Aerosol particles are key components of the earth system important in radiative balance, human health, and other areas of key societal concern. Understanding their formation, evolution and impacts relies on developments from multiple disciplines covering both experimental laboratory work, field studies and numerical modelling. In this general session all topics of Aerosol Chemistry and Physics are covered. Contributions from aerosol laboratory, field, remote sensing and model studies are all highly encouraged.

As in previous years, this year the session will dedicate some of its time to focus on a hot topic which this year is aerosol volatility. Despite significant advances in experimental techniques, it is still thought that an incomplete understanding of factors that dictate gas-particle partitioning remains one of the major uncertainties in predicting atmospheric aerosol concentrations, composition, life-time and subsequent impacts. With this in mind, aside from general submissions on aerosol research, we encourage contributions from work within the broad focus of aerosol volatility. These might include work on:
• New process pathway identification
• Molecular scale investigations, from single component to complex mixtures
• Evidence from field studies
• New experimental capabilities
• New modelling capabilities
• Impact studies

Atmospheric aerosol-cloud-climate interactions (e.g. particle oxidation and photosensitization, secondary aerosol and biogenic particle formation, molecular composition-, phase-, acidity- and structure- changes, heterogeneous ice nucleation ...) are fundamental processes in the atmosphere. Despite the importance of these processes in energy transfer, cloud dynamics, precipitation formation, and hence in climate change, little is known about the molecular mechanism and the respective contribution of different structural and chemical surface properties of the atmospheric aerosols and ice nuclei controlling these processes in the atmosphere. For example, observation of atmospheric ice nucleation has bridged the scales from macroscopic to microscopic levels (satellites, balloons, mountain stations, flight campaigns, and laboratory measurements) and has delivered a wide variety of important results in cloud microphysics, particularly concerning the ice nucleation ability of atmospheric aerosol particles. However, fundamental understanding of the cloud dynamics and properties, which play the major role in the climate system, will require the understanding of water-aerosol Surface Interactions.

To advance our knowledge about atmospheric processes, this session aims to bring together experimental and theoretical approaches concerned with investigating water- and ice-solid interactions as well as ice nucleation processes on the molecular level. The goal is to fill the gap between the cloud and atmospheric properties and the aerosol-water surface interactions. We aim to gather contributions from laboratory and theoretical investigations that deal with the interaction of water and ice with atmospheric relevant mineral and biological surfaces.

- Invited speaker: Prof. Dr. Mischa Bonn, Max Planck Institute for Polymer Research, Mainz , Germany.
- Solicited talk: "Hydrogen Bonding at the Ice Surface"

- Most exciting for non-scientific public talk: "Elucidating how trace gases interact with ice surfaces", by Dr. Jenée D. Cyran

Public information:
In the “Atmospheric Surface Science” session we bridge experimental and theoretical findings to elucidate water-ice-aerosol interactions that occur in the atmosphere. The focus is on the molecular level processes. We discuss the origin of the interactions and their impact on our hydrosphere in general and climate in particular.

Ice particles in the atmosphere, both in cirrus and mixed-phase clouds, contribute to the largest uncertainty in interpretations of the Earth’s changing energy budget. Their large variability in number, size and shape makes it difficult to understand and parameterize their microphysical and hence radiative properties.

To advance our understanding of these clouds, this session aims to bring together two research areas, namely (1) 'Ice Clouds (IC)' and (2) 'Ice Nucleating Particles (INP)':

(1) 'Ice Clouds (IC)' are investigated with different approaches and methodologies: observations (ground based, airborne and spaceborne), modelling (process-based, regional and global) as well as radiative transfer and transport studies. We aim to gather contributions from all these aspects including dynamical influence on ice cloud formation, life cycle, coverage, microphysical and radiative properties, crystal shapes, sizes and variability of ice particles for mixed-phase as well as cirrus clouds.

(2) 'Ice Nucleating Particles (INP)' are examined in the laboratory on a fundamental level, trying to understand the nucleation processes. For characterizing INP in the atmosphere, their temperature dependent number concentrations are determined by ground based and aircraft measurements, and also remote sensing.

This session is intended to promote the exchange of knowledge between the different communities, and welcomes contributions from all topics mentioned above.

