Scientific Publications

@article{sauvage2017,
title = {Source attribution using FLEXPART and carbon monoxide emission inventories: SOFT-IO version 1.0},
author = {B Sauvage and A Fontaine and S Eckhardt and A Auby and D Boulanger and H Petetin and R Paugam and G Athier and J -M Cousin and S Darras and P Nédélec and A Stohl and S Turquety and J -P Cammas and V Thouret},
url = {https://www.atmos-chem-phys.net/17/15271/2017/},
doi = {10.5194/acp-17-15271-2017},
year = {2017},
date = {2017-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {17},
number = {24},
pages = {15271-15292},
abstract = {Since 1994, the In-service Aircraft for a Global Observing System (IAGOS) program has produced in situ measurements of the atmospheric composition during more than 51 000 commercial flights. In order to help analyze these observations and understand the processes driving the observed concentration distribution and variability, we developed the SOFT-IO tool to quantify source–receptor links for all measured data. Based on the FLEXPART particle dispersion model (Stohl et al., 2005), SOFT-IO simulates the contributions of anthropogenic and biomass burning emissions from the ECCAD emission inventory database for all
locations and times corresponding to the measured carbon monoxide mixing ratios along each IAGOS flight. Contributions are simulated from emissions occurring during the last 20 days before an observation, separating individual contributions from the different source regions. The main goal is to supply added-value products to the IAGOS database by evincing the geographical origin and emission sources driving the CO enhancements observed in the troposphere and lower stratosphere. This requires a good match between observed and modeled CO enhancements. Indeed, SOFT-IO detects more than 95 % of the observed CO anomalies over
most of the regions sampled by IAGOS in the troposphere. In the majority of cases, SOFT-IO simulates CO pollution plumes with biases lower than 10–15 ppbv. Differences between the model and observations are larger for very low or very high observed CO values. The added-value products will help in the understanding of the trace-gas distribution and seasonal variability. They are available in the IAGOS database via http://www.iagos.org. The SOFT-IO tool could also be applied to similar data sets of CO observations (e.g., ground-based measurements, satellite observations). SOFT-IO could also be used for statistical validation as well as for intercomparisons of emission inventories using large amounts of data.},
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pubstate = {published},
tppubtype = {article}
}

@article{berkes2017,
title = {In situ temperature measurements in the upper troposphere and lowermost stratosphere from 2 decades of IAGOS long-term routine observation},
author = {F Berkes and P Neis and M G Schultz and U Bundke and S Rohs and H G J Smit and A Wahner and P Konopka and D Boulanger and P Nédélec and V Thouret and A Petzold},
url = {https://www.atmos-chem-phys.net/17/12495/2017/},
doi = {10.5194/acp-17-12495-2017},
year = {2017},
date = {2017-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {17},
number = {20},
pages = {12495-12508},
abstract = {Despite several studies on temperature trends in the tropopause region, a comprehensive understanding of the evolution of temperatures in this climate-sensitive region of the atmosphere remains elusive. Here we present a unique global-scale, long-term data set of high-resolution in situ temperature data measured aboard passenger aircraft within the European Research Infrastructure IAGOS (In-service Aircraft for a Global Observing System; http://www.iagos.org). This data set is used to investigate temperature trends within the global upper troposphere and lowermost stratosphere (UTLS,  <  13 km) for the period of 1995–2012 in different geographical regions and vertical layers of the UTLS. The largest number of observations is available over the North Atlantic. Here, a neutral temperature trend is found within the lowermost stratosphere. This contradicts the temperature trend in the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis, in which a significant (95 % confidence) temperature increase of +0.56 K decade−1 is found. Differences between trends derived from observations and reanalysis data can be traced back to changes in the temperature difference between observation and model data over the period studied. This study underpins the value of the IAGOS temperature observations as an anchor point for the evaluation of reanalyses and its suitability for independent trend analyses.},
