| 1. |
- Roldin, Pontus, et al.
(författare)
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Modelling non-equilibrium secondary organic aerosol formation and evaporation with the aerosol dynamics, gas- and particle-phase chemistry kinetic multilayer model ADCHAM
- 2014
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 14:15, s. 7953-7993
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Tidskriftsartikel (refereegranskat)abstract
- We have developed the novel Aerosol Dynamics, gas- and particle-phase chemistry model for laboratory CHAMber studies (ADCHAM). The model combines the detailed gas-phase Master Chemical Mechanism version 3.2 (MCMv3.2), an aerosol dynamics and particle-phase chemistry module (which considers acid-catalysed oligomerization, heterogeneous oxidation reactions in the particle phase and non-ideal interactions between organic compounds, water and inorganic ions) and a kinetic multilayer module for diffusion-limited transport of compounds between the gas phase, particle surface and particle bulk phase. In this article we describe and use ADCHAM to study (1) the evaporation of liquid dioctyl phthalate (DOP) particles, (2) the slow and almost particle-size-independent evaporation of alpha-pinene ozonolysis secondary organic aerosol (SOA) particles, (3) the mass-transfer-limited uptake of ammonia (NH3) and formation of organic salts between ammonium (NH4+) and carboxylic acids (RCOOH), and (4) the influence of chamber wall effects on the observed SOA formation in smog chambers. ADCHAM is able to capture the observed alpha-pinene SOA mass increase in the presence of NH3(g). Organic salts of ammonium and carboxylic acids predominantly form during the early stage of SOA formation. In the smog chamber experiments, these salts contribute substantially to the initial growth of the homogeneously nucleated particles. The model simulations of evaporating alpha-pinene SOA particles support the recent experimental findings that these particles have a semi-solid tar-like amorphous-phase state. ADCHAM is able to reproduce the main features of the observed slow evaporation rates if the concentration of low-volatility and viscous oligomerized SOA material at the particle surface increases upon evaporation. The evaporation rate is mainly governed by the reversible decomposition of oligomers back to monomers. Finally, we demonstrate that the mass-transfer-limited uptake of condensable organic compounds onto wall-deposited particles or directly onto the Teflon chamber walls of smog chambers can have a profound influence on the observed SOA formation. During the early stage of the SOA formation the wall-deposited particles and walls themselves serve as an SOA sink from the air to the walls. However, at the end of smog chamber experiments the semi-volatile SOA material may start to evaporate from the chamber walls. With these four model applications, we demonstrate that several poorly quantified processes (i.e. mass transport limitations within the particle phase, oligomerization, heterogeneous oxidation, organic salt formation, and chamber wall effects) can have a substantial influence on the SOA formation, lifetime, chemical and physical particle properties, and their evolution. In order to constrain the uncertainties related to these processes, future experiments are needed in which as many of the influential variables as possible are varied. ADCHAM can be a valuable model tool in the design and analysis of such experiments.
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| 2. |
- Hooshmand, Babak, et al.
(författare)
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Homocysteine and holotranscobalamin and the risk of Alzheimer disease : a longitudinal study
- 2010
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Ingår i: Neurology. - 0028-3878 .- 1526-632X. ; 75:16, s. 1408-1414
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To examine the relation between serum levels of homocysteine (tHcy) and holotranscobalamin (holoTC), the active fraction of vitamin B12, and risk of incident Alzheimer disease (AD) in a sample of Finnish community-dwelling elderly. METHODS: A dementia-free sample of 271 subjects aged 65-79 years derived from the Cardiovascular Risk Factors, Aging, and Dementia (CAIDE) study was followed up for 7 years to detect incident AD. The association between serum tHcy and holoTC with AD was analyzed with multiple logistic regression after adjusting for several potential confounders, including common vascular risk factors. RESULTS: The odds ratios (ORs) (95% confidence interval [CI]) for AD were 1.16 (1.04-1.31) per increase of 1 μmol/L of tHcy at baseline and 0.980 (0.965-0.995) for each increase of 1 pmol/L baseline holoTC. Adjustment for several potential confounders including age, sex, education, APOE ε4 allele, body mass index, Mini-Mental State Examination, smoking, stroke, and blood pressure did not alter the associations: ORs (95% CI) for AD became 1.19 (1.01-1.39) for tHcy and 0.977 (0.958-0.997) for holoTC. Adjusting for holoTC attenuated the tHcy-AD link (OR changed from 1.16 to 1.10, 95% CI 0.96-1.25). The holoTC-AD relationship was less influenced by controlling for tHcy (OR changed from 0.980 to 0.984, 95% CI 0.968-1.000). Addition of folate did not change any of the results. CONCLUSIONS: This study suggests that both tHcy and holoTC may be involved in the development of AD. The tHcy-AD link may be partly explained by serum holoTC. The role of holoTC in AD should be further investigated.
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| 3. |
- Rusanen, Minna, et al.
