For the period 1860-2100 (SRES scenario A1B for 2000-2100), the impact of road transport, maritime shipping and aviation on climate is studied using an Atmosphere Ocean General Circulation Model (AOGCM). In addition to carbon dioxide (CO2) emissions from these transport sectors, most of their non-CO2 emissions are also taken into account, i.e., the forcing from ozone, methane, black carbon, organic carbon, sulfate, CFC-12 and HFC-134a from air conditioning systems in cars, and contrails. For the year 2000, the CO2 emissions from all sectors together induce a global annual-mean surface air temperature increase of around 0.1 K. In 2100, the CO2 emissions from road transport induce a global mean warming of 0.3 K, while shipping and aviation each contribute 0.1 K. For road transport, the non-CO2 impact is largest between 2000 and 2050 (of the order of 0.1 K) becoming smaller at the end of the 21st century. The non-CO2 impact from shipping is negative, reaching -0.1 K between 2050 and 2100, while for aviation it is positive and its estimate varies between 0 and 0.15 K in 2100. The largest changes in sea-level from thermal expansion in 2000 are 1.6 mm for the CO2 emissions from road transport, and around -3 mm from the non-CO2 effects of shipping. In 2100, sea-level rises by 18 mm due to the CO2 emissions from road transport and by 4.6 mm due to shipping or aviation CO2 emissions. Non-CO2 changes are of the order of 1 mm for road transport, -6.6 mm for shipping, and the estimate for aviation varies between -1.2 and 4.3 mm. When focusing on the geographical distribution, the non-CO2 impact from road transport and shipping on the surface air temperature is only slightly stronger in northern than in southern mid-latitudes, while the impact from aviation can be a factor of 5 stronger in the northern than in the Southern Hemisphere. Further it is observed that most of the impacts are more pronounced at high latitudes, and that the non-CO2 emissions from aviation strongly impact the NAO index. The impacts on the oceanic meridional overturning circulation and the Niño3.4 index are also quantified.
We present mean altitude profiles of NO<sub>x</sub>, NO<sub>y</sub>, O<sub>3</sub>, and CO as measured by the DLR Falcon aircraft during the MINOS 2001 campaign over the Mediterranean in August 2001 and compare the data with results from other aircraft campaigns, namely the SIL 1996 (North Atlantic flight corridor), the POLINAT-2 (North Atlantic flight corridor), and the EXPORT 2000 (central Europe) campaigns. The MINOS NO<sub>y</sub>, O<sub>3</sub>, and CO mixing ratios in the free troposphere, especially between 4?8 km, are very similar to those measured during the EXPORT 2000 campaign. However, compared to the other campaigns the MINOS O<sub>3</sub> and CO were significantly higher in the boundary layer, by about 20 ppbV and 50 ppbV, respectively. In the second part of the paper the D[O<sub>3</sub>]/D[NO<sub>y</sub>], D[O<sub>3</sub>]/D[CO], D[CO]/D[NO<sub>y</sub>], and D[NO<sub>x</sub>]/D[NO<sub>y</sub>] trace gas correlations were calculated for the MINOS 2001 campaign. It was found that, within the scatter of the data, the overall average altitude profiles of the correlations compared well with data from a literature survey. The analysis of the mean vertical correlation profiles as measured during MINOS 2001 does therefore not single out special meteorological conditions and air mass origins over the Mediterranean in summer but reflects a more general condition of the free troposphere in the northern hemisphere. Correlation analyses for single flights at different altitudes, however, unambiguously identify air masses influenced by the stratosphere, whereas pollution plumes could only be identified with the help of back trajectories.
We present simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) for the Arctic winter 2002/2003. We integrated a Lagrangian denitrification scheme into the three-dimensional version of CLaMS that calculates the growth and sedimentation of nitric acid trihydrate (NAT) particles along individual particle trajectories. From those, we derive the HNO3 downward flux resulting from different particle nucleation assumptions. The simulation results show a clear vertical redistribution of total inorganic nitrogen ( ), with a maximum vortex average permanent removal of over 5ppb in late December between 500 and 550K and a corresponding increase of of over 2ppb below about 450K. The simulated vertical redistribution of is compared with balloon observations by MkIV and in-situ observations from the high altitude aircraft Geophysica. Assuming a globally uniform NAT particle nucleation rate of 7.8x10<sup>-6</sup>cm<sup>-3</sup>h<sup>-1</sup> in the model, the observed denitrification is well reproduced.
In the investigated winter 2002/2003, the denitrification has only moderate impact (≤14%) on the simulated vortex average ozone loss of about 1.1ppm near the 460K level. At higher altitudes, above 600K potential temperature, the simulations show significant ozone depletion through -catalytic cycles due to the unusual early exposure of vortex air to sunlight.
During the ASTAR (Arctic Study of Tropospheric Aerosol and Radiation) campaign nucleation mode particles (4 to 13 nm) were quite frequently observed at altitudes below 4000 m. However, in the upper free troposphere, nucleation mode particles were only observed once, namely during the flight on 24 May 2004 (7000 m). To investigate if vertical motion are the reason for this difference that on one particular day nucleation mode particles were observed but not on the other days we employ a microphysical box model. The box model simulations were performed along air parcel trajectories calculated 6-d backwards based on European Center for Medium-Range Weather Forecasts (ECMWF) meteorological analyses using state parameters such as pressure and temperature in combination with additional parameters such as vertical stability. Box model simulations were performed for the 24 May where nucleation mode particles were observed (nucleation event) as well as for the day with measurements before and after (22 and 26 May) which are representative for no nucleation (none nucleation event). A nucleation burst was simulated along all trajectories, however, in the majority of the simulations the nucleation rate was either too low or too high so that no nucleation mode particles were left at the time were the measurements were performed. Further, the simulation results could be divided into three cases. Thereby, we found that for case 1 the temperature was the only driving mechanism while for case 2 and 3 vertical motion have influenced the formation of new particles. The reason why nucleation mode particles were observed on 24 May, but not on the other day, can be explained by the conditions under which particle formation occurred. On 24 May the particle formation was caused by a slow updraft, while on the other two days the particle formation was caused by a fast updraft.
A DUALER (dual-channel airborne peroxy radical chemical amplifier) instrument has been developed and optimised for the airborne measurement of the total sum of peroxy radicals during the AMMA (African Monsoon Multidisciplinary Analyses) measurement campaign which took place in Burkina Faso in August 2006. The innovative feature of the instrument is that both reactors are sampling simultaneously from a common pre-reactor nozzle while the whole system is kept at a constant pressure to ensure more signal stability and accuracy.
Laboratory experiments were conducted to characterise the stability of the NO<sub>2</sub> detector signal and the chain length with the pressure. The results show that airborne measurements using chemical amplification require constant pressure at the luminol detector. Wall losses of main peroxy radicals HO<sub>2</sub> and CH<sub>3</sub>O<sub>2</sub> were investigated. The chain length was experimentally determined for different ambient mixtures and compared with simulations performed by a chemical box model.
The DUALER instrument was successfully mounted within the German DLR-Falcon. The analysis of AMMA data utilises a validation procedure based on the O<sub>3</sub> mixing ratios simultaneously measured onboard. The validation and analysis procedure is illustrated by means of the data measured during the AMMA campaign. The detection limit and the accuracy of the ambient measurements are also discussed.
During the POLARCAT summer campaign in 2008, two episodes (2–5 July and 7–10 July 2008) occurred where low-pressure systems traveled from Siberia across the Arctic Ocean towards the North Pole. The two cyclones had extensive smoke plumes embedded in their associated air masses, creating an excellent opportunity to use satellite and aircraft observations to validate the performance of atmospheric transport models in the Arctic, which is a challenging model domain due to numerical and other complications.
