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Stefan F. Schreier

Bio: Stefan F. Schreier is an academic researcher from University of Natural Resources and Life Sciences, Vienna. The author has contributed to research in topics: Environmental science & Differential optical absorption spectroscopy. The author has an hindex of 9, co-authored 20 publications receiving 247 citations. Previous affiliations of Stefan F. Schreier include International Institute for Applied Systems Analysis & University of Bremen.

Papers
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Journal ArticleDOI
TL;DR: The second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring instruments (CINDI-2) as discussed by the authors was held in 2016 and the three major goals of the campaign were (1) characterising and better understanding the differences between a large number of multi-axis differential optical absorption (MAX-DOAS) and zenith-sky DOAS instruments, (2) defining a robust methodology for performance assessment of all participating instruments, and (3) contributing to a harmonisation of the measurement settings and retrieval methods.
Abstract: . In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17 d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97 ∘ N, 4.93 ∘ E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation. The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide ( NO2 ), the oxygen collision complex ( O4 ) and ozone ( O3 ) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions. The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques.

54 citations

Journal ArticleDOI
TL;DR: In this paper, the authors developed an improved retrieval for glyoxal (CHOCHO) from measurements by the OMI instrument and determined a fitting window and a polynomial degree.
Abstract: . Satellite observations from the SCIAMACHY, GOME-2 and OMI spectrometers have been used to retrieve atmospheric columns of glyoxal (CHOCHO) with the DOAS method. High CHOCHO levels were found over regions with large biogenic and pyrogenic emissions, and hot-spots have been identified over areas of anthropogenic activities. This study focuses on the development of an improved retrieval for CHOCHO from measurements by the OMI instrument. From sensitivity tests, a fitting window and a polynomial degree are determined. Two different approaches to reduce the interference of liquid water absorption over oceanic regions are evaluated, achieving significant reduction of the number of negative columns over clear water regions. The impact of using different absorption cross-sections for water vapour is evaluated and only small differences are found. Finally, a high-temperature (boundary layer ambient: 294 K) absorption cross-section of nitrogen dioxide (NO2) is introduced in the DOAS retrieval to account for potential interferences of NO2 over regions with large anthropogenic emissions, leading to improved fit quality over these areas. A comparison with vertical CHOCHO columns retrieved from GOME-2 and SCIAMACHY measurements over continental regions is performed, showing overall good consistency. However, SCIAMACHY CHOCHO columns are systematically higher than those obtained from the other instruments. Using the new OMI CHOCHO data set, the link between fires and glyoxal columns is investigated for two selected regions in Africa. In addition, mapped averages are computed for a fire event in Russia between mid-July and mid-August 2010. In both cases, enhanced CHOCHO levels are found in close spatial and temporal proximity to elevated levels of MODIS fire radiative power, demonstrating that pyrogenic emissions can be clearly identified in the new OMI CHOCHO product.

44 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used a simple statistical approach to derive fire emission rates (FERs) of NOx for different types of vegetation using the monthly means of tropospheric NO2 vertical columns (TVC NO2) for five consecutive years from 2007 to 2011.
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.

35 citations

Journal ArticleDOI
TL;DR: In this paper, a 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.

