Strong Airflow Research Articles

Numerical study of a mesoscale vortex in the planetary boundary layer of the meiyu front

It was found that the heavy rainfall event along the Meiyu front in the lower reaches of the Yangtze River on 23 June 2009 was connected with a mesoscale disturbance vortex, which originated from the planetary boundary layer (PBL) and developed upward later and was discovered by using the Shuman-Shapiro filtering method. The mesoscale disturbance vortex in the PBL (PMDV) in this process corresponded well to the short-time rainstorm in the Doppler radar echo. Analysis of the high-resolution simulation results from the Advanced Weather Research and Forecasting Model (ARW) showed that there were several surface disturbances along the southern warm section of the Meiyu front prior to the generation of the PMDV. The PMDV interacted with the mesoscale convective system (MCS) and intensified the local convective precipitation. The north and southwest flows in the PBL converged at the time of the PMDV formation. Meanwhile, a southwesterly jet on the top of the PBL to the south side of the vortex reinforced the ascending motion and convergence. Hence, it is concluded that the PMDV was generated when the strong cold air flows north of the shear line encountered the southwest flow south of the shear line. The convergence line in the PBL, the intensification of the southwest wind, and the southward aggression of the north wind were critical for the development of the PMDV. The release of latent heat was found crucial for the formation of the PMDV as it facilitated the convergence at low levels.

Flame radiation feedback to fuel surface in medium ethanol and heptane pool fires with cross air flow

The work in this paper is to clarify and quantify experimentally the effect of cross air flow on flame radiation feedback to fuel surface in medium pool fires. Square pools with dimensions ranged in 10–25cm are burnt under cross air flow speed ranged in 0–2.5m/s, using ethanol and heptane as representative fuel producing flame of definitely different sootiness and luminosity as to compare their response to the cross air flow in radiation feedback. The incident radiation heat flux to the fuel surface is measured by a step-sum method using water-cooled radiation gauges on discrete regions of the surface, along with the fuel mass burning history recorded simultaneously by an electronic balance with resolution of 0.1g. Results show that the cross air flow, by deflecting the flame, reduces the radiation feedback remarkably to finally approach a nearly stable lower value with increase in flow speed. Such reduction relative to that with no wind is quantified, as found to be more effective for heptane pool fire (50–70%) than that for ethanol pool fire (25–35%). However, at the same time, the burning rate is enhanced by the cross air flow. The two fractions, χa (fraction of radiation heat absorbed by fuel surface to that needed for evaporation) and χs (fraction of incident feedback radiation to total heat released by combustion), are then further quantified. They both decrease considerably with increase in flow speed. The χa and χs under no wind are shown to be quite different for heptane (range in 20–60% (χa) and 0.5–1.5% (χs) increasing with pool size) and ethanol (nearly constant 25% (χa) and 2% (χs) independent of pool size). However, when subjected to a relative strong wind as Froude number (Fr) beyond 1, χa is found to be similar for these two different fuels (in 5–15%), but χs found in 0.4–1% for ethanol and in 0.1–0.5% for heptane. The behaviors of pool scale effect on both flame radiation feedback fraction (χa), and accordingly mass burning flux, with a cross air flow are shown to be quite different from those without cross air flow. The flame radiation feedback fraction (χa) increases with pool size and is much higher for heptane than that of ethanol at no cross air flow; while it is similar for these two fuels under a cross air flow and being much lower than that with no cross air flow. Accordingly, the mass burning flux increases with pool size at no cross air flow; while being similar at a relative higher value regardless of pool size for a given Fr with a cross air flow than that with no cross air flow (pool scale effect showing to be well converged by Fr when subjected to a relative strong cross air flow as Fr beyond the critical value of about 1). These quantifications and findings reveal that under a cross air flow, the relative importance of different heat feedback mechanism of a pool fire has been altered prominently due to the deflection of the flame. Flame radiation feedback declines remarkably while those from wall conduction and flame convection should be enhanced to be predominant, which is essential in re-considering the heat balance to characterize and especially to scale the burning behavior of a pool fire in cross air flows.

