Angelo Lupi

Aerosols in polar regions: A historical overview based on optical depth and in situ observations

Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and ...

Improved algorithm for calculations of Rayleigh-scattering optical depth in standard atmospheres

Precise calculations of the total Rayleigh-scattering optical depth have been performed at 88 wavelengths ranging from 0.20 to 4.00 microm for the six well-known standard atmosphere models by integrating the volume Rayleigh-scattering coefficient along the vertical atmospheric path from sea level to a 120-km height. The coefficient was determined by use of an improved algorithm based on the Ciddor algorithm [Appl. Opt. 35, 1566 (1996)], extended by us over the 0.20-0.23-microm wavelength range to evaluate the moist air refractive index as a function of wavelength, air pressure, temperature, water-vapor partial pressure, and CO2 volume concentration. The King depolarization factor was also defined taking into account the moisture conditions of air. The results indicate that the influence of water vapor on Rayleigh scattering cannot be neglected at tropospheric altitudes: for standard atmospheric conditions represented in terms of the U.S. Standard Atmosphere (1976) model, the relative variations produced by water vapor in the Rayleigh scattering parameters at a 0.50-microm wavelength turn out to be equal to -0.10% in the moist air refractivity at sea level (where the water-vapor partial pressure is equal to approximately 7.8 hPa), -0.04% in the sea-level King factor, -0.24% in the sea-level Rayleigh-scattering cross section, and -0.06% in the Rayleigh-scattering optical depth.

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.

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.

A Refined Calibration Procedure of Two-Channel Sun Photometers to Measure Atmospheric Precipitable Water at Various Antarctic Sites

Two-channel sun photometers can be easily employed at Antarctic sites, where harsh environmental conditions prevail, to carry out measurements of precipitable water W. In the very dry air conditions observed in the Antarctic atmosphere, water vapor does not produce strong absorption features along the sun path. Therefore, these instruments need to be calibrated using analytical forms different from the square root regime, which can be determined by simulating the output voltages measured at Antarctic sites, for the spectral near-IR curves of extraterrestrial solar irradiance, instrumental responsivity parameters, and atmospheric transmittance, relative to various measurement periods. For this purpose, average models of the Antarctic atmosphere from the ground level up to the 30-km altitude were considered for different solar zenith angles and relative humidity conditions. The ratios between the output voltages simulated in the band and window channels were plotted as a function of total water vapor content Cw, for each site and each period, to define the best-fit calibration curves, which were subsequently normalized to the field measurements to take into account the aging effects on the filter transmission characteristics. Each of the five calibration curves was found to present a slope coefficient decreasing gradually with Cw from values higher than 0.8 to about 0.6. Using these curves, measurements of W were obtained, which differ appreciably at both sea level and high-altitude sites from those given by the square root calibration curves, avoiding large overestimation errors of 10%–40% at the high-altitude sites and underestimation errors of 5%–15% at the sea level site.

Five-year analysis of background carbon dioxide and ozone variations during summer seasons at the Mario Zucchelli station (Antarctica)

Thework focuses on the analysis ofCO2 andO3 surface variations observed during five summer experimental campaigns carried out at the ‘Icaro Camp’ clean air facility (74.7◦S, 164.1◦E, 41 m a.s.l.) of the ‘Mario Zucchelli’ Italian coastal research station. This experimental activity allowed the definition of summer average background O3 values that ranged from 18.3 ± 4.7 ppbv (summer 2005–2006) to 21.3 ± 4.0 ppbv (summer 2003–2004). Background CO2 concentrations showed an average growth rate of 2.10 ppmv yr-1, with the highest CO2 increase between the summer campaigns 2002–2003 and 2001–2002 (+2.85 ppmv yr-1), probably reflecting the influence of the 2002/2003 ENSO event. A comparison with other Antarctic coastal sites suggested that the summer background CO2 and O3 at MZS-IC are well representative of the average conditions of the Ross Sea coastal regions. As shown by the analysis of local wind direction and by 3-D back-trajectory calculations, the highest CO2 and O3 values were recorded in correspondence to air masses flowing from the interior of the Antarctic continent. These results suggest that air mass transport from the interior of the continent exerts an important influence on air mass composition in Antarctic coastal areas.

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.

Analysis of near-surface ozone variations in Terra Nova Bay, Antarctica

Abstract Ozone concentration measurements were made during December from 2001–2005 to quantify the contributions of different processes to near-surface ozone concentrations (O3) in Terra Nova Bay, Antarctica. The average O3 concentration was 20.3 ppbv. On days characterized by high solar radiation fluxes (HSR), significantly higher concentrations of O3 (21.3 ppbv) were recorded compared to days with low solar radiation fluxes (LSR days, 16.8 ppbv). High O3 concentrations could be related to strong winds from SW–NW. Three-dimensional back-trajectories show that air from the interior of the continent could affect O3 at Terra Nova Bay. Moreover, during HSR days, high O3 concentrations were also recorded in connection with weak circulation, suggesting that emissions from the Italian base (located 2 km north) could also represent a significant source of O3. To clarify the role of local pollution in Terra Nova Bay, O3 values were also calculated using the photochemical steady state (PSS) approximation under clear sky and cloudy conditions.