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The hygroscopic properties of aerosol particles, composed of two different commercially available humic acids, have been investigated in the temperature range 293–295 K as a function of relative humidity using an electrodynamic balance. The measured mass growth factors of Sigma-Aldrich humic acid sodium salt (NaHA) and leonardite humic acid (LHA) at 90% relative humidity are 1.87±0.02 and 1.20±0.05, respectively. There is a general agreement between the results described in this study with previous TDMA results, which are undertaken with smaller particle ensembles and shorter aerosol–water equilibration times. The measured mass growth factors of Sigma-Aldrich humic acid sodium salt (NaHA) and leonardite humic acid (LHA) at 90% relative humidity are 1.87±0.05 and 1.20±0.05, respectively. The UNIFAC model was used to calculate the relationship between water activity and the concentrations of a modelled LHA molecule, and thus the hygroscopicity. The LHA molecule was modelled by both the Steelink monomer and the Northeastern–Temple–Birmingham humic acid monomer structural models.

This chapter describes the atmospheric chemistry governing the behaviour of reactive inorganic halogen compounds in the marine boundary layer (MBL). Particular emphasis is placed on the influence of the halogens on ozone and oxidising processes. The introduction indicates the lifecycle of reactive halogen species, their sources and sinks, as well as the chemical interactions with the background photochemistry of the troposphere. The gas-phase chemistry of the chlorine, bromine and iodine species is then described, indicating their differences in reactivity. The reactions which lead to ozone loss and coupling reactions with NO x and HO x species present in the MBL are also discussed. The next section deals with the heterogeneous reactions involving halogen species, in particular those which lead to activation of Cl - and Br - contained in sea-salt aerosols. A brief description of the properties of marine aerosols is given. The processes involved in chemical modification ('ageing') of sea-salt aerosol are described. The chemical mechanisms for halogen release by acid displacement, redox reactions involving NO x and redox reactions involving HOX (X = halogen) are then discussed in detail. A brief description of the evidence for halogen catalysed ozone loss and VOC degradation from atmospheric measurements and modelling studies is given.

A prevalence study of methicillin-resistant Staphylococcus aureus (MRSA) colonization was carried out in 17 nursing homes in Northamptonshire over a 20-month period. Thirteen of 275 residents swabbed (4.7%) were found to be colonized and six of the 17 homes (35%) had colonized residents. Only two homes had more than one colonized resident. Individual risk factors for colonization were gender (male) and the presence of skin ulcers and sores. There were no significant risk factors identified for homes. Spread may have occurred in the two homes which had more than one colonized resident. Both these homes had the epidemic strain EMRSA-15 whereas three of the four homes with a single colonized resident had EMRSA-16. It is suggested that homes with residents colonized with EMRSA-16 may be able to prevent spread by adherence to good infection control procedures but that this may not be adequate to prevent spread of EMRSA-15.

An outbreak of methicillin-resistant Staphylococcus aureus (MRSA) infection caused by a novel phage-type (now designated EMRSA-16) occurred in three hospitals in East Northamptonshire over a 21-month period (April 1991--December 1992). Four hundred patients were colonized or infected. Seven patients died as a direct result of infection. Chest infections were significantly associated with the outbreak strain when compared with methicillin-sensitive S. aureus. Twenty-seven staff and two relatives who cared for patients were also colonized. A 'search and destroy' strategy, as advocated in the current UK guidelines for control of epidemic MRSA was implemented after detection of the first case. Despite extensive screening of staff and patients and isolation of colonized and infected patients, the outbreak strain spread to all wards of the three hospitals except paediatrics and maternity. A high incidence of throat colonization (51%) was observed. Failure to recognize the importance of this until late in the outbreak contributed to the delay in containing its spread. Key parts of the strategy which eventually contained the local outbreak were the establishment of isolation wards in two hospitals, treatment of all colonized patients and staff to eradicate carriage and screening of all patients upon discharge from wards where MRSA had ever been detected. EMRSA-16 spread to neighbouring hospitals by early 1992 and to London and the South of England by 1993. It is distinguished from other epidemic strains by its characteristic phage-type, antibiogram (susceptibility to tetracycline and resistance to ciprofloxacin), and in the pattern given on pulse field electrophoresis.