Here we compare transport simulations of carbon monoxide (CO) from the Lagrangian transport model FLEXPART, the Eulerian chemical transport model TOMCAT, and for numerical aspects the limited-area chemical transport model WRF-Chem. Retrievals of total column CO from the IASI passive infrared sensor onboard the MetOp-A satellite are used as a total column CO reference for the two simulations. Main aspect of the comparison is how realistic horizontal and vertical structures are represented in the model simulations. Analysis of CALIPSO lidar curtains and in situ aircraft measurements provide further independent reference points to assess how reliable the model simulations are and what the main limitations are.
The horizontal structure of mid-latitude pollution plumes agrees well between the IASI total column CO and the model simulations. However, finer-scale structures are too quickly diffused in the Eulerian models. Aircraft data suggest that the satellite data are biased high, while TOMCAT and WRF-Chem are biased low. FLEXPART fits the aircraft data rather well, but due to added background concentrations the simulation is not independent from observations. The multi-data, multi-model approach allows separating the influences of meteorological fields, model realisation, and grid type on the plume structure. In addition to the very good agreement between simulated and observed total column CO fields, the results also highlight the difficulty to identify a data set that most realistically represents the actual state of the atmosphere.
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 (1 s ) 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.
Formation of new atmospheric aerosol particles is known to occur almost all over the world and the importance of these particles to climate and air quality has been recognized.
Recently, it was found that atmospheric aerosol formation begins at particle diameter of around 1.5–2.0 nm and a pool of sub-3 nm atmospheric particles – consisting of both charged and uncharged ones – was observed at the ground level. Here, we report on the first airborne observations of the pool of sub-3nm neutral atmospheric particles. Between 2 and 3 nm, their concentration is roughly two orders of agnitude larger than that of the ion clusters, depending slightly on the altitude. Our findings indicate that new particle formation takes place actively throughout the tropospheric column up to the tropopause. Particles were found to be formed via neutral pathways in the boundary layer, and there was no sign of an increasing role by ion-induced nucleation
toward the upper troposphere. Clouds, while acting as a source of sub-10nm ions, did not perturb the overall budget of atmospheric clusters or particles.
Airborne Differential Absorption Lidar (DIAL) observations of tropospheric water vapour over Brazil and between Brazil and south Europe in March 2004 are compared to 1-hourly short-range forecasts of the European Centre for Medium Range Weather Forecasts (ECMWF). On three along-flight sections across the tropical and sub-tropical Atlantic between 28° S and 37° N humidity fields are observed which represent typical low latitude conditions. H<sub>2</sub>O mixing ratios vary between q≈0.01–0.1 g/kg in the upper troposphere (UT), in subsiding air layers and a stratospheric intrusion. They reach up to 0.5 g/kg at UT levels inside the Intertropical Convergence Zone (ITCZ) and exceed 10 g/kg at lower levels. Back-trajectories reveal that the humidity fields are largely determined by transport.
The observed water vapour distributions are properly reproduced by 1-hourly ECMWF Integrated Forecasting System (IFS) short-range forecasts at T799/L91 spectral resolution. As transport largely determines the water vapour fields, the IFS skill is to a large extend based on a good representation of the dynamics. The mean relative bias accounts to few percent (0%, 3% and 6% for the three sections) being about or even below the accuracy of the DIAL measurements of 5%. The larger deviations between analyses and observations on small scales are due to relative spatial shifts of features with large gradients. The correlation is quite high, ranging between 0.71 and 0.88. Over sea the analyses tend to underestimate the PBL height. At mid-levels near deep convection the mid-troposphere tends to be analyzed too humid indicating shortcomings in the convection parameterization. Humid tendencies are also found in the upper troposphere, particularly in tropical regions.
The photochemical evolution of an anthropogenic plume from the New-York/Boston region during its transport at low altitudes over the North Atlantic to the European west coast has been studied using a Lagrangian framework. This plume, originally strongly polluted, was sampled by research aircraft just off the North American east coast on 3 successive days, and 3 days downwind off the west coast of Ireland where another aircraft re-sampled a weakly polluted plume. Changes in trace gas concentrations during transport were reproduced using a photochemical trajectory model including deposition and mixing effects.
Chemical and wet deposition processing dominated the evolution of all pollutants in the plume. The mean net O3 production was evaluated to be -5 ppbv/day leading to low values of O3 by the time the plume reached Europe. Wet deposition of nitric acid was responsible for an 80% reduction in this O3 production. If the plume had not encountered precipitation, it would have reached the Europe with O3 levels up to 80-90 ppbv, and CO levels between 120 and 140 ppbv. Photochemical destruction also played a more important role than mixing in the evolution of plume CO due to high levels of both O3 and water vapour showing that CO cannot always be used as a tracer for polluted air masses, especially for plumes transported at low altitudes. The results also show that, in this case, an important increase in the O3/CO slope can be attributed to chemical destruction of CO and not to photochemical O3 production as is often assumed.
We examine the effect of nanometer-sized aircraft-induced aqueous sulfuric acid (H2SO4/H2O) particles on atmospheric ozone as a function of temperature. Our calculations are based on a previously derived parameterization for the regional-scale perturbations of the sulfate surface area density due to air traffic in the North Atlantic Flight Corridor (NAFC) and a chemical box model. We confirm large scale model results that at temperatures T > 210 K additional ozone loss - mainly caused by hydrolysis of BrONO2 and N2O5 - scales in proportion with the aviation-produced increase of the background aerosol surface area. However, at lower temperatures (< 210K) we isolate two effects which efficiently reduce the aircraft-induced perturbation: (1) background particles growth due to H2O and HNO3 uptake enhance scavenging losses of aviation-produced liquid particles and (2) the Kelvin effect efficiently limits chlorine activation on the small aircraft-induced droplets by reducing the solubility of chemically reacting species. These two effects lead to a substantial reduction of heterogeneous chemistry on aircraft-induced volatile aerosols under cold conditions. In contrast we find contrail ice particles to be potentially important for heterogeneous chlorine activation and reductions in ozone levels. These features have not been taken into consideration in previous global studies of the atmospheric impact of aviation. Therefore, to parameterize them in global chemistry and transport models, we propose the following parameterisation: scale the hydrolysis reactions by the aircraft-induced surface area increase, and neglect heterogeneous chlorine reactions on liquid plume particles but not on ice contrails and aircraft induced ice clouds.
Airborne measurements of trace gases and aerosol particles have been made in two aged biomass burning (BB) plumes over the East Atlantic (Gulf of Guinea). The plumes originated from BB in the Southern Hemisphere African savanna belt. On the day of our measurements (13 August 2006), the plumes had ages of about 10 days and were respectively located in the middle troposphere (MT) at about 3000–5500 m altitude and in the upper troposphere (UT) at about 10 800–11 200 m. In the more polluted MT-plume, numerous measured trace species had markedly elevated abundances, particularly HNO3 (5000–8000 pmol/mol), SO2 (up to 1400 pmol/mol), and smoke particles with diameters larger than 250 nm (up to 2000 cm−3). Our MT-plume measurements indicate that SO2 released by BB had not experienced significant loss by deposition and cloud processes but rather had experienced OH-induced conversion to gas-phase sulfuric acid. By contrast, a large fraction of the released NOx had experienced loss, most likely as HNO3, by cloud processes and deposition. In the UT-plume, loss of NOy and SO2 by cloud processes and deposition was more pronounced compared to the MT-plume. Building on our measurements and accompanying model simulations, we have investigated trace gas transformations in the ageing and diluting plumes and their role in smoke particle processing and activation. Emphasis was placed upon the formation of sulfuric acid, nitric acid, and ammonium nitrate, and their influence on the activation potential of smoke particles. Our model simulations reveal that, after 13 August, the lower plume traveled across the Atlantic and descended to 1300 m and hereafter ascended again. During the travel across the Atlantic, the smoke particle mean diameter and sulfuric acid mass fraction increased sufficiently to allow the processed smoke particles to act as water vapor condensation nuclei already at very low water vapor supersaturations of only about 0.04%. Thereby, aged smoke particles had developed a potential to act as water vapor condensation nuclei in the formation of maritime clouds, including not only cumulus but even stratiform clouds.
