Inter- and Transdisciplinary Sessions
Disciplinary sessions AS–GM
Disciplinary sessions GMPV–TS

Session programme


AS – Atmospheric Sciences

Programme group chair: Athanasios Nenes

AS3 – Atmospheric Chemistry and Aerosols

Programme group scientific officer: Athanasios Nenes


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 surface phenomena. Aerosol surface characteristics and heterogeneous reactions on aerosol surfaces impact they formation and atmospheric lifetime, and are also associated with adverse health effects. In addition, processes in aqueous aerosol surfaces are shown to significantly affect the cloud droplet activation. Despite of potentially important role of aerosol surfaces in atmospheric process, there are still very limited selection of methods that can be applied to study the surface characteristics and processes. With this in mind, aside from general submissions on aerosol research, we encourage contributions from work within the broad focus of aerosol surface phenomena. These might include work on:
* Molecular scale investigations, from single component to complex mixtures
* Evidence from laboratory and field studies
* New experimental capabilities
* New modelling capabilities
* Impact studies

Convener: Annele Virtanen | Co-conveners: Ilona Riipinen, David Topping
| Attendance Tue, 05 May, 08:30–12:30 (CEST), Attendance Tue, 05 May, 14:00–15:45 (CEST)

The session focuses on the variability of the tropospheric and stratospheric chemical composition on the timescales from diurnal to decadal. It discusses the processes driving this variability and attribution of changes. 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.

Convener: Oksana Tarasova | Co-conveners: Pedro Jimenez-Guerrero, Euan Nisbet, Andrea Pozzer
| Attendance Mon, 04 May, 08:30–12:30 (CEST)

The chemical composition of the middle atmosphere is not only relevant for understanding radiative forcing or protection of the biosphere from harmful UV radiation, but it also has an influence on tropospheric circulation and dynamics that act as a feedback on climate. Increasing greenhouse gases are expected to modify the large-scale circulation of the stratosphere, termed Brewer-Dobson circulation (BDC), and the chemical compositions of radiatively active gases, notably ozone and water vapour, in the upper troposphere and lower stratosphere (UTLS) region. Such changes in the BDC and UTLS composition are expected to change levels of surface UV radiation, modify the radiative forcing of climate, and feedback on the dynamics both within the stratosphere and at the surface. This session is particularly interested in evidence of the direct influence of climate change upon stratospheric dynamics and chemistry, as well as indirect feedbacks from these changes back upon surface climate. We welcome abstracts focused on stratospheric composition changes on time-scales encompassing inter-annual to centennial timescales,on local to global spatial scales, future projections from chemistry climate models, and discussing changes induced by both natural and anthropogenic factors, observations, as well as theoretical studies.

Co-organized by CL3
Convener: Gabriel ChiodoECSECS | Co-conveners: William Ball, Mohamadou Diallo
| Attendance Thu, 07 May, 14:00–15:45 (CEST)

This session examines the variability of trace gases and aerosols in the troposphere,
and how the chemical heterogeneity challenges our ability to compare models and measurements. Papers will examine how transport, chemicophysical processes, and emissions can create the chemical patterns we observe, and how different modeling approaches (Lagrangian and Eulerian) are able to establish and sustain them. Resolved advective transport (e.g., jet streams, frontal systems) as well as convection, turbulence, precipitation and scavenging, create a mixture of chemically distinct air masses. We will examine how this heterogeneity can be observed and assessed in models. Even over the remote ocean basins we find a mixture of anthropogenic pollution mixed with the chemistry of the marine boundary layer. Pollution or land-based signatures are useful in tracing the history of air parcels, but it remains uncertain whether this diluted pollution can influence the chemical reactivity.
In addition, we look for observations and models that can evaluate the chemical patterns in terms of which combinations, or covariation of key species, makes some air parcels more reactive than others, and thus controls the evolution of tropospheric ozone and methane. Likewise, we look for observations and modeling techniques that help us understand how aerosols are modified by atmospheric processes, from generation of new particles to removal by precipitation. A fundamental evaluation of our current chemistry-climate models can be based on matching this heterogeneity.

