China has become the world’s largest emitter of NO_x, which mainly comes from vehicle exhaust, power plants, etc. However, there are no official ground-based measurements before 2013, so satellites have been widely used to monitor and analyze NO_x pollution here. Aerosol is the key factor influencing the accuracy of the satellite NO_x product. Our study provides a more accurate way to account for aerosol's influence compared to current widely used products.

The paper describes a ray-tracing approach for the proper reconstruction of GNSS signal paths through the lower atmosphere, identifies possible error sources during ray tracing and provides a strategy for reducing their effect on the GNSS tomography solution, thereby contributing to a more reliable reconstruction of the 3-D water vapor distribution in the lower atmosphere from GNSS measurements.

In order to study the carbon cycle, accurate remote sensing measurements of XCO₂ are required. This means that accurate absorption coefficients of CO₂ and O₂ in the retrieval algorithm are required. We use high-resolution laboratory spectra of O₂ to derive accurate absorption coefficients. By applying the O₂ absorption coefficients to the retrieval of XCO₂ from ground-based solar absorption spectra we show that the error on retrieved XCO₂ is decreased.

The version 4 (V4) release of the CALIPSO data products includes substantial improvements to the calibration of the CALIOP 1064 nm channel. In this paper we review the fundamentals of 1064 nm lidar calibration, explain the motivations for the changes made to the algorithm, and describe the mechanics of the V4 calibration technique. Internal consistency checks and comparisons to collocated high spectral resolution lidar measurements show the V4 1064 nm calibration coefficients to within ~ 3 %.

The GRUAN processor is a software developed to collocate radiosonde profiles and numerical weather prediction model fields, simulate top-of-atmosphere brightness temperature at frequencies used by space-borne instruments, and propagate the radiosonde uncertainties in that simulation. This work responds to an identified lack of metrologically traceable characterisation of uncertainties in model fields that are increasingly used for the validation and calibration of space-borne instruments.

We developed a shape model of coated soot particles and created a dataset of their optical properties. To simulate the detailed shape properties of mixtures of soot aggregates and adhered water-soluble substances, we propose a simple model of surface tension derived from the artificial surface potential. The results of some single-scattering properties including lidar backscattering were discussed.

Methane is currently the second most important greenhouse gas of anthropogenic origin (after carbon dioxide) and its concentration can be increased inside the boundary layer. So, the development of instruments for vertical profiling of the methane mixing ratio is an important task. We present the results of methane profiling in the lower troposphere using LILAS Raman lidar from the Lille University observatory platform (France).

We compared v3.0B of the BEHR satellite NO₂ product against independent measurements to verify its accuracy. We found that the BEHR product generally performs better than standard NO₂ products and the previous version of BEHR. Outside of the SE US, using daily NO₂ profiles results in similar or better agreement with independent measurements than using monthly profiles, and direct evaluation of those profiles shows they better describe NO₂ distribution in urban areas than monthly profiles.

Aerosol type seasonal variability and sources in Siberia are obtained from an automatic 808 nm micropulse lidar. A total of 540 aerosol backscatter vertical profiles have been retrieved using careful lidar calibration. Aerosol optical depth is retrieved using sun-photometer complementary observations and an aerosol source apportionment based on aerosol transport model simulations. Comparisons with satellite observations are discussed for three case studies.

Clouds or instrumental anomalies may perturb ground-based solar measurements used to calculate aerosol optical depth (AOD). This study presents a new algorithm of automated near-real-time (NRT) quality controls with improved cloud screening for AERONET AOD measurements. Results from the new and old algorithms have excellent agreement for the highest-quality AOD level, while the new algorithm provides higher-quality NRT AOD for applications such as data assimilation and satellite evaluation.

We present an intercomparison study of four airborne imaging DOAS instruments, dedicated to the retrieval and high-resolution mapping of tropospheric nitrogen dioxide (NO₂) vertical column densities (VCDs). The AROMAPEX campaign took place in Berlin, Germany, in April 2016 with the primary objectives (1) to test and intercompare the performance of experimental airborne imagers and (2) to prepare the validation and calibration campaigns for the Sentinel-5 Precursor/TROPOMI mission.

We propose a method to assess the accuracy of turbulence measurements by sonic anemometers. The idea is to compute the ratio of the vertical to along-wind velocity spectrum within the inertial subrange. We found that the Metek USA-1 and the Campbell CSAT3 sonic anemometers do not show the expected theoretical ratio. A wind-tunnel-based correction recovers the expected ratio for the USA-1. A correction for the CSAT3 does not, illustrating that this sonic anemometer suffers from flow distortion.

This paper presents an implementation of polarization diversity pulse-pair processing (PDPP) on the National Research Council of Canada airborne W-band radar (NAW) system. A description of the NAW PDPP pulsing schemes and an analysis of comprehensive airborne data collected in diverse weather conditions in Canada is presented. The analysis shows a successful airborne measurement of Doppler velocity exceeding 100 m s⁻¹ using PDPP approach, the first such measurement from a moving platform.

