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Annales Geophysicae

Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions

When the terrestrial magnetic field is disturbed, particles from the near-Earth space can precipitate into the upper atmosphere. This work presents, for the first time, numerical simulations of proton precipitation in the energy range associated with the production of aurora (∼1–30 keV) using a global kinetic model of the near-Earth space: Vlasiator. We find that nightside proton precipitation can be regulated by the transition region between stretched and dipolar geomagnetic field lines.

Solid Earth

How can geologic decision-making under uncertainty be improved?

Solid Earth
DOI 10.5194/se-10-1469-2019
3 September 2019

In this paper, we outline the key insights from decision-making research about how, when faced with uncertainty, humans constrain decisions through the use of heuristics (rules of thumb), making them vulnerable to systematic and suboptimal decision biases. We also review existing strategies to debias decision-making that have applicability in the geosciences, giving special attention to strategies that make use of information technology and artificial intelligence.

Geoscientific Model Development

Improved methodologies for Earth system modelling of atmospheric soluble iron and observation comparisons using the Mechanism of Intermediate complexity for Modelling Iron (MIMI v1.0)

MIMI v1.0 was designed for use within Earth system models to simulate the 3-D emission, atmospheric processing, and deposition of iron and its soluble fraction. Understanding the iron cycle is important due to its role as an essential micronutrient for ocean phytoplankton; its supply limits primary productivity in many of the world’s oceans. Human activity has perturbed the iron cycle, and MIMI is capable of diagnosing many of these impacts; hence, it is important for future climate studies.

Ocean Science

CO2 effects on diatoms: a synthesis of more than a decade of ocean acidification experiments with natural communities

Diatoms are a group of phytoplankton species responsible for ~ 25% of primary production on Earth. Ocean acidification (OA) could influence diatoms but the key question is if they become more or less important within marine food webs. We synthesize OA experiments with natural communities and found that diatoms are more likely to be positively than negatively affected by high CO² and larger species may profit in particular. This has important implications for ecosystem services diatoms provide.

Atmospheric Chemistry and Physics

Assessing the formation and evolution mechanisms of severe haze pollution in the Beijing–Tianjin–Hebei region using process analysis

The formation mechanism of a severe haze episode that occurred over North China in December 2015, the aerosol radiative impacts on the haze event and the influence mechanism were examined. The PM_2.5 increase during the aerosol accumulation stage was mainly attributed to strong production by the aerosol chemistry process and weak removal by advection and vertical mixing. Restrained vertical mixing was the main reason for near-surface PM_2.5 increase when aerosol radiative feedback was considered.

Earth Surface Dynamics

A global delta dataset and the environmental variables that predict delta formation on marine coastlines

River deltas are valuable resources that support biodiversity and human habitation. Despite this we do not have a global census of deltas nor do we know the conditions that promote their formation. We surveyed 5399 river mouths greater than 50 m wide and found that 2174 (40%) create a delta. The conditions that lead to delta formation are high sediment input and low wave and tide conditions. These results can be used to understand how deltas will adapt to environmental changes.

Hydrology and Earth System Sciences

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 1: Projected climate and meteorology

This article examines future atmospheric-related phenomena across the interior of western Canada associated with abusiness-as-usualclimate scenario. Changes in large-scale atmospheric circulation and extent of warming vary with season, and these generally lead to increases, especially after mid-century, in factors associated with winter snowstorms, freezing rain, drought, forest fires, as well as atmospheric forcing of spring floods, although not necessarily summer convection.

Geoscientific Instrumentation, Methods and Data Systems

A low-cost device for measuring local magnetic anomalies in volcanic terrain

Geoscientific Instrumentation, Methods and Data Systems
DOI 10.5194/gi-8-217-2019
22 August 2019

Our knowledge of the Earth’s magnetic field arises from magnetic signals stored in lavas. In rugged volcanic terrain, however, the magnetization of the underlying flows may influence the magnetic field as recorded by newly formed flows on top. To measure these local magnetic anomalies, we developed a low-cost field magnetometer with superior accuracy and user-friendliness. The first measurements on Mt. Etna show local magnetic variations that are much larger than expected.

