bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of the physical state of tropospheric ammonium-sulfate-nitrate particles on global aerosol direct radiative forcing
Authors: Martin S. T. , Hung H.-M. , Park R. J. , Jacob D. J. , Spurr R. J. D. , Chance K. V. , Chin V.
Published: April 2010

Abstract. The effect of aqueous versus crystalline sulfate-nitrate-ammonium tropospheric particles on global aerosol direct radiative forcing is assessed. A global three-dimensional chemical transport model predicts sulfate, nitrate, and ammonium aerosol mass. An aerosol thermodynamics model is called twice, once for the upper side (US) and once for lower side (LS) of the hysteresis loop of particle phase. On the LS, the sulfate mass budget is 40% solid ammonium sulfate, 12% letovicite, 11% ammonium bisulfate, and 37% aqueous. The LS nitrate mass budget is 26% solid ammonium nitrate, 7% aqueous, and 67% gas-phase nitric acid release due to increased volatility upon crystallization. The LS ammonium budget is 45% solid ammonium sulfate, 10% letovicite, 6% ammonium bisulfate, 4% ammonium nitrate, 7% ammonia release due to increased volatility, and 28% aqueous. LS aerosol water mass partitions as 22% effloresced to the gas-phase and 78% remaining as aerosol mass. The predicted US/LS global fields of aerosol mass are employed in a Mie scattering model to generate global US/LS aerosol optical properties, including scattering efficiency, single scattering albedo, and asymmetry parameter. Global annual average LS optical depth and mass scattering efficiency are, respectively, 0.023 and 10.7 m2  (g SO42−)−1, which compare to US values of 0.030 and 13.9 m2 (g SO42−)−1. Radiative transport is computed, first for a base case having no aerosol and then for the two global fields corresponding to the US and LS of the hysteresis loop. Regional, global, seasonal, and annual averages of top-of-the-atmosphere aerosol radiative forcing on the LS and US (FL and FU, respectively, in W m2−) are calculated. Including both anthropogenic and natural emissions, we obtain global annual averages of FL = −0.750, FU = −0.930, and ΔFU,L = 24% for full sky calculations without clouds and FL = −0.485, FU = −0.605, and ΔFU,L = 25% when clouds are included. Regionally, ΔFU,L = 48% over the USA, 55% over Europe, and 34% over East Asia. Seasonally, ΔFU,L varies from 18% in DJF to 75% in SON over the USA. The global annual average contribution from anthropogenic aerosol is FL = −0.314 and FU = −0.404, which yield normalized direct radiative forcings (G) of GL = −205 W (g SO42−)−1 and GU = −264 W (g SO42−)−1.
Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and analysis of the events during the years 2001 and 2002
Authors: Collaud Coen M. , Weingartner E. , Schaub D. , Hueglin C. , Corrigan C. , 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 (3580 m a.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 is usually positive, it becomes negative during Saharan dust events (SDE) due to the greater size of the mineral aerosols and to their different chemical composition. This change in the sign of the single scattering exponent turns out to be a simple means for detecting Saharan dust events. The occurrence of SDE detected by this new method was largely confirmed by visual inspection of filter colors and by studying long-range back-trajectories. An examination of SDE over a 22 months 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 96.5 h 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) at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the JFJ is 16 μg/m3, which corresponds to an annual mean of 0.8 μg/m3 or 24% of TSP.
Measurements of the sum of HO2NO2 and CH3O2NO2 in the remote troposphere
Authors: Murphy J. G. , Thornton J. A. , Wooldridge P. J. , Day D. A. , Rosen R. S. , Cantrell C. , Shetter R. E. , Lefer B. , Cohen R. C.
Published: April 2010

Abstract. The chemistry of peroxynitric acid (HO2NO2) and methyl peroxynitrate (CH3O2NO2) is predicted to be particularly important in the upper troposphere where temperatures are frequently low enough that these compounds do not rapidly decompose. At temperatures below 240 K, we calculate that about 20% of NOy in the mid and polar latitude upper troposphere is HO2NO2. Under these conditions, the reaction of OH with HO2NO2 is estimated to account for as much as one third of the permanent loss of hydrogen radicals. During the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign, we used thermal dissociation laser-induced fluorescence (TD-LIF) to measure the sum of peroxynitrates (SPNs equivanlent HO2NO2 + CH3O2NO2 + PAN + PPN + ...), aboard the NCAR C-130 research aircraft. We infer the sum of HO2NO2 and CH3O2NO2 as the difference between SPN measurements and gas chromatographic measurements of the two major peroxy acyl nitrates, peroxy acetyl nitrate (PAN) and peroxy propionyl nitrate (PPN). Comparison with NOy and other nitrogen oxide measurements confirms the importance of HO2NO2 and CH3O2NO2 to the reactive nitrogen budget and shows that current thinking about the chemistry of these species is approximately correct. The temperature dependence of the inferred concentrations corroborates the contribution of overtone photolysis to the photochemistry of peroxynitric acid.
Using neural networks to describe tracer correlations
Authors: Lary D. J. , Müller M .D. , Mussa H. Y.
Published: April 2010