Paleomonsoon route reconstruction along a W–E transect in the Chinese Loess Plateau using the anisotropy of magnetic susceptibility: summer monsoon model

article i nfo The anisotropy of magnetic susceptibility (AMS) was investigated in three Chinese Loess Plateau sedimentary sections along a W-E transect (400 km). The loess-paleosol sequences in our study represent the most recent 130 kyr interval. The measured AMS was compared to expected theoretically derived magnetic fabrics occurring in strong and weak current airflow conditions. The major and minor AMS ellipsoid axis orientations were used to evaluate the paleowind direction along the transect. Previously published models assumed that cold and dry winter monsoons bringing dust from northwestern desert areas were responsible for the magnetic fabric formation of loess sequences. In our new interpretation, the stronger summer monsoons from the southeast played the major role in magnetic fabric orientation in the studied west and central parts of the Chinese Loess Plateau. Although the material was brought to the area by the winter monsoon, the AMS was generated during the rainy summer monsoon when the sedimentary particles including magnetite were rearranged, settled, and fixed. We reconstruct the summer paleomonsoon routes for the last 130 kyr. These winds prevail from SE to NW but appear to be affected by regional topographic factors. In the western section, the corridor between the north and south Liupan Mountains disturbed the summer monsoon route, shifting it from SE to SEE.

Observation and numerical simulation of an event of vortex/wave shedding from a mountain near the Hong Kong International Airport

AbstractIn the evening of 11 April 2011, vortex/wave shedding from a mountain to the south of the Hong Kong International Airport (HKIA) appeared to occur following the establishment of fresh to strong easterly airflow in Hong Kong. This paper documents the observations by the various meteorological instruments of the event and discusses the possibility of forecasting the vortex/wave shedding using a high resolution numerical weather prediction (NWP) model. The vortex/wave shedding was well observed by the Light Detection and Ranging (LIDAR) system at HKIA. The vortex/wave appeared as an area of reversed flow against the background east to southeasterly airflow in the airport area. It was detached from the mountain and moved to the northwest with the background southeasterly flow, with a gradual decrease of the spatial extent in the area of reversed flow. The vortex/wave brought about significant wind shear to both arrival flight paths to the west of HKIA, as evidenced from the headwind profile data measured by the LIDARs and the aircraft data. It had rather large vertical extent, reaching the top of the boundary layer, but did not extend downward to the surface, as shown from the vertical scans of the LIDAR and the surface wind observations. The shedding event is successfully captured by high‐resolution NWP model with a spatial resolution of 50 m. The model output has a lead time of 6–7 h ahead of the event, indicating the possible occurrence of terrain‐induced wind shear in the form of vortex/wave shedding from a mountain. As a result, the numerical simulation could be useful in giving an early alert to the aviation weather forecaster about the significant wind shear event, which could be hazardous to the landing aircraft. Copyright © 2011 Royal Meteorological Society

Reconstructed index of summer monsoon dry-wet modes in East Asia for the last millennium

Monthly precipitation datasets collected at 160 stations in China as well as the monthly winds and humidity data derived from the US National Centers for Environmental Prediction (NCEP) were used to construct the relationship between six summer dry-wet modes in eastern China and the summer monsoon airflow northward advance in East Asia. A millennial series of the monsoon dry-wet index (MDWI) was reconstructed based on Wang’s six summer dry-wet modes in eastern China since 950 AD. A high (low) index indicates that the strong (weak) East Asian summer monsoon airflow can reach northern (southern) China and cause above (below) normal precipitation. Interdecadal periodic variations, such as the approximate 70-year oscillation, can be found in the MDWI series. In the last millennium, northern China has experienced persistent decadal wet periods and persistent decadal dry periods. At present, the MDWI is a low period on the interdecadal time scale so above-normal precipitation is observed in southern China and below-normal precipitation in northern China.

MBAS (Methylene Blue Active Substances) and LAS (Linear Alkylbenzene Sulphonates) in Mediterranean coastal aerosols: Sources and transport processes

