Column-averaged dry-air mole fractions of CO₂ and CH₄ measured by a solar viewing portable Fourier transform spectrometer (EM27/SUN) were validated with in situ profile data obtained during the transfer flights of two aircraft campaigns. Atmospheric dynamical properties based on ERA5 and WRF-Chem were used as criteria for selecting the best aircraft profiles for the validation. The resulting air-mass-independent correction factors for the EM27/SUN data were 0.9878 for CO₂ and 0.9829 for CH₄.

We present 1 year of dual-scan ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of aerosol and tropospheric NO₂ in Uccle (Belgium). Measuring tropospheric NO₂ vertical column densities (VCDs) in different azimuthal directions has a positive effect on comparison with measurements from TROPOMI. We prove that the use of inadequate a priori NO₂ profile shape data in the TROPOMI retrieval is responsible for the systematic underestimation of S5P NO₂ data.

This paper describes the feasibility of using a differential absorption radar technique for the remote sensing of total column water vapor from a spaceborne platform.

In this work, we report the demonstration and validation of the aerosol properties retrieved using AirHARP and GRASP for data from the NASA ACEPOL campaign 2017. These results serve as a proxy for the scale and detail of aerosol retrievals that are anticipated from future space mission data, as HARP CubeSat (mission begins 2020) and HARP2 (aboard the NASA PACE mission with the launch in 2023) are near duplicates of AirHARP and are expected to provide the same level of aerosol characterization.

The IASI satellite sensor is used to document the variability and evolution of tropospheric ozone (O₃). IASI O3 retrievals generally use a single a priori profile which can be responsible for biases and too-low variability. We have therefore implemented a dynamical a priori profile based on pixel location, month and tropopause height. Comparison with 10 years of global ozonesonde profiles shows large improvements in the retrieved tropospheric O₃, with biases corrected and enhanced variabilities.

Cloud-top pressure (CTP) is an important cloud property for climate and weather studies. Based on differential oxygen absorption, both oxygen A-band and B-band pairs can be used to retrieve CTP. However, it is currently very challenging to perform a CTP retrieval accurately due to the complicated in-cloud penetration effect. To address this issue, we propose an analytic transfer inverse model for DSCOVR EPIC observations to retrieve CTP considering in-cloud photon penetration.

Ozone lidar is a state-of-the-art remote-sensing instrument to measure atmospheric ozone concentrations with high spatiotemporal resolution. In this study, we show that an ozone lidar can also provide reliable aerosol measurements through intercomparison with colocated aerosol lidar observations.

Some quadrupole aerosol chemical speciation monitors (Q-ACSMs) have had issues with the quantification of particulate chloride, resulting in apparent negative chloride concentrations. We can show that this is due to the different behavior of Cl⁺ and HCl⁺, and we present a correction for the more accurate quantification of chloride. The correction can be applied to measurements in environments where the particulate chloride is dominated by NH₄Cl.

Long-term photometer measurements of two sites on Spitsbergen, Barentsburg and Ny-Ålesund, in the European Arctic are presented and compared. We find slightly higher aerosol optical depths at Barentsburg and attribute this to a higher concentration of small particles.

This paper presents a novel method to constrain the size distribution derived from low-cost optical particle counters (OPCs) using satellite data to develop higher-quality particulate matter (PM) estimates. Such estimates can enable cities that do not have access to expensive reference air quality monitors, especially those in the global south, to develop effective air quality management plans.

In summer 2017, the research vessel Polarstern performed cruise PS106 to the Arctic north of Svalbard. In the frame of the cruise, remote-sensing observations of the atmosphere were performed on Polarstern to continuously monitor aerosol and clouds above the vessel. In our study, we present the deployed instrumentation and applied data analysis methods and provide case studies of the aerosol and cloud observations made during the cruise. Statistics of low-cloud occurrence are presented as well.

Here we present a study performed to determine the methane detection capabilities of a novel remote thermal instrument, the Multiband Uncooled Radiometer Imager. We utilize a novel methane detection approach, the normalized differential methane index, that when applied to simulated multispectral thermal imagery with a single spectral channel dedicated to methane detection shows similar results to a state-of-the-art method, the matched-filter approach.

