports on WSOS (Kawamura et al., 1995, 2010; Narukawa et al., 2003; Fu et al., 2009). Moreover, unlike during winter and early spring seasons, the summertime Arctic air is relatively isolated from pollutants from the surrounding continental landmasses and hence summer provides a favorable period for studying the chemistry of aerosols originating from marine sources (Leck and Persson, 1996; Quinn et al., 2007). Therefore, to document their distribution it is important to characterize the water-soluble inorganic and organic components simultaneously in summertime Arctic aerosols.
As part of the US GEOTRACES Arctic Ocean (GN01) expedition, shipboard aerosol sampling was carried out over the Arctic Ocean during August–October 2015. We highlight the spatial distribution of the water-soluble inorganic and organic aerosol species, which include sea-salt, NSS-sulfate, ammonium, nitrate, MSA, and low molecular weight carboxylic acids. For mass-size distributions, only inorganic components and MSA are presented here. This information adds new insight on the chemical and physical properties of aerosols in the marine atmospheric boundary layer over the Arctic Ocean.
Section snippets
Sampling
Aerosol sampling was carried out on board the US Coast Guard icebreaker USCGC Healy in summer and fall 2015. The ship started its northward journey from Dutch Harbor in Alaska (53.89°N, 166.53°W) on August 10, crossing the Bering Sea and Makarov Basin, before reaching the North Pole on September 5. The return leg mostly followed the 150°W meridian, before crossing the Chukchi Sea and Bering Sea, returning to Dutch Harbor on October 12.
Along this route, eight sets of size-segregated aerosol
General distribution
The spatial distributions of water-soluble ionic species from bulk aerosols over the Arctic Ocean are shown in Fig. 3. The total mass of water-soluble species varied significantly as the ship traveled from the Bering Sea towards the North Pole and back. Total mass concentrations of soluble species decreased by a factor of ~8 near the high Arctic regions. This feature indicates the presence of cleaner air masses near the pole with significantly less impact from continental air masses and sea
Discussion
The spatial distribution, mass-size distribution and chemical composition of the water-soluble aerosol species varied widely during GN01. Aerosols from segments 1 and 3, which had influences from North Pacific/Bering Sea air masses or air masses that had spent time over land shared some features, while those from segment 2 (dominated by polar marine air) were more unique. On the other hand, water-soluble organic acids were more abundant in the polar marine air mass and may play a significant
Conclusion
The results from this study indicate that the summertime central Arctic Ocean was dominated by pristine marine air masses, with some influence from continental air at lower latitudes (below ~80°N). High concentrations of coarse mode sea-salt and nitrate were observed over the Bering Strait (segment 1) and Canada Basin (segment 3).
Biological productivity appears to have resulted in the accumulation of fine-mode NSS-sulfate and MSA over the Bering Sea, but their concentrations were significantly
Credit author statement
YG conceived the research. PM analyzed samples and wrote the 1st draft of the manuscript. YG, PM and SY prepared the aerosol sampling system and carried out laboratory procedures and data analyses. CM, WL and CB collected samples. All authors contributed to writing the manuscript.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments, Samples, and Data
This work was supported by the US National Science Foundation grants OCE-1435871 (YG), OCE-1438047 (CSB) and OCE-1437266 (WML). The authors are grateful to Goujie Xu and Tianyi Xu for assistance during the preparation for field aerosol sampling and Songyun Fan for help with checking the IC results. The authors are grateful to the crew of the USCGC Healy for hard work during the GN01 cruise. The data supporting the conclusions for this article are available from the US data repository in the
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2022, Atmospheric EnvironmentCitation Excerpt :Table 2 lists a comparison of our measurements to those from previous studies over the Arctic Ocean and subarctic western North Pacific Ocean. Results of our study were similar to the previous studies (Jung et al., 2013; Yu et al., 2020; Mukherjee et al., 2021) in some places: sea salt ions (contained Na+, Cl−, Mg2+, ss-SO42-, K+, and Ca2+) were the dominant ions, and then followed by nss-SO42-, while concentrations of NO3− and MSA− were much lower. Higher concentrations over the western north Pacific Ocean than those obtained in this study may be due to different study areas, that large area of open sea without sea ice may be originated more sea salts ions; and air masses originated from the Asian continent and the Kamchatka Peninsula indicating that the higher concentrations of ions may also affected by anthropogenic and crustal sources as well as the eruptions of two volcanoes (Jung et al., 2013).
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Current address: South Coast Air Quality Management District, Diamond Bar, CA.