Observations of meteoric material and implications for aerosol nucleation in the winter Arctic lower stratosphere derived from in situ particle measurements

Number concentrations of total and non-volatile aerosol particles with size diameters >0.01 μm as well as particle size distributions (0.4–23 μm diameter) were measured in situ in the Arctic lower stratosphere (10–20.5 km altitude). The measurements were obtained during the campaigns European Polar Stratospheric Cloud and Lee Wave Experiment (EUPLEX) and Envisat-Arctic-Validation (EAV). The campaigns were based in Kiruna, Sweden, and took place from January to March 2003. Measurements were conducted onboard the Russian high-altitude research aircraft Geophysica using the low-pressure Condensation Nucleus Counter COPAS (COndensation PArticle Counter System) and a modified FSSP 300 (Forward Scattering Spectrometer Probe). Around 18–20 km altitude typical total particle number concentrations nt range at 10–20 cm−3 (ambient conditions). Correlations with the trace gases nitrous oxide (N2O) and trichlorofluoromethane (CFC-11) are discussed. Inside the polar vortex the total number of particles >0.01 μm increases with potential temperature while N2O is decreasing which indicates a source of particles in the above polar stratosphere or mesosphere. A separate channel of the COPAS instrument measures the fraction of aerosol particles non-volatile at 250°C. Inside the polar vortex a much higher fraction of particles contained non-volatile residues than outside the vortex (~67% inside vortex, ~24% outside vortex). This is most likely due to a strongly increased fraction of meteoric material in the particles which is transported downward from the mesosphere inside the polar vortex. The high fraction of non-volatile residual particles gives therefore experimental evidence for downward transport of mesospheric air inside the polar vortex. It is also shown that the fraction of non-volatile residual particles serves directly as a suitable experimental vortex tracer. Nanometer-sized meteoric smoke particles may also serve as nuclei for the condensation of gaseous sulfuric acid and water in the polar vortex and these additional particles may be responsible for the increase in the observed particle concentration at low N2O. The number concentrations of particles >0.4 μm measured with the FSSP decrease markedly inside the polar vortex with increasing potential temperature, also a consequence of subsidence of air from higher altitudes inside the vortex. Another focus of the analysis was put on the particle measurements in the lowermost stratosphere. For the total particle density relatively high number concentrations of several hundred particles per cm3 at altitudes below ~14 km were observed in several flights. To investigate the origin of these high number concentrations we conducted air mass trajectory calculations and compared the particle measurements with other trace gas observations. The high number concentrations of total particles in the lowermost stratosphere are probably caused by transport of originally tropospheric air from lower latitudes and are potentially influenced by recent particle nucleation

Time scales and modes of reef lagoon infilling in the Maldives and controls on the onset of reef island formation

Faro are annular reefs, with reef flats near sea level and lagoons of variable depth, characteristic of both the perimeter and lagoons of Maldivian (Indian Ocean) atolls. Their geomorphic development remains largely unknown, but where faro lagoons (termed velu in Maldivian) have infilled and support reef islands, these provide precious habitable land. Understanding the timing and modes of velu infilling is thus directly relevant to questions about reef island development and vulnerability. Here we use a chronostratigraphic data set obtained from a range of atoll-interior faro with partially to fully filled velu (including those with reef islands) from Baa (South Maalhosmadulu) Atoll, Maldives, to determine time scales and modes of velu infilling, and to identify the temporal and spatial thresholds that control reef island formation. Our data suggest a systematic relationship between faro size, velu infilling, and island development. These relationships likely vary between atolls as a function of atoll lagoon depth, but in Baa Atoll, our data set indicates the following faro-size relationships exist: (1) faros <∼0.5 km2 have velu that were completely infilled by ca. 3000 calibrated years B.P. (cal yr B.P.) with islands having established on these deposits by ca. 2.5 cal kyr B.P.; (2) faros >0.5 km2 but <∼1.25 km2 have velu in late stages of infill, may support unvegetated sand cays and, given sufficient sand supply, may evolve into larger, more permanent islands; and (3) faros >∼1.25 km2 have unfilled (deeper) velu which might only infill over long time scales and which are thus unlikely to support new island initiation. These new observations, when combined with previously published data on Maldivian reef island development, suggest that while the velu of the largest faro are unlikely to fill over the next few centuries (at least), other faro with near-infilled velu may provide important foci for future reef-island building, even under present highstand (and slightly rising) sea levels