Just before the EGU, from 3rd to 6th April 2019, the Viennese colleagues Bernadett Weinzierl, Anne Kasper-Giebl and Hinrich Grothe will organize the 12th International Conference on Carbonaceous Particles in the Atmosphere (ICCPA) 2019, where ice nucleation will also be a highlighted topic: www.iccpa.net

Atmosphere and Cryosphere are closely linked and need to be investigated as an interdisciplinary subject. Most of the cryospheric areas have undergone severe changes in last decades while such areas have been more fragile and less adaptable to global climate changes. This AS-CR session invites model- and observational-based investigations on any aspects of linkages between atmospheric processes and snow and ice on local, regional and global scales. Emphasis is given on the Arctic, high latitudes and altitudes, mountains, sea ice, Antarctic regions. In particular, we encourage studies that address aerosols (such as Black Carbon, Organic Carbon, dust, volcanic ash, diatoms, bioaerosols, bacteria, etc.) and changes in the cryosphere, e.g., effects on snow/ice melt and albedo. The session also focus on dust transport, aeolian deposition, and volcanic dust, including health, environmental or climate impacts at high latitudes, high altitudes and cold Polar Regions. We emphasize contributions on biological and ecological sciences including dust-organisms interactions, cryoconites, bio-albedo, eco-physiological, biogeochemical and genomic studies. Related topics are light absorbing impurities, cold deserts, dust storms, long-range transport, glaciers darkening, polar ecology, and more. The scientific understanding of the AS-CR interaction needs to be addressed better and linked to the global climate predictions scenarios.

Aeolian processes operate at a myriad of spatial and temporal scales both on Earth and other planetary bodies. Process and form are linked by feedback mechanisms that drive the evolution of forms and at the larger scale the landscape itself. This session brings together research traversing the spectrum of scale, from long term landscape dating and evolution modelling to small-scale process studies. It will be of interest to researchers that study wind-blown sediment (both sand and dust sized particles) and associated bedforms in a range of environments, from coastal and semi-arid regions, to hyper arid deserts and other planets. Contributions that use novel instrumentation in field or laboratory studies, remote sensing at the landscape scale, innovative numerical modelling or theoretical approaches, are encouraged, particularly those which attempt to elucidate feedback between surface properties and sediment transport.

This session is co-sponsored by the International Society for Aeolian Research (ISAR; http://www.aeolianresearch.com/). The best student presentation (oral or poster) in this session will receive two-year ISAR membership and a book prize.

This session is the result of a merger of two sessions:
Session CL4.28/AS3.6/GM10.2/SSP3.25
"Aeolian dust: initiator, player, and recorder of environmental change", and
Session AS3.7
"Atmospheric Desert Dust characterisation through Remote Sensing observations".

Together, these two sessions cover a huge range of scientific disciplines that study mineral-dust generation, transport, and deposition, as well as the many roles that mineral dust plays in environmental change.

The merger has resulted in a very nice set of interesting dusty abstracts covering huge ranges of spatial and temporal scales and with contributions from many scientific disciplines including atmospheric science, remote sensing, (palaeo)climate science, geomorphology and sedimentology but also human health and environmental science. We look forward to an inspiring and challenging PICO session and we invite you to participate!

Public information:
We have three PICO blocks and two invited speakers (in between the 2-minute madness and PICOs):
1) Vassilis Amiridis (10.45 - 11.00) - Dust remote sensing advances in the framework of ACTRIS
2) Carlos Pérez García-Pando (14.00 - 14.15) - FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT)

Remote sensing of clouds and aerosols is of central importance for studying climate system processes and changes. Reliable information is required on climate-relevant parameters such as aerosol and cloud optical thickness, layer height, particle size, liquid or ice water path and vertical particulate matter columns. A number of challenges and unsolved problems remain in algorithms and their application. This includes remote sensing of clouds and aerosols with respect to 3D effects, remote sensing of polluted and mixed clouds, combination of ground-based and satellite-based systems, and the creation of long-term uniform global records. This session is aimed at the discussion of current developments, challenges and opportunities in aerosol and cloud remote sensing using active and passive remote sensing systems.

Invited speaker 2019: Otto Hasekamp, SRON - Netherlands Institute for Space Research

Over the last years, a growing number of Multi-AXis (MAX) and other scattered light DOAS instruments is operated world wide.
By probing the troposphere in different viewing angles and from different platforms, vertical profile information on aerosols and tropospheric trace gases, in particular NO2, can be derived.
Thereby, scattered light DOAS instruments provide an essential link between in-situ measurements of trace gas concentrations and column-integrated measurements from satellite, and thus play a key role in satellite validation.
This session is open for contributions about
- MAX-DOAS and other scattered light DOAS instrumentation and operation on various platforms (ground-based, mobile, aircraft)
- trace gas retrievals
- inversion algorithms
- identification and treatment of clouds
- comparisons to in-situ or satellite measurements and models
- scientific results.
Results from intercomparison campaigns like CINDI-2 (2016 in Cabauw) are particularly welcome.