Abstract Methylene Blue Active Substances (MBAS) and Linear Alkylbenzene Sulphonates (LAS) concentrations, together with organic carbon and ions were measured in atmospheric coastal aerosols in the NW Mediterranean Basin. Previous studies have suggested that the presence of surfactants in coastal aerosols may result in vegetation damage without specifically detecting or quantifying these surfactants. Coastal aerosols were collected at a remote site (Porquerolles Island-Var, France) and at a more anthropised site (San Rossore National Park-Tuscany, Italy). The chemical data were interpreted according to a comprehensive local meteorological analysis aiming to decipher the airborne source and transport processes of these classes of compounds. The LAS concentration (anthropogenic surfactants) was measured in the samples using LC-MS/MS, a specific analytical method. The values were compared with the MBAS concentration, determined by a non-specific analytical method. At Porquerolles, the MBAS concentration (103 ± 93 ng m −3 ) in the summer samples was significantly higher than in the winter samples. In contrast, LAS concentrations were rarely greater than in the blank filters. At San Rossore, the mean annual MBAS concentration (887 ± 473 ng m −3 in PM10) contributed about 10% to the total atmospheric particulate organic matter. LAS mean concentration in these same aerosol samples was 11.5 ± 10.5 ng m −3 . A similar MBAS (529 ± 454 ng m −3 ) – LAS (7.1 ± 4.1 ng m −3 LAS) ratio of ∼75 was measured in the fine (PM2.5) aerosol fraction. No linear correlation was found between MBAS and LAS concentrations. At San Rossore site the variation of LAS concentrations was studied on a daily basis over a year. The LAS concentrations in the coarse fraction (PM10–2.5) were higher during strong sea storm conditions, characterized by strong air flow coming from the sea sector. These events, occurring with more intensity in winter, promoted the formation of primary marine aerosols containing LAS from the sea surface microlayer. In contrast to LAS, MBAS concentrations in the coarse fraction peaked in summer. Therefore, different sources are suggested for the two classes of compounds. In summer, increased MBAS concentration could be an indicator of phytoplanktonic blows enriching the sea surface microlayer with biogenic surfactants. In winter, some spikes in MBAS concentrations in the coarse fraction could be related to LAS concentrations and sea storm events. Moreover, in the fine fraction MBAS have a large concentration maxima in winter, corresponding to air masses coming from polluted continental areas. It is concluded that MBAS concentration in the fine or the coarse fraction is not an appropriate surrogate measurement of LAS concentration in aerosols because of the significant contribution from other sources to the MBAS concentration.

Mapping multiple gas/odor sources in an uncontrolled indoor environment using a Bayesian occupancy grid mapping based method

In this paper we address the problem of autonomously localizing multiple gas/odor sources in an indoor environment without a strong airflow. To do this, a robot iteratively creates an occupancy grid map. The produced map shows the probability each discrete cell contains a source. Our approach is based on a recent adaptation (Jakuba, 2007) [16] to traditional Bayesian occupancy grid mapping for chemical source localization problems. The approach is less sensitive, in the considered scenario, to the choice of the algorithm parameters. We present experimental results with a robot in an indoor uncontrolled corridor in the presence of different ejecting sources proving the method is able to build reliable maps quickly (5.5 minutes in a 6 m×2.1 m area) and in real time.

Paleomonsoon route reconstruction along a W–E transect in the Chinese Loess Plateau using the anisotropy of magnetic susceptibility: Summer monsoon model

The anisotropy of magnetic susceptibility (AMS) was investigated in three Chinese Loess Plateau sedimentary sections along a W–E transect (400 km). The loess–paleosol sequences in our study represent the most recent 130 kyr interval. The measured AMS was compared to expected theoretically derived magnetic fabrics occurring in strong and weak current airflow conditions. The major and minor AMS ellipsoid axis orientations were used to evaluate the paleowind direction along the transect. Previously published models assumed that cold and dry winter monsoons bringing dust from northwestern desert areas were responsible for the magnetic fabric formation of loess sequences. In our new interpretation, the stronger summer monsoons from the southeast played the major role in magnetic fabric orientation in the studied west and central parts of the Chinese Loess Plateau. Although the material was brought to the area by the winter monsoon, the AMS was generated during the rainy summer monsoon when the sedimentary particles including magnetite were rearranged, settled, and fixed. We reconstruct the summer paleomonsoon routes for the last 130 kyr. These winds prevail from SE to NW but appear to be affected by regional topographic factors. In the western section, the corridor between the north and south Liupan Mountains disturbed the summer monsoon route, shifting it from SE to SEE.

Removal of Liquid in a Long Pore Opened at Both Ends Using High-Intensity Aerial Ultrasonic Waves

We experimentally verified a method by which a liquid that has entered a long pore with open ends can be removed from the pore by using the acoustic radiation force produced by high-intensity aerial ultrasonic waves at a frequency of 20 kHz. The intensity of the ultrasonic waves was about 6 to 10 kPa. By using this method, it was confirmed that a liquid in pores of 1.5 to 5.0 mm diameter and 3 to 20 mm length could be instantaneously removed from the pores. This method, which did not use any air flow at a high pressure, has the significant advantage that it does not produce any strong air flow around the pore. We consider the intensity of the ultrasonic waves required to remove the liquid, the time required to remove the liquid, and the quantity of liquid removed, all of which were determined by varying the diameter and length of the pore.

