Seminar

Abstract

The vertical profile of the short-lived climate forcer (SLCF) particulate carbon is not well simulated in atmospheric models and this contributes substantially to uncertainty in climate projections because radiative scattering is altitude dependent. Changes in emissions, SOA partitioning parameters, (among other efforts) do not improve model-predicted vertical profiles, but inclusion of aqueous phase organic chemistry (e.g., cloud processing of VOCs) does.

Organic "brown" carbon, often associated with humic-like substances (HULIS) is ubiquitous and sources are thought to include multi- or mixed-phase atmospheric processes (e.g., aqueous phase chemistry in cloud droplets). It has been demonstrated in recent laboratory experiments that products of aqueous phase oxidation of water soluble atmospheric gases such as, glyoxal, methylglyoxal and phenols include HULIS and other light-absorbing products. In Mexico City, where glyoxal contributes substantially to SOA, absorption from "brown" carbon at UV wavelengths accounts for up to 40% of the heating rate of BC. When the scattering/absorption properties of brown carbon are accounted for with observed black-to-brown carbon mass ratios, the calculated surface and top of atmosphere (TOA) radiative forcing is significant. Future work is aimed at representing mixed phase chemistry so that effective control strategies can be developed that mitigate the deleterious effects associated with climate impacts.