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- Sharma, Prabhakar, 1976-, et al.
(författare)
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Gaseous Oxygen Uptake in Porous Media at Different Moisture Contents and Airflow Velocities
- 2009
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Ingår i: Journal of the Air & Waste Management Association. - : Informa UK Limited. - 1047-3289 .- 1096-2247 .- 2162-2906. ; 59:6, s. 676-682
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Tidskriftsartikel (refereegranskat)abstract
- The presence and distribution of water in the pore space isa critical factor for flow and transport of gases throughunsaturated porous media. The water content also affectsthe biological activity necessary for treatment of pollutedgas streams in biofilters. In this research, microbial activityand quantity of inactive volume in a porous mediumas a function of moisture content and gas flow rate wereinvestigated. Yard waste compost was used as a test medium,and oxygen uptake rate measurements were used toquantify microbial activity and effective active compostvolume using batch and column flow-through systems.Compost water contents were varied from air-dry to fieldcapacity and gas flows ranged from 0.2 to 2 L min1. Theresults showed that overall microbial activity and therelative fraction of active compost medium volume increasedwith airflow velocity for all levels of water contentup to a certain flow rate above which the oxygen uptakerate assumed a constant value independent of gas flow.The actual value of the maximum oxygen uptake rate wascontrolled by the water content. The oxygen uptake ratealso increased with increasing water content and reacheda maximum between 42 and 48% volumetric water content,above which it decreased, again likely because offormation of inactive zones in the compost medium.Overall, maximum possible oxygen uptake rate as a functionof gas flow rate across all water contents and gas flowscould be approximated by a linear expression. The relativefraction of active volume also increased with gas flowrate and reached approximately 80% for the highest gasflows used.
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| 3. |
- Winnes, Hulda, 1975, et al.
(författare)
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Particle Emissions from Ships: Dependence on Fuel Type
- 2009
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Ingår i: Journal of the Air & Waste Management Association. - : Informa UK Limited. - 1047-3289 .- 1096-2247 .- 2162-2906. ; 59:12, s. 1391-1398
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of field emission measurements that have been carried out on the 4500-kW four-stroke main engine on-board a product tanker. Two fuel qualities-heavy fuel oil (HFO) and marine gas oil (MGO)-have been tested on the same engine for comparable load settings. A fuel switch within the marine sector is approaching and the aim of this study is to draw initial conclusions on the subsequent effects on ship exhaust gas composition and emission factors with a focus on particles. Measurements on exhaust gas concentrations of carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), total hydrocarbons (HCs), and particulate matter (PM) were conducted. The gases, except SO2, did not show any major differences between the fuels. Specific PM emissions were generally higher for HFO than for MGO; however, for the smallest size-fraction measured containing particles 0.300.40 mu m in diameter, the opposite is observed. This finding emphasizes that to minimize negative health effects of particles from ships, further regulation may be needed to reduce small-sized particles; a fuel shift to low sulfur fuel alone does not seem to accomplish this reduction. The average of this and previously published data from on-board studies on particle emissions from ships results in emissions factors of 0.33 and 1.34 g/kWh for marine distillate oil (MDO) and HFO, respectively. Accounting for 1 standard deviation in each direction from the average values gives a range of 0.18-0.48 g/kWh for MDO and 0.56-2.12 g/kWh for HFO.
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- Hedberg Larsson, E, et al.
(författare)
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Is Levoglucosan a Suitable Quantitative Tracer for Wood Burning? - Comparison with Receptor Modeling on Trace Elements in Lycksele, Sweden
- 2006
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Ingår i: Journal of the Air and Waste Management Association. - 1096-2247. ; 56:12, s. 1669-1678
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Tidskriftsartikel (refereegranskat)abstract
- Particle emissions from residential wood combustion in small communities in Northern Sweden can sometimes increase the ambient particle concentrations to levels comparable to densely trafficked streets in the center of large cities. The reason for this is the combination of increased need for domestic heating during periods of low temperatures, leading to higher emission rates, and stable meteorological conditions. In this work, the authors compare two different approaches to quantify the wood combustion contribution to fine particles in Northern Sweden: a multivariate source-receptor analysis on inorganic compounds followed by multiple linear regression (MLR) of fine particle concentrations and levoglucosan used as a tracer. From the receptor model, it can be seen that residential wood combustion corresponds with 70% of modeled particle mass. Smaller contributions are also seen from local nonexhaust traffic particles, road dust, and brake wear (each contributing 14%). Of the mass, 1.5% is explained by long-distance transported particles, and 2% derives from a regional source deriving from either oil combustion or smelter activities. In samples collected in ambient air, a significant linear correlation was found between wood burning particles and levoglucosan. The levoglucosan fraction in the ambient fine particulate matter attributed to wood burning according to the multivariate analysis ranged from < 2% to 50%. This is much higher than the fraction found in the emission from the boilers expected to be responsible for most emissions at this site (between 3% and 6%). A laboratory emission study of wood and pellet boilers gave 0.3%(wt) to 22%(wt) levoglucosan to particle mass, indicating that the levoglucosan fraction may be highly dependent on combustion conditions, making it uncertain to use it as a quantitative tracer under real-world burning conditions. Thus, quantitative estimates of wood burning contributions will be very uncertain using solely levoglucosan as a tracer.
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