The following 19 research recommendations are divided into near- (1 to 2 years), middle- (3 to 5 years), and long- (5 to 10 years) time periods. Most recommendations cut across the different topics addressed at the workshop. The recommendations emerged out of the plenary brainstorming session at the end of the workshop in which each participant present shared their thoughts on what needs to be done.
Ideally, each recommendation specifies an expected product, an approach to obtaining that product, and a summary of how the product might be used to support other research recommendations and practical applications.
This project would produce a data base of specific organic compounds and compound groups along with important properties. The data base would include Chemical Abstract Service and common names for identified compounds, references to reports of their detection, reported concentration ranges, water activities, melting point, boiling point, vapor pressures, codes indicating primary or secondary or both, codes indicating potential sources of precursors, potential quantification methods, and detection limits. The data base would be updatable as new information became available and downloadable from a central location. Queries would allow users to extract data and to place it into usable formats. This data base would be assembled from existing tables created by atmospheric organic chemistry researchers via a survey of these researchers. It would be used to identify which compounds are lacking data that need to be quantified in subsequent experiments. It could also be used by decision-makers to determine organic compounds that might result from different source emissions (John Watson).
project would provide a consistent set of reporting conventions for smog chamber
secondary organic aerosol experiments. Currently
smog chamber experiments tend to fall into two groups, those characterizing the
dynamics of aerosol formation and those emphasizing aerosol chemical speciation.
Data acquired during these experiments are not always presented in a
consistent format. Possible common
reported data might include the following information: temperature, type of
lightsource, NO2 photolysis rate, humidity, seed particle
concentration and type, chamber volume, material and surface/volume ratio,
initial and final concentrations of VOC, NO, NO2, O3 and
aerosol. If a
Evaluate methods to measure black carbon as a normalization for primary and secondary organic carbon.
Most of the SOA compounds have intermediate volatilities and therefore exist in both the gas and particulate phases in the atmosphere. Their fraction in the particulate phase depends strongly on temperature and on the concentrations of other organic PM components, and also somewhat on relative humidity. While the framework for understanding these partitioning processes exists, there is little information about the physical properties of the SOA compounds (volatility, behavior in organic and aqueous solutions, etc.). We recommend the measurement of these parameters and their dependence on temperature and composition. A variety of approaches can be used including the investigation of individual compounds, or the analysis of appropriate smog chamber measurements.
compound speciation provides the most valuable information about organic aerosol
composition, sources, and atmospheric transformation processes. The molecular
level methods usually require extraction of a sample with organic solvent(s),
followed by analysis by gas chromatography/mass spectrometry (GC/MS), GC/FTIR/MS,
GC with various detectors, HPLC/MS and other methods. Sequential extractions
with solvents of increasing polarity and liquid chromatographic separations are
frequently used prior to GC/MS analysis to simplify complex organic mixtures.
There is a need to optimize the selection of solvents and extraction procedures
to assure the integrity of less stable organic compounds, as well as a need for
development of more selective separation methods (particularly solid phase
V. Doskey, Environmental Research Division, Argonne National Laboratory)
Monoterpenes, which are emitted by vegetation, and aromatic compounds, originating from the production and consumption of petroleum fuels, are two classes of gas-phase organic compounds that have been found to produce high aerosol yields in chamber experiments. Aerosol formation events should be investigated in locations where emission rates of these precursors and levels of atmospheric oxidants are expected to be large. Monoterpene emission rates in the United States are greatest in the southeast, northeast Texas, central and northern California, the Pacific Northwest, and high elevations of the Southwest. Forested ecosystems in the southeast, northeast Texas, central California, and the southwest are likely receptors of a complex mixture of atmospheric oxidants from major urban areas. Aromatic compound emissions in Houston and Mexico City are large and produce ambient levels in air that frequently exceed 5 ppbv. These urban areas would be good locations for studies of aerosol formation from anthropogenic precursors. Field experiments should focus on measuring precursors, oxidants, and the likely products of the chemical oxidations to generate data for aerosol model evaluation. Meteorological measurements to support the chemical measurements are essential. It would be desirable to have surface sites established at the candidate locations for long-term monitoring and for conducting intensive field campaigns when, e.g., measurements from aircraft could supplement the surface observations.
Source types of particulate
carbon in the majority of field studies have not been characterized very well.
For example, in one recent source apportionment study from Los Angeles, only two
medium-duty (rather low mileage) diesel vehicles were used to collect source
samples to construct a source signature to represent diesel exhaust.
and test operational mechanisms for secondary aerosol formation for forecasting
While the description of the formation of the SOA compounds with a constant yield (e.g., 2% of the oxidized precursor) is a first step it is an oversimplification of the chemical processes leading to these products. Several reactions steps are, in general, needed for the formation of the SOA species. Development and testing of the chemical mechanisms leading to these compounds based on smog chamber work will be necessary for the efficient control of these compounds (for example for understanding the effect of NOx on the formation rates of SOA). The corresponding detailed models should be evaluated against field measurements of the concentrations of these compounds.