Aerosol optical depth is more consistent than aerosol size over large distances during KORUS-AQ

We show the consistency over spatial scales of the Aerosol Optical Depth (AOD), and the aerosol intensive properties (Angstrom exponent - AE, fine mode fraction - FMF) measured by an airborne platform over Korea during the KORUS-AQ (KORean-US Air Quality) experiment occurring in May-June 2016. We compare the column aerosol extensive property, AOD, intensive properties, AE and FMF, obtained from 4STAR (Spectrometers for Sky-Scanning Sun Tracking Atmospheric Research), GOCI (Geostationary Ocean Color Imager Yonsei aerosol retrieval v2), MERRA-2 reanalysis (Modern-Era Retrospective Analysis for Research and Applications, v2), and from airborne in situ aerosol optical measurements by LARGE (NASA Langley Aerosol Research Group Experiment). The majority of AODs due to fine mode aerosol is observed at altitudes lower than 2 km and is significantly dependent on KORUS-AQs four time periods separated by prevailing meteorological conditions; 1- dynamic meteorology and complex aerosol vertical profiles, 2- stagnation under a persistent anticyclone, 3- dynamic meteorology, low-level transport, and haze development with extreme pollution and 4- blocking pattern. AE and FMF are found to be more spatially variable than AOD during all of KORUS-AQ, which is repeatably observed by 4STAR, GOCI, LARGE, and MERRA-2, even when accounting for potential sampling biases by using Monte Carlo resampling. Averaging between measurements and model (4STAR, MERRA-2, GOCI, and LARGE), the distance to reduce the autocorrelation by 15% for AOD is 65 km, while AE at 22.7 km. While there are observational and model differences (MERRA-2 consistently shows longer distances at high autocorrelation, while GOCI and LARGE in situ observations shorter, than 4STAR), the predominant factor influencing the distances where autocorrelation remains above 85% is the meteorological period. The shortest distances occur during extreme pollution period (2531 May), and the longest distances with high autocorrelation amid the blocking (17 June) and stagnation (1722 May) periods. This indicates that microphysical processes like aerosol particle formation, growth, and coagulation impact the dominant aerosol size at shorter scales than their combined effect on the aerosol optical depth by the aerosol emission, transport, and removal.