(författare)
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Heavy smoking in midlife and long-term risk of Alzheimer disease and vascular dementia
- 2011
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Ingår i: Archives of Internal Medicine. - : American Medical Association (AMA). - 0003-9926 .- 1538-3679. ; 171:4, s. 333-339
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Smoking is a risk factor for several life-threatening diseases, but its long-term association with dementia is controversial and somewhat understudied. Our objective was to investigate the long-term association of amount of smoking in middle age on the risk of dementia, Alzheimer disease (AD), and vascular dementia (VaD) several decades later in a large, diverse population.METHODS: We analyzed prospective data from a multiethnic population-based cohort of 21,123 members of a health care system who participated in a survey between 1978 and 1985. Diagnoses of dementia, AD, and VaD made in internal medicine, neurology, and neuropsychology were collected from January 1, 1994, to July 31, 2008. Multivariate Cox proportional hazards models were used to investigate the association between midlife smoking and risk of dementia, AD, and VaD.RESULTS: A total of 5367 people (25.4%) were diagnosed as having dementia (including 1136 cases of AD and 416 cases of VaD) during a mean follow-up period of 23 years. Results were adjusted for age, sex, education, race, marital status, hypertension, hyperlipidemia, body mass index, diabetes, heart disease, stroke, and alcohol use. Compared with nonsmokers, those smoking more than 2 packs a day had an elevated risk of dementia (adjusted hazard ratio [HR], 2.14; 95% CI, 1.65-2.78), AD (adjusted HR, 2.57; 95% CI, 1.63-4.03), and VaD (adjusted HR, 2.72; 95% CI, 1.20-6.18).CONCLUSIONS: In this large cohort, heavy smoking in midlife was associated with a greater than 100% increase in risk of dementia, AD, and VaD more than 2 decades later. These results suggest that the brain is not immune to long-term consequences of heavy smoking.
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| 4. |
- Rusanen, M, et al.
(författare)
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Midlife smoking, apolipoprotein E and risk of dementia and Alzheimer's disease : a population-based cardiovascular risk factors, aging and dementia study
- 2010
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Ingår i: Dementia and Geriatric Cognitive Disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 30:3, s. 277-284
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Tidskriftsartikel (refereegranskat)abstract
- AIM: To elucidate the effect of midlife smoking on the risk of dementia and Alzheimer's disease (AD), and the possible modification of this relation by the apolipoprotein E (APOE) ε4.METHODS: Participants of the Cardiovascular Risk Factors, Aging and Dementia study were randomly selected from population-based samples originally studied in midlife (1972, 1977, 1982 or 1988). After an average follow-up of 21 years, 1,449 persons (73%) aged 65-79 years took part in a reexamination in 1998.RESULTS: Smoking in midlife increased the risk of dementia (odds ratio, OR: 4.93; 95% CI: 1.51-16.11) and AD (OR: 6.56; 95% CI: 1.80-23.94) among the APOE ε4 carriers, but not among the APOE ε4 noncarriers.CONCLUSION: Midlife smoking was associated with an increased risk of dementia and AD later in life only among those individuals carrying the APOE ε4 allele. These results suggest that the association between smoking and AD may be complex and vary according to genotype.
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| 5. |
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| 6. |
- Öström, Emilie, et al.
(författare)
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Biogenic SOA formation through gas-phase oxidation and gas-to-particle partitioning-a comparison between process models of varying complexity
- 2014
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 14:21, s. 11853-11869
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Tidskriftsartikel (refereegranskat)abstract
- Biogenic volatile organic compounds (BVOCs) emitted by vegetation play an important role for aerosol mass loadings since the oxidation products of these compounds can take part in the formation and growth of secondary organic aerosols (SOA). The concentrations and properties of BVOCs and their oxidation products in the atmosphere are poorly characterized, which leads to high uncertainties in modeled SOA mass and properties. In this study, the formation of SOA has been modeled along an air-mass trajectory over northern European boreal forest using two aerosol dynamics box models where the prediction of the condensable organics from the gas-phase oxidation of BVOC is handled with schemes of varying complexity. The use of box model simulations along an air-mass trajectory allows us to compare, under atmospheric relevant conditions, different model parameterizations and their effect on SOA formation. The result of the study shows that the modeled mass concentration of SOA is highly dependent on the organic oxidation scheme used to predict oxidation products. A near-explicit treatment of organic gas-phase oxidation (Master Chemical Mechanism version 3.2) was compared to oxidation schemes that use the volatility basis set (VBS) approach. The resulting SOA mass modeled with different VBS schemes varies by a factor of about 7 depending on how the first-generation oxidation products are parameterized and how they subsequently age (e.g., how fast the gas-phase oxidation products react with the OH radical, how they respond to temperature changes, and if they are allowed to fragment during the aging process). Since the VBS approach is frequently used in regional and global climate models due to its relatively simple treatment of the oxidation products compared to near-explicit oxidation schemes, a better understanding of the above-mentioned processes is needed. Based on the results of this study, fragmentation should be included in order to obtain a realistic SOA formation. Furthermore, compared to the most commonly used VBS schemes, the near-explicit method produces less-but more oxidized-SOA.
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