The Sentinel-5 Precursor mission, launched on Oct. 13 2017, is the first atmospheric Sentinel and will support Copernicus services in particular for atmospheric applications, including activities such as air quality, ozone and climate monitoring. The instrument TROPOMI (Tropospheric Monitoring Instrument) is the single payload of the Sentinel-5 Precursor satellite and was co-funded by ESA and The Netherlands. Sentinel-5 Precursor will ensure on the one hand continuity of atmospheric satellite data provision from the ESA ERS (GOME), ENVISAT (SCIAMACHY), and the USA EOS-AURA (OMI) missions in the various application and scientific domains and prepares on the other hand for the future atmospheric Sentinel-4 and Sentinel-5 instruments hosted on EUMETSAT platforms. Key features of the TROPOMI instrument are to have global coverage within one day and providing a spatial resolution of 7x3.5 km.
The Sentinel-5 Precursor mission has successfully finalised its Commissioning Phase on April 24 2018. During Commissioning Phase only pre-operational sample data products have been provided to selected Cal/Val experts. The staggered data release to the public has started on July 11 including Level 1B, Ozone, Nitrogen Dioxide, Carbon Monoxide and Cloud & Aerosol information. It is planned that during the ramp-up phase, which has a duration of 8 months all products will be provided to the public (by end Dec. 2018). All data will be provided to the public through the Copernicus Open Data Access Hub at https://scihub.copernicus.eu/. This session will include contributions about the Sentinel-5 Precursor mission status, calibration/validation results, and the demonstration of first applications using TROPOMI products.

Over the last years, more and more satellite data on tropospheric composition have become available and are now being used in numerous applications. In this session, we aim at bringing together reports on new or improved data products and their validation as well as studies using satellite data for applications in tropospheric chemistry, emission inversions and air quality. This includes both studies on trace gases and on aerosols.

We welcome presentations based on studies analysing current and future satellite missions, in particular Sentinel 5P, inter-comparisons of different remote sensing measurements dedicated to tropospheric chemistry sounding and/or analyses with ground-based measurements and chemical transport models.

The Middle East is home to about 350 million people. It is endowed with about half the proven oil and gas reserves on the planet, and also has rich solar resources. The Middle East also has exceptional environmental qualities, with extensive deserts, and is among the most water-scarce regions on Earth. It is subject to dust storms and heat extremes, and in some parts photochemical air pollution is unparalleled (Alizadeh-Choobari et al., 2014). Model simulations show that climate change in the Middle East is associated with particularly rapid warming in summer, and that effectively the hot desert climate is intensifying (Lelieveld et al., 2016). When the surface temperature increases over dry desert soils, relative humidity decreases, which promotes dust mobilization (Klingmuller et al., 2016). Although the Middle East is a global change hot spot, it receives relatively little attention, e.g., in reports of the Intergovernmental Panel on Climate Change (IPCC,2013). One reason is that observational data are insufficient, unavailable or of limited quality.
AQABA was a comprehensive ship borne measurement and modeling campaign of reactive gases and particles, to study the pronounced regional contrasts that occur in atmospheric pollutant and dust concentrations. It took place in summer 2017 covering a track from Toulon, France to Kuwait through the Mediterranean and around the Arabian Peninsula and back.
The session invites all relevant contributions from the region and results from the AQABA campaign will be presented.

The aim of this general session is to bring together the scientific community within air pollution modelling. The focus is ongoing research, new results and current problems related to the field of modelling the atmospheric transport and transformation on global, regional and local scales.

All presentations covering the research area of air pollution modelling are welcome, including recent model developments, applications and evaluations, physical and chemical parameterisations, process understanding, model testing, evaluation and uncertainty estimates, emissions, numerical methods, model systems and integration, forecasting, event-studies, scenarios, ensembles, assessment, etc.

This is a general open session on all aspects of gas phase chemistry. The focus of this year will be on processes affecting the oxidation capacity of the atmosphere, particularly perturbations to HOx and NOx levels in the troposphere. Field measurements, laboratory and theoretical studies which do not fit into one of the other special sessions are welcome.

Air pollution is of great concern by the public and government in Asia, specifically in India and China, due to the risk to human health. To elucidate the formation mechanisms of air pollution in Asia, numerous field studies and modelling studies have been conducted in different Asian countries in the recent years, accompanied by mandatory emission restriction strategies that have been put into action.
This session aims for presentations about recent results from field studies, and also air quality monitoring activities in Asia linked to photochemistry, aerosols, emissions of air pollutants and tropospheric chemical composition.
All stages of data analysis are welcome in this session, including presentations of early field data, modelling studies, and results on the global impact of air pollution in Asia.

Cities are hotspots for the emissions of air pollutants and greenhouse gases from traffic, industries, household heating and energy production. Air pollution impacts are episodic and often co-occur with heat waves and allergenic pollen release. Greenhouse gases are often co-emitted with air pollutants. Urban air quality and the effect of policy measures are a challenge to monitor with traditional fixed stations or with models, because of the extreme variability in the cities’ geometry and emission patterns.
This session intends to bring together researchers of urban air quality and greenhouse gases and will accept submissions of topics related to urban air quality, heat stress, and air pollution impacts including health. The presentations focus on new developments in the field of ground and satellite observations, process modelling, data merging and downscaling related to urban air quality. Topics include sensor networks, personal monitoring, observations from space and UAV’s, high spatial and temporal resolution model approaches, downscaling, source apportionment, optical properties, atmospheric processes, mechanisms for air quality deterioration, community and personal exposure quantification and air pollution effects. Air pollution species may include anthropogenic and biogenic ones, including greenhouse gases and allergenic pollen, their isotopes and concentration ratios.

