bluuebunny/crossref_metadata_2025 huggingface dataset:
Partitioning of reactive nitrogen (NOy) and dependence on meteorological conditions in the lower free troposphere
Authors: Zellweger C. , Forrer J. , Hofer P. , Nyeki S. , Schwarzenbach B. , Weingartner E. , Ammann M. , Baltensperger U.
Published: April 2010

Abstract. Results of continuous nitrogen oxide (NO), nitrogen dioxide (NO2), peroxyacetyl nitrate (PAN) and total reactive nitrogen (NOy) measurements along with seasonal field campaigns of nitric acid (HNO3) and particulate nitrate (NO3-) measurements are presented for a two-year period at the high-alpine research station Jungfraujoch (JFJ), 3580 m asl. The NOy mixing ratio and partitioning is shown to strongly depend on meteorological conditions. Knowledge of these meteorological transport processes allows discrimination between undisturbed (i.e. clean) and disturbed (i.e. influenced by regional pollution sources) free tropospheric (FT) conditions at the JFJ. Median NOy concentrations during undisturbed FT periods ranged from 350 pptv (winter, December to February) to 581 pptv (spring, March to May). PAN was found to be the dominant NOy species during spring and summer, whereas NO2 was most abundant during autumn and winter. Particulate nitrate was found to contribute significantly to total NOy during thermally induced vertical transport. Föhn events, synoptical lifting (e.g. fronts) and thermally induced vertical transport resulted in mixing ratios up to 10 times higher at the JFJ compared to undisturbed FT conditions. Furthermore this meteorological variability of the NOy concentration and partitioning often dominated the seasonal variability. As a consequence the use of filters at the JFJ (and other mountainous sites) is crucial for the interpretation of data from such measurement sites. This study presents a further development of meteorological filters for the high-alpine site Jungfraujoch, which also could be modified and adapted to other mountainous measurement sites.
The roles of dynamical variability and aerosols in cirrus cloud formation
Authors: Kärcher B. , Ström J.
Published: April 2010

Abstract. The probability of occurrence of ice crystal number densities in young cirrus clouds is examined based on airborne measurements. The observations have been carried out at midlatitudes in both hemispheres at equivalent latitudes (52-55°N/S) during the same season (local autumn in 2000). The in situ measurements considered in the present study include temperatures, vertical velocities, and total ice crystal concentrations, the latter determined with high precision and accuracy using a counterflow virtual impactor. Most young cirrus clouds typically contain high number densities (1-10 cm-3) of small (diameter <20 mm) ice crystals. This mode dominates the probability distributions and is shown to be caused by rapid cooling rates associated with updraft speeds in the range 10-100 cm s-1. A second mode containing larger crystals extends from ~1 cm-3 to low concentrations close to the detection threshold (~3 x 10-4 cm-3) and could be associated with lower updraft speeds. Results of a statistical analysis provide compelling evidence that the dynamical variability of vertical air motions on the mesoscale is the key factor determining the observed probability distributions of pristine ice crystal concentrations in cirrus. Other factors considered are changes of temperature as well as size, number, and ice nucleation thresholds of the freezing aerosol particles. The variability in vertical velocities is caused by atmospheric gravity waves leading to small-scale temperature fluctuations. Inasmuch as gravity waves are widespread, mesoscale variability in vertical velocities can be viewed as a universal feature of young cirrus clouds. Large-scale models that do not account for this subgrid-scale variability yield erroneous predictions of the variability of basic cirrus cloud properties. Climate change may bring about changes in the global distribution of updraft speeds, mean air temperatures, and aerosol properties. As shown in this work, these changes could significantly modify the probability distribution of cirrus ice crystal concentrations. This study emphasizes the key role of vertical velocities and mesoscale variability in vertical velocities in controlling cirrus properties. The results suggest that, in any effort to ascribe cause to trends of cirrus cloud properties, a careful evaluation of dynamical changes in cloud formation should be done before conclusions regarding the role of other anthropogenic factors, such as changes in aerosol composition, are made.
Dynamics and chemistry of vortex remnants in late Arctic spring 1997 and 2000: Simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS)
Authors: Konopka P. , Grooß J.-U. , Bausch S. , Müller R. , McKenna D. S. , Morgenstern O. , Orsolini Y.
Published: April 2010