Abstract. Neural networks are ideally suited to describe the spatial and temporal dependence of tracer-tracer correlations. The neural network performs well even in regions where the correlations are less compact and normally a family of correlation curves would be required. For example, the CH4-N2O correlation can be well described using a neural 5 network trained with the latitude, pressure, time of year, and CH4 volume mixing ratio (v.m.r.). In this study a neural network using Quickprop learning and one hidden layer with eight nodes was able to reproduce the CH4-N2O correlation with a correlation co-efficient of 0.9995. Such an accurate representation of tracer-tracer correlations allows more use to be made of long-term datasets to constrain chemical models. Such as the 10 dataset from the Halogen Occultation Experiment (HALOE) which has continuously observed CH4 (but not N2O) from 1991 till the present. The neural network Fortran code used is available for download
Problems regarding the tropospheric O3 residual method and its interpretation in Fishman et al. (2003)
Authors: de Laat A. D. J. , Aben I.
Published: April 2010

Abstract. In this article we will show that the Total Ozone Residuals (TOR) method as presented by Fishman et al. (2003) contains an erroneous assumption, due to which the TOR as presented in this article reflects mainly a tropospheric O3 climatology (Logan, 1999), scaled to the layer between the surface and the tropopause height, rather than a satellite measured TOR. We will show that it is possible to obtain a tropospheric O3  column that is very similar to what is being presented in Fishman et al. (2003), solely based on the Logan (1999) tropospheric O3  climatology and an estimate for the tropopause heights without using satellite data. Furthermore, we will show that one of the interpretations of observed O3  variability (high TOR values over Southeast Asia) is not the result of pollution, but primarily of tropopause height variations. We suggest adjusting the method in such a way that the final retrieved TOR product becomes independent of the actual values of the Logan (1999) O3  climatology. The proposed adjustments are also more in line with the original methodology suggested by Fishman and Balok (1999) in a previous paper. We furthermore show that the assumption that the stratospheric O3  column is nearly constant within a 5-day period is not always valid. This can introduce errors in the final TOR product, although we recognize that these errors may become small when averaging the TOR product over longer periods of time. However, we feel that a detailed study on this assumption is also needed.
The nitrate aerosol field over Europe: simulations with an atmospheric chemistry-transport model of intermediate complexity
Authors: Schaap M. , van Loon M. , ten Brink H. M. , Dentener F. J. , Builtjes P. J. H.
Published: April 2010

Abstract. Nitrate is an important component of fine aerosols in Europe. We present a model simulation for the year 1995 in which we account for the formation of the ammonium nitrate, a semi volatile component. For this purpose, LOTOS, a chemistry-transport model of intermediate complexity, was extended with a thermodynamic equilibrium module and additional relevant processes to account for aerosol formation and deposition. Our earlier analysis of data on (ammonium) nitrate in Europe was used for model evaluation. During winter, fall and especially spring high nitrate levels are projected over north western, central and eastern Europe. During winter nitrate concentrations are highest in the Po valley, Italy. This is in accordance with the field that was constructed from the data. In winter nitric acid, the precursor for aerosol nitrate, is formed through heterogeneous reactions on the surface of aerosols. Appreciable ammonium nitrate concentrations in summer are limited to those areas with high ammonia emissions, e.g. The Netherlands, since high ammonia concentrations are necessary to stabilise this aerosol component at high temperatures. Averaged over all stations the model reproduces the measured concentrations for NO3, SO4, NH4, TNO3, TNH4 and SO2 within 20%. The daily variation is captured well, albeit that the model does not always represents the amplitude of single events. The model underestimates wet deposition which was attributed to the crude representation of cloud processes. The treatment of ammonia was found to be the major source for uncertainties in the model representation of secondary aerosols. Also, inclusion of sea salt is necessary to properly assess the nitrate and nitric acid levels in marine areas. Over Europe the annual forcing by nitrate is calculated to be 25% of that by sulphate. In summer nitrate is found to be regionally important, e.g. in The Netherlands, where the forcing of nitrate and sulphate are calculated to be equal. In winter, spring and fall the nitrate forcing over Europe is about half that by sulphate. Over north western Europe and the alpine region the forcing by nitrate was calculated to be similar to that of sulphate. Overall, nitrate forcing is significant and should be taken into account to estimate the impact of regional climate change in Europe.
Near-IR photodissociation of peroxy acetyl nitrate
Authors: Nizkorodov S. A. , Crounse J. D. , Fry J. L. , Roehl C. M. , Wennberg P. O.
Published: April 2010

