Development of balloon-borne Impactor payload for profiling free tropospheric aerosol

<p>Size-segregated aerosol vertical profiles in the troposphere are critically important for source attribution, transformation processes, atmospheric stability, and radiative forcing. For the first time, the development of a 6-stage Impactor for real-time balloon-borne measurements of size-segregated (cut-off diameter (D<sub>ae</sub>): 0.15-5 µm) aerosol mass concentrations in the free troposphere (FT) was tested during spring 2016 over Hyderabad, India, is presented. Total aerosol mass concentrations obtained with the 6-stage Impactor (M<sub>TI</sub>) and a co-located optical particle counter (OPC) (M<sub>TOPC</sub>) measurements at the surface under ambient conditions agreed to within 15%. The effect of aerosol particle growth on the M<sub>TI</sub> data are assessed using an urban aerosol particle model by scaling mass concentration of water-soluble (hydrophilic) aerosol particles at ambient RH to that at RH =50%. An overall uncertainty of the measurement of the M<sub>TI</sub> was estimated to be about 19%. The altitude variation of size-segregated mass concentrations of aerosol particles along with thermodynamic variables depicted convectively well-mixed layer extending up to about 4.5 km within which aerosol particles showed two distinct layers, one at ∼2 km, and another at about 4.5 km. The size-resolved air samples containing aerosol particles collected using the balloon-borne 6-stage Impactor will be useful for their chemical characterization and also long-range transport studies.</p>