Abstract. High-resolution simulations of the chemical composition of the Arctic stratosphere during late spring 1997 and 2000 were performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations were performed for the entire northern hemisphere on two isentropic levels 450 K (~18 km) and 585 K (~24 km). The spatial distribution and the lifetime of the vortex remnants formed after the vortex breakup in May 1997 display different behavior above and below 20 km. Above 20 km, vortex remnants propagate southward (up to 40°N) and are "frozen in'' in the summer circulation without significant mixing. Below 20 km the southward propagation of the remnants is bounded by the subtropical jet. Their lifetime is shorter by a factor of 2 than that above 20 km, owing to significant stirring below this altitude. The behavior of vortex remnants formed in March 2000 is similar but, due to an earlier vortex breakup, dominated during the first 6 weeks after the vortex breakup by westerly winds, even above 20 km. Vortex remnants formed in May 1997 are characterized by large mixing ratios of HCl indicating negligible, halogen-induced ozone loss. In contrast, mid-latitude ozone loss in late boreal spring 2000 is dominated, until mid-April, by halogen-induced ozone destruction within the vortex remnants, and subsequent transport of the ozone-depleted polar air masses (dilution) into the mid-latitudes. By varying the intensity of mixing in CLaMS, the impact of mixing on the formation of ClONO2 and ozone depletion is investigated. We find that the photochemical decomposition of HNO3 and not mixing with NOx-rich mid-latitude air is the main source of NOx within the vortex remnants in March and April 2000. Ozone depletion in the remnants is driven by ClOx photolytically formed from ClONO2. At the end of May 1997, the halogen-induced ozone deficit at 450 K poleward of 30°N amounts to ~12% with ~10% in the polar vortex and ~2% in well-isolated vortex remnants after the vortex breakup.
Formaldehyde over the eastern Mediterranean during MINOS: Comparison of airborne in-situ measurements with 3D-model results
Authors: Kormann R. , Fischer H. , de Reus M. , Lawrence M. , Brühl Ch. , von Kuhlmann R. , Holzinger R. , Williams J. , Lelieveld J. , Warneke C. , de Gouw J. , Heland J. , Ziereis H. , Schlager H.
Published: April 2010

Abstract. Formaldehyde (HCHO) is an important intermediate product in the photochemical degradation of methane and non-methane volatile organic compounds. In August 2001, airborne formaldehyde measurements based on the Hantzsch reaction technique were performed during the Mediterranean INtensive Oxidant Study, MINOS. The detection limit of the instrument was 42 pptv (1s) at a time resolution of 180 s (10-90%). The overall uncertainty of the HCHO measurements was 30% at a mixing ratio of 300 pptv. In the marine boundary layer over the eastern Mediterranean Sea average HCHO concentrations were of the order of 1500 pptv, in reasonable agreement with results from a three-dimensional global chemical transport model of the lower atmosphere including non-methane volatile organic compound (NMVOC) chemistry. Above the boundary layer HCHO mixing ratios decreased with increasing altitude to a minimum level of 250 pptv at about 7 km. At higher altitudes (above 7 km) HCHO levels showed a strong dependency on the airmass origin. In airmasses from the North Atlantic/North American area HCHO levels were of the order of 300 pptv, a factor of 6 higher than values predicted by the model. Even higher HCHO levels, increasing to values of the order of 600 pptv at 11 km altitude, were observed in easterlies transporting air affected by the Indian monsoon outflow towards the Mediterranean basin. Only a small part (~30 pptv) of the large discrepancy between the model results and the measurements of HCHO in the free troposphere could be explained by a strong underestimation of the upper tropospheric acetone concentration by up to a factor of ten by the 3D-model. Therefore, the measurement-model difference in the upper troposphere remains unresolved, while the observed dependency of HCHO on airmass origin might indicate that unknown, relatively long-lived NMVOCs - or their reaction intermediates - associated with biomass burning are at least partially responsible for the observed discrepancies.
Global distribution of tropospheric ozone from satellite measurements using the empirically corrected tropospheric ozone residual technique: Identification of the regional aspects of air pollution
Authors: Fishman J. , Wozniak A. E. , Creilson J. K.
Published: April 2010

Abstract. Using coincident observations of total ozone from the Total Ozone Mapping Spectrometer (TOMS) and stratospheric ozone profiles from the Solar Backscattered Ultraviolet (SBUV) instruments, detailed maps of tropospheric ozone have been derived on a daily basis over a time period spanning more than two decades. The resultant climatological seasonal depictions of the tropospheric ozone residual (TOR) show much more detail than an earlier analysis that had used coincident TOMS and Stratospheric Aerosol and Gas Experiment (SAGE) ozone profiles, although there are many similarities between the TOMS/SAGE TOR and the TOMS/SBUV TOR climatologies. In particular, both TOR seasonal depictions show large enhancements in the southern tropics and subtropics in austral spring and at northern temperate latitudes during the summer. The much greater detail in this new data set clearly defines the regional aspect of tropospheric ozone pollution in northeastern India, eastern United States, eastern China, and west and southern Africa. Being able to define monthly climatologies for each year of the data record provides enough temporal resolution to illustrate significant interannual variability in some of these regions.
Mountain wave PSC dynamics and microphysics from ground-based lidar measurements and meteorological modeling
Authors: Reichardt J. , Dörnbrack A. , Reichardt S. , Yang P. , McGee T. J.
Published: April 2010

Abstract. The day-long observation of a polar stratospheric cloud (PSC) by two co-located ground-based lidars at the Swedish research facility Esrange (67.9° N, 21.1° E) on 16 January 1997 is analyzed in terms of PSC dynamics and microphysics. Mesoscale modeling is utilized to simulate the meteorological setting of the lidar measurements. Microphysical properties of the PSC particles are retrieved by comparing the measured particle depolarization ratio and the PSC-averaged lidar ratio with theoretical optical data derived for different particle shapes. In the morning, nitric acid trihydrate (NAT) particles and then increasingly coexisting liquid ternary aerosol (LTA) were detected as outflow from a mountain wave-induced ice PSC upwind Esrange. The NAT PSC is in good agreement with simulations for irregular-shaped particles with length-to-diameter ratios between 0.75 and 1.25, maximum dimensions from 0.7 to 0.9 µm, and a number density from 8 to 12 cm-3 and the coexisting LTA droplets had diameters from 0.7 to 0.9 µm, a refractive index of 1.39 and a number density from 7 to 11 cm-3. The total amount of condensed HNO3 was in the range of 8–12 ppbv. The data provide further observational evidence that NAT forms via deposition nucleation on ice particles as a number of recently published papers suggest. By early afternoon the mountain-wave ice PSC expanded above the lidar site. Its optical data indicate a decrease in minimum particle size from 3 to 1.9 µm with time. Later on, following the weakening of the mountain wave, wave-induced LTA was observed only. Our study demonstrates that ground-based lidar measurements of PSCs can be comprehensively interpreted if combined with mesoscale meteorological data.
Aerosol-ozone correlations during dust transport episodes
Authors: Bonasoni P. , Cristofanelli P. , Calzolari F. , Bonafè U. , Evangelisti F. , Stohl A. , Zauli Sajani S. , van Dingenen R. , Colombo T. , Balkanski Y.
Published: April 2010