Solid Earth

Fault-controlled dolomitization in the Montagna dei Fiori Anticline (Central Apennines, Italy): record of a dominantly pre-orogenic fluid migration

The dolomitized intervals of the Lower Jurassic deposits exposed in the Montagna dei Fiori Anticline (Central Apennines, Italy) have been investigated. Accordingly, two fault-related dolomitization events were recognised and interpreted as having occurred before and during the Apenninic orogeny. The analyses suggest significant involvement of evaporitic fluids in both events, most likely derived from the underlying Upper Triassic Burano Formation in the detachment level.

Natural Hazards and Earth System Sciences

Load-resistance analysis: an alternative approach to tsunami damage assessment applied to the 2011 Great East Japan tsunami

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-19-1807-2019
20 August 2019

It is known that fragility functions reflect localities (building design standards and topography) and flow velocity is more important, as damage might occur before flow depth reaches its maximum value. This research demonstrates that it is possible to accurately predict building damage by considering related forces with high accuracy, including resistant force, based on building design standards. This method will be useful for damage assessment in areas that have no experience of tsunamis.

Geoscience Communication

Seismic risk: the biases of earthquake media coverage

Exploring a corpus of 320 888 news articles published by 32 worldwide newspapers in 2015, this paper shows the following: news covers a very small proportion of the total number of earthquakes occurring in a year; the duration of coverage is very short, which does not allow for proper coverage of long-term issues; and there is a typical framing of the news about earthquakes that introduces major biases in representation, impeding proper appropriation of the seismic risk by the public.

Nonlinear Processes in Geophysics

Unravelling the spatial diversity of Indian precipitation teleconnections via a non-linear multi-scale approach

We examined the spatial diversity of Indian rainfall teleconnection at different timescales, first by identifying homogeneous communities and later by computing non-linear linkages between the identified communities (spatial regions) and dominant climatic patterns, represented by climatic indices such as El Nino–Southern Oscillation, Indian Ocean Dipole, North Atlantic Oscillation, Pacific Decadal Oscillation and Atlantic Multi-Decadal Oscillation.

Climate of the Past

Modelling ice sheet evolution and atmospheric CO2 during the Late Pliocene

The Late Pliocene, 3.65–2.75 million years ago, is the most recent period in Earth’s history that was warmer than the present. This makes it interesting for climatological research, because it provides a possible analogue for the near future. We used a coupled ice-sheet–climate model to simulate the behaviour of these systems during this period. We show that the warmest moment saw a sea-level rise of 8–14 m, with a CO₂ concentration of 320–400 ppmv.

Geoscientific Instrumentation, Methods and Data Systems

Multiresolution wavelet analysis applied to GRACE range-rate residuals

Geoscientific Instrumentation, Methods and Data Systems
DOI 10.5194/gi-8-197-2019
15 August 2019

In this paper, we present an approach to represent underlying errors in measurements and physical models in the temporal gravity field determination using GRACE observations. This study provides an opportunity to improve the error model and the accuracy of the GRACE parameter estimation, as well as its successor GRACE Follow-On.

Biogeosciences

Ideas and perspectives: is shale gas a major driver of recent increase in global atmospheric methane?

Atmospheric methane has risen rapidly since 2008 and has become more depleted in ¹³C, in contrast to the trend towards more ¹³C enrichment in the late 20th century. Many have used this isotopic evidence to infer an increased biogenic source. Here I analyze the ¹³C trend with the consideration that methane from shale gas is somewhat depleted in ¹³C compared to other fossil fuels. I conclude that shale gas may be responsible for a third of the global increase from all sources.

Ocean Science

High-resolution underwater laser spectrometer sensing provides new insights into methane distribution at an Arctic seepage site

Methane seepage from the seafloor west of Svalbard was investigated with a fast-response membrane inlet laser spectrometer. The acquired data were in good agreement with traditional sparse discrete water sampling, subsequent gas chromatography, and with a new 2-D model based on echo-sounder data. However, the acquired high-resolution data revealed unprecedented details of the methane distribution, which highlights the need for high-resolution measurements for future climate studies.