35 citations

Journal ArticleDOI
01 Jan 2020
TL;DR: In this article, two recently installed MAX-DOAS instruments in Vienna, Austria, and evaluate horizontal path-averaged near-surface nitrogen dioxide (NO2), formaldehyde (HCHO), and glyoxal (CHOCHO) volume mixing ratios (VMRs) over the urban area by applying a state-of-the-art retrieval approach.
Abstract: We characterize two recently installed MAX-DOAS instruments in Vienna, Austria, and evaluate horizontal path-averaged near-surface nitrogen dioxide (NO2), formaldehyde (HCHO), and glyoxal (CHOCHO) volume mixing ratios (VMRs) over the urban area by applying a state-of-the-art retrieval approach. As Vienna is influenced by Pannonian continental climate, characterized by hot summers and cold winters, a temperature correction is introduced and applied to the NO2 differential slant column densities (DSCDs) retrieved in the visible spectral range to correct for the temperature dependence of the NO2 cross-section. The results show that not accounting for such a correction leads to an overestimation of absolute values by up to 15% in the winter season. Path-averaged NO2 VMRs from selected horizontal viewing directions are compared with surface NO2 VMRs from air quality monitoring stations located below and/or in close proximity to the particular MAX-DOAS line of sight. Good agreement between the two independent data sets is found, in particular during the summer season, with correlation coefficents ranging between 0.76 and 0.94. Seasonal and diurnal cycles of path-averaged NO2, HCHO, and CHOCHO VMRs are evaluated for a full year of measurements taken at the lowest elevation angles. While the highest daytime monthly averages of NO2 VMRs are found in winter, peaks of HCHO occur in summer. Highest amounts of CHOCHO conversely are observed over the course of the year, with the exception of summer. Seasonally-averaged diurnal cycles indicate that elevated NO2 and CHOCHO amounts are generally found in the morning hours and that there is a clear difference in trace gas amounts between weekdays and weekends when pointing at anthropogenic sources. The horizontal variabilty of tropospheric NO2, HCHO, and CHOCHO amounts is investigated by analyzing seasonally-averaged path-averaged VMRs, again obtained from measurements taken at the lowest elevation angles. The results show that highest amounts of NO2 and CHOCHO are found when the MAX-DOAS instruments are pointing towards the city center and/or towards busy roads and industrial areas, whereas highest amounts of HCHO are found over northern and western parts of Vienna, in particular in summer, which implies that anthropogenic sources are not the dominant drivers of HCHO production during that time of the year. Finally, the influence of wind direction and wind speed on tropospheric NO2, HCHO, and CHOCHO amounts is evaluted. The results show that tropospheric pollution levels over the city center of Vienna are highest at low wind speeds and wind directions from the Southeast.

26 citations


Cited by
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01 Jan 2011
TL;DR: The GMTED2010 layer extents (minimum and maximum latitude and longitude) are a result of the coordinate system inherited from the 1-arcsecond SRTM.
Abstract: For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. 10. Diagram showing the GMTED2010 layer extents (minimum and maximum latitude and longitude) are a result of the coordinate system inherited from the 1-arc-second SRTM

802 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented an updated compilation of biomass emission factors and derived estimates of pyrogenic emissions for important species released by the various types of biomass burning, using the same methodology as Andreae and Merlet(2001).
Abstract: . Since the publication of the compilation of biomass burning emission factors by Andreae and Merlet (2001), a large number of studies have greatly expanded the amount of available data on emissions from various types of biomass burning. Using essentially the same methodology as Andreae and Merlet (2001), this paper presents an updated compilation of emission factors. The data from over 370 published studies were critically evaluated and integrated into a consistent format. Several new categories of biomass burning were added, and the number of species for which emission data are presented was increased from 93 to 121. Where field data are still insufficient, estimates based on appropriate extrapolation techniques are proposed. For key species, the updated emission factors are compared with previously published values. Based on these emission factors and published global activity estimates, I have derived estimates of pyrogenic emissions for important species released by the various types of biomass burning.

364 citations

Journal ArticleDOI
TL;DR: In this article, a field survey was conducted in the city of Tel Aviv, Israel in several outdoor urban spaces during summers and winters of 2007-2011, accompanied by subjective thermal sensation questionnaires and the relation between the calculated PET values for the investigated sites and the Thermal Sensation Vote (TSV) were examined.