Abstract. Its location in the Mediterranean region and its physical characteristics render Mt. Cimone (44°11′ N, 10°42′ E), the highest peak of the Italian northern Apennines (2165 m asl), particularly suitable to study the transport of air masses from the north African desert area to Europe. During these northward transports 12 dust events were registered in measurements of the aerosol concentration at the station during the period June–December 2000, allowing the study of the impact of mineral dust transports on free tropospheric ozone concentrations, which were also measured at Mt. Cimone. Three-dimensional backward trajectories were used to determine the air mass origin, while TOMS Aerosol Index data for the Mt. Cimone area were used to confirm the presence of absorbing aerosol over the measurement site. A trajectory statistical analysis allowed identifying the main source areas of ozone and aerosols. The analysis of these back trajectories showed that central Europe and north and central Italy are the major pollution source areas for ozone and fine aerosol, whereas the north African desert regions were the most important source areas for coarse aerosol and low ozone concentrations. During dust events, the Mt. Cimone mean volume concentration for coarse particles was 6.18 µm3/cm3 compared to 0.63 µm3/cm3 in dust-free conditions, while the ozone concentrations were 4% to 21% lower than the monthly mean background values. Our observations show that surface ozone concentrations were lower than the background values in air masses coming from north Africa, and when these air masses were also rich in coarse particles, the lowest ozone values were registered. Moreover, preliminary results on the possible impact of the dust events on PM10 and ozone values measured in Italian urban and rural areas showed that during the greater number of the considered dust events, significant PM10 increases and ozone decreases have occurred in the Po valley.
Model calculations of the age of firn air across the Antarctic continent
Authors: Kaspers K. A. , van de Wal R. S. W. , van den Broeke M. R. , Schwander J. , van Lipzig N. P. M. , Brenninkmeijer C. A. M.
Published: April 2010

Abstract. The age of firn air in Antarctica at pore close-off depth is only known for a few specific sites where firn air has been sampled for analyses. We present a model that calculates the age of firn air at pore close-off depth for the entire Antarctic continent. The model basically uses four meteorological parameters as input (surface temperature, pressure, accumulation rate and wind speed). Using parameterisations for surface snow density, pore close-off density and tortuosity, in combination with a density-depth model and data of a regional atmospheric climate model, distribution of pore close-off depth for the entire Antarctic continent is determined. The deepest pore close-off depth was found for the East Antarctic Plateau near 72° E, 82° S, at 150±15 m (2σ). A firn air diffusion model was applied to calculate the age of CO2 at pore close-off depth. The results predict that the oldest firn gas (CO2 age) is located between Dome Fuji, Dome Argos and Vostok at 43° E, 78° S being 148±23 (1σ or 38 for 2σ) years old. At this location an atmospheric trace gas record should be obtained. In this study we show that methyl chloride could be recorded with a predicted length of 125 years as an example for trace gas records at this location. The longest record currently available from firn air is derived at South Pole, being 80 years. Sensitivity tests reveal that the locations with old firn air (East Antarctic Plateau) have an estimated uncertainty (2σ) for the modelled CO2 age at pore close-off depth of 30% and of about 40% for locations with younger firn air (CO2 age typically 40 years). Comparing the modelled age of CO2 at pore close-off depth with directly determined ages at seven sites yielded a correlation coefficient of 0.90 and a slope close to 1, suggesting a high level of confidence for the modelled results in spite of considerable remaining uncertainties.
A study of the phase transition behavior of internally mixed ammonium sulfate - malonic acid aerosols
Authors: Braban C. F. , Abbatt J. P. D.
Published: April 2010

Abstract. This is a study into the phase transitions of aerosol composed of the ternary system ammonium sulfate (AS) - malonic acid (MA) - water using infrared extinction spectroscopy. Twelve compositions were studied in both deliquescence and efflorescence mode experiments. The presence of a MA fraction, by dry mass, (fMA) of 0.1 in an AS aerosol altered the relative humidity at which the phase transitions occur in an atmospherically significant manner. For compositions with 0.25
Dust altitude and infrared optical depth from AIRS
Authors: Pierangelo C. , Chédin A. , Heilliette S. , Jacquinet-Husson N. , Armante R.
Published: April 2010

