Exploring Natural Aerosol Formation from Dimethyl Sulfide (DMS) Oxidation and Implications for Aerosol Forcing

Principal Investigator(s):
Jesse Kroll, Massachusetts Institute of Technology
Colette Heald, Massachusetts Institute of Technology

Atmospheric aerosols are the dominant contributor to uncertainty in global climate forcing. Through both their direct effects (scattering and absorption of radiation) and indirect effects (in determining cloud properties and lifetime), the overall impact of atmospheric aerosols is estimated to be a cooling that globally counterbalances a significant fraction of the warming associated with greenhouse gases. Aerosol climate forcing is dominated by the rise of aerosol of anthropogenic origin, but a detailed understanding of natural (background) aerosol is critical for assessing radiative forcing and future climate trends. However, the chemistry underlying the formation of a large fraction of natural aerosol – sulfate produced by the oxidation of dimethyl sulfide, or DMS – remains poorly constrained. In particular, DMS oxidation under pristine/pre-industrial (low NO) conditions is poorly understood, as is the aqueous phase oxidation of DMS and its reaction products. Such processes are therefore generally neglected in most three-dimensional atmospheric chemistry models, leading to substantial uncertainty in estimates of the natural aerosol burden, and hence in estimates of present and future aerosol radiative forcing.

We target this critical gap in understanding the lifecycle and impacts of natural aerosols with a collaborative experimental and modeling project. The specific components of this project are:

  1. Laboratory studies: investigating and characterizing the formation of sulfate aerosol from DMS oxidation under a range of conditions, representative of both the pre-industrial era and present day.
  2. Global modeling studies: investigating how an improved characterization of the natural sulfate aerosol background impacts estimates of aerosol radiative forcing.

A suite of laboratory studies of DMS oxidation under a wide range of conditions will yield new insights into the formation of natural aerosols. These experimental results will be the basis for the development of a new model scheme, which will be implemented in the global Community Atmospheric Model (CAM) of the Community Earth System Model (CESM). The resulting model will be tested against field measurements, including the Variability of the American Monsoon System (VAMOS) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-Rex) and the Aerosol-Cloud Experiments in the North Atlantic (ACE-ENA) DOE airborne campaigns, and ultimately applied to investigate how the natural sulfate aerosol background has evolved over time. This work will also help inform future development of the DOE Energy Exascale Earth System Model (E3SM).

This project will lead to improved estimates of global aerosol loadings and hence aerosol climate effects in both the pre-industrial and the present-day atmosphere, a crucial and necessary step in improving the accuracy of regional and global climate models.