Measurements of atmospheric trace gases by absorption spectroscopy are frequently supported by recording the amount of trace gas in absorption cells. These are typically small glass (or quartz) cylinders containing the gas to be studied. Here we show in the example of NO₂-absorption cells that the effective amount of gas seen by the instrument can deviate greatly from expected values (by orders of magnitude in severe cases). Some suggestions for improving the situation are discussed.

We present a feasibility study on retrieving ¹²CH₄ and ¹³CH₄ using the recently launched TROPOMI on the Copernicus Sentinel 5P satellite and the future UVNS instrument on Sentinel 5. The ratio of ¹²CH₄ and ¹³CH₄ can be used to calculate the δ¹³C value, which has been shown to be able to distinguish between biological and non-biological sources of methane. We show that Sentinel 5/UVNS may be used to distinguish between methane source types, while Sentinel 5P/TROPOMI is subject to large biases.

Isotopic analysis offers a potential tool to distinguish between sources and interpret transformation pathways of atmospheric species. We applied recently developed techniques in our lab to characterize the isotopic composition of reactive nitrogen species (NO_x, HONO, HNO₃, pNO₃^-) in fresh biomass burning emissions. Intercomparison with other techniques confirms the suitability of our methods, allowing for future applications of our techniques in a variety of environments.

Single scattering albedo (SSA) is critical for reducing uncertainties in radiative forcing assessment. This paper presents two methods to retrieve SSA from satellite observations of the near-UV absorbing aerosol index (UVAI). The first is physically based radiative transfer simulations; the second is a statistically based machine learning algorithm. The result of the latter is encouraging. Both methods show that the ALH is necessary to quantitatively interpret aerosol absorption from UVAI.

The overlapping beams of some satellite observations contain spatial information that is discarded by most data processing techniques. This study applies an established technique in a new way to improve the spatial resolution of retrieval targets, effectively using the overlapping information to achieve a higher ultimate resolution. It is argued that this is a more optimal use of the total information available from current microwave sensors, using AMSR2 as an example.

Continuous measurements of greenhouse gases using high-precision spectrometers started in 2011 on a tall tower with three sampling inlets at 10 m, 50 m and 120 m above the ground at the OPE station, in the eastern part of France. The measurement strategy for carbon dioxide (CO₂), methane (CH₄) and carbon monoxide (CO) follows the ICOS recommendations. Over the 2011–2018 period, the CO₂ and CH₄ data show trends with annual growth rates of 2.4 ppm yr⁻¹ and 8.8 ppb yr⁻¹ at the 120 m level.

This study demonstrates the use of a low-cost sensor in a citizen-science network, Citizen-Enabled Aerosol Measurements for Satellites (CEAMS), to measure air quality in participants’ backyards. The pilot network was conducted in the fall and winter of 2017 in northern Colorado. Measurements of aerosols taken by the citizens are also compared to standard air quality instruments.

Turbulence is the variation of wind velocity on short timescales. In this study we introduce a new method to measure turbulence in a two-dimensionial plane with lidar instruments. The method allows for the detection and quantification of subareas of distinct turbulence conditions in the observed plane. We compare the results to point and profile measurements with more established instruments. It is shown that turbulence below low-level jets and in wind turbine wakes can be investigated this way.

This work evaluates the performance of three sensors that monitor black carbon (soot). These sensors exhibit similar behavior to their rack-mounted counterparts and are therefore promising for more extended use. A reconstruction of the black carbon mass vertical distribution above Athens, Greece, is shown using drones, similar to those acquired by remote-sensing techniques. The potential of combining miniature sensors with drones for at least the lower part of the atmosphere is exhibited.

Nitrous acid (HONO) is key species for understanding tropospheric chemistry, yet accurate and precise measurements are challenging. Here we report an inter–comparison exercise of a number of instruments that measured HONO in a highly polluted location (Beijing). All instruments agreed on the temporal trends yet displayed divergence in absolute concentrations. The cause of this divergence was unclear, but it may in part be due to spatial variability in instrument location.