Airborne in-situ observations of ClO in the tropics
were made during the TROCCINOX (Aracatuba, Brazil,
February 2005) and SCOUT-O3 (Darwin, Australia, November/ December 2005) field campaigns. While during most flights significant amounts of ClO (10–20 parts per trillion, ppt) were present only in aged stratospheric air, instances of enhanced ClO mixing ratios of up to 40 ppt – significantly exceeding those expected from gas phase chemistry – were observed
in air masses of a more tropospheric character. Most
of these observations are associated with low temperatures or with the presence of cirrus clouds (often both), suggesting that cirrus ice particles and/or liquid aerosol at low temperatures may promote significant heterogeneous chlorine activation
in the tropical upper troposphere lower stratosphere
(UTLS). In two case studies, particularly high levels of ClO observed were reproduced by chemistry simulations only under the assumption that significant denoxification had occurred in the observed air. However, to reproduce the ClO observations in these simulations, O3 mixing ratios higher than observed had to be assumed, and at least for one of these flights, a significant denoxification is in contrast to the
observed NO levels, suggesting that the coupling of chlorine and nitrogen compounds in the tropical UTLS may not be completely understood.
During airborne in situ measurements of particle size distributions in a
forest fire plume originating in Northern Canada, an accumulation mode
number mean diameter of 0.34 μm} was observed over Lindenberg,
Germany on 9 August 1998. Realizing that this is possibly the largest
value observed for this property in a forest fire plume, scenarios of
plume ageing by coagulation are considered to explain the observed size
distribution, concluding that the plume dilution was inhibited in parts
of the plume. The uncertainties in coagulation rate and transition from
external to internal mixture of absorbing forest fire and non-absorbing
background particles cause uncertainties in the plume's solar
instantaneous radiative forcing of 20-40% and of a factor of 5-6,
respectively. Including information compiled from other studies on this
plume, it is concluded that the plume's characteristics are
qualitatively consistent with a radiative-convective mixed layer.
The aerosol dynamics module MADE has been coupled to the general
circulation model ECHAM4 to simulate the chemical composition,
number concentration, and size distribution of the global submicrometer
aerosol. The present publication describes the new model system
ECHAM4/MADE and presents model results in comparison with
observations. The new model is able to simulate the full life cycle of
particulate matter and various gaseous particle precursors including
emissions of primary particles and trace gases, advection, convection,
diffusion, coagulation, condensation, nucleation of sulfuric acid vapor,
aerosol chemistry, cloud processing, and size-dependent dry and wet
deposition. Aerosol components considered are sulfate (SO<sub>4</sub>),
ammonium (NH<sub>4</sub>), nitrate (NO<sub>3</sub>), black carbon (BC),
particulate organic matter (POM), sea salt, mineral dust, and aerosol
The model is numerically efficient enough to allow long
term simulations, which is an essential requirement for application in
general circulation models. Since the current study is focusing on the submicrometer aerosol, a
coarse mode is not being simulated. The model is run in a
passive mode, i.e. no feedbacks between the MADE aerosols and clouds
or radiation are considered yet. This allows the investigation of the
effect of aerosol dynamics, not interfered by feedbacks of the altered
aerosols on clouds, radiation, and on the model dynamics.
In order to evaluate the results obtained with this new model system,
calculated mass concentrations, particle number concentrations, and
size distributions are compared to observations.
The intercomparison shows, that ECHAM4/MADE is able to reproduce the major
features of the geographical patterns, seasonal cycle, and vertical
distributions of the basic aerosol parameters. In particular, the
model performs well under polluted continental conditions in the
northern hemispheric lower and middle troposphere. However, in
comparatively clean remote areas, e.g. in the upper troposphere or in
the southern hemispheric marine boundary layer, the current model
version tends to underestimate particle number concentrations.
This paper reports on backscatter and depolarization measurements by an airborne lidar in the Arctic during the ASTAR 2004 campaign. A unique weather situation facilitated the observation of the aerosol concentration under strongly forced atmospheric conditions. The vigorous easterly winds distorted the flow past Svalbard in such a way that mesoscale features were visible in the remote-sensing observations: The formation of a well-mixed aerosol layer inside the Adventdalen and the subsequent thinning of the aerosol plume were observed over the Isfjorden. Additionally, mobilization of sea salt aerosols due to a coastal low-level jet at the northern tip of Svalbard resulted in a sloped boundary layer toward north. Mesoscale numerical modelling was applied to identify the sources of the aerosol particles and to explain the observed patterns.
An air pollution plume from Southern and Eastern Asia, including regions in India and China, was predicted by the FLEXPART particle dispersion model to arrive in the upper troposphere over Europe on 24–25 March 2006. According to the model, the plume was exported from Southeast Asia only six days earlier, transported into the upper troposphere by a warm conveyor belt, and travelled to Europe in a fast zonal flow. This is confirmed by the retrievals of carbon monoxide (CO) from AIRS satellite measurements, which are in excellent agreement with the model results over the entire transport history. The research aircraft DLR Falcon was sent into this plume west of Spain on 24 March and over Southern Europe on 25 March. On both days, the pollution plume was indeed found close to the predicted locations and, thus, the measurements taken allowed the first detailed characterization of the aerosol content and chemical composition of an anthropogenic pollution plume after a nearly hemispheric transport event. The mixing ratios of CO, reactive nitrogen (NOy) and ozone (O3) measured in the Asian plume were all clearly elevated over a background that was itself likely elevated by Asian emissions: CO by 17–34 ppbv on average (maximum 60 ppbv) and O3 by 2–9 ppbv (maximum 22 ppbv). Positive correlations existed between these species, and a ΔO3/ΔCO slope of 0.25 shows that ozone was formed in this plume, albeit with moderate efficiency. Nucleation mode and Aitken particles were suppressed in the Asian plume, whereas accumulation mode aerosols were strongly elevated and correlated with CO. The suppression of the nucleation mode was likely due to the large pre-existing aerosol surface due to the transported larger particles. Super-micron particles, likely desert dust, were found in part of the Asian pollution plume and also in surrounding cleaner air. The aerosol light absorption coefficient was enhanced in the plume (average values for individual plume encounters 0.25–0.70 Mm−1), as was the fraction of non-volatile Aitken particles. This indicates that black carbon (BC) was an important aerosol component. During the flight on 25 March, which took place on the backside of a trough located over Europe, a mixture of Asian pollution and stratospheric air was found. Asian pollution was mixing into the lower stratosphere, and stratospheric air was mixing into the pollution plume in the troposphere. Turbulence was encountered by the aircraft in the mixing regions, where the thermal stability was low and Richardson numbers were below 0.2. The result of the mixing can clearly be seen in the trace gas data, which are following mixing lines in correlation plots. This mixing with stratospheric air is likely very typical of Asian air pollution, which is often lifted to the upper troposphere and, thus, transported in the vicinity of stratospheric air.
The chemical composition of submicron (fine mode) and supermicron (coarse mode) aerosol particles has been investigated since 1999 within the GAW aerosol monitoring program at the high alpine research station Jungfraujoch (3580 m a.s.l., Switzerland). Clear seasonality was observed for all major components in the last 9 years with low concentrations in winter (predominantly free tropospheric aerosol) and higher concentrations in summer (enhanced vertical transport of boundary layer pollutants). In addition, mass closure was attempted during intensive experiments in March 2004, February–March 2005 and August 2005. Ionic, carbonaceous and refractory components of the aerosol were quantified as well as the PM1 and coarse mode total aerosol mass concentrations. A relatively low conversion factor of 1.8 for organic carbon (OC) to particulate organic matter (OM) in winter (February–March 2005) was found. Organics, sulfate, ammonium, and nitrate were the major identified components of the fine aerosol fraction, while calcium and nitrate were the two major measured components in the coarse mode. The aerosol mass concentrations for fine and coarse mode aerosol during the intensive campaigns were not typical of the long term seasonality due largely to dynamical differences. Average fine and coarse mode concentrations during the intensive field campaigns were 1.7 μg m-3 and 2.4 μg m-3 in winter and 2.5 μg m-3 and 2.0 μg m-3 in summer, respectively. The mass balance of aerosols showed higher contributions of calcium and nitrate in the coarse mode during Saharan dust events (SDE) than without SDE.
