-
Frey W,
Borrmann S,
Kunkel D,
Weigel R,
M. de Reus, Schlager H,
Roiger A,
Voigt C,
Hoor P,
Curtius J, [......],
Ulanovsky A,
Ravegnani F,
N. M. Sitnikov,
Viciani S,
D&apos,
Amato F,
G. N. Shur,
G. V. Belyaev,
K. S. Law,
Cairo F
[show abstract]
[hide abstract]
ABSTRACT: In-situ measurements of ice crystal size distributions in tropical upper troposphere/lower stratosphere (UT/LS) clouds were performed during the SCOUT-AMMA campaign over West Africa in August 2006. The cloud properties were measured with a Forward Scattering Spectrometer Probe (FSSP-100) and a Cloud Imaging Probe (CIP) operated aboard the Russian high altitude research aircraft M-55 ''Geophysica'' with the mission base in Ouagadougou, Burkina Faso. A total of 117 ice particle size distributions were obtained from the measurements in the vicinity of Mesoscale Convective Systems (MCS). Two or three modal lognormal size distributions were fitted to the average size distributions for different potential temperature bins. The measurements showed proportionate more large ice particles compared to former measurements above maritime regions. With the help of trace gas measurements of NO, NOy, CO2, CO, and O3, and satellite images clouds in young and aged MCS outflow were identified. These events were observed at altitudes of 11.0 km to 14.2 km corresponding to potential temperature levels of 346 K to 356 K. In a young outflow (developing MCS) ice crystal number concentrations of up to 8.3 cm−3 and rimed ice particles with maximum dimensions exceeding 1.5 mm were found. A maximum ice water content of 0.05 g m−3 was observed and an effective radius of about 90 μm. In contrast the aged outflow events were more diluted and showed a maximum number concentration of 0.03 cm−3, an ice water content of 2.3 × 10−4 g m−3, an effective radius of about 18 μm, while the largest particles had a maximum dimension of 61 μm. Close to the tropopause subvisual cirrus were encountered four times at altitudes of 15 km to 16.4 km. The mean ice particle number concentration of these encounters was 0.01 cm−3 with maximum particle sizes of 130 μm, and the mean ice water content was about 1.4 × 10−4 g m−3. All known in-situ measurements of subvisual tropopause cirrus are compared and an exponential fit on the size distributions is established in order to give a parameterisation for modelling. A comparison of aerosol to ice crystal number concentrations, in order to obtain an estimate on how many ice particles result from activation of the present aerosol, yielded low activation ratios for the subvisual cirrus cases of roughly one cloud particle per 30 000 aerosol particles, while for the MCS outflow cases this resulted in a high ratio of one cloud particle per 300 aerosol particles.
Atmospheric Chemistry and Physics Discussions. 01/2011;
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Barret B,
J.E. Williams,
Bouarar I,
Yang X,
Josse B,
Law K,
Pham M,
E. Le Flochmoën,
Liousse C,
V.-H. Peuch,
G. D. Carver,
J. A. Pyle,
Sauvage B,
P. van Velthoven, Schlager H,
Mari C,
Cammas J.-P
[show abstract]
[hide abstract]
ABSTRACT: Within the African Monsoon Multidisciplinary Analysis (AMMA), we investigate the impact of nitrogen oxides produced by lightning (LiNO<sub>x</sub>) and convective transport during the West African Monsoon (WAM) upon the composition of the upper troposphere (UT) in the tropics. For this purpose, we have performed simulations with 4 state-of-the-art chemistry transport models involved within AMMA, namely MOCAGE, TM<sub>4</sub>, LMDz-INCA and p-TOMCAT. The model intercomparison is complemented with an evaluation of the simulations based on both spaceborne and airborne observations. The baseline simulations show important differences between the UT CO and O<sub>3</sub> distributions simulated by each of the 4 models when compared to measurements of the African latitudinal transect from the MOZAIC program and to distributions measured by the Aura/MLS spaceborne sensor. We show that such model discrepancies can be explained by differences in the convective transport parameterizations and, more particularly, the altitude reached by convective updrafts (ranging between ~200–125 hPa). Concerning UT O<sub>3</sub>, the majority of models exhibit low concentrations compared to both MOZAIC and MLS observations south of the equator, with good agreement in the Northern Hemisphere. Sensitivity studies are performed to quantify the effect of deep convective transport and the influence of LiNO<sub>x</sub> production on the UT composition. These clearly indicate that the CO maxima and the elevated O<sub>3</sub> concentrations south of the equator are due to convective uplift of air masses impacted by Southern African biomass burning, in agreement with previous studies. Moreover, during the WAM, LiNO<sub>x</sub> from Africa are responsible for the highest UT O<sub>3</sub> enhancements (10–20 ppbv) over the tropical Atlantic between 10° S–20° N. Differences between models are primarily due to the performance of the parameterizations used to simulate lightning activity which are evaluated using spaceborne observations of flash frequency. Combined with comparisons of in-situ NO measurements we show that the models producing the highest amounts of LiNO<sub>x</sub> over Africa during the WAM (INCA and p-TOMCAT) capture observed NO profiles with the best accuracy, although they both overestimate lightning activity over the Sahel.