Over a 21-month period an outbreak of methicillin-resistant Staphylococcus aureus infection occurred in east Northamptonshire. The outbreak was caused by a novel phage-type (EMRSA-16) and affected 400 patients. It was centred on three hospitals but spread was also detected in the community, particularly among clients of nursing and residential homes. Three hundred and fifty residents in 15 care homes were screened for MRSA. Cross-infection of MRSA was demonstrated in 14 patients in six different homes. A key aspect of the overall containment of the outbreak was the implementation of infection control measures in the community, together with treatment and screening of known positive patients following their discharge from hospital.

In Britain wheat is an important crop accounting for 41% of the total cereal production. In this study ozone concentrations for 1989 estimated as described in Part 1 of the paper are integrated with the estimated wheat distribution to derive a detailed estimate of the impact of ozone on wheat yields at a fine spatial scale (1km × 1km). These data provide estimates for calculating regional and national yield losses. The methodology can be applied to other crop species. Recent research on a range of crops has established relationships between the economic yield loss for certain crops, including wheat, and ozone exposure. Exposure is described as the accumulated exposure above a threshold experienced during the daylight hours (AOT). Critical AOT values are derived from yield exposure relationships which show linear reductions of yield loss with increasing ozone concentrations. This study has made use of land cover data from remotely sensed imagery at 25m resolution and nationally collected agricultural statistics for counties. These data were combined using an areal interpolation technique to provide more spatially articulate estimates of the location and intensity of wheat production. The results demonstrate the economic importance of ozone as a pollutant. Wheat yield losses attributed to ozone vary between different parts of the country but, for years when ozone levels are high, yield losses are likely to be significant in some areas.

A new visible absorption spectrum arising from a gaseous transient species in the bromine sensitized decomposition of ozone has been observed. The spectrum shows a series of absorption bands from 400–600 nm superimposed on a continuum, with a maximum absorption near 505 nm and is attributed to the symmetrical bromine oxide, OBrO, possibly formed from the reaction of BrO with O3. The implications for the partitioning of BrOx in the atmosphere are briefly discussed.

Absorption cross-sections for CF3COCl, CF3COF, CH3COF, CCl3CHO and CFCOOH have been measured in the wavelength region 200-360 nm, using a dual-beam diode-array spectrometer, with a spectral resolution (FWHM) of 1.2 nm. The temperature dependence of the absorption cross-sections was investigated for CF3COCl, CF3COF and CCl3CHO. Absorption over most of the wavelength range showed a distinct temperature dependence, with a significant decline in the cross-section in the long wavelength tail with decreasing temperature. The calculated atmospheric photolysis lifetimes suggest that in the troposphere, photolysis is an important removal process for both CF3COCl and CC13CHO but is unimportant for CF3COF, CF3COOH and CH3COF.

The location of DNA polymerase-α within nuclei of a macroplasmodium of Physarum polycephalum was identified at successive stages of the highly synchronous mitotic cycle by indirect immunofluorescence. The distribution of α-tubulin, the nucleolar protein fibrillarin and DNA were also identified. In G2-phase the polymerase-α was found mainly in the region of the nucleolus. In prophase the polymerase became dispersed into the nucleus with the breakdown of the nucleolus. In metaphase, the polymerase-α was located in two zones separated by the metaphase plate. In S-phase, which follows immediately after mitosis, the distribution of the polymerase was initially punctate but later segments were noted during nucleolar reconstruction. We infer that DNA polymerase-α is stored mainly in the region of the nucleolus (or the reconstructing nucleolus) when it is not needed for DNA replication.

The molecular modulation technique, coupled with UV spectroscopy, was used to monitor the behaviour of HO 2 radicals produced by the near-UV-modulated photolysis of Cl 2 in the presence of H 2 and O 2 . Experiments were carried out at both the Max-Planck-Institut (Mainz) and AEA Technology (Harwell), allowing two separate determinations of the HO 2 UV absorption spectrum. These are in excellent agreement throughout the wavelength range 200–260 nm, with σ 220 (HO 2 ) = 3.4 × 10 −18 cm 2 molecule −1 . A comparison with previous measurements is made. Removal of HO 2 in the chemical system used in the present experiments occurs by self-reaction (eqn. (4)). The value of k 4 at 298 K and 760 Torr was found to be (2.44 ± 0.20) × 10 −12 cm 3 molecule −1 s −1 with O 2 as the bath gas, and (2.84 ± 0.30) × 10 −12 cm 3 molecule −1 s −1 with a bath gas of predominantly N 2 .

