Mauro Mazzola

Nitrate dry deposition in Svalbard

ABSTRACT Arctic regions are generally nutrient limited, receiving an extensive part of their bio-available nitrogen from the deposition of atmospheric reactive nitrogen. Reactive nitrogen oxides, as nitric acid (HNO3) and nitrate aerosols (p-NO3), can either be washed out from the atmosphere by precipitation or dry deposited, dissolving to nitrate ( ). During winter, is accumulated in the snowpack and released as a pulse during spring melt. Quantification of deposition is essential to assess impacts on Arctic terrestrial ecology and for ice core interpretations. However, the individual importance of wet and dry deposition is poorly quantified in the high Arctic regions where in-situ measurements are demanding. In this study, three different methods are employed to quantify dry deposition around the atmospheric and ecosystem monitoring site, Ny-Ålesund, Svalbard, for the winter season (September 2009 to May 2010): (1) A snow tray sampling approach indicates a dry deposition of –10.27±3.84 mg m−2 (± S.E.); (2) A glacial sampling approach yielded somewhat higher values –30.68±12.00 mg m−2; and (3) Dry deposition was also modelled for HNO3 and p-NO3 using atmospheric concentrations and stability observations, resulting in a total combined nitrate dry deposition of –10.76±1.26 mg m−2. The model indicates that deposition primarily occurs via HNO3 with only a minor contribution by p-NO3. Modelled median deposition velocities largely explain this difference: 0.63 cm s−1 for HNO3 while p-NO3 was 0.0025 and 0.16 cm s−1 for particle sizes 0.7 and 7 µm, respectively. Overall, the three methods are within two standard errors agreement, attributing an average 14% (total range of 2–44%) of the total nitrate deposition to dry deposition. Dry deposition events were identified in association with elevated atmospheric concentrations, corroborating recent studies that identified episodes of rapid pollution transport and deposition to the Arctic.

Atmospheric observations at the Amundsen-Nobile Climate Change Tower in Ny-Ålesund, Svalbard

The Amundsen-Nobile Climate Change Tower (CCT) is one of the important scientific platforms operating in Ny-Ålesund, Svalbard. The CCT is equipped with a consistent set of meteorological sensors installed at different heights to provide continuous measurements of the atmospheric parameters that affect the climate and its variability. In this paper, some features of the main meteorological parameters observed during the 6 years of measurements since November 2009 are presented in order to describe the thermodynamic characteristic of the lower layers of the atmosphere and the peculiarities of CCT. Monthly and seasonal behavior of temperature, humidity and wind as well as radiation budget and albedo variability are also shown. Such preliminary statistical description aims to provide an overview of the phenomenology occurring in the Kongsfjord area, useful to proceed with further analysis of the arctic climatic system. Even if the time series are not long enough to consider the parameters variability on a climatological time scale, useful assumptions can be made for detailed analysis concerning turbulence studies, data intercomparison at different time and space scales, validation of theory and numerical model results. CCT dataset is stored in a dedicated built-in digital infrastructure that allows other users, in the frame of international cooperations, to visualize, access and download the data and contribute to strengthen the collaboration within the scientific community operating in Svalbard.

Vertical Profiles and Chemical Properties of Aerosol Particles upon Ny-Ålesund (Svalbard Islands)

Size-segregated particle samples were collected in the Arctic (Ny-Alesund, Svalbard) in April 2011 both at ground level and in the free atmosphere exploiting a tethered balloon equipped also with an optical particle counter (OPC) and meteorological sensors. Individual particle properties were investigated by scanning electron microscopy coupled with energy dispersive microanalysis (SEM-EDS). Results of the SEM-EDS were integrated with particle size and optical measurements of the aerosols properties at ground level and along the vertical profiles. Detailed analysis of two case studies reveals significant differences in composition despite the similar structure (layering) and the comparable texture (grain size distribution) of particles in the air column. Differences in the mineral chemistry of samples point at both local (plutonic/metamorphic complexes in Svalbard) and remote (basic/ultrabasic magmatic complexes in Greenland and/or Iceland) geological source regions for dust. Differences in the particle size and shape are put into relationship with the mechanism of particle formation, that is, primary (well sorted, small) or secondary (idiomorphic, fine to coarse grained) origin for chloride and sulfate crystals and transport/settling for soil (silicate, carbonate and metal oxide) particles. The influence of size, shape, and mixing state of particles on ice nucleation and radiative properties is also discussed.