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pubstate = {published},
tppubtype = {article}
}

@article{fischbeck2017,
title = {Acetone CO enhancement ratios in the upper troposphere based on 7 years of CARIBIC data: new insights and estimates of regional acetone fluxes},
author = {G Fischbeck and H Bönisch and M Neumaier and C A M Brenninkmeijer and J Orphal and J Brito and J Becker and D Sprung and P F J van Velthoven and A Zahn},
url = {http://www.atmos-chem-phys.net/17/1985/2017/},
doi = {10.5194/acp-17-1985-2017},
year = {2017},
date = {2017-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {17},
number = {3},
pages = {1985-2008},
publisher = {Copernicus GmbH},
abstract = {Acetone and carbon monoxide (CO) are two important trace gases controlling the oxidation capacity of the troposphere; enhancement ratios (EnRs) are useful in assessing their sources and fate between emission and sampling, especially in pollution plumes. In this study, we focus on in situ data from the upper troposphere recorded by the passenger-aircraft-based IAGOS–CARIBIC (In-service Aircraft for a Global Observing System–Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) observatory over the periods 2006–2008 and 2012–2015. This dataset is used to investigate the seasonal and spatial variation of acetone–CO EnRs. Furthermore, we utilize a box model accounting for dilution, chemical degradation and secondary production of acetone from precursors. In former studies, increasing acetone–CO EnRs in a plume were associated with secondary production of acetone. Results of our box model question this common presumption and show increases of acetone–CO EnR over time without taking secondary production of acetone into account. The temporal evolution of EnRs in the upper troposphere, especially in summer, is not negligible and impedes the interpretation of EnRs as a means for partitioning of acetone and CO sources in the boundary layer. In order to ensure that CARIBIC EnRs represent signatures of source regions with only small influences by dilution and chemistry, we limit our analysis to temporal and spatial coherent events of high-CO enhancement. We mainly focus on North America and Southeast Asia because of their different mix of pollutant sources and the good data coverage. For both regions, we find the expected seasonal variation in acetone–CO EnRs with maxima in summer, but with higher amplitude over North America. We derive mean (± standard deviation) annual acetone fluxes of (53 ± 27) 10−13 kg m−2 s−1 and (185 ± 80) 10−13 kg m−2 s−1 for North America and Southeast Asia, respectively. The derived flux for North America is consistent with the inventories, whereas Southeast Asia acetone emissions appear to be underestimated by the inventories.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{bieser2017,
title = {Multi-model study of mercury dispersion in the atmosphere: vertical and interhemispheric distribution of mercury species},
author = {J Bieser and F Slemr and J Ambrose and C Brenninkmeijer and S Brooks and A Dastoor and F DeSimone and R Ebinghaus and C N Gencarelli and B Geyer and L E Gratz and I M Hedgecock and D Jaffe and P Kelley and C -J Lin and L Jaegle and V Matthias and A Ryjkov and N E Selin and S Song and O Travnikov and A Weigelt and W Luke and X Ren and A Zahn and X Yang and Y Zhu and N Pirrone},
url = {https://www.atmos-chem-phys.net/17/6925/2017/},
doi = {10.5194/acp-17-6925-2017},
year = {2017},
date = {2017-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {17},
number = {11},
pages = {6925-6955},
abstract = {Atmospheric chemistry and transport of mercury play a key role in the global mercury cycle. However, there are still considerable knowledge gaps concerning the fate of mercury in the atmosphere. This is the second part of a model intercomparison study investigating the impact of atmospheric chemistry and emissions on mercury in the atmosphere. While the first study focused on ground-based observations of mercury concentration and deposition, here we investigate the vertical and interhemispheric distribution and speciation of mercury from the planetary boundary layer to the lower stratosphere. So far, there have been few model studies investigating the vertical distribution of mercury, mostly focusing on single aircraft campaigns. Here, we present a first comprehensive analysis based on various aircraft observations in Europe, North America, and on intercontinental flights.

