PMEL Programs and Plans
Accomplishments in FY 98 and Plans for FY 99

Atmospheric Chemistry Project

Figures (a) Climatic effects of tropospheric aerosol, and (b) locatons of PMEL aerosol field studies.

Atmospheric Chemistry Program

Accomplishments in FY 98

PMEL plays a lead role in the planning and execution of the Aerosol Characterization Experiments (ACE) of the International Global Atmospheric Chemistry Project (IGAC). ACE 1 took place in the remote marine atmosphere south of Australia in order to characterize aerosol properties in a minimally polluted environment. The ACE 1 Special Section of the Journal of Geophysical Research was published in FY 98 with papers describing the chemical, physical, radiative, and cloud nucleating properties of aerosols over the remote ocean and the controlling processes. These data currently are being used to develop aerosol process models.

PMEL ACE 1 results include the following: Submicron sea salt can be the most significant component in remote oceanic regions in terms of both aerosol chemical composition and light scattering (Quinn et al., J. Geophys. Res., 1998). This is a new understanding of the importance of a natural background aerosol in determining the optical properties over large regions of the globe. Local closure experiments where measured and modeled aerosol optical properties were compared showed that we are able to accurately model the optical properties of relatively simple marine aerosol (Quinn and Coffman, J. Geophys. Res., 1998). The next step is to adapt our models to more complex aerosol found in continentally-influenced atmospheres. In addition, measurements of the aerosol number size distribution identified the modal characteristics needed as input for radiative transfer models (Bates et al., J. Geophys. Res., 1998).

ACE 2 took place in the northeast Atlantic off the coast of Portugal in the summer of 1997 to determine the impact of the European pollution plume on marine aerosol. Much of the PMEL data analysis was accomplished in FY 98. Results will be reported in the ACE 2 Special Section of Tellus scheduled for publication in January of 2000. PMEL results indicate that relative to the ACE 1 aerosol, aerosol in the ACE 2 region is impacted by continental sources even during periods of marine flow. The impact was seen in higher sulfate aerosol concentrations, a more pronounced wavelength dependence in the aerosol scattering coefficient, and higher single scattering albedos due to larger aerosol absorption coefficients.

Also during FY 98 shipboard aerosol data collected by PMEL over the past 5 years were used to test the output of a coupled chemical transport/radiative transfer model. It was shown that the model severely neglects the importance of submicron sea salt in terms of its mass concentration and optical depth. Hence, the measurements were able to improve the accuracy of the model in estimating extinction due to background marine aerosol (Quinn and Coffman, J. Geophys Res., 1999).

Atomspheric Chemistry Program

Plans for FY 99

• Participate in an Atlantic Ocean and Indian Ocean (INDOEX) field experiment to characterize the aerosol properties and determine the controlling processes in this region.
• Continue long-term monitoring of aerosol chemical composition at the NOAA Aerosol Regional Monitoring Network of stations at Barrow, AK, Bondville, IL, and Sable Island, NS.
• Initiate monitoring of aerosol chemical composition at the DOE ARM site located at Southern Great Plains, OK.
• Continue the organization of ACE Asia. (Planning meeting on Cheju Island, Korea, November, 1998; Scientific Steering Committee meeting, May, 1999).
• Finish ACE 2 data analysis, attend ACE 2 data workshop, and prepare manuscripts for publication in the ACE 2 Tellus Special Section.
• Complete manuscript describing aerosol chemical composition for marine, perturbed marine, clean continental, and polluted continental air masses.
• Complete data analysis and manuscripts describing region of higher aerosol backscatter in the central Equatorial North Pacific.