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Atmospheric black carbon makes an important but poorly quantified contribution to the warming of the global atmosphere. Laboratory and modelling studies have shown that the addition of non-black carbon materials to black carbon particles may enhance the particles’ light absorption by 50 to 60% by refracting and reflecting light. Real world experimental evidence for this ‘lensing’ effect is scant and conflicting, showing that absorption enhancements can be less than 5% or as large as 140%. Here we present simultaneous quantifications of the composition and optical properties of individual atmospheric black carbon particles. We show that particles with a mass ratio of non-black carbon to black carbon of less than 1.5, which is typical of fresh traffic sources, are best represented as having no absorption enhancement. In contrast, black carbon particles with a ratio greater than 3, which is typical of biomass burning emissions, are best described assuming optical lensing leading to an absorption enhancement. We introduce a generalised hybrid model approach for estimating scattering and absorption enhancements based on laboratory and atmospheric observations. We conclude that the occurrence of the absorption enhancement of black carbon particles is determined by the particles’ mass ratio of non-black carbon to black carbon.

Article, Cloud condensation nuclei counter (CCNC) measurements performed at 14 locations around the world within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) framework have been analysed and discussed with respect to the cloud condensation nuclei (CCN) activation and hygroscopic properties of the atmospheric aerosol. The annual mean ratio of activated cloud condensation nuclei (NCCN) to the total number concentration of particles (NCN), known as the activated fraction A, shows a similar functional dependence on supersaturation S at many locations – exceptions to this being certain marine locations, a free troposphere site and background sites in south-west Germany and northern Finland. The use of total number concentration of particles above 50 and 100 nm diameter when calculating the activated fractions (A50 and A100, respectively) renders a much more stable dependence of A on S; A50 and A100 also reveal the effect of the size distribution on CCN activation. With respect to chemical composition, it was found that the hygroscopicity of aerosol particles as a function of size differs among locations. The hygroscopicity parameter κ decreased with an increasing size at a continental site in south-west Germany and fluctuated without any particular size dependence across the observed size range in the remote tropical North Atlantic and rural central Hungary. At all other locations κ increased with size. In fact, in Hyytiälä, Vavihill, Jungfraujoch and Pallas the difference in hygroscopicity between Aitken and accumulation mode aerosol was statistically significant at the 5 % significance level. In a boreal environment the assumption of a size-independent κ can lead to a potentially substantial overestimation of NCCN at S levels above 0.6 %. The same is true for other locations where κ was found to increase with size. While detailed information about aerosol hygroscopicity can significantly improve the prediction of NCCN, total aerosol number concentration and aerosol size distribution remain more important parameters. The seasonal and diurnal patterns of CCN activation and hygroscopic properties vary among three long-term locations, highlighting the spatial and temporal variability of potential aerosol–cloud interactions in various environments., published version, http://purl.org/eprint/status/PeerReviewed

Aerosol particles can serve as cloud condensation nuclei (CCN) to form cloud droplets, and its composition is a main factor governing whether an aerosol particle is an effective CCN. Pure mineral dust particles are poor CCN; however, changes in chemical composition of mineral dust aerosol particles, due to heterogeneous reactions with reactive trace gases in the troposphere, can modify their CCN properties. In this study we investigated the CCN activities of CaCO3 (as a surrogate for mineral dust) and its six atmospheric ageing products: Ca(NO3)2, CaCl2, CaSO4, Ca(CH3SO3)2, Ca(HCOO)2, and Ca(CH3COO)2. CaCO3 has a very low CCN activity with a hygroscopicity parameter (κ) of 0.001-0.003. The CCN activities of its potential atmospheric ageing products are significantly higher. For example, we determined that Ca(NO3)2, CaCl2 and Ca(HCOO)2 have κ values of ∼0.50, similar to that of (NH4)2SO4. Ca(CH3COO)2 has slightly lower CCN activity with a κ value of ∼0.40, and the κ value of CaSO4 is around 0.02. We further show that exposure of CaCO3 particles to N2O5 at 0% relative humidity (RH) significantly enhances their CCN activity, with κ values increasing to around 0.02-0.04. Within the experimental uncertainties, it appears that the variation in exposure to N2O5 from ∼550 to 15,000 ppbv s does not change the CCN activities of aged CaCO3 particles. This observation indicates that the CaCO3 surface may be already saturated at the shortest exposure. We also discussed the atmospheric implications of our study, and suggested that the rate of change in CCN activities of mineral dust particles in the troposphere is important to determine their roles in cloud formation.

