bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Primary combustion source organic carbon-to-elemental carbon (OC/EC) ratio using ambient OC and EC measurements: Secondary OC-EC correlation minimization method
Authors: Wu Cheng , Yu Jian Zhen
Published: January 2016

Abstract. Elemental carbon (EC), due to its exclusive origin in primary combustion sources, has been widely used as a tracer to track the portion of co-emitted primary organic carbon (OC) and, by extension, to estimate secondary OC (SOC) from ambient observations of EC and OC. Key to this EC tracer method is to determine an appropriate OC/EC ratio that represents primary combustion emission sources (i.e., (OC/EC)pri) at the observation site. The conventional approaches include regressing OC against EC within a fixed percentile of the lowest (OC/EC) ratio data (usually 5-20%) or relying on a subset of sampling days with low photochemical activity and dominated by local emissions. The drawback of these approaches is rooted in its empirical nature, i.e., a lack of clear quantitative criteria in the selection of data subsets for the (OC/EC)pri determination. We examine here a method that derives (OC/EC)pri through calculating a hypothetical set of (OC/EC)pri and SOC followed by seeking the minimum of the coefficient of correlation (R2) between SOC and EC. The hypothetical (OC/EC)pri that generates the minimum R2(SOC,EC) then represents the actual (OC/EC)pri ratio if variations of EC and SOC are independent. This Minimum R Squared (MRS) method has a clear quantitative criterion for the (OC/EC)pri calculation. The general concept embodied in the MRS method was initially proposed by Miller et al (2005), but has not been evaluated for accuracy or utility since its debut. This work uses numerically simulated data to evaluate the accuracy of SOC estimation by the MRS method and to compare with two commonly used methods: minimum OC/EC (OC/ECmin) and OC/EC percentile (OC/EC10%). Log-normally distributed EC and OC concentrations with known proportion of SOC are numerically produced through a Mersenne twister pseudorandom number generator. Three scenarios are considered, including a single primary source, two independent primary sources, and two correlated primary sources. Among the three SOC estimation methods, the MRS method consistently yields the most accurate SOC estimation. Unbiased SOC estimation by OC/ECmin and OC/EC10% only occur when the left tail of OC/EC distribution is aligned with the peak of the (OC/EC)pri distribution, which is fortuitous rather than norm. In contrast, MRS provides an unbiased SOC estimation since it is insensitive to the position of (OC/EC)pri relative to the (OC/EC) distribution. Sensitivity tests of OC and EC measurement uncertainty on SOC estimation demonstrate the superior accuracy of MRS over the other two approaches.
Hotspot of Glyoxal Over the Pearl River Delta Seen from the OMI Satellite Instrument: Implications for Emissions of Aromatic Hydrocarbons
Authors: Chan Miller Christopher , Jacob Daniel J. , González Abad Gonzalo , Chance Kelly
Published: January 2016

Abstract. The Pearl River Delta (PRD) is a densely populated hub of industrial activity located in southern China. OMI satellite observations reveal a large hotspot of glyoxal (CHOCHO) over the PRD that is almost twice as large as any other in Asia. Formaldehyde (HCHO) and NO2 observed by OMI are also high in the PRD but no more than in other urban/industrial areas of China. The CHOCHO hotspot in the PRD can be explained by industrial paint and solvent emissions of aromatic volatile organic compounds (VOCs), with toluene being a dominant contributor. By contrast, HCHO in the PRD originates mostly from VOCs emitted by combustion (principally vehicles). By applying a plume transport model to wind-segregated OMI data, we show that the CHOCHO and HCHO enhancements over the PRD observed by OMI are consistent with current VOC emission inventories. Prior work using CHOCHO retrievals from the SCIAMACHY satellite instrument suggested that aromatic VOC emissions in the PRD were too low by a factor of 10-20; we attribute this result in part to bias in the SCIAMACHY data and in part to underestimated CHOCHO yields from oxidation of aromatics. Our work points to the importance of better understanding CHOCHO yields from the oxidation of aromatics in order to interpret CHOCHO observations from space.
Sky camera geometric calibration using solar observations
Authors: Urquhart B. , Kurtz B. , Kleissl J.
Published: January 2016

Abstract. A camera model and associated automated calibration procedure for stationary daytime sky imaging cameras is presented. The specific modeling and calibration needs are motivated by remotely deployed cameras used to forecast solar power production where cameras point skyward and use 180° fisheye lenses. Sun position in the sky and on the image plane provides a simple and automated approach to calibration; special equipment or calibration patterns are not required. Sun position in the sky is modeled using a solar position algorithm (requiring latitude, longitude, altitude and time as inputs). Sun position on the image plane is detected using a simple image processing algorithm. The performance evaluation focuses on the calibration of a camera employing a fisheye lens with an equisolid angle projection, but the camera model is general enough to treat most fixed focal length, central, dioptric camera systems with a photo objective lens. Calibration errors scale with the noise level of the sun position measurement in the image plane, but the calibration is robust across a large range of noise in the sun position. Calibration performance on clear days ranged from 0.94 to 1.24 pixel root mean square error.
Quantification and parameterization of non-linearity effects by higher order sensitivity terms in scattered light Differential Optical Absorption Spectroscopy
Authors: Puķīte Jānis , Wagner Thomas
Published: January 2016

