Atmospheric Chemistry and Physics

The joint ACP/AMT special issue on "Observations and modeling of aerosol and clouds properties for climate studies" brings together publications on characterization of aerosol and cloud properties and their impact on climate.

This special issue is motivated by presentations and discussions happened during the Workshop on "Observations and modeling of aerosol and clouds properties for climate studies" held in Paris, Université Pierre et Marie Curie, 12-14 September 2011 (http://www-loa.univ-lille1.fr/workshop). The Workshop gathered more than 130 scientists already involved in decades of collaboration, and generated a number of insightful discussions on the community accomplishments and outlined the most appealing dynamics for near future remote sensing activities. The advances and challenges of accessing aerosol and cloud effects on climate dynamics were discussed. It also included coordination between the international space-based observations of the atmosphere activities and evaluation of satellite products with the help of modelers, ground-based remote sensing and in situ measurement scientists.

We encourage submissions describing the studies presented at the workshop and also coming from relevant broader community.

Main topics are:

• Achievements in characterization of aerosols, clouds and Earth's atmosphere.
• Inversions, new ideas and algorithms to derive detailed aerosol and cloud properties: passive and active remote sensing, characterization from satellite, ground-based, airborne and in situ.
• Modeling of aerosols, clouds and their climate effects.
• Progress expected from future satellite missions.

Developing Arctic Modelling and Observing Capabilities for Long-term Environmental Studies (DAMOCLES) was the flagship EU project for the IPY. It concerned 47 partners from about 10 European Countries and triggered an active international scientific cooperation with Russia, China, Japan and the USA. At the time the DAMOCLES contract ended about one year ago, more than 150 scientific papers appeared in peer-reviewed publications under DAMOCLES. There are more publications to come as evidenced during the final General Assembly of Damocles in Tromsø, Norway in May 2010. During this final GA it was agreed and decided that DAMOCLES should find an appropriate scientific journal to release an important set of publications based on 6 synthetic papers and up to 30 topical papers. After some investigation it was decided to contact the European Geosciences Union Copernicus Publications to check the adequacy for submitting Damocles results dedicated to Ocean, Atmosphere and Sea Ice sciences in three Copernicus relevant journals: Atmospheric Chemistry and Physics (ACP), The Cryosphere (TC) and Ocean Science (OS).

The special issue publishes results from the BORTAS aircraft campaign in summer 2011 and related ground-based and space-borne measurement studies in 2010 and 2011. The overarching goal of BORTAS is to investigate the connection between the composition and the distribution of boreal biomass burning outflow, ozone production and loss within the outflow, and the resulting perturbation to oxidant chemistry in the troposphere. In July 2011, the FAAM146 research aircraft was used to sample the outflow from boreal fires over the Western boundary of the North Atlantic. These aircraft-based measurements were complemented by satellite data and a range of ground-based measurements.

The data obtained in the BORTAS campaign are used to:

• describe observed chemistry within plumes, with particular attention to the NOy and organic chemistry;
• derive a reduced chemical mechanism from the Master Chemical Mechanism (MCM), informed by the measurements, suitable for use in a global chemical transport model to reproduce observed chemistry within the plumes;
• quantify the impact of boreal forest fires on oxidant chemistry over the temperate and subtropical Atlantic using a nested 3-D chemistry transport model, driven by assimilated field measurements and the reduced chemical mechanism; and
• detect, validate and quantify the impact of boreal biomass burning on global tropospheric composition using data from space-borne sensors.

This special issue addresses the problem of distinguishing aspherical from spherical particles in the atmosphere. In particular, separating liquid from ice particles in clouds and distinguishing dust, ash, bioaerosols and other types of aspherical particles from those that are spherical.

Papers that discuss the theoretical background that relates depolarization to physical features of aerosol and cloud particles are welcome, as are those that apply the theory to actual measurement of ambient particles.

