| 1. |
- Abdelkader, M., et al.
(author)
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Dust-air pollution dynamics over the eastern Mediterranean
- 2015
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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 15:16, s. 9173-9189
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Journal article (peer-reviewed)abstract
- Interactions of desert dust and air pollution over the eastern Mediterranean (EM) have been studied, focusing on two distinct dust transport events on 22 and 28 September 2011. The atmospheric chemistry-climate model EMAC has been used at about 50 km grid spacing, applying an on-line dust emission scheme and calcium as a proxy for dust reactivity. EMAC includes a detailed tropospheric chemistry mechanism, aerosol microphysics and thermodynamics schemes to describe dust aging. The model is evaluated using ground-based observations for aerosol concentrations and aerosol optical depth (AOD) as well as satellite observations. Simulation results and back trajectory analysis show that the development of synoptic disturbances over the EM can enhance dust transport from the Sahara and Arabian deserts in frontal systems that also carry air pollution to the EM. The frontal systems are associated with precipitation that controls the dust removal. Our results show the importance of chemical aging of dust, which increases particle size, dust deposition and scavenging efficiency during transport, overall reducing the lifetime relative to non-aged dust particles. The relatively long travel periods of Saharan dust result in more sustained aging compared to Arabian dust. Sensitivity simulations indicate 3 times more dust deposition of aged relative to pristine dust, which significantly decreases the dust lifetime and loading.
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| 2. |
- Abdelkader, Mohamed, et al.
(author)
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Sensitivity of transatlantic dust transport to chemical aging and related atmospheric processes
- 2017
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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:6, s. 3799-3821
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Journal article (peer-reviewed)abstract
- We present a sensitivity study on transatlantic dust transport, a process which has many implications for the atmosphere, the ocean and the climate. We investigate the impact of key processes that control the dust outflow, i.e., the emission flux, convection schemes and the chemical aging of mineral dust, by using the EMAC model following Abdelkader et al. (2015). To characterize the dust outflow over the Atlantic Ocean, we distinguish two geographic zones: (i) dust interactions within the Intertropical Convergence Zone (ITCZ), or the dust-ITCZ interaction zone (DIZ), and (ii) the adjacent dust transport over the Atlantic Ocean (DTA) zone. In the latter zone, the dust loading shows a steep and linear gradient westward over the Atlantic Ocean since particle sedimentation is the dominant removal process, whereas in the DIZ zone aerosol-cloud interactions, wet deposition and scavenging processes determine the extent of the dust outflow. Generally, the EMAC simulated dust compares well with CALIPSO observations; however, our reference model configuration tends to overestimate the dust extinction at a lower elevation and underestimates it at a higher elevation. The aerosol optical depth (AOD) over the Caribbean responds to the dust emission flux only when the emitted dust mass is significantly increased over the source region in Africa by a factor of 10. These findings point to the dominant role of dust removal (especially wet deposition) in transatlantic dust transport. Experiments with different convection schemes have indeed revealed that the transatlantic dust transport is more sensitive to the convection scheme than to the dust emission flux parameterization. To study the impact of dust chemical aging, we focus on a major dust outflow in July 2009. We use the calcium cation as a proxy for the overall chemical reactive dust fraction and consider the uptake of major inorganic acids (i.e., H2SO4, HNO3 and HCl) and their anions, i.e., sulfate (SO42-), bisulfate (HSO4-), nitrate (NO 3) and chloride (Cl), on the surface of mineral particles. The subsequent neutralization reactions with the calcium cation form various salt compounds that cause the uptake of water vapor from the atmosphere, i.e., through the chemical aging of dust particles leading to an increase of 0.15 in the AOD under subsaturated conditions (July 2009 monthly mean). As a result of the radiative feedback on surface winds, dust emissions increased regionally. On the other hand, the aged dust particles, compared to the non-aged particles, are more efficiently removed by both wet and dry deposition due to the increased hygroscopicity and particle size (mainly due to water uptake). The enhanced removal of aged particles decreases the dust burden and lifetime, which indirectly reduces the dust AOD by 0.05 (monthly mean). Both processes can be significant (major dust outflow, July 2009), but the net effect depends on the region and level of dust chemical aging.
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| 3. |
- Carmichael, Gregory R., et al.
