###### Abstract  
Concentrations of particulate aerosols and their vertical placement in the atmosphere determine their interaction with the Earth system and their impact on air quality. Space-based lidar, such as the Cloud-Aerosol Transport System (CATS) technology demonstration instrument, is well-suited for determining the vertical structure of these aerosols and their diurnal cycle. Through the implementation of aerosol-typing algorithms, vertical layers of aerosols are assigned a type, such as marine, dust, and smoke, and a corresponding extinction-to-backscatter (lidar) ratio. With updates to the previous aerosol-typing algorithms, we find that CATS, even as a technology demonstration, observed the documented seasonal cycle of aerosols, comparing favorably with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) space-based lidar and the NASA Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) model reanalysis. By leveraging the unique orbit of the International Space Station, we find that CATS can additionally resolve the diurnal cycle of aerosol altitude as observed by ground-based instruments over the Maritime Continent of Southeast Asia. lidar; aerosol; algorithm; seasonal; diurnal cycle +
Footnote †: journal: _Atmosphere_  
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distribution of aerosols within the atmosphere. Compared to passive instruments, airborne and space-based lidars excel in providing high-resolution vertical profiles of clouds and aerosols. The most recent lidars to operate in orbit designed for cloud and aerosol observations are NASA's Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite from 2006 to present [9] and the Cloud-Aerosol Transport System (CATS) aboard the International Space Station (ISS) from 2015 to 2017 [10; 11]. CALIOP was originally part of the NASA A-Train constellation of polar-orbiting Earth-observing instruments with a local equatorial crossing time of around 1:30 a.m. and p.m. In contrast, the precessing orbit of the ISS between 51\({}^{\circ}\) N-51\({}^{\circ}\) S enabled the CATS lidar to observe the vertical distribution of clouds and aerosols at a variety of local times. This variety of times sampled allows the diurnal cycle to be observed with CATS where CALIOP is set with its two equatorial crossing times, e.g., [12; 13]. Aerosols exhibit both a seasonal and diurnal cycle because their concentrations and altitudes depend on a variety of factors that vary seasonally and diurnally, including emissions, local meteorology, transport, removal, and chemistry, e.g., [14]. For example, smoke aerosols concentrations are primarily emitted through biomass burning which is highly dependent on local meteorological and source conditions. These conditions vary depending on the season and time of day, e.g., [15], with tropical agricultural burning emissions increasing in the morning (\(\sim\)1000 local) to an early afternoon peak (1200 to 1400 local) [16; 17]. Dust aerosol concentrations likewise vary depending on the regional atmospheric transport and the local conditions at the source regions, e.g., [13; 18]. Quantifying the diurnal emission and convective process impacts on the aerosol vertical distributions is essential for determining the aerosol transport pathways and air quality within the planetary boundary layer (PBL) [19; 20; 21]. In this study, we describe our most recent aerosol-typing algorithms (V3-00) applied to the 33-month lifetime of the CATS lidar data and compare the seasonal variability in the CATS aerosol type to Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) aerosols and CALIOP observations in Section 2. In Section 3, we leverage the unique orbit of the CATS lidar to quantify the diurnal cycle of smoke aerosols over the Maritime Continent of Southeast Asia and compare this to NASA's ground-based Micro-Pulse Lidar Network (MPLNET) lidar [22].