The Pan European Gas AeroSOls-climate interaction Study (PEGASOS) European large scale integrating project brings together most of the leading European research groups, with state of the art observational and modeling facilities to:

1. Quantify the magnitude of regional to global feedbacks between atmospheric chemistry and a changing climate and to reduce the corresponding uncertainty of the major ones.
2. Identify mitigation strategies and policies to improve air quality while limiting their impact on climate change.

The project will combine development of anthropogenic and biogenic emission inventories, laboratory studies in some of the premier European smog chamber facilities, field measurements over Europe using a Zeppelin combined with mobile and fixed ground platforms, air quality and climate models, and policy analysis to achieve its objectives.

The SI will include papers on the experimental, theoretical and modelling results related to the CERN CLOUD experiment. The scientific focus of the experiment is to make fundamental measurements of aerosol nucleation under highly controlled laboratory conditions, including the effects of natural and synthetic cosmic rays. There were two campaigns of a month long: the first (2010) focused on inorganic aerosols and cosmic ray influences (NH3/H2SO4). The second campaign (June 2011) focuses on organic impacts on nucleation. There are also detailed modelling studies, plus papers on parameterisation development and global model applications.

The special issue aims at collecting research papers from the WAVACS final workshop and, more in general, from the broader community involved in the action.

Main topics are:

• Water vapor time series and trends;
• Cirrus inhomogeneities and relationship to the environmental water vapor field and radiative transfer Submissions of papers dealing with broader WAVACS objectives are also encouraged:
  • Accuracy of atmospheric water vapor observations and harmonization;
  • Results from specific field campaign;
  • Process related to water vapor isotopes;
  • Regional/Global modelling and data assimilation.

Understanding and quantifying the chemical interactions of ice and snow with trace gases in the atmosphere is a major challenge in atmospheric chemistry. Ice in the environment, from ice particles in clouds, to sea ice and snow at the Earth's surface, has a profound influence on atmospheric composition and climate. A quantitative, mechanistic understanding of trace gas-ice interactions is critical for predicting the effects of climate change on atmospheric composition, for the interpretation of ice core chemical records, and for modeling atmospheric chemistry. There are significant gaps in our current understanding of the uptake of gases by ice, including uncertainty regarding the microphysical location of species upon uptake, rates and mechanisms of chemical processes taking place in/on ice, the role of interfacial layers at the ice surface, and the role of biological activity in the ice.

This special issue is comprised of a series of review articles originating from the 3rd Workshop on Air-Ice Chemical Interactions, which was held at Columbia University in New York, NY from June 6-8, 2011.

iLEAPS is the land-atmosphere core project of the International Geosphere-Biosphere Programme (IGBP). The scientific goal of iLEAPS is to provide understanding how interacting physical, chemical and biological processes transport and transform energy and matter through the land-atmosphere interface. Atmospheric Chemistry and Physics (ACP) and Biogeosciences (BG) have opened a joint special issue on iLEAPS-related science, and you are welcome to contribute by sending manuscripts on land-atmosphere interactions to this joint issue via either ACP or BG.

The HUMPPA-COPEC 2010 intensive field measurement campaign was conducted at the Boreal forest research station SMEAR II (Station for Measuring Ecosystem-Atmosphere Relation) in Hyytiälä, Finland from 12th July-12th August 2010. This campaign was focused on characterizing the summertime chemistry and physics over the Boreal forest when emission fluxes of volatile organic compounds (VOC), OH initiated photochemistry, and particle growth rates reach their seasonal maximum. An international consortium co-ordinated by the Max Planck Institute for Chemistry, Germany and the University of Helsinki, Finland was assembled to quantity a comprehensive suite of gas and particle phase species. The natural biogenic emissions from the surrounding coniferous forest were characterized under the long summer daylight and warm temperature conditions. Furthermore the campaign sought to capture and characterize influences from biomass burning, urban anthropogenic pollution and nearby sawmills at the site.