Geoscience Communication

Taking a Breath of the Wild: are geoscientists more effective than non-geoscientists in determining whether video game world landscapes are realistic?

Game worlds in modern computer games, while they include very Earth-like landscapes, are ultimately fake. Since games can be used for learning, we wondered if people pick up wrong information from games. Using a survey we tested if people with a background in geoscience are better than people without such a background at distinguishing if game landscapes are realistic. We found that geoscientists are significantly better at this, but the difference is small and overall everyone is good at it.

Climate of the Past

Spatial pattern of accumulation at Taylor Dome during Marine Isotope Stage 4: stratigraphic constraints from Taylor Glacier

An ice core from Taylor Glacier, Antarctica, spans a period ~ 70 000 years ago when Earth entered the last ice age. Chemical analyses of the ice and air bubbles allow for an independent determination of the ages of the ice and gas bubbles. The difference between the age of the ice and the bubbles at any given depth, called ∆age, is unusually high in the Taylor Glacier core compared to the Taylor Dome ice core situated to the south. This implies a dramatic accumulation gradient between the sites.

Natural Hazards and Earth System Sciences

Improving the understanding of flood risk in the Alsatian region by knowledge capitalization: the ORRION participative observatory

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-19-1653-2019
7 August 2019

The article presents the Alsatian regional flood risk observatory ORRION, a participative online platform on which information is shared between individuals, stakeholders, engineers, and scientists. This maximizes knowledge capitalization and contributes to building a common knowledge base for flood risk. From this information, long chronicles of floods are derived for the Rhine, and most of its main Alsatian tributaries and their main characteristics are identified and analysed.

Climate of the Past

Past climate and continentality inferred from ice wedges at Batagay megaslump in the Northern Hemisphere’s most continental region, Yana Highlands, interior Yakutia

To reconstruct past winter climate, we studied ice wedges at two sites in the Yana Highlands, interior Yakutia (Russia), the most continental region of the Northern Hemisphere. Our ice wedges of the upper ice complex unit of the Batagay megaslump and a river terrace show much more depleted stable-isotope compositions than other study sites in coastal and central Yakutia, reflecting lower winter temperatures and a higher continentality of the study region during Marine Isotope Stages 3 and 1.

Hydrology and Earth System Sciences

A salinity module for SWAT to simulate salt ion fate and transport at the watershed scale

Salinity is one of the most common water quality threats in river basins and irrigated regions worldwide. Available watershed models, however, do not simulate the fate and transport of salt species. This paper presents a modified version of the popular SWAT watershed model that simulates the transport of major salt ions in a watershed system. Salt is transported via surface runoff, soil percolation, groundwater flow, and streamflow. The model can be used in salt-affected watersheds worldwide.

Biogeosciences

Global soil–climate–biome diagram: linking surface soil properties to climate and biota

Surface soils interact strongly with both climate and biota and provide fundamental ecosystem services. However, the quantitative linkages between soil, climate, and biota remain unclear at a global scale. By compiling a large global soil database, we mapped eight major soil properties based on machine learning algorithms and developed a global soil–climate–biome diagram. Our results suggest shifts in soil properties under global climate and land cover change.

Hydrology and Earth System Sciences

Assessing the characteristics and drivers of compound flooding events around the UK coast

Flooding can arise from multiple sources, including waves, extreme sea levels, rivers, and severe rainfall. When two or more sources combine, the consequences can be greatly multiplied. We find the potential for the joint occurrence of extreme sea levels and river discharge to be greater on the western coast of the UK compared to the eastern coast. This is due to the weather conditions generating each flood source around the UK. These results will help increase our flood forecasting ability.