The session focuses on the variability of the tropospheric and stratospheric chemical composition on diurnal, seasonal and longer timescales and looks at the processes driving this variability. Special emphasis is put on the scientific value of high-quality long-term measurement data sets and supporting model simulations. Both approaches contribute to improved understanding of the mechanisms that control the variability of atmospheric chemical composition (including multiple gaseous species). Presentations related to the projections of the atmospheric composition are welcome in this session as well.
Researchers are invited to present novel scientific results from mid- and long-term observational time series from various programmes and networks such as the Global Atmosphere Watch (GAW) Programme, European Monitoring and Evaluation Programme (EMEP), Network for the Detection of Atmospheric Composition Change (NDACC), Southern Hemisphere Additional Ozonesondes (SHADOZ), Advanced Global Atmospheric Gases Experiment (AGAGE), National Oceanic and Atmospheric Administration (NOAA), regular airborne (e.g. CARIBIC, IAGOS, CONTRAIL) and other campaigns as well as satellite data and model simulations. Data relevant to tropospheric and stratospheric composition, in particular related to ozone depletion, climate change and air quality as well as firn data on past atmospheric composition are welcome. We welcome contributions from multi-year modeling studies and inter-comparison exercises which address past and future tropospheric or stratospheric composition changes, carried out in the framework of international projects and initiatives. The session will be dedicated in particular to the celebration of the 30th anniversary of the GAW Programme.

Measurements of gaseous compounds and particles in the atmosphere play a critical role in our understanding of air quality, human and ecosystem health and the mechanisms governing the Earth's climate. Monitoring long term spatial and temporal changes in amount fractions of regulated air pollutants, greenhouse gases, precursors to secondary pollutants (e.g. ozone and particulate matter) and particle number and size distributions are essential to establish the scientific links and feedbacks between atmospheric composition, air quality and climate and to ensure legislative compliance. Ambient amount fractions and stable isotope ratios of many trace gases as well as particle number concentrations and size distributions are routinely observed within networks of monitoring sites and on mobile measurement platforms around the globe. Ensuring the quality and comparability of all these datasets is critical to improve reliability and reduce uncertainty in our understanding of the Earths system. This session invites contributions that seek to address the fundamental metrology needed to underpin long term ambient monitoring of trace gases and particles ensuring coherent and comparable measurements.

Significant uncertainties exist in our understanding of the CO2 and CH4 fluxes between land or ocean and atmosphere on regional and global scales. Remotely-sensed CO2 and CH4 observations provide a significant potential for improving our understanding of the natural carbon cycle and for the monitoring of anthropogenic emissions. Over the last few years, remote sensing technologies for measuring CO2 and CH4 from space, aircraft, and from the ground made great advances and new passive and active instruments from different platforms became available offering unprecedented accuracy and coverage.

This session is open to contributions related to all aspects of remote sensing of the greenhouse gases CO2 and CH4 from current, upcoming and planned satellite missions (e.g., OCO-2, TanSat, Sentinel 5P), as well as ground-based (e.g., TCCON), aircraft, other remote sensing instruments. This includes, e.g., advances in retrieval techniques, instrumentational concepts, and validation activities, but we specifically encourage contributions that focus on the interpretation of observations in respect to natural fluxes or anthropogenic emissions.

Accurate and precise atmospheric measurements of greenhouse gas (GHG) concentrations reveal the rapid and unceasing rise of global GHG concentrations due to human activity. The resulting increases in global temperatures, sea-level, glacial retreat, and other negative impacts are clear. In response to this evidence, nations, states, and cities, private enterprises and individuals have been accelerating GHG reduction efforts while meeting the needs of global development. The urgency, complexity and economic implications of GHG reductions demand strategic investment in science-based information for planning and tracking emission reduction policies and actions. In response, the World Meteorological Organization (WMO) Global Atmosphere Watch Program (GAW) and its partners have initiated the development of an Integrated Global Greenhouse Gas Information System (IG3IS). IG3IS combines atmospheric GHG concentration measurements and human-activity data in an inverse modeling framework to help decision-makers take better-informed action to reduce emissions of greenhouse gases and pollutants that reduce air quality. This service is based on existing and successful measurement and analysis methods and use-cases for which the scientific and technical skill is proven or emerging.
This session intends to gather presentations from researchers and decision-makers (user-community) on the development, implementation and use of atmospheric measurement-based “top-down” and data-driven “bottom-up” GHG emission inventory estimates, and the combination of both approaches, explicit in space and time, to deliver actionable emissions information at scales where human activity occurs and emission reduction is most effective. This session is part of the EGU General Assembly 2019 30th anniversary celebration of the WMO’s Global Atmosphere Watch Program and its commitment to science-based services.