The MEGAPOLI PARIS campaigns in summer 2009 and in winter 2010 aimed at better quantifying sources of primary and secondary aerosol in and around a large agglomeration and to document their evolution in the megacity plume. A focus was put on carbonaceous aerosol, where uncertainties are major. As related issues, also gas phase photochemistry and the evolution of dynamical conditions during the campaign were addressed. Analysis of experimental data and modelling studies are solicited. Papers on timescales beyond the campaign, but dealing with this target region, are also welcome.

The atmospheric composition of the past is stored in the bubbles of polar ice sheets and glaciers. This archive now reaches back to 800,000 years before present. The last several decades of the atmospheric composition history is not yet occluded in the ice but can be found in the open porous layer at the surface of the ice sheet at high resolution. In this layer a large amount of gas is available which allows for analyses not (yet) possible from the bubble section, and in many cases recovery of atmospheric histories of compounds for which there were no direct measurements in the atmosphere. Within the NEEM deep drilling project in Greenland air was collected from the firn during two very comprehensive field sampling seasons and several surface drillings. Laboratories from Europe, Australia, the US and Japan have measured this air for a suite of components in what is the most extensive set of firn air measurements yet made. In addition, as part of this project an extensive modeling effort is being conducted to better understand the translation from the composition found in the firn to the atmospheric history. The purpose of this issue is to bundle all information from the NEEM measuring campaign and the corresponding modeling attempt at one place. However, we do not want to limit the issue to the NEEM project. We welcome contributions from other ongoing and previous firn air campaigns, and hope that the special issue will provide a comprehensive state-of-the-art view of firn air science.

From 09 – 24 October 2009 the IFM-GEOMAR (Kiel, Germany) conducted a cruise with RV Sonne in the tropical western Pacific to investigate trace gas emissions on a transit between Tomakomai (Japan) and Townsville (Australia) in different biogeochemical regimes and their stratospheric contribution.

The project aims to reduce uncertainties in stratospheric halogen loading and ozone depletion resulting from oceanic emissions and atmospheric transport of ozone depleting substances. The tropical oceans are a known source of reactive bromine and iodine to the atmosphere in the form of short-lived brominated and iodinated methanes as e.g. bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). Elevated atmospheric concentrations above the oceans are related to oceanic supersaturations of the compounds and to natural photochemical and biological production. Increasing scientific evidence suggests that there could be significant contributions from the ocean derived, halogen-containing short lived substances to stratospheric ozone depletion, which is addressed in the scientific program of the Sonne ship cruise. This cruise is part of the national research project "TransBrom"(www.ifm-geomar.de/~transbrom). The tropical western Pacific is a largely uncharacterized region for the oceanic compounds and a projected hot spot for their emissions and transport pathways into the stratosphere.

Of particular relevance during the cruise was the characterization of the climate-sensitive oceanic emission strengths of a suite of halogenated gases in various biogeochemical regimes and the investigation of the real contribution of these emissions to stratospheric bromine with a new transport model. This was validated by the atmospheric structure determination through intense radio, ozone and water vapor sounding during the cruise. We further investigated more marine trace gases as nitrous oxide (N2O), dimethylsulfide (DMS), oxygen (O2) and carbon dioxide (CO2), and possible relationships between these compounds. Satellite measurements of phytoplankton groups, obtained by special retrieval methods from the SCIAMACHY and GOME-2 instruments give further information about biogeochemical conditions during the cruise. The total atmospheric column concentrations and atmospheric concentration profiles of several other long-lived trace gases were also determined. These measurements allow studying the transport of tropospheric trace gases through the tropopause, in this way yielding information on the entry of natural and anthropogenic tropospheric trace gases into the stratosphere.

