Weather radars are offering improved capabilities to investigate storm physics, which remain poorly understood. We investigate enhanced use of such data near Houston, Texas, where pollution sources often provide a convenient contrast between polluted and clean air. We conclude that Houston is a favorable location to conduct a future field campaign during June through September because isolated storms are common and tend to last an hour, allowing frequent observations of a full life cycle.

A selection for homogeneous scenes for the assimilation of IASI radiances is proposed by using information on the collocated imager pixels inside each infrared observation. A revised method for the selection, which represents a compromise between two methods to select homogeneous scenes using homogeneity criteria already proposed in the literature, has a positive impact on the observation minus the simulation statistics. It has been tested in a numerical weather prediction model for clear sky.

Undertaking atmospheric observations from ships provides important data in regions where measurements are impossible by other means. However, making measurements so close to a diesel exhaust plume is difficult. In this paper, we describe an algorithm that utilises ongoing measurements of aerosol number concentrations, black carbon mass concentrations, and mixing ratios of carbon monoxide and carbon dioxide to accurately distinguish between exhaust and background data periods.

The authors carried out dual flights of RS-11G and RS92-SGP radiosondes and investigated the differences in the performance of the radiosondes to help characterize GRUAN data products. A novel aspect of GRUAN data products is that vertically resolved uncertainty estimates and metadata are provided for each sounding and comparison of GRUAN data products is important in securing the temporal homogeneity of climate data records.

Optical array probe measurements of clouds are widely used to inform and validate numerical weather and climate models. In this paper, we discuss artefacts which may bias data from these instruments. Using laboratory and synthetic datasets, we demonstrate how greyscale analysis can be used to filter data, constraining the sample volume and improving data quality particularly at small sizes where their measurements are considered unreliable.

From 2016 to 2018 a NASA aircraft profiled the atmosphere from 180 m to ~12 km from the Arctic to the Antarctic over both the Pacific and Atlantic oceans. This program, ATom, sought to sample atmospheric chemical composition to compare with global climate models. We describe the how measurements of particulate matter were made during ATom, and show that the instrument performance was excellent. Data from this project can be used with confidence to evaluate models and compare with satellites.

In this work we describe a highly sensitive optical spectrometer for simultaneous measurement of methane, ethane, and the isotopic composition of methane. The coupling of the spectrometer with a dissolved gas extraction system will provide a suitable tool for understanding the origins of the dissolved hydrocarbons and discriminate between the different sources (e.g., biogenic vs. thermogenic).

The Solar Occultation for Ice Experiment (SOFIE) has measured nitric oxide (NO) from satellite since 2007. The observations are validated through error analysis and comparisons with other satellite observations. Calculated SOFIE NO uncertainties are less than 50 % for altitudes from 40 to 140 km. SOFIE agrees with other measurements to within 50 % for altitudes from roughly 50 to 105 km for spacecraft sunrise and 50 to 140 km for sunsets.

Volatile organic compound (VOC) emissions influence air quality and particulate distributions, particularly in major source regions such as the Amazon. A sampler for collecting VOCs from an unmanned aerial vehicle (UAV) is described. Field tests of its performance and an initial example data set collected in the Amazon are also presented. The low cost, ease of use, and maneuverability of UAVs give this method the potential to significantly advance knowledge of the spatial distribution of VOCs.

Delays or losses of gases in sampling tubing and instrumental surfaces due to surface interactions can lead to inaccurate quantification. By sampling with several chemical ionization mass spectrometers and six tubing materials, we quantify delays of semivolatile organic compounds and small polar gases. Delay times generally increase with decreasing volatility or increasing polarity and also depend on materials. The method and results will inform inlet material selection and instrumental design.