Impact of North American intense fires on aerosol optical properties measured over the European Arctic in July 2015

In this paper impact of intensive biomass burning (BB) in North America in July 2015, on aerosol optical and microphysical properties measured in the European Arctic is discussed. This study was made within the framework of the Impact of Absorbing Aerosols on radiating forcing in the European Arctic (iAREA) project. During the BB event aerosol optical depth (AOD) at 500 nm exceeded 1.2 in Spitsbergen and 0.7 in Andenes (Norway). Angstrom Exponent (AE) exceeded 1.4 while the absorbing Angstrom Exponent (AAE) varied between 1 and 1.25. BB aerosols were observed in humid atmosphere with a total water vapor column between 2 and 2.5 cm. In such conditions aerosols are activated and may produce clouds at different altitudes. Vertical structure of aerosol plumes over Svalbard, obtained from ceilometers and lidars, shows variability of range corrected signal between surface and middle and upper troposphere. Aerosol backscattering coefficients show values up to 10 -5m-1sr-1at 532 nm. Aerosol surface observations indicate chemical composition typical for biomass burning particles and very high single scattering properties. Scattering and absorption coefficients at 530 nm were up to 130 and 15 Mm-1, respectively. Single scattering albedo at the surface varied from 0.9 to 0.94. The averaged values over the entire atmospheric column, ranged from 0.93 to 0.99. Preliminary statistics of model and sunphotometer data as well as previous studies indicate that this event, in the Arctic region, must be considered extreme (such AOD was not observed in Svalbard since 2005) with a significant impact on energy budget.

Variations of UV irradiance at Antarctic station Concordia during the springs of 2008 and 2009

Abstract The features of solar UV irradiance measured at the Italian-French Antarctic Plateau station, Concordia, during the springs of 2008 and 2009 are presented and discussed. In order to study the impact of the large springtime variations in total ozone column on the fraction of ultraviolet B (UV-B) irradiance (from c. 290–315 nm) reaching the Earth surface, irradiance datasets corresponding to fixed solar zenith angles (SZAs = 65°, 75° and 85°) are correlated to the daily ozone column provided by different instruments. For these SZAs the radiation amplification factor varied from 1.58–1.94 at 306 nm and from 0.68–0.88 at 314 nm. The ultraviolet index reached a maximum level of 8 in the summer, corresponding to the typical average summer value for mid latitude sites. The solar irradiance pertaining to the ultraviolet A (UV-A, 315–400 nm) spectral band was found to depend closely on variations of atmospheric transmittance characteristics as reported by previous studies. Model simulations of UV-B irradiance showed a good agreement with field measurements at 65° and 75° SZAs. For SZA = 85° the ozone vertical distribution significantly impacted model estimations. Sensitivity analysis performed by hypothetically varying the ozone distribution revealed some features of the ozone profiles that occurred in the period studied here.

