Identical EC systems on two sides of a building in central Helsinki were used to assess the uncertainty of the vertical fluxes on the single measurement point from July 2013 to September 2015. Sampling at only one point yielded up to 12% underestimation in the cumulative carbon fluxes; for sensible and latent heat the respective values were up to 5 and 8%. The commonly used statistics, kurtosis and skewness, are not necessarily suitable for filtering out data in a densely built urban area.

Clouds are a very important component of the climate system and of the hydrological cycle in the Arctic and sub-Arctic. A joint analysis of the cloud parameters obtained remotely from satellite and ground-based observations near St Petersburg, Russia, has been made. Our study has revealed considerable differences between the cloud properties over land and over water areas in the region under investigation.

Fog and low clouds (FLCs) are a valuable source of water for many ecosystems in the Namib. This study presents the first fully diurnal satellite detection of FLCs, revealing the spatial and temporal patterns in the Namib. A validation is conducted against station measurements in the central Namib and shows a high overall accuracy. The average timing and persistence of FLCs seem to depend on the distance to the coast, suggesting that the region is dominated by advection-driven FLCs.

We developed a technique for inferring the physical properties (amount, size and density) of falling snow from radar observations made using multiple different frequencies. We tested this method using measurements from airborne radar and compared the results to direct measurements from another aircraft, as well as ground-based radar. The results demonstrate that multifrequency radars have significant advantages over those with a single frequency in determining the snow size and density.

Chemical analysis of sub-30 nm aerosol particles is important for understanding aerosol nucleation and early growth, yet it is still an experimental challenge. In this study, we present a novel device for size resolved chemical analysis of nucleation and Aitken mode particles (from ~10 to ~30 nm) while allowing gas phase measurements with the same detector. Particles are charged, size selected, electrostatically collected and then thermally desorbed in a carrier gas.

On 13 October 2017, the S5-P satellite was launched with TROPOMI as its only payload. One of the primary products is atmospheric CO observed with daily global coverage and spatial resolution of 7 × 7 km². The new dataset allows the sensing of CO enhancements above cities and industrial areas and can track pollution transport from biomass burning regions. Through validation with ground-based TCCON measurements we show that the CO data product is already well within the mission requirement.

With the recent commercial availability of rotary-wing unmanned aircraft systems (rwUAS), their ability to collect observations in the lower atmosphere is quickly being realized. However, integrating sensors with an rwUAS can introduce errors if not sited properly. This study discusses an objective method of determining some of these error sources in temperature, including improper airflow and rotary motor heating. Errors can be mitigated by mounting thermistors under propellers near the tips.

The objective of this work is to minimize the errors at the highest altitudes of a lidar temperature profile which arise due to background estimation and a priori choice. The systematic method in this paper has the effect of cooling the temperatures at the top of a lidar profile by up to 20 K – bringing them into better agreement with satellite temperatures. Following the description of the algorithm is a 20-year cross-validation of two lidars which establishes the stability of the technique.

A newly developed hemispherical thermal infrared cloud camera (IRCCAM) is presented. The IRCCAM allows automatic cloud detection during the day and at night-time. The cloud fraction determined from the IRCCAM is compared with the cloud fraction determined from other instruments over a time period of 2 years. The IRCCAM has an agreement of +/- 2 oktas cloud fraction in 90 % of the data compared to other instruments. There are no significant differences between seasons or different times of day.

For long-term monitoring of CO₂ in the atmosphere it is crucial that standard reference gas mixtures stored in high-pressure aluminum cylinders, used to calibrate global measurements, remain stable over their whole time of use. This study finds a reproducible small enrichment as a cylinder is emptied at a low-flow rate, as well as somewhat larger and variable effects when a cylinder is emptied using a high-flow rate.

In this work we further developed and evaluated an operational weather diagnostic application, the WegenerNet Wind Product Generator (WPG), and applied it to the WegenerNet Johnsbachtal (JBT), a dense meteorological station network located in a mountainous Alpine region. The WPG automatically generates gridded high-resolution wind fields in near-real time with a temporal resolution of 30 min and a spatial resolution of 100 m x 100 m.

The detection of low concentrations of ice-nucleating particles (INPs) is challenging. Here we present a new technique (IR-NIPI) that is sensitive to low concentrations of INPs (> 0.01 L⁻¹) and uses an infrared camera with a novel calibration to detect the freezing of experimental suspensions. IR-NIPI temperature measurements prove to be robust with a series of comparisons to thermocouple measurements. Experimental comparisons to other freezing assay instruments are also in agreement.

This study introduces an in situ experimental approach to direct measurement of N₂O₅ heterogeneous reactivity in polluted environments. Laboratory tests, model simulations, and field deployment of the method at a polluted site in south China demonstrated its applicability in accurately measuring N₂O₅ uptake coefficient with high ambient pollutants levels and air mass changes. The introduced method is also applicable to in situ measurement of reactivity of other trace gases on ambient aerosols.

We present the error budget for the calibrated and geolocated spectra of the MIPAS limb sounder which flew on the ENVISAT satellite from 2002 to 2012. The impact of the different error sources on the spectra is characterized in terms of spectral, vertical, and temporal correlation. The radiometric error is in the order of 1 to 2.4 %, the spectral accuracy is better than 0.3 ppm, and the line of sight accuracy at the tangent point is around 400 m. All errors are well within the requirements.