(author)
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Global Atmospheric Composition Observations : The Heart of Vital Climate and Environmental Action
- 2023
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In: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 104:3, s. E666-E672
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Journal article (peer-reviewed)abstract
- Further long-term investments in high-quality, research-driven, fit-for-purpose observations of atmospheric composition are needed globally to meet urgent societal needs related to weather, climate, air quality, and other environmental issues. Challenges include maintaining current observing systems in the face of eroding budgets for long-term monitoring and filling the geographical gaps for key constituents needed for sound services and policies. The observing systems can be bolstered through science-for-services applications, by embracing interoperable observation systems and standardized metadata, and ensuring that the data are findable, accessible, interoperable, and reusable. There is an urgent need to move from opportunities-driven one-component observations to more systematic, planned multifunctional infrastructure, where the observational data flow is coupled with Earth system models to serve both operational and research purposes. This approach fosters a community where user experience feeds back into the research components and where mature research results are translated into operational applications. This will lead to faster exploration and exploitation of atmospheric composition information and more impactful applications for science and society. We discuss here the urgent need to (i) achieve global coverage, (ii) harmonize infrastructure operations, (iii) establish focused policies, and (iv) strengthen coordination of atmospheric composition infrastructure.
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| 4. |
- Chiacchio, Marc, et al.
(author)
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On the links between meteorological variables, aerosols, and tropical cyclone frequency in individual ocean basins
- 2017
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In: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 122:2, s. 802-822
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Journal article (peer-reviewed)abstract
- A generalized linear model based on Poisson regression has been used to assess the impact of environmental variables modulating tropical cyclone frequency in six main cyclone development areas: the East Pacific, West Pacific, North Atlantic, North Indian, South Indian, and South Pacific. The analysis covers the period 1980-2009 and focuses on widely used meteorological parameters including wind shear, sea surface temperature, and relative humidity from different reanalyses as well as aerosol optical depth for different compounds simulated by the Goddard Chemistry Aerosol Radiation and Transport model. Circulation indices are also included. Cyclone frequency is obtained from the International Best Track Archive for Climate Stewardship. A strong link is found between cyclone frequency and the relative sea surface temperature, Atlantic Meridional Mode, and wind shear with significant explained log likelihoods in the North Atlantic of 37%, 27%, and 28%, respectively. A significant impact of black carbon and organic aerosols on cyclone frequency is found over the North Indian Ocean, with explained log likelihoods of 27%. A weaker but still significant impact is found for observed dust aerosols in the North Atlantic with an explained log likelihood of 11%. Changes in lower stratospheric temperatures explain 28% of the log likelihood in the North Atlantic. Lower stratospheric temperatures from a subset of Coupled Model Intercomparison Project Phase 5 models properly simulate the warming and subsequent cooling of the lower stratosphere that follows a volcanic eruption but underestimates the cooling by about 0.5 degrees C.
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| 5. |
- Freud, Eyal, et al.
(author)
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Pan-Arctic aerosol number size distributions : seasonality and transport patterns
- 2017
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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:13, s. 8101-8128
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Journal article (peer-reviewed)abstract
- The Arctic environment has an amplified response to global climatic change. It is sensitive to human activities that mostly take place elsewhere. For this study, a multi-year set of observed aerosol number size distributions in the diameter range of 10 to 500 nm from five sites around the Arctic Ocean (Alert, Villum Research Station - Station Nord, Zeppelin, Tiksi and Barrow) was assembled and analysed. A cluster analysis of the aerosol number size distributions revealed four distinct distributions. Together with Lagrangian air parcel back-trajectories, they were used to link the observed aerosol number size distributions with a variety of transport regimes. This analysis yields insight into aerosol dynamics, transport and removal processes, on both an intra- and an inter-monthly scale. For instance, the relative occurrence of aerosol number size distributions that indicate new particle formation (NPF) event is near zero during the dark months, increases gradually to similar to 40% from spring to summer, and then collapses in autumn. Also, the likelihood of Arctic haze aerosols is minimal in summer and peaks in April at all sites. The residence time of accumulation-mode particles in the Arctic troposphere is typically long enough to allow tracking them back to their source regions. Air flow that passes at low altitude over central Siberia and western Russia is associated with relatively high concentrations of accumulation-mode particles (N-acc) at all five sites - often above 150 cm(-3). There are also indications of air descending into the Arctic boundary layer after transport from lower latitudes. The analysis of the back-trajectories together with the meteorological fields along them indicates that the main driver of the Arctic annual cycle of N-acc, on the larger scale, is when atmospheric transport covers the source regions for these particles in the 10-day period preceding the observations in the Arctic. The scavenging of these particles by precipitation is shown to be important on a regional scale and it is most active in summer. Cloud processing is an additional factor that enhances the N-acc annual cycle. There are some consistent differences between the sites that are beyond the year-to-year variability. They are the result of differences in the proximity to the aerosol source regions and to the Arctic Ocean sea-ice edge, as well as in the exposure to free-tropospheric air and in precipitation patterns - to mention a few. Hence, for most purposes, aerosol observations from a single Arctic site cannot represent the entire Arctic region. Therefore, the results presented here are a powerful observational benchmark for evaluation of detailed climate and air chemistry modelling studies of aerosols throughout the vast Arctic region.
