SF₆ total columns are successfully retrieved from FTIR measurements (Saint Denis and Maïdo) at Reunion Island (21° S, 55° E) between 2004 and 2016 using the SFIT4 algorithm: the retrieval strategy and the error budget are discussed. The trend of SF₆ is analysed based on the FTIR retrievals at Reunion Island, the in situ measurements at America Samoa (SMO) and the collocated satellite measurements (MIPAS and ACE-FTS) in the southern tropics. The results show good agreement.

We discuss the relationships that link the observed fluctuation spectra of the amplitude and phase of signals used for the radio occultation sounding of the Earth's atmosphere with the spectra of atmospheric inhomogeneities. We demonstrate that the main contribution into the radio signal fluctuations comes from the internal gravity waves. These results may serve as the basis for the global monitoring of the wave activity in the stratosphere and upper troposphere.

This study assesses the potential of space-borne imagery of CO₂ atmospheric concentrations for monitoring the emissions from the Paris area. Such imagery could be provided by European and American missions in the next decade. It highlights the difficulty to improve current knowledge on CO₂ emissions for urban areas with CO₂ observations from satellites, and calls for more technological innovations in the remote sensing of CO₂ and in the models that exploit it.

The affordability and small size of low-cost particle sensors make them attractive for air pollution experiments that require multiple instruments, or take place in hard-to-access locations or low-income countries. For any sensor to be useful, its accuracy and precision need to be known. We evaluate the Alphasense OPC-N2 for monitoring airborne particles at typical UK urban background sites. The devices were found to be accurate provided they are correctly calibrated.

Ground-level ozone is a pollutant that affects both global climate change and regional air quality. Its complex formation chemistry makes the implementation of reduction strategies challenging and needs to be well understood to develop efficient strategies. This publication reports the development of an instrument capable of monitoring the ozone formation rate in the atmosphere. Its reliability was tested in the laboratory and in the field and important recommendations are given for improvement.

The GPS signal going through the atmosphere will experience refraction or bending, which can be precisely measured and used to infer the atmospheric properties. This paper demonstrates that high-quality atmospheric measurement with less than ~ 0.4 K is achievable from a GPS recording system with a simple antenna mounted on top of an aircraft cruising at ~ 13 km. Such a simple airborne GPS system can be implemented on commercial aircraft to provide valuable data for weather models in the future.

The paper focusses on gas-velocity retrievals in emission plumes using optical flow (OF) algorithms applied to remote sensing imagery. OF algorithms can measure the velocities on a pixel level between consecutive images. An issue of OF algorithms is that they often fail to detect motion in contrast-poor image areas. A correction based on histograms of an OF vector field is proposed. The new method is applied to two example volcanic data sets from Mt Etna, Italy and Guallatiri, Chile.

A new generation of the Infrared Atmospheric Sounding Interferometer (IASI) sounders, whose highly accurate measurements are commonly used in environment applications, has already been designed: IASI New Generation (IASI-NG). A database of IASI and IASI-NG simulated observations was built to set a common framework for future impact studies. This first study showed the IASI-NG benefit with an improvement of the temperature retrievals throughout the atmosphere and a lower benefit for the humidity.

In this study we focus on evaluating zero-difference processing of BDS RO data vs. single-difference processing. From the statistics, average bias (and standard deviation) of the bending angle and refractivity profiles were found to be as small as about 0.05–0.2 % (and 0.7–1.6 %) over the upper troposphere and lower stratosphere, including for the GEO, IGSO, and MEO subsets. Zero differencing was found to perform slightly better, as may be expected from its lower vulnerability to noise.

This work focuses on making unambiguous measurements of Arctic cloud phase and assessing those measurements within the context of cloud radiative effects. It is found that effects related to lidar data recording systems can cause retrieval ambiguities that alter the interpretation of cloud phase in as much as 30 % of the available data. This misinterpretation of cloud-phase data can cause a misinterpretation of the effect of cloud phase on the surface radiation budget by as much as 10 to 30 %.

Measuring the phase (liquid and ice) of Arctic clouds is essential for understanding the changing global climate. Using a lidar, two polarized signals are usually needed. At CRL lidar, one of these signals is small, so phase measurements have low resolution. Another method can use a large unpolarized signal in place of the small polarized signal. We show how to use the original low-resolution measurement to calibrate the new high-resolution method. At CRL, this gives 20 times higher resolution.