Abstract. We address the application of Differential Optical Absorption Spectroscopy (DOAS) of scattered light observations in the presence of strong absorbers (in particular ozone), for which the absorption optical depth is a non-linear function of the trace gas concentration. This is the case, because Beer-Lambert law generally does not hold for scattered light measurements due to many light paths contributing to the measurement. While in many cases linear approximation can be made, for scenarios with strong absorptions non-linear effects cannot always be neglected. This is especially the case for observation geometries, for which the light contributing to the measurement is crossing the atmosphere under spatially well separated paths differing strongly in length and location, like e.g. in limb geometry. In these cases, often full retrieval algorithms are applied to address the non-linearities requiring iterative forward modelling of absorption spectra involving time consuming wavelength by wavelength radiative transfer modelling. In this study, we propose to describe the non-linear effects by additional sensitivity parameters that can be used e.g. to build up a look up table. Together with widely used box air mass factors (effective light paths) describing the linear response to the increase in the trace gas amount, the higher order sensitivity parameters eliminate the need for repeating the radiative transfer modelling when modifying the absorption scenario even in presence of a strong absorption background. While the higher order absorption structures can be described as separate ﬁt parameters in the spectral analysis (so called DOAS ﬁt), in practice their quantitative evaluation requires good measurement quality (typically better than that available from current measurements). Therefore, we introduce an iterative retrieval algorithm correcting for the higher or- der absorption structures not yet considered in the DOAS ﬁt as well as the absorption dependence on temperature and scattering processes.
EddyUH: an advanced software package for eddy covariance flux calculation for a wide range of instrumentation and ecosystems
Authors: Mammarella I. , Peltola O. , Nordbo A. , Järvi L. , Rannik Ü.
Published: January 2016

Abstract. We have carried out an inter-comparison between EddyUH and EddyPro®, two public software packages for post-field processing of eddy covariance data. Datasets including carbon dioxide, methane and water vapour fluxes measured over two months at a wetland in Southern Finland and carbon dioxide and water vapour fluxes measured over three months at an urban site in Helsinki, were processed and analysed. The purpose was to estimate the flux uncertainty due to the use of different software packages and to evaluate the most critical processing steps, determining the largest deviations in the calculated fluxes. Turbulent fluxes calculated with a reference combination of processing steps were in good agreement, the systematic difference between the two software packages being up to 2% and 6.7% for half-hour and cumulative sum values, respectively. The raw data preparation and processing steps were consistent between the software packages, and most of the deviations in the estimated fluxes were due to the flux corrections. Among the different calculation procedures analysed, the spectral correction had biggest impact for closed-path latent heat fluxes, reaching nocturnal median value of 15% at the wetland site. We found up to 43% median value of deviation (with respect to the run with all corrections included) if closed path carbon dioxide flux is calculated without the dilution correction, while the methane fluxes were up to 10% lower without both dilution and spectroscopic corrections. The density (and spectroscopic) correction was the most critical step for open-path systems. However, we found also large spectral correction factors for the open-path methane fluxes, due to the sensor separation effect.
Influence of the melting temperature on the measurement of the mass concentration and size distribution of black carbon in snow
Authors: Kinase T. , Kita K. , Ogawa Y. , Goto-Azuma K.
Published: January 2016

Abstract. The influence of temperature and time for the melting snow samples on the measurement of mass concentration and its size distribution of black carbon (BC) in snow was evaluated with experiments. In the experiments, fresh (Shirouma) and aged (Hakusan) snow samples were melted at different temperatures or time conditions, and BC mass concentration and its size distribution in the melted snow samples were measured with a nebulizer and a single particle soot photometer (SP2). The experiment changing the melting temperature conditions indicated that BC mass concentration in the liquid decreased at high melting temperature of 70 ºC. The decrease was 9.1 % for the Shirouma sample and 42.3 % for the Hakusan sample. This decrease depended on the BC particle size: significant decrease was found at BC diameter less than 350 nm. Similar decrease of the BC mass concentration was also found when the Hakusan snow sample melted at 5 ºC was heated to 70 ºC. The experiment changing the melting time condition indicated that BC mass concentration in the liquid did not change for the Shirouma sample, and that it decreased significantly with longer melting time for the Hakusan sample (37.7 %). These results indicated that the snow sample melting at a high temperature or in a long time can significantly affect the measurement of BC mass and its size distribution, especially for aged snow samples.
Cirrus cloud optical and microphysical property retrievals from eMAS during SEAC4RS using bi-spectral reflectance measurements within the 1.88 μm water vapor absorption band
Authors: Meyer K. , Platnick S. , Arnold G. T. , Holz R. E. , Veglio P. , Yorks J. , Wang C.
Published: January 2016

Abstract. Previous bi-spectral imager retrievals of cloud optical thickness (COT) and effective particle radius (CER) based on the Nakajima and King (1990) approach, such as those of the operational MODIS cloud optical property retrieval product (MOD06), have typically paired a non-absorbing visible or near-infrared wavelength, sensitive to COT, with an absorbing shortwave or midwave infrared wavelength sensitive to CER. However, in practice it is only necessary to select two spectral channels that exhibit a strong contrast in cloud particle absorption. Here it is shown, using eMAS observations obtained during NASA's SEAC4RS field campaign, that selecting two absorbing wavelength channels within the broader 1.88 μm water vapor absorption band, namely the 1.83 and 1.93 μm channels that have sufficient differences in ice crystal single scattering albedo, can yield COT and CER retrievals for thin to moderately thick single-layer cirrus that are reasonably consistent with other solar and IR imager-based and lidar-based retrievals. A distinct advantage of this channel selection for cirrus cloud retrievals is that the surface contribution to measured cloudy TOA reflectance is minimized due to below-cloud water vapor absorption, thus reducing retrieval uncertainty resulting from errors in the surface reflectance assumption, as well as reducing the frequency of retrieval failures for thin cirrus clouds.
Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens
Authors: Diémoz H. , Eleftheratos K. , Kazadzis S. , Amiridis V. , Zerefos C.S.
Published: January 2016

