Synthesis of in situ and remote sensing measurements of aerosol properties to refine understanding of trends and processes
Authors
Allison C. McComiskey — Brookhaven National Laboratory
Hagen Telg — Cooperative Institute for Research in Environmental Sciences
Category
General topics – Aerosols
Description
Dry aerosol total light scattering (and extinction, not shown) at the surface has decreased over the 20-year time period of record at SGP. This trend is consistent with findings at many locations across the US, attributed to the 1990 Clean Air Act (e.g., Attwood et al. 2014). Coarse mode scattering, often from natural sources, has remained relatively constant resulting in an increasingly larger coarse mode fraction of scattering (extinction) through time. Examination of such trends can provide information regarding fundamental changes in processes that result in aerosol radiative impacts and identify important areas of study for the future. The aerosol coarse mode has been under-studied in the past owing to the assumption that it is not of large significance for physical or radiative processes.
Long-term records of aerosol properties indicate significant shifts across the continental US in the source, properties, and impacts of aerosol both geographically and through time. However, analyses tend to focus on a single measurement network within which limited sets of properties are observed, potentially biasing interpretations. The 20-year aerosol record at the DOE ARM Southern Great plains site comprises surface in situ as well as active and passive remote sensing records that can inform different aspects of the aerosol and how it is changing. Co-location with meteorological and thermodynamical measurements provide ancillary information for determining drivers of change. For example, the surface record at SGP indicates the coarse mode fraction of aerosol has increased substantially in the past 10 years while the column record shows evidence of declining aerosol burden overall, but a mid-record increase in stratospheric aerosol which may confound interpretations of tropospheric processes from remote sensing measurements if not removed. We examine trends in various records of aerosol properties over the 20-year SGP record and reconcile these trends with processes that studies using US-scale networks (e.g., IMPROVE, SURFRAD) have suggested are responsible for the observed spatio-temporal shifts.
