Investigation of Two Optical Methods for Aerosol‐Type Classification Extended to a Northern Indian Ocean Site

Abstract

Methods for determining aerosol types in cases where chemical composition measurements are not available are useful for improved aerosol radiative forcing estimates. In this study, two aerosol characterization methods by Cazorla et al. (2013Cazorla et al. ( , https://doi.org/10.5194/acp-13-9337-2013 CA13) and Costabile et al. (2013Costabile et al. ( , https://doi.org/10.5194/acp-13-2455Costabile et al. ( -2013; CO13) using wavelength-dependent particle absorption and scattering are used, to assess their applicability and examine their limitations. Long-term ambient particle optical property and chemical composition (major inorganic ions and bulk carbon) measurements from the Maldives Climate Observatory Hanimaadhoo as well as concurrent air mass trajectories are utilized to test the classifications based on the determined absorption Ångström exponent, scattering Ångström exponent, and single scattering albedo. The resulting aerosol types from the CA13 method show a good qualitative agreement with the particle chemical composition and air mass origin. In general, the size differentiation using the scattering Ångström exponent works very well for both methods, while the composition identification depending mainly on the absorption Ångström exponent can result in aerosol misclassifications at Maldives Climate Observatory Hanimaadhoo. To broaden the applicability of the CA13 method, we suggest to include an underlying marine aerosol group in the classification scheme. The classification of the CO13 method is less clear, and its applicability is limited when it is extended to aerosols in this environment at ambient humidity.Anthropogenic aerosol emissions, including BC, are still increasing in certain regions. For instance, India reports almost a doubling in energy use and coal combustion from 2001 to 2011, which led to an estimated BC emission of approximately 0.9 Tg/year in 2011 (Paliwal et al., 2016). This is almost three times more than the BC emission of Western Europe in 2010 (Granier et al., 2011). Due to growing population and industry, further increase in anthropogenic aerosol emissions in India is expected (Paliwal et al., 2016).Global climate models and emission inventories are used to quantify different large-scale aerosol climate effects, but the uncertainty can be high because of the uneven distribution of aerosols in space and time due to their short atmospheric residence times, diverse composition, and emission intensities. Better quantification of the aerosol effects on climate requires exact characterization of their physical and chemical properties. This calls for extensive observations over a range of regions, but these types of measurement efforts are costly. Thus, methods where we obtain as much information as possible from fewer cost-effective

Emissions from the Open Laboratory Combustion of Cheatgrass (Bromus Tectorum)

“…The differences between 405/532 and 405/781 AAE were driven by BrC that absorbed mostly in the UV and blue and by BC absorption that was less dependent on wavelength (AAEBC ~ 1). SAE gives information on particle sizes, indicating coarse-mode particles for small values (i.e., <1.5) and fine-mode particles for larger SAE values (i.e., >1.5) [55]. The SAE values observed for cheatgrass (i.e., 0.5-3.5,…”

Long-term variation of aerosol optical properties associated with aerosol types over East Asia using AERONET and satellite (VIIRS, OMI) data (2012–2019)

“…This AAE-SAE algorithm was used in several studies, most of which focused on the overall characteristics of several areas (e.g. Hopner et al, 2018;Kaskaoutis et al, 2021). Several studies have examined the global and regional frequency distributions of various aerosol types according to their optical properties (e.g., Lin et al, 2022;Logothetis et al, 2020;Mok et al, 2017;Schmeisser et al, 2017), but these studies have limitations in terms of long-term variation.…”

Long-Term Variation of Aerosol Optical Properties Associated with Aerosol Types Over East Asia Using Aeronet and Satellite (Viirs, Omi) Data

“…This AAE-SAE algorithm was used in several studies, most of which focused on the overall characteristics of several areas (e.g. Hopner et al, 2018;Kaskaoutis et al, 2021). Several studies have examined the global and regional frequency distributions of various aerosol types according to their optical properties (e.g., Lin et al, 2022;Logothetis et al, 2020;Mok et al, 2017;Schmeisser et al, 2017), but these studies have limitations in terms of long-term variation.…”