Long-Term Measurements of Chemical and Physical Properties of Atmospheric Aerosol at Dome C

Financed by: MIUR (PNRA 2015 / AC3.04 - PNRA14_00091-Line A3) Period: November 2015 - June 2021

Introduction

Aerosols have high spatial and temporal variability and global radiative forcing models revealed that 45% of the variability depends on uncertainty in natural rather than anthropogenic emissions. This result leads to consider the importance of characterizing the natural aerosol reaching Antarctica. Long-term measurements of aerosols and their gaseous precursors at Dome C will lead to a better understanding of the sources, atmospheric and transport reactions, de positional and post-depositional processes (including the interaction at the air / snow interface) of the aerosol present in Antarctica, leading to a better understanding of climate-environment feedback processes, a better development of climate models and interpretation of past aerosol changes in the Antarctic ice.

Description

Measurements will include: particulate material; gases (NO_x, O₃) involved in aerosol processes; monitoring of cosmic rays (neutrons, muons), as potential agents for in-situ nucleation. The instrumentation will be installed in the Dome C Atmospheric Studies station. Daily snow samples will be collected in a clean area. Direct measurements (with a resolution of a few minutes) and sampling (from 24 hours to 15 days) will include: particle size distribution (DMPS + OPC); PM₁₀ for ions and metals; PM₁₀ for PIXE elemental analysis; PM₁₀ for the EC / OC fraction; PM₁₀ for the geochemical characterization of dust particles; 4-stage sampling for ions and metals; high-volume 5-stage sampling for organic compounds (WSOC, amino acids, methoxyphenols, sugars, anhydrous sugars) and for halogens (I and Br); measurements of ozone, VOC and NO_x; counting of neutrons and muons. At the same time surface snow will be collected to study the air / snow interface. Sea ice dynamics will also be investigated by determining seasonal trends of Br, I and MSA in order to evaluate the role of sea ice in promoting phytoplankton activity. The identification of the areas of potential source (PSA) of aerosol dust will be performed by a PM₁₀ of geochemical characterization (REEs and isotope ratios of Pb, Sr and Nd). The role of photochemistry will be studied by comparing solar irradiation (BSRN DC Observatory) with particle concentrations of nss-SO₄^2-, MSA, nitrate, organic compounds and halogens. Ground-level ozone will be continuously measured to evaluate the oxidizing capacity of the atmosphere at Dome C. The snow source for nitrogen compounds (N) will be evaluated by comparing atmospheric and snow measurements of NO particles.₃^- and no₂^- with NO gases_x well no₂ measured at two heights above the snow. The efficiency of the PM₁₀ in nitrate sampling it will be evaluated with a denuder at the sampler inlet (to eliminate HNO₃ gaseous) and with a back-up nylon filter (to eliminate the volatilization of acid and volatile species). The study of nitrate sources will also include troposphere-stratosphere exchanges. The identification and temporal evolution (speed of formation and new growth of particles) of nucleation events will be performed with DMPS measurements (40 dimensional classes; 3 - 1000 nm). The role of Cosmic Rays in forming the new particles will be evaluated by comparing the relative trends with the DMPS data.

Aims

Goals for long-term aerosol measurements include:

• understand the aerosol-climate feedback processes in the regions most sensitive to environmental and climate changes;
• establish the background values ​​of the atmospheric load, particle size and chemical composition of the aerosol;
• improve the reliability of climate models by making long-term data available for an effective assessment of global aerosol (ERFari and ERFaci);
• study with sufficient statistics the seasonal and annual trends of important aerosol components (S-, N- and C-; biogenic emissions; dust; sea spray);
• assess the strength of the source and the efficiency of long-range transport of the aerosol formed in marine and continental areas at lower latitudes;
• estimate the contribution of local and regional sources of Antarctic aerosol;
• study the effects of photochemistry and radical sources (ozone) on the chemical reactions of the gaseous precursors and on the formation of new particles in very atypical atmospheric conditions (temperature, continuous summer irradiation);
• improve the reliability of paleo-climatic and paleo-environmental reconstructions from ice stratigraphies and also improve knowledge of the aerosol-surface snow exchange;
• evaluate the possible role of Cosmic Rays in the New Particle Formation (NPF) in an area where nucleation is unlikely due to the low atmospheric concentrations of their precursors.

 

CNR-IIA activities

Specific scientific objectivesi:

• determine the quantity and the atmosphere-snow exchanges of organic compounds and reactive nitrogen compounds (NO_x,HNO₃,HNO₂ and their salts, VOC including aldehydes, and carboxylic acids);
• optimize the measurement of particulate nitrous in the coarse and fine fraction by removing gaseous interferences and quantifying the volatile and non-volatile nitrate part;
• understand the possible processes of chemical transformation during long-range atmospheric transport.

  Field activities in Antarctica Summer 2016-2017 and winter 2017. The efficiency of PM nitrate sampling₁₀ was evaluated using two denuders (to eliminate HNO₃ and NH₃) and Teflon and Nylon back-up filters (to correct the volatilization of HNO₃ and NH₃) installed at the inlet of the PM sampler₁₀. These measurements were compared to another PM sampler₁₀ (without denuder and back-up filters) on a daily and weekly basis. Summer 2017-2018 Atmospheric measurements of the largest organic fraction (VOC, aldehydes, carboxylic acids) were performed by means of traps and filters. Measurements of nitrogen oxides were not obtained due to malfunction of the chemiluminescence analyzer. Surface snow was also collected daily and at the same time as atmospheric measurements to evaluate atmosphere-snow exchanges. Summer 2018-2019 As for summer 2017/2018, atmospheric measurements of the largest organic fraction (VOC, aldehydes, carboxylic acids) were performed. Measurements of nitrogen oxides were not obtained due to malfunction of the chemiluminescence analyzer. Surface snow was also collected daily and at the same time as atmospheric measurements to evaluate atmosphere-snow exchanges.   Activities in Italy Summer 2017-2018 Determination of all ionic compounds, including MSA, and carboxylic acids, was performed by IC and HPLC / UV techniques. All values ​​were corrected by the whites. The atmospheric concentrations of the carbonyl compounds were determined by derivatization with 2,4 - DNPH and subsequent HPLC / UV analysis. In the case of the snow samples, the solid phase extraction (SPE) procedure was performed after derivatization. The VOCs were thermally desorbed from the traps and analyzed by GC-MS. Summer 2018-2019 As for summer 2017/2018.  

Participants

• CNR-IIA
• University of Florence, UNIFI, Italy
• CNR-ISAC
• University of Venice, UNIVE, Italy
• University of Genoa, UNIGE, Italy
• LGGE (Grenoble, France
• KOPRI (Incheon, South Korea)
• Institute of Alpine and Arctic Research (INSTAAR); University of Colorado (Boulder, USA)
• Desert Research Institute (Reno, Nevada)
• Dept. Analytical Chemistry Ghent Univ. (Ghent, Belgium)
• IMF (Helsinki, Finland)
• EMPA (CH)

Working group