The majority of aerosol data are obtained from daytime measurements using the Sun as a light source, and there are few datasets available for studying nighttime aerosol characteristics. To estimate the aerosol optical depth (AOD) during the nighttime using the moon as a light source, a radiometer for the daytime was modified, and a new calibration method was developed. As a result, the estimations of the nighttime AOD were made with the same degree of precision and accuracy during the daytime.

The intercomparison of satellite- and ground-measured aerosol absorption properties, such as presented here using Aura-OMI and SKYNET sensors, constitutes an important exercise to evaluate relative performance, track algorithm changes, and to diagnose retrieval accuracy and issues. The two datasets are found to agree reasonably well under moderate to higher aerosol loading but show disagreement under lower aerosol amounts due to retrieval issues in both techniques.

For two cases from the NASA ORACLES experiments, we retrieve aerosol and cloud properties and calculate a direct aerosol radiative effect (DARE). We investigate the relationship between DARE and the cloud albedo by specifying the albedo for which DARE transitions from a cooling to warming radiative effect. Our new aerosol retrieval algorithm is successful despite complexities associated with scenes that contain aerosols above clouds and decreases the uncertainty on retrieved aerosol parameters.

Aerosols are one of the drivers of climate change, and more information about aerosol vertical distribution is needed to analyze the role of aerosols in the atmosphere. In this work, we match and substitute a pixel along the lidar ground track for every pixel that is not on the track based on the radiance measured by a passive imager, therefore expanding the atmosphere profiles to a nearby region. The accuracy of the construction is confirmed through a procedure mimicking the construction.

Aerosol optical depth (AOD) from a geostationary satellite has been retrieved, and validated and diurnal cycles of aerosols are discussed over the eastern hemisphere and a 2-month period of May–June 2016. The new AOD product matches well with AERONET as well as with the standard MODIS product. Future work to make this algorithm operational will need to re-examine masking including snow masks, re-evaluate assumed aerosol models for geosynchronous geometry and address the surface characterization.

The Universal Cloud and Aerosol Sounding System (UCASS) is a low-cost miniature optical particle counter (OPC) capable of sizing particles in the size range 0.4–40 μm. The open-geometry design makes the instrument suitable for deployment on balloon-borne sounding systems, dropsonde systems or as part of an unmanned aerial vehicle (UAV). Laboratory and field experiments show good agreement with reference instruments in a range of cloudy and dusty environments.

In the present paper, we present a novel remote-sensing technique for the measurement of ice crystal number concentrations in clouds. The fall velocity of ice crystals measured with values from cloud radar and a radar wind profiler is used in order to derive information about ice crystal size and number concentration. In contrast to existing methods based on the combination of lidar and cloud radar, the present method can also be used in optically thick clouds.

This paper discusses a neural network forward model used by the operational aerosol layer height (ALH) retrieval algorithm for the TROPOspheric Monitoring Instrument (TROPOMI) on board the European Sentinel-5 Precursor satellite mission. This model replaces online radiative transfer calculations within the oxygen A-band, improving the speed of the algorithm by 3 orders of magnitude. With this advancement in the algorithm's speed, TROPOMI is set to deliver the ALH product operationally.

A novel chemical ionization methodology for rapid gas–phase environmental monitoring is presented. The usefulness of the new inlet design is demonstrated by measuring various aerosol precursor compounds that are present at very low concentrations by using two consecutive ionization schemes. This new inlet enables the detection of a wide range of compounds of interest with a minimum of effort and at a fast repetition rate.

Deposition or other passive measurement techniques are used to sample mineral dust from the atmosphere. However, there exist a multitude of different collection instruments with different, usually not well-characterized sampling efficiencies, so the resulting data might be considerably biased with respect to their size representatively. In the paper, we report on collection properties of different deposition and other passive samplers based on single-particle measurements.

This paper demonstrates the use of high-resolution 2-D plume imagery from airborne remote sensing retrievals to quantify methane point-source emissions. It shows significant improvements on the flux estimates without the need for direct wind speed measurements. This paves the way for enhanced flux estimates in future field campaign and space-based observations to better understand the magnitude and distribution of various point sources of methane.

