A. Richter

Universität Bremen, Bremen, Bremen, Germany

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Publications (501)849.01 Total impact

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    Atmospheric Chemistry and Physics 02/2015; 15(4):4265-4331. DOI:10.5194/acpd-15-4265-2015 · 4.88 Impact Factor
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    Geoscientific Model Development Discussions 01/2015; 8(2-2):1117-1169. DOI:10.5194/gmdd-8-1117-2015
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    ABSTRACT: In November 2011, ship-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were performed within the SHIVA campaign on board RV Sonne in the South China and Sulu Sea. Spectral measurements for a total of eleven days could be used to retrieve tropospheric slant column densities (SCDs) of nitrogen dioxide (NO2) and sulfur dioxide (SO2) in the marine environment. The NO2 fit was performed following recommendations developed during the CINDI campaign and adapted for the ship-based measurements. We found that the inclusion of a cross section for liquid water and an empirical correction spectrum accounting for the effects of liquid water and vibrational Raman scattering (VRS) slightly improved the NO2 fit quality, especially at lower elevation angles and for lower NO2 levels. The conversion of SCDs into tropospheric NO2 vertical columns (TVC NO2) has been achieved using both a simple geometric approach and the Bremian advanced MAX-DOAS Retrieval Algorithm (BREAM), which is based on the optimal estimation method and accounts for atmospheric radiative transfer. We found good agreement between the geometric approach using the 15° measurements and BREAM, revealing that measurements at 15° elevation angle can be used for retrieving TVC NO2 in tropical marine environments when SZA is smaller than 75°. As expected, the values of TVC NO2 were generally low (<0.5 × 1015 molec cm−2) when no sources of NOx were in proximity to the RV Sonne. However, we found increased values of TVC NO2 (>2 × 1015 molec cm−2) in the morning when the RV Sonne was heading along the coast of Borneo. This is in good agreement with satellite measurements. The results of the profile retrieval show that the boundary layer values of NO2 are <30 pptv in the open and clean tropical marine environment. Interestingly, we also found elevated tropospheric SO2 amounts for measurements taken in a busy shipping lane, consistent with the time series of tropospheric NO2.
    Atmospheric Environment 12/2014; 102:331-343. DOI:10.1016/j.atmosenv.2014.12.015 · 3.06 Impact Factor
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    Atmospheric Measurement Techniques 12/2014; DOI:10.5194/amt-7-4203-2014 · 3.21 Impact Factor
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    Atmospheric Measurement Techniques 12/2014; DOI:10.5194/amt-7-4133-2014 · 3.21 Impact Factor
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    Dataset: paper
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    ABSTRACT: Long time series of ozone and NO 2 total column measurements in the southern tropics are available from two ground-based SAOZ (Système d'Analyse par Observation Zénithale) UV-visible spectrometers operated within the Net-work for the Detection of Atmospheric Composition Change (NDACC) in Bauru (22 • S, 49 • W) in S-E Brazil since 1995 and Reunion Island (21 • S, 55 • E) in the S-W Indian Ocean since 1993. Although the stations are located at the same lat-itude, significant differences are observed in the columns of both species, attributed to differences in tropospheric con-tent and equivalent latitude in the lower stratosphere. These data are used to identify which satellites operating during the same period, are capturing the same features and are thus best suited for building reliable merged time series for trend studies. For ozone, the satellites series best matching SAOZ observations are EP-TOMS (1995–2004) and OMI-TOMS (2005–2011), whereas for NO 2 , best results are obtained by combining GOME version GDP5 (1996–2003) and SCIA-MACHY – IUP (2003–2011), displaying lower noise and seasonality in reference to SAOZ. Both merged data sets are fully consistent with the larger columns of the two species above South America and the seasonality of the differences between the two stations, reported by SAOZ, providing reli-able time series for further trend analyses and identification of sources of interannual variability in the future analysis.