Abstract. We show that mineral dust optical depth and altitude can be retrieved from the Aqua - Advanced Infrared Radiation Sounder (AIRS) measurements. Sensitivity studies performed with a high spectral resolution radiative transfer code show that dust effect on brightness temperatures may reach about 10 Kelvins for some channels. Using a Look-Up-Table approach, we retrieve not only the 10 µm optical depth but also the altitude of Saharan dust layer, above the Atlantic Ocean, from April to September 2003. A key point of our method is its ability to retrieve dust altitude from satellite observations. The time and space distribution of the optical depth is in good agreement with the Moderate resolution Imaging Spectroradiometer (MODIS) products. Comparing MODIS and AIRS aerosol optical depths, we find that the ratio between infrared and visible optical depths decreases during transport from 0.35 to 0.22, revealing a loss in coarse particles caused by gravitational settling. The evolution of dust altitude from spring to summer is in agreement with current knowledge on transport seasonality.
Refinements in the use of equivalent latitude for assimilating sporadic inhomogeneous stratospheric tracer observations, 2: Precise altitude-resolved information about transport of Pinatubo aerosol to very high latitude
Authors: Good P. , Pyle J.
Published: April 2010

Abstract. From high latitude lidar observations, quite precise information is extracted about the temporal evolution and vertical distribution of volcanic aerosol in the high latitude lower stratosphere following the eruption of Mount Pinatubo. Irreversible mixing of lower stratospheric aerosol, to the arctic pole during early 1992, is demonstrated, as a function of potential temperature and time. This work complements previous studies, which either identify vortex intrusions - without demonstrating irreversible transport, or use lower resolution satellite observations. The observed transport is associated tentatively with the vortex disturbance during late January, 1992. A very large number of high resolution lidar observations of Mount Pinatubo aerosol are analysed, without any data averaging. Averaging in measurement or analysis can cause tracer mixing to be overestimated. Averaging in the analysis can also require assumptions about which quantity has the dominant error (in this case, the equivalent latitude coordinate or the measurement), and which part of the data contains real structure. The method below attempts to avoid such assumptions.
Ion production rate in a boreal forest based on ion, particle and radiation measurements
Authors: Laakso L. , Petäjä T. , Lehtinen K. E. J. , Kulmala M. , Paatero J. , Hõrrak U. , Tammet H. , Joutsensaari J.
Published: April 2010

Abstract. In this study the ion production rates in a boreal forest were studied based on two different methods: 1) cluster ion and particle concentration measurements, 2) external radiation and radon concentration measurements. Both methods produced reasonable estimates for ion production rates. The average ion production rate calculated from aerosol particle size distribution and air ion mobility distribution measurements was 2.6 ion pairs cm-3s-1, and based on external radiation and radon measurements, 4.5 ion pairs cm-3s-1. The first method based on ion and particle measurements gave lower values for the ion production rates especially during the day. A possible reason for this is that particle measurements started only from 3nm, so the sink of small ions during the nucleation events was underestimated. It may also be possible that the hygroscopic growth factors of aerosol particles were underestimated. Another reason for the discrepancy is the nucleation mechanism itself. If the ions are somehow present in the nucleation process, there could have been an additional ion sink during the nucleation days.
Atmospheric particle formation events at Värriö measurement station in Finnish Lapland 1998-2002
Authors: Vehkamäki H. , Dal Maso M. , Hussein T. , Flanagan R. , Hyvärinen A. , Lauros J. , Merikanto P. , Mönkkönen M. , Pihlatie K. , Salminen K. , Sogacheva L. , Thum T. , Ruuskanen T. M. , Keronen P. , Aalto P. P. , Hari P. , Lehtinen K. E. J. , Rannik Ü , Kulmala M.
Published: April 2010

Abstract. During the calendar years 1998-2002, 147 clear 8nm diameter particle formation events have been identified at the SMEAR I station in Värriö, northern Finland. The events have been classified in detail according to the particle formation rate, growth rate, event starting time, different trace gas concentrations and pre-existing particle concentrations as well as various meteorological conditions. The frequency of particle formation and growth events was highest during the spring months between March and May, suggesting that increasing biological activity might produce the precursor gases for particle formation. The apparent 8nm particle formation rates were around 0.1 /cm3s, and they were uncorrelated with growth rates that varied between 0.5 and 10nm/h. The air masses with clearly elevated sulphur dioxide concentrations (above 1.6ppb) came, as expected, from the direction of the Nikel and Monschegorsk smelters. Only 15 formation events can be explained by the pollution plume from these sources.
A Lagrangian model with simple primary and secondary aerosol scheme 1: comparison with UK PM10 data
Authors: Emmerson K. M. , MacKenzie A. R. , Owen S. M. , Evans M. J. , Shallcross D. E.
Published: April 2010