The molecular-modulation—UV/visible-absorption-spectroscopy technique has been used to investigate the simultaneous time-resolved behaviour of IO and HO2 produced by the photolysis of O3 in the presence of CH3OH, I2, O2 and Ar. This has enabled a direct measurement of the rate coefficient for the reaction IO + HO2 → HOI + O2 to be made at 760 Torr and 289 K. The value obtained was k5= (6.4 ± 0.7) × 10−11 cm3 molecule−1 s−1.

Acetonyl radicals and acetonylperoxy radicals were produced by pulse radiolysis of gas mixtures with varying concentrations of CH3COCH3 and O2 in 1 atm of SF6 to initiate the reactions (1) F+CH3COCH3→HF+CH3COCH2, (2) 2CH3COCH2 → products, (3) CH3COCH2+O2(+M) → CH3COCH2O2(+M) and (4) 2CH3COCH2O2 → products. The ultraviolet absorption spectrum of the acetonyl radical is composed of a fairly weak band centered at 315 nm and a stronger band in the range of 200–250 nm. The absorption cross section has been determined, σ(310 nm) = (8.73 ± 0.50) × 10−19 cm2 molecule−1. The values k2=(4.8 ± 0.4) × 10−11, k3=(1.5 ± 0.3) × 10−12 and k4=(8.3 ± 1.6) × 10−12 cm3 molecule−1 s−1 at 298 K were derived by computer modelling of the observed kinetic features.

A detailed mechanism for the oxidation of acetaldehyde at temperatures between 500–1000 K has been assembled using 77 elementary reactions involving 32 reactant, product, and intermediate species. Rate coefficients were taken from recent critical evaluations of experimental data. Where experimental measurements were not available, the rate parameters were estimated from the body of currently available kinetics information. The mechanism was shown to predict correctly the rates and products observed in CH 3 CHO oxidation studies in a low-pressure static reactor. The same mechanism was used in a model for nonisothermal oxidation of CH 3 CHO at low pressure in a stirred flow reactor and at high pressure in a rapid compression machine. The oscilatory phenomena in the flow system and the two-stage ignition observed at high pressure were satisfactorily described by the mechanism. It is shown that cool flames are caused by degenerate branching mainly by peracetic acid and that hydrogen peroxide promotes hot ignition.

Article synthese sur la destruction de l'ozone atmospherique et les interactions atmospheriques des polluants de l 'air : les chlorofluorocarbones, les oxydes d'azote et les composes soufres

An outbreak of respiratory syncytial virus (RSV) infection affected seven premature infants in a special care baby unit during November and December 1999. Conventional infection control measures (cohorting infected babies, strict reinforcement of the use of gloves and aprons, emphasis on hand disinfection) failed to prevent spread. Palivizumab, a respiratory syncytial virus monoclonal antibody, was given to eight high-risk preterm infants. There were no further cases of RSV in the unit and none of the babies given palivizumab developed RSV. One baby who acquired RSV during the outbreak (and who was not given palivizumab) was subsequently admitted to hospital with another episode of RSV bronchiolitis. The role of palivizumab in the control of hospital outbreaks of RSV infection merits further investigation.

Seven patients developed Pseudomonas aeruginosa urinary tract infections following urodynamic studies, over a two-month period. One patient developed septicaemia and meningitis and died following rupture of a berry aneurysm. Two others required hospital admission for intravenous antibiotic treatment. Pseudomonas aeruginosa was isolated from a pressure dome which covered the pressure transducer of the urodynamic system used for assessing bladder pressure. The device packaging carried the symbol designating this as a 'single use' product, but as an economy measure, a local decision had been taken to change the device monthly.