Consequences of high transitory airflows generated by segmented pulse-jet cleaning of dust collector filter bags

Baghouse dust collectors are commonly used in industry for removing solid particles from dust-laden gas. Baghouse filter media need to be periodically cleaned in order to remove collected particles from the filter surface. Pulse-jet cleaning is the most commonly used method but the detachment forces involved always affect downstream particle emission adversely. Although it is possible to find information about the mechanisms and the factors that cause particle emission, no link has been made between the distribution of the dirty airflow via the filter elements and the increase in released downstream particles after the bag cleaning. Innovative instrumentation of a pulse-jet-cleaned pilot dust collector allowed measuring the variation in the individual airflows which pass through each filter bag during clogging and cleaning cycles. The way in which segmented pulse-jet cleaning influences total dirty airflow distribution amongst filter elements was investigated. The consequences on bag airflow resistance and downstream particle emission were studied. Filtration cycles can be related to a succession of segmented pulse-jet cleaning, leading to imbalanced bag airflow resistances, and clogging. This in turn leads to compensations between bag resistances as a function of dust-laden individual bag airflow values. Airflow resistance variations are caused by two complementary phenomena: permeation of high transitory airflows on the first bags cleaned and the re-suspension of detached particles after a pulse-jet cleaning. During a cleaning sequence, strong airflow increases on the first cleaned bags are mainly prejudicial to dust collector downstream particle concentration.

An electromagnetic energy scavenger from direct airflow

This paper presents two types of electromagnetic power generators exploiting direct conversion of airflow into mechanical vibration: (1) a windbelt-based vibratory linear energy scavenger targeting strong airflows and (2) a Helmholtz-resonator-based generator capable of scavenging energy from weaker airflows, i.e. environmental airflows. Both devices consist of two tightly coupled parts: a mechanical resonator, which produces high-frequency mechanical oscillation from quasi-constant airflow, and a permanent magnet/coil system, which generates electrical power from the resonator's motion. The proposed energy scavengers obviate the typically required matching of the resonant frequencies of the scavenger and the ambient energy sources it taps. This enables a device that is simpler, smaller and higher-frequency than the previously reported resonant power generator. The windbelt-based energy scavenger demonstrated a peak-to-peak output voltage of 81 mV at 0.53 kHz, from an input pressure of 50 kPa. The Helmholtz-resonator-based energy scavenger achieved a peak-to-peak output voltage of 4 mV at 1.4 kHz, from an input pressure of 0.2 kPa, which is equivalent to 5 m s−1 (10 mph) of wind velocity.

Characterization of a Prefilming Airblast Atomizer in a Strong Swirl Flow Field

Most gas turbine engines in service use a prefilming airblast atomizer in combination with strong swirling flow. An experimental investigation of the characteristics of a hollow cone prefilming airblast atomizer in a strong swirling air flow is presented in this paper. The measured quantities include the spray cone angle by planar imaging, pattemation using planar laser-induced fluorescence, planar droplet velocity field using two-component particle image velocimetry, and droplet size and velocity distributions using a phase Doppler particle-size analyzer and laser Doppler velocimetry. Patternation of the spray field showed regions of high droplet concentration and volume flux fluctuations in various cross-sectional planes. The investigation revealed the presence of droplets of narrow size range up to 25 μ around the axis of the atomizer in the central toroidal recirculation zone of the swirler. The presence of vortical structures entraining the droplets is observed from the instantaneous velocity vector fields. The velocity data shows entrainment of the droplets in the central toroidal recirculation zone. Examining the size and the velocity data reveals that the centrifugal action of the swirling air flowfield from the atomizer carries the bigger droplets outward, toward the periphery of the spray.

SPIRAL: A novel biologically-inspired algorithm for gas/odor source localization in an indoor environment with no strong airflow

This work describes the design and experimental results of an algorithm, designed to localize a gas source in an indoor environment with no strong airflow by using an autonomous agent. This condition exacerbates the patchiness and intermittency of odor distribution, typical of turbulent flows in the presence of strong mean flows. Furthermore, no information about the wind can be used to detect the position of the source. In the approach proposed here, the robot moves along spirals. A spiral can be reset and a new one started, based on the information acquired about gas distribution. This enables the robot to get close to the ejecting source, without relying on airflow measurements. Results from experiments are also described and discussed, to assess the efficiency of the proposed method.

