Search

We report the oxygen isotopic anomaly (Δ17O) and clumped isotopic composition (Δ47) of CO2 sampled from the middle troposphere (~10 km above ground) during two CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) flights in summer and winter seasons: one from Düsseldorf to Isla Margarita on 11 August 2001 and the other from Puerto Plata to Munich on 21 February 2002. The mid‐tropospheric Δ17O values were higher than the near‐surface values by 0.051 ± 0.010 ‰, indicating enhanced stratospheric influence. The Δ47 values were also higher by 0.160 ± 0.015 ‰ compared to that from the lower troposphere. Stratospheric influence is supported by the observed correlations of the Δ17O values with the mixing ratios of N2O, O3, and 14CO, which carry stratospheric signatures. The increase in the anomaly in the free troposphere represents a balance between the stratosphere‐troposphere exchange fluxes and biogeochemical/hydrospheric isotopic resetting rates at the Earth surface. Using a simple two box model with the free tropospheric Δ17O values, an average surface exchange rate of CO2 between 327 and 772 PgC/year is inferred, giving a CO2 turnover time of 1.4 to 2.8 years in the atmosphere. The present estimates are based on a rather small set of free tropospheric data and have relatively large uncertainties, but they agree with the existing model and proxy‐based estimates.

Methane (CH4) is an important greenhouse gas, and its atmospheric budget is determined by interacting sources and sinks in a dynamic global environment. Methane observations indicate that after almost a decade of stagnation, from 2006, a sudden and continuing global mixing ratio increase took place. We applied a general circulation model to simulate the global atmospheric budget, variability, and trends of methane for the period 1997–2016. Using interannually constant CH4 a priori emissions from 11 biogenic and fossil source categories, the model results are compared with observations from 17 Advanced Global Atmospheric Gases Experiment (AGAGE) and National Oceanic and Atmospheric Administration (NOAA) surface stations and intercontinental Civil Aircraft for the Regular observation of the atmosphere Based on an Instrumented Container (CARIBIC) flights, with > 4800 CH4 samples, gathered on > 320 flights in the upper troposphere and lowermost stratosphere. Based on a simple optimization procedure, methane emission categories have been scaled to reduce discrepancies with the observational data for the period 1997–2006. With this approach, the all-station mean dry air mole fraction of 1780 nmol mol−1 could be improved from an a priori root mean square deviation (RMSD) of 1.31 % to just 0.61 %, associated with a coefficient of determination (R2) of 0.79. The simulated a priori interhemispheric difference of 143.12 nmol mol−1 was improved to 131.28 nmol mol−1, which matched the observations quite well (130.82 nmol mol−1). Analogously, aircraft measurements were reproduced well, with a global RMSD of 1.1 % for the measurements before 2007, with even better results on a regional level (e.g., over India, with an RMSD of 0.98 % and R2=0.65). With regard to emission optimization, this implied a 30.2 Tg CH4 yr−1 reduction in predominantly fossil-fuel-related emissions and a 28.7 Tg CH4 yr−1 increase of biogenic sources. With the same methodology, the CH4 growth that started in 2007 and continued almost linearly through 2013 was investigated, exploring the contributions by four potential causes, namely biogenic emissions from tropical wetlands, from agriculture including ruminant animals, and from rice cultivation, and anthropogenic emissions (fossil fuel sources, e.g., shale gas fracking) in North America. The optimization procedure adopted in this work showed that an increase in emissions from shale gas (7.67 Tg yr−1), rice cultivation (7.15 Tg yr−1), and tropical wetlands (0.58 Tg yr−1) for the period 2006–2013 leads to an optimal agreement (i.e., lowest RMSD) between model results and observations.

The CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) passenger aircraft observatory performed in situ measurements at 10–12 km altitude in the South Asian summer monsoon anticyclone between June and September 2008. These measurements enable us to investigate this atmospheric region, which so far has mostly been observed from satellites, using the broad suite of trace gases and aerosols measured by CARIBIC. Elevated levels of a range of atmospheric pollutants were recorded e.g. carbon monoxide, total reactive nitrogen oxides, aerosol particles and several volatile organic compounds. The measurements provide detailed information about the chemical composition of air in different parts of the monsoon anticyclone, particularly of ozone precursors. While covering a range of 3500 km inside the monsoon anticyclone, CARIBIC observations show remarkable consistency, i.e. with regular latitudinal patterns of trace gases during the entire monsoon period. Trajectory calculations indicate that these air masses originated mainly from South Asia and Mainland Southeast Asia. Using the CARIBIC trace gas and aerosol measurements in combination with the Lagrangian particle dispersion model FLEXPART we investigated the characteristics of monsoon outflow and the chemical evolution of air masses during transport. Estimated photochemical ages of the air were found to agree well with transport times from a source region east of 95° E. The photochemical ages of the air in the southern part of the monsoon anticyclone were consistently younger (less than 7 days) and the air masses mostly in an ozone forming chemical regime. In its northern part the air masses were older (up to 13 days) and had unclear ozone formation or destruction potential. Based on analysis of forward trajectories several receptor regions were identified. In addition to predominantly westward transport, we found evidence for efficient transport (within 10 days) to the Pacific and North America, particularly during June and September, and also of cross-tropopause exchange, which was strongest during June and July. Westward transport to Africa and further to the Mediterranean was the main pathway during July.

Impact of acetone (photo)oxidation on HOx production in the UT/LMS based on CARIBIC passenger aircraft observations and EMAC simulations

Between May 2005 and March 2008 the CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) observatory was deployed to make atmospheric observations on 42 flights between Frankfurt, Germany and Manila, the Philippines. This nearly 3 year flight series provides information about atmospheric composition in the upper troposphere over Europe and Asia during all seasons and was used to investigate seasonal and regional differences in trace gas distributions and the influence of long range transport and local convection on composition. The flight route was separated into three different regions having characteristic differences in transport and composition; these were Europe and Western Asia (5°E–60°E), Central Asia (60°E–100°E) and Southeast Asia (100°E–125°E). The region over Europe and Western Asia was strongly influenced by air masses from North America, while the region over Southeast Asia was mostly influenced by local emissions, particularly from biomass/biofuel burning as indicated by high levels of acetonitrile and carbon monoxide. Air masses over Central Asia were found to be influenced by both recent convection from the Indian subcontinent and mid-range transport from Europe, Western Asia and the Middle East. Elevated levels of propane and other non-methane hydrocarbons, both with and without concomitant elevations in other trace gases (i.e. carbon monoxide, acetonitrile) was a persistent feature over Central Asia in all seasons except summer, and were particularly prominent in fall. Influences on composition over Central Asia were investigated in detail for a case study from a series of flights in October 2006, where elevated levels of pollutants were found to be the result of convective transport of both biomass/biofuel burning and urban emissions from South Asia and fossil fuel related emissions from Eastern Europe.

A unique set of gaseous mercury measurements in the upper troposphere and lower stratosphere (UT/LS) has been obtained during the monthly CARIBIC (www. caribic-atmospheric. com) flights since May 2005. The passenger Airbus 340-600 of Lufthansa covered routes to the Far East, North America, India, and the southern hemisphere. The accompanying measurements of CO, O-3, NOy, H2O, aerosols, halocarbons, hydrocarbons, greenhouse gases, and several other parameters as well as backward trajectories enable a detailed analysis of these measurements. Speciation tests have shown that the CARIBIC measurements represent a good approximation of total gaseous mercury (TGM) concentrations. Above the tropopause TGM always decrease with increasing potential vorticity (PV) and O-3 which implies its conversion to particle bound mercury. The observation of the lowest TGM concentrations at the highest particle concentrations in the stratosphere provides further evidence for such conversion. We will show how a seasonally dependent conversion rate could be derived using concomitantly measured SF6 mixing ratios as a timer. Tropospheric mercury data suggest the existence of a decreasing trend in the northern hemisphere whose size is comparable with the trend derived from long- term measurements by ship cruises, at Cape Point (South Africa) and Mace Head (Ireland).

