Climate Change Tower Integrated Project

Aerosol Chemical and Physical Characterization

The Artic regions are the first areas where present climatic changessignificantly affects terrestrial and marine ecosystems. Suchvariations deserve particular attention because the polar regions playan essential role in controlling bio-geo-chemical cycles of chemicalsubstances involved in environment-climate feedback processes. Indeed,climatic changes affect production and atmospheric transport ofchemical species at regional scale and their exchanges processes at theair/water and water/sediment interfaces. In this scenario, the study ofthe chemical composition and physico-optical characteristics ofparticulate matter in the polar areas is important in assessing directand indirect effects of aerosols on the climate system, inunderstanding how climate changes can affect these regions, and inforecasting future effects, by pointing out possible temporal trends oranomalies. In particular, organic and inorganic pollutants emitted intothe atmosphere at medium-low latitudes reach the polar areas throughlong-range transport pathways. In order to evaluate their impact onhigh-latitude atmospheric processes, it is important to know, andpossibly quantify, production processes, source intensity and location,and transport efficiency from the source areas of natural and anthropicatmospheric particles reaching the polar regions.

Measurements of chemical and physical properties of aerosols in the Arctic are stillnot well distributed in space and time and more information, inparticular long-term, high resolution studies, are needed about Arcticaerosol, its spatial and temporal variability, temporal trends andseasonal patterns in atmospheric load and composition of submicrometric ( nucleation and accumulation modes) and large aerosolparticles produced by primary and secondary processes. Besides, theatmosphere-snow interchanges (including uptake by superficial snowcrystals, photolysis reactions by solar irradiation on snow surface andpost-depositional processes due to sublimation-condensation cycles ofsemi-volatile compounds), make particularly complex the study ofatmospheric load variations and aerosol chemical composition in polarregions. A better knowledge of the processes controlling aerosol andgas components in the Arctic will be achieved by:

thecharacterization of the particle population in the atmosphere at thesurface as well as at the first 500 m atmospheric layer; correlation ofthe chemical composition of the aerosol to its size distribution andoptical properties;
the understanding long range transportto Arctic of anthropogenic and natural aerosols from their sourceregions, by using organic and inorganic compounds (includingatmospheric pollutants) as selective chemical markers. Identificationand quantification of primary and secondary aerosol sources.Correlation of changes in aerosol load and composition to variation intransport efficiency and/or pathways by air mass back trajectoryanalysis;
highlighting atmosphere/snow mass exchanges by simultaneous snow and aerosol analysis.

Long-termfield activities will be devoted to obtain (a) direct measurements ofextinction, single scattering albedo, and the extinction-to-backscatterratio, in order to characterize from a radiative point of view theaerosol particle population; (b) chemical speciation of the particlepopulation present in the very stable and stratified ABL, includinginformation on their size distribution; (c) comparison of chemical andphysical features of atmospheric particles with optical properties; (d) measurements at sea level to be compared with results obtainedanalysing samples collected at Zeppelin Station (450 a.s.l.) and withremote sensing measurements, to have a complete picture of the aerosolsin the ABL and to assess the role of different physical and chemicalatmospheric processes. Intensive spring, summer and winter campaigns,covering about 2-3 months each, will allow to increase samplingresolution for chemical composition analysis Summer campaigns willdeserve particular attention, since this period is characterized bystill high contributions of processes of pollutants transport from theanthropogenic areas and, contemporaneously, by the highest transportintensity of dust from the Asian desert regions. During summer, thesources of biogenic aerosol are also predominant, particularly thosecoming from the activity of the oceanic phytoplankton. Shorter wintercampaigns will allow the comparison among periods characterized byintense and absent insulation. Transport processes of the sampled airmasses will be followed by back-trajectories analysis (HYSPLIT - NOAAweb site).

Aerosols & Clouds Vertical Stratification

Warming is faster in the Arctic than in any other region of theworld. Non greenhouse gas pollutants are known to have an importantinfluence on Arctic climate, and aerosol play a pivotal role. Theso-called Arctic haze, entering the Arctic atmosphere in winterand spring and accumulating there due to the strong surface temperatureinversions and low scavenging rates, shows high concentrations of agedparticles - mainly sulphates, black carbon (BC), organic carbon, andnitrate. In the summer the Arctic atmosphere is cleaner but isepisodically perturbed by aerosol produced by large boreal forestfires. This aerosol influx has profound effects on the radiativebalance and the microphysics of the Arctic atmosphere and cryosphere.The very low natural cloud condensation nuclei sources in the regionmake the Arctic clouds microphysical processes particularly sensitiveto changes in aerosol loadings. An increased man-made aerosol pollutionin the last years is suggested to explain changes in short andlong-wave radiation of several Wm-2. In addition, deposition of BC onsnow and ice reduces their albedo. The quantification of these effectsdemand to improve our understanding of processes controllinganthropogenic and natural aerosol pollution and deposition in theArctic, to identify the processes controlling Arctic aerosol, includingthe seasonal variations and long term changes, to assess the impact ofclimate change on Arctic aerosol and the contribution of pollution tolong term changes in aerosol radiative forcing and cryospheric changes.