Convener: Athanasios Nenes | Co-conveners: Sabine Eckhardt, Valérie Thouret
| Attendance Wed, 06 May, 16:15–18:00 (CEST)

The composition of the upper troposphere and the stratosphere (UTS) plays a key role in the climate system. Our understanding of the interactions between dynamics, chemistry and climate in this region has been rapidly increasing over the last years thanks to combined observational and model based studies. In this session we invite studies of dynamical, transport and chemical processes determining the variability at all scales and long-term trends in the composition of the UTS. We particularly encourage studies bringing together recent in-situ and/or remote sensing observations and model simulations.

Convener: Daniel KunkelECSECS | Co-conveners: Marta AbalosECSECS, Thomas Birner, Harald Boenisch, Felix Ploeger
| Attendance Tue, 05 May, 14:00–18:00 (CEST)

A better understanding of the role of natural aerosols in the atmosphere is essential for assessing anthropogenic radiative forcing and the climate response. Our session explores primary aerosols and those formed from precursor gases emitted by natural sources, e.g. from wildfires, deserts, volcanoes and both the marine and terrestrial biosphere. The session intends to bring together experts from different fields to assess the state-of-the-science knowledge on natural aerosols and to identify future directions to reduce uncertainty. We encourage submissions that use models across different spatial scales and consider past, present or future perspectives, as well as measurements from remote sensing, field campaigns and laboratory experiments. Questions of particular interest are, but are not limited to: 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 and deposition changed over time? What are the consequences of these changes? Where are the missing links in our understanding of 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?

Co-organized by CL3
Convener: Stephanie Fiedler | Co-conveners: Hugh Coe, Douglas Hamilton, Kerstin Schepanski, Catherine Scott
| Attendance Mon, 04 May, 08:30–10:15 (CEST)

The interactions between aerosols, climate, and weather are among the large uncertainties of current atmospheric research. Mineral dust is an important natural source of aerosol with significant implications on radiation, cloud microphysics, atmospheric chemistry and the carbon cycle via the fertilization of marine and terrestrial ecosystems.
In addition, properties of dust deposited in sediments and ice cores are important (paleo-)climate indicators.

This interdivision session is open to contributions dealing with:
(1) measurements of all aspects of the dust cycle (emission, transport, deposition, size distribution, particle characteristics) with in situ and remote sensing techniques,
(2) numerical simulations of dust on global and regional scales,
(3) meteorological conditions for dust storms, dust transport and deposition,
(4) interactions of dust with clouds and radiation,
(5) influence of dust on atmospheric chemistry,
(6) fertilization of ecosystems through dust deposition,
(7) any study using dust as a (paleo-)climate indicator including investigations of Loess, ice cores, lake sediments, ocean sediments and dunes.

We especially encourage to submit papers on the integration of different disciplines and/or modeling of past, present and future climates.

Public information:
Please be aware that there are a number (N=3) changes in the order in which the presentations will be discussed. Please have a look at the provided session materials for the final program.

Co-organized by BG1/CL4/GM8/SSP3, co-sponsored by ISAR
Convener: Jan-Berend Stuut | Co-conveners: Paola Formenti, Joanna Nield, Claire Ryder, Mingjin TangECSECS
| Attendance Fri, 08 May, 10:45–12:30 (CEST)

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, 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, shape, and surface properties makes it difficult to understand and parameterize their microphysical and hence radiative properties.
Fundamental understanding of the cloud dynamics and aerosol properties, which play the major role in the climate system, will require the understanding of gas-, water-, and ice-aerosol surface interactions. To advance our knowledge about atmospheric processes, this session aims to bring together two research areas, namely (1) Atmospheric Surface Science (ASS) and (2) Ice particles (IP) and Ice Nucleating Particles (INP):
(1) ASS is concerned with the experimental and theoretical approaches investigating atmospheric interactions as well as ice nucleation processes “on the molecular level”. The goal is to fill the gap between the large scale atmospheric processes and gas-, water-, and ice- interactions with atmospherically relevant mineral and biological surfaces.
(2) IP and INP are concerned with the laboratory examination, on a fundamental level, trying to understand the nucleation processes and characterizing IP and INP in the atmosphere.