The investigated models proved to be able to reproduce the distribution of total and elemental mercury concentrations in the troposphere including interhemispheric trends. One key aspect of the study is the investigation of mercury oxidation in the troposphere. We found that different chemistry schemes were better at reproducing observed oxidized mercury patterns depending on altitude. High concentrations of oxidized mercury in the upper troposphere could be reproduced with oxidation by bromine while elevated concentrations in the lower troposphere were better reproduced by OH and ozone chemistry. However, the results were not always conclusive as the physical and chemical parameterizations in the chemistry transport models also proved to have a substantial impact on model results.},
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pubstate = {published},
tppubtype = {article}
}

@article{eckstein2017,
title = {An assessment of the climatological representativeness of IAGOS-CARIBIC trace gas measurements using EMAC model simulations},
author = {J Eckstein and R Ruhnke and A Zahn and M Neumaier and O Kirner and P Braesicke},
url = {http://www.atmos-chem-phys.net/17/2775/2017/},
doi = {10.5194/acp-17-2775-2017},
year = {2017},
date = {2017-02-01},
journal = {Atmospheric Chemistry and Physics},
volume = {17},
pages = {2775-2794},
publisher = {Copernicus GmbH},
abstract = {Measurement data from the long-term passenger aircraft project IAGOS-CARIBIC are often used to derive climatologies of trace gases in the upper troposphere and lower stratosphere (UTLS). We investigate to what extent such climatologies are representative of the true state of the atmosphere. Climatologies are considered relative to the tropopause in mid-latitudes (35 to 75° N) for trace gases with different atmospheric lifetimes. Using the chemistry–climate model EMAC, we sample the modeled trace gases along CARIBIC flight tracks. Representativeness is then assessed by comparing the CARIBIC sampled model data to the full climatological model state. Three statistical methods are applied for the investigation of representativeness: the Kolmogorov–Smirnov test and two scores based on the variability and relative differences.

Two requirements for any score describing representativeness are essential: representativeness is expected to increase (i) with the number of samples and (ii) with decreasing variability of the species considered. Based on these two requirements, we investigate the suitability of the different statistical measures for investigating representativeness. The Kolmogorov–Smirnov test is very strict and does not identify any trace-gas climatology as representative – not even of long-lived trace gases. In contrast, the two scores based on either variability or relative differences show the expected behavior and thus appear applicable for investigating representativeness. For the final analysis of climatological representativeness, we use the relative difference score and calculate a representativeness uncertainty for each trace gas in percent.

In order to justify the transfer of conclusions about representativeness of individual trace gases from the model to measurements, we compare the trace gas variability between model and measurements. We find that the model reaches 50–100 % of the measurement variability. The tendency of the model to underestimate the variability is caused by the relatively coarse spatial and temporal model resolution.

In conclusion, we provide representativeness uncertainties for several species for tropopause-referenced climatologies. Long-lived species like CO2 have low uncertainties ( ≤ 0.4 %), while shorter-lived species like O3 have larger uncertainties (10–15 %). Finally, we translate the representativeness score into a number of flights that are necessary to achieve a certain degree of representativeness. For example, increasing the number of flights from 334 to 1000 would reduce the uncertainty in CO to a mere 1 %, while the uncertainty for shorter-lived species like NO would drop from 80 to 10 %.},
keywords = {},
pubstate = {published},
tppubtype = {article}
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@article{perimdefaria2017,
title = {Airborne and laboratory studies of an IAGOS instrumentation package containing a modified CAPS particle extinction monitor},
author = {J Perim de Faria and Bundke. U. and M Berg and Freedman. A. and T B Onasch and A Petzold},
url = {http://dx.doi.org/10.1080/02786826.2017.1355547},