The chemistry in large thunderstorm clouds is influenced by local lightning-NOx production and uplift of boundary layer air. Under these circumstances trace gases like nitrous acid (HONO) or formaldehyde (HCHO) are expected to be formed or to reach the tropopause region. However, up to now only few observations of HONO at this altitude have been reported. Here we report on a case study where enhancements in HONO, HCHO and nitrogen oxides (NOx) were observed by the CARIBIC flying laboratory (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container). The event took place in a convective system over the Caribbean Sea in August 2011. Inside the cloud the light path reaches up to 100 km. Therefore the DOAS instrument on CARIBIC was very sensitive to the tracers inside the cloud. Based on the enhanced slant column densities of HONO, HCHO and NO2, average mixing ratios of 37, 468 and 210 ppt, respectively, were calculated. These data represent averages for constant mixing ratios inside the cloud. However, a large dependency on the assumed profile is found; for HONO a mixing ratio of 160 ppt is retrieved if the total amount is assumed to be situated in the uppermost 2 km of the cloud. The NO in situ instrument measured peaks up to 5 ppb NO inside the cloud; the background in the cloud was about 1.3 ppb, and hence clearly above the average outside the cloud (≈ 150 ppt). The high variability and the fact that the enhancements were observed over a pristine marine area led to the conclusion that, in all likelihood, the high NO concentrations were caused by lighting. This assumption is supported by the number of flashes that the World Wide Lightning Location Network (WWLLN) counted in this area before and during the overpass. The chemical box model CAABA is used to estimate the NO and HCHO source strengths which are necessary to explain our measurements. For NO a source strength of 10 × 109 molec cm−2 s−1 km−1 is found, which corresponds to the lightning activity as observed by the World Wide Lightning Location network, and lightning emissions of 5 × 1025 NO molec flash−1 (2.3–6.4 × 1025). The uncertainties are determined by a change of the input parameters in the box model, the cloud top height and the flash density. The emission rate per flash is scaled up to a global scale and 1.9 (1.4–2.5) tg N a−1 is estimated. The HCHO updraught is of the order of 120 × 109 molec cm−2 s−1 km−1. Also isoprene and CH3OOH as possible HCHO sources are discussed.

Carbon monoxide (CO) and other atmospheric trace constituents were measured from onboard an Airbus 340�600 passenger aircraft in the upper troposphere (UT) between south China and the Philippines during Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC) flights from May 2005 until March 2008. A total of 132 events having CO enhancements were observed in the UT over the region during the 81 CARIBIC flights from Frankfurt, Germany, to Manila, Philippines, with a stopover in Guangzhou, China. Among these, 51 high�CO events with enhancements more than 50 ppb above background were observed. For these events enhancements ranged from 52.7 to 221.3 ppb and persisted for 3 to 78 min (�40 to 1200 km), indicating an influence of strong pollution from biomass/biofuel/fossil fuel burning on the trace gas composition of the UT. Back trajectory analysis shows that south China, the Indochinese Peninsula, and the Philippines/Indonesia are the main source regions of the high�CO events. The composition of air parcels originating from south China was found to be primarily influenced by anthropogenic urban/industrial emissions, while emissions from biomass/biofuel burning contributed substantially to CO enhancements from the Indochinese Peninsula. During the Philippines/Indonesia events, air parcel composition suggests contributions from both biomass/biofuel burning and urban/industrial sources. Long�range transport of air parcels from northeast Asia and India also contributed to CO enhancements in the UT over the region. The general features of regional influence, typical cases, and the contributions of biomass/biofuel burning and anthropogenic emissions are presented and discussed to characterize the air parcels during the observed high�CO events.