Abstract. A MkIV Brewer spectrophotometer has been operating in Athens since 2004. Direct sun measurements originally scheduled for nitrogen dioxide retrievals were reprocessed to provide aerosol optical depths (AODs) at a wavelength of about 440 nm. A novel retrieval algorithm was specifically developed and the resulting AODs were compared to those obtained from a colocated Cimel filter radiometer belonging to the Aerosol Robotic Network (AERONET). The series are perfectly correlated, with Pearson’s correlation coefficients being as large as 0.996 and with 90% of AOD deviations between the two instruments being within the World Meteorological Organisation (WMO) traceability limits. In order to reach such a high agreement, several instrumental factors impacting the quality of the Brewer retrievals must be taken into account, including sensitivity to the internal temperature, and the state of the external optics and pointing accuracy must be carefully checked. Furthermore, the long-term radiometric stability of the Brewer was investigated and the performances of in situ Langley extrapolations as a way to track the absolute calibration of the Brewer were assessed. Other sources of error, such as slight shifts of the wavelength scale, are discussed and some recommendations to Brewer operators are drawn. Although MkIV Brewers are rarely employed to retrieve AODs in the visible range, they represent a key source of information about aerosol changes in the past three decades and a potential worldwide network for present and future coordinated AOD measurements. Moreover, a better understanding of the AOD retrieval at visible wavelengths will also contribute in improving similar techniques in the more challenging UV range.
Sampling strategies and post-processing methods for increasing the time resolution of organic aerosol measurements requiring long sample collection times
Authors: Modini R. L. , Takahama S.
Published: January 2016

Abstract. The composition and properties of atmospheric Organic Aerosols (OAs) change on timescales of minutes to hours. However, some important OA characterization techniques typically require greater than a few hours of sample collection time (e.g. Fourier Transform Infrared (FTIR) spectroscopy). In this study we have performed numerical modeling to investigate and compare sample collection strategies and post-processing methods for increasing the time resolution of OA measurements requiring long sample collection times. Specifically, we modeled the measurement of Hydrocarbon-like OA (HOA) and Oxygenated OA (OOA) concentrations at a polluted urban site in Mexico City, and investigated how to construct hourly-resolved time series from samples collected for 4, 6, and 8 h. We modeled two sampling strategies – sequential and staggered sampling – and a range of post-processing methods including interpolation and deconvolution. The results indicated that relative to the more sophisticated and costly staggered sampling methods, linear interpolation between sequential measurements is a surprisingly effective method for increasing time resolution. Additional error can be added to a time series constructed in this manner if a suboptimal sequential sampling schedule is chosen. Staggering measurements is one way to avoid this effect. There is little to be gained from deconvolving staggered measurements, except at very low values of random measurement error (< 5 %). Assuming 20 % random measurement error, one can expect average recovery errors of 1.33–2.81 μg m−3 when using 4–8 h long sequential and staggered samples to measure time series of concentration values ranging from 0.13–29.16 μg m−3. For 4 h samples, 19–47 % of this total error can be attributed to the process of increasing time resolution alone, depending on the method used, meaning that measurement precision would only be improved by 0.30–0.75 μg m−3 if samples could be collected over 1 h instead of 4 h. Devising a suitable sampling strategy and post-processing method is a good approach for increasing the time resolution of measurements requiring long sample collection times.
Update on GOSAT TANSO-FTS performance, operations, and data products after more than six years in space
Authors: Kuze A. , suto H. , Shiomi K. , kawakami S. , Tanaka M. , Ueda Y. , Deguchi A. , Yoshida J. , Yamamoto Y. , Kataoka F. , Taylor T. E. , Buijs H.
Published: January 2016

Abstract. A dataset containing more than six years (February 2009 to present) of radiance-spectra for carbon dioxide (CO2) and methane (CH4) observations has been acquired by the Greenhouse gases Observing SATellite (GOSAT), nicknamed "Ibuki", Thermal And Near infrared Sensor for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS). This manuscript provides updates on the performance of the satellite and TANSO-FTS sensor and describes important changes to the data product, which has recently been made available to users. With these changes the typical accuracy of retrieved column-averaged dry air mole fractions of CO2 and CH4 (XCO2 and XCH4) are 2 ppm or 0.5 % and 13 ppb or 0.7 %, respectively. Three major anomalies of the satellite system affecting TANSO-FTS are reported: a failure of one of the two solar paddles in May 2014, a switch to the secondary pointing system in January 2015 and most recently, a cryo-cooler shutdown and restart in August 2015. The Level 1A (L1A) (raw interferogram) and the Level 1B (L1B) (radiance spectra) of version V201.201 (V201) described here have long-term uniform quality and provide consistent retrieval accuracy even after the satellite system anomalies. In addition, we discuss the unique observation abilities of GOSAT, made possible by an agile pointing mechanism, which allows for optimization of global sampling patterns.
Polarimetric remote sensing in O2 A and B bands: Sensitivity study and information content analysis for vertical profile of aerosols
Authors: Ding Shouguo , Wang Jun , Xu Xiaoguang
Published: January 2016