Abstract. Measurements of the C-H overtone transition strengths combined with estimates of the photodissociation cross sections for these transitions suggest that near-IR photodissociation of peroxy acetyl nitrate (PAN) is less significant (Jnear-IR≈3×10−8s−1 at noon) in the lower atmosphere than competing sinks resulting from unimolecular decomposition and ultraviolet photolysis. This is in contrast to the photochemical behavior of a related peroxy nitrate, pernitric acid (PNA), that undergoes rapid near-IR photolysis in the atmosphere with Jnear-IR≈10−5s−1 at noon (Roehl et al., 2002). This difference is attributed to the larger binding energy and larger number of vibrational degrees of freedom in PAN, which make 4νCH the lowest overtone excitation with a high photodissociation yield (as opposed to 2νOH in PNA).
3-D chemistry-transport model Polair: numerical issues, validation and automatic-differentiation strategy
Authors: Mallet V. , Sportisse B.
Published: April 2010

Abstract. We briefly present in this short paper some issues related to the development and the validation of the three-dimensional chemistry-transport model Polair. Numerical studies have been performed in order to let Polair be an efficient and robust solver. This paper summarizes and comments choices that were made in this respect. Simulations of relevant photochemical episodes were led to assess the validity of the model. The results can be considered as a validation, which allows next studies to focus on fine modeling issues. A major feature of Polair is the availability of a tangent linear mode and an adjoint mode entirely generated by automatic differentiation. Tangent linear and adjoint modes grant the opportunity to perform detailed sensitivity analyses and data assimilation. This paper shows how inverse modeling is achieved with Polair.
Release and dispersion of vegetation and peat fire emissions in the atmosphere over Indonesia 1997/1998
Authors: Langmann B. , Heil A.
Published: April 2010

Abstract. Smoke-haze episodes caused by vegetation and peat fires affect parts of Indonesia every year with significant impacts on human health and climate. Particularly fires in degenerated peat areas release huge amounts of trace gases and particles into the atmosphere, exceeding by far the emissions per unit area from fires in surface vegetation. However, only limited information is available about the current distribution of pristine and degenerated peat areas in Indonesia, their depth, drainage condition and modification by fire. In this paper we study the contribution of peat fire emissions in Indonesia during the strong El Niño event in 1997/1998. A regional three-dimensional atmosphere-chemistry model is applied over Indonesia using two emission estimates, which only differ in the size of the fire affected peat areas. We evaluate simulated rainfall and particle concentrations by comparison with observations to draw conclusions on the peat area burned.
Ozone loss and chlorine activation in the Arctic winters 1991–2003 derived with the TRAC method
Authors: Tilmes S. , Müller R. , Grooß J.-U. , Russell J. M.
Published: April 2010

Abstract. In this paper chemical ozone loss in the Arctic stratosphere was investigated for twelve years between 1991 and 2003. The accumulated local ozone loss and the column ozone loss were consistently derived mainly on the basis of HALOE observations. The ozone-tracer correlation (TRAC) method is used, where the relation between ozone and a long-lived tracer is considered over the lifetime of the polar vortex. A detailed quantification of uncertainties was performed. This study demonstrates the interaction between meteorology and ozone loss. The correlation between temperature conditions and chlorine activation becomes obvious in the HALOE HCl measurements, as well as the dependence between chlorine activation and ozone loss. Additionally, the degree of homogeneity of ozone loss is shown to depend on the meteorological conditions, as there is a possible influence of horizontal mixing of the air inside a weak polar vortex edge. Results estimated here are in agreement with the results obtained from other methods. However, there is no sign of very strong ozone losses as deduced from SAOZ for January considering HALOE measurements. In general, strong accumulated ozone loss is found to occur in conjunction with a strong cold vortex containing a large potential area of PSCs, whereas moderate ozone loss is found if the vortex is less strong and moderately warm. Hardly any ozone loss was calculated for very warm winters with small amounts of the area of possible PSC existence (APSC) during the entire winter. Nevertheless, the analysis of the relationship between APSC (derived using the PSC threshold temperature) and the accumulated ozone loss indicates that this relationship is not a strictly linear relation. An influence of other factors could be identified. A significant increase of ozone loss (of ≈40 DU) was found due to the different duration of illumination of the polar vortex in different years. Further, the increased burden of aerosols in the atmosphere after the Pinatubo volcanic eruption in 1991 and the location of the cold parts of the vortex in different years may impact the extent of chemical ozone loss.
High ozone at rural sites in India
Authors: Chand D. , Lal S.
Published: April 2010

Abstract. Past observations of O3 at urban, rural and lower free tropospheric sites in India have shown generally low values rarely exceeding 60 ppbv. We show that this can not be generated to all over India. Surface ozone (O3) concentrations are obtained from measurements in rural, urban and free tropospheric environments in January 2001 and 2002 as a part of Mobile Lab Experiments (MOLEX) conducted in western India. Elevated O3 from 70 to 110 ppbv (nmole/mole) are recorded during afternoon hours at rural sites in downwind of major industrial region of Gujarat adjoining the Arabian Sea. Repeated observations during both the years indicate that this is a regular process in this region. The average background ozone is found to be 42±6 ppbv. The elevated ozone in the downwind site is about 60% higher than that in the major urban center and its surroundings and by a factor of 2 higher than the background levels of O3 in this region. In comparison to the downwind observations; the ozone observed at the continental stations in rural (Gadanki), urban (Ahmedabad) and free tropospheric (Mt. Abu) sites in India are low and rarely exceeded 60 ppbv during the month of January. Forward trajectory analysis shows that the polluted plumes from this urban area can get transported more than 3000 km to the marine boundary layer over the Arabian Sea and the Indian Ocean within a week. Similar transport of pollutants from major urban sites like Delhi and other cities can enhance O3 in their downwind rural sites and can affect the human health as well as vegetation significantly.
On the distribution of relative humidity in cirrus clouds
Authors: Spichtinger P. , Gierens K. , Smit H. G. J. , Ovarlez J. , Gayet J.-F.
Published: April 2010

