In order to address questions concerning climate forcing by anthropogenic aerosol particles (Charlson et al., 1992; Penner et al., 1994), ESRL/GMD is continually making measurements at a variety of regional aerosol monitoring stations. Two of the stations are in rural continental locations that are frequently perturbed by anthropogenic aerosols. A third station is in a marine location which may not only be perturbed by anthropogenic emissions from the US, but may also be impacted by dust and pollutants transported across the Pacific Ocean. The above links describe the site characteristics, and their current status. Each station operates in close collaboration with a local university or government agency, which provides on-site support for the measurements.

The scientific questions that define the context of the measurements at these sites include

Clearly, ground-based measurements at a few sites will provide answers to only a few of these questions. Recognizing this, the strategy of the ESRL/GMD regional aerosol measurement program is

The measurements will provide ground-truth for satellite measurements and global models, as well as key aerosol parameters for global-scale models (e.g., scattering efficiency of sulfate particles, hemispheric backscattering fraction). An important aspect of this strategy is that the chemical measurements are linked to the physical measurements through simultaneous, size-selective sampling and thermal analysis, which allows the observed aerosol properties to be connected to the atmospheric cycles of specific chemical species.

When the sites are fully operational, continuous measurements will include the total particle number concentration (Ntot), and components of the aerosol extinction coefficient at one or more wavelengths (total scattering (ssp), backwards hemispheric scattering (sbsp), and absorption (sap)). Size-resolved impactor and filter samples (submicrometer and supermicrometer size fractions) will be obtained for gravimetric and chemical (ion chromatographic) analyses. All size-selective sampling, as well as the measurements of the components of the aerosol extinction coefficient, will be performed at a low, controlled relative humidity (<40%) to eliminate confounding effects due to changes in ambient relative humidity.

Summary of Measurements at Active Regional Stations

Category Perturbed Continental Perturbed Continental Perturbed Marine
Location Bondville, Illinois, USA Lamont, Oklahoma, USA Trinidad Head, California, USA
Designator BND SGP THD
Latitude +40.05 +36.61 +40.80
Longitude +88.37 +97.49 +124.16
Elevation (m) 230 315 107
Collaborating Institute University of Illinois,
Illinois State Water Survey
Status Operational July, 1994 Operational July, 1996 Operational April, 2002
Sample RH RH<40% RH<40% RH<40%
Sample Size Fractions D<1 µm, 10<D<1 µm D<1 µm, 10<D<1 µm D<1 µm, 10<D<1 µm
Optical measurements ssp(3l), sap(1l), sbsp(3l) ssp(3l), sap(1l), sbsp(3l),f(RH) ssp(3l), sap(1l), sbsp(3l),f(RH)
Microphysical measurements Ntot Ntot Ntot
Chemical measurements) major ions, mass major ions, mass major ions, mass