Lee waves have been detected in clear-sky conditions over the Mediterranean Sea using the total column water vapour (TCWV) fields. The products were generated applying the Advanced Infra-Red WAter Vapour Estimator (AIRWAVE) retrieval algorithm to the thermal infrared measurements of the Along Track Scanning Radiometer (ATSR) instrument series. A subset of the occurrences has been compared with both independent observations and model simulations.

The Copernicus Anthropogenic CO₂ Monitoring (CO2M) mission is a proposed constellation of imaging satellites with a CO₂ instrument as main payload and optionally instruments for NO₂, CO and aerosols. This study demonstrates the huge benefit of an NO₂ instrument for detecting city plumes and weak point sources. Its main advantages are the higher signal-to-noise ratio and the lower sensitivity to clouds that significantly increases the number of observations available for quantifying CO₂ emission.

We investigate the radiance offset in the O₂ A band of GOSAT spectrometer and quality of the offset-corrected solar-induced chlorophyll fluorescence (SIF). An analysis of temporal variation of the offset suggests that the radiometric sensitivity of the spectrometer changed after switching the optics path selector in January 2015. Comparisons at multiple spatial scales show good agreement between GOSAT SIF and OCO-2 SIF, which supports the consistency among the present satellite SIF data.

We evaluated the performance of HONO measurement by a wet-denuder--ion0chromatography system (WD/IC, MARGA). We found significant artificial HONO formed from the reaction of NO₂ oxidizing SO₂ in the denuder solution. High ambient NH₃ would elevate the pH of the denuder solution and promote the overestimation of HONO. A method was established to correct the HONO measurement by WD/IC instruments.

The anisotropy of Earth's surface reflection plays an important role in satellite-based retrievals of cloud, aerosol, and trace gases. Most current ultraviolet and visible satellite retrievals utilize climatological surface reflectivity databases that do not account for surface anisotropy. The GLER concept was introduced to account for such features. Here we evaluate GLER for water surfaces by comparing with OMI measurements and show that it captures these surface anisotropy features.

We introduce an algorithm that is used to simultaneously derive the abundances of the important atmospheric constituents carbon monoxide and methane from the TROPOMI instrument onboard the Sentinel-5 Precursor satellite, which enables the determination of both gases with an unprecedented level of detail on a global scale. The quality of the resulting data sets is assessed and the first results are presented.

Accurate measurement of variations in atmospheric O₂ can provide useful information about atmospheric, biospheric, and oceanic processes, which is a challenge for existing measurement techniques. Here, we introduce a newly built high-precision, stable CRDS analyzer (Picarro G2207) that can measure O₂ mixing ratios with a short-term precision of < 1 ppm and only requires calibration every 12 h. Measurements from tower and mountain sites are also presented.

This paper presents the TROPOMI-SWIR performance and health after a year of full operations. Using the on-going monitoring program, TROPOMI-SWIR is shown to be in excellent health and is performing as well as, if not better than, expected. With the exception of a tiny loss of detector pixels (less than 0.05 % over a full year), no components appear to be degrading. We show that TROPOMI-SWIR is expected to keep on providing excellent data for the full S5-P lifetime.

A tethered-balloon system deployed supercooled liquid water content sondes and fiber optic distributed temperature sensing to collect in situ atmospheric measurements within mixed-phase Arctic clouds. These data were validated against collocated surface-based and remote sensing datasets. From these measurements and sensor evaluations, tethered-balloon flights are shown to offer an effective method of collecting data to inform numerical models and calibrate remote sensing instrumentation.

Here we present the development and applicability of the DRoplet Ice Nuclei Counter Zurich (DRINCZ). DRINCZ allows for ice nuclei in the immersion mode to be quantified between 0 and -25 °C with an uncertainty of ±0.9 °C. Furthermore, we present a new method for assessing biases in drop-freezing apparatuses and cumulative ice-nucleating-particle concentrations from snow samples collected in the Austrian Alps at the Sonnblick Observatory.