This might have been the first oceanic study, we are aware of, where the transport of oceanic emission of halogenated trace gases from the surface into the stratosphere was investigated. The impact of the natural ozone depleting substances will be highly sensitive to climate change in terms of their emissions to the atmosphere, their transport, and their chemical processing. Future changes in the mechanisms, that regulate these processes, are largely unknown. Therefore the oceanic emissions have the potential to cause surprises in the future evolution of the ozone layer in the changing climate, unless they are better understood. The measurements are thus needed to improve the understanding of future stratospheric halogen loading and therewith ozone depletion.

Atmospheric research around the 300 meters tall Bialystok tower, Poland (53.23N, 23.03E; 183m a.s.l.) has started in 2003 with regular aircraft profiling. A low maintenance system for semi-continuous measurement of CO2, O2/N2, CH4, CO, N2O and SF6 from five tower levels (up to 300 m) and the associated flask programme were added in 2005. In 2007, the station was equipped with a ceilometer that works like a small LIDAR system and has been designed to detect cloud base height. The data provides cloud statistics for the station which is important for sun-dependent measurements (e.g. FTS). A long term goal is to also retrieve information on the planetary boundary layer from analysis of the backscatter signals. In the frame of two EU projects, Global Earth Observation and Monitoring (GEOmon) and Infrastructure for Measurements of the European Carbon Cycle (IMECC), an automated FTS system was set up and is operational since March 2009. This qualifies Bialystok also as a Total Carbon Column Observing Network (TCCON) site. FTS measurements, calibrated against the global in-situ surface network, permit to link satellite CO2 observations (e.g. the GOSAT programme) to the global surface network. The current equipment set makes Bialystok one of the most important sites for greenhouse gas in situ measurements in Europe. It is also one of only four sites worldwide where co-located solar absorption FTS (total column measurement) and vertically resolved measurements on tall towers are performed. Footprint analysis using the Stochastic Time-Inverted Lagrangian Transport model (STILT) shows that the measurements made at the 300 m level are regionally representative, with dominant wind directions advecting air travelled across central Europe to the station. The much larger footprints for the total column measurements of the FTS instrument were calculated using the TM3 model.

In this context, we think that the Bialystok site offers a rare opportunity to study atmospheric greenhouse and related gases using multiple methods (from measurement to modeling). The purpose of the special issue is to provide a forum to integrate the multi-faceted science performed at the site (observations, measurement techniques, data analysis, modeling). The anticipated papers for this special issue include: 1) papers focussing on the measurements themself, quality, new methods, comparison with other in-situ data and satellite data, etc. - and 2) papers using an integrated approach - using a combination of meaurements and modelling to interpret the results and increase our understanding of greenhouse and related gas concentrations, fluxes, transport patterns, footprints, processes, etc. We are convinced the such an integrated case study would also be of interest for other similar sites worldwide.

Eastern Asia has a large number of megacities including many regions of ongoing rapid urbanization with the potential to produce new megacities in the coming decades. Recent field experiments and associated modeling studies in eastern China, Korea and Japan have demonstrated that human activities in Eastern Asia megacities have had dramatic impacts on atmospheric chemistry and physics in this region which have important implications for air quality and climate. These studies are characterizing emission and ambient distributions, atmospheric chemical processing, aerosol and oxidant production and growth, urban/rural interactions, and long range transport. It is widely recognized that individual megacities can influence other regions and effective air pollution control strategies in any of these locations requires a better understanding of emissions, chemical processing and interactions within the entire region. This special issue will highlight recent field studies and associated modeling investigations that address scientific questions associated with the impact of Eastern Asia megacities on atmospheric chemistry and physics. Papers submitted to this special issue will focus on Eastern Asia megacity studies of chemical emission and deposition, atmospheric chemical composition and processing, impacts on weather and climate, regional transport and related topics. This will include investigations conducted within specific megacities of Korea, Japan and Eastern China as well as larger scale studies linking individual Eastern Asia megacities to the regional and global environment.