Abstract. We have analysed relative humidity statistics from measurements in cirrus clouds taken unintentionally during the Measurement of OZone by Airbus In-service airCraft project (MOZAIC). The shapes of the in-cloud humidity distributions change from nearly symmetric in relatively warm cirrus (warmer than −40°) to considerably positively skew (i.e. towards high humidities) in colder clouds. These results are in agreement to findings obtained recently from the INterhemispheric differences in Cirrus properties from Anthropogenic emissions (INCA) campaign (Ovarlez et al., 2002). We interprete the temperature dependence of the shapes of the humidity distributions as an effect of the length of time a cirrus cloud needs from formation to a mature equilibrium stage, where the humidity is close to saturation. The duration of this transitional period increases with decreasing temperature. Hence cold cirrus clouds are more often met in the transitional stage than warm clouds.
Alpha-pinene oxidation by OH: simulations of laboratory experiments
Authors: Capouet M. , Peeters J. , Nozière B. , Müller J.-F.
Published: April 2010

Abstract. This paper presents a state-of-the-art gas-phase mechanism for the degradation of α-pinene by OH and its validation by box model simulations of laboratory measurements. It is based on the near-explicit mechanisms for the oxidation of α-pinene and pinonaldehyde by OH proposed by Peeters and co-workers. The extensive set of α-pinene photooxidation experiments performed in presence as well as in absence of NO by Nozière et al. (1999a) is used to test the mechanism. The comparison of the calculated vs measured concentrations as a function of time shows that the levels of OH, NO, NO2 and light are well reproduced in the model. Noting the large scatter in the experimental results as well as the difficulty to retrieve true product yields from concentrations data, a methodology is proposed for comparing the model and the data. The model succeeds in reproducing the average apparent yields of pinonaldehyde, acetone, total nitrates and total PANs in the experiments performed in presence of NO. In absence of NO, pinonaldehyde is fairly well reproduced, but acetone is largely underestimated. The dependence of the product yields on the concentration of NO and α-pinene is investigated, with a special attention on the influence of the multiple competitions of reactions affecting the peroxy radicals in the mechanism. We show that the main oxidation channels differ largely according to photochemical conditions. E.g. the pinonaldehyde yield is estimated to be about 10% in the remote atmosphere and up to 60% in very polluted areas. We stress the need for additional theoretical/laboratory work to unravel the chemistry of the primary products as well as the ozonolysis and nitrate-initiated oxidation of α-pinene.
Actinic flux and O1D photolysis frequencies retrieved from spectral measurements of irradiance at Thessaloniki, Greece
Authors: Kazadzis S. , Topaloglou C. , Bais A. F. , Blumthaler M. , Balis D. , Kazantzidis A. , Schallhart B.
Published: April 2010

Abstract. The results of two methods retrieving actinic flux and ozone photolysis frequencies from measurements of irradiance with a Brewer MKIII spectroradiometer are investigated in this paper. The first method uses actinic flux retrieved from irradiance measurements by the use of known formulas while the second is an empirical method converting irradiance to ozone photolysis frequencies through polynomials extracted from a study of synchronous actinic flux and irradiance measurements. When examining the actinic fluxes derived from the first method to those measured by an actinic flux spectrometer, data agree within ±10% for solar zenith angles lower than 75° for the UV-B and the UV-A wavelength band. Also, the actinic to global irradiance ratio derived, deviates within ±6% for solar zenith angles lower than 70° compared with cloudless sky calculations of the TUV model. For both cases the deviations are in the order of the magnitude of the measurements or model uncertainties. The ozone photolysis frequencies calculated by the second method show a mean ratio of 0.98±0.12 (1σ and 0.97±0.06 for all data and for cloudless skies, respectively, when compared with ozone photolysis frequencies derived by a Bentham actinic flux spectroradiometer. Finally, the agreement of the two methods is within ±5% comparing two years' data of ozone photolysis frequencies retrieved from irradiance measurements at Thessaloniki, Greece. The use of such methods on extensive data sets of global irradiance can provide JO1D values with acceptable uncertainty, a parameter of particular importance for chemical process studies.
NOGAPS-ALPHA model simulations of stratospheric ozone during the SOLVE2 campaign
Authors: McCormack J. P. , Eckermann S. D. , Coy L. , Allen D. R. , Kim Y.-J. , Hogan T. , Lawrence B. , Stephens A. , Browell E. V. , Burris J. , McGee T. , Trepte C. R.
Published: April 2010