The nonlinear features of the relationships between concentrations of aerosol and volatile organic compounds (VOC) and oxides of nitrogen (NOx) in urban environments are derived directly from data of long-term routine measurements of NOx, VOC, and total suspended particulate matter (PM). The main idea of the method used for the analysis is creation of special empirical models based on artificial neural networks. These models which are in essence the nonlinear extension of commonly used linear statistical models are believed to provide the best fit for the real (nonlinear) PM-NOx-VOC relationships under different atmospheric conditions. It is believed that such models may be useful in context of various scientific and practical problems concerning atmospheric aerosols. The method is demonstrated by the example of two empirical models created with independent data-sets collected at two air quality monitoring stations at South Coast Air Basin, California. It is shown that in spite of considerable distance between the monitoring stations (more than 50 km) and thus substantially different environmental conditions, the empirical models manifest several common qualitative features. Specifically, it is found that, under definite conditions, the decrease of the level of NOx or VOC may lead to the increase of mass concentration of aerosol. It is argued that these features are caused by the nonlinear dependence of hydroxyl radical on VOC and NOx.
A new database of trace gases and aerosols with global coverage, derived from high vertical resolution profile measurements, has been assembled as a collection of binary data files; hereafter referred to as the “Binary DataBase of Profiles” (BDBP). Version 1.0 of the BDBP, described here, includes measurements from different satellite- (HALOE, POAM II and III, SAGE I and II) and ground-based measurement systems (ozonesondes). In addition to the primary product of ozone, secondary measurements of other trace
gases, aerosol extinction, and temperature are included. All data are subjected to very strict quality control and for every measurement a percentage error on the measurement is included. To facilitate analyses, each measurement is added to 3 different instances (3 different grids) of the database where measurements are indexed by: (1) geographic latitude, longitude, altitude (in 1 km steps) and time, (2) geographic latitude,
longitude, pressure (at levels ~1 km apart) and time, (3) equivalent latitude, potential temperature (8 levels from 300K to 650 K) and time.
In contrast to existing zonal mean databases, by including a wider range of measurement sources (both satellite and ozonesondes), the BDBP is sufficiently dense to permit calculation of changes in ozone by latitude, longitude and altitude. In addition, by including other trace gases such as water vapour, this database can be used for comprehensive radiative transfer calculations. By providing the original measurements rather than derived monthly means, the BDBP is applicable to a wider range of applications than databases containing only monthly mean data. Monthly mean zonal mean ozone concentrations calculated from the BDBP are compared with the database of Randel and Wu, which has been used in many earlier analyses. As opposed to that database which is generated from regression model fits, the BDBP uses the original (quality controlled) measurements with no smoothing applied in any way and as a result displays higher natural variability.
Recent field observations suggest that the fraction of organic-containing aerosol particles in ice cloud particles is diminished when compared to the background aerosol prior to freezing. In this work, we use model calculations
to investigate possible causes for the observed behavior. In particular, homogeneous freezing processes in cooling air parcels containing aqueous inorganic particles and organic particles are studied with a detailed microphysical model. A disparate water uptake and resulting size differences that occur between organic and inorganic particles prior to freezing are identified as the most likely reason for the poor partitioning of organic aerosols into the ice phase. The differences in water uptake can be caused by changes in the relationship between solute mass fraction and water activity of the supercooled liquid phase, by modifications of the accommodation coefficient for water molecules, or by a combination thereof.
The behavior of peak ice saturation ratios and total ice crystal number concentrations is examined, and the dependence of the results on cooling rate is investigated. Finally, processes are discussed that could possibly modify the homogeneous freezing behavior of organic particles.
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
The effect of nitric acid on the equilibrium size distributions of upper tropospheric aerosols is calculated as a function of relative humidity. It is shown that HNO3 concentrations above a few tenths of a ppb can cause substantial increases in haze mode particle concentrations at relative humidities at about 60% and above. The effect can be strongly magnified when letovicite particles are present in addition to sulfuric acid aerosols. This is mainly due to the lowering of the deliquescence RH of letovicite in the presence of gaseous nitric acid at low temperatures. We have also compared equilibrium calculations of the HNO3 effect with observations of increased haze mode concentrations at relative humidities above 50% (Petzold et al., 2000). Nitric acid mixing ratios on the order of 0.5-2 ppb may explain the observed increase of haze mode particles at least partially.
During the "African Monsoon Multidisciplinary Analysis" (AMMA) field phase in August 2006, a variety of measurements focusing on deep convection were performed over West Africa. The German research aircraft Falcon based in Ouagadougou (Burkina Faso) investigated the chemical composition in the outflow of large mesoscale convective systems (MCS). Here we analyse two different types of MCS originating north and south of the intertropical convergence zone (ITCZ, ~10° N), respectively. In addition to the airborne trace gas measurements, stroke measurements from the Lightning Location Network (LINET), set up in Northern Benin, are analysed. The main focus of the present study is (1) to analyse the trace gas composition (CO, O3, NO, NOx, NOy, and HCHO) in the convective outflow as a function of distance from the convective core, (2) to investigate how different trace gas compositions in the boundary layer (BL) and ambient air may influence the O3 concentration in the convective outflow, and (3) to estimate the rate of lightning-produced nitrogen oxides per flash in selected thunderstorms and compare it to our previous results for the tropics. The MCS outflow was probed at different altitudes (~10–12 km) and distances from the convective core (
During the CIRCLE-2 experiment carried out over Western Europe in May 2007, combined in situ and remote sensing observations allowed to describe microphysical and optical properties near-top of an overshooting convective
cloud (11 080 m/−58 C). The airborne measurements were
performed with the DLR Falcon aircraft specially equipped
with a unique set of instruments for the extensive in situ
cloud measurements of microphysical and optical properties
(Polar Nephelometer, FSSP-300, Cloud Particle Imager and
PMS 2-D-C) and nadir looking remote sensing observations
(DLR WALES Lidar). Quasi-simultaneous space observations
from MSG/SEVIRI, CALIPSO/CALIOP-WFC-IIR
and CloudSat/CPR combined with airborne RASTA radar reflectivity from the French Falcon aircraft flying above the
DLR Falcon depict very well convective cells which overshoot
by up to 600m the tropopause level. Unusual high
values of the concentration of small ice particles, extinction,
ice water content (up to 70 cm−3, 30 km−1 and 0.5 gm−3,
respectively) are experienced. The mean effective diameter
and the maximum particle size are 43 μm and about 300 μm,
respectively. This very dense cloud causes a strong attenuation of the WALES and CALIOP lidar returns. The SEVIRI retrieved parameters confirm the occurrence of small
ice crystals at the top of the convective cell. Smooth and
featureless phase functions with asymmetry factors of 0.776
indicate fairly uniform optical properties. Due to small ice
crystals the power-law relationship between ice water content
(IWC) and radar reflectivity appears to be very different
from those usually found in cirrus and anvil clouds. For
a given equivalent reflectivity factor, IWCs are significantly
larger for the overshooting cell than for the cirrus. Assuming the same prevalent microphysical properties over the depth
of the overshooting cell, RASTA reflectivity profiles scaled
into ice water content show that retrieved IWC up to 1 gm−3
may be observed near the cloud top. Extrapolating the relationship for stronger convective clouds with similar ice particles, IWC up to 5 gm−3 could be experienced with reflectivity factors no larger than about 20 dBZ. This means that for similar situations, indication of rather weak radar echo does not necessarily warn the occurrence of high ice water content carried by small ice crystals. All along the cloud penetration the shape of the ice crystals is dominated by chainlike aggregates of frozen droplets. Our results confirm previous observations that the chains of ice crystals are found
in a continental deep convective systems which are known
generally to generate intense electric fields causing efficient
ice particle aggregation processes. Vigorous updrafts could
lift supercooled droplets which are frozen extremely rapidly
by homogeneous nucleation near the −37 C level, producing
therefore high concentrations of very small ice particles
at upper altitudes. They are sufficient to deplete the water
vapour and suppress further nucleation as confirmed by
humidity measurements. These observations address scientific
issues related to the microphysical properties and structure
of deep convective clouds and confirm that particles
smaller than 50 μm may control the radiative properties in
convective-related clouds. These unusual observations may
also provide some possible insights regarding engineering issues related to the failure of jet engines commonly used on
commercial aircraft during flights through areas of high ice
water content. However, large uncertainties of the measured
and derived parameters limit our observations.