Modeling the evolution of aerosol particles in a ship plume using PartMC-MOSAIC

This study investigates the evolution of ship-emitted aerosol particles using the stochastic particle-resolved model PartMC-MOSAIC (Particle Monte Carlo model-Model for Simulating Aerosol Interactions and Chemistry). Comparisons of our results with observations from the QUANTIFY (Quantifying the Climate Impact of Global and European Transport Systems) study in 2007 in the English Channel and the Gulf of Biscay showed that the model was able to reproduce the observed evolution of total number concentration and the vanishing of the nucleation mode consisting of sulfate particles. Further process analysis revealed that during the first hour after emission, dilution reduced the total number concentration by four orders of magnitude, while coagulation reduced it by an additional order of magnitude. Neglecting coagulation resulted in an overprediction of more than one order of magnitude in the number concentration of particles smaller than 40 nm at a plume age of 100 s. Coagulation also significantly altered the mixing state of the particles, leading to a continuum of internal mixtures of sulfate and black carbon. The impact on cloud condensation nuclei (CCN) concentrations depended on the supersaturation threshold <i>S</i> at which CCN activity was evaluated. For the base case conditions, characterized by a low formation rate of secondary aerosol species, neglecting coagulation, but simulating condensation, led to an underestimation of CCN concentrations of about 37% for <i>S</i> = 0.3% at the end of the 14-h simulation. In contrast, for supersaturations higher than 0.7%, neglecting coagulation resulted in an overestimation of CCN concentration, about 75% for <i>S</i> = 1%. For <i>S</i> lower than 0.2% the differences between simulations including coagulation and neglecting coagulation were negligible. Neglecting condensation, but simulating coagulation did not impact the CCN concentrations below 0.2% and resulted in an underestimation of CCN concentrations for larger supersaturations, e.g., 18% for <i>S</i> = 0.6%. We also explored the role of nucleation for the CCN concentrations in the ship plume. For the base case the impact of nucleation on CCN concentrations was limited, but for a sensitivity case with higher formation rates of secondary aerosol over several hours, the CCN concentrations increased by an order of magnitude for supersaturation thresholds above 0.3%

Technical Note: Characterisation of a DUALER instrument for the airborne measurement of peroxy radicals during AMMA 2006

A DUALER (dual-channel airborne peroxy radical chemical amplifier) instrument has been developed and optimised for the airborne measurement of the total sum of peroxy radicals during the AMMA (African Monsoon Multidisciplinary Analyses) measurement campaign which took place in Burkina Faso in August 2006. The innovative feature of the instrument is that both reactors are sampling simultaneously from a common pre-reactor nozzle while the whole system is kept at a constant pressure to ensure more signal stability and accuracy. &lt;br&gt;&lt;br&gt; Laboratory experiments were conducted to characterise the stability of the NO&lt;sub&gt;2&lt;/sub&gt; detector signal and the chain length with the pressure. The results show that airborne measurements using chemical amplification require constant pressure at the luminol detector. Wall losses of main peroxy radicals HO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; were investigated. The chain length was experimentally determined for different ambient mixtures and compared with simulations performed by a chemical box model. &lt;br&gt;&lt;br&gt; The DUALER instrument was successfully mounted within the German DLR-Falcon. The analysis of AMMA data utilises a validation procedure based on the O&lt;sub&gt;3&lt;/sub&gt; mixing ratios simultaneously measured onboard. The validation and analysis procedure is illustrated by means of the data measured during the AMMA campaign. The detection limit and the accuracy of the ambient measurements are also discussed

Constraining tropospheric mixing timescales using airborne observations and numerical models

International audienceA technique is demonstrated for estimating atmospheric mixing time-scales from in-situ data, using a Lagrangian model initialised from an Eulerian chemical transport model (CTM). This method is applied to airborne tropospheric CO observations taken during seven flights of the Mediterranean Intensive Oxidant Study (MINOS) campaign, of August 2001. The time-scales derived, correspond to mixing applied at the spatial scale of the CTM grid. Specifically, they are upper bound estimates of the mix-down lifetime that should be imposed for a Lagrangian model to reproduce the observed small-scale tracer structure. They are relevant to the family of hybrid Lagrangian-Eulerian models, which impose Eulerian grid mixing to an underlying Lagrangian model. The method uses the fact that in Lagrangian tracer transport modelling, the mixing spatial and temporal scales are decoupled: the spatial scale is determined by the resolution of the initial tracer field, and the time scale by the trajectory length. The chaotic nature of lower-atmospheric advection results in the continuous generation of smaller spatial scales, a process terminated in the real atmosphere by mixing. Thus, a mix-down lifetime can be estimated by varying trajectory length so that the model reproduces the observed amount of small-scale tracer structure. Selecting a trajectory length is equivalent to choosing a mixing timescale. For the cases studied, the results are very insensitive to CO photochemical change calculated along the trajectories. The method is most appropriate for relatively homogeneous regions, i.e. it is not too important to account for changes in aircraft altitude or the positioning of stratospheric intrusions, so that small scale structure is easily distinguished. The chosen flights showed a range of mix-down time upper limits: 1 and 3 days for 8 August and 3 August, due to recent convective and boundary layer mixing respectively, and 7?9 days for 16, 17, 22a, 22c and 24 August. For the flight of 3 August, the observed concentrations result from a complex set of transport histories, and the models are used to interpret the observed structure, while illustrating where more caution is required with this method of estimating mix-down lifetimes