Cloud radars are unique instruments for observing cloud processes, but uncertainties in radar calibration have frequently limited data quality. Here, we present three novel methods for calibrating vertically pointing cloud radars. These calibration methods are based on microphysical processes of liquid clouds, such as the transition of cloud droplets to drizzle drops. We successfully apply the methods to cloud radar data from the North Slope of Alaska (NSA) and Oliktok Point (OLI) ARM sites.

A new instrument, the High Speed Particle Phase Discriminator (PPD-HS), is presented, with the goal of quantifying liquid and ice fraction in conditions relevant for mixed-phase clouds. PPD-HS captures the near-forward spatial intensity distribution of scattered light on a single particle basis. Symmetry analysis of the scattering pattern is used to determine the shape of the particles, with cloud droplets and ice crystals producing symmetrical and asymmetrical scattering patterns, respectively.

Using nighttime observations from the Visible Infrared Imager Radiometer Suite (VIIRS) Day/Night band (DNB), the characteristics of artificial light sources are evaluated as functions of observation conditions, and incremental improvements are documented on nighttime aerosol retrievals on a regional scale. Results from the study indicate the potential of this method to begin filling critical gaps in diurnal aerosol optical thickness information at both regional and global scales.

A dual-channel CRDS system for NO₂ and NO detection is reported. The detection limits of the developed CRDS system for NO₂ and NO_x measurements are estimated to be about 0.030 ppb (1σ, 1 s) and 0.040 ppb (1σ, 1 s), respectively. The measurements of on-road vehicle emission plumes by this mobile CRDS instrument show the different emission characteristics in the urban and suburban areas of Hefei. The instrument provides a new method for retrieving fast variations in NO and NO₂ plumes.

Tropical clouds are a key climate component but are still not fully understood. Therefore, we analyze airborne remote sensing measurements that were taken in the dry and wet seasons over the Atlantic east of Barbados. From these we derive sub-kilometer resolution data of vertically integrated atmospheric water vapor and liquid water. Results show that although the humidity is lower in the dry season, clouds are more frequent, contain more water, and produce more rain than in the wet season.

We present new results of vertically resolved extensive aerosol optical properties (backscattering, scattering and extinction) and volume concentrations retrieved with the GRASP algorithm from ceilometer and photometer measurements. Long-term evaluation with in situ data gathered at the Montsec mountaintop observatory (northeastern Spain) shows good agreement, being a step forward towards a better representation of aerosol vertical distribution with wide spatial coverage.

Detecting aerosol layer height from space is challenging. The traditional method relies on active sensors such as lidar that provide the detailed vertical structure of the aerosol profile but is costly with limited spatial coverage (more than 1 year is needed for global coverage). Here we developed a passive remote sensing technique that uses backscattered sunlight to retrieve smoke aerosol layer height over both water and vegetated surfaces from a sensor 1.5 million kilometers from the Earth.

Ground-based MAX-DOAS has been utilized for the remote sensing of aerosol and trace gases for more than 10 years. Here we developed a new method to determine the aerosol optical properties, including scattering and absorption, from multiple-wavelength O₄ absorptions from ground-based MAX-DOAS observations, which were validated well by other independent instruments at low elevations. It is beneficial to obtain the vertical profiles of aerosol properties using multiple elevations.

To investigate the relationship between BLH and air pollution under different conditions, a compact micro-pulse lidar integrating both direct-detection lidar and coherent Doppler wind lidar is built. Evolution of atmospheric boundary layer height (BLH), aerosol layer and fine structure in cloud base are well retrieved. Negative correlation exists between BLH and PM_2.5. Different trends show that the relationship between PM_2.5 and BLH should be considered in different boundary layer categories.

A scanning strategy is proposed for the upcoming GeoCarb instrument that minimizes predicted retrieval errors of CO₂ by optimizing signal-to-noise ratio with respect to air mass factor and solar zenith angle. The strategy is generated using a modified greedy algorithm that optimizes over these stationary processes while also considering operational constraints. This method increases the number of soundings with predicted CO₂ retrieval error less than 2 ppm by 18–41 %.