doi = {10.1080/02786826.2017.1355547},
year = {2017},
date = {2017-01-01},
journal = {Aerosol Science and Technology},
pages = {1-14},
abstract = {An evaluation of the operation and performance of a Cavity Attenuated Phase-Shift Particle Extinction Monitor (CAPS PMex) was performed for use on board commercial aircraft as part of the research infrastructure IAGOS (In-service Aircraft for a Global Observing System, www.iagos.org). After extensive laboratory testing, a new flow system, using mass flow controllers, was installed to maintain constant purge and sample flows under low and varying pressure conditions. The instrument was then tested for pressures as low as 200 hPa and evaluated against particle-free compressed air and CO2. Extinction coefficients for the studied gases were in close agreement with literature values with differences between 2.2% and 8%, proving that the CAPS technology works at low pressures. The instrument's limit of detection, with respect to 3 times the variability of the background signal for the full pressure range, was 0.2 Mm−1 for 60s integration time. During its first research aircraft operations, the IAGOS instrument prototype, composed of one CAPS PMex and one OPC, showed excellent results regarding the stability of the instruments and the potential for characterizing different aerosol types and for estimating the contribution of sub- and super-μm sized particles to aerosol light extinction.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{feng2017,
title = {Consistent regional fluxes of CH4 and CO2 inferred from GOSAT proxy XCH4: XCO2 retrievals, 2010-2014},
author = {L Feng and P I Palmer and H Bösch and R J Parker and A J Webb and C S C Correia and N M Deutscher and L G Domingues and D G Feist and L V Gatti and E Gloor and F Hase and R Kivi and Y Liu and J B Miller and I Morino and R Sussmann and K Strong and O Uchino and J Wang and A Zahn},
url = {http://www.atmos-chem-phys.net/17/4781/2017/},
doi = {10.5194/acp-17-4781-2017},
year = {2017},
date = {2017-04-01},
journal = {Atmospheric Chemistry and Physics},
volume = {17},
number = {7},
pages = {4781-4797},
publisher = {Copernicus GmbH},
abstract = {We use the GEOS-Chem global 3-D model of atmospheric chemistry and transport and an ensemble Kalman filter to simultaneously infer regional fluxes of methane (CH4) and carbon dioxide (CO2) directly from GOSAT retrievals of XCH4 : XCO2, using sparse ground-based CH4 and CO2 mole fraction data to anchor the ratio. This work builds on the previously reported theory that takes into account that (1) these ratios are less prone to systematic error than either the full-physics data products or the proxy CH4 data products; and (2) the resulting CH4 and CO2 fluxes are self-consistent. We show that a posteriori fluxes inferred from the GOSAT data generally outperform the fluxes inferred only from in situ data, as expected. GOSAT CH4 and CO2 fluxes are consistent with global growth rates for CO2 and CH4 reported by NOAA and have a range of independent data including new profile measurements (0–7 km) over the Amazon Basin that were collected specifically to help validate GOSAT over this geographical region. We find that large-scale multi-year annual a posteriori CO2 fluxes inferred from GOSAT data are similar to those inferred from the in situ surface data but with smaller uncertainties, particularly over the tropics. GOSAT data are consistent with smaller peak-to-peak seasonal amplitudes of CO2 than either the a priori or in situ inversion, particularly over the tropics and the southern extratropics. Over the northern extratropics, GOSAT data show larger uptake than the a priori but less than the in situ inversion, resulting in small net emissions over the year. We also find evidence that the carbon balance of tropical South America was perturbed following the droughts of 2010 and 2012 with net annual fluxes not returning to an approximate annual balance until 2013. In contrast, GOSAT data significantly changed the a priori spatial distribution of CH4 emission with a 40 % increase over tropical South America and tropical Asia and a smaller decrease over Eurasia and temperate South America. We find no evidence from GOSAT that tropical South American CH4 fluxes were dramatically affected by the two large-scale Amazon droughts. However, we find that GOSAT data are consistent with double seasonal peaks in Amazonian fluxes that are reproduced over the 5 years we studied: a small peak from January to April and a larger peak from June to October, which are likely due to superimposed emissions from different geographical regions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{sahu2016,
