| 1. |
- Abdelkader, Mohamed, et al.
(författare)
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Sensitivity of transatlantic dust transport to chemical aging and related atmospheric processes
- 2017
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:6, s. 3799-3821
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Dasari, Sanjeev, 1989-
(författare)
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Isotope-based constraints on sources and processing of black carbon, carbon monoxide, and brown carbon in South Asia
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The highly populated South Asian region is facing rapid economic growth and urbanization. Here, both climate- and health-affecting atmospheric agents such as light-absorbing aerosols black carbon (BC) and brown carbon (BrC), trace gas carbon monoxide (CO), are often found in relatively high levels compared to in other regions. However, atmospheric chemistry-transport/climate models are unable to fully capture the extent of the abundance of BC, CO, and BrC in the regional atmosphere during winter. The Thesis aims to address potentially important uncertainties that may be contributing to the model-observation offset — uncertainties in the ambient optical properties of BrC, uncertainties in the relative source contributions of BC (biomass burning vs. fossil fuel combustion) and CO (direct emission-derived vs. atmospheric chemical oxidation-derived), uncertainties in the regional lifetime and absolute emission fluxes of BC. For the Thesis work, field sampling was conducted at three sites, megacity Delhi (key source region), the Bangladesh Climate Observatory–Bhola Island (BCOB; receptor site for the highly-polluted Indo-Gangetic Plain) and the Maldives Climate Observatory–Hanimaadhoo Island (MCOH; receptor site for wider South Asia).The light-absorptivity of water-soluble BrC is found to decrease by ~84% during transport of haze from source-to-receptor regions i.e., Delhi-to-BCOB-to-MCOH — much greater than estimated in chamber studies and accounted in models. Atmospheric photochemical oxidation is found to be a likely driver for the loss of water-soluble BrC light-absorption in the S Asian outflow (with an estimated bleaching rate of 0.20±0.05 day−1) (Paper I). Radiocarbon (Δ14C)-based source apportionment of BC aerosols shows a stark similarity in the relative contributions of fossil (~50%) and biomass sources (~50%) at BCOB as well as at MCOH, suggesting a regional homogeneity in BC source contributions. However, a distinct stable isotopic fingerprint (δ13C) of BC in the N Indian Ocean is found to be arising from a small yet significant contribution (upto 10%) from C4-biomass burning in peninsular India (region south of 23.4°N) (Paper II). Comparison of source-segregated observed and emission inventory-driven modeled BC concentrations indicates regional offsets in the anthropogenic emission fluxes of BC in emission inventories—overestimated fossil-BC in the Indo-Gangetic Plain and underestimated biomass-BC in peninsular India (Paper II). Dual-isotope (δ13C, δ18O)-based source apportionment of CO shows a significantly large contribution (~80%) from direct emissions of primary sources (biomass burning and fossil fuel combustion) in South Asia, in contrast to modeled CO budget (Paper III). The BC-to-CO ratio in South Asia is found to be higher, by a factor of 2-3, than in other polluted regions such as in East Asia during winter. The regional lifetime and emission flux of BC are estimated to be 8±0.5 days (higher than values used in models) and ~2.4±1 Tg/yr (significantly higher than estimated in current emission inventories), respectively (Paper IV).Taken together, for convergence between models and observations in wintertime South Asia, i) the ‘dynamic’ nature of BrC light-absorption should be considered in models, ii) improvements in emission information of BC and CO are needed for better-simulating concentrations. Controls on activities such as open burning (such as agricultural crop residue burning, domestic burning of wood and dung as fuel) in South Asia could enable a reduction in BC, CO, and BrC, thereby leading to improved air quality and paving the way for achieving some of the key sustainable development goals outlined by the United Nations.
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| 3. |
- Kirkby, Jasper, et al.
(författare)
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Atmospheric new particle formation from the CERN CLOUD experiment
- 2023
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Ingår i: Nature Geoscience. - 1752-0894 .- 1752-0908. ; 16:11, s. 948-957
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol particles in the atmosphere profoundly influence public health and climate. Ultrafine particles enter the body through the lungs and can translocate to essentially all organs, and they represent a major yet poorly understood health risk. Human activities have considerably increased aerosols and cloudiness since preindustrial times, but they remain persistently uncertain and underrepresented in global climate models. Here we present a synthesis of the current understanding of atmospheric new particle formation derived from laboratory measurements at the CERN CLOUD chamber. Whereas the importance of sulfuric acid has long been recognized, condensable vapours such as highly oxygenated organics and iodine oxoacids also play key roles, together with stabilizers such as ammonia, amines and ions from galactic cosmic rays. We discuss how insights from CLOUD experiments are helping to interpret new particle formation in different atmospheric environments, and to provide a mechanistic foundation for air quality and climate models. The CLOUD experiment provides important insights into new particle formation in different atmospheric environments.
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| 4. |
- Wang, Mingyi, et al.
(författare)
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Synergistic HNO3–H2SO4–NH3 upper tropospheric particle formation
- 2022
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 605:7910, s. 483-489
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Tidskriftsartikel (refereegranskat)abstract
- New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN). However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles—comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO3–H2SO4–NH3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.
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