HSRL-2 aerosol optical measurements and microphysical retrievals vs. airborne in situ measurements during DISCOVER-AQ 2013: an intercomparison study

• Published in: Atmospheric chemistry and physics Vol. 17; no. 11; pp. 7229 - 7243
• Main Authors: Sawamura, Patricia, Moore, Richard H, Burton, Sharon P, Chemyakin, Eduard, Müller, Detlef, Kolgotin, Alexei, Ferrare, Richard A, Hostetler, Chris A, Ziemba, Luke D, Beyersdorf, Andreas J, Anderson, Bruce E
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 16-06-2017; Copernicus Publications
• Subjects: Aerosol concentrations; Aerosol effects; Aerosol measurements; Aerosol properties; Aerosols; Air quality; Airborne particulates; Airborne sensing; Aircraft; Algorithms; Automation; Backscatter; Backscattering; Bias; Coefficients; Comparative analysis; Drying; Environmental aspects; Estimates; Evaluation; Extinction; Ground stations; Humidity; In situ measurement; In situ measurements; Instrumentation; Instruments; Intercomparison; Lidar; Mathematical models; Measurement; Methods; Mie scattering; Mie theory; Optical measurement; Optical properties; Particle mass; Particulate matter; Physical properties; Profiles; Properties; Properties (attributes); Relative humidity; Remote sensing; Retrieval; Satellites; Sensors; Spectra; Stress concentration; Vertical distribution; Wavelength; United States > US; Texas; California; San Joaquin Valley
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-17-7229-2017

We present a detailed evaluation of remotely sensed aerosol microphysical properties obtained from an advanced, multi-wavelength high-spectral-resolution lidar (HSRL-2) during the 2013 NASA DISCOVER-AQ field campaign. Vertically resolved retrievals of fine-mode aerosol number, surface-area, and volume concentration as well as aerosol effective radius are compared to 108 collocated, airborne in situ measurement profiles in the wintertime San Joaquin Valley, California, and in summertime Houston, Texas. An algorithm for relating the dry in situ aerosol properties to those obtained by the HSRL at ambient relative humidity is discussed. We show that the HSRL-2 retrievals of ambient fine-mode aerosol surface-area and volume concentrations agree with the in situ measurements to within 25 and 10 %, respectively, once hygroscopic growth adjustments have been applied to the dry in situ data. Despite this excellent agreement for the microphysical properties, extinction and backscatter coefficients at ambient relative humidity derived from the in situ aerosol measurements using Mie theory are consistently smaller than those measured by the HSRL, with average differences of 31 ± 5 % and 53 ± 11 % for California and Texas, respectively. This low bias in the in situ estimates is attributed to the presence of coarse-mode aerosol that are detected by HSRL-2 but that are too large to be well sampled by the in situ instrumentation. Since the retrieval of aerosol volume is most relevant to current regulatory efforts targeting fine particle mass (PM2. 5), these findings highlight the advantages of an advanced 3β + 2α HSRL for constraining the vertical distribution of the aerosol volume or mass loading relevant for air quality.