Abstract. This paper presents three-dimensional prognostic ozone simulations with parameterized photochemistry from the new NOGAPS-ALPHA middle atmosphere forecast model. We compare 5-day NOGAPS-ALPHA hindcasts of stratospheric ozone with a combination of satellite and DC-8 aircraft measurements for two specific cases during the SOLVE II campaign: (1) the cold, isolated vortex during 11–16 January 2003; and (2) the rapidly developing stratospheric warming of 17–22 January 2003. In the first case we test three different photochemistry parameterizations. NOGAPS-ALPHA ozone simulations using the NRL-CHEM2D parameterization give the best overall agreement with SAGE III and POAM III profile measurements. 5-day NOGAPS-ALPHA hindcasts of polar ozone initialized with the NASA GEOS4 ozone analyses produce better agreement with observations than do the operational ECMWF ozone forecasts. In the second case, comparisons between NOGAPS-ALPHA and ECMWF 114-h forecasts of the split vortex structure in stratospheric ozone on 21 January 2003 show comparable skill. Updated ECMWF ozone forecasts of this case at hour 42 display marked improvement from the 114-h forecast; corresponding updated 42-h NOGAPS-ALPHA prognostic ozone simulations do not improve significantly. In general, these results demonstrate that the spectral advection component in NOGAPS-ALPHA is well-suited for middle atmosphere tracer transport. In particular, we find that stratospheric ozone forecasts at high latitudes in winter can depend on both model initial conditions and the treatment of photochemistry even over a period of 5 days.
Aerosol seasonal variability over the Mediterranean region and relative impact of maritime, continental and Saharan dust particles over the basin from MODIS data in the year 2001
Authors: Barnaba F. , Gobbi G. P.
Published: April 2010

Abstract. The one-year (2001) record of aerosol data from the space borne Moderate Resolution Imaging Spectroradiometer (MODIS) was analyzed focusing on the Mediterranean region. The MODIS aerosol optical thickness standard product (AOT at 550 nm) provided over both land and ocean was employed to evaluate the seasonal and spatial variability of the atmospheric particulate over the region. Expected accuracy of the MODIS AOT is (±0.05±0.2×AOT) over land and (±0.03±0.05×AOT) over ocean. The seasonal analysis revealed a significant AOT variability all over the region, with minimum values in Winter (AOT<0.15) and maximum in Summer (AOT>0.2). The spatial variability is also found to be considerable, particularly over land. The impact of some major urban sites and industrialized areas is detectable. For the sole Mediterranean basin, a method (aerosol mask) was implemented to separate the contribution of maritime, continental and desert dust aerosol to the total AOT. Input of both continental and desert dust particles is well captured, showing, respectively, a North-to-South and a South-to-North AOT gradient. A quantitative summary of the AOT seasonal and regional variability is given for different sectors of the Mediterranean basin. Results of this summary were also used to test the aerosol mask assumptions and indicate the method adopted to be suitable for the aerosol type selection. Estimates of the atmospheric aerosol mass load were performed employing specifically-derived mass-to-extinction efficiencies (α). For each aerosol type, a reliable mean α value was determined on the basis of lidar measurements of extinction and aerosol models. These estimates indicate a total of 43 Mtons of desert dust suspended over the basin during 2001. A comparable value is derived for maritime aerosol. Opposite to the dust case, a minor seasonal variability (within 15%) of maritime aerosol mass is found. This latter result is considered a further check of the suitability of the methodology adopted to separate, on the basis of MODIS data, the three aerosol types which dominate the Mediterranean region.
Investigation of inertia-gravity waves in the upper troposphere/lower stratosphere over northern Germany observed with collocated VHF/UHF radars
Authors: Serafimovich A. , Hoffmann P. , Peters D. , Lehmann V.
Published: April 2010

Abstract. A case study to investigate the properties of inertia-gravity waves in the upper troposphere/lower stratosphere has been carried out over Northern Germany during the occurrence of an upper tropospheric jet in connection with a poleward Rossby wave breaking event from 17-19 December 1999. The investigations are based on continuous radar measurements with the OSWIN VHF radar at Kühlungsborn (54.1° N, 11.8° E) and the 482 MHz UHF wind profiler at Lindenberg (52.2° N, 14.1° E). Both radars are separated by about 265 km. Based on wavelet transformations of both data sets, the dominant vertical wavelengths of about 2–4 km for fixed times as well as the dominant observed periods of about 11 h for the altitude range between 5 and 8 km are comparable. Gravity wave parameter have been estimated at both locations separately and by a complex cross-spectral analysis of the data of both radars. The results show the appearance of dominating inertia-gravity waves with characteristic horizontal wavelengths between 600 and 300 km moving in the opposite direction than the mean background wind and a secondary less pronounced wave with a horizontal wavelength in the order of about 200 km moving with the wind. Temporal and spatial differences of the observed waves are discussed.
Microphysics and heterogeneous chemistry in aircraft plumes – high sensitivity on local meteorology and atmospheric composition
Authors: Meilinger S. K. , Kärcher B. , Peter Th.
Published: April 2010

