Vertical Profiles of Light-Absorbing Aerosol: In-situ and AERONET Observations during NASA DISCOVER-AQ

Understanding the vertical profile of atmospheric aerosols plays a vital role in utilizing spaceborne, column-
integrated satellite observations. The properties and distribution of light-absorbing aerosol are particularly
uncertain despite significant air quality and climate ramifications. Advanced retrieval algorithms are able to
derive complex aerosol properties (e.g., wavelength-dependent absorption coefficient and single scattering
albedo) from remote-sensing measurements, but quantitative relationships to surface conditions remain a
challenge. Highly systematic atmospheric profiling during four unique deployments for the NASA
DISCOVER-AQ project (Baltimore, MD, 2011; San Joaquin Valley, CA, 2013; Houston, TX, 2013; Denver,
CO, 2014) allow statistical assessment of spatial, temporal, and source-related variability for light-absorbing
aerosol properties in these distinct regions. In-situ sampling in conjunction with a dense network of
AERONET sensors also allows evaluation of the sensitivity, limitations, and advantages of remote-sensing
data products over a wide range of conditions.

In-situ aerosol and gas-phase observations were made during DISCOVER-AQ aboard the NASA P-3B
aircraft. Aerosol absorption coefficients were measured by a Particle Soot Absorption Photometer (PSAP).
Approximately 200 profiles for each of the four deployments were obtained, from the surface (25-300m
altitude) to 5 km, and are used to calculate absorption aerosol optical depths (AAODs). These are
quantitatively compared to AAOD derived from AERONET Level 1.5 retrievals to 1) explore discrepancies
between measurements, 2) quantify the fraction of AAOD that exists directly at the surface and is often
missed by airborne sampling, and 3) evaluate the potential for deriving ground-level black carbon (BC)
concentrations for air quality prediction. Aerosol size distributions are used to assess absorption
contributions from mineral dust, both at the surface and aloft. SP2 (Single Particle Soot Photometer) mixing
state and coating thickness analyses will be explored to explain in-situ/AERONET discrepancies, and
ground-based absorption coefficient and BC-mass observations will be utilized whenever possible to fully
obtain the true absorption vertical profile