Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> Aerosol particles can be emitted, transported, removed, or transformed, leading to aerosol variability at scales impacting the climate (days to years and over hundreds of kilometers) or the air quality (hours to days and from meters to hundreds of kilometers). We present the temporal and spatial scales of changes in AOD (aerosol optical depth) and aerosol size (using à ngström exponent â AE; fine-mode fraction â FMF) over Korea during the 2016 KORUS-AQ (KOReaâUS Air Quality) atmospheric experiment. We use measurements and retrievals of aerosol optical properties from airborne instruments for remote sensing (4STAR; Spectrometers for Sky-Scanning Sun-Tracking Atmospheric Research) and in situ (LARGE; NASA Langley Aerosol Research Group Experiment) on board the NASA DC-8 and geostationary satellites (GOCI; Geostationary Ocean Color Imager; Yonsei aerosol retrieval â YAER, version 2) as well as from reanalysis (MERRA-2; Modern-Era Retrospective Analysis for Research and Applications, version 2). Measurements from 4STAR when flying below 1000â<span class="inline-formula">m</span> show an average AOD at 501â<span class="inline-formula">nm</span> of 0.36 and an average AE of 1.11 with large standard deviation (0.12 and 0.15 for AOD and AE, respectively), likely due to mixing of different aerosol types (fine and coarse mode). The majority of AOD due to fine-mode aerosol is observed at altitudes lower than 2â<span class="inline-formula">km</span>. Even though there are large variations, for 18 out of the 20 flight days, the column AOD measurements by 4STAR along the NASA DC-8 flight trajectories match the South Korean regional average derived from GOCI. GOCI-derived FMF, which was found to be slightly low compared to AErosol RObotic NETwork (AERONET) sites (Choi et al., 2018), is lower than 4STAR's observations during KORUS-AQ. Understanding the variability of aerosols helps reduce uncertainties in the aerosol direct radiative effect by quantifying the errors due to interpolating between sparse aerosol observation sites or modeled pixels, potentially reducing uncertainties in the upcoming observational capabilities. We observed that, contrary to the prevalent understanding, AE and FMF are more spatially variable than AOD during KORUS-AQ, even when accounting for potential sampling biases by using Monte Carlo resampling. Averaging between measurements and models for the entire KORUS-AQ period, the reduction in correlation by 15â% is 65.0â<span class="inline-formula">km</span> for AOD and shorter at 22.7â<span class="inline-formula">km</span> for AE. While there are observational and model differences, the predominant factor influencing spatialâtemporal homogeneity is the meteorological period. High spatiotemporal variability occurs during the dynamic period (25â31 May), and low spatiotemporal variability occurs during the blocking pattern (1â7 June). While AOD and FMFâ<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="073414a2b77546d8d5847ae97897d626"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-11275-2022-ie00001.svg" width="8pt" height="14pt" src="acp-22-11275-2022-ie00001.png"/></svg:svg></span></span>âAE are interrelated, the spatial variability and relative variability of these parameters in this study indicate that microphysical processes vary at scales shorter than aerosol concentration processes at which microphysical processes such as aerosol particle formation, growth, and coagulation mostly impact the dominant aerosol size (characterized by, e.g., FMFâ<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="36bd7baae116a5efc17e692d563c2b51"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-11275-2022-ie00002.svg" width="8pt" height="14pt" src="acp-22-11275-2022-ie00002.png"/></svg:svg></span></span>âAE) and to some degree AOD. In addition to impacting aerosol size, aerosol concentration processes such as aerosol emission, transport, and removal mostly impact the AOD.
Highlights
Aerosol interactions with light are governed by their intensive and extensive properties (Rajesh and Ramachandran, 2020)
Black and brown carbon aerosol are not the only aerosol types found in this region, their mass concentrations are reported to vary by a factor of 5 over Korea, forming multiple gradients, regional maxima and mimina within 350 the boundaries of the peninsula (Li et al, 2020)
The aerosol optical depth (AOD) measured during KORUS-AQ by airborne sampling using 4STAR, satellite remote 815 sensing using Geostationary Ocean Color Imager (GOCI), and reanalysis from MERRA-2 was found to follow general climatological trends for the Korean peninsula (Choi and Ghim, 2021)
Summary
Aerosol interactions with light are governed by their intensive and extensive properties (Rajesh and Ramachandran, 2020). Intensive properties represent the aerosol optical properties that do 65 not scale with aerosol concentration or mass, such as angstrom exponent (AE), fine mode fraction (FMF), single scattering albedo, asymmetry parameter, index of refraction, and hemispheric backscatter fraction. These intensive properties depend on the intrinsic properties of the aerosol; its size, shape and composition (Russell et al, 2010). The spatio-temporal scales at which the extensive and intensive properties vary are directly linked to the processes governing the emission, transport, removal, and transformation of the aerosol particles. Targino et al (2005) presented cases where the aerosol extensive 85 properties (scattering and absorption coefficients) change at scales smaller than the airmass/mesoscale, compared to intensive properties (AE and single scattering albedo) that varied much less
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