192 citations

Journal ArticleDOI
TL;DR: In this article, the authors present the new version (v14) of the BIRA-IASB algorithm for the retrieval of formaldehyde (H2CO) columns from spaceborne UV-visible sensors.
Abstract: . We present the new version (v14) of the BIRA-IASB algorithm for the retrieval of formaldehyde (H2CO) columns from spaceborne UV–visible sensors. Applied to OMI measurements from Aura and to GOME-2 measurements from MetOp-A and MetOp-B, this algorithm is used to produce global distributions of H2CO representative of mid-morning and early afternoon conditions. Its main features include (1) a new iterative DOAS scheme involving three fitting intervals to better account for the O2–O2 absorption, (2) the use of earthshine radiances averaged in the equatorial Pacific as reference spectra, and (3) a destriping correction and background normalisation resolved in the across-swath position. For the air mass factor calculation, a priori vertical profiles calculated by the IMAGES chemistry transport model at 09:30 and 13:30 LT are used. Although the resulting GOME-2 and OMI H2CO vertical columns are found to be highly correlated, some systematic differences are observed. Afternoon columns are generally larger than morning ones, especially in mid-latitude regions. In contrast, over tropical rainforests, morning H2CO columns significantly exceed those observed in the afternoon. These differences are discussed in terms of the H2CO column variation between mid-morning and early afternoon, using ground-based MAX-DOAS measurements available from seven stations in Europe, China and Africa. Validation results confirm the capacity of the combined satellite measurements to resolve diurnal variations in H2CO columns. Furthermore, vertical profiles derived from MAX-DOAS measurements in the Beijing area and in Bujumbura are used for a more detailed validation exercise. In both regions, we find an agreement better than 15 % when MAX-DOAS profiles are used as a priori for the satellite retrievals. Finally, regional trends in H2CO columns are estimated for the 2004–2014 period using SCIAMACHY and GOME-2 data for morning conditions, and OMI for early afternoon conditions. Consistent features are observed, such as an increase of the columns in India and central–eastern China, and a decrease in the eastern US and Europe. We find that the higher horizontal resolution of OMI combined with a better sampling and a more favourable illumination at midday allow for more significant trend estimates, especially over Europe and North America. Importantly, in some parts of the Amazonian forest, we observe with both time series a significant downward trend in H2CO columns, spatially correlated with areas affected by deforestation.

161 citations

01 Dec 2012
TL;DR: In this paper, the seasonal and diurnal cycles of the HONO near-surface concentration are found to be similar in shape and in relative amplitude to the corresponding cycles of HONNO total vertical column densities and are therefore likely driven mainly by the balance between NH sources and the photolytic sink, whereas dilution effects appear to play only a minor role.
Abstract: Ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements of nitrous acid (HONO) and its precursor NO2 (nitrogen dioxide) as well as aerosols have been performed daily in Beijing city centre (39.98° N, 116.38° E) from July 2008 to April 2009 and at the suburban site of Xianghe (39.75° N, 116.96° E) located ~60 km east of Beijing from March 2010 to December 2012. This extensive dataset allowed for the first time the investigation of the seasonal cycle of HONO as well as its diurnal variation in and in the vicinity of a megacity. Our study was focused on the HONO and NO2 near-surface concentrations (0–200 m layer) and total vertical column densities (VCDs) and also aerosol optical depths (AODs) and extinction coefficients retrieved by applying the Optimal Estimation Method to the MAX-DOAS observations. Monthly averaged HONO near-surface concentrations at local noon display a strong seasonal cycle with a maximum in late fall/winter (~0.8 and 0.7 ppb at Beijing and Xianghe, respectively) and a minimum in summer (~0.1 ppb at Beijing and 0.03 ppb at Xianghe). The seasonal cycles of HONO and NO2 appear to be highly correlated, with correlation coefficients in the 0.7–0.9 and 0.5–0.8 ranges at Beijing and Xianghe, respectively. The stronger correlation of HONO with NO2 and also with aerosols observed in Beijing suggests possibly larger role of NO2 conversion into HONO in the Beijing city center than at Xianghe. The observed diurnal cycle of HONO near-surface concentration shows a maximum in the early morning (about 1 ppb at both sites) likely resulting from night-time accumulation, followed by a decrease to values of about 0.1–0.4 ppb around local noon. The HONO / NO2 ratio shows a similar pattern with a maximum in the early morning (values up to 0.08) and a decrease to ~0.01–0.02 around local noon. The seasonal and diurnal cycles of the HONO near-surface concentration are found to be similar in shape and in relative amplitude to the corresponding cycles of the HONO total VCD and are therefore likely driven mainly by the balance between HONO sources and the photolytic sink, whereas dilution effects appear to play only a minor role. The estimation of OH radical production from HONO and O3 photolysis based on retrieved HONO near-surface concentrations and calculated photolysis rates indicate that in the 0–200 m altitude range, HONO is by far the largest source of OH radicals in winter as well as in the early morning at all seasons, while the contribution of O3 dominates in summer from mid-morning until mid-afternoon.

146 citations