Our results demonstrated the benefits and challenges of using new SPME Arrow over SPME fiber for the sampling of BVOCs emitted by terrestrial vegetation in the atmosphere. The new SPME Arrow system showed significant improvement on sampling capacity, with collected amounts being approximately 2 times higher for monoterpenes and 7–8 times higher for aldehydes than with SPME fiber. Higher extraction efficiencies were obtained with dynamic collection prior to equilibrium regime.

Existing chamber technologies for direct measurements of number concentration of cloud condensation nuclei (NCCN) are sophisticated and expensive. In this paper, a new method is proposed to calculate NCCN based only on measurements of a humidified nephelometer system which have accounted for influences of both aerosol size and aerosol hygroscopicity on NCCN calculation. This new method makes NCCN measurements more convenient and is capable of obtaining NCCN at lower supersaturations.

Continuous monitoring of solar energy from space is critical for its efficient exploitation and distribution. For this reason we developed neural-network- and function-based real-time models, which are capable of producing massive radiation outputs in high spectral, spatial and temporal resolution. The models' performance against ground-based measurements revealed a dependence on input quality and resolution, and an overall accuracy under cloudless and high solar energy potential conditions.

We study the collocation mismatch uncertainty related to validating coarse-resolution satellite-based aerosol data against point-like ground based measurements. We use the spatial variability in the satellite data to estimate the upper limit for the uncertainty and study the effect of sampling parameters in the validation. We find that accounting for the collocation mismatch uncertainty increases the fraction of consistent data in the validation.

HIRS channel 12 on the series of NOAA weathersatellites is sensitive to humidity in the upper troposphere. A change in its central wavelength between NOAA 14 and 15 made it necessary to perform an intercalibration to retain a homogeneous time series. Here we show that the intercalibration of Shi and Bates (2011), which is based on statistical methods, can be underpinned by physical arguments using results of radiative transfer calculations.

Observations of multiwavelength Mie–Raman lidar during smoke episode over West Africa are compared with the vertical distribution of aerosol parameters provided by the MERRA-2 model. The values of modeled and observed extinctions at both 355 nm and 532 nm are also rather close. The model predicts significant concentration of dust particles inside the smoke layer. This is supported by a high depolarization ratio of 15 % observed in the center of this layer.

We describe a new algorithm for the Atmospheric Infrared Sounder (AIRS) that uses its thermal infrared spectra directly rather than using “cloud-clearing.” By additionally modelling clouds within an AIRS field-of-view, we retrieve temperature and water vapor profiles on the AIRS ~13.5 km horizontal footprint (at nadir) rather than the ~45 km footprint of cloud-cleared spectra. Initial validation is presented, and avenues for future development are discussed.

This paper describes the algorithm that will be used for estimating surface UV radiation from TROPOMI (TROPOspheric Monitoring Instrument) measurements. TROPOMI is the only payload of the Sentinel-5 Precursor (S5P), which is a polar-orbiting satellite mission of the European Space Agency (ESA). The presented algorithm has been tested using input based on previous satellite measurements. These preliminary results indicate that the algorithm is functioning according to expectations.

Data fusion is an important tool to reduce data volume and to improve data quality. This paper introduces a generalization of the complete data fusion method, which takes into account interpolation and coincidence errors. This upgraded algorithm extends the applicability of the technique to a wider range of cases. In fact, it also makes it possible to fuse vertical profiles of atmospheric parameters when they are represented on different altitude grids and refer to different true profiles.

The distribution of ice and liquid particles in clouds (i.e., their thermodynamic phase) has a large impact on Earth's climate. We report a global high spatial resolution survey of cloud phase based on a decade of data from the Hyperion orbital imaging spectrometer. Seasonal and latitudinal trends corroborate observations by the Atmospheric Infrared Sounder (AIRS). Most variance observed at climate model grid scales of 100 km is explained by spatial structure at finer spatial resolutions.

Temperature profiles from operational weather satellites are used to determine the global distribution of gravity wave activity. This is an important information to constrain global climate models. The quality of this data set is assessed by systematic comparison to model fields from ECMWF which are considered very high quality. This reveals good agreement between model and observations, albeit the model misses localized centers of wave activity if model resolution is too low.

