Dominance of Plastic Emission in the High Arctic Aerosol in Light Spring

Arctic haze has attracted considerable scientific interest for decades. However, limited studies have focused on the molecular composition of atmospheric particulate matter that contributes to Arctic haze. Our study collected atmospheric particles at Alert in the Canadian high Arctic from mid-February to early May 2000. Over 100 organic species were identified in the solvent-extractable fraction by gas chromatography-mass spectrometry, which were grouped by their functional groups. Plasticizer-derived phthalates were the most abundant, followed by polyacids, sugars, sugar alcohols, biogenic SOA tracers, and fossil fuel combustion tracers. During the dark winter, major contributors to Arctic aerosols include plastic emissions, biomass burning, secondary oxidation products, and fossil fuel combustion products. In the light spring, phthalates (58-76% of the identified organics) dominated, followed by microbial and marine sources and secondary oxidation products. By employing a tracer-based method, we discovered that naphthalene and sesquiterpene oxidation products were the major contributors to SOC, and these contributions were much higher in the winter than in the spring. However, monoterpene and isoprene oxidation products peaked in light spring. Our results confirm that organic aerosols in the Arctic atmosphere are dominated by anthropogenic sources, which consist of both long-range-transported particles and combustion-emitted organics, as well as aged anthropogenic secondary organic aerosols. Despite decreasing anthropogenic pollution being replaced by natural emissions, plastic-derived pollution, represented by phthalates, increased significantly in the high Arctic atmosphere after the polar sunrise.

Vibrational Spectra of Atmospherically Relevant Hydrogen-Bonded MSA···(H2SO4)n (n = 1-3) Clusters

Methanesulfonic acid (CH₃SO₃H), also known as MSA, has been found to be capable of forming a strong hydrogen-bonded interaction with sulfuric acid (H₂SO₄) under ambient conditions. The energetic stability of the MSA···H₂SO₄ clusters increases with decreasing temperature at higher altitudes in the troposphere, which is relevant in the context of atmospheric aerosol formation. We have performed, in the present work, a detailed and systematic quantum-chemical calculation with high-level density functional theory to characterize the hydrogen bond formation in the binary MSA···H₂SO₄, ternary MSA···(H₂SO₄)₂, and quaternary MSA···(H₂SO₄)₃ clusters. The five different conformations of MSA···(H₂SO₄)₂ and six conformations of MSA···(H₂SO₄)₃, considered in the present work for the spectroscopic analysis, have been taken from our previous work [J. Phys. Chem. A. 2020, 124, 11072-11085]. The hydrogen bonds were analyzed on the basis of infrared vibrational frequencies of different O-H stretching modes and quantum theory of atoms in molecules (QTAIM). A strong positive correlation has been observed between the red shift of the OH groups in MSA and H₂SO₄ and the corresponding O-H elongation as a result of hydrogen bond formation. Topological analysis employing QTAIM shows that most of the charge density and the Laplacian values at bond critical points (BCPs) of the hydrogen bonds of the MSA···(H₂SO₄)_n (n = 1-3) complexes fall within the standard hydrogen-bond criteria. However, those outside these criteria fall in the category of a very strong hydrogen bond with a hydrogen bond length as low as 1.41 Å and an O-H bond elongation as high as 0.096 Å. In general, the charge densities of the BCPs located on hydrogen bonds increase as the hydrogen-bond lengths decrease. Proportionately, a larger number of hydrogen bonds in ternary MSA···(H₂SO₄)₂ demonstrate a partial covalent character when compared with the quaternary clusters.

Photochemical and other sources of organic compounds in the Canadian high arctic aerosol pollution during winter-spring

Total suspended particles collected at Alert in the Canadian high Arctic (February-June) were analyzed for solvent extractable organic compounds using gas chromatography-mass spectrometry to better understand the sources and source apportionment of aerosol pollution that can affect the Arctic climate. More than 100 organic species were detected in the aerosols and were grouped into different compound classes based on the functional groups. Polyacids were found to be the most abundant compound class, followed by phthalates, aromatic acids, fatty acids, fatty alcohols, sugars/sugar alcohols, and n-alkanes, while polycyclic aromatic hydrocarbons, sterols, and lignin and resin acids were minor. Concentrations of total quantified organics seemed slightly higher in darkwinter aerosols (13.2-16.6 ng m(-3), average 14.5 ng m(-3)) than those after polar sunrise (6.70-17.7 ng m(-3), average 11.8 ng m(-3)). During dark winter, fossil fuel combustion products (30-51%), secondary oxidation products, as well as higher plant emissions were found as major contributors to the Arctic aerosols. However, after polar sunrise on 5 March, secondary oxidation products (5-53%) and plasticizer-derived phthalates became the dominant compound classes, followed by fossil fuel combustion and microbial/marine sources. Biomass burning emissions were found to contribute only 0.4-6% of the total identified organics, although they maximized in dark winter. This study demonstrates that long-range atmospheric transport, changes in the solar irradiance, and ambient temperature can significantly control the chemical composition of organic aerosols in the Arctic region.

Diurnal cycles of gaseous mercury within the snowpack at Kuujjuarapik/Whapmagoostui, Québec, Canada

Mercury is a globally dispersed and toxic pollutant that can be transported far from its emission sources. In polar and subpolar regions, recent research activities have demonstrated its ability to be converted and deposited rapidly onto snow surfaces during the so-known Mercury Depletion Events (MDEs). The fate of mercury once deposited onto snow surfaces is still unclear: a part could be re-emitted to the atmosphere, the other part could contaminate water systems at the snowmelt. Its capacity to transform to more toxic form and to bioaccumulate in the food chain has consequently made mercury a threat for Arctic ecosystems. The snowpack is a medium that greatly interacts with a variety of atmospheric gases. Its role in the understanding of the fate of deposited mercury is crucial though it is poorly understood. In April 2002, we studied an environmental component of mercury, which is interstitial gaseous mercury (IGM) present in the air of the snowpack at Kuujjuarapik/Whapmagoostui (55 degrees N, 77 degrees W), Canada on the east shore of the Hudson Bay. We report here for the first time continuous IGM measurements at various depths inside a seasonal snowpack. IGM concentrations exhibit a well-marked diurnal cycle with uninterrupted events of Hg0 depletion and production within the snowpack. A possible explanation of Hg0 depletion within the snowpack may be Hg0 oxidation processes. Additionally, we assume that the notable production of Hg0 during the daytime may be the results of photoreduction and photoinitiated reduction of Hg(II) complexes. These new observations show that the snowpack plays undoubtedly a role in the global mercury cycle.