Abstract. An aircraft plume model has been developed on the basis of two coupled trajectory box models. Two boxes, one for plume and one for background conditions, are coupled by means of a mixing parameterization based on turbulence theory. The model considers comprehensive gas phase chemistry for the tropopause region including acetone, ethane and their oxidation products. Heterogeneous halogen, N2O5 and HOx chemistry on various types of background and aircraft-induced aerosols (liquid and ice) is considered, using state-of-the-art solubility dependent uptake coefficients for liquid phase reactions. The microphysical scheme allows for coagulation, gas-diffusive particle growth and evaporation, so that the particle development from 1s after emission to several days can be simulated. Model results are shown, studying emissions into the upper troposphere as well as into the lowermost stratosphere for contrail and non-contrail conditions. We show the microphysical and chemical evolution of spreading plumes and use the concept of mean plume encounter time, t1 to define effective emission and perturbation indices (EEIs and EPIs) for the North Atlantic Flight Corridor (NAFC) showing EEI(NOy) and EPI(O3) for various background conditions, such as relative humidity, local time of emission, and seasonal variations. Our results show a high sensitivity of EEI and EPIs on the exact conditions under which emissions take place. The difference of EEIs with and without considering plume processes indicates that these processes cannot be neglected.
Influence of mountain waves and NAT nucleation mechanisms on Polar Stratospheric Cloud formation at local and synoptic scales during the 1999–2000 Arctic winter
Authors: Svendsen S. H. , Larsen N. , Knudsen B. , Eckermann S. D. , Browell E. V.
Published: April 2010

Abstract. A scheme for introducing mountain wave-induced temperature pertubations in a microphysical PSC model has been developed. A data set of temperature fluctuations attributable to mountain waves as computed by the Mountain Wave Forecast Model (MWFM-2) has been used for the study. The PSC model has variable microphysics, enabling different nucleation mechanisms for nitric acid trihydrate, NAT, to be employed. In particular, the difference between the formation of NAT and ice particles in a scenario where NAT formation is not dependent on preexisting ice particles, allowing NAT to form at temperatures above the ice frost point, Tice, and a scenario, where NAT nucleation is dependent on preexisting ice particles, is examined. The performance of the microphysical model in the different microphysical scenarios and a number of temperature scenarios with and without the influence of mountain waves is tested through comparisons with lidar measurements of PSCs made from the NASA DC-8 on 23 and 25 January during the SOLVE/THESEO 2000 campaign in the 1999–2000 winter and the effect of mountain waves on local PSC production is evaluated in the different microphysical scenarios. Mountain wave-induced temperature fluctuations are introduced in vortex-covering model runs, extending the full 1999–2000 winter season, and the effect of mountain waves on large-scale PSC production is estimated in the different microphysical scenarios.
Measurements of organic gases during aerosol formation events in the boreal forest atmosphere during QUEST
Authors: Sellegri K. , Hanke M. , Umann B. , Arnold F. , Kulmala M.
Published: April 2010

Abstract. Biogenic VOCs are important in the growth and possibly also in the formation of atmospheric aerosol particles. In this work, we present 10 min-time resolution measurements of organic trace gases at Hyytiälä, Finland during March 2002. The measurements were part of the project QUEST (Quantification of Aerosol Nucleation in the European Boundary Layer) and took place during a two-week period when nucleation events occurred with various intensities nearly every day. Using a ground-based Chemical Ionization Mass Spectrometer (CIMS) instrument, the following trace gases were detected: acetone, TMA, DMA, mass 68 amu (candidate=isoprene), monoterpenes, Methyl Vinyl Ketone (MVK) and Methacrolein (MaCR), cis-3-hexenyl acetate and MonoTerpene Oxidation Products (MTOP). For all of them except for the amines, we present daily variations during different classes of event days, and non-event days. Isoprene, monoterpenes, MVK+MaCR, cis-3-hexenyl acetate and MTOP are found to show significant correlations with the condensational sink (CS), which indicates that a fraction of these compounds are participating to the growth of the nucleated particles and generally secondary organic aerosol formation. Moreover, the terpene oxidation products (TOP) (MVK, MaCR and MTOP) show a higher ratio to the CS on event days compared to non-event days, indicating that their abundance relative to the surface of aerosol available is higher on nucleation days.
A transboundary transport episode of nitrogen dioxide as observed from GOME and its impact in the Alpine region
Authors: Schaub D. , Weiss A. K. , Kaiser J. W. , Petritoli A. , Richter A. , Buchmann B. , Burrows J. P.
Published: April 2010

