Detection of iodine monoxide radicals in the marine boundary layer using laser induced fluorescence spectroscopy

A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere. An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of the IO A²Π_3/2 ← X²Π_3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N₂O/CF₃I/N₂ mixtures with O₃ actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer) campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF.     

Aerodynamic Parameters of a UK City Derived from Morphological Data

Detailed three-dimensional building data and a morphometric model are used to estimate the aerodynamic roughness length z ₀ and displacement height d over a major UK city (Leeds). Firstly, using an adaptive grid, the city is divided into neighbourhood regions that are each of a relatively consistent geometry throughout. Secondly, for each neighbourhood, a number of geometric parameters are calculated. Finally, these are used as input into a morphometric model that considers the influence of height variability to predict aerodynamic roughness length and displacement height. Predictions are compared with estimations made using standard tables of aerodynamic parameters. The comparison suggests that the accuracy of plan-area-density based tables is likely to be limited, and that height-based tables of aerodynamic parameters may be more accurate for UK cities. The displacement heights in the standard tables are shown to be lower than the current predictions. The importance of geometric details in determining z ₀ and d is then explored. Height variability is observed to greatly increase the predicted values. However, building footprint shape only has a significant influence upon the predictions when height variability is not considered. Finally, we develop simple relations to quantify the influence of height variation upon predicted z ₀ and d via the standard deviation of building heights. The difference in these predictions compared to the more complex approach highlights the importance of considering the specific shape of the building-height distributions. Collectively, these results suggest that to accurately predict aerodynamic parameters of real urban areas, height variability must be considered in detail, but it may be acceptable to make simple assumptions about building layout and footprint shape.     

Shortage in the midst of plenty: Labour strategies in four Central and Eastern European cities

Labour shortage was an integral feature of the communist system of economic management and one that seemed most unlikely to persist in the face of systemic transformation. A casual examination of the unemployment rates that have emerged throughout most of Central and Eastern Europe (CEE) during the course of the past decade might suggest that this early assumption was correct. However, within the region the aggregate rate of joblessness, as well as the behaviour of national output, mask the fact that certain, major urban centres appear to have weathered well the storms caused by exposure to western markets and stringent fiscal and monetary policies. In these centres transformation has meant, to a greater or lesser degree, industrial modernisation and this begs the question of whether the human capital portfolios of the inherited labour force match up to the requirements of the new environment. This paper examines the meaning of the concept of labour shortage and presents the findings from a survey of employers in four leading cities of three major CEE economies designed to elicit if, and how, manpower requirements are being met in the present climate. The results indicate that, somewhat paradoxically, labour shortage persists in the more flexible markets of the post-communist era and that firms do not expect the situation to change radically in the near future. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental validation of seismic retrofit solutions for URM chimneys

Clay-brick unreinforced masonry (URM) chimneys are a common architectural feature of vintage domestic and commercial URM and timber-framed buildings widely encountered worldwide. URM chimneys include a cantilevered appendage above the roofline that during earthquakes-induced shaking is susceptible to significant damage and collapse, which can result in fatalities, injuries, and property damage. To mitigate this risk, many vintage URM chimneys are removed, braced, or eventually replaced with modern alternatives. The earthquake performance of 15,400 URM chimneys damaged during the 2010/2011 Canterbury earthquake sequence was investigated using a photographic database and insurance claims data. The widespread damage and failure of a large proportion of retrofitted chimneys was the impetus for an experimental shake-table testing campaign that was undertaken to assess the performance of five prototypical URM chimneys in their as-built and retrofitted conditions. Cost-effective retrofit techniques with low aesthetic impact, including the use of near surface mounted carbon-fibre reinforced polymer strips and post-tensioning, were investigated. Tested chimneys were constructed to replicate the most commonly encountered geometric characteristics and construction details collected during an in-field pilot survey of 351 undamaged vintage URM chimneys.     