The origin of aerosol particles in the upper troposphere and lowermost stratosphere over the Eurasian continent was investigated by applying cluster analysis methods to in situ measured data. Number concentrations of submicrometer aerosol particles and trace gas mixing ratios derived by the CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container) measurement system on flights between Germany and South-East Asia were used for this analysis. Four cluster analysis methods were applied to a test data set and their capability of separating the data points into scientifically reasonable clusters was assessed. The best method was applied to seasonal data subsets for summer and winter resulting in five cluster or air mass types: stratosphere, tropopause, free troposphere, high clouds, and boundary layer influenced. Other source clusters, like aircraft emissions could not be resolved in the present data set with the used methods. While the cluster separation works satisfactory well for the summer data, in winter interpretation is more difficult, which is attributed to either different vertical transport pathways or different chemical lifetimes in both seasons. The geographical distribution of the clusters together with histograms for nucleation and Aitken mode particles within each cluster are presented. Aitken mode particle number concentrations show a clear vertical gradient with the lowest values in the lowermost stratosphere (750–2820 particles/cm3 STP, minimum of the two 25% – and maximum of the two 75%-percentiles of both seasons) and the highest values for the boundary-layer-influenced air (4290–22 760 particles/cm3 STP). Nucleation mode particles are also highest in the boundary-layer-influenced air (1260–29 500 particles/cm3 STP), but are lowest in the free troposphere (0–450 particles/cm3 STP). The given submicrometer particle number concentrations represent the first large-scale seasonal data sets for the upper troposphere and lowermost stratosphere over the Eurasian continent.

Total gaseous mercury (TGM) was measured onboard a passenger aircraft during monthly CARIBIC flights (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrumented Container) made between May 2005 and March 2007 on the routes Frankfurt–São Paulo–Santiago de Chile and back and Frankfurt–Guangzhou–Manila and back. The data provide for the first time an insight into the seasonal distributions of TGM in the upper troposphere and lower stratosphere (UT/LS) of both hemispheres and demonstrate the importance of mercury emissions from biomass burning in the Southern Hemisphere. Numerous plumes were observed in the upper troposphere, the larger of which could be characterized in terms of Hg/CO emission ratios and their probable origins. During the flights to China TGM correlated with CO in the upper troposphere with a seasonally dependent slope reflecting the longer lifetime of elemental mercury when compared to that of CO. A pronounced depletion of TGM was always observed in the extratropical lowermost stratosphere. TGM concentrations there were found to decrease with the increasing concentrations of particles. Combined with the large concentrations of particle bond mercury in the stratosphere observed by others, this finding suggests either a direct conversion of TGM to particle bound mercury or an indirect conversion via a semivolatile bivalent mercury compound. Based on concurrent measurements of SF6 during two flights, the rate of this conversion is estimated to 0.4 ng m−3 yr−1. A zero TGM concentration was not observed during some 200 flight hours in the lowermost stratosphere suggesting an equilibrium between the gaseous and particulate mercury.

Particle number and mass concentrations of submicrometer aerosol particles were determined for the upper troposphere over the mid-latitude North Atlantic within the Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container project (CARIBIC, http://www.caribic-atmospheric.com). Between May 2001 and April 2002, 22 flights from Germany to the Caribbean were conducted using an automated measurement container on a B767 passenger aircraft. Spatial and seasonal probability distributions for ultrafine and Aitken mode particles as well as mass concentrations of particulate sulphur in 8–12 km altitude are presented. High particle number concentrations (mostly 2500–15 000 particles cm -3 STP) are particularly found in summer over the western North Atlantic Ocean close to the North American continent. The distributions together with an analysis of particle source processes show that deep vertical transport is the dominant process leading to most of the events with high particle number concentrations (≳8000 particles cm -3 STP) for ultrafine particles as well as for Aitken mode particles. This study emphasizes the importance of deep vertical transport and cloud processing for the concentration of aerosol particles in the upper troposphere. DOI: 10.1111/j.1600-0889.2007.00323.x

Measurements of nitrogen oxides performed in the upper troposphere and lower stratosphere are presented. NO and NOy measurements contribute to the identification of specific sources determining the trace gas budget around the tropopause. These observations were carried out within the CARIBIC project (Civil aircraft for the regular investigation on the atmosphere based on an instrument container). Since its first deployment in spring 2002 the NO and NOy instrument has been successfully operated during more than 70 flights with a Lufthansa Airbus. Most of the flights have been performed between Germany and South America (Sao Paulo and Santiago de Chile) and between Germany and the Far East (Guangzhou and Manila). During these long-haul flights NO and NOy concentrations in the upper troposphere and lowermost stratosphere have been determined along with species as CO, O3, particles, and others. These data were used to study the influence of long range transport, deep convection, lightning, and air traffic emissions on the nitrogen oxides budget in the UTLS region. Case studies and correlation analyses are presented. First attempts have also been made at assessing the seasonal variation of nitrogen oxides in the probed UTLS region. Average NO and NOy concentrations obtained during CARIBIC are compared to the results obtained during other aircraft measuring campaigns like NOXAR and SCOUT.

