Classifying aerosol type using in situ surface spectral aerosol optical properties

Abstract

Abstract. Knowledge of aerosol size and composition is important for determining radiative forcing effects of aerosols, identifying aerosol sources and improving aerosol satellite retrieval algorithms. The ability to extrapolate aerosol size and composition, or type, from intensive aerosol optical properties can help expand the current knowledge of spatiotemporal variability in aerosol type globally, particularly where chemical composition measurements do not exist concurrently with optical property measurements. This study uses medians of the scattering Ångström exponent (SAE), absorption Ångström exponent (AAE) and single scattering albedo (SSA) from 24 stations within the NOAA/ESRL Federated Aerosol Monitoring Network to infer aerosol type using previously published aerosol classification schemes.Three methods are implemented to obtain a best estimate of dominant aerosol type at each station using aerosol optical properties. The first method plots station medians into an AAE vs. SAE plot space, so that a unique combination of intensive properties corresponds with an aerosol type. The second typing method expands on the first by introducing a multivariate cluster analysis, which aims to group stations with similar optical characteristics and thus similar dominantPublished by Copernicus Publications on behalf of the European Geosciences Union. L. Schmeisser et al.: Classifying aerosols with optical propertiesaerosol type. The third and final classification method pairs 3-day backward air mass trajectories with median aerosol optical properties to explore the relationship between trajectory origin (proxy for likely aerosol type) and aerosol intensive parameters, while allowing for multiple dominant aerosol types at each station.The three aerosol classification methods have some common, and thus robust, results. In general, estimating dominant aerosol type using optical properties is best suited for site locations with a stable and homogenous aerosol population, particularly continental polluted (carbonaceous aerosol), marine polluted (carbonaceous aerosol mixed with sea salt) and continental dust/biomass sites (dust and carbonaceous aerosol); however, current classification schemes perform poorly when predicting dominant aerosol type at remote marine and Arctic sites and at stations with more complex locations and topography where variable aerosol populations are not well represented by median optical properties. Although the aerosol classification methods presented here provide new ways to reduce ambiguity in typing schemes, there is more work needed to find aerosol typing methods that are useful for a larger range of geographic locations and aerosol populations.

Continuous light absorption photometer for long-term studies

“…The CLAP has proven to be a reliable instrument for determining the aerosol light absorption coefficient under a wide variety of sampling conditions, including from research aircraft (Aliabadi et al, 2015;Backman et al, 2016;Sherman et al, 2015;Schmeisser et al, 2017;Sinha et al, 2017;Sorribas et al, 2017). The two-part design, with the associated need to separate the two halves for each filter change, has been mostly problem-free.…”

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

“…Here, one focus is on identifying marine particles in aerosol‐type classifications from in situ measurements. In summary, this study meets a need for further validation analysis of aerosol classification methods with concurrent aerosol optical and chemical measurements and their possible extension to other environments as called for by for instance Schmeisser et al ().…”

“…Several previous studies of wavelength‐dependent particle absorption and scattering and the relation to aerosol composition have been presented (e.g., Bahadur et al, ; Cappa et al, ; Cazorla et al, ; Costabile et al, ; Russell et al, ; Wiegand et al, ; Schmeisser et al, ). These studies suggest various ways to detect the aerosol type by evaluating the intensive particle optical properties.…”

“…Many of the aerosol characterization approaches result from ground‐based or even satellite remote sensing measurements, such as Aerosol Robotic Network (AERONET) or MODIS, and an assumed dominant aerosol type depending on the station location and/or air mass source region (e.g., Bahadur et al, ; Cazorla et al, ; Giles et al, ; Russell et al, ). Some other studies use surface in situ measurements to determine the particle optical properties but still base their aerosol categorization on site classifications, such as continental polluted and marine (e.g., Cappa et al, ; Costabile et al, ; Schmeisser et al, ). There have been only a few attempts to verify the classification approaches with simultaneous in situ chemical measurements of the ambient air (e.g., Cazorla et al, ; Lee et al, ; Russell et al, ; Valenzuela et al, ).…”

“…The latter means that marine particles were not very prominent when the aerosol classification categories were defined. Only a few studies tried to include marine aerosols in their optical aerosol classification approaches (e.g., Costabile et al, ; Kumar et al, ; Schmeisser et al, ). Here, one focus is on identifying marine particles in aerosol‐type classifications from in situ measurements.…”