Traditional instruments for detection and quantification of toxic metals in the atmosphere are expensive. In this study, we have designed, fabricated, and tested a low-cost instrument, which employs cheap components to detect and quantify toxic metals. Advanced machine learning (ML) techniques have been used to improve the instrument's performance. This study demonstrates how the combination of low-cost sensors with ML can address problems that traditionally have been too expensive to be solved.

We study O₃ retrievals in the 3040 cm^-1 spectral range from FTIR measurements at Xianghe China (39.75° N, 116.96° E; 50 m a.s.l.) between June 2018 and December 2019. It was found that the FTIR O₃ (3040 cm^-1) retrievals capture the seasonal and synoptic variations of O₃ very well. The systematic and random uncertainties of FTIR O₃ (3040 cm^-1) total column are about 13.6 % and 1.4 %, respectively. The DOFS is 2.4±0.3 (1σ), with two individual pieces of information in surface–20 km and 20–40 km.

We have developed a small, light-weight (radiosonde of 20 g with battery), low-cost, and easy-to-use upper-air radiosonde system: the Storm Tracker. With the ability to receive multiple radiosondes simultaneously, the system enables high temporal and spatial resolution atmospheric observations. In the 2018 field campaign, the accuracy of the Storm tracker was tested using co-launched data with Vaisala RS41-SGP radiosondes, and the measurements show an overall good agreement.

Online instruments have been widely applied for the measurement of PM_2.5 and its chemical components; however, these instruments have a major shortcoming in terms of the limited number (or lack) of species in field measurements. To this end, a new mass closure PM_2.5 online-integrated system was developed and applied in this work to achieve more comprehensive information on chemical species in PM_2.5, thus providing a powerful tool for PM_2.5 long-term daily measurement and source apportionment.

In this work we present experimental results of a novel actively heated fiber-optic (AHFO) observational wind-probing technique. We utilized a controlled wind-tunnel setup to assess both the accuracy and precision of AHFO under a range of operational conditions (wind speed, angles of attack and temperature differences). AHFO has the potential to provide high-resolution distributed observations of wind speeds, allowing for better spatial characterization of fine-scale processes.

The PurpleAir PA-II is a low-cost sensor for monitoring changes in the concentrations of particulate matter of various sizes. This study examined the behaviour of multiple PA-II units in four locations in the USA under atmospheric conditions when exposed to a variety of pollutants and different PM_2.5 concentrations. The PA-II unit is a promising tool for measuring PM_2.5 concentrations and identifying relative concentration changes, as long as the PA-II PM_2.5 values can be corrected.

Space agencies use moderate-resolution satellite imagery to study how smoke, dust, pollution (aerosols) and cloud types impact the Earth's climate; these space agencies include NASA, ESA and the China Meteorological Administration. We demonstrate in this paper that an algorithm with convolutional neural networks can greatly enhance the automated detection of aerosols and cloud types from satellite imagery. Our algorithm is an improvement on current aerosol and cloud detection algorithms.

Long-term monitoring of satellite-derived variables is necessary for a better understanding of the evolution of Earth parameters at global scale. However different instruments' observations used over the years need to be inter-calibrated with each other to provide meaningful information. This paper describes how a linear correction can improve the observations from the Scanning Multichannel Microwave Radiometer over continental surfaces to be more consistent with more recent radiometers.

This paper highlights a technique for facilitating anvil cloud detection based on visible observations that relies on comparative analysis with expected cloud reflectance for a given set of angles. A 1-year database of anvil-identified pixels, as determined from IR observations, from several geostationary satellites was used to construct a bidirectional reflectance distribution function model to quantify typical anvil reflectance across almost all expected viewing, solar, and azimuth angles.

The AROMAT campaigns took place in Romania in 2014 and 2015. They aimed to test airborne observation systems dedicated to air quality studies and to verify the concept of such campaigns in support of the validation of space-borne atmospheric missions. We show that airborne measurements of NO₂ can be valuable for the validation of air quality satellites. For H₂CO and SO₂, the validation should involve ground-based measurement systems at key locations that the AROMAT measurements help identify.

