GACP Projects
July 17, 2000
SECOND YEAR GACP ACCOMPLISHMENT REPORT
Submitted to
National Aeronautics and Space Administration
Project title: Distribution and Properties of Carbonaceous aerosols: An Analysis of Existing Data
P.I.: Tihomir NOVAKOV
Institution: Lawrence Berkeley National Laboratory
Environmental Energy Technologies Division
MS - 73
One Cyclotron Road
Berkeley, CA 94720
Phone: (510) 486-5319; fax: (510) 486-4733; E-mail: tnovakov@lbl.gov
ABSTRACT: The objective of this three year project is to compile, summarize, analyze, and estimate the uncertainties in past field measurements of total (TC), organic (OC) and black carbon (BC), as well as, the physical and chemical properties of this aerosol component. The values of reported concentrations may be influenced by method and sampling dependent artifacts which, if unaccounted for, may either over- or underestimate the actual concentrations. Consequently, evaluation of uncertainties is important because these may be large enough to render some of the reported concentrations unacceptable for achieving either mass or radiative closure. This activity will identify global regions where useful data exists and regions where there is a severe lack of data, and provide a needed level of quality assurance of the existing field data. The secondary objective is to examine the changes that occurred over the past 20 years in regional use of fuels whose combustion are the principal sources of anthropogenic carbonaceous aerosols. The purpose is to derive surrogates for changing aerosol concentration that can be used as indicators of geographic regions where aerosol forcing might be detectable from space-based observations.
ACCOMPLISHMENTS
Specific research objectives, related to the objectives of GACP, are to critically evaluate existing data on concentrations and properties of natural and anthropogenic carbonaceous aerosols. The project has the following tasks:
- To compile and summarize the data on mass concentrations (and properties) of total (TC), organic (OC) and black carbon (BC) measured in different parts of the world over the past two decades. These data are complemented with concurrently measured data on aerosol mass and concentrations of inorganic species whenever available.
- To estimate the uncertainties in the reported data. These data may be influenced by method and sampling dependent artifacts which, if unaccounted for, may either over- or underestimate the actual concentrations. 3)
- To empirically analyze the data (obtained from the above tasks) to infer the global distributions, geographic and temporal trends of carbonaceous aerosols.
- Examination of regional emissions and their influence on composition and concentrations of ambient carbonaceous aerosols especially over the oceans.
During the FIRST year we have assembled and compiled surface data obtained from approximately 1978 at 197 locations and sites worldwide. These were subdivided into URBAN, RURAL, MARINE and REMOTE sites. For each site the data on concentrations and methods of measurements were compiled.
SECOND YEAR PROGRESS
During the SECOND project year this activity was extended by including the data from the literature that was either unavailable or not yet published during the first year of the project. Additionally, results of (1) aircraft measurements (including the most recent measurements, such as INDOEX) and (2) temporal concentration trends are now included in the data survey. For each site the following information has been compiled: Year and month of measurements, mass concentrations of all reported aerosol species, sample type, particle size cuts, analytical methods, corrections (if any) reported by the authors, and complete reference list. The latest version of this document (compendium) will be available for distribution at the forthcoming GACP Science Team Meeting.
Information about specific properties of carbonaceous aerosols such as the water-soluble organic carbon fraction, altitude dependence of aerosol species concentrations, in-cloud and interstitial black carbon concentrations have been compiled and presented separately from the mass concentration data.
During the second year we have initiated two new activities. The first concerns the comparison of organic and black carbon ratios measured over the oceans with these ratios determined in the suspected source regions. The second, is aimed at assembling the historical data on particularly black carbon concentrations either directly measured, inferred from fuel consumption data, or from indirect measurements employed in the past air quality monitoring activities.
Finally, an analysis of the methods and associated uncertainties in black carbon determinations is under way. The objective is to reconcile large differences in the reported mass absorption coefficients (cross sections). These may differ by a factor of five even when apparently similar measurement methods are used.
3rd YEAR STATEMENT OF WORK
Research plan for the THIRD year of our participation in GACP focuses on data evaluation with the objective of estimating the uncertainties in the reported organic and black carbon data. We will also continue with the empirical data analyzes (initiated during the second year) to infer the global distributions, geographic and temporal trends of carbonaceous aerosols. Complete the final version of the data survey/compendium manuscript that will include all information referred to above
GACP BIBLIOGRAPHY
Origin of carbonaceous aerosols over the Tropical Indian Ocean: Biomass or fossil?, T. Novakov, V. Ramanathan, M. O. Andreae, O. Mayol, T. W. Kirchstetter, and R. Gabriel, Submitted to Geophysical Research Letters.