Uncovering dispersion properties in semiconductor waveguides to study photon-pair generation

This work was supported by the FWF through project no. I-2065-N27, the DFG Project no. SCHN1376/2-1, the ERC project EnSeNa (257531) and the State of Bavaria.We investigate the dispersion properties of ridge Bragg-reflection waveguides to deduce their phasematching characteristics. These are crucial for exploiting them as sources of parametric down-conversion (PDC). In order to estimate the phasematching bandwidth we first determine the group refractive indices of the interacting modes via Fabry–Perot experiments in two distant wavelength regions. Second, by measuring the spectra of the emitted PDC photons, we gain access to their group index dispersion. Our results offer a simple approach for determining the PDC process parameters in the spectral domain, and provide important feedback for designing such sources, especially in the broadband case.Publisher PDFPeer reviewe

Lightning-produced NO_x over Brazil during TROCCINOX: Airborne measurements in tropical and subtropical thunderstorms and the importance of mesoscale convective systems

International audienceDuring the TROCCINOX field experiments in February?March 2004 and February 2005, airborne in situ measurements of NO, NOy, CO, and O3 mixing ratios and the J(NO2) photolysis rate were carried out in the anvil outflow of thunderstorms over southern Brazil. Both tropical and subtropical thunderstorms were investigated, depending on the location of the South Atlantic convergence zone. Tropical air masses were discriminated from subtropical ones according to the higher equivalent potential temperature (?e) in the lower and mid troposphere, the higher CO mixing ratio in the mid troposphere, and the lower wind velocity and proper wind direction in the upper troposphere. During thunderstorm anvil penetrations, typically at 20?40 km horizontal scales, NOx mixing ratios were on average enhanced by 0.2?1.6 nmol mol?1. This enhancement was mainly attributed to NOx production by lightning and partly due to upward transport from the NOx-richer boundary layer. In addition, CO mixing ratios were occasionally enhanced, indicating upward transport from the boundary layer. For the first time, the composition of the anvil outflow from a large, long-lived mesoscale convective system (MCS) advected from northern Argentina and Uruguay was investigated in more detail. Over a horizontal scale of about 400 km, NOx, CO and O3 mixing ratios were significantly enhanced in these air masses in the range of 0.6?1.1, 110?140 and 60?70 nmol mol?1, respectively. Analyses from trace gas correlations and a Lagrangian particle dispersion model indicate that polluted air masses, probably from the Buenos Aires urban area and from biomass burning regions, were uplifted by the MCS. Ozone was distinctly enhanced in the aged MCS outflow, due to photochemical production and entrainment of O3-rich air masses from the upper troposphere ? lower stratosphere region. The aged MCS outflow was transported to the north, ascended and circulated, driven by the Bolivian High over the Amazon basin. In the observed case, the O3-rich MCS outflow remained over the continent and did not contribute to the South Atlantic ozone maximum

Intercomparison of aircraft instruments on board the <i>C-130</i> and <i>Falcon 20</i> over southern Germany during EXPORT 2000

International audienceIn the summer 2000 Export aircraft campaign (European eXport of Precursors and Ozone by long-Range Transport), two comprehensively instrumented research aircraft measuring a variety of chemical species flew wing tip to wing tip for a period of one and a quarter hours. During this interval a comparison was undertaken of the measurements of nitrogen oxide (NO), odd nitrogen species (NOy), carbon monoxide (CO) and ozone (O3). The comparison was performed at two different flight levels, which provided a 10-fold variation in the concentrations of both NO (10 to 1000 parts per trillion by volume (pptv)) and NOy (200 to over 2500 pptv). Large peaks of NO and NOy observed from the Falcon 20, which were at first thought to be from the exhaust of the C-130, were also detected on the 4 channel NOx,y instrument aboard the C-130. These peaks were a good indication that both aircraft were in the same air mass and that the Falcon 20 was not in the exhaust plume of the C-130. Correlations and statistical analysis are presented between the instruments used on the two separate aircraft platforms. These were found to be in good agreement giving a high degree of correlation for the ambient air studied. Any deviations from the correlations are accounted for in the estimated inaccuracies of the instruments. These results help to establish that the instruments aboard the separate aircraft are reliably able to measure the corresponding chemical species in the range of conditions sampled and that data collected by both aircraft can be co-ordinated for purposes of interpretation