Constraining Aerosol Vertical Profile in the Boundary Layer Using Hyperspectral Measurements of Oxygen Absorption

This study attempts to infer aerosol vertical structure in the urban boundary layer using passive hyperspectral measurements. A spectral sorting technique is developed to retrieve total aerosol optical depth (AOD) and effective aerosol layer height (ALH) from hyperspectral measurements in the 1.27-μm oxygen absorption band by the mountaintop Fourier Transform Spectrometer at the California Laboratory for Atmospheric Remote Sensing instrument (1,673 m above sea level) overlooking the LA basin. Comparison to AOD measurements from Aerosol Robotic Network and aerosol backscatter profile measurements from a Mini MicroPulse Lidar shows agreement, with coefficients of determination (r2) of 0.74 for AOD and 0.57 for effective ALH. On average, the AOD retrieval has an error of 24.9% and root-mean-square error of 0.013, while the effective ALH retrieval has an error of 7.8% and root-mean-square error of 67.01 m. The proposed method can potentially be applied to existing and future satellite missions with hyperspectral oxygen measurements to constrain aerosol vertical distribution on a global scale. Plain Language Summary Satellite and ground-based measurements have enabled accurate and continuous monitoring of total aerosol loading. However, these measurements provide little or no information on the vertical distribution of aerosols. In particular, there is poor measurement of aerosols in the planetary boundary layer, the part of the atmosphere closest to the surface. In this study, we develop an algorithm to retrieve the vertical structure of aerosols in the boundary layer using remote sensing observations of oxygen absorption with high spectral resolution. The algorithm is applied to infer the vertical profile of air pollutants in the Los Angeles basin using measurements made by a mountaintop instrument overlooking the basin. The proposed retrieval algorithm can potentially be applied to existing and future satellite missions with hyperspectral oxygen measurements to constrain the aerosol vertical distribution on a global scale. This important piece of information on aerosol vertical structure will potentially address several key priorities in the 2017 U.S. National Research Council Earth Science Decadal Survey, from forecasting air pollution in cities, quantifying the aerosol impact on Earth’s climate, and reducing biases in greenhouse gas retrievals.