Climate of the Past

Early instrumental meteorological measurements in Switzerland

The 18th and early 19th centuries saw pronounced climatic variations with impacts on the environment and society. Although instrumental meteorological data for that period exist, only a small fraction has been the subject of research. This study provides an overview of early instrumental meteorological records in Switzerland resulting from an archive survey and demonstrates the great potential of such data. It is accompanied by the online publication of the imaged data series and metadata.

Annales Geophysicae

Converging photospheric vortex flows close to the polarity inversion line of a fully emerged active region

We describe a technique used to locate and classify critical points in 2-D flow fields at the solar photosphere obtained from the evolution of the line-of-sight magnetic field in a region close to the magnetic polarity inversion line of a fully emerged active region. We apply this technique to locate a particular kind of critical point associated to vortex flows, which are considered important, since they can twist and interweave the foot points of flux tubes and generate magnetic reconnection.

Atmospheric Chemistry and Physics

Towards monitoring localized CO2 emissions from space: co-located regional CO2 and NO2 enhancements observed by the OCO-2 and S5P satellites

The quantification of anthropogenic emissions with current CO₂ satellite sensors is difficult, but NO₂ is co-emitted, making it a suitable tracer of recently emitted CO₂. We analyze enhancements of CO₂ and NO₂ observed by OCO-2 and S5P and estimate the CO₂plume cross-sectional fluxes that we compare with emission databases. Our results demonstrate the usefulness of simultaneous satellite observations of CO₂ and NO₂ as envisaged for the European Copernicus anthropogenic CO₂ monitoring mission

The Cryosphere

Brief communication: Updated GAMDAM glacier inventory over high-mountain Asia

The Glacier Area Mapping for Discharge from the Asian Mountains (GAMDAM) glacier inventory was updated to revise the underestimated glacier area in the first version. The total number and area of glaciers are 134 770 and 100 693 ± 11 790 km² from 453 Landsat images, which were carefully selected for the period from 1990 to 2010, to avoid mountain shadow, cloud cover, and seasonal snow cover.

Atmospheric Chemistry and Physics

Quantification of water vapour transport from the Asian monsoon to the stratosphere

We investigate the transport pathways of water vapour from the upper troposphere in the Asian monsoon region to the stratosphere. In the employed chemistry-transport model we use a tagging method, such that the impact of different source regions on the stratospheric water vapour budget can be quantified. A key finding is that the Asian monsoon (compared to other source regions) is very efficient in transporting air masses and water vapour to the tropical and extratropical stratosphere.

Earth Surface Dynamics

Evaluating post-glacial bedrock erosion and surface exposure duration by coupling in situ optically stimulated luminescence and 10Be dating

Assessing the impact of glaciation at the Earth’s surface requires simultaneous quantification of the impact of climate variability on past glacier fluctuations and on bedrock erosion. Here we present a new approach for evaluating post-glacial bedrock surface erosion in mountainous environments by combining two different surface exposure dating methods. This approach can be used to estimate how bedrock erosion rates vary spatially and temporally since glacier retreat in an alpine environment.

Biogeosciences

Dissolved organic matter at the fluvial–marine transition in the Laptev Sea using in situ data and ocean colour remote sensing

In this article, we present the variability and characteristics of dissolved organic matter at the fluvial–marine transition in the Laptev Sea from a unique dataset collected during 11 Arctic expeditions. We develop a new relationship between dissolved organic carbon (DOC) and coloured dissolved organic matter absorption, which is used to estimate surface water DOC concentration from space. We believe that our findings help current efforts to monitor ongoing changes in the Arctic carbon cycle.

Atmospheric Chemistry and Physics

Atmospheric measurements of the terrestrial O2:CO2 exchange ratio of a midlatitude forest

Predictions of global warming require predictions of how much CO₂ will be taken up by the oceans, how much by land plants, and how much will stay in the atmosphere. Measurements of atmospheric oxygen (O₂) help with these predictions if we also know the ratio of O₂ release to CO₂ uptake in land plants. We have measured this ratio in a midlatitude forest and find a lower value than the one in wide use. If truly applicable, our results call for a modest adjustment in the global carbon budget.