The special issue "Chemistry, microphysics and dynamics of the polar stratosphere: ozone loss and climate-chemistry interactions" was motivated by the EU-project RECONCILE (Reconciliation of essential process parameters for an enhanced predictability of arctic stratospheric ozone loss and its climate interactions) and covers all aspects of polar stratospheric ozone, polar stratospheric clouds, and other dynamical and chemical processes relevant in the polar stratosphere. It is open for contributions on chemistry, microphysics, radiation, dynamics, small and large scale transport phenomena, mesoscale processes and polar-midlatitudinal exchange. We particularly encourage contributions on ClOx/BrOx chemistry, chlorine activation, NAT nucleation mechanisms, on transport and mixing of processed air to lower latitudes, and 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.

The HUMPPA-COPEC 2010 intensive field measurement campaign was conducted at the Boreal forest research station SMEAR II (Station for Measuring Ecosystem-Atmosphere Relation) in Hyytiälä, Finland from 12 July – 12 August 2010. This campaign was focused on characterizing the summertime chemistry and physics over the Boreal forest when emission fluxes of volatile organic compounds (VOC), OH initiated photochemistry, and particle growth rates reach their seasonal maximum. An international consortium co-ordinated by the Max Planck Institute for Chemistry, Germany and the University of Helsinki, Finland was assembled to quantity a comprehensive suite of gas and particle phase species. The natural biogenic emissions from the surrounding coniferous forest were characterized under the long summer daylight and warm temperature conditions. Furthermore the campaign sought to capture and characterize influences from biomass burning, urban anthropogenic pollution and nearby sawmills at the site.

There is growing evidence that human activities in an increasingly globalized, industrialized and interconnected world are influencing both air quality and climate ranging from urban and regional to continental and global scales. Rapid population growth and increased energy demand are the primary forces driving unprecedented environmental changes. Most growth occurs in urban regions and surrounding suburban areas, leading to the phenomenon of megacities.

This special issue is dedicated to the contributed papers presented at the special sessions on "Megacities: Air Quality and Climate Impacts from Local to Global Scales," which were convened at the EGU General Assembly in 2009 and 2010 and will include contributions from the EGU-2011 session.

In addition, this special issue will consider articles related to the topic, including key findings from the three large projects MILAGRO, MEGAPOLI, CITYZEN, as well as other atmospheric science studies conducted in large urban centers around the world, highlighting the following areas:

• Emissions;
• Photochemistry;
• Aerosol and trace gas measurements;
• Meteorological measurements;
• Dynamics and radiative effects;
• Regional climate;
• Air quality modeling;
• Satellite remote sensing of air quality in cities;
• Implications of policy to reduce air pollution (air quality, health, climate change).

Clouds constitute one of the major uncertainties in understanding the climate system and changes in the clouds as a consequence of global climate change is not well constrained by observations. This is particularly true in the Arctic, where clouds constitute the larges single factor affecting the surface energy balance, and therefore on melting and freezing of sea ice.

ASCOS is a highly interdisciplinary project with a major field experiment in the central Arctic Ocean during August/September 2008, approximately at 87N and 7W, deployed on the Swedish icebreaker Oden as a part of the International Polar Year (IPY). The ASCOS main target is to study the formation and life cycle of Arctic summer low-level clouds. To achieve this we deployed instruments for process level observations in a column from 0.5 km in to the ocean, through the ocean/ice surface up through the atmospheric boundary layer, and to the top of the troposphere (also see http://www.ascos.se). ASCOS measurements range from in-situ observations, to surface-based remote sensing, to airborne observations. The most intense observations were during a 3-week ice drift, starting with typical Arctic summer melt conditions and ending with the initial freeze-up of autumn. ASCOS was also coordinated with the Arctic Mechanisms of Interaction between the Surface and Atmosphere (AMISA) project, providing airborne measurements from the NASA DC8 research aircraft in the vicinity of the ASCOS column, flying in from Kiruna, Sweden.