An extensive set of measurements were performed to investigate the effect of different engine conditions (i.e. load, speed, temperature, "driving scenarios") and emission control devices (with/without diesel oxidative catalyst, DOC) on the composition and abundance of unregulated exhaust gas emissions from a light-duty diesel engine. Exhaust emissions were introduced into an atmospheric chamber and measured using thermal desorption comprehensive two-dimensional gas chromatography coupled to a flame ionisation detector (TD-GC×GC-FID). In total, 16 individual and 8 groups of volatile organic compounds (VOCs) were measured in the exhaust gas, ranging from volatile to intermediate volatility. The total speciated VOC (∑SpVOC) emission rates varied significantly with different engine conditions, ranging from 70 to 9268 milligrams of VOC mass per kilogram of fuel burnt (mg kg-1). ∑SpVOC emission rates generally decreased with increasing engine load and temperature, and to a lesser degree, engine speed. The exhaust gas composition changed as a result of two main influencing factors, the DOC hydrocarbon (HC) removal efficiency and engine combustion efficiency. Increased DOC HC removal efficiency and engine combustion efficiency resulted in a greater percentage contribution of the C7 to C12 branched aliphatics and C7 to C12 n-alkanes, respectively, to the ∑SpVOC emission rate. The investigated DOC removed 46 ± 10 % of the ∑SpVOC emissions, with removal efficiencies of 83 ± 3 % for the single-ring aromatics and 39 ± 12 % for the aliphatics (branched and straight-chain). The DOC aliphatic removal efficiency generally decreased with increasing carbon chain length. The emission factors of n-nonane to n-tridecane were compared with on-road diesel emissions from a highway tunnel in Oakland California. Comparable emission factors were from experiments with relatively high engine loads and speeds, engine conditions which are consistent with the driving conditions of the on-road diesel vehicles. Emission factors from low engine loads and speeds (e.g. cold-start) showed no agreement with the on-road diesel emissions as expected, with the emission factors observed to be 2 to 8 times greater. To our knowledge, this is the first study which has explicitly discussed the effect of the DOC HC removal efficiency and combustion efficiency on the exhaust gas composition. With further work, compositional differences in exhaust gas emissions as a function of engine temperature, could be implemented into air-quality models, resulting in improved refinement and better understanding of diesel exhaust emissions on local air quality.

Water uptake by aerosol particles controls their ability to form cloud droplets, and reconciliation between different techniques for examining cloud condensation nuclei (CCN) properties is important to our understanding of these processes and our ability to measure and predict them. Reconciliation between measurements of sub-saturated and supersaturated aerosol particle water uptake was attempted at a wide range of locations between 2007 and 2013. The agreement in derived number of CCN (NCCN or particle hygroscopicity was mixed across the projects, with some data sets showing poor agreement across all supersaturations and others agreeing within errors for at least some of the supersaturation range. The degree of reconciliation did not seem to depend on the environment in which the measurements were taken. The discrepancies can only be attributable to differences in the chemical behaviour of aerosols and gases in each instrument, leading to under- or overestimated growth factors and/or CCN counts, though poorer reconciliation at lower supersaturations can be attributed to uncertainties in the size distribution at the threshold diameter found at these supersaturations. From a single instrument, the variability in NCCN calculated using particle hygroscopicity or size distribution averaged across a project demonstrates a greater sensitivity to variation in the size distribution than chemical composition in most of the experiments. However, the discrepancies between instruments indicate a strong requirement for reliable quantification of CCN in line with an improved understanding of the physical processes involved in their measurement. Without understanding the reason for discrepancies in the measurements, it is questionable whether quantification of CCN behaviour is meaningful.

The wet removal of black carbon aerosol (BC) in the atmosphere is a crucial factor in determining its atmospheric lifetime and thereby the vertical and horizontal distributions, dispersion on local and regional scales, and the direct, semi-direct and indirect radiative forcing effects. The in-cloud scavenging and wet deposition rate of freshly emitted hydrophobic BC will be increased on acquisition of more-hydrophilic components by coagulation or coating processes. The lifetime of BC is still subject to considerable uncertainty for most of the model inputs, which is largely due to the insufficient constraints on the BC hydrophobic-to-hydrophilic conversion process from observational field data. This study was conducted at a site along UK North Norfolk coastline, where the BC particles were transported from different regions within Western Europe. A hygroscopicity tandem differential mobility analyser (HTDMA) was coupled with a single particle soot photometer (SP2) to measure the hygroscopic properties of BC particles and associated mixing state in real time. In addition, a Soot Particle AMS (SP-AMS) measured the chemical compositions of additional material associated with BC particles. The ensemble of BC particles persistently contained a less-hygroscopic mode at a growth factor (gf) of around 1.05 at 90% RH (dry diameter 163 nm). Importantly, a more-hygroscopic mode of BC particles was observed throughout the experiment, the gf of these BC particles extended up to ~1.4–1.6 with the minimum between this and the less hygroscopic mode at a gf ~1.25, or equivalent effective hygroscopicity parameter κ ~0.1. The gf of BC particles (gfBC) was highly influenced by the composition of associated soluble material: increases of gfBC were associated with secondary inorganic components, and these increases were more pronounced when ammonium nitrate was in the BC particles; however the presence of secondary organic matter suppressed the gfBC below that of pure inorganics. The Zdanovskii-Stokes-Robinson (ZSR) mixing rule captures the hygroscopicity contributions from different compositions within ±30% compared to the measured results, however is subject to uncertainty due to the complex morphology of BC component and potential artefacts associated with semivolatile particles measured with the HTDMA. This study provides detailed insights on BC hygroscopicity associated with its mixing state, and the results will importantly constrain the microphysical mixing schemes of BC as used by a variety of high level models. In particular, this provides direct evidence to highlight the need to consider ammonium nitrate ageing of BC particles because this will result in particles becoming hydrophilic on much shorter timescales than for sulphate formation, which is often the only mechanism considered.

