The hydroxyl radical is the primary atmospheric oxidant in the atmosphere, and measurements of its concentration provide a rigorous test of our understanding of atmospheric chemistry. This paper presents measurements of a potential interference with measurements of OH using laser-induced fluorescence techniques, which may contribute to measurements of OH in forested environments. The results may help to explain discrepancies between measurements and model predictions in these environments.

In this paper, we focus on the validation of OMI ozone (PROFOZ) product in the stratosphere using MLS ozone observations. This paper, with its companion paper focusing on the validation in the troposphere by using global ozonesonde observations, provides us with a comprehensive understanding of the data quality of OMI PROFOZ product and impacts of the “row anomaly”.

We have developed a laboratory system that provides mass spectra of individual particles, roughly 20 microns in diameter, after they have been levitated in an electric field. Measured evaporation of polyethylene glycol particles was found to agree with a kinetic model. The system can be used to study fundamental chemical and physical processes involving particles that are difficult to isolate and study with other techniques, and hence improve our understanding of atmospheric particles.

Vapor pressures of low-volatility organic molecules at atmospheric temperatures reported in the literature often differ by several orders of magnitude between measurement techniques. These discrepancies exceed the stated uncertainty of each technique, which is generally reported to be smaller than a factor of 2. We determined saturation vapor pressures for the homologous series of polyethylene glycols ranging in vapor pressure at 298 K from 1E⁻⁷ Pa to 5E⁻² Pa as a reference set.

Reactive oxygen species (ROS) in the particle phase may induce oxidative stress in the human lungs upon inhalation. Here we present and thoroughly characterize a modified online and offline ROS analyzer. Selected model organic compounds were tested and potential interferences from gas-phase and matrix effects of particulate constituents were evaluated. ROS measurements of filter samples revealed the rapid decay of a substantial ROS fraction, supporting the application of online measurements.

The estimation of precipitable water vapour (W) content is of great interest in both meteorological and climatological studies. Sun photometers allowed the development of W automatic estimations with high temporal resolution. A new methodology, based on the hypothesis that the calibration parameters characterizing the atmospheric transmittance are dependent on vertical profiles of temperature, air pressure and moisture typical of each measurement site, has been presented providing good results.

This paper describes measurements of the conversion efficiency of several organic peroxy radicals upon reaction with nitric oxide to the hydroperoxy radical, which can interfere with measurements of the latter. This interference could explain some of the discrepancies between measurements and model predictions of the hydroperoxy radical. Previous measurements of the hydroperoxy radical during the Mexico City Metropolitan Area campaign in 2006 are reanalyzed to account for the interference.

We study the systematic discreapancies between atmospheric refractivity derived from radio occulation (RO) sounding of the Earth's atmosphere and the reanalyses of the European Centre for Medium-Range Weather Forecasts. We construct a regression-based bias model. The model can be used for the RO data propagation in the new reference occultation processing system (rOPS) including the uncertainty propagation through the retrieval chain.

Precise global measurement of CO₂ in the Earth’s atmosphere is needed to understand carbon–climate feedbacks. Ideally we would measure from space 24/7 over all land and sea surfaces, in all-sky conditions, clouds, haze or dust and achieve near 100 % usable data. NASA-GSFC has developed a laser instrument to measure CO₂ from an aircraft flying at over 40 000 feet as a satellite precursor. Here we demonstrate this measurement capability, highlighting data in the presence of a variety of clouds.

A comparison of measurements of 7 volatile organic compounds (VOCs) in urban air by 3 different methods is presented. An uncertainty was calculated for each method and VOCs measured to provide some idea of the reliability of the data. Even when this uncertainty was accounted for, the measurements from the different methods did not agree for 4 of the 7 VOCs. Thus, there is unaccounted uncertainty in VOC measurements which must be considered when utilizing the data and assessing their reliability.

Estimating aerosol layer height in the atmosphere from satellite data in the oxygen A band (758–770 nm) over land is challenging over land, since the surface is generally very bright in this wavelength region. This paper discusses an interplay between the surface and the atmosphere in their contributions to the top-of-atmosphere reflectance spectrum and the consequent biases obtained while estimating aerosol layer height, using synthetic data and real data from the GOME-2 satellite instrument.

We launched the DSCOVR spacecraft to an orbit located near the earth–sun gravitational plus centrifugal force balance point known as Lagrange 1. One of the earth-viewing instruments, EPIC, measures earth-reflected radiances in 10 wavelength channels ranging from 317.5 nm to 779.5 nm. We use the UV channels to retrieve O₃ and scene reflectivity, and to derive the first measurement of erythemal flux (sunburn) from sunrise to sunset at the earth's surface.