The atmospheric chemistry general circulation model ECHAM5/MESSy is used to simulate polar surface air temperature effects of geomagnetic activity variations. A transient model simulation was performed for the years 1960–2004 and is shown to develop polar surface air temperature patterns that depend on geomagnetic activity strength, similar to previous studies. In order to eliminate influencing factors such as sea surface temperatures (SST) or UV variations, two nine-year long simulations were carried out, with strong and weak geomagnetic activity, respectively, while all other boundary conditions were held to year 2000 levels. Statistically significant temperature effects that were observed in previous reanalysis and model results are also obtained from this set of simulations, suggesting that such patterns are indeed related to geomagnetic activity. In the model, strong geomagnetic activity and the associated NOx (= NO + NO2) enhancements lead to polar stratospheric ozone loss. Compared with the simulation with weak geomagnetic activity, the ozone loss causes a decrease in ozone radiative cooling and thus a temperature increase in the polar winter mesosphere. Similar to previous studies, a cooling is found below the stratopause, which other authors have attributed to a decrease in the mean meridional circulation. In the polar stratosphere this leads to a more stable vortex. A strong (weak) Northern Hemisphere vortex is known to be associated with a positive (negative) Northern Annular Mode (NAM) index; our simulations exhibit a positive NAM index for strong geomagnetic activity, and a negative NAM for weak geomagnetic activity. Such NAM anomalies have been shown to propagate to the surface, and this is also seen in the model simulations. NAM anomalies are known to lead to specific surface temperature anomalies: a positive NAM is associated with warmer than average northern Eurasia and colder than average eastern North Atlantic. This is also the case in our simulation. Our simulations suggest a link between geomagnetic activity, ozone loss, stratospheric cooling, the NAM, and surface temperature variability. Further work is required to identify the precise cause and effect of the coupling between these regions.
The demand for intercontinental transportation is increasing and people are requesting short travel times, which supersonic air transportation would enable. However, besides noise and sonic boom issues, which we are not referring to in this investigation, 5 emissions from supersonic aircraft are known to alter the atmospheric composition, in particular the ozone layer, and hence affect climate significantly more than subsonic aircraft. Here, we suggest a metric to quantitatively assess different options for supersonic transport with regard to the potential destruction of the ozone layer and climate impacts. Options for fleet size, engine technology (nitrogen oxide emission level), cruis10 ing speed, range, and cruising altitude, are analyzed, based on SCENIC emissions scenarios for 2050, which underlay the requirements to be as realistic as possible in terms of e.g. economic markets and profitable market penetration. This methodology is based on a number of atmosphere-chemistry and climate models to reduce mode dependencies. The model results differ significantly in terms of the response to a re15 placement of subsonic aircraft by supersonic aircraft. However, model differences are smaller when comparing the different options for a supersonic fleet. The base scenario, where supersonic aircraft get in service in 2015, a first fleet fully operational in 2025 and a second in 2050, lead in our simulations to a near surface temperature increase in 2050 of around 7mK and with constant emissions afterwards to around 21mK in 2100. The related total radiative forcing amounts to 22 mW/m<sup>2</sup> 20 in 2050, with an uncertainty between 9 and 29 mW/m<sup>2</sup> . A reduced supersonic cruise altitude or speed (from March 2 to Mach 1.6) reduces both, climate impact and ozone destruction, by around 40%. An increase in the range of the supersonic aircraft leads to more emissions at lower latitudes since more routes to SE Asia are taken into account, which increases ozone 25 depletion, but reduces climate impact compared to the base case.
During the TROCCINOX field experiments in February–March 2004 and February 2005, airborne in situ measurements of NO, NO<sub>y</sub>, CO, and O<sub>3</sub> mixing ratios and the J(NO<sub>2</sub>) photolysis rate were carried out in the anvil outflow of thunderstorms over southern Brazil. Both tropical and subtropical thunderstorms were investigated, depending on the location of the South Atlantic convergence zone. Tropical air masses were discriminated from subtropical ones according to the higher equivalent potential temperature ( Θ<sub>e</sub> ) in the lower and mid troposphere, the higher CO mixing ratio in the mid troposphere, and the lower wind velocity in the upper troposphere within the Bolivian High (north of the subtropical jet stream). During thunderstorm anvil penetrations, typically at 20–40 km horizontal scales, NO<sub>x</sub> mixing ratios were distinctly enhanced and the absolute mixing ratios varied between 0.2–1.6 nmol mol<sup>−1</sup> on average. This enhancement was mainly attributed to NO<sub>x</sub> production by lightning and partly due to upward transport from the NO<sub>x</sub>-richer boundary layer. In addition, CO mixing ratios were occasionally enhanced, indicating upward transport from the boundary layer. For the first time, the composition of the anvil outflow from a large, long-lived mesoscale convective system (MCS) advected from northern Argentina and Uruguay was investigated in more detail. Over a horizontal scale of about 400 km, NO<sub>x</sub>, CO and O<sub>3</sub> absolute mixing ratios were significantly enhanced in these air masses in the range of 0.6–1.1, 110–140 and 60–70 nmol mol<sup>−1</sup>, respectively. Analyses from trace gas correlations and a Lagrangian particle dispersion model indicate that polluted air masses, probably from the Buenos Aires urban area and from biomass burning regions, were uplifted by the MCS. Ozone was distinctly enhanced in the aged MCS outflow, due to photochemical production and entrainment of O<sub>3</sub>-rich air masses from the upper troposphere – lower stratosphere region. The aged MCS outflow was transported to the north, ascended and circulated, driven by the Bolivian High over the Amazon basin. In the observed case, the O<sub>3</sub>-rich MCS outflow remained over the continent and did not contribute to the South Atlantic ozone maximum.
A new algorithm is presented to reproduce the three-dimensional structure of clouds from airborne measurements of microphysical parameters. Data from individual flight legs are scanned for characteristic patterns, and the autocorrelation functions for several directions are used to extrapolate the observations along the flight path to a full three-dimensional distribution of the cloud field. Thereby, the mean measured profiles of microphysical parameters are imposed to the cloud field by mapping the measured probability density functions onto the model layers. The algorithm was tested by simulating flight legs through synthetic clouds (by means of Large Eddy Simulations (LES)) and applied to a stratocumulus cloud case measured during the first field experiment of the EC project INSPECTRO (INfluence of clouds on the SPECtral actinic flux in the lower TROposphere) in East Anglia, UK. The number and position of the flight tracks determine the quality of the retrieved cloud field. If they provide a representative sample of the entire field, the derived pattern closely resembles the statistical properties of the real cloud field
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, N<sub>2</sub>O<sub>5</sub> and HO<sub>x</sub> 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, t <sub>1</sub> to define effective emission and perturbation indices ( EEI s and EPI s) for the North Atlantic Flight Corridor (NAFC) showing EEI (NO<sub>y</sub>) and EPI (O<sub>3</sub>) for various background conditions, such as relative humidity, local time of emission, and seasonal variations. Our results show a high sensitivity of EEI and EPI s on the exact conditions under which emissions take place. The difference of EEI s with and without considering plume processes indicates that these processes cannot be neglected.