To properly understand the transport processes of aerosol in the Arcticatmosphere, their influence on the radiative balance and on cloudmicrophysics, a detailed analysis of their vertical distribution andits daily and interseasonal variation should be accurately determined.Measurements of aerosol burden and thermo dynamical phase inside thePlanetary Boundary Layer and in the free troposphere can be achieved byremote sensing technique using a one wavelength (532 nm) twopolarizations lidar looking upward from the ground in a range of about10000 m., with a relative error in estimating the aerosol concentrationof 0.01 at 100 m of altitude for a measurement of 1 minute and avertical resolution of 15 m. Lidar technique is based on laser sourcessounding the atmosphere at different range distances from theinstrument. The atmosphere backscatters part of the polarized laserlight into the instrument. The amount of backscattered light includestwo contributions, the Rayleigh scattering proportional to themolecular density and the Mie scattering by particles depending ontheir nature, their concentration and their size distribution. Theparticle phase is retrieved by the ratio between the main and thecross-polarized signal at 532 nm (volume depolarization): zero or verylow values of depolarization indicate aerosols in liquid phase; ratiosaround 50 are peculiar of well formed (radius > 1 micron) icecristals; intermediate values of depolarization indicate mixed phasesor amorphous particles. An estimate of the particles characteristics,as size distribution and albedo is also possible.

A semi-automated, one wavelengths (532 nm) micro lidar station (MULID) ispresent at Ny-Ålesund since November 2008, hosted in the German base ofKoldewey in the framework of a collaboration between CNR-ISAC and theGerman Alfred Wegener Institute, and it is aimed at determiningvertical structure of aerosols and cloudiness in the troposphere andthen provide fundamental information to investigate their role inmodulating radiation budget at the surface. The peculiar configurationof the system allows a reconstruction of the aerosol profile from thefirst few metres from the ground up to the free troposphere, with arelative error in estimating the aerosol backscatter ratio of 0.01 at100 m of altitude for a measurement of 1 minute and a verticalresolution of 1.75 m. Lidar data will be successively constrainedthanks to AOD evaluations provided by sun-photometer measurements.Thanks to its little dimension/weight, power consumption and capabilityto work unattended for long period in an hard environment (as alreadyproven on board an icebreaker during the ASCOS campaign), the Italianmicro lidar system will contribute to improve instrumentation in remotesites, as onboard the drifting NP platforms, providing information onthe vertical structure of the marine PBL on remote sites.

Pollutants in the Arctic troposphere

The reasons for studying heavy metals and organic compounds inmountains are various and principally relate to the potential pollutionimpact to the human health and to the Arctic ecosystem. The snow coverin Arctic regions works as a temporary storage reservoir that releasesmassive quantity of the accumulated chemicals in the snowpack intolakes or fresh waters representing a significant load of contaminantsover the short snow cover melting period. In addition, many Arcticareas are not directly influenced by close anthropogenic activities andthus they are suitable for studying the sources, the transportmechanisms and the fate of pollutants from urban to remote areas. Heavymetals, short-chain carboxylic acids, POP's and aldehydes, andmethanesulphonic acid are among the chemical markers present inairborne particulate matter that can be used to identify the source andorigin of several pollutants. In particular recent studies indicated aseasonal trend for the input of heavy metals having anthropogenicorigin such as Pb, Zn, Pt, Pd, Rh, Cu and non-soil fractions of V andMn, into the aerosol sampled in Arctic areas in Canada. Theconcentrations of these metals are higher in late winter and spring,when polluted air masses are more effectively transported from lowerlatitudes.

The chemical characterisation of the Arctic heavy metals content of theArctic aerosol and snow (collected during a whole year) would permit toconfirm their seasonal trend in the Arctic region, to better understandthe sources of different metals and to lay the basis for aninterpretation of the chemical and physical processes concerning thetransport of those pollutants to the Arctic troposphere. Anotherobjective of this project is the quantification in the aerosol ofpersistent organic pollutants (POPs) as polycyclic aromatichydrocarbons (PAHs), Polychlorobiphenyls (PCB), Polychlorinatednaphthalenes (PCNs), polybromodiphenyls ethers (PBDE) that arenon-polar semivolatile organic compounds. Some of these compounds arechemically very stable, persistent in the environment, toxic withendocrine-disrupting properties and bio-accumulate in the food chain.For all these reasons, they are generally considered prioritypollutants, thus making the studies of their toxic effects on livingorganisms and their monitoring in the environment of prime importance.Studies that elucidate the nature and amount of the major compoundspresent in the water-soluble organic compounds (WSOCs) fraction are tobe improved for the understanding of how they influence the atmosphericchemistry and climate.

The concentration of heavy metals, POPs and WSOCs will be evaluated in the different size-dimensional classes (10-7.2 μm; 7.2-3 μm; 3-1.5 μm; 1.5-0.95 μm; 0.95-0.49 μm; ≤0,49 μm) of the aerosol collected by asix-stage cascade impactor mounted on high volume pumps equipped withPM10 size-selective inlets. A specific sampling technique will be usedto assess the level of pollutants (organic and inorganic) in the Arctictroposphere and snow. One of the greatest benefits of carrying onmeasurements at Ny-Ålesund is the availability of two monitoringstations, one near the sea on the coast of the fiord (ground level) andthe 2nd on Mount Zeppelin, 474 m a.s.l..