- Solicited talk_1: "The Portable Ice Nucleation Experiment chamber (PINE): laboratory characterization and field test for its semi-automated ice-nucleating particle measurements in the Southern Great Plains".
Speaker: Naruki Hiranuma, West Texas A&M University, USA.

Convener: Ahmed Abdelmonem | Co-conveners: Hinrich Grothe, Christian Rolf, Odran Sourdeval, Sylvia Sullivan
| Attendance Wed, 06 May, 16:15–18:00 (CEST)

This symposium seeks to bring together environmental and atmospheric photochemists to help bridge the topics of aquatic photochemistry and aerosol photochemistry. The field of aquatic photochemistry seeks to understand the photochemical properties of dissolved organic matter which lead to the degradation of pollutants, particularly in the context of water treatment. On the other hand, the field of aerosol photochemistry seeks to understand the properties of the organic fraction in atmospheric aerosol capable of impacting climate through aerosol-radiation and aerosol-cloud interactions. Both fields have similar goals of characterizing the response of organic matter whether it be in lakes, rivers and oceans or in the atmosphere to sunlight exposure. This symposium will facilitate these two fields coming together to share techniques, sampling protocols and chemical insights. The symposium will gather field and laboratory researchers, environmental engineers, aerosol scientists, and atmospheric chemistry modelers with the goal of discussing emerging research in photochemistry of organic matter both in the aquatic and aerosol phases.

Co-organized by OS3
Convener: Nadine Borduas-DedekindECSECS | Co-conveners: Nir BluvshteinECSECS, Ulrich Krieger
| Attendance Mon, 04 May, 10:45–12:30 (CEST)

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".

Public information:
Session invited talk (live presentations on Zoom Meetings):

Mon, 04 May, 14:00-15:45 (Vienna Time)

14:00-14:35 Markku Kulmala, Reducing urban new particle formation as a plausible solution to
mitigate particulate air pollution in Beijing and other Chinese megacities
14:35-15:10 Gregory Carmichael, Aerosol Chemistry and Effects in the Anthropocene
15:10-15:45 Meng Gao, Aerosol Pollution in Asia and Its Interactions with Climate

Join Zoom Meeting: https://zoom.us/j/8425924612
Meeting ID: 842 592 4612
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Convener: Yafang Cheng | Co-conveners: Pingqing Fu, Jingkun Jiang, Nan MaECSECS, Hang Su
| Attendance Mon, 04 May, 14:00–15:45 (CEST)

The gas-phase oxidation of organic compounds leads to the formation of less volatile organic compounds that may condense on aerosol surfaces. One key aspect of the transformation of organic species is the fate of organic peroxy radicals that are formed after the initial radical attack. This session aims for contributions connecting the gas-phase oxidation of organic compounds with the formation of secondary organic aerosol. Oxidation agents can be the hydroxyl radical, ozone or the nitrate radical. We invite contributions on the investigation of the gas-phase chemistry leading to secondary organic aerosol or on the investigation of aerosol properties as a consequence of the oxidation process. Contributions can include the development and test of mechanisms describing the chemical transformation of organic compounds in laboratory and in experiments in simulation chambers as well as insights from field studies.

Convener: Hendrik Fuchs | Co-conveners: Patrick DewaldECSECS, Juliane Fry, Anna NovelliECSECS, Luc Vereecken
| Attendance Wed, 06 May, 14:00–15:45 (CEST)

Methane is an important greenhouse gas that has contributed ∼25% of the radiative forcing experienced to date. Despite methane’s short atmospheric lifetime (~10 years), global methane concentrations have grown more than three times faster than carbon dioxide since the industrial revolution. This makes methane emission mitigation an effective way to reduce the short-term rate of warming. In contrast to carbon dioxide, anthropogenic methane emissions originate from a large variety and number of diffuse point sources that are mostly independent of combustion processes. As a result, systematic atmospheric measurements are needed to inform emission inventories and mitigation strategies.

This session will highlight research that focuses on methane emissions from human activities (e.g., fossil fuel infrastructure, fire, rice production, ruminants, landfills and waste). Particular emphasis is on studies collecting atmospheric observations at different spatio-temporal scales with the aim to (1) reduce the uncertainty in the measured magnitude of emissions, (2) identify source-specific emission patterns and mitigation opportunities, and (3) inform stakeholders, such as regulators and industry representatives, on mitigation pathways.