Abstract. Theoretical analysis is conducted to reveal the information content of aerosol vertical profile in space-borne measurements of the backscattered radiance and degree of linear polarization (DOLP) in the O2 A and B bands. Assuming a quasi-Gaussian shape for aerosol vertical profile characterized by peak height H and half width γ (at half maximum), the Unified Linearized Vector Radiative Transfer Model (UNL-VRTM) is used to simulate the Stokes 4-vector elements of upwelling radiation at the top of atmosphere (TOA) and their Jacobians with respect to H and γ. Calculations for different aerosol types and different combinations of H and γ values show that the wide range of gas absorption optical depth in O2 A and B band enables the sensitivity of backscattered DOLP and radiance at TOA to the aerosol layer at different altitudes. Quantitatively, DOLP in O2 A and B bands is found to be more sensitive to H and γ than radiance, especially over the bright surfaces (with large visible reflectance). In many O2 wavelengths, Degree of Freedom for Signal (DFS) for retrieving H (or γ) generally increases with H (and γ) and can be close to unity in many cases, assuming that the composite uncertainty from surface and aerosol scattering properties as well as measurements is less than 5%. Further analysis demonstrates that DFS needed for simultaneous retrieval of H and γ for high-lofted aerosol profiles (H > 2 km) can be obtained from a combined use of DOLP measurements at ~10 O2 absorption A and B absorption wavelengths. However, challenges still remain for resolving aerosol profiles with H less than 2 km. Future hyperspectral measurements of DOPL in O2 A and B bands are needed to continue studying their potential and their combination with radiance and DOPL in atmospheric window channels for retrieving the vertical profiles of aerosols, especially highly scattering aerosols, over land.
On instrumental errors and related correction strategies of ozonesondes: possible effect on calculated ozone trends for the nearby sites Uccle and De Bilt
Authors: Van Malderen R. , Allaart M. A. F. , De Backer H. , Smit H. G. J. , De Muer D.
Published: January 2016

Abstract. The ozonesonde stations at Uccle (Belgium) and De Bilt (Netherlands) are separated by only 175 km, but use different ozonesonde types, different operating procedures, and different correction strategies. As such, these stations form a unique test bed for the Ozonesonde Data Quality Assessment (O3S-DQA) activity, which aims at providing a revised, homogeneous, consistent dataset with an altitude-dependent estimated uncertainty for each revised proﬁle. For the Electrochemical Concentration Cell (ECC) ozonesondes at Uccle mean relative uncertainties in the 4−6 % range are obtained. To study the impact of the corrections on the ozone proﬁles and trends, we compared the Uccle and De Bilt average ozone proﬁles and vertical ozone trends, calculated from the operational corrections at both stations and the O3S-DQA corrected proﬁles. In the common ECC 1997-2014 period, the O3S-DQA corrections effectively reduce the differences between the Uccle and De Bilt ozone partial pressure values with respect to the operational corrections only for the stratospheric layers below the ozone maximum. The upper stratospheric ozone measurements at both sites are substantially different, regardless the used correction methodology, the origin of which is not clear. The discrepancies in the tropospheric ozone concentrations between both sites can be ascribed to the problematic background measurement and correction at De Bilt, especially in the period before November 1998. The Uccle operational correction method, applicable to both ozonesonde types used, diminishes the relative stratospheric ozone differences of the Brewer-Mast sondes in the 1993-1996 period with De Bilt from about 20−30 % compared to the standard pump corrections to less than 5 %. The O3S-DQA corrections bring the Uccle and De Bilt ozone trend estimates for 1997-2014 closer to each other in the lower stratosphere and lower troposphere. Throughout whole the vertical proﬁle, these trend estimates are however not signiﬁcantly different from each other, and only in the troposphere signiﬁcantly positive. For the entire Uccle observation period (1969−2014), the operational corrections lead to height-independent and consistent ozone trends for both the troposphere and the stratosphere, with rates respectively +2 to +3 %dec −1 , and −1 to −2 %dec−1.
A miniDOAS instrument optimised for ammonia field-measurements
Authors: Sintermann J. , Dietrich K. , Häni C. , Bell M. , Jocher M. , Neftel A.
Published: January 2016