Atmospheric Chemistry and Physics Discussions. 01/2010;
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Real E,
Orlandi E,
K. S. Law,
Fierli F,
Josset D,
Cairo F, Schlager H,
Borrmann S,
Kunkel D,
C. M. Volk,
J. B. McQuaid,
D. J. Stewart,
Lee J,
A. C. Lewis,
J. R. Hopkins,
Ravegnani F,
Ulanovski A,
Liousse C
[show abstract]
[hide abstract]
ABSTRACT: Pollutant plumes with enhanced concentrations of trace gases and aerosols were observed over the southern coast of West Africa during August 2006 as part of the AMMA wet season field campaign. Plumes were observed both in the mid and upper troposphere. In this study we examined the origin of these pollutant plumes, and their potential to photochemically produce ozone (O3) downwind over the Atlantic Ocean. Their possible contribution to the Atlantic O3 maximum is also discussed. Runs using the BOLAM mesoscale model including biomass burning carbon monoxide (CO) tracers were used to confirm an origin from central African biomass burning fires. The plumes measured in the mid troposphere (MT) had significantly higher pollutant concentrations over West Africa compared to the upper tropospheric (UT) plume. The mesoscale model reproduces these differences and the two different pathways for the plumes at different altitudes: transport to the north-east of the fire region, moist convective uplift and transport to West Africa for the upper tropospheric plume versus north-west transport over the Gulf of Guinea for the mid-tropospheric plume. Lower concentrations in the upper troposphere are mainly due to enhanced mixing during upward transport. Model simulations suggest that MT and UT plumes are 16 and 14 days old respectively when measured over West Africa. The ratio of tracer concentrations at 600 hPa and 250 hPa was estimated for 14–15 August in the region of the observed plumes and compares well with the same ratio derived from observed carbon dioxide (CO2) enhancements in both plumes. It is estimated that, for the period 1–15 August, the ratio of Biomass Burning (BB) tracer concentration transported in the UT to the ones transported in the MT is 0.6 over West Africa and the equatorial South Atlantic. Runs using a photochemical trajectory model, CiTTyCAT, initialized with the observations, were used to estimate in-situ net photochemical O3 production rates in these plumes during transport downwind of West Africa. The mid-troposphere plume spreads over altitude between 1.5 and 6 km over the Atlantic Ocean. Even though the plume was old, it was still very photochemically active (mean net O3 production rates over 10 days of 2.6 ppbv/day and up to 7 ppbv/day during the first days) above 3 km especially during the first few days of transport westward. It is also shown that the impact of high aerosol loads in the MT plume on photolysis rates serves to delay the peak in modelled O3 concentrations. These results suggest that a significant fraction of enhanced O3 in mid-troposphere over the Atlantic comes from BB sources during the summer monsoon period. According to simulated occurrence of such transport, BB may be the main source for O3 enhancement in the equatorial south Atlantic MT, at least in August 2006. The upper tropospheric plume was also still photochemically active, although mean net O3 production rates were slower (1.3 ppbv/day). The results suggest that, whilst the transport of BB pollutants to the UT is variable (as shown by the mesoscale model simulations), pollution from biomass burning can make an important contribution to additional photochemical production of O3 in addition to other important sources such as nitrogen oxides (NOx) from lightning.
Atmospheric Chemistry and Physics. 01/2010;
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C. E. Reeves,
Formenti P,
Afif C,
Ancellet G,
Attie J.-L,
Bechara J,
Borbon A,
Cairo F,
Coe H,
Crumeyrolle S, [......],
G. P. Mills,
Minikin A,
J. G. Murphy,
J. K. Nielsen,
D. E. Oram,
D. J. Parker,
Richter A, Schlager H,
Schwarzenboeck A,
Thouret V
[show abstract]
[hide abstract]
ABSTRACT: During June, July and August 2006 five aircraft took part in a campaign over West Africa to observe the aerosol content and chemical composition of the troposphere and lower stratosphere as part of the African Monsoon Multidisciplinary Analysis (AMMA) project. These are the first such measurements in this region during the monsoon period. In addition to providing an overview of the tropospheric composition, this paper provides a description of the measurement strategy (flights performed, instrumental payloads, wing-tip to wing-tip comparisons) and points to some of the important findings discussed in more detailed in other papers in this special issue. The ozone data exhibits an "S" shaped vertical profile which appears to result from significant losses in the lower troposphere due to rapid deposition to forested areas and photochemical destruction in the moist monsoon air, and convective uplift of O3-poor air to the upper troposphere. This profile is disturbed, particularly in the south of the region, by the intrusions in the lower and middle troposphere of air from the Southern Hemisphere impacted by biomass burning. Comparisons with longer term data sets suggest the impact of these intrusions on West Africa in 2006 was greater than in other recent wet seasons. There is evidence for net photochemical production of ozone in these biomass burning plumes as well as in urban plumes, in particular that from Lagos, convective outflow in the upper troposphere and in boundary layer air affected by nitrogen oxide emissions from recently wetted soils. This latter effect, along with enhanced deposition to the forested areas, contributes to a latitudinal gradient of ozone in the lower troposphere. Biogenic volatile organic compounds are also important in defining the composition both for the boundary layer and upper tropospheric convective outflow. Mineral dust was found to be the most abundant and ubiquitous aerosol type in the atmosphere over Western Africa. Data collected within AMMA indicate that injection of dust to altitudes favourable for long-range transport (i.e. in the upper Sahelian planetary boundary layer) can occur behind the leading edge of mesoscale convective system (MCS) cold-pools. Research within AMMA also provides the first estimates of secondary organic aerosols (SOA) across the West African Sahel and have shown that organic mass loadings vary between 0 and 2 μg m−3 with a median concentration of 1.07 μg m−3. The vertical distribution of nucleation mode particle concentrations reveals that significant and fairly strong particle formation events did occur for a considerable fraction of measurement time above 8 km (and only there). Very low aerosol concentrations were observed in general in the fresh outflow of active MCSs, likely as the result of efficient wet removal of aerosol particles due to heavy precipitation inside the convective cells of the MCSs. This wet removal initially affects all particle size ranges as clearly shown by all measurements in the vicinity of MCSs.