The science team on Oden consisted of 33 researchers from 14 institutes in 11 different countries; many more are involved in analysis and associated modelling studies. This, and the experimental set-up, makes ASCOS the most extensive atmosphere-oriented experiment in the central Arctic for the entire IPY. ASCOS science cuts across several disciplines, with links to microbial life in ocean and ice, atmospheric chemistry and physics, cloud microphysics, turbulent exchange at the surfaces above and below the ice, and atmospheric circulation. A large part of ASCOS (atmospheric gas and particulate chemistry, aerosol physics, boundary-layer and synoptic meteorology) fall within the remit of ACP while physical oceanography and marine biology/chemistry fall within the remit of OS which is the incentive for a joint ACP/OS issue; only this way will it become possible to develop a special issue spanning the whole width of the science in ASCOS.

The Earth system is undergoing extensive change, with important implications for human health, resource management, ecosystem services and the environment. The ability to predict these changes and their impacts on time scales of months to a decade is becoming increasingly important. Key to improving the predictability of Earth system behavior over these time scales is an improved understanding of the coupling between water, energy and biogeochemical cycles in a multi-scale modeling framework. Robust predictions at these time scales require coordinated modeling, observations and process studies that explicitly address the coupled water, energy and biogeochemical cycles at multiple temporal and spatial scales. The BEACHON (Biosphere-atmosphere-hydrosphere-interactions of Energy, Aerosols, Carbon, Organics, and Nitrogen) project initiated two complementary field studies in a ponderosa pine woodland to enhance understanding of the roles of biogenic volatile organic compounds (BVOC), aerosols, nitrogen trace gases and oxidants in linking and regulating the carbon and water cycles. The BEACHON-ROCS (Rocky mountain Organic Carbon Study) was conducted in summer 2010 and was focused on understanding BVOC oxidation and the impact on atmospheric oxidants. The BEACHON-RoMBAS (Rocky Mountain Biogenic Aerosol Study) will be conducted in summer 2011 and will be focused on understanding the formation, growth and properties of biogenic organic aerosol. This special issue will highlight field and modeling investigations associated with the BEACHON ROCS and ROMBAS studies.

The special issue is dedicated to scientific studies of the volcanic eruption of Eyjafjallajökull, the evolution and properties of the resulting plume, and their consequences. The topics range from the characterization of volcanic emissions to the description and forecast of plume dynamics and transport; physical and chemical observations encompassing satellite, aircraft, ground-based remote sensing and in-situ data collection; and the atmospheric implications of volcanic eruptions.

DOMINO (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) is a research campaign that took place from mid November to mid December at the atmospheric research station "El Arenosillo" operated by INTA (National Institute for Aerospace Technology, Spain). A complete suite of measurements needed to study the oxidation chemistry in ambient air has been conducted by an international team of scientists. The "El Arenosillo" station is located in the nature preserve Parque Natural del Entorno de Doñana near the cities of Seville and Huelva in Spain. The focus of this special issue is the study of atmospheric oxidation chemistry based on the data from the DOMINO campaign during the entire diel cycle, dominated by OH radicals during daytime and NO3 radicals during nighttime, in air masses of various origins. A predominant wind direction during this time of year is from the northeast, transporting air from Sevilla (ca. 70 km distance) over the pine and eucalyptus forests in the national park. Air from the northwest transported fresher industrial and urban emissions from the city of Huelva (ca. 25 km), while air from southwesterly directions was of relatively clean marine origin.

The VAMOS Ocean-Cloud-Atmosphere-Land Study (VOCALS) is an international CLIVAR/VAMOS program designed to develop and promote scientific activities leading to improved understanding, model simulations, and predictions of the southeastern Pacific (SEP) coupled ocean-atmosphere-land system, on diurnal to interannual timescales. The major components of VOCALS are a modeling program with a model hierarchy ranging from the local to global scales, a major international field program (The VOCALS Regional Experiment, VOCALS-REx), and a suite of extended observations from regular research cruises, instrumented moorings, and satellites. The combination of intensive field measurements, long-term observations, and modeling will provide important insights that will directly benefit climate modeling. Some 200 scientists from 40 institutions in 8 nations are currently participating in VOCALS. Details of the three main components of VOCALS are given below.