This paper is about a feasibility study of applying a machine learning technique to derive aerosol properties from a single MAX-DOAS sky scan, which detects sky-scattered UV–visible photons at multiple elevation angles. Evaluation of retrieved aerosol properties shows good performance of the ML algorithm, suggesting several advantages of a ML-based inversion algorithm such as fast data inversion, simple implementation and the ability to extract information not available using other algorithms.

We present the design of a nano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) apparatus that enables high accuracy and precision in hygroscopic growth measurements of aerosol nanoparticles with diameters less than 10 nm. We further introduce comprehensive methods for system calibration and validation of the performance of the system. We then study the size dependence of the deliquescence and the efflorescence of aerosol nanoparticles for sizes down to 6 nm.

The direct-Sun and inversion products of urban atmospheric aerosols, obtained from a Cimel Sun–sky radiometer in Pune, India, under the AERONET program since October 2004, have been reported in this paper. The mean seasonal variations in AOD from cloud-free days indicated greater values during the monsoon season, revealing dominance of hygroscopic aerosols over the station. Such results are sparse in India and are important for estimating aerosol radiative forcing and validating climate models.

In this study, we developed a new algorithm for cloud classification using solar radiation and cloud base height measurements. Our objective was to develop a simple and inexpensive but effective algorithm for the needs of studies related to ecosystem and atmosphere interactions. In the present study, we used the algorithm for obtaining cloud statistics at a measurement station in southern Finland, and we discuss the advantages and shortcomings of the algorithm.

A lidar intercomparison campaign was conducted over a period of 28 nights at Observatoire de Haute-Provence (OHP) in 2017 and 2018. The objective is to validate the ozone and temperature profiles at OHP to ensure the quality of data submitted to the NDACC database remains high. A mobile reference lidar operated by NASA was transported to OHP and operated concurrently with the French lidars. Agreement for ozone was better than 5 % between 20 and 40 km, and temperatures were equal within 3 K.

A new approach to derive stratospheric aerosol extinction profiles from SCIAMACHY solar occultation measurements based on an onion-peeling method is presented. The resulting extinctions at 452, 525 and 750 nm compare well with other limb and occultation data from, e.g. SAGE and SCIAMACHY, but show small oscillating features which vanish in monthly anomalies. Major volcanic eruptions, polar stratospheric clouds and influences of the quasi-biennial oscillation can be identified in the time series.

The time response of electrochemical concentration cell (ECC) ozonesondes points to at least two distinct reaction pathways with time constants of approximately 20 s and 25 min. Properly considering these time constants eliminates the need for a poorly defined "background" and allows reducing ad hoc corrections based on laboratory tests. This reduces the uncertainty of ECC ozonesonde measurements throughout the profile and especially in regions of low ozone and strong gradients of ozone.

The Balloon Lidar Experiment was the first lidar dedicated to measurements in the mesosphere flown on a balloon. During a 6 d flight, it made high-resolution observations of polar mesospheric clouds which form at high latitudes during summer at ~ 83 km altitude and are the highest clouds in Earth's atmosphere. We describe the instrument and assess its performance. We could detect fainter clouds with higher resolution than what is possible with ground-based instruments.

Currently, we do not know whether clouds will accelerate or moderate climate. We look to the past and ask whether cloudiness has changed over the last 4 decades. Using a suite of nine satellite instruments, we need to ensure that the first satellite, which was launched in 1980 and died in 1991, observed the same measurement as the eight other satellite instruments used in the record. If the instruments were measuring length and observing a 1.00 m long stick, they would all see 0.99 to 1.01 m.

Aerosol mass spectrometers (AMSs) are frequently applied in atmospheric aerosol research in connection with climate, environmental or health-related projects. The paper describes a new real-time technique for the measurement of organic peroxides, which play an important role in new particle formation and as reactive oxygen species in aerosol–health-related aspects of atmospheric aerosols.

We present a new instrument for the measurement of NO_x and NO_y based on a combination of the thermal dissociation of NO_y to NO_x and cavity ring-down spectroscopic detection of NO₂. It features a denuder to separate the contributions of gas-phase and particulate nitrates to NO_y. We provide a detailed characterization of the instrument and briefly outline results from first deployments.