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- Dasari, Sanjeev, et al.
(författare)
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Observation-constrained atmospheric lifetime and emission fluxes of black carbon aerosols over South Asia
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Black carbon (BC) aerosols cause climate perturbation and affect air quality/human health. In densely populated South Asia—where the warming effect of BC is estimated to be ~ orders of magnitude higher than the global average—model simulations underestimate the wintertime atmospheric abundance of BC relative to surface observations. Two possible explanations for this model-observation offset are ill-constrained regional emission fluxes and atmospheric BC lifetime (τBC). Here, we combine hourly-resolved BC and carbon monoxide (CO) measurements for three successive winters from a South Asian receptor site—the Maldives Climate Observatory at Hanimaadhoo (MCOH)—in inverse frameworks, to assess the impact of emissions fluxes and lifetimes on ambient BC concentrations. The average ΔBC/ΔCO ratio (background corrected) at MCOH of 14±5 ng m-3 ppb-1 is found to be 2-3 times higher than in the East Asian outflow (range: 2 to 8 ng m-3 ppb-1). A BC transport efficiency of ~86% suggests low influence of wet scavenging processes during the dry South Asian winter period. Using statistical time series analysis, the τBC for dry wintertime South Asia is estimated to be 8±0.5 days, which is higher than commonly used in models. By coupling air mass back trajectories, lifetimes, and the ΔBC/ΔCO time-series data within an inverse modelling framework, we provide an observation-based “top-down” BC emission flux for South Asia estimated to be ~2.4±1 Tg/year. This is significantly higher than estimates from current “bottom-up” emission inventories (EIs). Taken together, this study suggests that to reconcile long-standing BC model-observation offsets in South Asia, existing emission estimates may need to be more than doubled in magnitude.
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- Strömqvist, Johan, 1976-, et al.
(författare)
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Nitroxide Spin-Label Quenching of Fluorophore’s Triplet Stateas a Tool for Studying Diffusion Mediated Reactions in LipidMembranes
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Annan publikation (populärvet., debatt m.m.)abstract
- In this work, we introduce an approach to study bimolecularinteractions in model lipid bilayers and biologicalmembranes, which exploits the influence of membrane-associatedElectron Spin Resonance (ESR) labels on the fluorescencesignal of likewise membrane-bound fluorophoremarkers. It is shown how one can exploit the high detectionsensitivity of the fluorescence signal without loosing the abilityto follow low-frequency molecular interactions, takingplace on a time scale well beyond that of the fluorescencelifetimes. The approach utilizes triplet state monitoring byFluorescence Correlation Spectroscopy (FCS), whereby thefluctuations in a strong fluorescence signal is used to characterizetransition rates to and from the lowest triplet stateof the fluorophores, which take place on a time scale 3 to 6orders of magnitude slower than the fluorescence lifetimesof the fluorophores. FCS measurements were performed onthe dye Lissamine Rhodamine B (LRB) in aqueous solutionsand bound to a lipid in a liposome, and in the presence of differentlocal concentrations of the ESR label TEMPO. Bothin the aqueous solution and in the lipid membrane measurements,the measured relative changes in the singlet-triplettransitions rates were found to well reflect the collisionalfrequencies between the LRB and TEMPO molecules. Theproposed approach, allowing low-frequency interactionsto be monitored with a bright fluorescence signal offers abroad applicability, both in terms of read-out means, typesof molecular interactions that can be followed, and in whatenvironment these interactions can be measured. From thispoint of view, it can prove useful for a broad category ofmolecular interaction studies.
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