Methane is a powerful greenhouse gas emitted from numerous human activities. Space-based observation of point sources would be a cost-effective monitoring solution, but the resolution of most current and planned methane-observing satellites is too coarse to resolve individual emitters. We simulate fine-resolution (50 m) satellite observations of methane plumes as would be measured by GHGSat (to be launched in 2019) and show that such data can usefully quantify large methane point sources.

Compositional analysis of atmospheric and laboratory aerosols is often conducted with mass spectrometry. In this study, machine learning is used to automatically differentiate particles on the basis of chemistry and size. The ability of the machine learning algorithm was then tested on a data set for which the particles were not initially known to judge its ability.

This paper describes comprehensive upgrades to the algorithms used to retrieve altitude-resolved profiles of cloud and aerosol extinction coefficients from the elastic backscatter measurements made by the space-based CALIPSO lidar. The CALIPSO version 4 data products generated by these new algorithms are explored in detail, and the many areas of improvement are highlighted using extensive comparisons both to previous versions and to collocated measurements made by space-based passive sensors.

This study presents the first measurements of ambient methylglyoxal, an important atmospheric α-dicarbonyl, using proton transfer reaction time-of-flight mass spectrometry. These measurements mostly agree with concomitant measurements from a reference technique: the DNPH derivatization technique and high-performance liquid chromatography with UV detection. In addition, a careful investigation of the differences between the two techniques is carried out to explain the disagreements observed.

MAIAC algorithm used for the MODIS C6 processing is described. MAIAC combines time series analysis and pixel/image-based processing to improve the accuracy of cloud detection, aerosol retrievals and atmospheric correction. MAIAC offers an interdisciplinary suite of atmospheric, land surface and snow products. Due to generally high quality, high resolution and high coverage, MAIAC AOD and surface reflectance/BRDF have been widely used for air quality and land research and applications.

The oxidative potential (OP) of ambient particulate matter (PM) has recently gained attention as an alternative metric for assessing the ambient PM toxicity. However, a major constraint in measuring the OP is its labor-intensive protocol. Here, we developed a new online instrument by coupling a mist chamber to an automated analytical system which can measure the real-time OP of ambient PM. We also report for the first time, the hourly averaged diurnal profile of ambient PM OP at an urban site.

The performance of the lidar measurements in comparison with radio soundings generally shows small RMSD (bias) for wind speed of around 1 m s⁻¹ (0.1 m s⁻¹) and for a wind direction of around 10° (1°). The post-processing of the non-motion-stabilized data shows comparably high quality to studies with motion stabilized systems. Ship-based doppler lidar measurements can contribute to filling the data gap over oceans, particularly in polar regions.

The GNSS Occultation Sounder (GNOS) is one of the new-generation payloads on board the Chinese FengYun 3 (FY-3) series of operational meteorological satellites for sounding the Earth’s neutral atmosphere and ionosphere. FY-3C GNOS, on board the FY-3 series C satellite launched in September 2013, was designed to acquire setting and rising radio occultation (RO) data by using GNSS signals from both the Chinese BDS and the US GPS. This paper reviews the FY-3C GNOS mission.

A new snow/snowmelt screening approach – combining a normalized difference snow index (NDSI)- and brightness temperature (BT)-based snow test, snow adjacency test and spatial filter – is proposed to significantly reduce the snow/snowmelt contamination in the NOAA’s operational Visible Infrared Imaging Radiometer Suite (VIIRS) aerosol optical depth (AOD) product, particularly over Northern Hemisphere high-latitude regions during spring thaw.

CFC-11 is a stratospheric-ozone-depleting molecule which is banned under the Montreal Protocol but still present in the atmosphere due to its long lifetime. Using infrared limb sounders on satellite platforms to monitor its concentration crucially requires accurate laboratory spectroscopic data. This paper describes a new high-resolution infrared absorption cross-section dataset for remote-sensing purposes; this improves upon the one currently available in the HITRAN and GEISA databases.

We introduce a new global satellite product of aerosol amounts lofted above the clouds from near-UV observations of Aura/OMI. The global decadal record derived from the product has revealed unprecedented quantitative information of light-absorbing aerosols above the cloud over several oceanic and continental regions of the world. The new dataset characterizing the optical properties of aerosol-cloud overlap will help quantify their radiative effects and representation in climate models.

The French and German space agencies (CNES, DLR) are currently developing MERLIN, a satellite that will measure atmospheric concentration of methane, a powerful greenhouse gas. To reach the desired precision, horizontally averaging the measurements along the satellite track is performed but leads to a processing bias due to non-linear equations. This article studies the processing biases for several averaging schemes and bias correction algorithms and recommends a best approach to limit biases.

Polar stratospheric clouds (PSC) have major relevance to the processes leading to polar ozone depletion. A good understanding of these particles is a prerequisite to predict their role in a changing climate. We present the first global set of PSC volume density profiles derived from the MIPAS satellite measurements covering the entire mission period between 2002 and 2012. A comparison to CALIOP lidar measurements is provided. The dataset can serve as a basis for evaluation of atmospheric models.

Ultra-high-frequency radar wind profilers are widely used for remote sensing of horizontal and vertical wind velocity. They emit electromagnetic radiation at a wavelength of 60 cm and receive signals from both falling particles and the air itself. In this paper, we describe a method to separate both signal components with the help of an additional cloud radar system in order to come up with undisturbed measurements of both vertical air velocity and the fall velocity of particles.