The SEP climate is a tightly coupled system involving poorly understood interactions between clouds, aerosols, marine boundary layer (MBL) processes, upper ocean dynamics and thermodynamics, coastal currents and upwelling, large-scale subsidence, and regional diurnal circulations, to the west of the Andes mountain range.

Further information on VOCALS can be found on the program website http://www.eol.ucar.edu/projects/vocals

Beijing as a megacity has experienced fast economical and social developments in the last decades. With the air pollution control efforts in recent years, the air quality in Beijing has been improved significantly. Yet this improvement was undermined by rapid increases in the number of vehicles and energy consumption in Beijing, and the regional transport of air pollutants from the surrounding heavy industrialized regions. For the 2008 Olympics, air pollution in Beijing was a serious concern.

In order to understand the transport and transformation processes of the regional air pollution in Beijing and surrounding region, and to formulate air pollution control strategies for the 2008 Beijing Olympics, Peking University initialized and organized an international collaborative project, CAREBEIJING (Campaigns of Air Quality Research in Beijing and Surrounding Regions). Field campaigns were conducted in 2006, 2007, and 2008, with the participation of more than 200 scientists and students from 21 research institutes.

The major findings of the CAREBEIJING studies about the transport and transformation processes of the regional air pollution in Beijing and surrounding region as well as air pollution controll results during the 2008 Beijing Olympics will be reported in this special issue.

Active radical chemistry has been observed in the air above sunlit snow surfaces. Past observations of hydroxyl radicals in Greenland showed evidence of unrecognized chemical processes leading to OH concentrations different from those predicted in constrained box models. To investigate if halogen chemistry could explain the observations of unusual hydroxyl radical levels the Greenland Halogen and Hydrogen Radical Photochemistry Experiment (GSHOX) was performed at Summit Greenland in the Summers of 2007 and 2008.

In this special section the following results of the GSHOX experiment will be presented.

• Meteorological and radiative conditions that impact atmospheric chemistry at Summit.
• Direct evidence for the presence of reactive bromine.
• Indirect evidence of halogen chemistry through hydrocarbon clock.
• Sources of bromine and bromide on the Greenland ice sheet.
• mpact of halogen chemistry on OH/HO2 chemistry.
• Impact of halogen chemistry on mercury chemistry.
• NOx and bromine chemistry in the firn.
• Influence of firn chemistry on atmospheric chemistry.

POLARCAT is an International Polar Year project, which is also endorsed by AMAP, IGAC, iLEAPS and SPARC. The project organized large, mostly aircraft- and ship-based campaigns into the Arctic during spring and summer 2008 but also had ground-based campaigns at major Arctic surface stations, and uses long-term monitoring data, satellite observations and models to study the chemical composition of the Arctic atmosphere, effects of aerosols on radiative forcing, etc. For more information, see www.polarcat.no

POLARCAT acts as an umbrella for a number of independent but coordinated campaigns conducted by North American, European and other institutes, e.g., ARCPAC, ICEALOT and ARCTAS in the U.S. and POLARCAT-Norway, POLARCAT-France, GRACE (Germany) in Europe.

We would like to submit the results of the project to a special issue in Atmospheric Chemistry and Physics. Since the different POLARCAT projects have different time schedules for publishing their results, we are asking for a special issue that should be opened in April or May 2009 (the first few papers will soon be ready for submission) but should be open for submission until at least the end of the year 2010 (we might ask for an extension of the deadline in fall 2010).

