Airborne observations of the physical and optical properties of atmospheric aerosol

Aerosols have a significant influence on both human health and global climate, and are associated with a potentially important role in future climate change. The microphysical and optical properties of aerosols need to be well quantified to understand the radiative impact, important in weather and climate models. This work focuses on two globally significant species from two different aircraft campaigns, mineral dust and biomass burning aerosol. An analysis is presented of mineral dust properties from the Saharan region during the Fennec campaign in June 2011 and 2012. In making observations it is crucial to understand the associated measurement limitations. The Low Turbulence Inlet (LTI) was designed to improve inlet efficiency and is shown to quantifiably measure coarse mode mineral dust up to 10 μm. This has allowed for Rosemount inlet characterisation with enhancements relative to the LTI determined to be 8 times for particles up to 3.0 μm.The physical and optical properties and vertical structure of aged Rondônian regional haze from the SAMBBA campaign in Rondônia, Brazil in September 2012 are
characterised. Good agreement is shown between in-situ extinction coefficients and those retrieved using lidar remote sensing. Characterisation of airborne thermo-optical techniques for measuring black carbon content is achieved through comparisons with SP2 measurements. Total number concentration was reduced by 77 % compared with 96 % for the SP2, suggesting not all volatile material was removed with the thermooptical
technique. The imaginary part of the aerosol refractive index was 40 % lower using the Maxwell-Garnett mixing rule compared with the volume-mixing rule for Rondônian regional haze. This difference is small compared with the uncertainty derived from the assumed refractive index of the sub-components, articularly for organic carbon; the singlescattering albedo at 550 nm is shown to range from 0.88 to 0.95. Humidification effects on the optical properties of biomass burning aerosol were found to be negligible due to modest ambient relative humidities. Comparisons with retrieved properties from the SCAR-B campaign in 1995 suggest consistency in biomass burning and agricultural
practices over time.