It is now known that single-monochromator Brewer spectrophotometer ozone and sulfur dioxide measurements suffer from non-linearity at large ozone slant column amounts due to the presence of instrumental stray light caused by scattering within the optics of the instrument. This paper presents a simple and practical method of correcting for the effects of stray light.

A MARGA was combined with an additional IC system specialized for the 2 h interval online quantification of 12 low-molecular-weight organic acids in the gas and particle phases. Low limits of detection and good precision were achieved. The suitability for field measurements was shown. This setup reduces laboratory work and filter sampling artifacts. Diurnal profiles, sources and phase distributions of these compounds will improve the knowledge of the tropospheric multiphase chemistry.

This paper is an evaluation of methods used to generate OH radicals under conditions with high concentrations of NO and NO₂ to simulate oxidation chemistry in polluted urban atmospheres over equivalent atmospheric timescales of ~ 1 day.

We developed an automated compact mobile Raman lidar (MRL) system for measuring the vertical distribution of the water vapor mixing ratio in the lower troposphere, which has an affordable cost and is easy to operate. The MRL was installed in a small trailer for easy deployment and can start measurement in a few hours, and it is capable of unattended operation for several months. We describe the MRL system and present validation results obtained by comparing with the other humidity sensors.

This study documents the error caused by the effect of stray light in the Brewer and Dobson total ozone measurements using a mathematical model for each instrument. The errors caused by stray light are particularly significant at high latitudes in the late winter and early spring when measurements are made at large solar zenith angles and large total ozone column. Such errors are of considerable importance if those data are to be used for trend analysis or satellite data validation.

Assimilation of satellite navigation data into a popular weather model is yet another example of how to turn non-meteorological data into valuable information about the current state of the troposphere. Results show that observations from ground-based GPS receivers can improve humidity and rain forecasts in most severe weather events. It is another reason to extend the adoption of GPS data into weather forecasting across Europe.

During the 2017 Ozone Water Land Environmental Transition Study (OWLETS), the Langley mobile ozone lidar system utilized a new small diameter receiver to improve the retrieval of near-surface signals from 0.1 to 1 km in altitude. This allowed for improved near-surface ozone concentration measurements, those most important to human health, while also measuring profiles up to stratospheric altitudes. OWLETS provided multiple instrument comparisons for validation of the system improvement.

The total column water vapour (TCWV) is a key atmospheric variable. The AIRWAVE (Advanced Infra-Red WAter Vapour Estimator) v1 algorithm was developed to retrieve TCWV from satellite measurements. Comparisons with independent TCWV show good agreement with an overall bias of 0.72 kg m⁻² due to the polar and coastal regions. Here, we describe the AIRWAVEv2 dataset, which shows significant improvements with a global bias of 0.02 kg m⁻². This dataset was used to produce a climatology from 1991 to 2012.

A detection method for high-level cloud, such as ice clouds, is developed using the water vapor saturated channels (2  μm) of the solar reflected spectrum observed by the TANSO-FTS on board GOSAT. The clouds detected by this method are optically relatively thin (0.01 or less) and located at high altitudes. Approximately 85  % of the results from this method for clouds with a cloud-top altitude above 5  km agree with Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) cloud classification.

Permittivity models for microwave frequencies of liquid water below 0°C are poorly constrained due to limited laboratory experiments and observations, especially for high microwave frequencies. This uncertainty translates directly into errors in retrieved liquid water paths of up to 80 %. This study investigates the effect of different liquid water permittivity models including models based on the most recent observations.

The SHOW instrument is a prototype satellite concept that is being developed through collaboration between the University of Saskatchewan, the Canadian Space Agency, and ABB Inc. to provide high vertical resolution (< 200 m) measurements of UTLS water vapour with < 1 ppm accuracy. This paper presents suborbital measurements obtained during a demonstration flight aboard NASA's ER-2 aircraft. These measurements are validated through a comparison with coincident radiosonde measurements.

We use a near-infrared camera for the investigation of gravity waves. The camera observes the airglow layer, which is modulated by the gravity waves. The image processing, including the removal of the stars is explained. We describe the analysis with a 2D fast Fourier transform and automatic derivation of the wave parameters. The results show a clear seasonal and intra-diurnal variability, which is characterised in order to improve our understanding of gravity waves in the middle atmosphere.

Many ceilometers are influenced by water vapor absorption in the spectral range around 910 nm. Thus, a correction is required to retrieve aerosol optical properties. Validation of this correction scheme was performed in the framework of CeiLinEx2015 for several ceilometers with good agreement for Vaisala's CL51 ceilometer. For future applications we recommend monitoring the emitted wavelength and providing dark measurements on a regular basis to be able to correct for signal artifacts.

The reference OMI tropospheric NO₂ product was reprocessed by new aerosol correction parameters retrieved from the 477 nm O₂–O₂ band over eastern China and South America for 2 years. These new parameters are from different and separate algorithms, allowing improved use of the 477 nm O₂–O₂ band. All the tested approaches improve the aerosol correction in the OMI tropospheric NO₂ product. We demonstrate the possibility of applying an explicit aerosol correction based on the 477 nm O₂–O₂ band.