title = {Impact of tropical convection and ENSO variability in vertical distributions of CO and O3 over an urban site of India},
author = {L K Sahu and V Sheel and M Kajino and M Deushi and S S Gunthe and P R Sinha and R Yadav and D Pal and P Nedelec and V Thouret and H G Smit},
url = {http://link.springer.com/article/10.1007%2Fs00382-016-3353-7},
doi = {10.1007/s00382-016-3353-7},
year = {2017},
date = {2017-07-01},
journal = {Climate Dynamics},
volume = {49},
number = {1-2},
pages = {449-469},
publisher = {Springer Nature},
abstract = {This study is based on the analysis of the measurement of ozone and water vapor by airbus in-service aircraft (MOZAIC) data of vertical ozone (O3) and carbon monoxide (CO) over Hyderabad during November 2005–March 2009. Measurements in the upper troposphere show highest values of O3 (53–75 ppbv) and CO (80–110 ppbv) during the pre-monsoon and post-monsoon seasons, respectively. The episodes of strong wind shears (>20 ms−1) were frequent during the monsoon/post-monsoon months, while weak shear conditions (<10 ms−1) were prevalent during the winter season. The profiles of both O3 and CO measured under southerly winds showed lower values than under northerly winds in each season. The strong and weak wind shears over the study region were associated with the El Niño and La Niña conditions, respectively. The outgoing long-wave radiation (OLR) and wind shear data indicate enhancement in the convective activity from monsoon to post-monsoon period. Higher levels of O3 were measured under the strong shear conditions, while CO and H2O show enhancements under weak shear conditions. The near surface observation and simulations show increase of O3 with increasing OLR, while insignificant relation in the upper region. In case of CO, the MOZAIC and CCM2 show weaker dependence while MOZART-4 shows rapid increase with OLR indicating large overestimation of convective transport. A modified Tiedtke convective scheme provides better representation compared to the Hack/Zhang-McFarlane schemes for both O3 and CO during the monsoon season. The difference between observation and simulations were particularly large during transition from El Niño to La Niña phases. The different convection scheme and horizontal resolution in the MOZART-4 and CCM2 seem to be the major causes of disagreement between these models. Vertical profiles of both O3 and CO during extreme events such a tropical cyclones (TCs) show strong influence of the convective-dynamics over Bay of Bengal (BOB).},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{weimer2017,
title = {An emission module for ICON-ART 2.0: implementation and simulations of acetone},
author = {M Weimer and J Schröter and J Eckstein and K Deetz and M Neumaier and G Fischbeck and L Hu and D B Millet and D Rieger and H Vogel and B Vogel and T Reddmann and O Kirner and R Ruhnke and P Braesicke},
url = {http://www.geosci-model-dev-discuss.net/gmd-2016-259/},
doi = {10.5194/gmd-2016-259},
year = {2017},
date = {2017-01-01},
journal = {Geoscientific Model Development Discussions},
volume = {10},
pages = {2471-2494},
publisher = {Copernicus GmbH},
abstract = {We present a new emissions module for the ICON (ICOsahedral Non-hydrostatic)-ART (Aerosols and Reactive Trace gases) modelling framework. The emissions module processes external flux data sets and increments the tracer volume mixing ratios in the boundary layer accordingly. In addition, the module for online calculations of biogenic emissions (MEGAN2.1) is implemented in ICON-ART and can replace the offline biogenic emission data sets.

The performance of the emissions module is illustrated with simulations of acetone, using a simplified chemical depletion mechanism based on a reaction with OH and photolysis only.

In our model setup, we calculate a tropospheric acetone lifetime of 33 days, which is in good agreement with the literature. We compare our results with airborne IAGOS-CARIBIC measurements in the upper troposphere and lowermost stratosphere (UTLS) in terms of phase and amplitude of the annual cycle. In all our ICON-ART simulations the general seasonal variability is well represented but questions remain concerning the magnitude of the acetone emissions and its atmospheric lifetime.