    Atmospheric Measurement Techniques 10/2014; 7(10):3337-3354. DOI:10.5194/amt-7-3337-2014 · 3.21 Impact Factor
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    ABSTRACT: Total and tropospheric NO 2 columns have been operationally retrieved from the GOME-2/MetOp instruments since the first MetOp platform was put in orbit in October 2006. GOME-2 NO 2 data products are retrieved in three main steps: (1) a DOAS spectral analysis yielding the total column amount of NO 2 along the slant optical path, (2) an estimation of the stratospheric NO 2 column using tropospheric masking and spatial interpolation, to be subtracted from the total column to derive the tropospheric contribution, and (3) a conversion of the total and tropospheric slant columns into vertical columns based on airmass factor calculations which require a-priori knowledge of the NO 2 vertical distribution and surface albedo, as well as cloud information retrieved from GOME-2 spectra. In this study we combine correlative measurements available from complementary ground-based remote sensing networks to address the geophysical validation of the GOME-2 NO 2 data products. Zenith-sky DOAS/SAOZ measurements at the usually unpolluted stations of the NDACC network are used to validate the stratospheric NO 2 columns retrieved from the satellite, while direct-sun Pandora and multi-axis MAXDOAS data sets from a number of stations of the NDACC and MADRAS networks are used to investigate the consistency of GOME-2 total and tropospheric NO 2 columns in urban, sub-urban and background conditions. Results are discussed in terms of observed biases between satellite and ground-based data sets, their dependence on location, season and cloud conditions, and for the stratospheric columns, their photochemical effects.
    EUMETSAT conference, Geneva, Switzerland; 09/2014
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    ABSTRACT: A representation of atmospheric chemistry has been included in the Integrated Forecasting System (IFS) of the European Centre for Medium-range Weather Forecasts (ECMWF). The new chemistry modules complement the aerosol modules of the IFS for atmospheric Composition, which is named C-IFS. C-IFS for chemistry supersedes a coupled system, in which the chemical transport model (CTM) MOZART 3 was two-way coupled to the IFS (IFS-MOZART). This paper contains a description of the new on-line implementation, an evaluation with observations and a comparison of the performance of C-IFS with IFS-MOZART. The chemical mechanism of C-IFS is an extended version of the CB05 chemical mechanism as implemented in the CTM TM5. CB05 describes tropospheric chemistry with 54 species and 126 reactions. Wet deposition and lightning NO emissions are modelled in C-IFS using the detailed input of the IFS physics package. A one-year simulation for 2008 at a horizontal resolution of about 80 km is evaluated against ozone sondes, CO MOZAIC profiles, European surface observations of ozone, CO, SO2 and NO2 as well as satellite retrievals of CO, tropospheric NO2 and formaldehyde. MACCity anthropogenic emissions and biomass burning emissions from the GFAS data set were used in the simulations by both C-IFS and MOZART. C-IFS (CB05) showed an improved performance with respect to MOZART for CO, upper tropospheric ozone, winter time SO2 and was of a similar accuracy for other evaluated species. C-IFS (CB05) is about ten times more computationally efficient than IFS-MOZART.
    ECMWF Technical Memorandum 730; 09/2014
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    ABSTRACT: Current fire emission inventories apply universal emission factors (EFs) for the calculation of NOx emissions over large biomes such as boreal forest. However, recent satellite-based studies over tropical and subtropical regions have indicated spatio-temporal variations in EFs within specific biomes. In this study, satellite measurements of tropospheric NO2 vertical columns (TVC NO2) from the GOME-2 instrument and fire radiative power (FRP) from MODIS are used for the estimation of fire emission rates (FERs) of NOx over Eurasian and North American boreal forests. The retrieval of TVC NO2 is based on a stratospheric correction using simulated stratospheric NO2 instead of applying the reference sector method, which was used in a previous study. The model approach is more suitable for boreal latitudes. TVC NO2 and FRP are spatially aggregated to a 1° × 1° horizontal resolution and temporally averaged to monthly values. The conversion of the satellite-derived tropospheric NO2 columns into production rates of NOx from fire (Pf) is based on the NO2/NOx ratio as obtained from the MACC reanalysis data set and an assumed lifetime of NOx. A global land cover map is used to define boreal forests across these two regions in order to evaluate the FERs of NOx for this biome. The FERs of NOx, which are derived from the gradients of the linear relationship between Pf and FRP, are more than 30% lower for North American than for Eurasian boreal forest fires. We speculate that these discrepancies are mainly related to the variable nitrogen content in plant tissues, which is higher in deciduous forests dominating large parts in Eurasia. In order to compare the obtained values with EFs found in the literature, the FERs are converted into EFs. The satellite-based EFs of NOx are estimated at 0.83 and 0.61 g kg−1 for Eurasian and North American boreal forests, respectively, which is in good agreement with the value found in a recent emission factor compilation. However, recent fire emission inventories are based on EFs of NOx that are 3–5 times larger, which indicates that there are still large uncertainties in estimates of NOx from biomass burning, especially on the regional scale.