Abstract. We present a DOAS instrument, called "miniDOAS", optimised for optical open-path field-measurements of ambient ammonia (NH3) alongside nitrogen oxide (NO) and sulphur dioxide (SO2). The instrument is a further development of the miniDOAS presented by Volten et al. (2012). Here, we use a temperature-controlled spectrometer, a deuterium light source and a modified optical arrangement. The system was set up in a robust, field-deployable, temperature-regulated housing. For the evaluation of light spectra we use a new high-pass filter routine based upon robust baseline extraction with local regression. In order to fit differential absorption cross-sections to the measurements, multiple linear regression is performed including terms of an autoregressive-moving-average model. For NH3 the instrument's precision is 0.8 to 1.4 %. Accuracy is larger than precision and derives from the precision, uncertainty in DOAS absorption cross-sections (± 3 %) and an uncertain estimation of concentration offsets (c0) present through the definition of reference spectrum I0. Accuracy will at minimum be approximately 0.3 μg m−3. The limit of detection against I0 is around 0.2 μg m−3. Comparisons of miniDOAS measurements to those by NH3 acid trap devices showed good agreement. The miniDOAS can be flexibly used for a wide range of field trials, such as micrometeorological NH3 flux measurements with approaches based upon horizontal or vertical concentration gradients. Results from such applications, covering concentration dynamics of sub-ppb to ppm mixing ratios, are presented.
Bias corrections of GOSAT SWIR XCO2 and XCH4 with TCCON data and their evaluation using aircraft measurement data
Authors: Inoue M. , Morino I. , Uchino O. , Nakatsuru T. , Yoshida Y. , Yokota T. , Wunch D. , Wennberg P. O. , Roehl C. M. , Griffith D. W. T. , Velazco V. A. , Deutscher N. M. , Warneke T. , Notholt J. , Robinson J. , Sherlock V. , Hase F. , Blumenstock T. , Rettinger M. , Sussmann R. , Kyrö E. , Kivi R. , Shiomi K. , Kawakami S. , De Mazière M. , Arnold S. G. , Feist D. G. , Barrow E. A. , Barney J. , Dubey M. , Schneider M. , Iraci L. , Podolske J. R. , Hillyard P. , Machida T. , Sawa Y. , Tsuboi K. , Matsueda H. , Sweeney C. , Tans P. P. , Andrews A. E. , Biraud S. C. , Fukuyama Y. , Pittman J. V. , Kort E. A. , Tanaka T.
Published: January 2016

Abstract. We describe a method for removing systematic biases of column-averaged dry air mole fractions of CO2 (XCO2) and CH4 (XCH4) derived from short-wavelength infrared (SWIR) spectra of the Greenhouse gases Observing SATellite (GOSAT). We conduct correlation analyses between the GOSAT biases and simultaneously-retrieved auxiliary parameters. We use these correlations to bias correct the GOSAT data, removing these spurious correlations. Data from Total Carbon Column Observing Network (TCCON) were used as reference values for this regression analysis. To evaluate the effectiveness of this correction method, the uncorrected/corrected GOSAT data were compared to independent XCO2 and XCH4 data derived from aircraft measurements taken for the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) project, the National Oceanic and Atmospheric Administration (NOAA), the U.S. Department of Energy (DOE), the National Institute for Environmental Studies (NIES), the Japan Meteorological Agency (JMA), the HIAPER Pole- to-Pole observations (HIPPO) program, and the GOSAT validation aircraft observation campaign over Japan. These comparisons demonstrate that the empirically-derived bias correction improves the agreement between GOSAT XCO2/XCH4 and the aircraft data. Finally, we present latitudinal distributions and temporal variations of the derived GOSAT biases.
Composite Catalogues of Optical and Fluorescent Signatures Distinguish Bioaerosol Classes
Authors: Hernandez M. , Perring A. , McCabe K. , Kok G. , Granger G. , Baumgardner D.
Published: January 2016

Abstract. Rapid bioaerosol characterization has immediate applications in the military, environmental and public health sectors. Recent technological advances have facilitated single particle detection of fluorescent aerosol in near real-time; this leverages controlled exposures with single or multiple ultraviolet wavelengths, followed by the characterization of associated fluorescence. This type of Ultravio let induced fluorescence has been used to detect some intact airborne microorganisms in laboratory studies, and has been extended to field studies which implicate bioaerosol to compose a substantial fraction of supermicron atmospheric particles. To enhance the information yield which new generation fluorescence instruments provide, we report the compilation of a systematic referential catalogue including more than fifty pure cultures of common airborne bacteria, fungi and pollens. This catalogue juxtaposes intrinsic optical properties and multiple bandwidths of fluorescence spectra, which manifest to clearly distinguish between major classes of airborne microbes and pollen.
Atmospheric mercury measurements onboard the CARIBIC passenger aircraft
Authors: Slemr F. , Weigelt A. , Ebinghaus R. , Kock H. H. , Bödewadt J. , Brenninkmeijer C. A. M. , Rauthe-Schöch A. , Weber S. , Hermann M. , Zahn A. , Martinsson B.
Published: January 2016

Abstract. Goal of the project CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrumented Container) is to carry out regular and detailed observations of atmospheric composition (particles and gases) at cruising altitudes of passenger aircraft, i.e. at 9 – 12 km. Mercury has been measured since May 2005 by a modified Tekran instrument (Tekran-Analyzer Model 2537 A, Tekran Inc., Toronto, Canada) during monthly intercontinental flights between Europe and South and North America, Africa and Asia. Here we describe the instrument modifications, the post-flight processing of the raw Tekran signal, and the speciation experiments.
Radiocarbon analysis of stratospheric CO2 retrieved from AirCore sampling.
Authors: Paul Dipayan , Chen Huilin , Been Henk A. , Kivi Rigel , Meijer Harro A. J.
Published: January 2016