The MINOS (Mediterranean INtensive Oxidant Study) campaign was an international, multi-platform field campaign to measure long-range transport of air-pollution and aerosols from South East Asia and Europe towards the Mediterranean basin during August 2001. High pollution events were observed during this campaign. For the Mediterranean region enhanced tropospheric nitrogen dioxide (NO<sub>2</sub>) and formaldehyde (HCHO), which are precursors of tropospheric ozone (O<sub>3</sub>), were detected by the satellite based GOME (Global Ozone Monitoring Experiment) instrument and compared with air-borne in-situ-measurements as well as with the output from the global 3D photochemistry-transport model MATCH-MPIC (Model of Atmospheric Transport and CHemistry - Max-Planck-Institute for Chemistry). The increase of pollution in that region leads to severe air quality degradation with regional and global implications.
The scavenging of black carbon (BC) in liquid and mixed phase clouds was investigated during intensive experiments in winter 2004, summer 2004 and winter 2005 at the high alpine research station Jungfraujoch (3580m a.s.l.,
Switzerland). Aerosol residuals were sampled behind two well characterized inlets; a total inlet which collected cloud particles (droplets and ice particles) as well as interstitial (unactivated) aerosol particles; an interstitial inlet which collected only interstitial aerosol particles. BC concentrations were measured behind each of these inlets along with the submicrometer aerosol number size distribution, from which a volume concentration was derived. These measurements were complemented by in-situ measurements of cloud microphysical parameters. BC was found to be scavenged into the condensed phase to the same extent as the bulk aerosol, which suggests that BC was covered with soluble material through aging processes, rendering it more hygroscopic. The scavenged fraction of BC (FScav,BC), defined as the fraction
of BC that is incorporated into cloud droplets and ice crystals, decreases with increasing cloud ice mass fraction (IMF) from F(Scav, BC) = 60% in liquid phase clouds to F(Scav,BC) = 5–10% in mixed-phase clouds with IMF>0.2. This can be explained by the evaporation of liquid droplets in the presence
of ice crystals (Wegener-Bergeron-Findeisen process), releasing BC containing cloud condensation nuclei back into the interstitial phase. In liquid clouds, the scavenged BC fraction is found to decrease with decreasing cloud liquid water content. The scavenged BC fraction is also found to decrease with increasing BC mass concentration since there is an increased ompetition for the available water vapour.
A polar cirrus case study is discussed with the help of a one-dimensional model with explicit aerosol and ice microphysics. It is demonstrated that continuous cooling of air in regions with small amounts of ice and slow ice deposition rates of water vapor drives significant in-cloud supersaturations over ice, with potentially important consequences for heterogeneous halogen activation. Radiatively important cloud properties such as ice crystal size distributions are investigated, showing the presence of high number concentrations of small crystals in the cloud top region at the tropopause, broad but highly variable size spectra in the cloud interior, and mostly large crystals at the cloud base. It is found that weakly forced Arctic cirrostratus are highly efficient at dehydrating upper tropospheric air. Estimating nitric acid uptake in cirrus with an unprecedented treatment of diffusion-limited trapping in growing ice crystals suggests that such clouds could also denitrify upper tropospheric air masses efficiently, but a closer comparison to suitable observations is needed to draw a definite conclusion on this point. It is also shown that low temperatures, high ice supersaturations, and the absence of ice above but close to the cloud top region cause efficient uptake of nitric acid in background aerosol particles.
n-situ measurements of the long-lived trace gases N2O, CFC-11 (CCl3F), H-1211 (CBrClF2), CH4, O3 and H2O performed in the Arctic winter 2003 on board the high-altitude aircraft M55 Geophysica are presented and used to study transport into the lowermost stratosphere (LMS). Fractions of air in the LMS originating in i) the troposphere, ii) the extra-vortex stratosphere above 400 K and iii) the Arctic vortex above 400 K are determined using a simple mass balance calculation. The analysis exhibits a strong tropospheric influence of 50% or more in the lowest 20 K of the high-latitude LMS. Above this region the LMS is dominated by air masses having descended from above 400 K. Below the Arctic vortex region at potential temperatures above 360 K, air in the LMS is a mixture of extra-vortex stratospheric and vortex air masses. The vortex fraction increases from about 40% at 360 K to 100% at 400 K for equivalent latitudes >70° N. This influence of air masses descending through the bottom of the polar vortex increases over the course of the winter. By the end of winter a significant fraction of 30% vortex air in the LMS is found even at an equivalent latitude of 40° N. Since the chemical and dynamical history of vortex air is distinct from that of mid-latitude stratospheric air masses, this study implies that the composition of the mid- to high-latitude LMS during late winter and spring is significantly influenced by the Arctic vortex.
During the EU-project QUEST atmospheric gaseous sulphuric acid was measured and its influence on particle formation and growth was investigated building on aerosol data at two measurement sites (Hyytiälä, Finland, March–April 2003 and Heidelberg, Germany, March–April 2004). From a comprehensive data set including particle number size distributions, sulphuric acid, and meteorological data, particle growth rates, particle formation rates and source rates of condensable vapors were calculated. Growth rates were determined in two different ways, from particle size distributions as well as from a so-called timeshift analysis. Moreover, correlations between sulphuric acid and particle number concentration between 3 and 6 nm were examined.
Phase transitions of atmospheric water play a ubiquitous role in the Earth's
climate system, but their direct impact on atmospheric dynamics has escaped
wide attention. Here we examine and advance a theory as to how condensation
influences atmospheric pressure through the mass removal of water from the gas
phase with a simultaneous account of the latent heat release. Building from the
fundamental physical principles we show that condensation is associated with a
decline in air pressure in the lower atmosphere. This decline occurs up to a
certain height, which ranges from 3 to 4 km for surface temperatures from 10 to
30 deg C. We then estimate the horizontal pressure differences associated with
water vapor condensation and find that these are comparable in magnitude with
the pressure differences driving observed circulation patterns. The water vapor
delivered to the atmosphere via evaporation represents a store of potential
energy available to accelerate air and thus drive winds. Our estimates suggest
that the global mean power at which this potential energy is released by
condensation is around one per cent of the global solar power -- this is
similar to the known stationary dissipative power of general atmospheric
circulation. We conclude that condensation and evaporation merit attention as
major, if previously overlooked, factors in driving atmospheric dynamics.
We present a new statistical method to optimally link local weather extremes to large-scale atmospheric circulation structures. The method is illustrated using July-August daily mean temperature at 2m height (T2m) time-series over the Netherlands and 500 hPa geopotential height (Z500) time-series over the Euroatlantic region of the ECMWF reanalysis dataset (ERA40). The method identifies patterns in the Z500 time-series that optimally describe, in a precise mathematical sense, the relationship with local warm extremes in the Netherlands. Two patterns are identified; the most important one corresponds to a blocking high pressure system leading to subsidence and calm, dry and sunny conditions over the Netherlands. The second one corresponds to a rare, easterly flow regime bringing warm, dry air into the region. The patterns are robust; they are also identified in shorter subsamples of the total dataset. The method is generally applicable and might prove useful in evaluating the performance of climate models in simulating local weather extremes. Comment: 10 pages, 7 figures, 14 eps figure files; to appear in J. Atmos. Chem. Phys
This study shows that it is possible to retrieve the temporal evolution of cloud base heights in convective broken cloud fields from data of the SEVIRI instrument onboard the geostationary satellite Meteosat-9. Presented and
discussed are time dependent base heights with a temporal
resolution of 15 min from morning to afternoon. Cloud base heights retrieved from SEVIRI data are also compared with independent measurements of a ceilometer, with condensation levels calculated from radiosonde data and with
base heights obtained from an application of the method to NOAA/AVHRR data. The validation has been performed for three days in the year 2007 and for seven test areas distributed over Germany and neighbouring countries. The standard deviations of the absolute differences between cloud base heights from Meteosat-9 and radiosonde measurements as well as between NOAA/AVHRR and Meteosat-9 results are both of the order of ±290 m. The correlation coefficient
is 0.53 for the comparison of satellite with radiosonde measurements
and 0.78 for the intercomparison of the satellite measurements. Furthermore, it is shown that the method retrieves the temporal evolution of cloud base heights in very good agreement with time dependent ceilometer measurements.