Abstract. High tropospheric NO2 amounts are occasionally detected by satellite-borne spectrometers even though clouds shield the highly polluted boundary layer. We present a method to investigate such events and apply the model to the high NO2 vertical tropospheric column densities (VTCs) over middle Europe observed from the Global Ozone Monitoring Experiment (GOME) instrument on 17 February 2001. Our case study shows that pollution originally residing near the ground has been advected to higher tropospheric levels by a passing weather front. With backward trajectories, the NO2 source region is located in central Germany, the Ruhr area and adjacent parts of the Netherlands and Belgium. The highly polluted air masses are traced by forward trajectories starting from the GOME columns to move further to the Alpine region. Their impact on the air quality there is modeled by combining the NO2 VTCs observed by GOME with the trajectory calculations and a given NO2 lifetime. Considering ground-based in-situ measurements in the Alpine region we conclude that for this episode, 50% to 90% of the NO2 concentration recorded at the sites can be attributed to transboundary transport during the frontal passage.
Organic aerosol and global climate modelling: a review
Authors: Kanakidou M. , Seinfeld J. H. , Pandis S. N. , Barnes I. , Dentener F. J. , Facchini M. C. , van Dingenen R. , Ervens B. , Nenes A. , Nielsen C. J. , Swietlicki E. , Putaud J. P. , Balkanski Y. , Fuzzi S. , Horth J. , Moortgat G. K. , Winterhalter R. , Myhre C. E. L. , Tsigaridis K. , Vignati E. , Stephanou E. G. , Wilson J.
Published: April 2010

Abstract. The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol (SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The up-to-date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies.
Iterative maximum a posteriori (IMAP)-DOAS for retrieval of strongly absorbing trace gases: Model studies for CH4 and CO2 retrieval from near infrared spectra of SCIAMACHY onboard ENVISAT
Authors: Frankenberg C. , Platt U. , Wagner T.
Published: April 2010

Abstract. In the past, differential optical absorption spectroscopy (DOAS) has mostly been employed for trace gas retrieval in the UV/Vis spectral region. New spectrometers such as SCIAMACHY onboard ENVISAT also provide near infrared channels and thus allow for the detection of greenhouse gases like CH4, CO2, or N2O. However, modifications of the classical DOAS algorithm are necessary to account for the idiosyncrasies of this spectral region, i.e. the temperature and pressure dependence of the high resolution absorption lines. Furthermore, understanding the sensitivity of the measurement of these high resolution, strong absorption lines by means of a non-ideal device, i.e. having finite spectral resolution, is of special importance. This applies not only in the NIR, but can also prove to be an issue for the UV/Vis spectral region. This paper presents a modified iterative maximum a posteriori-DOAS (IMAP-DOAS) algorithm based on optimal estimation theory introduced to the remote sensing community by Rodgers (1976). This method directly iterates the vertical column densities of the absorbers of interest until the expected total optical density fits the measurement. Although the discussion in this paper lays emphasis on satellite retrieval, the basic principles of the algorithm also hold for arbitrary measurement geometries. For a quantitative test of this new approach and a comparison with classical algorithms, it is applied to modelled spectra based on a comprehensive set of atmospheric temperature and pressure profiles. This analysis reveals that the sensitivity of measurement strongly depends on the prevailing pressure-height. The IMAP-DOAS algorithm properly accounts for the sensitivity of measurement on pressure due to pressure broadening of the absorption lines. Thus, biases in the retrieved vertical columns that would arise in classical algorithms, are obviated. Here, we analyse and quantify these systematic biases as well as errors due to variations in the temperature and pressure profiles, which is indispensable for the understanding of measurement precision and accuracy in the near infrared as well as for future intercomparisons of retrieval algorithms.
Polar stratospheric cloud observations by MIPAS on ENVISAT: detection method, validation and analysis of the northern hemisphere winter 2002/2003
Authors: Spang R. , Remedios J. J. , Kramer L. J. , Poole L. R. , Fromm M. D. , Müller M. , Baumgarten G. , Konopka P.
Published: April 2010

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on ENVISAT has made extensive measurements of polar stratospheric clouds (PSCs) in the northern hemisphere winter 2002/2003. A PSC detection method, based on a ratio of radiances (the cloud index), has been implemented for MIPAS and is validated in this study with respect to ground based lidar and space borne occultation measurements. A very good correspondence in PSC sighting and cloud altitude between MIPAS detections and those of other instruments is found for cloud index values less than four. Comparisons with data from the Stratospheric Aerosol and Gas Experiment (SAGE) III are used to show further that the sensitivity of the MIPAS detection method for this threshold value of cloud index is approximately equivalent to an extinction limit of 10−3 km−1 at 1022 nm, a wavelength used by solar occultation experiments. The MIPAS cloud index data are subsequently used to examine, for the first time with any technique, the evolution of PSCs throughout the Arctic polar vortex up to a latitude of 90° north on a near-daily basis. We find that the winter of 2002/2003 is characterised by three phases of very different PSC activity: First, an unusual, extremely cold phase in the first three weeks of December resulted in high PSC occurrence rates. This was followed by a second phase of only moderate PSC activity from 5–13 January, separated from the first phase by a minor warming event. Finally there was a third phase from February to end of March where only sporadic and mostly weak PSC events took place. The composition of PSCs during the winter period has also been examined, exploiting particularly an infra-red spectral signature which is probably characteristic of NAT. The MIPAS observations show the presence of these particles on a number of occasions in December but very rarely in January. The PSC type differentiation from MIPAS indicates that future comparisons of PSC observations with microphysical and denitrification models might be revealing about aspects of solid particle existence and location.
Sulphuric acid closure and contribution to nucleation mode particle growth
Authors: Boy M. , Kulmala M. , Ruuskanen T. M. , Pihlatie M. , Reissell A. , Aalto P. P. , Keronen P. , Dal Maso M. , Hellen H. , Hakola H. , Jansson R. , Hanke M. , Arnold F.
Published: April 2010