Atmospheric Chemistry and Physics Discussions. 01/2010;
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[show abstract]
[hide abstract]
ABSTRACT: Airborne measurements of trace gases and aerosol particles have been made in two aged biomass burning (BB) plumes over the East Atlantic (Gulf of Guinea). The plumes originated from BB in the Southern Hemisphere African savanna belt. On the day of our measurements (13 August 2006), the plumes had ages of about 10 days and were respectively located in the middle troposphere (MT) at about 3000–5500 m altitude and in the upper troposphere (UT) at about 10 800–11 200 m. In the more polluted MT-plume, numerous measured trace species had markedly elevated abundances, particularly HNO<sub>3</sub> (5000–8000 pmol/mol), SO<sub>2</sub> (up to 1400 pmol/mol), and smoke particles with diameters larger than 250 nm (up to 2000 cm<sup>−3</sup>). Our MT-plume measurements indicate that SO<sub>2</sub> released by BB had not experienced significant loss by deposition and cloud processes but rather had experienced OH-induced conversion to gas-phase sulfuric acid. By contrast, a large fraction of the released NO<sub>x</sub> had experienced loss, most likely as HNO<sub>3</sub>, by cloud processes and deposition. In the UT-plume, loss of NO<sub>y</sub> and SO<sub>2</sub> by cloud processes and deposition was more pronounced compared to the MT-plume. Building on our measurements and accompanying model simulations, we have investigated trace gas transformations in the ageing and diluting plumes and their role in smoke particle processing and activation. Emphasis was placed upon the formation of sulfuric acid, nitric acid, and ammonium nitrate, and their influence on the activation potential of smoke particles. Our model simulations reveal that, after 13 August, the lower plume traveled across the Atlantic and descended to 1300 m and hereafter ascended again. During the travel across the Atlantic, the smoke particle mean diameter and sulfuric acid mass fraction increased sufficiently to allow the processed smoke particles to act as water vapor condensation nuclei already at very low water vapor supersaturations of only about 0.04%. Thereby, aged smoke particles had developed a potential to act as water vapor condensation nuclei in the formation of maritime clouds, including not only cumulus but even stratiform clouds.
Atmospheric Chemistry and Physics Discussions. 01/2010;
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Voigt C,
Schumann U,
Jurkat T,
Schäuble D, Schlager H,
Petzold A,
Gayet J.-F,
Krämer M,
Schneider J,
Borrmann S, [......],
Holzäpfel F,
Arnold F,
Wendisch M,
Döpelheuer A,
Gottschaldt K,
Baumann R,
Zöger M,
Sölch I,
Rautenhaus M,
Dörnbrack A
[show abstract]
[hide abstract]
ABSTRACT: Lineshaped contrails were detected with the research aircraft Falcon during the CONCERT – CONtrail and Cirrus ExpeRimenT – campaign in October/November 2008. Thereby the Falcon was equipped with a set of instruments to measure particle properties such as the particle size distribution, shape, extinction, chemical composition as well as trace gas concentrations of sulfur dioxide (SO2), reactive nitrogen and halogen species (NO, NOy, HNO3, HONO, HCl), ozone (O3) and carbon monoxide (CO). During 12 mission flights over Western Europe numerous contrails and cirrus clouds were probed at altitudes between 8.5 and 11.6 km and temperatures above 213 K. 22 contrails from 11 different aircraft were observed near and below ice saturation. The observed NO mixing ratios, ice crystal and soot number densities are compared to a process based contrail model. Further we investigate in detail the contrail from a CRJ-2 aircraft detected on 19 November 2008 in 10.1 km altitude. The contrail with an age of 1 to 2 min had average ice crystal concentrations of 128 cm−3 in the size range 0.4y) ratios of 0.037 (0.024) are in the range of previous measurements in the gaseous exhaust. With HONO/NO ratio we can derive a lower limit of the conversion efficiency (εS) of fuel sulfur into H2SO4 of 2.9%. In addition to individual contrails and aircraft plumes, regional stratospheric NO enhancements were detected in the lowest stratosphere. Simulations show that aviation NO emissions could have contributed by more than 40% to the observed NO levels. Besides contrails, also cirrus clouds and a volcanic aerosol layer were measured during the CONCERT campaign. The observations serve to investigate the chemical processing of trace gases on contrails and and help to better quantify the climate impact from contrails.