This work investigates the potential of an innovative differential absorption radar for retrieving relative humidity inside ice clouds. The radar exploits the strong spectral dependence of the water vapour absorption for frequencies close to the 183 GHz water vapour band. Results show that observations from a system with 4–6 frequencies can provide novel information for understanding the formation and growth of ice crystals.

A new technique for calibrating photo-acoustic absorption spectrometers (PASs) has been developed utilizing polydisperse, highly-absorbing aerosol and a commercially available instrument that measures particle extinction and scattering. This is the first calibration technique for multi-pass PAS instruments that does not require particles with known refractive index or reactive gases. Three substances were tested: Aquadag, Regal Black, and Nigrosin. All calibrations were consistent to within 5 %.

ICAD allows a precise in situ measurement of gases like NO₂ in a relatively simple and compact setup. The main advantage in comparison to most other optical methods is that it does not require a stable total light intensity. This allows a simpler and mobile instrument setup and additionally it features no observed cross-interferences. We validated the high quality for an ICAD NO₂ instrument in different inter-comparisons with a detection limit of 0.02 ppbv.

We present a flexible method that employs a power series expansion and Fourier series analysis to characterize the average long-term change and seasonal cycle, respectively, from a time series of observations of a trace atmospheric species. This approach maximizes the statistically significant information derived, including non-linear aspects of the long-term trends, without over fitting the data. Generally, a small set of parameter values (e.g., 7 or 8) provides this characterization.

We present a proof-of-concept method of concentrating aerosols in a continuous stream using an applied electric field. Potential enrichment was estimated using a trajectory model, predicting values of up to 65 % for 75–200 nm aerosol, using voltages of up to 30 kV. Experimental results using similar geometry yielded up to 15 % observed enrichment for the same conditions. These results imply that aerosol enrichment using an applied electric field can be achieved in continuous-flow applications.

The open-path FTIR (OP-FTIR) is often used to measure the atmospheric gas composition and concentrations. The OP-FTIR, however, is sensitive to the changed ambient factors, which likely led to quantitative biases. This study developed methods to minimize the effect of the ambient temperature and humidity on N2O/CO2 quantification. These methods can help the users who implement the OP-FTIR to estimate gas fluxes in the agroecosystem achieve more precise and accurate estimations.

This research project assesses biases in traditional, filter-based, aerosol absorption measurements by comparison to state-of-the-art, non-filter-based, or in situ, measurements. We assess biases in traditional absorption measurements for three main aerosol types, including dust and fresh and aged biomass burning aerosols. The main results of this study are that the traditional and state-of-the-art absorption measurements are well correlated and that biases in the former are up to 45 %.

The goal is to evaluate the capabilities of the new Rapid-E monitor and to construct a first-level pollen recognition algorithm. The output data were treated with ANN aiming at classification of the injected pollen. Algorithms based on scattering and fluorescence data alone fall short of acceptable quality. The combinations of these exceeded 80 % accuracy for 5 out of 11 pollen species. Constructing multistep algorithms with sequential discrimination of pollen can be a possible way forward.

Losses or measurement delays of gas-phase compounds sampled through tubing are important to atmospheric science. Here we characterize 14 tubing materials by measuring the effects on step changes in organic compound concentration. We find that polymeric tubings exhibit absorptive partitioning behaviour while glass and metal tubings show adsorptive partitioning. Adsorptive materials impart complex humidity, concentration, and VOC–VOC interaction dependencies that absorptive tubings do not.

Wakes are volumes of air with low wind speed that form downwind of wind turbines. Their properties and behaviour determine optimal turbine spacing in wind farms. We use scanning Doppler lidar to accurately and precisely measure wake characteristics at a complex terrain site in Portugal. We develop and apply an automatic processing algorithm to detect wakes and quantify their characteristics. In higher wind speeds, the wake centres are lower. Wake centres are also lower in convective conditions.