Abstract
ABSTRACTAirborne particulate matter (PM) is derived from diverse sources—natural and anthropogenic. Climate change processes and remote sensing measurements are affected by the PM properties, which are often lumped into homogeneous size fractions that show spatiotemporal variation. Since different sources are attributed to different geographic locations and show specific spatial and temporal PM patterns, we explored the spatiotemporal characteristics of the PM2.5/PM10 ratio in different areas. Furthermore, we examined the statistical relationships between AERONET aerosol optical depth (AOD) products, satellite-based AOD, and the PM ratio, as well as the specific PM size fractions. PM data from the northeastern United States, from San Joaquin Valley, CA, and from Italy, Israel, and France were analyzed, as well as the spatial and temporal co-measured AOD products obtained from the MultiAngle Implementation of Atmospheric Correction (MAIAC) algorithm. Our results suggest that when both the AERONET AOD and the AERONET fine-mode AOD are available, the AERONET AOD ratio can be a fair proxy for the ground PM ratio. Therefore, we recommend incorporating the fine-mode AERONET AOD in the calibration of MAIAC. Along with a relatively large variation in the observed PM ratio (especially in the northeastern United States), this shows the need to revisit MAIAC assumptions on aerosol microphysical properties, and perhaps their seasonal variability, which are used to generate the look-up tables and conduct aerosol retrievals. Our results call for further scrutiny of satellite-borne AOD, in particular its errors, limitations, and relation to the vertical aerosol profile and the particle size, shape, and composition distribution. This work is one step of the required analyses to gain better understanding of what the satellite-based AOD represents.Implications: The analysis results recommend incorporating the fine-mode AERONET AOD in MAIAC calibration. Specifically, they indicate the need to revisit MAIAC regional aerosol microphysical model assumptions used to generate look-up tables (LUTs) and conduct retrievals. Furthermore, relatively large variations in measured PM ratio shows that adding seasonality in aerosol microphysics used in LUTs, which is currently static, could also help improve accuracy of MAIAC retrievals. These results call for further scrutiny of satellite-borne AOD for better understanding of its limitations and relation to the vertical aerosol profile and particle size, shape, and composition.
Highlights
Airborne particulate matter (PM) is derived from diverse sources—natural and anthropogenic
Higher PM10 concentrations are observed in Israel, while the lowest median and IQ range for both PM2.5 and PM10 concentrations have been reported in northeastern United States (NE-USA)
Trends were observed for both the PM and aerosol optical depth (AOD) parameters, representing the seasonality of these parameters and attributed to sampling bias related to the day of the year
Summary
Airborne particulate matter (PM) is derived from diverse sources—natural and anthropogenic. Crustal material and natural sources (e.g., sea spray) contribute significant amounts of suspended matter, normally in the coarser size fraction (Deshmukh et al, 2012; Laden et al, 2000). PM is usually characterized by its physical and chemical properties, which are affected by its diverse sources and by the aging processes it has experienced. The PM optical properties (i.e., reflectance, absorbance, and scattering) vary across particle size and show spatiotemporal variation (Pelletier et al, 2007). Associations between ground PM observations and satellite-based aerosol optical depth (AOD) retrievals have been studied extensively in many geographical regions worldwide, using different statistical models for estimating the PM2.5 or PM10
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