Atmospheric Chemistry and Physics Discussions. 01/2010;
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M. von Hobe,
Grooß J.-U,
Günther G,
Konopka P,
Gensch I,
Krämer M,
Spelten N,
Afchine A,
Schiller C,
Ulanovsky A, [......],
Ravegnani F,
Cairo F,
Roiger A,
Voigt C, Schlager H,
Weigel R,
Frey W,
Borrmann S,
Müller R,
Stroh F
[show abstract]
[hide abstract]
ABSTRACT: Airborne in-situ observations of ClO in the tropics were made during the TROCCINOX (Aracatuba, Brasil, February 2005) and SCOUT-O3 (Darwin, Australia, November/December 2005) field campaigns. While during most flights significant amounts of ClO (≈10–20 parts per trillion, ppt) were present only in aged stratospheric air, instances of enhanced ClO mixing ratios of up to 40 ppt – significantly exceeding those expected from gas phase chemistry – were observed in air masses of a more tropospheric character. Most of these observations concur with low temperatures or with the presence of cirrus clouds (often both), suggesting that cirrus ice particles and/or liquid aerosol at low temperatures may promote significant heterogeneous chlorine activation in the tropical upper troposphere lower stratosphere (UTLS). In two case studies, particularly high levels of ClO observed were reproduced by chemistry simulations only under the assumption that significant denoxification had occurred in the observed air. At least for one of these flights, a significant denoxification is in contrast to the observed NO levels suggesting that the coupling of chlorine and nitrogen compounds in the tropical UTLS may not be completely understood.
Atmospheric Chemistry and Physics Discussions. 01/2010;
-
C. E. Reeves,
Formenti P,
Afif C,
Ancellet G,
Attié J.-L,
Bechara J,
Borbon A,
Cairo F,
Coe H,
Crumeyrolle S, [......],
G. P. Mills,
Minikin A,
J. G. Murphy,
J. K. Nielsen,
D. E. Oram,
D. J. Parker,
Richter A, Schlager H,
Schwarzenboeck A,
Thouret V
[show abstract]
[hide abstract]
ABSTRACT: During June, July and August 2006 five aircraft took part in a campaign over West Africa to observe the aerosol content and chemical composition of the troposphere and lower stratosphere as part of the African Monsoon Multidisciplinary Analysis (AMMA) project. These are the first such measurements in this region during the monsoon period. In addition to providing an overview of the tropospheric composition, this paper provides a description of the measurement strategy (flights performed, instrumental payloads, wing-tip to wing-tip comparisons) and points to some of the important findings discussed in more detail in other papers in this special issue. The ozone data exhibits an "S" shaped vertical profile which appears to result from significant losses in the lower troposphere due to rapid deposition to forested areas and photochemical destruction in the moist monsoon air, and convective uplift of ozone-poor air to the upper troposphere. This profile is disturbed, particularly in the south of the region, by the intrusions in the lower and middle troposphere of air from the southern hemisphere impacted by biomass burning. Comparisons with longer term data sets suggest the impact of these intrusions on West Africa in 2006 was greater than in other recent wet seasons. There is evidence for net photochemical production of ozone in these biomass burning plumes as well as in urban plumes, in particular that from Lagos, convective outflow in the upper troposphere and in boundary layer air affected by nitrogen oxide emissions from recently wetted soils. This latter effect, along with enhanced deposition to the forested areas, contributes to a latitudinal gradient of ozone in the lower troposphere. Biogenic volatile organic compounds are also important in defining the composition both for the boundary layer and upper tropospheric convective outflow. Mineral dust was found to be the most abundant and ubiquitous aerosol type in the atmosphere over Western Africa. Data collected within AMMA indicate that injection of dust to altitudes favourable for long-range transport (i.e. in the upper Sahelian planetary boundary layer) can occur behind the leading edge of mesoscale convective system (MCS) cold-pools. Research within AMMA also provides the first estimates of secondary organic aerosols across the West African Sahel and have shown that organic mass loadings vary between 0 and 2 μg m−3 with a median concentration of 1.07 μg m−3. The vertical distribution of nucleation mode particle concentrations reveals that significant and fairly strong particle formation events did occur for a considerable fraction of measurement time above 8 km (and only there). Very low concentrations were observed in general in the fresh outflow of active MCSs, likely as the result of efficient wet removal of aerosol particles due to heavy precipitation inside the convective cells of the MCSs. This wet removal initially affects all particle size ranges as clearly shown by all measurements in the vicinity of MCSs.
Atmospheric Chemistry and Physics. 01/2010;
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Voigt C,
Schumann U,
Jurkat T,
Schäuble D, Schlager H,
Petzold A,
Gayet J.-F,
Krämer M,
Schneider J,
Borrmann S, [......],
Holzäpfel F,
Arnold F,
Wendisch M,
Döpelheuer A,
Gottschaldt K,
Baumann R,
Zöger M,
Sölch I,
Rautenhaus M,
Dörnbrack A
[show abstract]
[hide abstract]
ABSTRACT: Lineshaped contrails were detected with the research aircraft Falcon during the CONCERT – CONtrail and Cirrus ExpeRimenT – campaign in October/November 2008. The Falcon was equipped with a set of instruments to measure the particle size distribution, shape, extinction and chemical composition as well as trace gas mixing ratios of sulfur dioxide (SO2), reactive nitrogen and halogen species (NO, NOy, HNO3, HONO, HCl), ozone (O3) and carbon monoxide (CO). During 12 mission flights over Europe, numerous contrails, cirrus clouds and a volcanic aerosol layer were probed at altitudes between 8.5 and 11.6 km and at temperatures above 213 K. 22 contrails from 11 different aircraft were observed near and below ice saturation. The observed NO mixing ratios, ice crystal and soot number densities are compared to a process based contrail model. On 19 November 2008 the contrail from a CRJ-2 aircraft was penetrated in 10.1 km altitude at a temperature of 221 K. The contrail had mean ice crystal number densities of 125 cm−3 with effective radii reff of 2.6 μm. The presence of particles with r>50 μm in the less than 2 min old contrail suggests that natural cirrus crystals were entrained in the contrail. Mean HONO/NO (HONO/NOy) ratios of 0.037 (0.024) and the fuel sulfur conversion efficiency to H2SO4 (εS↓) of 2.9 % observed in the CRJ-2 contrail are in the range of previous measurements in the gaseous aircraft exhaust. On 31 October 2010 aviation NO emissions could have contributed by more than 40% to the regional scale NO levels in the mid-latitude lowest stratosphere. The CONCERT observations help to better quantify the climate impact from contrails and will be used to investigate the chemical processing of trace gases on contrails.