Atmospheric Chemistry and Physics

Evaluation of global simulations of aerosol particle and cloud condensation nuclei number, with implications for cloud droplet formation

Effects of aerosols on clouds are important for climate studies but are among the largest uncertainties in climate projections. This study evaluates the skill of global models to simulate aerosol, cloud condensation nuclei (CCN) and cloud droplet number concentrations (CDNCs). Model results show reduced spread in CDNC compared to CCN due to the negative correlation between the sensitivities of CDNC to aerosol number concentration (air pollution) and updraft velocity (atmospheric dynamics).

Natural Hazards and Earth System Sciences

Flood risk in a range of spatial perspectives – from global to local scales

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-19-1319-2019
5 July 2019

Considering flood risk composed of hazard, exposure, and vulnerability from global to local scales, this paper reviews and presents increasing observed flood losses and projections of flood hazard and losses. We acknowledge existence of multiple driving factors and of considerable uncertainty, in particular with regards to projections for the future. Finally, this paper analyses options for flood risk reduction from a global framework to regional and local scales.

Atmospheric Measurement Techniques

Description of a formaldehyde retrieval algorithm for the Geostationary Environment Monitoring Spectrometer (GEMS)

The Geostationary Environment Monitoring Spectrometer (GEMS) will be launched by South Korea in 2019, and it will measure radiances ranging from 300 to 500 nm every hour with a fine spatial resolution of 7 km x 8 km over Seoul in South Korea to monitor column concentrations of air pollutants including O₃, NO₂, SO₂, and HCHO, as well as aerosol optical properties. This paper describes a GEMS formaldehyde retrieval algorithm including a number of sensitivity tests for algorithm evaluation.

The Cryosphere

Converting snow depth to snow water equivalent using climatological variables

We present a new statistical model for converting snow depths to water equivalent. The only variables required are snow depth, day of year, and location. We use the location to look up climatological parameters such as mean winter precipitation and mean temperature difference (difference between hottest month and coldest month). The model is simple by design so that it can be applied to depth measurements anywhere, anytime. The model is shown to perform better than other widely used approaches.

Atmospheric Chemistry and Physics

Emission of trace gases and aerosols from biomass burning – an updated assessment

Biomass burning is one of the largest sources of atmospheric pollutants worldwide. This paper presents an up-to-date compilation of emission factors for over 120 trace gas and aerosol species from the different forms of open vegetation fires and domestic biofuel use, based on an analysis of over 370 published studies. Using these emission factors and current global burning activity data, the annual emissions of important species released by the various types of biomass burning are estimated.

Climate of the Past

Mid-Holocene climate change over China: model–data discrepancy

The mid-Holocene has been an excellent target for comparing models and data. This work shows that, over China, all the ocean–atmosphere general circulation models involved in PMIP3 show a very large discrepancy with pollen data reconstruction when comparing annual and seasonal temperature. It demonstrates that to reconcile models and data and to capture the signature of seasonal thermal response, it is necessary to integrate non-linear processes, particularly those related to vegetation changes.

Earth Surface Dynamics

Alluvial channel response to environmental perturbations: fill-terrace formation and sediment-signal disruption

We performed seven physical experiments to explore terrace formation and sediment export from a braided alluvial river system that is perturbed by changes in water discharge, sediment supply, or base level. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace formation, and (3) the transient response of sediment discharge. Our findings provide guidelines for interpreting fill terraces and sediment export from fluvial systems.

Atmospheric Chemistry and Physics

Contrail cirrus radiative forcing for future air traffic

The climate impact of air traffic is to a large degree caused by changes in cirrus cloudiness resulting from the formation of contrails. We use an atmospheric climate model with a contrail cirrus parameterization to investigate the climate impact of contrail cirrus for the year 2050. The strong increase in contrail cirrus radiative forcing due to the projected increase in air traffic volume cannot be compensated for by the reduction of soot emissions and by improvements in propulsion efficiency.