We conclude that the new emissions module performs well and allows the simulation of the annual cycles of emissions dominatedconcentrations even with a simple chemistry only.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{verma2017b,
title = {The constraint of CO2 measurements made onboard passenger aircraft on surface-atmosphere fluxes: the impact of transport model errors in vertical mixing},
author = {S Verma and J Marshall and C Gerbig and C R"odenbeck and K U Totsche},
url = {https://www.atmos-chem-phys.net/17/5665/2017/},
doi = {10.5194/acp-17-5665-2017},
year = {2017},
date = {2017-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {17},
number = {9},
pages = {5665-5675},
abstract = {Inaccurate representation of atmospheric processes by transport models is a dominant source of uncertainty in inverse analyses and can lead to large discrepancies in the retrieved flux estimates. We investigate the impact of uncertainties in vertical transport as simulated by atmospheric transport models on fluxes retrieved using vertical profiles from aircraft as an observational constraint. Our numerical experiments are based on synthetic data with realistic spatial and temporal sampling of aircraft measurements. The impact of such uncertainties on the flux retrieved using the ground-based network and those retrieved using the aircraft profiles are compared. We find that the posterior flux retrieved using aircraft profiles is less susceptible to errors in boundary layer height, compared to the ground-based network. This finding highlights a benefit of utilizing atmospheric observations made onboard aircraft over surface measurements for flux estimation using inverse methods. We further use synthetic vertical profiles of CO2 in an inversion to estimate the potential of these measurements, which will be made available through the IAGOS (In-service Aircraft for a Global Observing System) project in the future, in constraining the regional carbon budget. Our results show that the regions of tropical Africa and temperate Eurasia, that are under-constrained by the existing surface-based network, will benefit the most from these measurements, with a reduction of posterior flux uncertainty of about 7 to 10 %.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{verma2017,
title = {Extending methane profiles from aircraft into the stratosphere for satellite total column validation using the ECMWF C-IFS and TOMCAT/SLIMCAT 3-D model},
author = {S Verma and J Marshall and M Parrington and A Agustí-Panareda and S Massart and M P Chipperfield and C Wilson and C Gerbig},
url = {https://www.atmos-chem-phys.net/17/6663/2017/},
doi = {10.5194/acp-17-6663-2017},
year = {2017},
date = {2017-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {17},
number = {11},
pages = {6663-6678},
abstract = {Airborne observations of greenhouse gases are a very useful reference for validation of satellite-based column-averaged dry air mole fraction data. However, since the aircraft data are available only up to about 9–13 km altitude, these profiles do not fully represent the depth of the atmosphere observed by satellites and therefore need to be extended synthetically into the stratosphere. In the near future, observations of CO2 and CH4 made from passenger aircraft are expected to be available through the In-Service Aircraft for a Global Observing System (IAGOS) project. In this study, we analyse three different data sources that are available for the stratospheric extension of aircraft profiles by comparing the error introduced by each of them into the total column and provide recommendations regarding the best approach. First, we analyse CH4 fields from two different models of atmospheric composition – the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System for Composition (C-IFS) and the TOMCAT/SLIMCAT 3-D chemical transport model. Secondly, we consider scenarios that simulate the effect of using CH4 climatologies such as those based on balloons or satellite limb soundings. Thirdly, we assess the impact of using a priori profiles used in the satellite retrievals for the stratospheric part of the total column. We find that the models considered in this study have a better estimation of the stratospheric CH4 as compared to the climatology-based data and the satellite a priori profiles. Both the C-IFS and TOMCAT models have a bias of about −9 ppb at the locations where tropospheric vertical profiles will be measured by IAGOS. The C-IFS model, however, has a lower random error (6.5 ppb) than TOMCAT (12.8 ppb). These values are well within the minimum desired accuracy and precision of satellite total column XCH4 retrievals (10 and 34 ppb, respectively). In comparison, the a priori profile from the University of Leicester Greenhouse Gases Observing Satellite (GOSAT) Proxy XCH4 retrieval and climatology-based data introduce larger random errors in the total column, being limited in spatial coverage and temporal variability. Furthermore, we find that the bias in the models varies with latitude and season. Therefore, applying appropriate bias correction to the model fields before using them for profile extension is expected to further decrease the error contributed by the stratospheric part of the profile to the total column.},