Atmospheric Chemistry and Physics. 01/2010;
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Schumann U,
Weinzierl B,
Reitebuch O, Schlager H,
Minikin A,
Forster C,
Baumann R,
Sailer T,
Graf K,
Mannstein H, [......],
Mallaun C,
Gayet J.-F,
Lieke K,
Kandler K,
Ebert M,
Weinbruch S,
Stohl A,
Gasteiger J,
Olafsson H,
Sturm K
[show abstract]
[hide abstract]
ABSTRACT: Airborne measurements of Lidar backscatter, aerosol concentrations (particle diameters of 4 nm to 50 μm), trace gas mixing ratios (SO2, CO, O3, H2O), single particle properties, and meteorological parameters have been performed in volcanic ash plumes with the Falcon aircraft operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR). A series of 17 flights was performed over Europe between Southern Germany and Iceland during the eruption period of the Eyjafjalla1 volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with Lidar directly over the volcano and up to a distance of 2700 km downwind. Lidar and in-situ measurements covered plume ages of 7 h to 120 h. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 μm diameter, with size and age dependent composition. Ash mass concentration was evaluated for a material density of 2.6 g cm−3 and for either weakly or moderately absorbing coarse mode particles (refractive index 1.59+0i or 1.59+0.004i). In the absorbing case, the ash concentration is about a factor of four larger than in the non-absorbing limit. Because of sedimentation constraints, the smaller results are the more realistic ones for aged plumes. The Falcon flew in ash clouds up to about 1 mg m−3 for a few minutes and in an ash cloud with more than 0.2 mg m−3 mean-concentration for about one hour without engine damages. In fresh plumes, the SO2 concentration was correlated with the ash mass concentration. Typically, 0.5 mg m−3 ash concentration was related to about 100 nmol mol−31 SO2 mixing ratio and 70 nmol mol−1 CO mixing ratio increases for this volcano period. In aged plumes, layers with enhanced coarse mode particle concentration but without SO2 enhancements occurred. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. The ash plumes were often visible as faint dark layers even for concentrations below 0.1 mg m−3. The ozone concentrations and the humidity inside the plumes were often reduced compared to ambient values. The large abundance of volatile Aitken mode particles suggests nucleation of sulfuric acid droplets. Ammonium sulfate particles were also found on the impactors. The effective diameters decreased from about 5 μm in the fresh plume to about 1 μm for plume ages of up to 6 days. The distal ash mass flux on 2 May was of the order 1800 kg s−1; the SO2 mass flux was about a factor of 3–4 smaller. The volcano ejected about 40 Tg of ash mass and 10 Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash. The data described may be used for further studies, including comparisons to satellite and ground or space based Lidar observations, and for model improvements. 1 Also known as Eyjafjallajökull or Eyjafjöll volcano, http://www.britannica.com/EBchecked/topic/1683937/Eyjafjallajokull-volcano
Atmospheric Chemistry and Physics 01/2010; · 4.88 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: During the "African Monsoon Multidisciplinary Analysis" (AMMA) field phase in August 2006, a variety of measurements focusing on deep convection were performed over West Africa. The German research aircraft Falcon based in Ouagadougou (Burkina Faso) investigated the chemical composition in the outflow of large mesoscale convective systems (MCS). Here we analyse two different types of MCS originating north and south of the intertropical convergence zone (ITCZ, ~10° N), respectively. In addition to the airborne trace gas measurements, stroke measurements from the Lightning Location Network (LINET), set up in Northern Benin, are analysed. The main focus of the present study is 1) to analyse the trace gas composition (CO, O3, NO, NOx, NOy, and HCHO) in the convective outflow as a function of distance from the convective core, 2) to investigate how different trace gas compositions in the boundary layer (BL) and ambient air may influence the O3 concentration in the convective outflow, and 3) to estimate the rate of lightning-produced nitrogen oxides per flash in selected thunderstorms and compare it to our previous results for the tropics. The MCS outflow was probed at different altitudes (~10–12 km) and distances from the convective core (<500 km). Trace gas signatures similar to the conditions in the MCS inflow region were observed in the outflow close to the convective core, due to efficient vertical transport. In the fresh MCS outflow, low O3 mixing ratios in the range of 35–40 nmol mol−1 were observed. Further downwind, O3 mixing ratios in the outflow rapidly increased with distance, due to mixing with the ambient O3-rich air. After 2–3 h, O3 mixing ratios in the range of ~65 nmol mol−1 were observed in the aged outflow. Within the fresh MCS outflow, mean NOx (=NO+NO2) mixing ratios were in the range of ~0.3–0.4 nmol mol−1 (peaks ~1 nmol mol−1) and only slightly enhanced compared to the background. Both lightning-produced NOx (LNOx) and NOx transported upward from the BL contributed about equally to this enhancement. On the basis of Falcon measurements, the mass flux of LNOx in the investigated MCS was estimated to be ~100 g(N) s−1. The average stroke rate of the probed thunderstorms was 0.04–0.07 strokes s−1 (here only strokes with peak currents ≥10 kA contributing to LNOx were considered). The LNOx mass flux and the stroke rate were combined to estimate the LNOx production rate. For a better comparison with other published results, LNOx estimates per LINET stroke were scaled to Lightning Imaging Sensor (LIS) flashes. The LNOx production rate per LIS flash was estimated to 1.0 and 2.5 kg(N) for the MCS located south and north of the ITCZ, respectively. If we assume, that these different types of MCS are typical thunderstorms occurring globally (LIS flash rate ~44 s−1), the annual global LNOx production rate was estimated to be ~1.4 and 3.5 Tg(N) a−1.