Laboratory investigation on cooling effect of duct-ventilated embankment with a chimney in permafrost regions

In construction and maintenance of road construction in cold regions, permafrost has been the main influence on embankment stability. The cooling effect of duct-ventilated embankments on the underlying soil layers has been recognized as one technique but if the embankment is located such that there is little or no ambient wind, its effectiveness may be limited. In this paper the addition of vertical “chimneys” to the horizontal ventilated ducts was presented and two duct-ventilated embankments with and without a chimney were examined with the similarity theory, and it is found that the chimneys result in more effective cooling effect under windless conditions than if they are not present. The effect is straightforward: when the ambient air temperature is lower than the internal temperature of the embankment, cold air flows into the embankment from the ventilated ducts and out from the chimneys as a result of warming of the air by the internal temperatures in the embankment. When the ambient air temperature is above the internal temperature of the embankment, no strong air flow occurs within the ventilated ducts and the chimneys. The overall result is a net cooling effect through several cycles of varying temperatures and greater than that achieved by horizontal ventilated ducts alone. Therefore, the special duct-ventilated embankment with a chimney should be considered as an effective measure to protect embankment in warm and low wind permafrost regions.

Asian dust storm influence on North American ambient PM levels: observational evidence and controlling factors

Abstract. New observational evidence of the trans-Pacific transport of Asian dust and its contribution to the ambient particulate matter (PM) levels in North America was revealed, based on the interannual variations between Asian dust storms and the ambient PM levels in western North America from year 2000 to 2006. A high correlation was found between them with an R2 value of 0.83. From analysis of the differences in the correlation between 2005 and 2006, three factors explain the variation of trans-Pacific transport and influences of Asian dust storms on PM levels in western North America. These were identified by modeling results and the re-analysis data. They were 1) Strength of frontal cyclones from Mongolia to north eastern China: The frontal cyclones in East Asia not only bring strong cold air outbreaks, generating dust storms in East Asia, but also lift Asian dust into westerly winds of the free troposphere for trans-Pacific transport; 2) Pattern of transport pathway over the North Pacific: The circulation patterns of westerlies over the North Pacific govern the trans-Pacific transport pattern. Strong zonal airflow of the westerly jet in the free troposphere over the North Pacific favor significant trans-Pacific transport of Asian dust; 3) Variation of precipitation in the North Pacific: The scavenging of Asian dust particles by precipitation is a major process of dust removal on the trans-Pacific transport pathway. Therefore, variation of precipitation in the North Pacific could affect trans-Pacific transport of Asian dust.

Dilute suspension flow with nanoparticle deposition in a representative nasal airway model

The human nasal cavities with an effective length of only 10cm feature a wide array of basic flow phenomena because of their complex geometrics. Employing a realistic nasal airway model and demonstrating that laminar, quasisteady airflow can be assumed, dilute nanoparticle suspension flow and nanoparticle deposition are simulated and analyzed for 7.5⩽Q⩽20L∕min and 1⩽dp⩽150nm. The understanding and quantitative assessment of mixture flow fields and local nanoparticle wall concentrations in nasal airways with a thin mucus layer are very important for estimating the health risks of inhaled toxic aerosols, determining proper drug-aerosol delivery to target sites such as the olfactory regions and developing algebraic transfer functions for overall nasal dose-response analyses. Employing a commercial software package with user-supplied programs, the validated computer modeling results can be summarized as follows: (i) Most of the air flows through the middle-to-low main passageways. Higher airflow rates result in stronger airflow in the olfactory region and relatively lower flow rates in the meatuses. (ii) Nanoparticle deposition in human nasal airways is significant for tiny nanoparticles, i.e., 1⩽dp⩽2nm, which also represent some vapors. The smaller the nanoparticle size and the lower the flow rate, the higher are the total deposition efficiencies because of stronger diffusion and longer residence times. (iii) Nanoparticles with dp<5nm flow preferentially through the middle-to-low main passageway along with the major portion of the airflow. For relatively large nanoparticles (dp⩾5nm), due to the low diffusivities, fewer particles will deposit onto the wall leaving a much thinner nanoparticle gradient layer near the wall, i.e., such nanoparticles pass through the nasal cavities more uniformly with minor wall deposition. (iv) Secondary flows may enhance nanoparticle transport and deposition, especially in the meatuses by convecting nanoparticles into these particular regions. (v) For the olfactory region, an optimal particle size may exist due to the combined effects of nanoparticle transport and local deposition mechanisms. However, because of the low deposition flux and small surface area, the olfactory channels account for only very small total deposition values. (vi) A compact correlation for predicting nanoparticle deposition in human nasal airways has been developed.