Anthropogenic methane emissions are responsible for roughly one quarter of net radiative forcing from GHGs. Its short atmospheric lifetime makes its mitigation an impactful way to reduce the near-term rate of warming. Atmospheric observations can provide valuable information to (1) reduce uncertainty on magnitude of emissions (2) attribute emissions to specific sources and (3) identify mitigation opportunities.
This session solicits research that focuses on methane emissions from human activities (e.g., fossil fuel infrastructure, rice production, ruminants, landfills and waste sector). We encourage submissions that highlight how atmospheric observations -at different scales- better constrain the magnitude of different emission sources and provide information that can guide relevant stakeholders to reduce emissions.

Public information:
Anthropogenic methane emissions are responsible for roughly one quarter of net radiative forcing from GHGs. We will present research that focuses on methane emissions from human activities (e.g., fossil fuel infrastructure, rice production, ruminants, landfills and waste sector).

Understanding atmospheric transport of trace species and aerosols is a topic that critically depends on bringing modeling and observational efforts together. The purpose of this session is to enable such connections, with a secondary focus on Lagrangian modeling of the atmosphere.

Vertical and long-range transport of trace species and aerosols are key factors controlling their concentrations and variability. Various surface emissions have a strong direct influence on the upper troposphere via several vertical transport processes, especially cumulus convection and lifting associated with frontal systems (warm and cold conveyor belts). Downward transport occurs via accompanying subsidence, while precipitation scavenging is one of the key sinks for many gases and aerosols. Long-range and intercontinental transport result in measurable enhancements of gas and aerosol concentrations in populated and agricultural regions due to industrial and biomass burning emissions thousands of kilometers upstream. Even many "remote" marine regions are far from being free from the direct influence of relatively short-lived anthropogenically produced gases and aerosols produced over far away continents. Additional processes such as stratosphere-troposphere exchange and lightning can also influence the chemical composition of downwind locations. Numerous methods have been applied to study transport-related issues, including targeted and long-term in-situ measurements as well as remote sensing (ground-based and satellite) and models (cloud-scale to global).

Lagrangian models are a very important research tool in this context, yet numerous scientific issues remain. We therefore invite studies contributing to advancing Lagrangian models, including the improvement of parameterizations of atmospheric processes, the quantitative assessment of uncertainties, improving model performance, and the proper coupling of Lagrangian models to Eulerian Numerical Weather Prediction and General Circulation models. In addition we invite contributions from applied Lagrangian research, involving observational data. We specially encourage those studies which synergistically combine various types of models and observations.

Reactive halogen species can have an important influence on the chemistry of the troposphere. For instance chlorine atoms react faster with most hydrocarbons than OH does and inorganic bromine and iodine can catalytically destroy tropospheric ozone and oxidise mercury. These reactions have been shown to be important in environments as different as the polar troposphere during the springtime ozone depletion events, the boundary layer over salt lakes, and volcanic plumes. There is strong evidence that halogens play a spatially even wider role in the marine boundary layer and free troposphere for ozone destruction, changes in the ratios of OH/HO2 and NO/NO2, destruction of methane, in the oxidation of mercury and in the formation of secondary aerosol. There are indications that both, oceanic sources as well as the chemistry of halogens and volatile organic compounds (VOCs) and oxygenated VOCs (OVOCs) in the tropics are linked with potential implications not only for the photochemistry but also the formation of secondary organic aerosol (SOA). It has been shown how the variability in iodine´s distribution in the ocean can have an impact on iodine production and ozone loss in both the ocean surface and throughout the troposphere. Marine emissions of active halogens have been linked to further potential impacts on oxidants loading in coastal cities. Finally, bromine and iodine are also being proposed as proxies of past sea ice variability.

We invite contributions in the following areas dealing with tropospheric halogens on local, regional, and global scales:

- Model studies: Investigations of the chemical mechanisms leading to release, transformation and removal of reactive halogen species in the troposphere. Studies of consequences of the presence of reactive halogen species in the troposphere.

- Laboratory studies: Determination of gas- and aqueous-phase rate constants, study of complex reaction systems involving halogens, Henry's law and uptake coefficients, UV/VIS spectra, and other properties of reactive halogen species. Biogeochemical controls on iodide formation and loss in the ocean to improve the current parameterizations for iodine emission.

- Field experiments and satellite studies: Measurements of inorganic (X, XO, HOX, XONO2, ..., X = Cl, Br, I) and organic (CH3Br, CHBr3, CH3I, RX, ...) reactive halogen species and their fluxes in the troposphere with in situ and remote sensing techniques.