Atmospheric Chemistry and Physics Discussions. 01/2010;
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K. S. Law,
Fierli F,
Cairo F, Schlager H,
Borrmann S,
Streibel M,
Real E,
Kunkel D,
Schiller C,
Ravegnani F,
Ulanovsky A,
D&apos,
Amato F,
Viciani S,
C. M. Volk
Atmospheric Chemistry and Physics. 01/2010;
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M. D. Andrés-Hernández,
Stone D,
D. M. Brookes,
Commane R,
C. E. Reeves,
Huntrieser H,
D. E. Heard,
P. S. Monks,
J. P. Burrows, Schlager H,
Kartal D,
M J Evans,
C. F. A. Floquet,
Ingham T,
Methven J,
A. E. Parker
[show abstract]
[hide abstract]
ABSTRACT: Peroxy radicals were measured onboard two scientific aircrafts during the AMMA (African Monsoon Multidisciplinary Analysis) campaign in summer 2006. This paper reports results from the flight on 16 August 2006 during which measurements of HO2 by laser induced fluorescence spectroscopy at low pressure (LIF-FAGE) and total peroxy radicals (RO2* = HO2+ΣRO2, R = organic chain) by two similar instruments based on the peroxy radical chemical amplification (PeRCA) technique were subject of a blind intercomparison. The German DLR-Falcon and the British FAAM-BAe-146 flew wing tip to wing tip for about 30 min making concurrent measurements on 2 horizontal level runs at 697 and 485 hPa over the same geographical area in Burkina Faso. A full set of supporting measurements comprising photolysis frequencies, and relevant trace gases like CO, NO, NO2, NOy, O3 and a wider range of VOCs were collected simultaneously. Results are discussed on the basis of the characteristics and limitations of the different instruments used. Generally, no data bias are identified and the RO2* data available agree quite reasonably within the instrumental errors. The [RO2*]/[HO2] ratios, which vary between 1:1 and 3:1, as well as the peroxy radical variability, concur with variations in photolysis rates and in other potential radical precursors. Model results provide additional information about dominant radical formation and loss processes.
Atmospheric Chemistry and Physics. 01/2010;
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ABSTRACT: During the African Monsoon Multidisciplinary Analyses (AMMA) airborne measurements of ozone, CO and nitrogen oxides by the French and German falcon aircraft took place near three cities in West Africa (Cotonou, Niamey and Ouagadougou). Significant ozone production (O3 increase of 40–50 ppbv) took place during two specific events: one near Cotonou on the coast of the Guinea Gulf, and the other near Niamey in the Sahel region. In both cases a high level of NOx (>3 ppbv) is related to the ozone production. The ozone production is mainly driven by the Lagos-Cotonou anthropogenic emissions in Cotonou. In Niamey the combined effect of advection of VOC emissions from the forest and stagnation over the city area and the poorly vegetated soils recently wetted by convected systems is needed to achieve a similar level of ozone precursors. In Ouagadougou no ozone plume is found because of the absence of a pause in the convective activity and of the larger vegetated area around the city which prevented ozone plume formation during the wet season. To discuss the ozone increase near Cotonou two different approaches have been implemented: a FLEXPART simulation to quantify the probability of transport from the SH compared to air mass stagnation over the emission area and a simulation of the BOLAM mesoscale model with two different tracers for the anthropogenic emission (RETRO inventory for 2000) and the biomass burning. The BOLAM model shows a good agreement with the meteorological observations of the aircraft and allows to identify the key influence of the anthropogenic emissions in the first 3 km while the biomass burning plume remains above this altitude. The day to day variability of the ozone and CO in Niamey and Ouagadougou is discussed using FLEXPART simulations of the air mass stagnation in the 12° N–14° N latitude band and northward advection of air masses from the vegetated areas influenced by the biogenic volatile organic compound (VOC) emissions. Both conditions need to be fulfilled to be able to detect ozone increase within the city plume. The first condition is necessary to obtain a significant increase of the NOx concentrations by combining the city emission and the soil emission. It also shows that, contrary to the Niamey conditions, the Ouagadougou air mass transport and its timing respective to the convective activity did not correspond to favourable conditions for O3 formation during the time period of the aircraft data. Finally to check the magnitude of the ozone production related to the observed CO and NOx observations, a 2-days stationary run of the CittyCAT Lagrangian model was conducted at Cotonou location. The initialisation of the chemical concentrations not measured is done by scaling to the NOx and CO concentrations observed in the polluted plume. The scaling factor is derived from the low altitude observations provided by the DF20 and the BAe-146 aircraft during the AMMA campaign. Under such conditions, the simulation show that 50 ppbv of ozone can be produced in a 2-days period.