Abstract. A Lagrangian trajectory model used to simulate photochemistry has been extended to include a simple parameterisation of primary and secondary aerosol particles. The model uses emission inventories of primary particles for the UK from the NAEI (National Atmospheric Emissions Inventory for the UK), and for Europe from the TNO (Institute of Environmental Sciences, Energy Research and Process Innovation, the Netherlands) respectively, to transport tracers representing PM10. One biogenic and two anthropogenic organic compounds were chosen as surrogates to model the formation of condensable material suitable for the production of secondary organic aerosol (SOA). The SOA is added to the primary PM10 and compared to measured PM10 at one urban and two rural UK receptor sites. The results show an average under-prediction by factors of 4.5 and 8.9 in the urban and rural cases respectively. The model is also used to simulate production of two secondary inorganic species, H2SO4 and HNO3, which are assumed, as a limiting case, to be present in the particle phase. The relationships between modelled and measured total PM10 improved with the addition of secondary inorganic compounds, and the overall model under-prediction factors are reduced to 3.5 and 3.9 in the urban and rural cases respectively. Nevertheless, our conclusion is that current emissions and chemistry do not appear to provide sufficient information to model PM10 well (i.e. to within a factor of two). There is a need for further process studies to inform global climate modelling that includes climate forcing by aerosol.
Kinetic nucleation and ions in boreal forest particle formation events
Authors: Laakso L. , Anttila T. , Lehtinen K. E. J. , Aalto P. P. , Kulmala M. , Hõrrak U. , Paatero J. , Hanke M. , Arnold F.
Published: April 2010

Abstract. In order to gain a more comprehensive picture on different mechanisms behind atmospheric particle formation, measurement results from QUEST 2-campaign are analyzed with an aid of an aerosol dynamic model. A special emphasis is laid on air ion and charged aerosol dynamics. Model simulations indicate that kinetic nucleation of ammonia and sulphuric acid together with condensation of sulphuric acid and low-volatile organic vapours onto clusters and particles explain basic features of particle formation events as well as ion characteristics. However, an observed excess of negative ions in the diameter range 1.5-3nm and overcharge of 3-5nm particles demonstrate that ions are also involved in particle formation. These observations can be explained by preferential condensation of sulphuric acid onto negatively charged clusters and particles and/or contribution of ion-induced nucleation on particle formation. According to model simulations, which assume that the nucleation rate is equal to the sulfuric acid collision rate, the relative contribution of ion-based particle formation seems to be smaller than kinetic nucleation of neutral clusters. Conducted model simulations also corroborate the recently-presented hypothesis according to which a large number of so-called thermodynamically stable clusters (TSCs) having a diameter between 1-3nm exist in the atmosphere. TSCs were found to grow to observable sizes only under favorable conditions, e.g. when the pre-existing particle concentration was low.
Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis
Authors: Collaud Coen M. , Weingartner E. , Schaub D. , Hueglin C. , Corrigan C. , Henning S. , Schwikowski M. , Baltensperger U.
Published: April 2010

Abstract. Scattering and absorption coefficients have been measured continuously at several wavelengths since March 2001 at the high altitude site Jungfraujoch (3580ma.s.l.). From these data, the wavelength dependences of the Ångström exponent and particularly of the single scattering albedo are determined. While the exponent of the single scattering albedo usually increases with wavelength, it decreases with wavelength during Saharan dust events (SDE) due to the greater size of the mineral aerosol particles and their different chemical composition. This change in the sign of the single scattering exponent turns out to be a sensitive means for detecting Saharan dust events. The occurrence of SDE detected by this new method was confirmed by visual inspection of filter colors and by studying long-range back-trajectories. An examination of SDE over a 22-month period shows that SDE are more frequent during the March-June period as well as during October and November. The trajectory analysis indicated a mean traveling time of 96.5h, with the most important source countries situated in the northern and north-western part of the Saharan desert. Most of the SDE do not lead to a detectable increase of the 48-h total suspended particulate matter (TSP) concentration at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the Jungfraujoch is 16µg/m3, which corresponds to an annual mean of 0.8µg/m3 or 24% of TSP.
Polar mesosphere summer echoes (PMSE): Review of observations and current understanding
Authors: Rapp M. , Lübken F.-J.
Published: April 2010

Abstract. Polar mesosphere summer echoes (PMSE) are very strong radar echoes primarily studied in the VHF wavelength range from altitudes close to the polar summer mesopause. Radar waves are scattered at irregularities in the radar refractive index which at mesopause altitudes is effectively determined by the electron number density. For efficient scatter, the electron number density must reveal structures at the radar half wavelength (Bragg condition for monostatic radars; ~3 m for typical VHF radars). The question how such small scale electron number density structures are created in the mesopause region has been a longstanding open scientific question for almost 30 years. This paper reviews experimental and theoretical milestones on the way to an advanced understanding of PMSE. Based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region, a consistent explanation for the generation of these radar echoes has been developed. The main idea is that mesospheric neutral air turbulence in combination with a significantly reduced electron diffusivity due to the presence of heavy charged ice aerosol particles (radii ~5–50 nm) leads to the creation of structures at spatial scales significantly smaller than the inner scale of the neutral gas turbulent velocity field itself. Importantly, owing to their very low diffusivity, the plasma structures acquire a very long lifetime, i.e., 10 min to hours in the presence of particles with radii between 10 and 50 nm. This leads to a temporal decoupling of active neutral air turbulence and the existence of small scale plasma structures and PMSE and thus readily explains observations proving the absence of neutral air turbulence at PMSE altitudes. With this explanation at hand, it becomes clear that PMSE are a suitable tool to permanently monitor the thermal and dynamical structure of the mesopause region allowing insights into important atmospheric key parameters like neutral temperatures, winds, gravity wave parameters, turbulence, solar cycle effects, and long term changes.
New insights in the global cycle of acetonitrile: release from theocean and dry deposition in the tropical savanna of Venezuela
Authors: Sanhueza E. , Holzinger R. , Kleiss B. , Donoso L. , Crutzen P. J.
Published: April 2010