Co-organized by BG2
Convener: Stefan Schwietzke | Co-conveners: Andreea Calcan, Bryce F.J. Kelly, Christopher Konek
| Attendance Wed, 06 May, 14:00–15:45 (CEST)

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-3, GOSAT-2, Sentinel 5P, CO2M), as well as ground-based (e.g., TCCON, COCCON), aircraft, other remote sensing instruments. This includes, e.g., advances in retrieval techniques, instrumental concepts, and validation activities, but we specifically encourage contributions that focus on the interpretation of observations in respect to natural fluxes or anthropogenic emissions.

Convener: Sander Houweling | Co-conveners: Hartmut Boesch, Dietrich G. Feist, Justus Notholt, Maximilian Reuter
| Attendance Wed, 06 May, 08:30–10:15 (CEST)

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.

Public information:
Based on the outcome of a poll among the presenting authors, the live chat of this session has been cancelled.

A subset of the presentations will be given in a video session on Wednesday, 27nd of May. If you are interested to join, please contact the convenors for details.

We are sorry that we cannot have a live EGU session this year and hope to see you all again in Vienna next year!

Andreas Richter, Anja Schönhardt, Cathy Clerbaux, Pieternel Levelt

Convener: Andreas Richter | Co-conveners: Cathy Clerbaux, Pieternel Levelt, Anja Schoenhardt
| Attendance Fri, 08 May, 08:30–12:30 (CEST)

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 will also showcase the new projects and efforts to develop “good-practice” standards under the World Meteorological Organization (WMO) Integrated Global Greenhouse Gas Information System (IG3IS), which is part of WMO’s commitment to science-based services.

Co-organized by BG2/CL3/ERE1
Convener: Phil DeCola | Co-conveners: Thomas Lauvaux, Kimberly Mueller, Tomohiro Oda, Oksana Tarasova, Maša Zorana Ostrogović Sever
| Attendance Wed, 06 May, 14:00–18:00 (CEST)

High surface ozone concentrations are of major concern in many regions of the world. Despite major efforts to reduce emissions, some areas (e.g Asia) regularly experience a large number of ozone pollution events in the summer. In addition, high ozone formation rates have also been observed in wintertime. Photochemical transformation of organic compounds in the presence of nitrogen oxides is responsible for ozone production. Due to the strong dependence of ozone production on nitric oxide concentrations, emission reduction of nitrogen oxides affects also ozone concentrations in the troposphere. The session aims for contributions reporting observations of ozone pollution and/or production for example in field campaigns and investigating reasons for high ozone pollution using observations and model calculations. In addition, contributions analysing trends of ozone concentrations and making suggestions for possible mitigation strategies are welcome.

Convener: Anna NovelliECSECS | Co-conveners: Xin Li, Keding Lu, Lisa Whalley
| Attendance Thu, 07 May, 10:45–12:30 (CEST)

Over the last decades, Earth’s atmospheric composition has been extensively monitored from space using different techniques and spectral ranges. The GOME (Global Ozone Monitoring Experiment) instrument launched in 1995 by ESA showed that atmospheric space missions with high spectral resolution and coverage can not only be used for ozone monitoring but also to measure a range of trace gases and aerosol for air quality and climate (research) applications. Several decades after these pioneering efforts, continuous progress in instrument design, and retrieval techniques allows operational monitoring of stratospheric and tropospheric concentrations of a wide range of species with implications for air quality and climate. This is well demonstrated with the successful operations of the Sentinel 5 Precursor (S-5P) satellite since 2018.
S-5P is the first of a series of atmospheric missions within the European Commission’s Copernicus Programme and provides continuity in the availability of global atmospheric data products between its predecessor missions SCIAMACHY (Envisat) and OMI (AURA) and the future Copernicus Sentinel-4 and -5 satellite series. The current/future European (Copernicus) atmospheric measurement capabilities are/will be complimented by other space missions like MetOp, MetOp-SG, SUOMI-NPP, GOSAT/2, TanSat, GaoFen 5, OCO2/3, TEMPO, GEMS and others.
This session will include latest results for S-5P operational products (e.g. radiance/irradiance, ozone, nitrogen dioxide, sulfur dioxide, formaldehyde, methane, cloud and aerosol information), results of algorithm studies to develop additional S5-P products (e.g. bromine monoxide, water vapour, glyoxal, AOD, SIF, chlorophyll, and chlorine dioxide) and their geophysical validation. Synergistic data usage or intercomparison results of S-5P measurements with con-current flying missions (e.g. MetOp, GOSAT) and algorithm studies for future mission retrieval algorithms (e.g. Sentinel-4/5) will be addressed. Opportunities that new instrument concepts can bring to the atmospheric air quality and climate monitoring communities will be included as well.