Atmospheric Chemistry and Physics Discussions. 01/2010;
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Huntrieser H, Schlager H,
Lichtenstern M,
Roiger A,
Stock P,
Minikin A,
Höller H,
Schmidt K,
Betz H.-D,
Allen G,
Viciani S,
Ulanovsky A,
Ravegnani F,
Brunner D
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ABSTRACT: During the SCOUT-O3/ACTIVE field phase in November–December 2005, airborne in situ measurements were performed inside and in the vicinity of thunderstorms over northern Australia with several research aircraft (German Falcon , Russian M55 Geophysica , and British Dornier-228 . Here a case study from 19 November is presented in detail on the basis of airborne trace gas measurements (NO, NO<sub>y</sub>, CO, O<sub>3</sub>) and stroke measurements from the German LIghtning Location NETwork (LINET), set up in the vicinity of Darwin during the field campaign. The anvil outflow from three different types of thunderstorms was probed by the Falcon aircraft: (1) a continental thunderstorm developing in a tropical airmass near Darwin, (2) a mesoscale convective system (MCS), known as Hector, developing within the tropical maritime continent (Tiwi Islands), and (3) a continental thunderstorm developing in a subtropical airmass ~200 km south of Darwin. For the first time detailed measurements of NO were performed in the Hector outflow. The highest NO mixing ratios were observed in Hector with peaks up to 7 nmol mol<sup>−1</sup> in the main anvil outflow at ~11.5–12.5 km altitude. The mean NO<sub>x</sub> (=NO+NO<sub>2</sub>) mixing ratios during these penetrations (~100 km width) varied between 2.2 and 2.5 nmol mol<sup>−1</sup>. The NO<sub>x</sub> contribution from the boundary layer (BL), transported upward with the convection, to total anvil-NO<sub>x</sub> was found to be minor (<10%). On the basis of Falcon measurements, the mass flux of lightning-produced NO<sub>x</sub> (LNO<sub>x</sub>) in the well-developed Hector system was estimated to 0.6–0.7 kg(N) s<sup>−1</sup>. The highest average stroke rate of the probed thunderstorms was observed in the Hector system with 0.2 strokes s<sup>−1</sup> (here only strokes with peak currents ≥10 kA contributing to LNO<sub>x</sub> were considered). The LNO<sub>x</sub> mass flux and the stroke rate were combined to estimate the LNO<sub>x</sub> production rate in the different thunderstorm types. For a better comparison with other studies, LINET strokes were scaled with Lightning Imaging Sensor (LIS) flashes. The LNO<sub>x</sub> production rate per LIS flash was estimated to 4.1–4.8 kg(N) for the well-developed Hector system, and to 5.4 and 1.7 kg(N) for the continental thunderstorms developing in subtropical and tropical airmasses, respectively. If we assume, that these different types of thunderstorms are typical thunderstorms globally (LIS flash rate ~44 s<sup>−1</sup>), the annual global LNO<sub>x</sub> production rate based on Hector would be ~5.7–6.6 Tg(N) a<sup>−1</sup> and based on the continental thunderstorms developing in subtropical and tropical airmasses ~7.6 and ~2.4 Tg(N) a<sup>−1</sup>, respectively. The latter thunderstorm type produced much less LNO<sub>x</sub> per flash compared to the subtropical and Hector thunderstorms, which may be caused by the shorter mean flash component length observed in this storm. It is suggested that the vertical wind shear influences the horizontal extension of the charged layers, which seems to play an important role for the flash lengths that may originate. In addition, the horizontal dimension of the anvil outflow and the cell organisation within the thunderstorm system are probably important parameters influencing flash length and hence LNO<sub>x</sub> production per flash.
Atmospheric Chemistry and Physics. 01/2009;
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Köppe M,
Hermann M,
C. A. M. Brenninkmeijer,
Heintzenberg J, Schlager H,
Schuck T,
Slemr F,
Sprung D,
P. F. J. van Velthoven,
Wiedensohler A,
Zahn A,
Ziereis H
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ABSTRACT: The origin of aerosol particles in the upper troposphere and lowermost stratosphere over the Eurasian continent was investigated by applying cluster analysis methods to in situ measured data. Number concentrations of submicrometer aerosol particles and trace gas mixing ratios derived by the CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container) measurement system on flights between Germany and South-East Asia were used for this analysis. Four cluster analysis methods were applied to a test data set and their capability of separating the data points into scientifically reasonable clusters was assessed. The best method was applied to seasonal data subsets for summer and winter resulting in five cluster or air mass types: stratosphere, tropopause, free troposphere, high clouds, and boundary layer influenced. Other source clusters, like aircraft emissions could not be resolved in the present data set with the used methods. While the cluster separation works satisfactory well for the summer data, in winter interpretation is more difficult, which is attributed to either different vertical transport pathways or different chemical lifetimes in both seasons. The geographical distribution of the clusters together with histograms for nucleation and Aitken mode particles within each cluster are presented. Aitken mode particle number concentrations show a clear vertical gradient with the lowest values in the lowermost stratosphere (750–2820 particles/cm3 STP, minimum of the two 25% – and maximum of the two 75%-percentiles of both seasons) and the highest values for the boundary-layer-influenced air (4290–22 760 particles/cm3 STP). Nucleation mode particles are also highest in the boundary-layer-influenced air (1260–29 500 particles/cm3 STP), but are lowest in the free troposphere (0–450 particles/cm3 STP). The given submicrometer particle number concentrations represent the first large-scale seasonal data sets for the upper troposphere and lowermost stratosphere over the Eurasian continent.