Manure application to managed grassland is a common agricultural practice. There are, however, limited studies looking at the fluxes and interactions of reactive N compounds and aerosols following fertilisation with manure. In this study, state-of-the-art chemical analysers (GRAEGOR, QCLAS, PTRMS) were used to investigate concentrations, fluxes and chemical interactions of reactive nitrogen containing trace gases (NH3, HNO3, HONO) and aerosols (NO3−) above a grassland fertilised with 164 kg N ha−1 of cattle slurry. Emissions of NH3 peaked at >67 μg m−2 s−1, based on a 30 min average. The estimated overall loss of total ammoniacal nitrogen (TAN) from the applied slurry through NH3 emissions in the first 5 days was 33.5%. The average trimethylamine flux in the first 31 h following the first slurry application was 40 ng m−2 s−1 and amounted to 0.38% of the NH3-N emissions. Apparent nitrate aerosol emissions were observed following the slurry application peaking at 13.0 ng m−2 s−1. This suggests formation of NH4NO3 from reaction of the emitted NH3 with atmospheric HNO3, consistent with the observation of gaseous concentration products exceeding the dissociation constants of ammonium nitrate. Fluxes of total nitrate (HNO3 + NO3−) were bi-directional and positive during the mid-day period after fertilisation, suggesting that the slurry acted as a net source for these compounds. There is evidence of small HONO emission following fertilisation (up to 1 ng m−2 s−1), although the production process is currently not identified. By contrast, all compounds showed deposition to the adjacent unfertilised grassland.

Aerosol particle size distributions were measured below and above a tropical rainforest canopy in Borneo, Malaysia, in June/July 2008 using the WIBS-3: a single particle dual channel fluorescence spectrometer. Material in the size range 0.8–20 μm was characterized according to optical equivalent diameter (DP), morphology and fluorescence at 310–400 nm and 400–600 nm following excitation at 280 nm and 370 nm respectively. Particles fluorescent after both excitations are likely to be fluorescent primary biological aerosol particles (FBAP). Measured FBAP number concentration (NFBAP) at both sites exhibited clear diurnal cycles. The largest variability was observed in the understorey, where NFBAP reached a minimum of 50–100 L−1 in late morning. In mid afternoon it exhibited strong transient fluctuations as large as 4000 L−1 that were followed by sustained concentrations of 1000–2500 L−1 that reduced steadily between midnight and sunrise. Above the canopy FBAP number ranged from 50–100 L−1 during the daytime to 200–400 L−1 at night but did not exhibit the transient enhancements seen in the understorey. The strong FBAP fluctuations were attributed to the release of fungal spores below the canopy and appeared to be linked to elevated relative humidity. The mean FBAP number fraction in the size range 0.8 μm

The coupled tasks scheduling problem was originally introduced for modeling complex radar devices. It is still used for controlling such devices and applied in similar applications. This paper considers a problem of coupled tasks scheduling on a single processor, under the assumptions that all processing times are equal to 1, the gap has exact integer length L and the precedence constraints are strict. We prove that the general problem, when L is part of the input and the precedence constraints graph is a general graph, is NP-hard in the strong sense. We also show that the special case when L=2 and the precedence constraints graph is an in-tree or an out-tree, can be solved in O(n) time.

We consider various single machine scheduling problems in which the processing time of a job depends either on its position in a processing sequence or on its start time. We focus on problems of minimizing the makespan or the sum of (weighted) completion times of the jobs. In many situations we show that the objective function is priority-generating, and therefore the corresponding scheduling problem under series-parallel precedence constraints is polynomially solvable. In other situations we provide counter-examples that show that the objective function is not priority-generating.