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pubstate = {published},
tppubtype = {article}
}

@article{borsdorff2017,
title = {Carbon monoxide column retrieval for clear-sky and cloudy atmospheres: a full-mission data set from SCIAMACHY 2.3,unitmum reflectance measurements},
author = {T Borsdorff and J aan de Brugh and H Hu and P Nedelec and I Aben and J Landgraf},
url = {https://www.atmos-meas-tech.net/10/1769/2017/},
doi = {10.5194/amt-10-1769-2017},
year = {2017},
date = {2017-01-01},
journal = {Atmospheric Measurement Techniques},
volume = {10},
number = {5},
pages = {1769-1782},
abstract = {We discuss the retrieval of carbon monoxide (CO) vertical column densities from clear-sky and cloud contaminated 2311–2338 nm reflectance spectra measured by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) from January 2003 until the end of the mission in April 2012. These data were processed with the Shortwave Infrared CO Retrieval algorithm (SICOR) that we developed for the operational data processing of the Tropospheric Monitoring Instrument (TROPOMI) that will be launched on ESA's Sentinel-5 Precursor (S5P) mission. This study complements previous work that was limited to clear-sky observations over land. Over the oceans, CO is estimated from cloudy-sky measurements only, which is an important addition to the SCIAMACHY clear-sky CO data set as shown by NDACC and TCCON measurements at coastal sites. For Ny-Ålesund, Lauder, Mauna Loa and Reunion, a validation of SCIAMACHY clear-sky retrievals is not meaningful because of the high retrieval noise and the few collocations at these sites. The situation improves significantly when considering cloudy-sky observations, where we find a low mean bias b = ±6. 0 ppb and a strong correlation between the validation and the SCIAMACHY results with a mean Pearson correlation coefficient r = 0. 7. Also for land observations, cloudy-sky CO retrievals present an interesting complement to the clear-sky data set. For example, at the cities Tehran and Beijing the agreement of SCIAMACHY clear-sky CO observations with MOZAIC/IAGOS airborne measurements is poor with a mean bias of b = 171. 2 ppb and 57.9 ppb because of local CO pollution, which cannot be captured by SCIAMACHY. For cloudy-sky retrievals, the validation improves significantly. Here the retrieved column is mainly sensitive to CO above the cloud and so not affected by the strong local surface emissions. Adjusting the MOZAIC/IAGOS measurements to the vertical sensitivity of the retrieval, the mean bias adds up to b = 52. 3 ppb and 5.0 ppb for Tehran and Beijing. At the less urbanised region around the airport Windhoek, local CO pollution is less prominent and so MOZAIC/IAGOS measurements agree well with SCIAMACHY clear-sky retrievals with a mean bias of b = 15. 5 ppb, but can be even further improved for cloudy SCIAMACHY observations with a mean bias of b = 0. 2 ppb. Overall the cloudy-sky CO retrievals from SCIAMACHY short-wave infrared measurements present a major extension of the clear-sky-only data set, which more than triples the amount of data and adds unique observations over the oceans. Moreover, the study represents the first application of the S5P algorithm for operational CO data processing on cloudy observations prior to the launch of the S5P mission.},
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pubstate = {published},
tppubtype = {article}
}

@article{thorenz2017,
title = {Investigating African trace gas sources, vertical transport, and oxidation using IAGOS-CARIBIC measurements between Germany and South Africa between 2009 and 2011},
author = {U R Thorenz and A K Baker and E C Leedham Elvidge and C Sauvage and H Riede and P F J van Velthoven and M Hermann and A Weigelt and D E Oram and C A M Brenninkmeijer and A Zahn and J Williams},
url = {https://doi.org/10.1016/j.atmosenv.2017.03.021},
doi = {10.1016/j.atmosenv.2017.03.021},
year = {2017},
date = {2017-01-01},
journal = {Atmospheric Environment},
volume = {158},
pages = {11-26},
abstract = {Between March 2009 and March 2011 a commercial airliner equipped with a custom built measurement container (IAGOS-CARIBIC observatory) conducted 13 flights between South Africa and Germany at 10–12 km altitude, traversing the African continent north-south. In-situ measurements of trace gases (CO, CH4, H2O) and aerosol particles indicated that strong surface sources (like biomass burning) and rapid vertical transport combine to generate maximum concentrations in the latitudinal range between 10°N and 10°S coincident with the inter-tropical convergence zone (ITCZ). Pressurized air samples collected during these flights were subsequently analyzed for a suite of trace gases including C2-C8 non-methane hydrocarbons (NMHC) and halocarbons. These