Abstract. Sulphuric acid concentrations were measured and calculated based on pseudo steady state model with corresponding measurements of CO, NOx, O3, SO2, methane and non-methane hydrocarbon (NMHC) concentrations as well as solar spectral irradiance and particle number concentrations with size distributions. The measurements were performed as a part of the EU project QUEST (Quantification of Aerosol Nucleation in the European Boundary layer) during an intensive field campaign, which was conducted in Hyytiälä, Finland in March–April 2003. In this paper, the closure between measured and calculated H2SO4 concentrations is investigated. Besides that, also the contribution of sulphuric acid to nucleation mode particle growth rates is studied. Hydroxyl and hydroperoxy radical concentrations were determined using a pseudo steady state box model including photo stationary states. The maximum midday OH concentrations ranged between 4.1×105 to 1.8×106molecules cm−3 and the corresponding values for HO2 were 1.0×107 to 1.5×108molecules cm−3. The dominant source term for hydroxyl radicals is the reaction of NO with HO2 (56%) and the reaction of CO with OH covers around 41% of the sinks. The sulphuric acid source term is the reaction SO2 with OH and the sink term is condensation of sulphuric acid. The closure between measured and calculated sulphuric acid concentrations is achieved with a high agreement to the measured values. In sensitivity studies, we used different values for the non-methane hydrocarbons, the peroxy radicals and nitrogen dioxide. The best fits between calculated and measured values were found by decreasing the NO2 concentration when it exceeded values of 1.5 ppb and doubling the non-methane hydrocarbon concentrations. The ratio, standard deviation and correlation coefficient between measured and calculated sulphuric acid concentrations are 0.99, 0.412 and 0.645, respectively. The maximum midday sulphuric acid concentrations varied between 3×105 to 1.9×107molecules cm−3 for the measurements and 3×105 to 1.4×107molecules cm−3 for the calculations, respectively. An average participation of sulphuric acid to the nucleation mode particle growth rates is 8.8%. Classifying the days into two groups – "polluted" days with air masses originated over Central Europe or UK, and "cleaner" days with air masses originated over the Northern Atlantic or the Polar regions – reflects an equal sulphuric acid contribution to the aerosol growth in both air mass classes.
Density changes of aerosol particles as a result of chemical reaction
Authors: Katrib Y. , Martin S. T. , Rudich Y. , Davidovits P. , Jayne J. T. , Worsnop D. R.
Published: April 2010

Abstract. This paper introduces the capability to study simultaneously changes in the density, the chemical composition, the mobility diameter, the aerodynamic diameter, and the layer thickness of multi-layered aerosol particles as they are being altered by heterogeneous chemical reactions. A vaporization-condensation method is used to generate aerosol particles composed of oleic acid outer layers of 2 to 30 nm on 101-nm polystyrene latex cores. The layer density is modified by reaction of oleic acid with ozone for variable exposure times. For increasing ozone exposure, the mobility diameter decreases while the vacuum aerodynamic diameter increases, which, for spherical particles, implies that particle density increases. The aerosol particles are confirmed as spherical based upon the small divergence of the particle beam in the aerosol mass spectrometer. The particle and layer densities are calculated by two independent methods, namely one based on the measured aerodynamic and mobility diameters and the other based on the measured mobility diameter and particle mass. The uncertainty estimates for density calculated by the second method are two to three times greater than those of the first method. Both methods indicate that the layer density increases from 0.89 to 1.12 g·cm−3 with increasing ozone exposure. Aerosol mass spectrometry shows that, concomitant with the increase in the layer density, the oxygen content of the reacted layer increases. Even after all of the oleic acid has reacted, the layer density and the oxygen content continue to increase slowly with prolonged ozone exposure, a finding which indicates continued chemical reactions of the organic products either with ozone or with themselves. The results of this paper provide new insights into the complex changes occurring for atmospheric particles during the aging processes caused by gas-phase oxidants.
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 Dobson units from 10 December 2002 to 10 March 2003 is derived 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 DU for the collar region (closest to the edge), 52 DU for the vortex centre and 68 DU for the middle region in between centre and collar.