- Measurements and model studies of the abundance of (reactive) halogen species in volcanic plumes and transformation processes and mechanisms.

- All aspects of tropical tropospheric halogens and links to (O)VOCs: their chemistry, sources and sinks, and their impact on local, regional, and global scales.

The session will cover all aspects of polar stratospheric ozone, other species in the polar regions as well as all aspects of polar stratospheric clouds. Special emphasis is given to results from recent polar campaigns, including observational and model studies.

We encourage contributions on chemistry, microphysics, radiation, dynamics, small and large scale transport phenomena, mesoscale processes and polar-midlatitudinal exchange. In particular, we encourage contributions on ClOx/BrOx chemistry, chlorine activation, NAT nucleation mechanisms and on transport and mixing of processed air to lower latitudes.

We welcome contributions on polar aspects of ozone/climate interactions, including empirical analyses and coupled chemistry/climate model results and coupling between tropospheric climate patterns and high latitude ozone as well as representation of the polar vortex and polar stratospheric ozone loss in global climate models.

We particularly encourage contributions from the airborne POLSTRACC field campaign (Polar Stratosphere in a Changing Climate) and related activities, which aim at providing new scientific knowledge on the Arctic lowermost stratosphere and upper troposphere in a changing climate. Contributions from WMO's Global Atmosphere Watch (GAW) Programme and from the Network for the Detection of Atmospheric Composition Change (NDACC) are also encouraged.

Variations in stratospheric aerosol -- arising primarily from sporadic volcanic eruptions -- are an important contributor to climate variability. Major volcanic eruptions have led to pronounced decreases in global surface temperature over seasonal-to-decadal timescales.

The transition from the unusual 1998-2002 period of a “fully decayed to quiescence” stratospheric aerosol layer, into a more typical period of modest volcanic activity temporarily offset a substantial proportion of the subsequent decadal forcing from increased greenhouse gases.

Advancing our understanding of the influence of volcanoes on climate relies upon better knowledge of the radiative forcings of past eruptions and the microphysical, chemical and dynamical processes which affect the evolution of stratospheric aerosol properties. This can only be achieved by combining information from satellite and in-situ observations of recent eruptions, stratospheric aerosol modelling activities, and reconstructions of past volcanic histories from proxies.

This session seeks presentations from research aimed at better understanding the stratospheric aerosol layer and its volcanic perturbations through the post-industrial period (1750-present) and also those further back in the historical record.

This year contributions addressing volcanic influences on atmospheric composition, such as changes in stratospheric water vapour, ozone and other trace gases are also particularly encouraged.

The session also aims to highlight research on volcanoes and climate contributing to current international SPARC-SSiRC, CMIP6-VolMIP, CMIP6-PMIP, and PAGES-VICS co-ordinated activities.

Over the past few years, major technological advances allowed to significantly increase both the spatial coverage and frequency bandwidth of geochemical and geophysical observations at active volcanoes. Establishment of high-rate GPS networks, continuous gravity meters, dense arrays of broad-band seismometers, and networks of instruments for the quantitative measurement of volcanic gas emissions now permits an unprecedented, multi-parameter vision of the surface manifestations of mass transport beneath volcanoes. Accompanying these progresses are new models and processing techniques leading to innovative paradigms for the interpretation and inversion of observational data. Within this context, this session aims at bringing together a multidisciplinary audience to discuss about the most recent innovations in monitoring approaches and to present observations, methods and models that increase our understanding of volcanic processes.

We welcome contribution related to (1) New instruments and techniques for the measurement of geophysical and geochemical parameters, from in-situ methods to ground-, air- and space-based remote sensing techniques; (2) Reports of significant case histories, documenting the relationships between the measured parameters and the evolving volcanic processes; (3) New modelling frameworks for the interpretation of the observed data, and their significance in terms of eruption forecasting.

The session will provide an opportunity to discuss volcanic activity from a monitoring perspective on a wide range of volcanoes. We therefore encourage submission of papers that are easily understandable to a broad, multi-disciplinary audience.