Abstract. In this decade understanding the impact of human activities on climate has been one of the key issues of discussion globally. In that respect, the continuous rise of the concentration of greenhouse gases, e.g., CO2, CH4, etc. in the atmosphere, predominantly due to human activities requires continuous monitoring to understand the dynamics. Radiocarbon (14C) is an important atmospheric tracer and one of the many used in the understanding of the global carbon budget, which includes the greenhouse gases CO2 and CH4. Measurement of radiocarbon in atmospheric CO2 generally requires collection of large air samples (few liters) from which CO2 is extracted and then the concentration of radiocarbon is determined using Accelerator Mass Spectrometry (AMS). However, the regular collection of air samples from the stratosphere, for example using aircraft and balloons, is prohibitively expensive. Here we describe radiocarbon measurements in stratospheric CO2 collected by the AirCore sampling method. AirCore is an innovative atmospheric sampling system, which comprises of a long tube descending from a high altitude with one end open and the other closed, and has been demonstrated to be a reliable, cost-effective sampling system for high-altitude profile (up to ≈ 30 km) measurements of CH4 and CO2. In Europe, AirCore measurements are being performed on a regular basis near Sodankylä (Northern Finland) since September 2013. Here we describe the analysis of samples from two such AirCore flights made there in July 2014, for determining the radiocarbon concentration in stratospheric CO2. The two AirCore profiles were collected on consecutive days. The stratospheric part of the AirCore was divided into six sections, each containing ≈ 35 µg CO2 (≈ 9.6 µgC). Each section was separately stored in a ¼ inch coiled stainless steel tubing (≈ 3m) for radiocarbon measurements. A small-volume extraction system was constructed which enabled ≈ 100% CO2 extraction from the stratospheric air samples. Also, a new small-volume high-efficiency graphitization system was constructed for graphitization of these extracted CO2 samples, which were later measured at the Groningen AMS facility. Since the stratospheric samples were very similar in mass, reference samples were also prepared in the same mass range to correct for contaminations. The results show that the Δ 14CO2 values for lower stratosphere up to about 18(± 1) km (first four samples from each profile) are very similar (10 ± 8‰) and represent the current tropospheric value. The next sample in each profile, corresponding to about 18(± 1)-22(± 2) km showed slight enrichment of 80 ± 20‰. The last section from one profile, corresponding to altitudes above 22(± 2), also showed enhanced Δ 14CO2 value of 79.1 ± 30‰. The last section from the other profile was spoiled during preparation.
Application of the Full Spectrum Inversion Algorithm for Airborne GPS Radio Occultation Measurements
Authors: Adhikari L. , Xie F. , Haase J. S.
Published: January 2016

Abstract. With a GPS receiver onboard an airplane, the airborne RO (ARO) technique provides dense lower troposphere soundings over target regions. The large variation of water vapor in the troposphere causes strong signal multipath, which could lead to systematic errors in RO retrievals with the geometric optics (GO) method. The spaceborne GPS RO community has successfully applied the Full Spectrum Inversion (FSI) technique to solve the multipath problem. This paper is the first to adapt the FSI technique to the ARO measurement with its unique perspective of having a receiver traveling on a non-circular trajectory inside the atmosphere. An end-to-end simulation system is implemented to test the newly developed FSI retrieval algorithm for ARO. The forward-simulated GPS L1 signal amplitude and phase is used to test the modified FSI algorithm. The ARO FSI method is capable of reconstructing the fine vertical structure of the moist lower troposphere in the presence of severe multipath, which leads to large retrieval errors in the GO retrieval. The sensitivity of the modified FSI retrieved bending angle and refractivity to the errors in signal amplitude and the measured refractivity at the receiver is presented. Accurate bending angle retrievals can be obtained from surface up to ~250 m below the receiver, where retrieved bending angle near the receiver altitude becomes sensitive to the measurement noise. Abrupt changes in the signal amplitude do not produce a systematic bias in the FSI retrievals when the SNR is high. A 1 % Gaussian noise in refractivity at the receiver causes ~ 0.5 % refractivity error near the receiver that reduces to ~0.05 % near the surface.
Increasing the accuracy and temporal resolution of two-filter radon–222 measurements by correcting for the instrument response
Authors: Griffiths A. D. , Chambers S. D. , Williams A. G. , Werczynski S.
Published: January 2016

Abstract. Dual-ﬂow-loop two-ﬁlter radon detectors have a slow time response, which can affect the interpretation of their output when making continuous observations of near-surface atmospheric radon concentrations. While concentrations are routinely reported hourly, a calibrated model of detector performance shows that ∼40% of the signal arrives more than an hour after a radon pulse is delivered. After investigating several possible ways to correct for the detector’s slow time response, we show that a Bayesian approach using a Markov Chain Monte Carlo sampler is an effective method. After deconvolution, the detector’s output is redistributed into the appropriate counting interval and a 10 minute temporal resolution can be achieved under test conditions when the radon concentration is controlled. In the case of existing archived observations, collected under less ideal conditions, the data can be retrospectively reprocessed at 30 minute resolution. In one case study, we demonstrate that a deconvolved radon time series was consistent with: measurements from a fast-response carbon dioxide monitor; grab samples from an aircraft; and a simple mixing height model. In another case study, a bias of 18% in the mean daily minimum radon concentration was eliminated by correcting for the instrument response during a period of stable nights and days with well-developed convective boundary layers.
A fast SWIR imager for observations of transient features in OH airglow
Authors: Hannawald P. , Schmidt C. , Wüst S. , Bittner M.
Published: January 2016