    Atmospheric Environment 08/2014; DOI:10.1016/j.atmosenv.2014.08.071 · 3.06 Impact Factor
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    ABSTRACT: We report on the evolution of tropospheric nitrogen dioxide (NO2) over Spain, focusing on the densely populated cities of Barcelona, Bilbao, Madrid, Sevilla and Valencia, during 17 years, from 1996 to 2012. This data series combines observations from in-situ air quality monitoring networks and the satellite-based instruments GOME and SCIAMACHY. The results in these five cities show a smooth decrease in the NO2 concentrations of ,2% per year in the period 1996–2008, due to the implementation of emissions control environmental legislation, and a more abrupt descend of,7% per year from 2008 to 2012 as a consequence of the economic recession. In the whole Spanish territory the NO2 levels have decreased by,22% from 1996 to 2012. Statistical analysis of several economic indicators is used to investigate the different factors driving the NO2 concentration trends over Spain during the last two decades.
    Scientific Reports 07/2014; 4(5887). DOI:10.1038/srep05887 · 5.08 Impact Factor
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    ABSTRACT: Tropospheric BrO was measured by a ground-based remote-sensing spectrometer at Halley in Antarctica in spring 2007, and BrO was measured by satellite-borne remote-sensing spectrometers using similar spectral regions and similar Differential Optical Absorption Spectroscopy (DOAS) analyses. Near-surface BrO was simultaneously measured in situ at Halley by Chemical Ionisation Mass Spectrometry (CIMS), and in an earlier year near-surface BrO was measured at Halley over a long path by a ground-based DOAS spectrometer. During enhancement episodes, total amounts of tropospheric BrO from the ground-based remote-sensor were similar to those from space, but if we assume that the BrO was confined to the mixed layer they were very much larger than values measured by either near-surface technique. This large apparent discrepancy can be resolved if substantial amounts of BrO were in the free troposphere during most enhancement episodes. Amounts observed by the ground-based remote sensor at different elevation angles, and their formal inversions to vertical profiles, demonstrate that much of the BrO was indeed often in the free troposphere. This is consistent with the ~5 day lifetime of Bry and with the enhanced BrO observed during some Antarctic blizzards.
    Journal of Quantitative Spectroscopy and Radiative Transfer 05/2014; 138. DOI:10.1016/j.jqsrt.2014.01.026 · 2.29 Impact Factor
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    ABSTRACT: We investigated the effect of surface reflectance anisotropy, Bidirectional Reflectance Distribution Function (BRDF), on satellite retrievals of tropospheric NO2. We assume the geometry of geostationary measurements over Tokyo, which is one of the worst air-polluted regions in the East Asia. We calculated air mass factors (AMF) and box AMFs (BAMF) for tropospheric NO2 to evaluate the effect of BRDF by using the radiative transfer model SCIATRAN. To model the BRDF effect, we utilized the Moderate Resolution Imaging Spectroradiometer (MODIS) products (MOD43B1 and MOD43B2), which provide three coefficients to express the RossThick-LiSparseReciprocal model, a semi-empirical and kernel-based model of BRDF. Because BRDF depends on the land cover type, we also utilized the High Resolution Land-Use and Land-Cover Map by the Advanced Land Observing Satellite (ALOS)/Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2), which classifies the ground pixels over Tokyo into six main types: water, urban, paddy, crop, deciduous forest and evergreen forest. We first develop an empirical model of the three BRDF coefficients for each land cover type over Tokyo, and then apply the model to the calculation of land cover type dependent AMFs and BAMFs. Results show that the variability of AMF among the land types is up to several tens percent, and if we neglect the reflectance anisotropy, the difference from BRDF's AMF reaches 10% or more. The evaluation of the BAMFs calculated shows that not to consider variations in BRDF will cause large errors if the concentration of NO2 is high close to the surface, although the importance of BRDF for AMFs decreases for large aerosol optical depth (AOD).