Organic aerosol constitutes one of the major components of atmospheric particulate matter globally and is emitted from various sources. Therefore, identifying and quantifying the sources of organic aerosol accurately is a key task in the field. In this study, we applied a rather novel procedure for an improved source apportionment method (ME-2) to resolve the less meaningful or mixed factors problems for organic aerosol using the traditional method (PMF).

The CHRONOS space mission would provide observations for emissions and transport studies of the highly uncertain air pollutants carbon monoxide and methane, with sub-hourly revisit at fine horizontal spatial resolution across North America. CHRONOS uses an imaging gas filter correlation radiometer hosted in geostationary orbit. CHRONOS' capability for monitoring evolving, or unanticipated, air pollution sources would find societal applications for air quality management and forecasting.

Wildland fires, whether natural or prescribed, are increasing in frequency and magnitude worldwide. Smoke from these fires poses a threat to public and environmental health. This paper describes the development and evaluation of a low-cost monitor for wildland fire smoke. The monitor was designed to be compact, capable of real-time and time-integrated PM_2.5 measures, and powered by a combination of solar and battery power. Initial field testing of this device gave encouraging results.

In July 2016, a new ground-based 22 GHz spectrometer for measuring lower and middle atmospheric water vapor was installed at the Thule High Arctic Atmospheric Observatory located at Thule Air Base (76.5° N, 68.8° W), Greenland. The spectrometer, VESPA-22, is designed to operate automatically with little maintenance. The intercomparison between VESPA-22 dataset and the satellite-based Microwave Limb Sounder dataset shows an average difference within 1.4 % up to 60 km altitude.

This paper presents different depolarization calibration procedures used to improve the quality of the depolarization data. The results illustrate a significant improvement of the depolarization lidar products for all the selected EARLINET lidar instruments. The calibrated volume and particle depolarization profiles at 532 nm show values that fall within a range that is accepted in the literature. The depolarization accuracy estimate at 532 nm is better than ±0.03 for all cases.

The purpose of this work is to retrieve integrated water vapour using spectral measurements from Precision Solar Spectroradiometer (PSR). Two different approaches were developed one using single-channel direct sun irradiance measurements, and the second one integrating at a certain spectral region. The results of the spectral approach are closer to the retrievals of non-photometric techniques (GPS, microwave radiometer and radiosondes), suggesting this method provide more accurate IWV product.

We present an assessment of the predicted information content and retrieval errors for ¹³CH₄ retrieval from the planned GOSAT-2 satellite, assuming a wide range of land surface conditions. Retrieval of this quantity may allow for estimation of methane source types (e.g. biological or non-biological) based on the δ¹³C metric. We conclude that GOSAT-2 can be used for this purpose (to an accuracy of 10 ‰) assuming sufficient spatial (regional) and temporal (at least monthly) averaging.

We apply linear and non-linear representations of wave fields, based on Fourier integral operators and Wigner distribution function, to the retrieval of reflected rays from radio occultation observations. We introduce a reflection index that characterizes the relative intensity of the reflected ray. A comparison of indices evaluated for a large base of events including the visual identification of reflections indicated a good agreement with our definition of reflection index.

This study cross-compares the 10-year record of GPS radio occultation (GPS-RO) specific humidity product against independent databases (e.g., AIRS satellite, NASA/MERRA, and ERA-Interim). Our objective is to investigate the suitability of the GPS-RO humidity as a climate variable, which the science community could use in climate research. GPS-RO offers high vertical resolution, low sensitivity to clouds, and long-term stability making GPS-RO humidity a valuable complementary data set.

Isotope measurements are useful for separating different methane sources. However, the lack of widely accepted standards and calibration methods for stable carbon and hydrogen isotopic ratios of methane in air has caused significant measurement offsets among laboratories. We conducted worldwide interlaboratory comparisons, surveyed the literature and assessed them systematically. This study may be of help in future attempts to harmonize data sets of isotopic composition of atmospheric methane.

A new data generation scheme that employs the Mersenne twister (MT) pseudorandom number generator is proposed to conduct benchmark tests on a variety of linear regression techniques. With an appropriate weighting, Deming regression (DR), weighted ODR (WODR), and York regression (YR) are recommended for atmospheric studies when both x and y data have measurement errors. An Igor-based program (Scatter Plot) is developed to facilitate the regression implementation.