Areas found at plate boundaries are characterized by the presence of seismic, volcanic and geothermal activity. These processes are enhanced by the circulation of hydrothermal fluids in the crust, which transport volatiles from the deep crust or mantle to the surface. Certainly not limited to plate boundaries, as magma rises from depth, decreasing pressure allows volatile species to partition to the gas phase. Bubbles form, grow, coalesce and gases start to flow through vesiculated magma. Eventually, fluids escape towards the surface using tectonic structures and are released in the atmosphere, in some cases diffused through a soil or bubbling through a water pool, in other cases forming large plumes or explosive eruption columns. Fluids play an important role in earthquake generation.
Geochemical and isotope composition of gases deriving from different settings can trace sources and chemical and physical processes, providing information about deep earth. Moreover, volatiles play a key role in magma transport and have significant impact on the style and timing of volcanic eruptions. In addition, noble gases deriving from the deep earth can provide important information about their crust or mantle origin because these gases hardly react with other materials during migration. While carbon dioxide is one of the major constituents in volcanic/geothermal areas, methane, dominating sedimentary low heat flow areas, is often linked to subsurface hydrocarbon reservoirs that due to tectonic discontinuities are released in the atmosphere. Furthermore, sulfur dioxide emissions that take place in volcanic environments can cause acid rain, influence aerosol formation and, if an eruption column reaches the stratosphere, cause global dimming and a decrease in Earth’s surface temperatures for years. Similarly, halogens can dramatically impact proximal ecosystems, influence the oxidation capacity of the troposphere and alter the stratospheric ozone layer. Gas composition and flux may change with time, reflecting variations in the system. Measuring gases therefore constitutes a powerful tool for monitoring and understanding Earth.
This session aims to merge different geo-disciplines and bring together researchers interested in the comprehension of the degassing processes that take place in various geodynamic regimes. Furthermore, identify the impact that the emissions can have on terrestrial environment, atmospheric composition, climate and human health at various temporal and spatial scales. We invite contributions discussing novel measurement techniques, field measurements, direct and remote ground- and space-based observations and modeling studies of degassing can provide new insights into volcanic, tectonic and atmospheric processes on local and global scales.

This session has been created from sessions AS3.31 ‘Radiative effects and global aerosol forcing estimates of natural and anthropogenic aerosols’ (Convenors: Cathrine Lund Myhre, Elisabeth Andrews, Andreas Petzold, Bjørn Samset, Michael Schulz) and session AS3.32 ‘Natural Aerosols from Pre-Industrial to Present Day and into the Future’ (Convenors: Catherine Scott, Stephanie Fiedler, Kerstin Schepanski, Hugh Coe, Douglas Hamilton).

Aerosol radiative effects are an important aspect of the climate system that have both anthropogenic and natural contributions. This broad session focuses on the life cycle and radiative effects of all aerosol species present in the atmosphere.

One key topic is the radiative properties and effects of aerosols (e.g. black and brown carbon, mineral dust, biomass burning and hygroscopic aerosols) and model evaluation using aerosol observations. Today, ever more high quality data of aerosol optical properties, aerosol humidification, size distributions, aerosol light absorption and aerosol extinction vertical profiles have become available through international cooperation such as ACTRIS, GAW and NOAA networks. At the same time exhaustive global aerosol model results from multiple groups have been assembled in the AeroCom database, and rapid developments are being made in advance of CMIP6.

A better understanding of the role of natural aerosols in the atmosphere is essential for accurately determining anthropogenic radiative forcing and the climate response. In this session we will explore what we consider to be natural aerosols (i.e., primary aerosols and those formed from precursor gases emitted by natural sources, such as: wildfire, dust, volcanoes and the marine and terrestrial biospheres) and what we can observe about them in today’s atmosphere. Crucial questions include:
- How can we distinguish between truly natural aerosols and those whose emissions or formation are influenced by anthropogenic activities?
- How have the contributions of natural aerosols to atmospheric composition changed over time?
- How well do we understand the lifecycle of natural aerosols in the atmosphere in the absence of anthropogenic influence?
- Can we identify any pristine environments in the present day that can help us understand the pre-industrial atmosphere?
- How well are natural aerosols represented in Earth System Models and which observations can be used to evaluate them?

We welcome contributions relating to the use of observations and/or modelling to inform us about past, present-day and future aerosol-climate interactions.

Volatile Organic Compounds (VOCs) in the atmosphere are globally dominated by a number of primary emission sources. These include biogenic sources (e.g. emissions from plants, flowers) or microbial VOCs (mVOCs), as well as anthropogenic and pyrogenic emissions. Once in the atmosphere, VOCs are oxidized and serve as precursors of secondary organic aerosol. They also contribute to the formation of tropospheric ozone, and can affect atmospheric oxidants. Mechanistic understanding of chemical pathways and surface-atmosphere exchange in rural and urban environments requires synergy between measurements at different spatiotemporal scales including laboratory oxidation experiments, embracing the broad diversity of VOC sources in the atmosphere. From a direct health perspective the largest human exposure to VOCs is likely not outdoors but in the indoor atmosphere. The use of solvents and consumer-care products by humans have also emerged as a prominent source of outdoor atmospheric VOCs. Extension of the range of VOCs measured in urban environments reveal large contributions of longer-chain semivolatile VOCs, and recent measurement technologies for extremely low volatility compounds (ELVOC) have bridged the gas-aerosol phase continuum.
We encourage a wide range of submissions of contributions based on in-situ measurements of VOCs at different scales, outdoors and indoors, flux measurements of emission and deposition processes, satellite observations, laboratory experiments and modeling.

