Atmospheric Measurement Techniques

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.

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.

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.

In June-July 2009, the Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI) took place at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands. More than thirty different in-situ and remote sensing instruments from all over the world have participated. The main objectives of CINDI were to determine the accuracy of state-of-the-art ground-based measurement techniques, both in-situ and remote sensing, for the detection of atmospheric nitrogen dioxide and to investigate their usability in satellite data validation. It is expected to result in recommendations regarding the operation and calibration of such instruments, retrieval settings, and observation strategies for the use in ground-based networks for air quality monitoring and satellite data validation. A large data set of continuous measurements of nitrogen dioxide and other atmospheric constituents has been collected under various meteorological conditions and various air pollution levels. This special issue contains papers that use the CINDI data set.

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.

Papers will be based on presentations given at the 16th WMO/IAEA Meeting on Carbon Dioxide, Other Greenhouse Gases, and Related Measurement Techniques to be held in Wellington, New Zealand on 25–28 October 2011. The meeting focusses on measurement techniques for the accurate observation of long-lived greenhouse and related gases in the atmosphere, their isotopic composition, calibration procedures and quality control. Topics will include laboratory and field techniques for measurement, calibration, and quality control; reports on comparison efforts; reports from national and regional observing networks; strategies for optimizing and expanding the observing networks; data management, distribution, and archiving; and new instrument capabilities and assessments.

The contribution of ship emissions to global air pollution is becoming increasingly important as ship traffic is growing rapidly (annual growth rate in total seaborne trade was 5.2% per year from 2002 – 2007) and ship emissions tend to be less limited by regulations than landbased emissions. Ship emissions appear to have a strong impact of concentrations of pollutants over the oceans, but as about 70% of all ship traffic takes place within 400 km from land, ship emissions also have a relevant impact on air pollution on land. Ship emissions of SO2 are particularly important, but studies have also shown an impact of ships on NOx and Black Carbon levels. The contribution to global anthropogenic CO2 emissions was 3.3% in 2007.

An international agreement, the MARPOL convention, will in the coming years reduce ship emissions of SO2 and NOx; the limit for sulphur content of ship fuels is planned to be reduced from the present 4.5% by weight to 3.5% in 2012 and then to 0.5% in 2020. In Sulphur Emission Control Areas (e.g. the Baltic Sea and the North Sea) the limit will be as low as 0.1%. Also NOx emission limits will be progressively reduced.

Experimental techniques for measurements of ship emissions have (at least) two principal scopes:

• provide reliable and comprehensive data on ship emissions in order to improve emission inventories;
• identify ships that do not comply with legal emission limits.

The Special Issue of AMT will present and discuss available techniques for observation of ship emissions, together with some information about the results they have provided. These techniques range from optical methods such as the UV camera, DOAS and Lidar, to point measurements, where the so called 'sniffer' method is applied, and on-board measurements with sampling from the stack of a ship. By the 'sniffer' method, air pollutants like SO2 or NOx are measured along with CO2 at a point within the plume of the stack emissions from a ship; knowing (approximately) the carbon content of the ship fuel, the emission factor for e.g. SO2 can be estimated from the ratio between SO2 and CO2, when their background concentrations have been subtracted.

Another issue regarding measurements of ship emissions is the type of platform that is applied for the instruments. In the papers that are expected for this Special Issue both shore based and several types of mobile platforms, airborne as well as ship-borne, have been tested, and contributions from studies using these and other platforms, including satellites, are very welcome.

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.

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.