Abstract. Since December 2013 the new imaging system FAIM (Fast Airglow IMager) for the study of smaller-scale features (both in space and time) is in routine operation at the NDMC (Network for the Detection of Mesospheric Change) station at DLR (German Aerospace Center) in Oberpfaffenhofen (48.1° N, 11.3° E). Covering the brightest OH vibrational bands between 1 and 1.7 μm, this imaging system can acquire two frames per second. The field of view is approximately 55 km times 60 km at the mesopause heights. A mean spatial resolution of 200 m at a zenith angle of 45° and up to 120 m for zenith conditions are achieved. The observations show a large variety of atmospheric waves. This paper introduces the instrument and compares the FAIM data with spectrally resolved GRIPS (GRound-based Infrared P-branch Spectrometer) data. In addition, a case study of a breaking gravity wave event, which we assume to be associated with Kelvin-Helmholtz-instabilities, is discussed.
The CU 2D-MAX-DOAS instrument - part 2: Raman Scattering Probability Measurements and Retrieval of Aerosol Optical Properties
Authors: Ortega Ivan , Coburn Sean , Berg Larry K. , Lantz Kathy , Michalsky Joseph , Ferrare Rich , Hair Johnathan , Hostetler Chris , Volkamer Rainer
Published: January 2016

Abstract. The multiannual global mean of aerosol optical depth at 550 nm (AOD550) over land is ~0.19, and that over oceans is ~0.13. About 45% of the Earth surface shows AOD550 smaller than 0.1. There is a need for measurement techniques that are optimized to measure aerosol optical properties under low AOD conditions. We present an inherently calibrated retrieval (i.e., no need for radiance calibration) to simultaneously measure AOD and the aerosol phase function parameter, g, based on measurements of azimuth distributions of the Raman Scattering Probability (RSP), the near-absolute Rotational Raman Scattering (RRS) intensity. We employ Radiative Transfer Model simulations to show that solar azimuth RSP measurements are insensitive to the vertical distribution of aerosols, and maximally sensitive to changes in AOD and g under near molecular scattering conditions. The University of Colorado two dimensional Multi-AXis Differential Optical Absorption Spectroscopy (CU 2D-MAX-DOAS) instrument was deployed as part of the Two Column Aerosol Project (TCAP) at Cape Cod, MA, during the summer of 2012 to measure direct sun spectra, and RSP from scattered light spectra at solar relative azimuth angles (SRAA) between 5° and 170°. During two case study days with (1) high aerosol load (17 July, 0.3 < AOD430 < 0.6) and (2) near-molecular scattering conditions (22 July, AOD430 < 0.13) we compare RSP based retrievals of AOD430 and g with data from a co-located CIMEL sun photometer, Multi-Filter Rotating Shadowband Radiometer (MFRSR), and airborne High Spectral Resolution Lidar (HSRL-2). The average difference (relative to DOAS) for AOD430 is: +0.012 ± 0.023 (CIMEL), –0.012 ± 0.024 (MFRSR), –0.011 ± 0.014 (HSRL-2), and +0.023 ± 0.013 (CIMEL – MFSRS); and yields the following expressions for correlations between different instruments: DOASAOD = –(0.019 ± 0.006) + (1.03 ± 0.02)·CIMELAOD (R2 = 0.98), DOAS = –(0.006 ± 0.005) + (1.08 ± 0.02)·MFRSRAOD (R2 = 0.98), and CIMELAOD = (0.013 ± 0.004) + (1.05 ± 0.01)·MFRSR = 0.99). The average g measured by DOAS on both days was 0.66 ± 0.03, with a difference of 0.014 ± 0.05 compared to CIMEL. Active steps to minimize RSP in the reference spectrum help to reduce the uncertainty in RSP retrievals of AOD and g. As AOD decreases, and solar zenith angle (SZA) increases the RSP signal-to-noise ratio increases. At AOD430 ~ 0.4 and 0.10 the absolute AOD errors are ~0.014 and 0.003 at 70° SZA, and 0.02 and 0.004 at 35° SZA. Inherently calibrated, precise AOD and g measurements are useful to better characterize the aerosol direct effect in urban polluted and remote pristine environments.
Turbulence measurements with a tethered balloon
Authors: Canut G. , Couvreux F. , Lothon M. , Legain D. , Piguet B. , Lampert A. , Moulin E.
Published: January 2016

Abstract. This study presents the ﬁrst deployment of a turbulence probe below a tethered balloon in ﬁeld campaigns. This system allows to measure turbulent temperature ﬂuxes, momentum ﬂuxes as well as turbulent kinetic energy in the lower part of the boundary layer. It is composed of a sonic thermoanemometer and inertial motion sensor. It has been validated during three campaigns with different convective boundary layer conditions using turbulent measurements from atmospheric towers and aircraft.
Instrumentation and Measurement Strategy for the NOAA SENEX Aircraft Campaign as Part of the Southeast Atmosphere Study 2013
Authors: Warneke C. , Trainer M. , de Gouw J. A. , Parrish D. D. , Fahey D. W. , Ravishankara A. R. , Middlebrook A. M. , Brock C. A. , Roberts J. M. , Brown S. S. , Neuman J. A. , Lerner B. M. , Lack D. , Law D. , Huebler G. , Pollack I. , Sjostedt S. , Ryerson T. B. , Gilman J. B. , Liao J. , Holloway J. , Peischl J. , Nowak J. B. , Aikin K. , Min K.-E. , Washenfelder R. A. , Graus M. G. , Richardson M. , Markovic M. Z. , Wagner N. L. , Welti A. , Veres P. R. , Edwards P. , Schwarz J. P. , Gordon T. , Dube W. P. , McKeen S. , Brioude J. , Ahmadov R. , Bougiatioti A. , Lin J. , Nenes A. , Wolfe G. M. , Hanisco T. F. , Lee B. H. , Lopez-Hilfiker F. D. , Thornton J. A. , Keutsch F. N. , Kaiser J. , Mao J. , Hatch C.
Published: January 2016