The Amazon basin is a vast continental area in which atmospheric composition is relatively unaffected by anthropogenic aerosol particles. Understanding the properties of the natural biogenic aerosol particles over the Amazon rainforest is key to understanding their influence on regional and global climate. While there have been a number of studies during the wet season, and of biomass burning particles in the dry season, there has been relatively little work on the transition period – the start of the dry season in the absence of biomass burning. As part of the Brazil-UK Network for Investigation of Amazonian Atmospheric Composition and Impacts on Climate (BUNIAACIC) project, aerosol measurements, focussing on unpolluted biogenic air masses, were conducted above the canopy at a remote rainforest site in the Amazon, during the transition from wet to dry seasons, in July, 2013. This period marks the start of the dry season, but before significant biomass burning occurs in the region. Median particle number concentrations were 266 cm−3, with size distributions dominated by an accumulation mode of 130–150 nm. During periods of low particle counts, a smaller Aitken mode could also be seen around 80 nm. While the concentrations were similar in magnitude to those seen during the wet season, the size distributions suggest an enhancement in the accumulation mode compared to the wet season, but not yet to the extent seen later in the dry season, when significant biomass burning takes place. Submicron non-refractory aerosol composition, as measured by an Aerosol Chemical Speciation Monitor (ACSM), was dominated by organic material (86 %). Aerosol hygroscopicity was probed using measurements from a Hygroscopicity Tandem Differential Mobility Analyser (HTDMA), and a quasi-monodisperse Cloud Condensation Nuclei counter (CCNc). The hygroscopicity parameter, κ, was found to be low, ranging from 0.12 for Aitken mode particles to 0.18 for accumulation mode particles. This was consistent with previous studies in the region, but lower than similar measurements conducted in Borneo, where κ ranged 0.17–0.37, possibly due to a stronger marine influence at that location, bringing higher sulphate loadings than are typically seen in the Amazon. A Wide Issue Bioaerosol Sensor (WIBS-3M) was deployed at ground level to probe the coarse mode, detecting primary biological aerosol by fluorescence (Fluorescent Biological Aerosol Particles, or FBAP). The mean FBAP number concentration was 404 ± 237 l−1, however this was subject to a strong diurnal cycle, and ranged from around 200 l−1 during the day to as much as 1200 l−1 at night. FBAP dominated the coarse mode particles, comprising more than 90 % of particles detected by the WIBS-3 during the night. This proportion was also subject to a diurnal cycle, dropping to between 55 % and 75 % during the day, since non-FBAP did not show a strong diurnal pattern. Comparison with previous FBAP measurements above canopy at the same location suggests there is a strong vertical gradient in FBAP concentrations through the canopy. Application of Ward linkage cluster analysis using the z-score normalisation to the data suggests that FBAP were dominated (around 70 %) by fungal spores. Further, long-term measurements will be required in order to fully examine the seasonal variability, and distribution through the canopy of primary biological aerosol particles. This is the first time that such a suite of measurements has been deployed at this site to investigate the chemical composition and properties of the biogenic contributions to Amazonian aerosol during the transition period from the wet to dry seasons, and thus provides a unique contrast to the aerosol properties observed during the wet season in previous, similar campaigns. This was also the first deployment of a WIBS in the Amazon rainforest to study coarse mode particles, particularly primary biological aerosol particles, which is likely to play an important role as ice nuclei in the region.

In this paper, we study a strongly NP-hard single machine scheduling problem in which each job consists of two operations that are separated by a time delay which lies within a specified range. The objective is to minimize the makespan. Determining the feasibility and, if applicable, makespan of any proposed permutation of the operations is non-trivial, requiring a longest path algorithm with O(n2) complexity for each permutation. Several heuristic algorithms are proposed: a deterministic and randomized construction algorithm, three descent algorithms and two reactive tabu search algorithms. The local search algorithms use a first improvement neighbourhood and mainly visit only feasible solutions within the search space. Results of extensive computational tests are reported, showing that the heavy computational burden of testing potential solutions renders the local search algorithms uncompetitive in comparison to the construction algorithms. The iterated descent algorithm performs least well.

The paper considers an on-line single machine scheduling problem where the goal is to minimize the makespan. The jobs are partitioned into families and a setup is performed every time the machine starts processing a batch of jobs of the same family. The scheduler is aware of the number of families and knows the setup time of each family, although information about a job only becomes available when that job is released. We give a lower bound on the competitive ratio of any on-line algorithm. Moreover, for the case of two families, we provide an algorithm with a competitive ratio that achieves this lower bound. As the number of families increases, the lower bound approaches 2, and we give a simple algorithm with a competitive ratio of 2.

In the min-max loop layout problem, machines are to be arranged around a loop of conveyor belt. The ordering of the machines dictates the number of circuits of the conveyor belt required to manufacture each of several products. The goal is to find an ordering of the machines that minimises the maximum number of circuits required for the manufacture of any of the products. Since the problem is strongly NP-hard, the study of heuristic methods is of interest. This paper proposes iterated descent and tabu search algorithms, and a randomised insertion algorithm. Results of extensive computational tests show that all of our algorithms outperform a previously known algorithm that applies a greedy heuristic to the solution of a linear programming relaxation. The best quality solutions are obtained with iterated descent. This adds further evidence to the belief that iterated descent can produce high quality solutions to a variety of combinatorial optimisation problems. Moreover, unlike some other local search algorithms, iterated descent does not require much tuning in order to be competitive.

Accurately accounting for new particle formation (NPF) is crucial to our ability to predict aerosol number concentrations and thus cloud properties, which is in turn vital in simulating radiative transfer and climate. Here we present an analysis of NPF events observed in the Greenland Sea during the summertime as part of the Aerosol-Cloud Coupling And Climate Interactions in the Arctic (ACCACIA) project. While NPF events have been reported in the Arctic before, we were able, for the first time, to detect iodine in the growing particles using an Aerosol Mass Spectrometer (AMS) during a persistent event in the region of the coastal sea ice near Greenland. Given the potency of iodine as a nucleation precursor, the results imply that iodine was responsible for the initial NPF, a phenomenon that has been reported at lower latitudes and associated with molecular iodine emissions from coastal macroalgae. The initial source of iodine in this instance is not clear, but it was associated with air originating approximately 1 day previously over melting coastal sea ice. These results show that atmospheric models must consider iodine as a source of new particles in addition to established precursors such as sulphur compounds.