Mineralogy of silicate mineral dust has a strong influence on climate and ecosystems due to variation in physiochemical properties that result from differences in composition and crystal structure (mineral phase). Traditional offline methods of analysing mineral phase are labour intensive and the temporal resolution of the data is lost. We introduce a novel technique that enables the online differentiation of mineral phase in silicate particles by single-particle mass spectrometry.

We investigate stratospheric gravity wave observations by the Atmospheric InfraRed Sounder (AIRS) and the High Resolution Dynamics Limb Sounder (HIRDLS). Waves seen by AIRS contribute significantly to momentum flux, which indicates a calculated momentum flux factor. AIRS and HIRDLS agree well in the phase structure of the wave events and also in the seasonal and latitudinal patterns of gravity wave activity and can be used complementary to each other.

Ice nucleating particles (INPs) affect the clouds' ice properties and can influence Earth’s hydrological cycle and climate. Here we present a detailed validation of WISDOM, a setup for the study of heterogeneous ice nucleation in an array of micron-sized droplets, and a demonstration of how it can be applied for the study of ice nucleation properties of ambient particles collected during dust storm events in Israel.

This article describes a method to determine the polarization sensitivity of SCIAMACHY, a spectrometer on Envisat, from in-orbit data. Polarization is a preference of a direction in which light oscillates, and many optical instruments suffer from a dependence of their measured signals on this. To measure and correct for this effect, a statistical analysis of in-flight data combined with a model of the atmosphere and the instrument was performed, showing that the instrument changed after launch.

Low-cost sensors promise neighborhood-scale air quality monitoring but have been plagued by inconsistent performance for precision, accuracy, and drift. CMU and SenSevere collaborated to develop the RAMP, which uses electrochemical sensors. We present a machine learning algorithm that overcomes previous performance issues and meets US EPA's data quality recommendations for personal exposure for NO₂ and tougher "supplemental monitoring" standards for CO & ozone across 19 RAMPs for several months.

The use of low-cost sensors for air pollution research has outpaced our understanding of their capabilities and limitations under real-world conditions. Here we describe the deployment, calibration and evaluation of electrochemical sensors on the Island of Hawai‘i. We obtain excellent performance (RMSE < 7 ppb, r² = 0.997) across a wide dynamic range (1 ppb–2 ppm). We introduce a hybrid regression algorithm which works across a large dynamic range and shows little decay in sensitivity over time.

Assessing emissions of volcanos has a three-fold importance: providing input for climate evolution models (CO₂ is one of the major constituents of emissions), quantifying pollutant emissions (HCl, HF and SO₂ are released in hundreds of tons/day) and monitoring the status of the magmatic chambers. For these purposes we realized gas analysers based on spectroscopic techniques, which must be sensitive, light and resistant to the emitted gases. This paper reports on the measurement of CO₂ and HF.

PHIPS-HALO is a novel aircraft instrument for cloud research. It combines microscopic imaging of single cloud particles with the measurement of their spacial light scattering properties. The knowledge of how atmospheric ice particles in clouds scatter visible light is important for improving future climate models.

The unique Earth view of the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) orbiting at the point of equal attraction from the Earth and the Sun can significantly augment the low-orbit remote sensing of aerosols, clouds and gases. We derive the relationship between the digital counts and the reflected sunlight intensity for some EPIC channels using collocated Earth views from EPIC and Moderate Resolution Imaging Spectroradiometer (MODIS) and EPIC moon views.

This study is a major version upgrade of the aerosol product from GOCI, the first and unique ocean color imager in geostationary earth orbit. It describes the improvement of version 2 of the GOCI Yonsei aerosol retrieval algorithm for near-real-time processing with improved accuracy from the modification of cloud masking, surface reflectance, etc. The product is validated against AERONET/SONET over East Asia with analyses of various errors features, and a pixel-level uncertainty is calculated.

In this paper we present the operational cloud retrieval algorithms for the TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5 Precursor (S5P) mission: OCRA (Optical Cloud Recognition Algorithm) retrieves the cloud fraction using measurements in the UV–VIS spectral regions, and ROCINN (Retrieval of Cloud Information using Neural Networks) retrieves the cloud top height and optical thickness using measurements in and around the oxygen A-band in the NIR.