The purpose of this report prepared on behalf of the European Commission is to review the current understanding of chemical and dynamical processes in the upper troposphere and lower stratosphere, and to assess how these processes could be perturbed as a result of current and future aircraft emissions. Specifically, perturbations in the atmospheric abundance of ozone and in climate forcing, as predicted by atmospheric models, will be presented. The goal is to compile and evaluate scientific information related to the atmospheric impact of subsonic and supersonic aircraft emissions and to review the state of knowledge concerning the various aspects of this problem. In Section 2, the issues and scientific questions relevant to the problem of aircraft perturbations will be presented. The key physical and chemical processes occurring in the troposphere and stratosphere will be discussed in Section 3. Estimates of air traffic and aircraft emissions will be given in Section 4. Section 5 and 6 will review the understanding of the atmospheric impact of aircraft emissions at small and large scale, respectively. The effect of aircraft emissions on climate forcing will be discussed in Section 7. Finally, conclusions will be provided in Section 8.

An outbreak of epidemic methicillin-resistant Staphylococcus aureus (MRSA) caused by EMRSA-16 has affected hospitals in north east Northamptonshire since April 1991. Between the start of the outbreak and December 1995, 74 healthcare staff (0.9% of the staff screened) were colonized by the outbreak strain. Thirty-two percent of colonized staff were excluded from work, and six were excluded for periods of longer than three weeks. Twenty-four percent of staff had more than one course of treatment to eradicate carriage. The contribution of staff carriage in hospitals where EMRSA-16 is endemic and strategies for the management of colonized staff are discussed. We conclude that screening of staff has a limited role in the control of outbreaks caused by EMRSA-16 and that when resources for screening are scarce priority should be given to patients.

The ultra-violet absorption spectrum of gaseous nitrous acid was quantitatively examined over the wavelength range 200 – 400 nm. In addition to the diffuse bands between 310 and 380 nm previously reported in the literature, an intense, broad absorption maximum was found at 215 nm. p]The absorption cross-sections reported here for 310–380 nm are about a factor of five to six times the previously accepted values. The quantum yield of OH radical production from the photolysis of nitrous acid at 365 ± 5 nm was found to be (0.92 ± 0.16). p]The implications of these measurements for the atmospheric chemistry of nitrous acid are discussed.

The formation of Cl 2 O 3 has been observed in the low-temperature photolysis of OClO-containing mixtures at 350 nm. The ultraviolet spectrum of Cl 2 O 3 has been recorded from 220 to 335 nm using diode array spectroscopy. Equilibrium constants for the reaction: ClO+OClO = Cl 2 O 3 have been determined from 233 to 273 K. The thermochemical parameters Δ H 3 0 =−62±12 kJ mol −1 and Δ S 3 0 =−151±50 J mol −1 K −1 have been derived for this reaction.

Some aspects of the chemistry of knock in internal combustion engines have been examined within the context of a model of autoignition of hydrocarbonair mixtures at high pressure. The basic model follows an earlier one developed by workers at Shell Research Ltd., which has been refined and extended using reactions and rate parameters which are compatible with the expanding body of kinetics information on the type of elementary processes involved. This model was able to predict moderately well the temperature, fuel, and O2 dependence of ignition delay time observed in previous experiments in a rapid compression machine, thus providing further support for the validity of the knock mechanisms. Fuel-structure dependent parameters were identified, and first indications of a rational basis for the stability ranking of alkane fuels with respect to autoignition have been found.

A photochemical modulation technique was employed to investigate the title reactions. IO radicals were monitored in absorption at 426.9 nm where the absorption cross section at this wavelength was determined to be (2.2 +/- 0.5) x 10/sup -17/ cm/sup 2/ molecule/sup -1/. The reaction IO + NO/sub 2/ + M ..-->.. IONO/sub 2/ + M, studied between 35 and 404 torr at 277 K, was found to be in the falloff region between second- and third-order kinetics for this pressure range. The self-reaction IO + IO ..-->.. products was investigated between 10 and 100 torr at 303 K and between 25 and 404 torr at 277 K. The reaction appeared to proceed by at least two pathways, one pressure dependent and the other pressure independent. The results also allowed an estimate of (9.6 +/- 3.0) x 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/ for the rate coefficient of the reaction I + O/sub 3/ ..-->.. IO + O/sub 2/ at 26 torr and 303 K. 16 references, 10 figures, 4 tables.