The chemical composition of 15–85 nm diameter particles was measured at Mace Head, Ireland, during May 2011 using the TDCIMS (thermal desorption chemical ionization mass spectrometer). Measurable levels of chloride, sodium, and sulfate were present in essentially all collected samples of these particles at this coastal Atlantic site. Acetaldehyde and benzoic acid were also frequently detected. Concomitant particle hygroscopicity observations usually showed a sea-salt mode and a lower hygroscopicity mode with growth factors near to that of ammonium sulfate. There were many periods lasting from hours to about 2 days during which the 10–60 nm particle number increased dramatically in polar oceanic air. These periods were correlated with the presence of benzoic acid in the particles and an increase in the number of lower hygroscopicity mode particles. Very small (< 10 nm) particles were also present, suggesting that new particle formation contributed to these nanoparticle enhancement events.

This paper considers combined scheduling and machine layout problems in a flexible manufacturing system (FMS). All machines have the capability of performing several different types of operation. However, each operation type is to be assigned to only one of the machines, which are to be positioned around a unidirectional conveyor belt loop. For a known set of products, the primary objective is to maximise the throughput and the secondary objective is to minimise the movement of work between machines. Throughput is maximised by balancing workload, which indicates that the primary objective is equivalent to minimising the bottleneck workload. A three-phase integer programming model is derived. The first phase balances the machine workload by assigning operations to machines. The second phase minimises inter-machine travel, while respecting the workload balance attained in the first phase. In the third phase, machines are assigned to positions in the loop layout so that the total number of circuits made by the products is minimised. It is shown that this phase can be modelled as a linear ordering problem. The three-phase method is applied to a case study.

Particle fluxes were measured over sea ice at Hudson Bay, Canada, during the COBRA experiment in February and March, 2008. Eddy covariance particle fluxes were measured using a condensation particle counter and an ultrasonic anemometer on a 2.5 m mast on the sea ice. After applying appropriate corrections and filtering, the mean net deposition velocity was 0.12 +/- 0.11 mm s(-1) for particles measured with a CPC 3776 (lower size threshold, D-p50 = 2.5 nm) and was at the detection limit of the measurement system. No evidence of nucleation events was seen. Two optical particle counters (at heights 0.2 and 1.35 m on the mast) allowed size segregated fluxes of particles in the accumulation and coarse mode diameter range 0.3-20 mu m to be derived using the aerodynamic flux gradient method. Strong net emission fluxes were observed around midday, 3rd March, when winds increased to around 10 m s(-1), suggesting ice particle resuspension. The fluxes during this period had a significant influence on the derived condensational loss rate to the available particle surfaces, k(t). Number fluxes were greatest in the smallest size channels, while the largest sizes dominated the mass flux. Number fluxes also increased with wind speed, and this relationship was strongest for the smaller sizes. Particle mass size distributions showed an enhanced mode around 400 nm (dry size). Values of k(t) were well approximated by the molecular regime and were found to be much smaller and less variable than values derived for marine air.

The REgents PARk and Tower Environmental Experiment (REPARTEE) comprised two campaigns in London in October 2006 and October/November 2007. The experiment design involved measurements at a heavily trafficked roadside site, two urban background sites and an elevated site at 160–190 m above ground on the BT Tower, supplemented in the second campaign by Doppler lidar measurements of atmospheric vertical structure. A wide range of measurements of airborne particle physical metrics and chemical composition were made as well as measurements of a considerable range of gas phase species and the fluxes of both particulate and gas phase substances. Significant findings include (a) demonstration of the evaporation of traffic-generated nanoparticles during both horizontal and vertical atmospheric transport; (b) generation of a large base of information on the fluxes of nanoparticles, accumulation mode particles and specific chemical components of the aerosol and a range of gas phase species, as well as the elucidation of key processes and comparison with emissions inventories; (c) quantification of vertical gradients in selected aerosol and trace gas species which has demonstrated the important role of regional transport in influencing concentrations of sulphate, nitrate and secondary organic compounds within the atmosphere of London; (d) generation of new data on the atmospheric structure and turbulence above London, including the estimation of mixed layer depths; (e) provision of new data on trace gas dispersion in the urban atmosphere through the release of purposeful tracers; (f) the determination of spatial differences in aerosol particle size distributions and their interpretation in terms of sources and physico-chemical transformations; (g) studies of the nocturnal oxidation of nitrogen oxides and of the diurnal behaviour of nitrate aerosol in the urban atmosphere, and (h) new information on the chemical composition and source apportionment of particulate matter size fractions in the atmosphere of London derived both from bulk chemical analysis and aerosol mass spectrometry with two instrument types.