Abstract. Using the proton transfer reaction mass spectrometry (PTR-MS) technique, acetonitrile was measured during the wet season in a Venezuelan woodland savanna. The site was located downwind of the Caribbean Sea and no biomass burning events were observed in the region. High boundary layer concentrations of 211±36pmol/mol (median, ±standard deviation) were observed during daytime in the well mixed boundary layer, which is about 60pmol/mol above background concentrations recently measured over the Mediterranean Sea and the Pacific Ocean. Most likely acetonitrile is released from the warm waters of the Caribbean Sea thereby enhancing mixing ratios over Venezuela. Acetonitrile concentrations will probably still be much higher in biomass burning plumes, however, the general suitability of acetonitrile as a biomass burning marker should be treated with care. During nights, acetonitrile dropped to levels typically around 120pmol/mol, which is consistent with a dry deposition velocity of 0.14cm/s when a nocturnal boundary layer height of 100m is assumed.
A new feedback mechanism linking forests, aerosols, and climate
Authors: Kulmala M. , Suni T. , Lehtinen K. E. J. , Dal Maso M. , Boy M. , Reissell A. , Rannik Ü. , Aalto P. , Keronen P. , Hakola H. , Bäck J. , Hoffmann T. , Vesala T. , Hari P.
Published: April 2010

Abstract. The possible connections between the carbon balance of ecosystems and aerosol-cloud-climate interactions play a significant role in climate change studies. Carbon dioxide is a greenhouse gas, whereas the net effect of atmospheric aerosols is to cool the climate. Here, we investigated the connection between forest-atmosphere carbon exchange and aerosol dynamics in the continental boundary layer by means of multiannual data sets of particle formation and growth rates, of CO2 fluxes, and of monoterpene concentrations in a Scots pine forest in southern Finland. We suggest a new, interesting link and a potentially important feedback among forest ecosystem functioning, aerosols, and climate: Considering that globally increasing temperatures and CO2 fertilization are likely to lead to increased photosynthesis and forest growth, an increase in forest biomass would increase emissions of non-methane biogenic volatile organic compounds and thereby enhance organic aerosol production. This feedback mechanism couples the climate effect of CO2 with that of aerosols in a novel way.
Validation of the calibration of a laser-induced fluorescence instrument for the measurement of OH radicals in the atmosphere
Authors: Bloss W. J. , Lee J. D. , Bloss C. , Heard D. E. , Pilling M. J. , Wirtz K. , Martin-Reviejo M. , Siese M.
Published: April 2010

Abstract. An assessment of the accuracy of OH concentrations measured in a smog chamber by a calibrated laser-induced fluorescence (LIF) instrument has been made, in the course of 9 experiments performed to study the photo-oxidation of benzene, toluene, 1,3,5-trimethylbenzene, para-xylene, ortho-cresol and ethene at the European Photoreactor facility (EUPHORE). The LIF system was calibrated via the water photolysis / ozone actinometry approach. OH concentrations were inferred from the instantaneous rate of removal of each hydrocarbon species (measured by FTIR or HPLC) via the appropriate rate coefficient for their reaction with OH, and compared with those obtained from the LIF system. Good agreement between the two approaches was found for all species with the exception of 1,3,5-trimethylbenzene, for which OH concentrations inferred from hydrocarbon removal were a factor of 3 lower than those measured by the LIF system. From the remaining 8 experiments, an overall value of 1.15±0.13 (±1σ) was obtained for [OH]LIF / [OH]Hydrocarbon Decay, compared with the estimated uncertainty in the accuracy of the water photolysis / ozone actinometry OH calibration technique of 26% (1σ).
Real-time measurements of ammonia, acidic trace gases and water-soluble inorganic aerosol species at a rural site in the Amazon Basin
Authors: Trebs I. , Meixner F. X. , Slanina J. , Otjes R. , Jongejan P. , Andreae M. O.
Published: April 2010

Abstract. We measured the mixing ratios of ammonia (NH3), nitric acid (HNO3), nitrous acid (HONO), hydrochloric acid (HCl), sulfur dioxide (SO2 and the corresponding water-soluble inorganic aerosol species, ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), chloride (Cl- and sulfate (SO42-), and their diel and seasonal variations at a pasture site in the Amazon Basin (Rondônia, Brazil). This study was conducted within the framework of LBA-SMOCC (Large Scale Biosphere Atmosphere Experiment in Amazonia - Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate). Sampling was performed from 12 September to 14 November 2002, extending from the dry season (extensive biomass burning activity), through the transition period to the wet season (background conditions). Measurements were made continuously using a wet-annular denuder (WAD) in combination with a Steam-Jet Aerosol Collector (SJAC) followed by suitable on-line analysis. A detailed description and verification of the inlet system for simultaneous sampling of soluble gases and aerosol compounds is presented. Overall measurement uncertainties of the ambient mixing ratios usually remained below 15%. The limit of detection (LOD) was determined for each single data point measured during the field experiment. Median LOD values (3σ-definition) were ≤0.015ppb for acidic trace gases and aerosol anions and ≤0.118ppb for NH3 and aerosol NH4+. Mixing ratios of acidic trace gases remained below 1ppb throughout the measurement period, while NH3 levels were an order of magnitude higher. Accordingly, mixing ratios of NH4+ exceeded those of other inorganic aerosol contributors by a factor of 4 to 10. During the wet season, mixing ratios decreased by nearly a factor of 3 for all compounds compared to those observed when intensive biomass burning took place. Additionally, N-containing gas and aerosol species featured pronounced diel variations. This is attributed to strong relative humidity and temperature variations between day and night as well as to changing photochemistry and stability conditions of the planetary boundary layer. HONO exhibited a characteristic diel cycle with high mixing ratios at nighttime and was not completely depleted by photolysis during daylight hours.
Modelling the impact of noctilucent cloud formation on atomic oxygen and other minor constituents of the summer mesosphere
Authors: Murray B. J. , Plane J. M. C.
Published: April 2010