Marine debris surveys at Volunteer Beach, Falkland Islands, during the summer of 2001/02

This survey evaluated the monthly accumulation rate of marine debris and the types of objects washed ashore at Volunteer Beach on East Falkland between October 2001 and March 2002. The mean (±SD) accumulation rate of marine debris was 77 ± 25 items/km/month, of a mean weight of 17.3 ± 12 kg. Forty different objects were collected and the five most frequent items were cotton fabric, string, polystyrene packing sheet, plastic packing tape and broken plastic pieces. The debris on Volunteer Beach was dominated by fishing debris; 42% of the items were discarded fishing equipment, while 39% of the items were of a packaging or associated nature. The mostly likely source of this household waste was fishing vessels, with Falkland Islands Government (FIG) fisheries observers seeing 27 of the 40 items of debris collected from Volunteer Beach being discarded from fishing vessels. It is suggested that, although further marine debris research is warranted, more effective at-sea ship waste disposal regulations are required in Falkland waters to reduce environmental and economic threats both at the local and international level.     

Novel measurements of atmospheric iodine species by resonance fluorescence

A field instrument has been developed for the purpose of measuring gas-phase atmospheric iodine species in the marine boundary layer. Vacuum UV resonance-fluorescence (RF), generated using a microwave discharge lamp, is employed to detect atomic iodine via the (5p⁴6s)–(5p⁵) transitions around 178–184 nm. The system can be operated in two modes; either to directly measure ambient iodine atoms, or to measure the total photolabile iodine loading of ambient air, through broadband visible photolysis of photolabile iodine-containing species, with subsequent RF detection of the iodine atoms released. In both cases the instrument allows for the in situ measurement of the species detected, which is advantageous for gathering information concerning their local sources and distribution. The instrument is calibrated through generation of a known concentration of iodine atoms from the photolysis of I₂ using a mercury pen-ray lamp. The instrument was deployed for the first time in August 2007 at Mace Head on the west coast of Ireland; initial results from this field trial are presented. Ambient iodine atoms were measured at levels up to 22 ± 4.8 ppt during the day, coinciding with the lowest tides, when Laminaria seaweed beds were exposed. The total photolabile iodine loading was also measured during several night-time and day-time periods and was found to correlate inversely with tidal height. Inferred I₂ concentrations based on these measurements indicate levels of several hundred ppt at the Mace Head site. These measurements represent the first direct observations of ambient iodine atoms and measurement of total photolabile iodine in the atmosphere.     

Resistivity monitoring of the tephra barrier at Crater Lake,Mount Ruapehu,New Zealand

The eruptions of Mt Ruapehu in the North Island of New Zealand in 1995 and 1996 caused a tephra barrier to be formed across the outlet of Crater Lake. By 2005 seepage from the refilled lake into the barrier raised the possibility of an eventual collapse of the barrier, releasing a catastrophic lahar down the mountain.As part of an extensive monitoring programme of the tephra barrier, direct current (dc) resistivity surveys were carried out on a number of lines along and across it in order to test whether the extent of the seepage could be measured (and monitored) by geophysical means. Two dimensional inversion of measured apparent resistivity data showed that between the initial measurements, made in January 2005, and February 2006, there was a gradual decrease in resistivity above the old outlet from ~ 50–60 Ωm to ~ 30 Ωm. This gave the first indication that lake water was seeping into the barrier. Between October and December 2006 there was a rapid rise in lake level to only 2 m below the top of the barrier, and a further resistivity survey in January 2007 showed that there had been a further decrease in resistivity throughout the entire barrier with values dropping to < 10 Ωm. The extent of this low resistivity indicated that the barrier was now saturated. At this stage lake water was penetrating the barrier and starting to cause erosion on its downstream side. Catastrophic collapse occurred on 18 March 2007, accompanied by a lahar in the Whangaehu river valley.Subsequent forward 3D numerical modelling of the resistivity structure of the barrier has confirmed that the observed changes in measured resistivity were directly related to the progress of seepage of lake water into the barrier.