Iodine emissions from the dominant six macroalgal species in the coastal regions around Roscoff, France, have been modelled to support the Reactive Halogens in the Marine Boundary Layer Experiment (RHaMBLe) undertaken in September 2006. A two-dimensional model is used to explore the relationship between geographically resolved regional emissions (based on maps of seaweed beds in the area and seaweed I2 emission rates previously measured in the laboratory) and in situ point and line measurements of I2 performed respectively by a broadband cavity ringdown spectroscopy (BBCRDS) instrument sited on the shoreline and a long-path differential optical absorption spectroscopy (LP-DOAS) instrument sampling over an extended light path to an off-shore island. The modelled point and line I2 concentrations compare quantitatively with BBCRDS and LP-DOAS measurements, and provide a link between emission fields and the different measurement geometries used to quantify atmospheric I2 concentrations during RHaMBLe. Total I2 emissions over the 100 km2 region around Roscoff are calculated to be 1.7×1019 molecules per second during the lowest tides. During the night, the model replicates I2 concentrations up to 50 pptv measured along the LP-DOAS instrument's line of sight, and predicts spikes of several hundred pptv in certain conditions. Point I2 concentrations up to 50 pptv are also calculated at the measurement site, in broad agreement with the BBCRDS observations. Daytime measured concentrations of I2 at the site correlate with modelled production and transport processes. However substantial recycling of the photodissociated I2 is required for the model to quantitatively match measured concentrations. This result corroborates previous modelling of iodine and NOx chemistry in the semi-polluted marine boundary layer which proposed a mechanism for recycling I2 via the formation, transport and subsequent reactions of the IONO2 reservoir compound. The methodology presented in this paper provides a tool for linking spatially distinct measurements to inhomogeneous and temporally varying emission fields.

Here we present the first observations of simultaneous ozone deposition fluxes and ultrafine particle emission fluxes over an extensive infra-littoral zone. Fluxes were measured by the eddy covariance technique at the Station Biologique de Roscoff, on the coast of Brittany, north-west France. This site overlooks a very wide (3 km) littoral zone controlled by very deep tides (9.6 m) exposing extensive macroalgae beds available for significant iodine mediated photochemical production of ultrafine particles. The aspect at the Station Biologique de Roscoff provides an extensive and relatively flat, uniform fetch within which micrometeorological techniques may be utilized to study links between ozone deposition to macroalgae (and sea water) and ultrafine particle production. Ozone deposition to seawater at high tide was significantly slower (vd[O3]=0.302±0.095 mm s−1) than low tidal deposition. A statistically significant difference in the deposition velocities to macroalgae at low tide was observed between night time (vd[O3]=1.00±0.10 mm s−1) and daytime (vd[O3]=2.05±0.16 mm s−1) when ultrafine particle formation results in apparent particle emission. Very high emission fluxes of ultrafine particles were observed during daytime periods at low tides ranging from 50 000 particles cm−2 s−1 to greater than 200 000 particles cm−2 s−1 during some of the lowest tides. These emission fluxes exhibited a significant relationship with particle number concentrations comparable with previous observations at another location. Apparent particle growth rates were estimated to be in the range 17–150 nm h−1 for particles in the size range 3–10 nm. Under certain conditions, particle growth may be inferred to continue to greater than 120 nm over tens of hours; sizes at which they may readily behave as cloud condensation nuclei (CCN) under reasonable supersaturations that may be expected to pertain at the top of the marine boundary layer. These results link direct depositional loss and photochemical destruction of ozone to the formation of particles and hence CCN from macroalgal emissions at a coastal location.

We present the first direct measurements of coastal ozone deposition and ultrafine particle emission fluxes alongside observation of particle growth to sizes where they will be active as cloud condensation nuclei (CCN). Simultaneous ozone deposition and particle emission from exposed macroalgae were observed during daytime low tide. Ozone deposition to seawater at high tide was significantly slower (v(d)[O(3)] = 0.302 +/- 0.095 mm s(-1)) than low tidal deposition. Low tide deposition was slower at night (1.00 +/- 0.10 mm s(-1)) than during daytime (2.05 +/- 0.16 mm s(-1)) when ultrafine particle formation results in apparent particle emission. Particle emission fluxes greater than 200,000 cm(-2) s(-1) were observed during some of the lowest daytime tides and these particles grew large enough to act as CCN. These results provide the first direct evidence of both direct depositional loss and photochemical destruction of ozone in the formation of particles from macroalgal emissions at a coastal location. Citation: Whitehead, J. D., G. B. McFiggans, M. W. Gallagher, and M. J. Flynn (2009), Direct linkage between tidally driven coastal ozone deposition fluxes, particle emission fluxes, and subsequent CCN formation, Geophys. Res. Lett., 36, L04806, doi:10.1029/2008GL035969.