Atmospheric Chemistry and Physics. 01/2009;
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Brunner D,
Siegmund P,
P. T. May,
Chappel L,
Schiller C,
Müller R,
Peter T,
Fueglistaler S,
A. R. MacKenzie,
Fix A, Schlager H,
Allen G,
A. M. Fjaeraa,
Streibel M,
N. R. P. Harris
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ABSTRACT: An aircraft measurement campaign involving the Russian high-altitude aircraft M55 Geophysica and the German DLR Falcon was conducted in Darwin, Australia in November and December 2005 as part of the European integrated project SCOUT-O3. The overall objectives of the campaign were to study the transport of trace gases through the tropical tropopause layer (TTL), mechanisms of dehydration close to the tropopause, and the role of deep convection in these processes. In this paper a detailed roadmap of the campaign is presented, including rationales for each flight, and an analysis of the local and large-scale meteorological context in which they were embedded. The campaign took place during the pre-monsoon season which is characterized by a pronounced diurnal evolution of deep convection including a mesoscale system over the Tiwi Islands north of Darwin known as "Hector". This allowed studying in detail the role of deep convection in structuring the tropical tropopause region, in situ sampling convective overshoots above storm anvils, and probing the structure of anvils and cirrus clouds by Lidar and a suite of in situ instruments onboard the two aircraft. The large-scale flow during the first half of the campaign was such that local flights, away from convection, sampled air masses downstream of the "cold trap" region over Indonesia. Abundant cirrus clouds enabled the study of active dehydration, in particular during two TTL survey flights. The campaign period also encompassed a Rossby wave breaking event transporting stratospheric air to the tropical middle troposphere and an equatorial Kelvin wave modulating tropopause temperatures and hence the conditions for dehydration.
Atmospheric Chemistry and Physics 01/2009; · 4.88 Impact Factor
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ABSTRACT: A large SO<sub>2</sub>-rich pollution plume of Chinese origin was detected by aircraft based CIMS (Chemical Ionization Mass Spectrometry) measurements at 3–7.5 km altitude over the North Atlantic on 3 May 2006 during the INTEX (Intercontinental Chemical Transport Experiment) campaign. Additional trace gases (NO, NO<sub>y</sub>, CO, H<sub>2</sub>O) were measured and used for comparison and source identification. All measurements took place aboard the German research aircraft Falcon. The atmospheric SO<sub>2</sub> mole fraction was markedly increased inside the plume and reached up to 900 pmol/mol. The measured ratio SO<sub>2</sub>/NO<sub>y</sub> of 1.4 suggests combustion of coal or fuel with a very high sulfur content as a source of the excess SO<sub>2</sub>. Accompanying FLEXPART particle dispersion model simulations indicate that the probed pollution plume originated at low altitudes over densely populated and industrialized areas in eastern China about 8–12 days prior to the measurements.
Atmospheric Chemistry and Physics Discussions. 01/2009;
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ABSTRACT: Peroxy radical measurements made on board the DLR-Falcon research aircraft over West Africa within the African Monsoon Multidisciplinary Analysis (AMMA) campaign during the 2006 wet monsoon are presented in this study. The analysis of data focuses on the photochemical activity of air masses sampled during episodes of intense convection and biomass burning. Generally, the total sum of peroxy radical mixing ratios, measured in the outflow of convective clouds, are quite variable but occasionally are coupled with the NO variations indicating the coexistence, or simultaneously emission of NOx, with a potential radical precursor (i.e., formaldehyde, acetone or peroxides) which has likely been transported to higher atmospheric layers. Based on the measurements, significant O3 production rates up to 2 ppb/h in the MCS outflow are estimated by using a box model with simplified chemistry. Peroxy radicals having mixing ratios around 20–25 pptv and with peak values of up to 60–70 pptv are measured within biomass burning plumes, detected at the coast in Ghana. Calculations of back-trajectory densities confirm the origin of these air masses being a biomass burning region at southern latitudes and close to the Gulf of Guinea, according to satellite pictures. Measured peroxy radical concentrations agree reasonably with modelled estimations taking into account simple local chemistry. Moreover the vertical profiles taken at the aircraft base in Ouagadougou, Burkina Faso, indicate the common feature of having maximum concentrations between 2 and 4 km, in agreement with other literature values obtained under similar conditions.
Atmospheric Chemistry and Physics Discussions. 01/2009;
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ABSTRACT: We report on sulfur dioxide (SO<sub>2</sub>) induced formation of aerosols and cloud condensation nuclei in an SO<sub>2</sub> rich aged (9 days) pollution plume of Chinese origin, which we have detected at 5–7 km altitude during a research aircraft mission over the East Atlantic off the West coast of Ireland. Building on our measurements of SO<sub>2</sub> and other trace gases along with plume trajectory simulations, we have performed model simulations of SO<sub>2</sub> induced formation of gaseous sulfuric acid (GSA, H<sub>2</sub>SO<sub>4</sub>) followed by GSA induced formation and growth of aerosol particles. We find that efficient photochemical SO<sub>2</sub> conversion to GSA took place in the plume followed by efficient formation and growth of H<sub>2</sub>SO<sub>4</sub>-H<sub>2</sub>O aerosol particles. Most particles reached sufficiently large sizes to act as cloud condensation nuclei whenever water vapor supersaturation exceeded 0.1–0.2%. As a consequence, smaller but more numerous cloud droplets are formed, which tend to increase the cloud albedo and to decrease the rainout efficiency. The detected plume represents an interesting example of the environmental impact of long range transport of fossil fuel combustion generated SO<sub>2</sub>.
Atmospheric Chemistry and Physics Discussions. 01/2009;
