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Andreas Beyersdorf

Publications and source records attributed to Andreas Beyersdorf.

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Understanding and Improving Model Representation of Aerosol Optical Properties for a Chinese Haze Event Measured During KORUS-AQ

KORUS-AQ was an international cooperative air quality field study in South Korea that measured local and remote sources of air pollution affecting the Korean Peninsula during May–June 2016. Some of the largest aerosol mass concentrations were measured during a Chinese haze transport event (24 May). Air quality forecasts using the WRF-Chem model with aerosol optical depth (AOD) data assimilation captured AOD during this pollution episode but overpredicted surface particulate matter concentrations in South Korea, especially PM2.5, often by a factor of 2 or larger. Analysis revealed multiple sources of model deficiency related to the calculation of optical properties from aerosol mass that explain these discrepancies. Using in situ observations of aerosol size and composition as inputs to the optical properties calculations showed that using a low-resolution size bin representation (four bins) underestimates the efficiency with which aerosols scatter and absorb light (mass extinction efficiency). Besides using finer-resolution size bins (8–16 bins), it was also necessary to increase the refractive indices and hygroscopicity of select aerosol species within the range of values reported in the literature to achieve better consistency with measured values of the mass extinction efficiency (6.7 m2 g−1 observed average) and light-scattering enhancement factor (f(RH)) due to aerosol hygroscopic growth (2.2 observed average). Furthermore, an evaluation of the optical properties obtained using modeled aerosol properties revealed the inability of sectional and modal aerosol representations in WRF-Chem to properly reproduce the observed size distribution, with the models displaying a much wider accumulation mode. Other model deficiencies included an underestimate of organic aerosol density (1.0 g cm−3 in the model vs. observed average of 1.5 g cm−3) and an overprediction of the fractional contribution of submicron inorganic aerosols other than sulfate, ammonium, nitrate, chloride, and sodium corresponding to mostly dust (17 %–28 % modeled vs. 12 % estimated from observations). These results illustrate the complexity of achieving an accurate model representation of optical properties and provide potential solutions that are relevant to multiple disciplines and applications such as air quality forecasts, health impact assessments, climate projections, solar power forecasts, and aerosol data assimilation.

Pablo E. Saide↗
NASA NTRS2015

TPSAS-NF1676L-22701-DND

The next generation of aerosol satellite instruments will include multi-spectral polarimetric measurements to retrieval aerosol size distribution and refractive index (Hasekamp et al., 2011; NRC, 2007). Refractive index is the “only means of constraining aerosol chemical composition from space” for passive sensors (Mischenko et al., 2007). A number of methods have been developed to derive refractive index from combined optical and electrical mobility sizing instruments (e.g., the “Alignment Method” of Hand and Kreidenweis, 2002). In this work, we evaluate the sensitivity of two, commercially-available, high-resolution optical particle counters for determining the size-resolved refractive index of laboratory-generated aerosols when used with a modified form of the Alignment Method.

Stephen Zimmerman↗
NASA NTRSDate not supplied

TPSAS-NF1676L-21952-DND

DISCOVER-AQ was a 4-year NASA project aimed to improve the interpretation of total column satellite observations to help diagnose near-surface conditions relating to air quality. During DISCOVER-AQ HSRL-2 was flown onboard the NASA Langley B200 King Air. A suite of in-situ instruments was flown onboard NASA Wallops P-3B aircraft which spiraled up and down over a number of ground stations. The two aircraft flew coordinated flight tracks, both flying over several designated ground stations with close time coincidence, allowing for colocation of measurements from the in situ instruments suite and the HSRL-2. HSRL-2 is the first multiwavelength airborne lidar system that provides profiles of 3β (backscatter)+2α(extinction),allowing the retrieval of microphysical parameters like number, surface-area, and volume concentrations, and effective radius.

Patricia Sawamura↗
NASA NTRSDate not supplied

TPSAS-NF1676L-23266-DND

Currently, near-surface air quality information (e.g. PM_2.5) must be inferred from column-integrated quantities (i.e. Aerosol Optical Thickness – AOT) obtained by passive remote sensing from downward-looking satellite instruments. Such retrievals must address the following questions: What do we use for the height of the aerosols? Mixed Layer (ML) height? Can we assume that near-surface aerosol extinction is about the same as the mean aerosol extinction in the ML? How well is near-surface extinction related to surface PM_2.5? How well can column AOT be used to infer near-surface aerosol extinction and PM_2.5?

Richard Ferrare↗