    Atmospheric Measurement Techniques 03/2014; 7(4). DOI:10.5194/amtd-7-3443-2014 · 3.21 Impact Factor
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    ABSTRACT: For the purpose of trace gas measurements and pollution mapping, the Airborne imaging DOAS instrument for Measurements of Atmospheric Pollution (AirMAP) has been developed, characterised and successfully operated from aircraft. From the observations with the AirMAP instrument nitrogen dioxide (NO2) columns were retrieved. A major benefit of the pushbroom imaging instrument is the spatially continuous, gap-free measurement sequence independent of flight altitude, a valuable characteristic for mapping purposes. This is made possible by the use of a frame-transfer detector. With a wide-angle entrance objective, a broad field-of-view across track of around 48° is achieved, leading to a swath width of about the same size as the flight altitude. The use of fibre coupled light intake optics with sorted light fibres allows flexible positioning within the aircraft and retains the very good imaging capabilities. The measurements yield ground spatial resolutions below 100 m. From a maximum of 35 individual viewing directions (lines of sight, LOS) represented by 35 single fibres, the number of viewing directions is adapted to each situation by averaging according to signal-to-noise or spatial resolution requirements. Exploitation of all the viewing directions yields observations at 30 m spatial resolution, making the instrument a suitable tool for mapping trace gas point sources and small scale variability. For accurate spatial mapping the position and aircraft attitude are taken into account using the Attitude and Heading Reference System of the aircraft. A first demonstration mission using AirMAP was undertaken. In June 2011, AirMAP has been operated on the AWI Polar-5 aircraft in the framework of the AIRMETH2011 campaign. During a flight above a medium sized coal-fired power plant in North-West Germany, AirMAP clearly detects the emission plume downwind from the exhaust stack, with NO2 vertical columns around 2 × 1016 molecules cm-2 in the plume center. The emission estimates are consistent with reports in the pollutant transfer register. Strong spatial gradients and variability in NO2 amounts across and along flight direction are observed, and small-scale enhancements of NO2 above a motorway are detected. The present study reports on the experimental setup and characteristics of AirMAP, and the first measurements at high spatial resolution and wide spatial coverage are presented which meet the requirements for NO2 mapping to observe and account for the intrinsic variability of tropospheric NO2.
    03/2014; 7(4). DOI:10.5194/amtd-7-3591-2014
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    ABSTRACT: Nitrogen oxides (NOx) play key roles in atmospheric chemistry, air pollution, and climate. While the largest fraction of these reactive gases is released by anthropogenic emission sources, a significant amount can be attributed to vegetation fires. In this study, NO2 from GOME-2 on board EUMETSAT's MetOp-A and OMI on board NASA's Aura as well as fire radiative power (FRP) from the measurements of MODIS on board NASA's Terra and Aqua satellites are used to derive fire emission rates (FERs) of NOx for different types of vegetation using a simple statistical approach. Monthly means of tropospheric NO2 vertical columns (TVC NO2) have been analyzed for their temporal correlation with the monthly means of FRP for five consecutive years from 2007 to 2011 on a horizontal 1° × 1° grid. The strongest correlation is found to be largely confined to tropical and subtropical regions, which account for more than 80% of yearly burned area, on average, globally. In these regions, the seasonal variation of fire intensity, expressed by the FRP data, is similar to the pattern of TVC NO2. As chemical models typically require values for the amount of NOx being released as a function of time, we have converted the retrieved TVC NO2 into production rates of NOx from fire (Pf) by assuming a constant lifetime of NOx. The comparison between Pf and NOx emissions from the Global Fire Emissions Database (GFEDv3.1) over 5 characteristic biomass burning regions in the tropics and subtropics shows good agreement. By separating the monthly means of Pf and FRP according to land cover type, FERs of NOx could be derived for different biomes. The estimated FERs for the dominating types of vegetation burned are lowest for open shrublands and savannas (0.28-1.03 g NOx s-1 MW-1) and highest for croplands and woody savannas (0.82-1.56 g NOx s-1 MW-1). This analysis demonstrates that the strong empirical relationship between TVC NO2 and FRP and the following simplified assumptions are a useful tool for the characterization of NOx emission rates from vegetation fires in the tropics and subtropics. Possible factors affecting the magnitude of the obtained values are discussed.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 02/2014; 14(5). DOI:10.5194/acp-14-2447-2014 · 5.30 Impact Factor
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    ABSTRACT: The ongoing regime shift of Arctic sea ice from perennial to seasonal ice is associated with more dynamic patterns of opening and closing sea-ice leads (large transient channels of open water in the ice), which may affect atmospheric and biogeochemical cycles in the Arctic. Mercury and ozone are rapidly removed from the atmospheric boundary layer during depletion events in the Arctic, caused by destruction of ozone along with oxidation of gaseous elemental mercury (Hg(0)) to oxidized mercury (Hg(ii)) in the atmosphere and its subsequent deposition to snow and ice. Ozone depletion events can change the oxidative capacity of the air by affecting atmospheric hydroxyl radical chemistry, whereas atmospheric mercury depletion events can increase the deposition of mercury to the Arctic, some of which can enter ecosystems during snowmelt. Here we present near-surface measurements of atmospheric mercury and ozone from two Arctic field campaigns near Barrow, Alaska. We find that coastal depletion events are directly linked to sea-ice dynamics. A consolidated ice cover facilitates the depletion of Hg(0) and ozone, but these immediately recover to near-background concentrations in the upwind presence of open sea-ice leads. We attribute the rapid recoveries of Hg(0) and ozone to lead-initiated shallow convection in the stable Arctic boundary layer, which mixes Hg(0) and ozone from undepleted air masses aloft. This convective forcing provides additional Hg(0) to the surface layer at a time of active depletion chemistry, where it is subject to renewed oxidation. Future work will need to establish the degree to which large-scale changes in sea-ice dynamics across the Arctic alter ozone chemistry and mercury deposition in fragile Arctic ecosystems.
