Smoke Particle Properties, Their Evolution, and Controlling Factors, from Space-Based Multi-Angle Imaging

The multi-spectral, multi-angle observational capabilities of the Multi-Angle Imaging Spectrometer (MISR) instrument aboard NASA’s Terra satellite allows for the retrieval of aerosol optical depth (AOD), and can place constraints on aerosol type and near-source aerosol plume height and associated motion vectors (e.g., from volcanoes, wildfires, and dust storms). The MISR Research Aerosol (RA) algorithm retrieves qualitative aerosol “type” as constraints on particle shape, size, light-absorption, and absorption spectral dependence. Over the course of the 23+ years of MISR operation, the RA and instrument radiometric calibration have been refined, resulting in greatly improved particle property retrievals compared to the MISR Standard Aerosol retrieval algorithm, at the cost of performing RA analyses on a case-by-case basis.

Under NASA’s ACMAP program, the MISR team’s efforts are gravitated increasingly toward the application of the RA. Here we report on our ongoing work characterizing wildfire smoke behavior across the globe, leveraging the RA to retrieve smoke particle properties and the MISR Interactive Explorer (MINX) tool to retrieve plume heights and derive smoke age. These results are compared statistically with available observations of fire radiative power (FRP), land cover characteristics, as well as short-term climate, meteorological, and drought information to discern patterns of behavior. Our analysis reveals connections between retrieved smoke properties, smoke age, local ambient conditions, and fuel type, allowing us in many cases to infer the dominant aging mechanisms and the timescales over which they occur (e.g., oxidation, condensation, gravitational settling, etc.). The results are likely to be useful for constraining climate models, as the factors affecting emitted smoke particle properties, particularly light-absorbing black smoke (BlS) and brown smoke (BrS), are currently not well characterized on regional or global scales, nor are the factors controlling smoke particle evolution downwind, during transport and atmospheric processing.

Our work on Canadian and Alaskan wildfires demonstrates distinct differences in the relative importance of oxidation/condensation vs. dilution in downwind particle aging, depending on whether the land cover type is grass or woody vegetation dominated. Here we compare these to our most recent studies of Siberian wildfires and Australian wildfires, highlighting further regional differences in plume particle properties, particle aging, and the forces driving these differences. We also present a brief overview of some of the other ongoing work in our team supported in part by the ACMAP program.