Abstract. The formation, evolution and eventual sublimation of noctilucent clouds (NLC) may have a significant effect on the odd oxygen and hydrogen chemistry of the high latitude summer mesosphere. Three mechanisms are considered here: the direct uptake of atomic oxygen on the surface of the ice particles; the redistribution of water vapour, which changes the photochemical source of odd hydrogen species; and the direct photolysis of the ice particles themselves to produce odd hydrogen species in the gas phase. A 1-D photochemical model is employed to investigate the potential importance of these mechanisms. This shows, using the recently measured uptake coefficients of O on ice, that the heterogeneous removal of O on the surface of the cloud particles is too slow by at least a factor of 5x103 to compete with gas-phase O chemistry. The second and third mechanisms involve the solar Lyman-α photolysis of H2O in the gas and solid phase, respectively. During twilight, Lyman-α radiation is severely attenuated and these mechanisms are insignificant. In contrast, when the upper mesosphere is fully illuminated there is a dramatic impact on the O profile, with depletion of O at the base of the cloud layer of close to an order of magnitude. A correspondingly large depletion in O3 is also predicted, while H, OH, HO2 and H2O2 are found to be enhanced by factors of 3-5. In fact, rocket-borne mass spectrometer measurements during summer have revealed local H2O2 enhancements in the region of the clouds. Rocket-borne measurements of atomic O and O3 profiles in the presence of mesospheric clouds in the daytime are highly desirable to test the predictions of this model and our understanding of the genesis of mesospheric clouds.
An evaluation of the performance of chemistry transport models - Part 2: Detailed comparison with two selected campaigns
Authors: Brunner D. , Staehelin J. , Rogers H. L. , Köhler M. O. , Pyle J. A. , Hauglustaine D. A. , Jourdain L. , Berntsen T. K. , Gauss M. , Isaksen I. S. A. , Meijer E. , van Velthoven P. , Pitari G. , Mancini E. , Grewe V. , Sausen R.
Published: April 2010

Abstract. This is the second part of a rigorous model evaluation study involving five global Chemistry-Transport and two Chemistry-Climate Models operated by different groups in Europe. Simulated trace gas fields were interpolated to the exact times and positions of the observations to account for the actual weather conditions and hence for the specific histories of the sampled air masses. In this part of the study we focus on a detailed comparison with two selected campaigns, PEM-Tropics A and SONEX, contrasting the clean environment of the tropical Pacific with the more polluted North Atlantic region. The study highlights the different strengths and weaknesses of the models in accurately simulating key processes in the UT/LS region including stratosphere-troposphere-exchange, rapid convective transport, lightning emissions, radical chemistry and ozone production. Model simulated Radon, which was used as an idealized tracer for continental influence, was occasionally much better correlated with measured CO than simulated CO pointing towards deficiencies in the used biomass burning emission fields. The abundance and variability of HOx radicals is in general well represented in the models as inferred directly from the comparison with measured OH and HO2 and indirectly from the comparison with hydrogen peroxide concentrations. Components of the NOy family such as PAN, HNO3 and NO were found to compare less favorably. Interestingly, models showing good agreement with observations in the case of PEM-Tropics A often failed in the case of SONEX and vice versa. A better description of NOx and NOy emissions, chemistry and sinks is thought to be key to future model improvements with respect to the representation of chemistry in the UT/LS region.
Formation of ice supersaturation by mesoscale gravity waves
Authors: Spichtinger P. , Gierens K. , Dörnbrack A.
Published: April 2010

Abstract. We investigate the formation and evolution of an ice-supersaturated region (ISSR) that was detected by means of an operational radiosonde sounding launched from the meteorological station of Lindenberg on 21 March 2000, 00:00 UTC. The supersaturated layer was situated below the local tropopause, between 320 and 408 hPa altitude. Our investigation uses satellite imagery from METEOSAT and the Advanced Very High Resolution Radiometer (AVHRR) and analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF). Mesoscale simulations reveal that the ISSR was formed by a temporary vertical uplift of upper tropospheric air parcels by 20 to 40 hPa in 1 to 2 h. This resulted in a significant local increase of the specific humidity by the moisture transport from below. The ascent was triggered by the superposition of two internal gravity waves, a mountain wave induced by flow past the Erzgebirge and Riesengebirge south of Lindenberg, and an inertial gravity wave excited by the anti-cyclonically curved jet stream over the Baltic Sea. The wave-induced ISSR was rather thick with a depth of about 2 km. The wave-induced upward motion causing the supersaturation also triggered the formation of a cirrus cloud. METEOSAT imagery shows that the cirrus cloud got optically thick within two hours. During this period another longer lasting thin but extended cirrus existed just beneath the tropopause. The wave-induced ISSR disappeared after about half a day in accordance with the decaying wave activity.
SCIAMACHY validation by aircraft remote sensing: design, execution, and first measurement results of the SCIA-VALUE mission
Authors: Fix A. , Ehret G. , Flentje H. , Poberaj G. , Gottwald M. , Finkenzeller H. , Bremer H. , Bruns M. , Burrows J. P. , Kleinböhl A. , Küllmann H. , Kuttippurath J. , Richter A. , Wang P. , Heue K.-P. , Platt U. , Pundt I. , Wagner T.
Published: April 2010