This study outlines a new methodology for assessing air pollution from space using observations from Multi-angle Imaging SpectroRadiometer (MISR). Both air pollution amounts – as well as the uncertainties associated with space observations – are simultaneously and consistently obtained from MISR measurements over oceans. The new products have superior quality to the previous versions and will benefit the air pollution community.

The hotplate precipitation gauge has the potential to solve some problems with conventional precipitation gauge measurements, especially for snowfall. This paper extends the seminal published work, Rasmussen et al. (2011). We assert that the precipitation rate algorithm we have developed for the hotplate is an improvement on that which was previously published.

This paper describes the absolute validation of the novel, calibration-free SEALDH-II hygrometer at a traceable humidity generator. During 23 days of permanent operation, 15 H₂O mole fractions levels (5–1200 ppmv) at 6 gas pressures (65–950 hPa) were validated. With this validation, SEALDH-II is the first metrologically validated humidity transfer standard which links several scientific airborne and laboratory measurement campaigns to the international metrological water vapor scale.

We present the retrieved volume emission rates (VERs) from the airglow of both the daytime and twilight O2(¹Σ) band and O2(¹Δ) band emissions in the mesosphere and lower thermosphere (MLT). We have investigated the daily mean latitudinal distributions and the time series of the retrieved VER in the altitude range from 53 to 149 km. These observations provide information about the chemistry and dynamics and can be used to infer ozone, solar heating rates, and temperature in the MLT.

OSIRIS satellite measurements of ozone in the stratosphere are corrected for slowly varying errors. These changes make the OSIRIS data compare better with other satellite measurements over the long term and make an impact on our understanding of the recovery of the ozone layer.

We revise selected findings regarding utilization of Global Positioning System radio occultation density profiles for analysis of internal gravity waves. The results show that previously published results are valid only for one specific data version only. Using radiosonde profiles, we also analyze a nonhydrostatic component in temperature profiles. The last part presents detailed study on the utilization of density profiles for characterization of the wave field stability.

Thermodynamic fields retrieved from orbiting infrared sounders use a derived set of measurements as their starting point, rather than the actual observations. This leads to problems with noise and sampling. We have developed a fast accurate model with a simple vertical representation of clouds in the atmosphere for use in retrievals, which allows us to use all the actual low-noise measurements at full resolution. These should eventually help produce more accurate weather forecasts.

We present SWING-UAV, an atmospheric observation system based on a compact scanning spectrometer (SWING) mounted on an unmanned aerial vehicle (UAV). SWING-UAV was operated in the exhaust plume of a power plant in Romania in September 2014, during the AROMAT campaign. SWING quantified the NO₂ emitted by the plant and the water vapour content in the boundary layer, in agreement with ancillary data. The system appears in particular promising to study emissions in rural areas.

In this paper we analyze GNSS radio occultation measurement data from the MetOp-A satellite using a particular operator called phase matching. We find that reflected GNSS signals can be distinguished using this method and that there are structures that differ significantly from simulated measurements. Making radio occultation measurements in the lower troposphere is difficult, and the motivation of this study is to investigate different ways of addressing this problem.

This research makes an application of the multifrequency technique (RIM) to the spectral analysis (frequency domain) for both atmospheric and precipitation, especially for precipitation echoes. Various precipitation conditions such as stratiform and convective precipitations were investigated with RIM for the first time. The effectiveness and potential capabilities of RIM in resolving small-scale precipitation and atmosphere structures have been verified by conditional averaging analysis.

In this study, we use an all-sky stereo camera network to perform geolocation of individual elements of a cloud field in order to track individual clouds and estimate some of their morphological characteristics and their evolution in time. Furthermore, this allows use of cloud geolocation for cloud airborne measurements. For example, in the case of instrumented UAVs, the GPS coordinates of the target cloud may be communicated in real time to the autopilot.

A method to estimate the amounts of ice, liquid water, and water vapor from aircraft radiation measurements at wavelengths just over and under 1 mm is presented and its performance is estimated. The method uses an ensemble of artificial neural networks. It strongly benefits from the submillimeter frequencies reducing the error for the estimated amount of ice by a factor of 2 compared to a traditional microwave method. The method was applied to measurement of a precipitating frontal system.

Data from the high-sensitivity CALIOP cloud lidar onboard the CALIPSO satellite have been used to evaluate cloud amounts estimated from satellite imagery and, specifically, from the climate data record CLARA-A2. The main purpose has been to study the limit of how thin clouds that can be detected efficiently (i.e., detected at the 50 % level) in CLARA-A2 data and how this limit varies globally. The study revealed very large geographical differences in the cloud detection efficiency.