Atmospheric Aerosols and Climate Change: Monitoring Studies
A Component of the NOAA OGP Aerosol-Climate Program
Presented by John Ogren, NOAA/CMDL
September 15, 1995
The monitoring studies described below must be considered as one component of an integrated set of process/closure, monitoring, and modelling studies. The ultimate goal of this integrated set of studies is to incorporate aerosols in three-dimensional chemical transport models that can be used to calculate the direct and indirect radiative forcing by the particles. Global climate models that explicitly incorporate the aerosol forcings would subsequently be used to calculate the response of the climate to the combined anthropogenic forcings, particularly from aerosols and greenhouse gases, in order to assist policy-makers in formulating measures to minimize the effects of the changing climate on human society. The objective of the monitoring component is to quantify the spatial and seasonal distributions, as well as trends, of the aerosol properties required to calculate and test radiative forcing in regional and global climate models, and to link those properties to the spatial distributions of the important chemical components of the aerosol.
What were the major research activities done?
The monitoring program involves research groups at NOAA/CMDL, NOAA/PMEL, University of Washington (UW), and University of Illinois at Urbana-Champaign (UIUC). Measurements were obtained of the chemical, microphysical, and radiative properties of aerosol particles at sites with considerable and minimal anthropogenic aerosol concentrations, at both continental and marine locations. During FY95, routine determination of gravimetric mass concentration was added to the suite of measurements, and the fourth station in the network (Niwot Ridge) was deployed with the same suite of measurements as at the other three stations. Table 1 lists the stations and the specific measurements obtained at each site. The major findings of the measurement program to date concern the relationships among the chemical, microphysical, and radiative properties of aerosol particles. Highlights include:
An additional function of the University participants is to serve as a test-bed for aerosol measurement method development for the NOAA aerosol network and for intensive campaigns such as ICAC/ACE-1 and ACE-2. In FY 1995, method development activities included development of humidity-controlled gravimetric techniques for weighing filter samples from low concentration environments, humidity-controlled sampling systems for determining the dependence on aerosol light scattering on relative humidity, studies of vertical pipe inlet efficiency, and improvements in filter carousel design. Extensive laboratory testing of the calibration and instrumental noise of the integrating nephelometer (used to directly measure the scattering and back scattering coefficients) has been done to determine the absolute accuracy of the atmospheric data.
What is the specific payoff to scientific understanding?
These data mark the beginning of the development of a record of the variability of aerosol chemical, microphysical, and optical properties at sites upwind, within, and downwind of the continental U.S., which is specifically designed as input for global climate models that include the radiative forcing by tropospheric aerosols.
Who were benefitted by the improved understanding of the environmental issue?
Aerosol forcing of climate has been identified (e.g., by IPCC) as one of the major factors contributing to uncertainties of anthropogenically-induced climate change. Reducing these uncertainties will benefit the populace as a whole by allowing more informed policy decisions concerning the societal response to future climate change.
What are the major research tasks and goals?
What is the hoped-for specific payoff to scientific understanding?
The specific payoff is a reduction in the uncertainties of the climate forcing by anthropogenic aerosols to a point where they no longer limit estimates of the overall forcing of climate by anthropogenic activities.
A summary of OGP funding for the NOAA aerosol/climate monitoring program is shown in Table 2. FY95 was an anomalous year for the aerosol monitoring budget, because the transfer of the contributions from UW and UIUC from open-access to "core" funding was not accompanied by full funding for those contributions. Support was shifted from the CMDL component to UW and UIUC for FY95, in order to keep the overall program afloat at a subsistence level. The FY96 budget request provides funding for UW and UIUC at a level sufficient to support CMDL and PMEL monitoring operations at the Cheeka Peak and Bondville sites, as well as an academic research program tightly focussed on aerosol forcing of climate. The increase requested for PMEL covers the costs of chemical sampling at additional sites as the network has been established, as well as the addition of gravimetric mass to the routine suite of chemical measurements. The amount requested for FY96 will allow monitoring at four sites of a comprehensive suite of aerosol chemical, microphysical, and radiative properties required for evaluation of climate forcing by anthropogenic aerosols. Reductions of the number of stations or of the suite of measurements will be necessary if budget limitations prevent funding at the level requested.
Anderson, T. L., Charlson, R. J., White, W. H. and McMurry, P. H., Comment on "Light scattering and cloud condensation nucleus activity of sulfate aerosol measured over the northeast Atlantic Ocean" by D.A. Hegg et al., J. Geophys. Res. 99, 25947-25949, 1994.
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McInnes, L. M., Quinn, P. K., Covert, D. S. and Anderson, T. L., Gravimetric analysis, ionic composition, and associated water mass of the marine aerosol, Atmos. Environ., submitted Mar 95.