The aim of this work was to study atmospheric aerosols, focusing on the chemical composition, the morphology and the origin of the aerosol in the upper troposphere and lowermost stratosphere. An aerosol sampler was developed for this purpose. A new method for quantitative analysis of the major components of the aerosol, i.e. C, N and O was developed, and methodologies for single-particle analysis to gain information on particle morphology and chemical composition were adapted and used for the aerosol samples. Samples collected during 60 intercontinental flights from 1999 to 2002 were analysed with regard to elemental composition with particle-induced X-ray emission. The results were used to study the properties and the origin of the aerosol in the lowermost stratosphere at northern mid-latitudes, focusing on the sulphur concentration. The results of this study show that particulate potassium and iron in the lowermost stratosphere originate in the troposphere and are transported across the tropopause, whereas particulate sulphur has a strong stratospheric origin in addition to transport across the tropopause. Approximately half of the mass of particulate sulphur transported from the stratospheric overworld to the lowermost stratosphere was formed from carbonyl sulphide the remainder being dominated by particulate sulphur and sulphur dioxide that was transported across the tropical tropopause. The production of particulate sulphur in the stratosphere was estimated to be 0.066 Tg S/y. A new multi-channel aerosol sampler was developed and calibrated for the second phase of the CARIBIC project, which improved the time resolution and produced samples for quantitative and individual particle analyses. It was found that the collection efficiency of the sampler was as high as 97% for particles larger than approximately 0.2 µm in diameter, and the cut-off was 0.08 µm at the calibration conditions. The time resolution of each sample was 1.5 hours. This sampler is a powerful tool for aerosol characterization from an aircraft. A new method for the analysis of carbon, nitrogen and oxygen based on the use of PESA has been developed for use on CARIBIC samples, which are collected on an organic backing film. For example, the detection limits of C, N O, S and Fe are 3, 1, 2, 2 and 0.1 ng/m3, normalized to STP. This analytical protocol is truly unique because it offers low detection limits and high analytical capability over a wide range of elements. Moreover, it yields quantitative information. This is the first quantitative measurement of the concentration of the carbonaceous aerosol component and other components such as N and O in the upper troposphere and the lowermost stratosphere. It was found that they, together with sulphur, are the major constituents of the aerosol in this region. Individual particles? characteristics have also been studied based on classification of individual particles with respect to morphology and composition along a transect from 50º N to 30º at 10 km altitude. The classification comprised of more than 30 particle types. Their morphology is complex and varied. A dependence of morphology on the location where they were collected was found. For further investigation of these aerosol particles, chemical analysis was undertaken. Two techniques, PIXE and PESA, were used to quantitatively determine the concentration of carbon and sulphur. Then the particulate carbon to sulphur ratio was used to express the composition of the samples. This ratio varied over the aerosol samples in a range 0.5 to 3.5. The largest value of this ratio appears at around the equator, south of ITCZ, whereas the lowest one was found in the lowermost stratosphere. Further chemical investigation using EFTEM was made to reveal the distributions of carbonaceous and sulphurous matter of individual particles. The results were used to explain the complex structures and the large variation in morphology of the aerosol from different regions. Particles with satellite patterns usually are interpreted as being composed of sulfuric acid. Analyses by EFTEM presented here show that these particles have a central particle composed of both carbonaceous and sulfurous matter and the satellites are composed of carbonaceous matter. Hence a morphological analysis alone could erroneously classify these mixed particles as being pure sulfuric acid. Små partiklar i form av vätska eller fast