Sporadic E is itself a stratification within the E-region. The seasonal, diurnal and geographic distributions are not easily explained on the basis of the popular windshear theory. Stratification of mid-latitude sporadic E into 2 or more layers was observed as early as 1956 and preferred heights for sporadic E layers evident from rocket measurements noted in 1968, and from incoherent backscatter in 1973. Recently phase ionosonde measurements and incoherent backscatter observations have provided further data. There is evidence of preferred heights near 97 and 102.5 km; a possible though not completely satisfactory explanation is that internal gravity waves are reflected from above the E-region with an amplitude reflection coefficient of more than 50%. Simultaneous existence of two layers within a kilometre height of each other may be due to different metallic ion compositions. Such layers 2 km apart have been observed by incoherent backscatter and require the existence of large electric fields.

Measurements of aerosol properties were made in aged polluted and clean background air masses encountered at the North Norfolk (UK) coastline as part of the TORCH2 field campaign in May 2004. Hygroscopic growth factors (GF) at 90% relative humidity (RH) for D0=27–217 nm particles and size-resolved chemical composition were simultaneously measured using a Hygroscopicity Tandem Differential Mobility Analyser (HTDMA) and an Aerodyne aerosol mass spectrometer (Q-AMS), respectively. Both hygroscopic properties and chemical composition showed pronounced variability in time and with particles size. With this data set we could demonstrate that the Zdanovskii-Stokes-Robinson (ZSR) mixing rule combined with chemical composition data from the AMS makes accurate quantitative predictions of the mean GF of mixed atmospheric aerosol particles possible. In doing so it is crucial that chemical composition data are acquired with high resolution in both particle size and time, at least matching the actual variability of particle properties. The closure results indicate an ensemble GF of the organic fraction of ~1.20±0.10 at 90% water activity. Thus the organics contribute somewhat to hygroscopic growth, particularly at small sizes, however the inorganic salts still dominate. Furthermore it has been found that most likely substantial evaporation losses of NH4NO3 occurred within the HTDMA instrument, exacerbated by a long residence time of ~1 min. Such an artefact is in agreement with our laboratory experiments and literature data for pure NH4NO3, both showing similar evaporation losses within HTDMAs with residence times of ~1 min. Short residence times and low temperatures are hence recommended for HTDMAs in order to minimise such evaporation artefacts.

Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended on improved methodologies, while ongoing challenges include gas-aerosol interactions, organic nitrogen and N2 fluxes. The NEU strategy applies a 3-tier Flux Network together with a Manipulation Network of global-change experiments, linked by common protocols to facilitate model application. Substantial progress has been made in modelling N fluxes, especially for N2O, NO and bi-directional NH3 exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes is highly uncertain and a key priority is for better data on agricultural practices. Finally, attention is needed to develop N flux verification procedures to assess compliance with international protocols., JRC.H.2-Climate change

Coupled task scheduling problems are known since more than 25 years. Several complexity results have been established in the meantime, but the status of the identical task case remains still unsettled. We describe a new class of equivalent 1-machine no-wait robotic cell problems. It turns out that scheduling of identical coupled tasks corresponds to the production of a single part type in the robotic cell. We shall describe new algorithmic procedures to solve this robotic cell problem, allowing lower and upper bounds on the production time and discussing in particular cyclic production plans.

Measurements are presented from a sampling location 50 km downwind of Greater London, UK, to investigate the timescales required for the atmospheric transformations of aerosol in urban emissions plumes in the context of photochemical age based on the benzene to toluene ratio. It is shown that particles at or around 100 nm in diameter exhibit the greatest systematic variability in chemical properties, and thus hygroscopic properties, on a timescale of 1–2 days. The smaller Aitken mode and larger accumulation mode particles exhibit less variability on these timescales, which we propose is as a result of their different residence times in the atmosphere. The larger accumulation particles have been in the atmosphere longer than the 100 nm particles and their chemistry and hygroscopic properties have been integrated over several days and potentially over several source regions. In contrast, the smaller Aitken mode particles show little systematic variability with photochemical age because their atmospheric lifetimes are short, thus chemical changes and hence changes in water affinity have not had time to occur. Increases in the particle diameter of up to 40% are observed at 90% relative humidity in the accumulation mode from the uptake of water as the particles become increasingly soluble in nature.

Ionization irregularities which are almost but not exactly aligned along the magnetic field may grow much more rapidly than purely aligned irregularities in the presence of a background gradient of ionization and current flow. The stability of these irregularities is considered, taking into account the finite thickness of the gradient and shear in the ion motion. It is shown in particular that the normal E region of the ionosphere is usually stable, whereas sporadic E is often unstable, and this may limit the compression of metallic ions to form such layers. The F region may sometimes be unstable. Temperate zone conditions are considered throughout.

The ground-based systems STARE and SABRE utilize radar auroral phenomena to estimate ionospheric electric fields. Some of the assumptions underlying these systems have been tested and general agreement with expectations have been found. However, as the results have been analysed in detail, it has become clear that the error in the irregularity drift velocity can at times amount to 100 ms−1. Direct comparisons with other E-field measurements, as well as assessments of the results of applications of the Stare data clearly demonstrate that the electric field, calculated on the basis of the irregularity drift velocity, is a useful estimate of the actual horizontal electric field in the ionosphere and is sufficiently accurate for a great variety of geophysical studies.