Convener: Claus Zehner | Co-conveners: Ilse Aben, Pieternel Levelt, Rosemary Munro, Christian Retscher
| Attendance Thu, 07 May, 08:30–12:30 (CEST)

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 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). Marine emissions of active halogens have been linked to 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.

- 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.

Convener: Alfonso Saiz-Lopez | Co-conveners: Nicole Bobrowski, Ulrich Platt, Rolf Sander
| Attendance Tue, 05 May, 16:15–18:00 (CEST)

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.

Convener: Jørgen Brandt | Co-conveners: Nikos Daskalakis, Ulas Im, Pedro Jimenez-Guerrero, Andrea Pozzer
| Attendance Thu, 07 May, 16:15–18:00 (CEST)

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.

Convener: Ulrike Dusek | Co-conveners: Dominik Brunner, Ru-Jin Huang, Michiel van der Molen, Felix Vogel
| Attendance Fri, 08 May, 08:30–12:30 (CEST), Attendance Fri, 08 May, 14:00–15:45 (CEST)

The number and size of urban conurbations, which comprise megacities and different urban agglomerations, collectively known as major population centres (MPC), has increased dramatically. By 2050, the population is predicted to rise to ~10 billion with about 75% being urban dwellers. MPCs require power, mostly generated from fossil fuel combustion for their transport systems, industry and domestic heating, cooling etc. MPCs are globally a growing and significant source of emissions of trace gases and aerosols into the troposphere. The air quality in the MPC and the transformation of the emitted pollutants is also often influenced by the transport of biomass burning and pollution plumes. Because of the variability of the naturally occurring emissions of trace constituents, the different characteristics of MPC, the mixing and interaction of the outflow from MPC with those from the surrounding areas, and the need to account for the local topography and meteorology, the assessment and prediction of the impact of pollution from MPC on tropospheric chemistry is challenging. The current knowledge of the effect of this anthropogenic pollution on the air quality and the regional tropospheric chemical composition, and its interaction with climate in a warming world is inadequate.
The trace constituent of interest from MPC emissions are short-lived climate pollutants, their precursors, and long lived greenhouse gases. To assess and better understand the local and regional impact of these pollutants, experimental and modelling investigations of the transformation of MPC emissions during their transport are required. This necessitates the consistent interpretation of observational data sets, having different spatial and temporal resolutions, generated from ground-based networks, airborne campaigns and satellite measurements. This further requires a hierarchy of model studies.
The purpose of this session is to present and discuss results from recent national and international projects studying the emissions from megacities and MPC and their transport and transformation. The session welcomes presentations about relevant observations, data interpretation and modelling studies. One focus is on the studies of MPC emissions from different continents, experiencing different meteorological conditions and the resultant local and regional impacts.

Public information:
In memory of the excellent scientist and colleague Andreas Hilboll

Convener: Maria Dolores Andrés Hernández | Co-conveners: Matthias Beekmann, Charles Chou, Helmut Ziereis
| Attendance Wed, 06 May, 10:45–12:30 (CEST)

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 polar airborne field campaigns as e.g. the POLSTRACC (Polar Stratosphere in a Changing Climate) and SouthTRAC (Southern Hemisphere - Transport Composition Dynamics) campaign as well as related activities, which aim at providing new scientific knowledge on the Arctic/Antarctic 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.

Convener: Farahnaz Khosrawi | Co-conveners: Hideaki Nakajima, Michael Pitts, Ines TritscherECSECS
| Attendance Mon, 04 May, 10:45–12:30 (CEST)