shorter-lived trace gases, originating from both natural and anthropogenic sources, also showed near equatorial maxima highlighting the effectiveness of convective transport in this region. Two source apportionment methods were used to investigate the specific sources of NMHC: positive matrix factorization (PMF), which is used for the first time for NMHC analysis in the upper troposphere (UT), and enhancement ratios to CO. Using the PMF method three characteristic airmass types were identified based on the different trace gas concentrations they obtained: biomass burning, fossil fuel emissions, and “background” air. The first two sources were defined with reference to previously reported surface source characterizations, while the term “background” was given to air masses in which the concentration ratios approached that of the lifetime ratios. Comparison of enhancement ratios between NMHC and CO for the subset of air samples that had experienced recent contact with the planetary boundary layer (PBL) to literature values showed that the burning of savanna and tropical forest is likely the main source of NMHC in the African upper troposphere (10–12 km). Photochemical aging patterns for the samples with PBL contact revealed that the air had different degradation histories depending on the hemisphere in which they were emitted. In the southern hemisphere (SH) air masses experienced more dilution by clean background air whereas in the northern hemisphere (NH) air masses are less diluted or mixed with background air still containing longer lived NMHC. Using NMHC photochemical clocks ozone production was seen in the BB outflow above Africa in the NH.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{baker2016,
title = {Evidence for strong, widespread chlorine radical chemistry associated with pollution outflow from continental Asia},
author = {A K Baker and C Sauvage and U R Thorenz and P van Velthoven and D E Oram and A Zahn and C A M Brenninkmeijer and J Williams},
url = {http://dx.doi.org/10.1038/srep36821},
doi = {10.1038/srep36821},
year = {2016},
date = {2016-01-01},
journal = {Scientific Reports},
volume = {6},
pages = {36821},
publisher = {Springer Nature},
abstract = {The chlorine radical is a potent atmospheric oxidant, capable of perturbing tropospheric oxidative cycles normally controlled by the hydroxyl radical. Significantly faster reaction rates allow chlorine radicals to expedite oxidation of hydrocarbons, including methane, and in polluted environments, to enhance ozone production. Here we present evidence, from the CARIBIC airborne dataset, for extensive chlorine radical chemistry associated with Asian pollution outflow, from airborne observations made over the Malaysian Peninsula in winter. This region is known for persistent convection that regularly delivers surface air to higher altitudes and serves as a major transport pathway into the stratosphere. Oxidant ratios inferred from hydrocarbon relationships show that chlorine radicals were regionally more important than hydroxyl radicals for alkane oxidation and were also important for methane and alkene oxidation (>10%). Our observations reveal pollution-related chlorine chemistry that is both widespread and recurrent, and has implications for tropospheric oxidizing capacity, stratospheric composition and ozone chemistry.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{rautheschoenach2016,
title = {Trapping, chemistry, and export of trace gases in the South Asian summer monsoon observed during CARIBIC flights in 2008},
author = {A Rauthe-Schöch and A K Baker and T J Schuck and C A M Brenninkmeijer and A Zahn and M Hermann and G Stratmann and H Ziereis and P F J van Velthoven and J Lelieveld},
url = {http://www.atmos-chem-phys.net/16/3609/2016/},
doi = {10.5194/acp-16-3609-2016},
year = {2016},
date = {2016-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {16},
number = {5},
pages = {3609-3629},
publisher = {Copernicus GmbH},
abstract = {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 aerosol particles measured by CARIBIC. Elevated levels of a variety of atmospheric pollutants (e.g. carbon monoxide, total reactive nitrogen oxides, aerosol particles, and several volatile organic compounds) were recorded. 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 distinct latitudinal patterns of trace gases during the entire monsoon period.

Using the CARIBIC trace gas and aerosol particle 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. The trajectory calculations indicate that these air masses originated mainly from South Asia and mainland Southeast Asia. Estimated photochemical ages of the air were found to agree well with transport times from a source region east of 90–95° E. The photochemical ages of the air in the southern part of the monsoon anticyclone were systematically younger (less than 7 days) and the air masses were mostly in an ozone-forming chemical mode. 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.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}