The photolysis at 330 – 380 nm of mixtures containing parts per million concentrations of gaseous nitrous acid in pure nitrogen and oxygen has been studied in a flow system. The rates of formation of the products NO and NO2, have been measured at low conversion of HNO2. From these data it has been shown that the predominant process following absorption by HNO2 in this wavelength region is the dissociation There is some evidence for the occurrence of the alternative process: which may account for ∼ 10% of the overall photodissociation. An estimate of the rate constant for the reaction has also been obtained. The value, k3 = 1.8 × 10−12 cm3 molecule−1 sec−1 (based on a literature value for the rate constant for the reaction of OH with NO2, is about one order of magnitude higher than for the analogous reaction of OH with HNO3.

Three tobacco varieties, differentially susceptible to ozone, were exposed outdoors 32 km west of central London, during the summer of 1972. At the same time the atmosphere was continuously monitored for ozone. Extensive damage appeared on the leaves of the sensitive variety (Bel-W3), but little or no damage was observed on the two more resistant varieties (Bel-B and Bel-C). The injury resembled that reported elsewhere for ozone on tobacco, and the amount of damage appearing in a given period was significantly positively correlated with the number of hours during the time that the ozone concentration exceeded the maximum natural level. It is concluded that the Bel-W3 tobacco variety is suitable for use as an indicator of low levels of atmospheric ozone under British conditions. The possibility of ozone damage occurring on crops in Britain is discussed.

The production of HCHO and HCOOH has been monitored during the near-UV photolysis of CH3ONONON2 and CH3ONOO2 mixtures at 8 Torr total pressure, and at 298 K, using IR diode laser spectroscopy. HCHO was observed in the former case, providing evidence for reaction (3b). The results suggest that k3b/(k3a + k3b) = 0.45 (±0.1) at 8 Torr. During the photolysis of CH3ONO in the presence of O2, both HCHO and HCOOH were produced. HCHO is formed primarily by reaction (1a) and also by reactions (3b) and (9a). The observed results were best simulated with k9 = 1.2 × 10−13 cm3 molecule−1 s−1. HCOOH was a minor product, its concentrations being lower than those of HCHO by a factor of about 200. Simulation of the chemical system indicated that the observed production may result from a small fraction (about 0.002) of the reaction of OH with HCHO.

Molecular modulation spectrometry has been employed to measure the rate constants for the reactions of CH3O2 with HO2, NO2 and NO. A negative temperature dependence is reported for the reaction with HO2. Product spectra are given for the reactions with HO2 and NO2.

b Nominal plume radius c Local concentration in plume Ca Drag coefficient D Drag force H Cloud depth k Constant in spreading equation L Semi-width of cloud L, Briggs' lift-off parameter l Characteristic length scale Q Total mass released (instantaneous release cases) or mass release rate (continuous release cases) Qe Volume of air entrained per unit time Ri Richardson Number r Radial distance from plume centreline t Time U Wind speed U e Entrainment velocity u Local velocity in plume u' Characteristic turbulence velocity u. Friction velocity u* Plume centreline velocity relative to surrounding air ul, u3 Horizontal and vertical rms. turbulence velocities x, y, z Along wind, crosswind and vertical coordinates c~ Constant in entrainment equation • 1 Jet mixing entrainment coefficient ~2 Buoyancy mixing entrainment coefficient ~3 Ambient turbulence entrainment coefficient p~ Air density Ap Density difference between plume and air ax, ay, az Dispersion parameters 0 Plume trajectory angle above horizontal

Work carried out under the European COST 61a Project on the homogeneous oxidation of sulphur compounds in the atmosphere is briefly reviewed. Mechanisms for sulphur dioxide can be divided into three classes; 1. (a) oxidation by free radicals generated photochemically, 2. (b) oxidation by intermediates produced in thermal reactions, and 3. (c) direct photo-oxidation. Only (a) makes a substantial contribution to SO2 oxidation with calculated maximum rates of between 2 and 6% h−1 in sunlight irradiated urban air during summer months and 1–2% h−1 in unpolluted air. Most of the oxidation is brought about by the attack of the OH radical on SO2 but the contribution of RO2 radical attack is not well determined due to uncertainties in RO2 rate constants. H2S, CH3SH and (CH3)2S react with OH radicals giving atmospheric life-times about 1 day.