We have used a one-step method for gravimetric preparation of CO₂-in-air standards in aluminum cylinders. We consider both adsorption to stainless steel surfaces used in the transfer of highly pure CO₂ and adsorption of CO₂ to cylinder walls. This work compliments ongoing efforts to support atmospheric monitoring of CO₂.

Mid-infrared spectra of particulate matter (PM) samples are complex but chemically informative and present an opportunity for cost-effective measurement of PM provided that quantitative calibration models can be built. We review an emerging strategy for building statistical calibration models using collocated measurements, interpreting the physical bases for such models and evaluating the suitability of existing calibration models to new samples.

This paper describes the temperature profiles in the stratosphere obtained from unique stellar scintillation measurements by the GOMOS instrument operated on board Envisat in 2002–2012. The high-resolution temperature profiles (HRTPs) are retrieved with a very good vertical resolution of ~ 200 m and a high accuracy of ~ 1–3 K for altitudes 15–32 km as well as a global coverage. HRTPs can be assimilated into atmospheric models and used in analyses of internal gravity wave activity.

The first intensive multicomponent observation by sky radiometer and MAX-DOAS was performed in Thailand during the 2016 dry season. We found that the concentration of formaldehyde (HCHO) was a useful tracer for biomass burning plumes. With the HCHO enhancement, the ratio of gaseous glyoxal to HCHO concentrations decreased and the aerosol absorption optical depths (AAODs) increased. The wavelength dependence of AAODs was quantified, providing evidence for the presence of brown carbon aerosols.

We present a methodology to infer the contribution of mineral dust and non-dust aerosol to the absorbing aerosol optical depth (AAOD) of mixed aerosol layers. The method presents an adaptation of a lidar-based aerosol-type separation technique to passive measurements with AERONET sun photometers by using lidar-specific parameters obtained from the AERONET inversion. The findings on BC-related AAOD are compared to CAMS aerosol reanalysis data with promising results for sites in east Asia.

The characterization of infrared radiation emitted by the atmosphere is a crucial task in the study of the Earth's climate. The Radiation Explorer in the Far Infrared (REFIR) spectroradiometer allows us to perform this task adding the capability of resolving, through spectroscopy, the atmospheric components responsible for the measured radiative effects. The analysis of the measurements also allows us to retrieve the atmospheric structure, making REFIR a complete tool for atmospheric studies.

We present a 10-year (Jan 2007–Dec 2016) time series of continuous in situ measurements of methane, carbon monoxide and nitrous oxide made by an in situ Fourier transform infrared trace gas and isotope analyser operated at Lauder, New Zealand. We perform a practical evaluation of multi-year performance of the analyser and report on operational methodology, measurement precision, reproducibility, accuracy and instrument reliability.

Coastal waters serve as transport pathways to the ocean for all runoff from terrestrial sources; they are also some of the most biologically productive waters on the planet. Here, we retrieve atmospheric aerosol loading (and properties) from the space-based instrument MISR over all types of water (dark, coastal, etc). Results from the MISR research aerosol retrieval algorithm agree well with validation, indicating that MISR may add value to commonly used ocean color imagers such as MODIS.

This research demonstrates the use of an unmanned aerial vehicle (UAV) to characterize the gaseous and diesel particle emissions of a ship at sea. The field study was part of the research voyage “The Great Barrier Reef as a significant source of climatically relevant aerosol particles” on board the RV Investigator around the Australian Great Barrier Reef. Measurements of the RV Investigator exhaust plume were carried out while the ship was operating at sea, at a steady engine load.

We describe the enhancements made to the cloud–aerosol discrimination (CAD) algorithms used to produce the CALIPSO version 4 (V4) data products. Revisions to the CAD probability distribution functions have greatly improved the recognition of aerosol layers lofted into the upper troposphere, and CAD is now applied to all layers detected in the stratosphere and all layers detected at single-shot resolution. Detailed comparisons show significant improvements relative to previous versions.

We study a novel remote-sensing technique for atmospheric trace gases absorbing in the UV and visible spectral range. Using Fabry–Perot interferometers with a spectral transmission matched to the trace gas's spectral absorption allows for imaging trace gases with high sensitivity and selectivity. The thereby achieved high spatio-temporal resolution enables the study of small-scale and dynamic processes in the atmosphere. We present sample calculations and a proof-of-concept study.

This paper presents a new dataset of temperature profiles in the upper stratosphere and mesosphere acquired with the GOMOS spectrometer on board the European satellite ENVISAT. The principle is to observe the scattering of sunlight by air molecules at the Earth limb. The observed signal is proportional to the atmospheric density from which the temperature is derived. This technique provides a new source of information on temperature where satellite observations are sparse.

We report five species (naphthalene, methyl nitrite, allene, acrolein and acetaldehyde) that were detected in biomass burning fires that had been seen before in burn studies, but are reported for the first time when using infrared spectroscopy for detection.