Intercomparison between satellite‐derived aerosol optical thickness and PM_2.5 mass: Implications for air quality studies

TLDR

The study investigates the relationship between MODIS‑derived aerosol optical thickness and surface PM₂.₅ in Jefferson County, Alabama, and discusses factors influencing their correlation, noting that further research is needed before applying the method elsewhere. The authors used MODIS satellite‑derived AOT and hourly surface PM₂.₅ measurements from seven sites in Jefferson County, Alabama, to examine their relationship. The analysis shows a strong correlation between MODIS AOT and PM₂.₅ (R≈0.7 overall, R>0.9 monthly), a distinct diurnal pattern in PM₂.₅, and that AOT can predict EPA air‑quality categories with over 90 % accuracy during cloud‑free periods.

Abstract

We explore the relationship between column aerosol optical thickness (AOT) derived from the Moderate Resolution Imaging SpectroRadiometer (MODIS) on the Terra/Aqua satellites and hourly fine particulate mass (PM 2.5 ) measured at the surface at seven locations in Jefferson county, Alabama for 2002. Results indicate that there is a good correlation between the satellite‐derived AOT and PM 2.5 (linear correlation coefficient, R = 0.7) indicating that most of the aerosols are in the well‐mixed lower boundary layer during the satellite overpass times. There is excellent agreement between the monthly mean PM 2.5 and MODIS AOT (R > 0.9), with maximum values during the summer months due to enhanced photolysis. The PM 2.5 has a distinct diurnal signature with maxima in the early morning (6:00 ∼ 8:00AM) due to increased traffic flow and restricted mixing depths during these hours. Using simple empirical linear relationships derived between the MODIS AOT and 24hr mean PM 2.5 we show that the MODIS AOT can be used quantitatively to estimate air quality categories as defined by the U.S. Environmental Protection Agency (EPA) with an accuracy of more than 90% in cloud‐free conditions. We discuss the factors that affect the correlation between satellite‐derived AOT and PM 2.5 mass, and emphasize that more research is needed before applying these methods and results over other areas.