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| 6. |
- Fu, Pingqing, et al.
(author)
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Fluorescent water-soluble organic aerosols in the High Arctic atmosphere
- 2015
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Journal article (peer-reviewed)abstract
- Organic aerosols are ubiquitous in the earth's atmosphere. They have been extensively studied in urban, rural and marine environments. However, little is known about the fluorescence properties of water-soluble organic carbon (WSOC) or their transport to and distribution in the polar regions. Here, we present evidence that fluorescent WSOC is a substantial component of High Arctic aerosols. The ratios of fluorescence intensity of protein-like peak to humic-like peak generally increased from dark winter to early summer, indicating an enhanced contribution of protein-like organics from the ocean to Arctic aerosols after the polar sunrise. Such a seasonal pattern is in agreement with an increase of stable carbon isotope ratios of total carbon (delta C-13(TC)) from -26.8 parts per thousand to -22.5 parts per thousand. Our results suggest that Arctic aerosols are derived from a combination of the long-range transport of terrestrial organics and local sea-to-air emission of marine organics, with an estimated contribution from the latter of 8.7-77% (mean 45%).
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| 7. |
- Kawana, Kaori, et al.
(author)
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Hygroscopicity and CCN Activity of Water-Soluble Extracts From the Arctic Aerosols in Winter to Early Summer
- 2022
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In: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 127:19
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Journal article (peer-reviewed)abstract
- The hygroscopicity and cloud condensation nuclei (CCN) activity of water-soluble extracts from Arctic lower tropospheric aerosols during winter to summer were investigated under sub- and super-saturated conditions, with chemical composition and air mass origin. The κ values from the hygroscopic growth factor at 80%–90% relative humidity (κHTDMA) during winter, spring, and summer were 0.34 ± 0.06, 0.41 ± 0.05, and 0.25 ± 0.02, respectively, whereas those derived from CCN activation diameter at 0.29%–0.59% supersaturation (κCCNC) were 0.42 ± 0.03, 0.43 ± 0.05, and 0.34 ± 0.11, respectively. The hygroscopicity and CCN activity showed clear seasonal variations following changes in composition that are linked to natural, anthropogenic, and biogenic sources. During winter and spring, κ was high when highly hygroscopic components such as sea salts, sulfate, and highly-oxidized/aged particles were dominant due to long-range atmospheric transport and photochemical reactions. In contrast, κ was significantly lower in summer when water-insoluble (22%) and water-soluble organic matter (OM) (17%) were dominated with high biogenic activity associated with ice-edge zones. The κCCNC and κHTDMA values agreed well within 8% and the surface tension agreed with that of pure water within 10%. The κ for OM (κOM) estimated from chemical composition during spring and summer was on average 0.04 ± 0.06 (up to ∼0.17). This result suggests that highly hygroscopic components such as sea salt and sulfate mainly controlled particle hygroscopicity and CCN activity in winter, but water-soluble OM could also contribute in spring and summer.
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| 8. |
- Seguin, Alison Michelle, et al.