Atmospheric Measurement Techniques

Evaluating biases in filter-based aerosol absorption measurements using photoacoustic spectroscopy

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 %.

Atmospheric Measurement Techniques

Detecting layer height of smoke aerosols over vegetated land and water surfaces via oxygen absorption bands: hourly results from EPIC/DSCOVR in deep space

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.

Hydrology and Earth System Sciences

Technical note: A microcontroller-based automatic rain sampler for stable isotope studies

Most commercial automatic rain samplers are costly and do not prevent evaporation from the collection bottles. Hence, we have developed a microcontroller-based collector enabling timer-actuated integral rain sampling. The simple, low-cost device is robust and effectively minimizes post-sampling evaporation. The excellent performance of the collector during an evaporation experiment in a lab oven suggests that even multi-week field deployments in warm climates are feasible.

Solid Earth

Induced seismicity in geologic carbon storage

To meet the goal of the Paris Agreement to limit temperature increase below 2 ºC, geologic carbon storage (GCS) will be necessary at the gigatonne scale. But to successfully deploy GCS, seismicity induced by CO₂injection should be controlled and maintained below a threshold that does not generate nuisances to the population. We conclude that felt induced seismicity can be minimized provided that a proper site characterization, monitoring and pressure management are performed.

Atmospheric Chemistry and Physics

Aerosol pH and its driving factors in Beijing

Aerosol acidity plays a key role in secondary aerosol formation. To provide a more comprehensive reference for aerosol pH and a basis for controlling secondary aerosol generation, this study used the latest data covering four seasons and different particle sizes to obtain the characteristics of aerosol pH and explore the main factors affecting aerosol pH and gas–particle partitioning in the Beijing area.

Earth System Dynamics

Including the efficacy of land ice changes in deriving climate sensitivity from paleodata

Processes causing the same global-average radiative forcing might lead to different global temperature changes. We expand the theoretical framework by which we calculate paleoclimate sensitivity with an efficacy factor. Applying the revised approach to radiative forcing caused by CO₂and land ice albedo perturbations, inferred from data of the past 800 000 years, gives a new paleo-based estimate of climate sensitivity.

Atmospheric Measurement Techniques

A sampler for atmospheric volatile organic compounds by copter unmanned aerial vehicles

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.

Natural Hazards and Earth System Sciences

Analysis of an extreme weather event in a hyper-arid region using WRF-Hydro coupling, station, and satellite data

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-19-1129-2019
13 June 2019

The work addresses the need for reliable precipitation forecasts in hyper-arid environments through state-of-the-art hydro-meteorological modeling. Accounting for land–atmosphere interactions in the applied model is shown to improve the accuracy of precipitation output. The chain of events controlling the soil moisture–precipitation feedback are diagnosed and verified by in situ observations and satellite data.

Atmospheric Chemistry and Physics

Global distribution of methane emissions, emission trends, and OH concentrations and trends inferred from an inversion of GOSAT satellite data for 2010–2015

We use 2010–2015 satellite observations of atmospheric methane to improve estimates of methane emissions and their trends, as well as the concentration and trend of tropospheric OH (hydroxyl radical, methane’s main sink). We find overestimates of Chinese coal and Middle East oil/gas emissions in the prior estimate. The 2010–2015 growth in methane is attributed to an increase in emissions from India, China, and areas with large tropical wetlands. The contribution from OH is small in comparison.

Biogeosciences

Responses of an abyssal meiobenthic community to short-term burial with crushed nodule particles in the south-east Pacific

To elucidate the potential effects of crushed nodule particle deposition on abyssal meiobenthos, we covered abyssal soft sediment in the Peru Basin (4200 m depth) with approximately 2 cm of this nodule material for 11 d. About half of the meiobenthos migrated from the sediment into the added material, and nematode feeding type proportions in that added layer were altered. These results considerably contribute to our understanding of the short-term responses of deep-sea meiobenthos to burial.

Atmospheric Measurement Techniques

Aerosol size distributions during the Atmospheric Tomography Mission (ATom): methods, uncertainties, and data products

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.