title: Monthly analysis of PM ratio characteristics and its relation to AOD.
abstract: Airborne 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/PM10ratio 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.
  
  
  
  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.
authors: a Faculty of Civil and Environmental Engineering , Technion Israel Institute , Haifa , Israel.|b Department of Geography and Environmental Development , Ben-Gurion University , Beer Sheva , Israel.
authors: Meytar
authors: M
authors: Sorek-Hamer
authors: a Faculty of Civil and Environmental Engineering , Technion Israel Institute , Haifa , Israel.
authors: David M
authors: DM
authors: Broday
authors: c NASA Ames Research Center , Moffett Field , CA , USA.
authors: Robert
authors: R
authors: Chatfield
authors: c NASA Ames Research Center , Moffett Field , CA , USA.
authors: Robert
authors: R
authors: Esswein
authors: d Department of Epidemiology , Lazio Region Health Service , Rome , Italy.
authors: Massimo
authors: M
authors: Stafoggia
authors: e INSERM and Université Grenoble-Alpes, IAB (U1209) , Team of Environmental Epidemiology , Grenoble , France.
authors: Johanna
authors: J
authors: Lepeule
authors: f NASA GSFC , Greenbelt , MD , USA.
authors: Alexei
authors: A
authors: Lyapustin
authors: b Department of Geography and Environmental Development , Ben-Gurion University , Beer Sheva , Israel.
authors: Itai
authors: I
authors: Kloog
mesh_terms: D000336:Aerosols / Q000737:chemistry*; D000393:Air Pollutants / Q000737:chemistry*; D000397:Air Pollution; D002138:Calibration; D002140:California; D004784:Environmental Monitoring / Q000379:methods*; D005602:France; D007557:Israel; D007558:Italy; D010316:Particle Size; D052638:Particulate Matter / Q000737:chemistry*
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D052638:Particulate Matter