Specific scientific questions to address the four major areas of non-greenhouse-gas atmospheric climate processes in the Arctic:
Q1: What are the chemical, optical, and microphysical characteristics of aerosols in the Arctic in springtime?
- What is the solar extinction and absorption of the aerosol, and how do these properties vary with relative humidity?
- What is the mass concentration and size distribution of soot?
- To what extent are soot particles coated with other materials, and do such coatings influence the radiative and cloud-nucleating properties of the soot particles?
- What is the contribution of organic material to the optical and chemical properties to the aerosol?
- How do aerosol concentrations, composition, optical properties, and cloud nucleating properties above the surface relate to values measured at the surface?
- What is the radiative forcing and resulting atmospheric heating rates due to the aerosol, and how do these values compare with those derived from spaceborne lidar, surface lidar, and surface aerosol measurements?
- How do the composition and hygroscopic properties of aerosols relate to chemical processing estimated from trace gases?
Q2: What are the source types (industrial, urban, biomass/biofuel, dust, sea-salt) of the aerosol components, and the absorbing components in particular?
- What are the correlations between aerosol components and trace gases?
- How does the composition of the aerosol and trace gases compare to that expected from transport and emission models such as FLEXPART?
- Does the vertical distribution of aerosol properties reflect differences in source region, transport, and removal?
- What are the major sources that contribute to atmospheric and surface soot during the critical springtime warming period?
Q3: What are the microphysical and optical characteristics of optically thin clouds in the lower Arctic troposphere in springtime, and do pollution particles affect these cloud properties?
- What is the number density of CCN present in aerosol layers and in clean air, and is there closure between the predicted CCN, from the observed aerosol composition and size distribution?
- How does the number concentration of CCN, as a function of water supersaturation, vary as a function of altitude?
- Is the cloud droplet number concentration in liquid clouds consistent with that predicted from the observed CCN and cloud cooling rate?
What is the relationship between measured IN concentrations and cloud ice number concentrations and size?Payload no longer includes IN counter What are the measured solar reflectance and transmission, the IR radiance, and the effective radius of Arctic clouds, and how do these values vary with CCN and IN concentration?Payload no longer includes IN counter
- How do directly measured and derived cloud properties compare with remotely measured and derived parameters at the DOE ARM site?
Q4: What are the concentration of particles that serve as ice nuclei (IN) in background and polluted air? Payload no longer includes IN counter
- What is the number density of IN present in aerosol layers and in clean air?
- What are the geographic sources of the IN in the Arctic?
Q5: Is soot present in particles that serve as
IN and CCN? Payload no longer includes IN counter
- Is soot efficiently scavenged by cloud droplet nucleation, ice crystals, and snowfall?
- What role do coatings on soot particles play in nucleation scavenging and removal of soot?
Q6: What halogen chemistry is occurring during Arctic spring?
- What is the distribution of gas phase chlorine and bromine compounds, especially ClNO2?
- What is the vertical distribution of sea-salt aerosol and what chemical processing has it undergone?
- What is the relative importance of the sources of O3 in the Arctic and subArctic lower troposphere in springtime (production vs. stratospheric vs. long-range transport)?
The six science questions lead to specific measurement requirements:
R1) The stratified nature of the Arctic lower stratosphere requires airborne and remote-sensing measurements so that the properties and processes occurring in and near radiatively important haze layers and stratiform clouds can be investigated.
R2) Because of the vertically stratified and spatially non-uniform distribution of Arctic haze, fast-response in situ gas- and aerosol-phase instruments are required.
R3) The climatic importance of aerosol optical properties and soot number and mass require accurate and fast-response measurements of these parameters, along with measurements of the variation in optical properties with relative humidity.
R4) Because of the strong potential climate interaction between aerosols and cloud microphysical and radiative properties, detailed cloud microphysical and visible and infrared radiation measurements are needed. Modeling is essential to interpret the aerosol, cloud and radiation observations and extrapolate them to climate-relevant scales.
R5) Improving understanding of halogen photochemistry in the Arctic requires accurate measurement of gas phase halogen species and their vertical distribution, as well as measurements of ozone and photolytic fluxes.
R6) Transport, chemistry, and climate models are needed to relate the observed aerosol and gas-phase characteristics to sources and transport mechanisms and to evaluate their importance.
R7) Because ground sites are essential for developing climatologies and for understanding the temporal changes in atmospheric processes in the Arctic, short term airborne studies should be made at locations and times that can be linked to the surface sites.