A case study is presented on the formation and evolution of an ice-supersaturated region (ISSR) that was detected by a radiosonde in NE Germany at 06:00 UTC 29 November 2000. The ISSR was situated in the vicinity of the outflow region of a warm conveyor belt associated with an intense event of cyclogenesis in the eastern North Atlantic. Using ECMWF analyses and trajectory calculations it is determined when the air parcels became supersaturated and later subsaturated again. In the case considered, the state of air parcel supersaturation can last for longer than 24h. The ISSR was unusually thick: while the mean vertical extension of ISSRs in NE Germany is about 500m, the one investigated here reached 3km. The ice-supersaturated region investigated was bordered both vertically and horizontally by strongly subsaturated air. Near the path of the radiosonde the ISSR was probably cloud free, as inferred from METEOSAT infrared images. However, at other locations within the ISSR it is probable that there were cirrus clouds. Relative humidity measurements obtained by the Lindenberg radiosonde are used to correct the negative bias of the ECMWF humidity and to construct two-dimensional maps of ice supersaturation over Europe during the considered period. A systematic backward trajectory analysis for the ISSRs on these maps shows that the ISSR air masses themselves experienced only a moderate upward motion during the previous days, whereas parts of the ISSRs were located just above strongly ascending air masses from the boundary layer. This indicates qualitatively that warm conveyor belts associated with mid-latitude cyclogenesis are disturbances that can induce the formation of ISSRs in the upper troposphere. The ISSR maps also lead us to a new perception of ISSRs as large dynamic regions of supersaturated air where cirrus clouds can be embedded at some locations while there is clear air at others.
Atmospheric particle number size distributions of airborne particles (diameter range 10–500 nm) were collected over ten weeks at three sites in the vicinity of the A100 urban motorway in Berlin, Germany. The A100 carries about 180 000 vehicles on a weekday. The roadside particle distributions showed a number maximum between 20 and 60 nm clearly related to the motorway emissions. The average total number concentration at roadside was 28 000 cm−3 with a total range of 1200–168 000 cm−3. At distances of 80 and 400 m from the motorway the concentrations decreased to mean levels of 11 000 and 9000 cm−3, respectively. An obstacle-resolving dispersion model was applied to simulate the 3-D flow field and traffic tracer transport in the urban environment around the motorway. By inverse modelling, vehicle emission factors were derived that are representative of a fleet with a relative share of 6% lorry-like vehicles, and driving at a speed of 80 km h−1. Three different calculation approaches were compared, which differ in the choice of the experimental winds driving the flow simulation. The average emission factor per vehicle was 2.1 (±0.2) · 1014 km−1 for particle number and 0.077 (±0.01) · 1014 cm3 km−1 for particle volume. Regression analysis suggested that lorry-like vehicles emit 123 (±28) times more particle number than passenger car-like vehicles, and lorry-like vehicles account for about 91% of particulate number emissions on weekdays. Our work highlights the increasing applicability of 3-D flow models in urban microscale environments and their usefulness for determining traffic emission factors.
The European integrated project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) focuses on understanding the interactions of climate and air pollution. As part of the EUCAARI intensive observational period, an aircraft field campaign (EUCAARI-LONGREX) was conducted in May 2008. The campaign aimed at studying the distribution and evolution of air mass properties on a continental scale. Airborne aerosol and trace gas measurements were performed aboard the German DLR Falcon 20 and the British FAAM BAe-146 aircraft. This paper outlines the meteorological situation over Europe during May 2008 and the temporal and spatial evolution of predominantly anthropogenic particulate pollution inside the boundary layer and the free troposphere. Time series data of six selected ground stations are used to discuss continuous measurements besides the single flights. The observations encompass total and accumulation mode particle number concentration (0.1–0.8 μm) and black carbon mass concentration as well as several meteorological parameters. Vertical profiles of total aerosol number concentration up to 10 km are compared to vertical profiles probed during previous studies.
During the first half of May 2008 an anticyclonic blocking event dominated the weather over Central Europe. It led to increased pollutant concentrations within the centre of the high pressure inside the boundary layer. Due to long-range transport the accumulated pollution was partly advected towards Western and Northern Europe. The measured aerosol number concentrations over Central Europe showed in the boundary layer high values up to 14 000 cm−3 for particles in diameter larger 10 nm and 2300 cm−3 for accumulation mode particles during the high pressure period, whereas the middle free troposphere showed rather low concentrations of particulates. Thus a strong negative gradient of aerosol concentrations between the well mixed boundary layer and the clean middle troposphere occurred.
The first global tropospheric forecasts of O<sub>3</sub> and its precursors have been used in the daily flight planning of field measurement campaigns. The 3-D chemistry-transport model MATCH-MPIC is driven by meteorological data from a weather center (NCEP) to produce daily 3-day forecasts of the global distributions of O<sub>3</sub> and related gases, as well as regional CO tracers. This paper describes the forecast system and its use in three field campaigns, MINOS, CONTRACE and INDOEX. An overview is given of the forecasts by MATCH-MPIC and by three other chemical weather forecast models (EURAD, ECHAM, and FLEXPART), focusing on O<sub>3</sub> and CO. Total CO and regional CO tracers were found to be the most valuable gases for flight planning, due to their relatively well-defined anthropogenic source regions and lifetimes of one to a few months. CO was in good agreement with the observations on nearly all the flights (generally r > 0.7, and the relative RMS differences for the deviations from the means was less than 20%). In every case in which the chemical weather forecasts were primarily responsible for the flight plans, the targeted features were observed. Three forecasted phenomena are discussed in detail: outflow from Asia observed in the Mediterranean upper troposphere during MINOS, outflow from North America observed in the middle troposphere over northern Europe during CONTRACE, and the location of the "chemical ITCZ'' over the Indian Ocean during INDOEX. In particular it is shown that although intercontinental pollution plumes such as those observed during MINOS and CONTRACE occur repeatedly during the months around the campaigns, their frequency is sufficiently low (~10--30% of the time) that global chemical weather forecasts are important for enabling them to be observed during limited-duration field campaigns. The MATCH-MPIC chemical weather forecasts, including an interface for making customized figures from the output, are available for community use via http://www.mpch-mainz.mpg.de/~lawrence/forecasts.html .
A solar eclipse is a rare but spectacular natural
phenomenon and furthermore it is a challenge for radiative
transfer modelling. Whereas a simple one-dimensional radiative
transfer model with reduced solar irradiance at the
top of the atmosphere can be used to calculate the brightness
during partial eclipses a much more sophisticated model is
required to calculate the brightness (i.e. the diffuse radiation)
during the total eclipse. The reason is that radiation reaching
a detector in the shadow gets there exclusively by horizontal
transport of photons in a spherical shell atmosphere, which
requires a three-dimensional radiative transfer model. In this
study the first fully three-dimensional simulations for a solar
eclipse are presented exemplified by the solar eclipse at
29 March 2006. Using a backward Monte Carlo model we
calculated the diffuse radiation in the umbra and simulated
the changing colours of the sky. Radiance and irradiance are
decreased by 3 to 4 orders of magnitude, depending on wavelength.