Incoherent scatter measurements using multiple-pulse techniques were performed at Arecibo to study the E region with a height resolution of 2.4 km. These simultaneous measurements of ion temperature, ion-neutral collision frequency, and electron density, as well as horizontal and vertical components of ion drift velocity, have allowed comparison between theories of sporadic-E and experiment. Sporadic-E layers were consistently observed to descend along the curve where the vertical ion drift velocity (Vz) was zero and its gradient ∂ Vz/∂z was negative, as predicted by redistribution theory. Assuming no diffusion, the calculated effective recombination coefficient at the layer peak is more than an order of magnitude too small for NO+ or O2+, and varies with height in a manner which is unacceptable for a recombination coefficient. This indicates that the layer is composed of long-lived ions (probably metallic), and that the peak layer density is controlled by diffusion rather than recombination. By ignoring recombination, the diffusion coefficient was estimated from the layer thickness and the vertical gradient in the vertical ion velocity. The results were compared with independent values calculated from the measurements of ion temperature and ion-neutral collision frequency. The two estimates were in good agreement over the range 110 to 120 km, showing that electron densities in sporadic-E layers are primarily determined by molecular diffusion.

Three coherent radars have been used to obtain simultaneous radial Doppler velocity measurements in three directions from a common volume in the E layer of the high-latitude ionosphere. The cosine relationship, which was derived in the fluid approximation of the plasma instabilities associated with radar aurora, provides a consistent framework in which to interpret radial Doppler velocity observations. However, a systematic discrepancy between the observed radial velocities and the cosine relationship is found and discussed. For observations in the eastward electrojet this discrepancy is qualitatively in line with expectations based on the kinetic theory of the instabilities. It appears that the possible phase velocities in the plasma are limited to lower values than previously thought. This implies that an estimate of the electron drift velocity obtained using the fluid approximation at times may represent an underestimate of the actual electron drift velocity.

An ionosonde has been used to measure the ordinary and extraordinary critical and blanketing frequencies separately. While the results support the idea that transparent sporadic-E reflections occur from small volumes within the E region, it is likely that the plasma density even in these volumes is often less than that required to cause total reflection. The structure of sporadic E is probably as follows: The peak plasma frequency varies by roughly equal amounts above and below a mean value often by a megahertz or so, within a few kilometers. Some intense blobs cause total reflection; other small volumes of increased plasma frequency strongly scatter radio waves of somewhat greater frequency.

Recently Einaudi and Hines discussed the fact that different wave parameters of acoustic–gravity waves may have different reflection heights. This raises the problem that there will be a range of heights over which one parameter is evanescent, whereas another parameter is in its normal propagation region. It is not obvious that for this second parameter the range of heights does not encompass many wavelengths and thus there would be a large relative phase change between the two parameters.However, it is shown that the extent of the relative phase change will often be less than 2π, and the conditions under which it may exceed 2π are derived.

Recent developments in wind-shear theory and other midlatitude ES theory, with a discussion of relevant experimental work, is given. The role of metallic ions and especially their production and loss is not understood. The gradient instability is specifically excluded from this discussion though it is likely to be important.

The advent of the phase ionosonde, which gives more precise experimental data than the conventional instrument, has made it necessary to seek improvement in the technique of true-height reduction by reducing calculation errors. The method described here gives errors of approximately a few meters when the lowest observable frequency is 0.6 MHz and both magnetoionic modes are used.

Internal gravity waves in the neutral air propagating through the ionosphere cause a corresponding disturbance in the ionization. This note discusses additional effects that arise owing to the presence of an electrostatic field and background wind and in particular the possibility of a ‘spatial resonance’ when the natural drift of ionization irregularities equals the phase velocity of the gravity wave. The electrostatic field may be the one associated with the tidal motions that drive the Sq current system. It is shown that short-period (τ

It is concluded that the metallic ion content of the E region is extremely variable in time; this variation is reflected in the variability of sporadic E. However, the production of metallic ions cannot be so variable; therefore the loss rate must be variable. The most efficient loss mechanism is the corkscrew mechanism that transports the metallic ions into the lower E or D region. By switching this mechanism on and off, the metallic ion content can be changed. Partial reflection of the gravity waves that themselves give the wind shear is suggested as a switching mechanism. There is direct evidence that this does happen. A reversed corkscrew that transports ions upward may sometimes be possible. However, the theory has a major defect in that it predicts most sporadic E where the horizontal component of the earth's field is least, which is just the opposite of what is observed.

A common test of the wind-shear theory of sporadic E is to compare wind profiles with corresponding electron density profiles. The relationship between the two measurements is not always obvious. The presence of electric fields and vertical movement of the wind profile has been suggested to account for this. However, it is shown that the position of electron density maxima relative to the horizontal winds must lie in certain height ranges irrespective of electric fields or wind profile movements, provided these are steady. If the winds were suddenly to change, it would take time for the electron density profile to change. The time constants involved are estimated. Thus it should be possible to say whether the experimental results are consistent with the idea that the elecron density profile is produced by the wind profile.