A climatological study of rural surface ozone in central Greece

Abstract. Recent studies show that surface ozone levels at rural sites in Greece are generally high when compared with rural ozone measurements at northern European sites. The area of SE Europe, including Greece, is not very well monitored regarding rural ozone in comparison to central and northern Europe. In order to have the best possible picture of the rural surface ozone climatology in the area, based on the available data-sets of long-term continuous monitoring stations, the 10-year measurement records (1987-1996) of the Athens peripheral station of Liossia, (12 km N of the city center) and the urban background station of Geoponiki (3 km W) as well as the 4-year record (1996-1999) of the rural station of Aliartos (100 km NW of Athens), are analyzed in this paper. The data for Liossia and Geoponiki stations are screened for cases of strong airflow from rural areas (N-NE winds stronger than 5 m/s). The variation characteristics of the average rural ozone afternoon levels (12:00-18:00), with the best vertical atmospheric mixing, are mainly examined since these measurements are expected to be representative of the broader area. In all three stations there is a characteristic seasonal variation of rural ozone concentrations with lowest winter afternoon values at about 50 μg/m3 in December-January and average summer afternoon values at about 120 μg/m3 in July-August, indicating that high summer values are observed all over the area. The rural summer afternoon ozone values are very well correlated between the three stations, implying spatial homogeneity all over the area but also temporal homogeneity, since during the 13-year period 1987-1999 the rural afternoon ozone levels remained almost constant around the value of 120 μg/m3.

Experimental analysis of gas-sensitive Braitenberg vehicles

This article addresses the problem of localizing a static gas source in an indoor environment by a mobile robot. In contrast to previous works, the environment is not artificially ventilated to produce a strong unidirectional airflow. Here, the dominant transport mechanisms of gas molecules are turbulence and convection flow rather than diffusion, which results in a patchy, chaotically fluctuating gas distribution. Two Braitenberg-type strategies (positive and negative tropotaxis) based on the instantaneously measured spatial concentration gradient were investigated. Both strategies were shown to be of potential use for gas source localization. As a possible solution to the problem of gas source declaration (the task of determining with certainty that the gas source has been found), an indirect localization strategy based on exploration and concentration peak avoidance is suggested. Here, a gas source is located by exploiting the fact that local concentration maxima occur more frequently near the gas source compared to distant regions.

Palaeolimnological investigation of atmospheric pollution in the Søndre Strømfjord region, southern West Greenland: accumulation rates and spatial patterns

High-latitude ecosystems are inherently sensitive to natural environmental stress as a result of extreme seasonal variations in light and temperature, nutrient limitations, as well as other physical and chemical characteristics; consequently, these regions are quite vulnerable to the addition of pollutant stress. There is a poor understanding of spatial and temporal patterns of atmospheric pollution in the Arctic, because of the lack of monitoring stations and networks for current and past atmospheric deposition. Today, however, the Arctic is recognised as an important focus for long-range transport of contaminants, particularly from strong air flows which carry airborne pollutants from industrial regions at lower latitudes, e.g. heavy metals and persistent organic pollutants (POPs). A diverse range of anthropogenic pollutants has been shown to be present across much of the region (Aarkrog et al. 1997; AMAP 1998). Of particular importance are compounds, such as mercury and POPs, which present a risk to native fauna and also inhabitants. It is hypothesised for some volatile organic compounds, as well as possibly for mercury, that there may be a latitudinal fractionation that contributes to the continued mobilisation of these compounds from warmer to colder climates, where they are ultimately deposited and stored (Wania & Mackay 1993). Experimental data and limited field research support this ‘cold-condensation’ hypothesis, at least for some POPs (Blais et al. 1998).

Removal of chlorinated rubber coatings from concrete surfaces using an RF excited CO 2 laser

This paper describes the effects of radio frequency excited CO 2 laser (RF-CO 2) radiation on the material characteristics of white chlorinated rubber (CR) paint on concrete substrates. Direct laser irradiation of a paint coating has been performed. Almost complete removal of the coating with very little to almost no damage (glazing or scabbling) to the concrete substrate has been achieved. Performing the process without additional process gas, i.e. purely with an optics shield gas resulted in the generation of a brittle ash layer, covering the coating and shielding it from further laser irradiation. Avoidance of this was accomplished by introducing a strong airflow parallel to the coating surface during the process. This resulted in almost perfect removal of the coating material down to the substrate. The residual ash has been analysed via EDX and SEM.