Research Projects

Project at a Glance

Project Status: complete

Report Published February 1992:

Title: Analysis of the ambient VOC data collected in the Southern California Air Quality Study.

Principal Investigator / Author(s): Lurmann, Frederick W

Contractor: Sonoma Technology, Inc

Contract Number: A832-130


Research Program Area: Atmospheric Processes


Abstract:

A detailed analysis of ambient hydrocarbon and carbonyl data collected in the Southern California Air Quality Study (SCAQS) was undertaken to develop an improved understanding of non methane organic compounds (NMOC) in California's South Coast Air Basin (SoCAB). The SCAQS data set, which was the most extensive ever collected in the SoCAB, was used to :

1. Characterize the spatial and temporal patterns of total NMOC concentrations and NMOC/Nox ratios;
2. Characterize the spatial and temporal patterns of individual organic compounds;
3. Assess the consistency between ambient and emissions inventory NMOC; and
4. Assess the extent of NMOC oxidation and carbonyl compound formation occurring in the atmosphere.

The first major finding of the study was that NMOC composition and NMOC/Nox ratios were fairly similar throughout the basin. The spatial, temporal, and day to day variations in the contributions of the major organic compound groups and the abundant organic species to NMOC were smaller than expected. However, the total NMOC concentrations have significant day to day and seasonal variations, which are undoubtably controlled by meteorology, and they have significant spatial variation within the basin due to the nonuniformity of emission rates and the effects of transport.

The second major finding was that the N MOC/Nox and CO/Nox ratios in the ambient data and emissions inventories were inconsistent and there were also discrepancies between the organic speciation of the inventories and ambient data. The inconsistencies in the NMOC/Nox and CO/Nox ratios strongly suggest current inventories underestimate NMOC and CO emissions from motor vehicles. Problems with the emissions from other types of sources may also contribute to emissions from specific source types to identify those sources with these data.

The third finding was that there appears to be a large amount of carbonyl species formation in the urban atmosphere from photo oxidation of hydrocarbons. The photochemical source of C1-C4 carbonyl compound is probably larger than the emissions source. C4+ carbonyl compounds were more abundant than expected and the sources of these higher carbonyl compounds were not identified.


 

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