We found that aerosol has a comparatively small impact
on the radiation in the umbra. We also estimated the
contribution of the solar corona to the radiation under the
umbra and found that it is negligible compared to the diffuse
solar radiation in the wavelength region from 310 to 500 nm.
A transient simulation with the interactively coupled
chemistry-climate model (CCM) E39/C has been carried
out which covers the 40-year period between 1960 and
1999. Forcing of natural and anthropogenic origin is prescribed
where the characteristics are sufficiently well known
and the typical timescales are slow compared to synoptic
timescale so that the simulated atmospheric chemistry and
climate evolve under a “slowly” varying external forcing.
Based on observations, sea surface temperature (SST) and
ice cover are prescribed. The increase of greenhouse gas and
chlorofluorocarbon concentrations, as well as nitrogen oxide
emissions are taken into account. The 11-year solar cycle is
considered in the calculation of heating rates and photolysis
of chemical species. The three major volcanic eruptions
during that time (Agung, 1963; El Chichon, 1982; Pinatubo,
1991) are considered. The quasi-biennial oscillation (QBO)
is forced by linear relaxation, also known as nudging, of the
equatorial zonal wind in the lower stratosphere towards observed
zonal wind profiles. Beyond a reasonable reproduction
of mean parameters and long-term variability characteristics
there are many apparent features of episodic similarities
between simulation and observation: In the years 1986
and 1988 the Antarctic ozone holes are smaller than in the
other years of that decade. In mid-latitudes of the Southern
Hemisphere ozone anomalies resemble the corresponding
observations, especially in 1985, 1989, 1991/1992, and
1996. In the Northern Hemisphere, the episode between
the late 1980s and the first half of the 1990s is dynamically
quiet, in particular, no stratospheric warming is found
between 1988 and 1993. As observed, volcanic eruptions
strongly influence dynamics and chemistry, though only for few years. Obviously, planetary wave activity is strongly
driven by the prescribed SST and modulated by the QBO.
Preliminary evidence of realistic cause and effect relationships
strongly suggests that detailed process-oriented studies
will be a worthwhile endeavour.
Dynamics and chemistry of the lower and middle stratosphere are characterized by manifold processes on different scales in time and space. The total column density of ozone, measured by numerous instruments, can be used to trace the resulting variability. In particular, satellite-borne spectrometers allow global observation of the total ozone distribution with proven accuracy and high temporal and spatial resolution. In order to analyse the zonal and hemispherical ozone variability a spectral statistical Harmonic Analysis is applied to multi-year total ozone observations from the Total Ozone Monitoring Spectrometer (TOMS). As diagnostic variables we introduce the hemispheric ozone variability indices one and two. They are defined as the hemispheric means of the amplitudes of the zonal waves number one and two, respectively, as traced by the total ozone field.
In order to demonstrate the capability of the diagnostic for intercomparison studies we apply the hemispheric ozone variability indices to evaluate total ozone fields of the coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM (hereafter: E39/C) against satellite observations. Results of a multi-year model simulation representing ''2000" climate conditions with an updated version of E39/C and corresponding total ozone data of TOMS from 1996 to 2004 (Version 8.0) are used. It is quantified to what extent E39/C is able to reproduce the zonal and hemispherical large scale total ozone variations. The different representations of the hemispheric ozone variability indices are discussed.
Summarizing the main differences of model and reference observations, we show that both indices, one and two, in E39/C are preferably too high in the Northern Hemisphere and preferably too low in the Southern Hemisphere. In the Northern Hemisphere, where the coincidence is generally better, E39/C produces a too strong planetary wave one activity in winter and spring as well as a too high interannual variability.
For the Southern Hemisphere we conclude that model and observations differ significantly during the ozone hole season. In October and November amplitudes of wave number one and two are underestimated. This explains that E39/C exhibits a too stable polar vortex and a too low interannual variability of the ozone hole. Further, a strong negative bias of wave number one amplitudes in the tropics and subtropics from October to December is identified, which may also contribute to the zonal-symmetric polar vortex. The lack of wave two variability in October and November leads to weak vortex elongation and eventually a too late final warming. Contrary, too high wave number two amplitudes in July and August indicate why the polar vortex is formed too late in season by E39/C.
In general, the hemispheric ozone variability indices can be regarded as a simple and robust approach to quantify differences in total ozone variability on a monthly mean basis. Therefore, the diagnostic represents a core diagnostic for model intercomparisons within the CCM Validation Activity for WCRP's (World Climate Research Programme) SPARC (Stratospheric Processes and their Role in Climate) regarding stratospheric dynamics.
Nitrogen oxide (NOx=NO+NO2) emissions from various sources contribute to the ozone budget. The identification of these contributions is important, e.g. for the assessment of emissions from traffic. The non-linear character of ozone chemistry complicates the online diagnosis during multi-decadal chemistry-climate simulations. A methodology is suggested, which is efficient enough to be incorporated in multi-decadal simulations. Eight types of NOx emissions are included in the model. For each a NOy (=all N components, except N2 and N2O) tracer and an ozone tracer is included in the model, which experience the same emissions and loss processes like the online chemistry fields. To calculate the ozone changes caused by an individual NOx emission, the assumption is made that the NOx contributions from various sources are identical to the NOy contributions. To evaluate this method each NOx emission has been increased by 5% and a detailed error analysis is given. In the regions of the main impact of individual sources the potential error of the calculated contribution is significantly smaller than the contribution. Moreover, the changes caused by an increase of the emissions of 5% were detected with a higher accuracy than the potential errror of the absolut contribution.
A set of performance metrics is applied to stratospheric-resolving chemistry-climate models (CCMs) to quantify their ability to reproduce key processes relevant for stratospheric ozone. The same metrics are used to assign a quantitative measure of performance (“grade”) to each model-observations comparison shown in Eyring et al. (2006). A wide range of grades is obtained, both for different diagnostics applied to a single model and for the same diagnostic applied to different models, highlighting the wide range in ability of the CCMs to simulate key processes in the stratosphere. No model scores high or low on all tests, but differences in the performance of models can be seen, especially for processes that are mainly determined by transport where several models get low grades on multiple tests. The grades are used to assign relative weights to the CCM projections of 21st century total ozone. For the diagnostics used here there are generally only small differences between weighted and unweighted multi-model mean and variances of total ozone projections. This study raises several issues with the grading and weighting of CCMs that need further examination. However, it does provide a framework and benchmarks that will enable quantification of model improvements and assignment of relative weights to the model projections.
Simulations of contrail-to-cirrus transition over up to 6 h were performed using a LES-model. The sensitivity of microphysical, optical and geometric contrail properties to relative humidity RHi, temperature T and vertical wind shear s was investigated in an extensive parametric study. The dominant parameter for contrail evolution is relative humidity. Substantial spreading is only visible for RHi≳120%. Vertical wind shear has a smaller effect on optical properties than human observers might expect from the visual impression. Our model shows that after a few hours the water vapour removed by falling ice crystals from the contrail layer can be several times higher than the ice mass that is actually present in the contrail at any instance.
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.
Mountain wave polar stratospheric clouds (PSCs) were detected on 8 February 2003 above the Scandinavian Mountains by in-situ instruments onboard the M55 Geophysica aircraft. PSC particle composition, backscatter and chlorine activation for this case are studied with a recently developed non-equilibrium microphysical box model for liquid aerosol. Results from the microphysical model, run on quasi-lagrangian trajectories, show that the PSC observed was composed of supercooled ternary (H2O/HNO3/H2SO4) solution (STS) particles, which are out of equilibrium with the gas phase. The measured condensed nitric acid and aerosol backscatter of the PSC can well be simulated with the model. Up to 0.15 ppbv Cl2 can be released by the PSC within 2 h, showing the propensity of these small-scale clouds for chlorine activation. Equilibrium calculations – of the sort commonly used in large scale chemistry transport models – overestimate the measured condensed nitrate by up to a factor of 3, and overestimates chlorine activation by 10%, in this mountain wave cloud