Abstract. The Southeast United States (US) might not have warmed as much as the rest of the country over the past 50-100 years. Providing an improved understanding of this potential anomaly, and specifically the roles played by aerosols, was one of the main goals for the Southeast Atmosphere Study (SAS). Natural emissions of ozone-and-aerosol-precursor gases such as isoprene and monoterpenes are high in the southeast of the US. In addition, anthropogenic emissions are significant inthe Southeast US and summertime photochemistry is rapid. The NOAA-led SENEX (Southeast Nexus) aircraft campaign was one of the major components of the SAS studyand was focused on studying the interactions between biogenic and anthropogenic emissions to form secondary pollutants. During SENEX, the NOAA WP-3D aircraft conducted 20 research flights between 27 May and 10 July 2013 based out of Smyrna, TN. Here we describe the experimental approach, the science goals and early results of the NOAA SENEX campaign. The aircraft, its capabilities and standard measurements are described. The instrument payload is summarized including detection limits, accuracy, precision and time resolutions for all gas-and-aerosol phase instruments. The inter-comparisons of compounds measured with multiple instruments on the NOAA WP-3D are presented and were almost all within the stated uncertainties. The SENEX flights included day- and nighttime flights in the Southeast as well as flights over areas with intense shale gas extraction (Marcellus, Fayetteville and Haynesville shale). We present one example flight on 16 June 2013, which was a daytime flight over the Atlanta region, where several crosswind transects of plumes from the city and nearby point sources, such as power plants, paper mills and landfills, were flown. The area around Atlanta has large biogenic isoprene emissions, which provided an excellent case for studying the interactions between biogenic and anthropogenic emissions. In this example flight, chemistry in and outside the Atlanta plumes was observed for several hours after emission. The analysis of this flight showcases the strategies implemented to answer some of the main SENEX science questions.
New and improved infrared absorption cross sections for chlorodifluoromethane (HCFC-22)
Authors: Harrison J. J.
Published: January 2016

Abstract. The most widely used hydrochlorofluorocarbon (HCFC) commercially since the 1930s has been chlorodifluoromethane, or HCFC-22, which has the undesirable effect ofdepleting stratospheric ozone. As this molecule is currently being phased out under the Montreal Protocol, monitoring its concentration profiles using infrared sounders cruciallyrequires accurate laboratory spectroscopic data. This work describes new high-resolution infrared absorption cross sections of chlorodifluoromethane over the spectral range 730 – 1380 cm−1, determined from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26-cm-pathlength cell. Spectra of chlorodifluoromethane/dry synthetic air mixtures were recorded at resolutions between 0.01and 0.03 cm−1 (calculated as 0.9/MOPD; MOPD = maximum optical path difference) over a range of temperatures and pressures (7.5–762 Torr and 191–295 K) appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN and GEISA databases; in particular it provides coverage over a wider range of pressures and temperatures, has more accurate wavenumber scales, more consistent integrated band intensities, improved signal-to-noise, is free of channel fringing, and additionally covers the v2 and v7 bands.
3D Water Vapor Field in the Atmospheric Boundary Layer Observed with Scanning Differential Absorption Lidar
Authors: Späth F. , Behrendt A. , Muppa S. K. , Metzendorf S. , Riede A. , Wulfmeyer V.
Published: January 2016

Abstract. The scanning differential absorption lidar (DIAL) of the University of Hohenheim (UHOH) determines fields of the atmospheric water vapor number density with a temporal resolution of a few seconds and spatial resolution of up to a few tens of meters. We present three case studies which show that this high resolution combined with 2- and 3-dimensional scans allows for new insights in the 3-dimensional structure of the water vapor field in the atmospheric boundary layer (ABL). In spring 2013, the UHOH DIAL was operated within the scope of the HD(CP)2 Observational Prototype Experiment (HOPE) in western Germany. HOPE was part of the project High Definition of Clouds and Precipitation for advancing Climate Prediction (HD(CP)2). Range-height indicator (RHI) scans of the UHOH DIAL show the water vapor heterogeneity within a range of a few kilometers and its impact on the formation of clouds at the ABL top. The uncertainty of the measured data was assessed by extending a technique, which was formerly applied to vertical time series, to scanning data. Typically, even during daytime, the accuracy of the DIAL measurements is between 0.5 and 0.8 g m−3 (or < 6 %) within the ABL, so that now the performance of an RHI scan from the surface to an elevation angle of 90 degrees becomes possible within 10 min. In summer 2014, the UHOH DIAL participated in the Surface-Atmosphere-Boundary-Layer-Exchange (SABLE) campaign in south-western Germany. Volume scans show the water vapor field in three dimensions. In this case, multiple humidity layers were present. Differences in their heights in different directions can be attributed to different surface elevation. With low elevation scans in the surface layer, the humidity profiles and gradients related to different land use and surface stabilities were also revealed.