Department of Environmental Sciences

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Seminar Abstracts
Environmental Sciences Seminar Abstract            

  Atmospheric Brown Clouds (ABCs): predicting the vertical profile of particulate carbon
Annmarie Carlton
Rutgers University

Atmospheric Brown Clouds (ABCs) are composed of submicrometer aerosols, including black carbon and other constituents (e.g., sulfate, organics). Globally, ABCs are a major agent of climate change and long range pollution transport. Single particle mass spectra indicate ABC particles in size ranges that efficiently scatter (e.g., 0.2-1.0 µm) are comprised predominantly of internal mixtures that include organic carbon. The vertical profile of organic 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 scattering of brown HULIS formed through cloud processing independently so that effective control strategies can be developed to mitigate the deleterious effects associated with climate impacts.

Last updated: 08/07/2011