material mellan 0.001 till 100 µm i diameter, kan sväva i luften och kallas då aerosolpartiklar. De påverkar direkt på klimatet genom att reflektera solstrålar ut till rymden. Detta gör att vi får ett kallare klimat. Indirekt kan de påverka klimatet genom att verka som kondensationskärnor vid molnbildning. Med detta påverkar de molnens strålningsegenskaper och livstid. Trots deras viktiga roll för klimat är kunskap om dem mycket mager. Min forskning gick ut på att utvidga den befintliga kunskapen om aerosolernas kemiska sammansättning, deras morfologi och ursprung. För detta syfte utvecklades en aerosolprovtagare, en ny metod för att kunna göra kvantitativ analys på huvudämnen (C, N och O) som finns i aerosolpartiklar och en ny metodik för att studera enskilda aerosolpartiklars morfologi och kemiska sammansättning. I det första arbetet analyserades prover som samlades under 60 flygningar mellan 1999 till 2002 för selektiva grundämnen med hjälp av den känsliga PIXE-metoden. Analysresultat användes sedan för att studera egenskaper av och källa till aerosoler i den lägsta delen av stratosfären vid norra jordklotets mittlatitud. Det visade sig att kalium och järn som finns på aerosol partiklar i den lägsta delen av stratosfären kommer från troposfären over tropopausen. Resultatet visade också att svavel transporterades till den lägsta delen av stratosfären från högre nivå i stratosfären samt från troposfären över tropopausen. En mångkanalprovtagare utvecklades och kalibrerades för användning inom ett internationellt projekt, CARIBIC (Civil Aircraft for Regular Investigations of the atmosphere Based on an Instrument Container). Med den här provtagaren förbättrades tidsupplösningen för provtagning av aerosol. Dessutom kan prov samlas för både kvantitativ analys och individuell partikelanalys. Vidare är insamlingseffektivitet 97 % för partiklar med diameter större än eller lika med 0.2 µm. Den är ett effektivt instrument for karakterisering av aerosolpartikel från ett flygplan. Utveckling av en ny metod för analys av kol, kväve och syre baserad på PESA-metod (particle elastic scattering analysis) genomfördes. Med den här metoden kan man analysera t.ex. ett kolrikt ämne som finns på ett underlag som just innehåller ämnet. Med hjälp av metoden kan man för första gången kvantitativt studera kol, kväve och syre i partiklar från övre troposfären och lägsta stratosfären. Mätningarna visar bl.a. att de här ämnena tillsammans med svavel är huvudämnen på aerosoler i tropopausområdet. Slutlighen har jag utvecklat en ny metodik för att studera individuella partiklar från tropopausen och mellan södra och norra jordklotet. Den går ut på att klassificera enskilda partiklars utseende och kemiska sammansättning längs flygrutten. Partiklarnas morfologi och kemiska sammansättning varierade med position där de samlades. Bland annat kan man hitta stora partiklar med komplicerad struktur på norra jordklotet och södra jordklotets midlatituder. Partiklar i över troposfären kan ha bildats där uppe genom koagulation och olika gas-till- partikelprocesser. Partiklar i den lägsta delen av stratosfären visade sig vara mer grenad struktur än de som fanns på övre troposfären. Detta beror troligen på att stratosfäriska partiklar befanns sig en längre tid i atmosfären än troposfäriska partiklar.

A strong pollution episode in the upper troposphere between South China and the Philippines was observed during CARIBIC flights in April 2007. Five pollution events were observed, where enhancements in aerosol and trace gas concentrations including CO, CO2, CH4, non-methane hydrocarbons (NMHCs) and halocarbons were observed along the flight tracks during four sequential flights. The importance of the contribution of biomass/biofuel burning was investigated using chemical tracers, emission factor analysis, back-trajectory analysis and satellite images. The Indochinese peninsula was identified as the probable source region of biomass/biofuel burning. However, enhancements in the urban/industrial tracer C2Cl4 during the events also indicate a substantial contribution from urban anthropogenic emissions. An estimation of the contribution of fossil fuel versus biomass/biofuel to the CO enhancement was made, indicating a biomass/biofuel burning contribution of ~54 to ~92% of the observed CO enhancements. Biomass/biofuel burning was found to be the most important source category during the sampling period.