Plant ecosystems exchange reactive trace gases, such as nitrogen oxides (NOx), ozone, and volatile organic compounds (VOCs), and particles. While some of these compounds are anthropogenically produced, many are biotic in origin and are emitted in-situ or produced from rapid photochemistry in the canopy. The oxidation products include low-volatility organic compounds that readily partition to the aerosol phase, particularly in the presence of anthropogenic pollutants such as ammonium, nitrate and sulphate. In addition to being strong sources, soil and leaves represent major sinks of these reaction products, with deposition to the surface also as a function of surface wetness and uptake into the leaf via the stomata. The canopy region thus represents a dynamic and rapidly changing environment in which a myriad biological, chemical and physical processes occur over very short time and spatial scales. Advanced techniques of flux measurements provide good knowledge of the overall net fluxes of these compounds above canopies, while additional in-canopy measurements enable more detailed study and understanding of the individual processes and reactions driving these fluxes. These rapidly advancing measurements can support parametrization of models for a mechanistic understanding of in-canopy dynamics of deposition and emission of these reactive gases, which can in turn allow fuller interpretation of in-situ measurements and inform the design of field experiments to test specific hypotheses. This session, sponsored by ILEAPS (Integrated Land Ecosystem Atmosphere Process Study), encourages the submission of contributions based on in-situ measurements and/or modeling that improve our understanding of biosphere-atmosphere exchange of reactive gases and aerosols and in-canopy processes.

The Amazon forest is the world’s largest intact forest landscape. Due to its large biodiversity, carbon storage capacity, and role in the hydrological cycle, it is an extraordinary interdisciplinary natural laboratory of global significance. In the Amazon rain forest biome, it is possible to study atmospheric composition and processes, biogeochemical cycling and energy fluxes at the geo-, bio-, atmosphere interface under near-pristine conditions for a part of the year, and under anthropogenic disturbance of varying intensity the rest of the year. Understanding its current functioning at process up to biome level is elemental for predicting its response upon changing climate and land use, and the impact this will have on global scale.

This session aims at bringing together scientists who investigate the functioning of the Amazon and comparable intact forest landscapes across spatial and temporal scales by means of remote and in-situ observational, modeling, and theoretical studies. Particularly welcome are also presentations of novel, interdisciplinary approaches and techniques that bear the potential of paving the way for a paradigm shift.

Organic material can make up a substantial fraction of ambient particulate matter, both in polluted urban areas and in cleaner rural and remote regions. Therefore they have the ability to impact the Earth radiative balance and human health at local, regional and global scales. Aerosols are made up of a complex mixture of inorganic and organic species with a wide range of functionalities and volatilities, making them one of the most challenging components of the atmosphere to characterize. Once organic compounds are emitted to the atmosphere they can undergo complex chemical and physical processes. The chemical processes involving aerosol species can also lead to changes in the physicochemical properties of ambient particles, such as their hygroscopicity, morphology and phase, diffusion of water and SVOCs, light scattering and absorption. Thus even with extensive study, our understanding of their sources, formation, evolution and vertical distribution in the atmosphere remains limited.

This session welcomes presentations that discuss the sources and evolution of organic aerosols in the atmosphere and how atmospheric processes transform ambient aerosols both in terms of their chemical composition and their physical properties.

Fine-particle pollution associated with haze threatens the health of more than 1 billion people in China. Extremely high PM2.5 concentrations are frequently observed especially during the winter haze event in northern China. Even after accounting for aerosol-radiation-meteorology feedback and improving the emission inventory, state-of-the-art models still fail to capture the observed high PM2.5 concentrations, suggesting the missing of key chemistry for the secondary aerosol formation. To improve the prediction and control strategy of PM2.5, we are in urgent need of a better understanding of the chemistry of secondary aerosol formation. Thus we propose the session "Multiphase chemistry of secondary aerosol formation under severe haze" to promote the research and discussion on this topic which is highly relevant for both atmospheric chemists and the public.

The session is open for all submissions which addresses, but is not limited to, the following questions concerning secondary aerosol formation: What are the key oxidation pathways leading to aerosol formation under clean and polluted conditions? What is the role of multiphase chemistry versus gas phase chemistry? Are laboratory determined kinetic data of multiphase chemistry directly applicable for ambient conditions and if not, how to derive and determine the reaction kinetics relevant for ambient conditions? What is the aerosol particles’ and droplets’ pH and how does it influence the multiphase chemistry? What is the role of the RH, temperature, mixing state and aerosol phase state in multiphase chemistry and how does aerosol mixing state play a role? What's the contribution of aqueous secondary organic aerosol (SOA) formation under highly polluted conditions?

A special issue of the same topic has already been approved and launched in the EGU journal "Atmospheric Chemistry and Physics".