Abstract. For the first time three different remote sensing instruments – a sub-millimeter radiometer, a differential optical absorption spectrometer in the UV-visible spectral range, and a lidar – were deployed aboard DLR's meteorological research aircraft Falcon 20 to validate a large number of SCIAMACHY level 2 and off-line data products such as O3, NO2, N2O, BrO, OClO, H2O, aerosols, and clouds. Within two validation campaigns of the SCIA-VALUE mission (SCIAMACHY VALidation and Utilization Experiment) extended latitudinal cross-sections stretching from polar regions to the tropics as well as longitudinal cross sections at polar latitudes at about 70° N and the equator were generated. This contribution gives an overview over the campaigns performed and reports on the observation strategy for achieving the validation goals. We also emphasize the synergetic use of the novel set of aircraft instrumentation and the usefulness of this innovative suite of remote sensing instruments for satellite validation.
Vortex-averaged Arctic ozone depletion in the winter 2002/2003
Authors: Christensen T. , Knudsen B. M. , Streibel M. , Andersen S. B. , Benesova A. , Braathen G. , Claude H. , Davies J. , De Backer H. , Dier H. , Dorokhov V. , Gerding M. , Gil M. , Henchoz B. , Kelder H. , Kivi R. , Kyrö E. , Litynska Z. , Moore D. , Peters G. , Skrivankova P. , Stübi R. , Turunen T. , Vaughan G. , Viatte P. , Vik A. F. , von der Gathen P. , Zaitcev I.
Published: April 2010

Abstract. A total ozone depletion of 68±7 Dobson units between 380 and 525K from 10 December 2002 to 10 March 2003 is derived from ozone sonde data by the vortex-average method, taking into account both diabatic descent of the air masses and transport of air into the vortex. When the vortex is divided into three equal-area regions, the results are 85±9DU for the collar region (closest to the edge), 52±5DU for the vortex centre and 68±7DU for the middle region in between centre and collar. Our results compare well with other studies: We find good agreement with ozone loss deduced from SAOZ data, with results inferred from POAM III observations and with results from tracer-tracer correlations using HF as the long-lived tracer. We find a higher ozone loss than that deduced by tracer-tracer correlations using CH4. We have made a careful comparison with Match results: The results were recalculated using a common time period, vortex edge definition and height interval. The two methods generally compare very well, except at the 475K level which exhibits an unexplained discrepancy.
Water activity and activation diameters from hygroscopicity data - Part I: Theory and application to inorganic salts
Authors: Kreidenweis S. M. , Koehler K. , DeMott P. J. , Prenni A. J. , Carrico C. , Ervens B.
Published: April 2010

Abstract. A method is described that uses particle hygroscopicity measurements, made with a humidified tandem differential mobility analyzer (HTDMA), to determine solution water activity as a function of composition. The use of derived water activity data in computations determining the ability of aerosols to serve as cloud condensation nuclei (CCN) is explored. Results for sodium chloride and ammonium sulfate are shown in Part I. The methodology yields solution water activities and critical dry diameters for ammonium sulfate and sodium chloride in good agreement with previously published data. The approach avoids the assumptions required for application of simplified and modified Köhler equations to predict CCN activity, most importantly, knowledge of the molecular weight and the degree of dissociation of the soluble species. Predictions of the dependence of water activity on the mass fraction of aerosol species are sensitive to the assumed dry density, but predicted critical dry diameters are not.
Systematic errors in global air-sea CO2 flux caused by temporal averaging of sea-level pressure
Authors: Kettle H. , Merchant C. J.
Published: April 2010

Abstract. Long-term temporal averaging of meteorological data, such as wind speed and air pressure, can cause large errors in air-sea carbon flux estimates. Other researchers have already shown that time averaging of wind speed data creates large errors in flux due to the non-linear dependence of the gas transfer velocity on wind speed (Bates and Merlivat, 2001). However, in general, wind speed is negatively correlated with air pressure, and a given fractional change in the pressure of dry air produces an equivalent fractional change in the atmospheric partial pressure of carbon dioxide (pCO2air). Thus low pressure systems cause a drop in pCO2air, which together with the associated high winds, promotes outgassing/reduces uptake of CO2 from the ocean. Here we quantify the errors in global carbon flux estimates caused by using monthly or climatological pressure data to calculate pCO2air (and thus ignoring the covariance of wind and pressure) over the period 1990-1999, using two common parameterisations for gas transfer velocity. Results show that on average, compared with estimates made using 6 hourly pressure data, the global oceanic sink is systematically overestimated by 7% (W92) and 10% (WM99) when monthly mean pressure is used, and 9% (W92) and 12% (WM99) when climatological pressure is used.