At a recent meeting of European POLARCAT partners, we have made an (incomplete) list of expected submissions to the special issue from the European POLARCAT partners (see following 2 pages). We have had no opportunity yet to fully discuss submission of papers from the American POLARCAT partners; however, we have had a few individual contacts with our American colleagues who indicated that they would like to contribute to an ACP POLARCAT special issue. NASA, for instance, has decided to not have their own special issue on ARCTAS, so we expect a large number of papers from ARCTAS to be published in the ACP POLARCAT special issue. This can possibly lead to a very large number of papers submitted to the ACP POLARCAT special issue (a total of 100 papers is not unreasonable if all POLARCAT partners decide to submit their publication to this special issue), so we are asking for help from several members of the ACP editorial board. It may also be necessary to extend the editorial board for the special issue if a large number of papers are submitted.

This special issue contains papers resulting from two separate but linked projects: "Oxidant and particle photochemical processes above a South-East Asian tropical rain forest" (OP3) and "Aerosol coupling in the Earth system" (ACES). OP3 utilised ground, tower and aircraft-based measurements at two locations (rainforest and oil palm plantation) in Borneo, with box, trajectory and global model simulations to study atmospheric composition and chemistry in this region. ACES utilised targeted measurements in Borneo, together with aerosol chamber experiments and chemical mechanism and model development, to augment the aerosol-phase work of OP3.

The theme for the special issue is the EMEP Programme as "an integrated system" of models, observations and overall assessment, with scientific work and findings in the hands of the parties and the centres in conjunction. The focus in ACP would be on the research issues, with a discussion of the relevant methodological issues. We will look at the past, the present and the possible future.

This special issue would also serve as a central location for the analysis of a range of scientific issues based on the EMEP programme (EMEP models and measurements programme incl overall assessment), cf www.emep.int and www.unece.org/env/lrtap/welcome.html.

European as well as global acidification, eutrophication, tropospheric ozone and other atmospheric contaminants:

• their state and trends;
• emissions and their trends;
• transboundary source-receptor relationships and their change;
• ecosystem recovery;
• air pollution changes as climate variability and trends change;
• particulate matter;
• the reactive nitrogen cycle and its change;
• toxic substances;
• the role of atmospheric and atmosphere-surface processes in the cycling of biogeochemical substances, e.g. deposition.

The Biosphere Effects on AeRosols and Photochemistry Experiment (BEARPEX) was a multi-investigator collaboration conducted as two eight week deployments, August-October 2007 and June-July 2009. The measurements were among the most comprehensive suite of gas and aerosol properties attempted at a single site. The project built on an extensive background of previous experiments in the foothills of the Sierra Nevada. Our goals were to develop an improved mechanistic understanding of chemical and ecological processes affecting atmospheric composition and to use this improved understanding to provide a clearer and more accurate evaluation of how chemical processing of biogenic and anthropogenic emissions affects the composition and radiative properties of the atmosphere on urban, regional and global scales. The experimental design paid particular attention to three crosscutting issues: a) chemistry downwind of urban areas where there is high VOC reactivity (due to emissions from forests) and low NOx, b) understanding the full oxidation sequence and subsequent fate of biogenic VOC and c) the processes leading to formation and removal of biogenic secondary organic aerosol (SOA) and the associated physical, chemical and optical properties of SOA. Results from the BEARPEX campaign will be published in this Special Issue of Atmospheric Chemistry and Physics.

This special issue is devoted to the international intensive field campaign MTX2006 held at the summit of Mount Tai in June 2006, focusing on:

• The chemistry and transport of ozone and its precursors;
• The composition, chemistry and transport of aerosols over Central East China (CEC), one of the most regionally polluted areas in the world.

Scientific papers related to the project will be considered for publication subject to peer review according to the regular guidelines and quality standards of Atmospheric Chemistry and Physics.

The Regents Park and Tower environmental experiment (REPARTEE) was a multi-partner collaboration involving two campaigns in London in 2006 and 2007. The experiment involved air sampling at ground-level in Regents Park and aloft at 160 metres above ground

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