Dark Matters – Challenges of Aerosol Absorption
The term “dark matter” has entered the common lexicon to refer to a great unobserved component of the universe that is (so far) only observed by inference through the gravitational effects on galaxies and universe at large. This is distinct from “dark energy” which may correspond to “negative mass” in Einstein’s general theory of relativity. Both of these “shadowy unknowns” have captured the interest of the public – but neither is the subject of this colloquium which instead focuses on the similarly poorly understood impacts that literal “dark” matter – material that absorbs light – has on our weather and climate. Unlike “dark matter” and “dark energy”, we actually know that dark absorbing aerosols exist as surely as smoke leads to fire. (Wink!) But beyond their bare existence, a quantitative understanding has been elusive. There are capability gaps in modeling the sources, formation, and lifetime of absorbing aerosols, corresponding gaps in accurate measurements of each of these aspects, and persistent gaps in understanding the impacts that the absorbing aerosols have on weather, on climate, and on our life on earth.
In this talk I will attempt with broad strokes to paint a picture of the challenges and unknowns associated with absorbing aerosols, and will then focus more directly on measurement aspects with which I have direct and semi-direct involvement at three different spatial scales: in situ measurements, vertically-integrated measurements with passive sun photometry, and vertically-resolved measurements with airborne sensors or active remote sensors.