    Nature 01/2014; DOI:10.1038/nature12924 · 42.35 Impact Factor
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    ABSTRACT: Record breaking loss of ozone (O3) in the Arctic transformations occurring in the Arctic polar vortex using total column and vertical profile data products for O3, bromine oxide (BrO), nitrogen dioxide (NO2), chlorine dioxide (OClO), and polar stratospheric clouds (PSC) retrieved from measurements made by SCIAMACHY (Scanning Imaging Absorption SpectroMeter for Atmospheric CHartography) onboard Envisat (Environmental Satellite), as well as total column ozone amount, retrieved from the measurements of GOME-2 (Global Ozone Monitoring Experiment) on MetOp-A (Meteorological Experimental Satellite). Similarly we use the retrieved data from DOAS (Differential Optical Absorption Spectroscopy) measurements made in NyÅlesund (78.55N, 11.55E). A chemical transport model (CTM) has been used to relate and compare Arctic winter– spring conditions in 2011 with those in the previous year. In late winter–spring 2010/2011 the chemical ozone loss in the polar vortex derived from SCIAMACHY observations confirms findings reported elsewhere. More than 70% of O3 was depleted by halogen catalytic cycles between the 425 and 525K isentropic surfaces, i.e. in the altitude range 16– 20 km. In contrast, during the same period in the previous winter 2009/2010, a typical warm Arctic winter, only slightly more than 20% depletion occurred below 20 km, while 40% of O3 was removed above the 575K isentrope (around 23 km). This loss above 575K is explained by the catalytic destruction by NOx descending from the mesosphere. In both Arctic winters 2009/2010 and 2010/2011, calculated O3 losses from the CTM are in good agreement to our observations and other model studies. The mid-winter 2011 conditions, prior to the catalytic cycles being fully effective, are also investigated. Surprisingly, a significant loss of O3 around 60 %, previously not discussed in detail, is observed in mid-January 2011 below 500K (around 19 km) and sustained for approximately 1 week. The low O3 region had an exceptionally large spatial extent. The situation was caused by two independently evolving tropopause elevations over the Asian continent. Induced adiabatic cooling of the stratosphere favoured the formation of PSC, increased the amount of active chlorine for a short time, and potentially contributed to higher polar ozone loss later in spring.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2014; 14(7):3247–3276. DOI:10.5194/acp-14-3247-2014 · 5.30 Impact Factor

Publication Stats

8k Citations
849.01 Total Impact Points

Institutions

  • 1970–2014
    • Universität Bremen
      • Institut für Umweltphysik (IUP)
      Bremen, Bremen, Germany
  • 2011
    • University of Toronto
      • Department of Physics
      Toronto, Ontario, Canada
  • 2008
    • Norwegian Institute for Air Research
      Kristiania (historical), Oslo County, Norway
  • 2007
    • German Aerospace Center (DLR)
      • Remote Sensing Technology Institute (IMF)
      Köln, North Rhine-Westphalia, Germany
  • 2004
    • Universität Heidelberg
      • Institute of Environmental Physics
      Heidelburg, Baden-Württemberg, Germany