(author)
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Evidence of sea ice source in aerosol sulfate loading and size distribution in the Canadian High Arctic from isotopic analysis
- 2014
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In: J GEOPHYS RES-ATMOS. - 2169-897X. ; 119:2, s. 1087-1096
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Journal article (peer-reviewed)abstract
- The influence of frost flowers and seawater brine on ion chemistry in snow, snowpack, ice cores, and aerosols is detected when a lower sulfate to sodium ratio than in seawater is present in polar regions. This evidence can be masked when large amounts of non-sea-salt sulfate are present from other sources such as biogenic and anthropogenic sulfate. Frost flower delta S-34 values weremeasured for the first time in frost flower sulfates and did not differ significantly from the sea salt delta S-34 values of + 21 parts per thousand. A method using stable isotopes is introduced to determine the limit of contributions from sea salt and sea ice sources (including frost flowers and brine) on sulfate concentrations in aerosol samples from Alert, Canada. Knowledge of the range of values of delta S-34(nss) and the SO4/Na ratio found in sea ice sources (i.e., frost flowers) is used to quantitatively constrain the contributions from frost flowers and sea salt in the Arctic aerosol mass during the onset of winter in 2007 and 2008, allowing for quantification of non-sea-salt sulfate amounts during times when frost flowers are present. Frost flower and/or brine influence was found predominantly in the coarse-mode aerosols (>0.95 mu m). This method to determine the contributions from sea salt and sea ice sources can be carried over to future studies with snow and ice cores.
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| 9. |
- Sharma, S., et al.
(author)
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A Factor and Trends Analysis of Multidecadal Lower Tropospheric Observations of Arctic Aerosol Composition, Black Carbon, Ozone, and Mercury at Alert, Canada
- 2019
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In: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 124:24, s. 14133-14161
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Journal article (peer-reviewed)abstract
- Observations from 1980 to 2013 of 20 aerosol constituents, ozone and mercury at Alert, Canada (82.50 degrees N, 62.35 degrees W), were analyzed for trends and dominant factors of the Arctic haze during winter and spring. Trends reflect changing emissions in Eurasia, the main source region for surface pollution in the high Arctic. SO42-, H+, NH4,+ K+, Cu, Ni, Pb, Zn, nonsoil V, nonsoil Mn, and equivalent black carbon decreased between 23% and 80% as emissions declined rapidly in northern Eurasia during the early 1990s. NO3- increased by 20% as aerosol acidity declined. Metals were linked to emissions from smelting and fossil fuel combustion. In winter, ozone increased by 5% over 23 years, consistent with other observations and global modeling. Twelve PMF factors emerged for the dark period (November to February) and 13 for the light period (March to May). Eleven PMF factors are common to both dark and light, a twelfth factor was associated with sulfate in the dark and nitrate in the light, and the thirteenth (light period) was related to ozone and gaseous mercury depletion near Alert. IODINE and NITRATE factors, important for Arctic chemistry, changed with sunlight. In the light, 50% of all NO3- was on the NITRATE factor, while in the dark, most was associated with MODIFIED SEA SALT and equivalent black carbon. In the dark (light), 90% (28%) of iodine were found on the factor IODINE and 58% associated with SEA-SALT and MODIFIED SEA-SALT. These results help in understanding the role of atmospheric chemistry in weather and climate processes.
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| 10. |
- Singh, Dharmendra Kumar, et al.
(author)
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Distributions of Polycyclic Aromatic Hydrocarbons, Aromatic Ketones, Carboxylic Acids, and Trace Metals in Arctic Aerosols : Long-Range Atmospheric Transport, Photochemical Degradation/Production at Polar Sunrise
- 2017
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 51:16, s. 8992-9004
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Journal article (peer-reviewed)abstract
- The distributions, correlations, and source apportionment of aromatic acids, aromatic ketones, polycyclic aromatic hydrocarbons (PAHs), and trace metals were studied in Canadian high Arctic aerosols. Nineteen PAHs including minor sulfur-containing heterocyclic PAH (dibenzothiophene) and major 6 carcinogenic PAHs were detected with a high proportion of fluoranthene followed by benzo[k]fluoranthene, pyrene, and chrysene. However, in the sunlit period of spring, their concentrations significantly declined likely due to photochemical decomposition. During the polar sunrise from mid-March to mid-April, benzo[a]pyrene to benzo[e]pyrene ratios significantly dropped, and the ratios diminished further from late April to May onward. These results suggest that PAHs transported over the Arctic are subjected to strong photochemical degradation at polar sunrise. Although aromatic ketones decreased in spring, concentrations of some aromatic acids such as benzoic and phthalic acids increased during the course of polar sunrise, suggesting that aromatic hydrocarbons are oxidized to result in aromatic acids. However, PAHs do not act as the major source for low molecular weight (LMW) diacids such as oxalic acid that are largely formed at polar sunrise in the arctic atmosphere because PAHs are 1 to 2 orders of magnitude less abundant than LMW diacids. Correlations of trace metals with organics, their sources, and the possible role of trace transition metals are explained.
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