This paper considers the usefulness of risk assessment in the analysis of hazards due to chemical process plant and similar installations. Risk assessment is first defined as a technique in which the probabilities and consequences of all possible accidents are quantified. The outputs from such an analysis may take the form of ‘frequency versus magnitude’ graphs, contours of constant risk or overall average rates of death or injury. The applications of the technique include siting and layout studies, comparison of alternative designs, ordering priorities for remedial action and setting insurance rates. Criticisms of the method include: inaccuracy (mainly in the probabilities); incompleteness; difficulty of checking final results; inadequate criteria for evaluating the results; and complexity and laboriousness of the method. Each of these criticisms is considered in the paper, and it is concluded that, while they all have some merit, the problems they represent can be overcome. Moreover, risk assessment is the only method available for dealing with the inherently probabilistic nature of the problems. Finally, priorities for future improvements in the methods are identified; these include achieving a consensus regarding the prediction of consequences and probabilities, developing labour-saving analytical techniques, and testing the final results against the actual experience of accidents.

The photolysis of low concentrations of nitrous acid in CO + N2 + O2 mixtures at 1 atm. has been used as a source of HO2 radicals. The photolyses were carried out in a flow system in which the rates of formation or removal of the oxides of nitrogen, NO and NO2, were measured at small conversion. From the effect of added NO and NO2 on these rates, it is concluded that the following reactions of HO2 radicals with the oxides of nitrogen occur: By computer simulation of the kinetic system using available literature rate constants for the reaction HO2 + HO2 → H2O2 + O2 (8) and the OH-radical reactions which occur, all of the experimental results could be accurately predicted using the following rate constants for the HO2 + NOx reactions at room temperature (296 ± 2K): k5 = 1.2 × 10−12; k10 = 1.4 × 10−13; k7 = 1.2 × 10−13 cm3 molecule−1 s−1. The uncertainty on these rate constants is ± 25%. These values of k5 and k7 are consistent with previous experimental estimates, although k5 has usually been assumed to be approximately a factor of five less than found in this work. The alternative path for NO + HO2, reaction (10), does not appear to have been proposed previously on the basis of experimental observations.

A review is given on selected aspects of the reaction mechanisms of current interest in the chemistry of atmospheric ozone. Atmospheric ozone is produced and removed by a complex series of elementary gas-phase photochemical reactions involving Ox , HOx , NOx , ClOx , and hydrocarbon species. At the present time there is a good knowledge of the basic processes involved in ozone chemistry in the stratosphere and the troposphere and the kinetics of most of the key reactions are well defined. There are a number of difficulties in the theoretical descriptions of observed ozone behaviour which may be due to uncertainties in the chemistry. Examples are the failure to predict present day ozone in the photochemically controlled region above 35 km altitude and the large reductions in the ozone column in the Antarctic Spring which has been observed in recent years.In the troposphere there is growing evidence that ozone and other trace gases have changed appreciably from pre-industrial concentrations, due to chemical reactions involving man-made pollutants. Quantitative investigation of the mechanisms by which these changes may occur requires a sound laboratory kinetics data base.

The molecular modulation technique was employed to observe the kinetic behaviour of OH and HO 2 radicals in the 253.7 nm photolysis of O 3 H 2 OO 2 N 2 (or O 3 H 2 OO 2 He) mixtures at 1 atm pressure. The radicals were monitored in absorption at 308.2 nm and 210 nm respectively. The rate coefficient for reaction (6) OH + HO 2 → H 2 O + O 2 was determined by computer simulation of the results; the value obtained was k 6 = (6.2 +4.0 −2.0 ) × 10 −11 cm 3 molecule −1 s −1 which was independent of temperature in the range 288 – 348 K. The possible role of polyoxide HO x complexes in reaction (6) is discussed.