Local vs. long-range sources of aerosol particles upon Ny-Ålesund (Svalbard Islands): mineral chemistry and geochemical records

Aerosol samplings were performed both at ground level and at different heights upon the Ny-Ålesund polar station in June–July 2012 using a tethered balloon equipped with a sampling pump and meteorological sensors. The samples were analyzed by ion chromatography and scanning electron microscopy to characterize the sources and the evolution of the aerosol particles in the planetary boundary layer. The results show the main contribution of long-range over local/regional transported particles and sediments in the aerosols in the period of interest. Among the long-range sources, a main contribution was represented by Siberian local soils and regional wildfires which provided typical particles (metal oxides, calcareous grains), and ion species (nss-K+, nss-SO42−) to the aerosols. Among the local sources, a main contribution was represented by fly ash emitted by the cruise ships frequently landing around Ny-Ålesund during summer. Another aspect which results from aerosol particle characterization is the clear stratification of the planetary boundary layer upon Ny-Ålesund. This typical feature, which has been already documented in spring on the same site (Moroni et al. 2015), is quite effective also in summertime despite the higher potential of local dust production and the lower atmospheric stability characterizing this period.

Annual changes of aerosol optical depth and Ångström exponent over Spitsbergen

In this work we present the annual changes of two major, climate related aerosol optical parameters measured at three Spitsbergen locations, Ny-Alesund, Longyearbyen and Hornsund over a period between 2000 and 2012. We discuss the changes of aerosol optical depth (AOD) at 500 nm and the Angstrom exponent (AE) (440–870 nm) measured with use of different types of sun photometers. For the measurement data we adopted several data quality assurance techniques and the calibration of the instruments was taken into consideration. The results obtained show that marine source has been a dominating of aerosol sources over Spitsbergen. Some years (2005, 2006, 2008 and 2011) show very high values of AOD due to strong aerosol events such as the Arctic Haze. In general the mean AOD values increase over the period of 2000 and 2012 over Spitsbergen. This may indicate the presence of larger scale of atmospheric pollution in the region.

Diurnally averaged direct aerosol-induced radiative forcing from cloud-free sky field measurements performed during seven regional experiments

Aerosol particles suspended in the atmosphere may originate from either natural or anthropic sources, or through mixed processes involving their variable combinations. Among the primary natural emissions, the most important are those leading to the formation of (i) mineral dust through wind erosion of natural soil and (ii) sea-salt particles from the ocean surface forced by winds. In addition, significant emission processes include biological particles released by plants and animals, combustion particles forming in forest fires and biomass-burning smokes, and volcanic debris ejections.

Dependence of direct aerosol radiative forcing on the optical properties of atmospheric aerosol and underlying surface

Airborne aerosol is a suspension of solid particulate matter and/or liquid particles in air, which are often observed as dust, haze and smoke. They present an overall number concentration usually varying between a few hundred per cubic centimeter of air in the remote areas of the planet and more than 104 cm-3 in the most polluted urban areas, with sizes ranging mainly between 0.01 and no more than 100 μm, and therefore varying by more than four orders of magnitude (Heintzenberg, 1994). Aerosol particles are present in the atmosphere as a result of primary emissions or are formed through secondary processes involving both natural and anthropogenic gaseous species.

Parameterization of clear sky effective emissivity under surface-based temperature inversion at Dome C and South Pole, Antarctica

Abstract For most parts of the year the Antarctic Plateau has a surface temperature inversion with strength c. 20 K. Under such conditions the warmer air at the top of the inversion layer contributes more to the clear sky atmospheric longwave radiation at surface level than does the colder air near the ground. Hence, it is more appropriate to relate longwave irradiance (LWI) to the top of the inversion layer temperature (Tm) than to the ground level temperature (Tg). Analysis of radio soundings carried out at Dome C and South Pole during 2006–08 shows that the temperature at 400 m above the surface (T400) is a good proxy for Tm and is linearly related to Tg with correlation coefficients greater than 0.8. During summer, radiosonde measurements show almost isothermal conditions, hence T400 still remains a good proxy for the lower troposphere maximum temperature. A methodology is presented to parameterize the clear sky effective emissivity in terms of the troposphere maximum temperature, using ground temperature measurements. The predicted LWI values for both sites are comparable with those obtained using radiative transfer models, while for Dome C the bias of 0.8 W m-2 and the root mean square (RMS) of 6.2 W m-2 are lower than those calculated with previously published parametric equations.