Air over Los Angeles: piece by piece.

Approaching Los Angeles from the sea, one is amazed at the shell of smog, ubiquitous and grim, surrounding the city Los Angeles is unlucky in locale, says Lynn M. Hildemann of Stanford University "They've got this ring of mountains that tends to hold air, and the way their prevailing winds work, pollution takes a long time to blow away."

Hildemann is part of a research team headed by Glen R. Cass of the California Institute of Technology in Pasadena that has been analyzing the air of the angels for 12 years. Their sixth study of sources of fine particulates (less than 2 micrometers in diameter) in the air focuses on cigarette smoke. It appears in the July Environmental Science & Technology.

The team worked to identify a tracer for cigarette smoke, as they had done earlier for other pollutants (SN: 7/27/91, p.60).

They found between 100 and 200 different chemicals in cigarette smoke, says Hildemann. From these, the team had to tracer that was unique to cigarette smoke, remained primarily in the particulate phase (not in the gas phase, which immediately disqualified nicotine), and wouldn't degrade quickly in the atmosphere,

Eventually, the group settled on isoalkanes and ant-isoalkanes [C.sub.29]-[C.sub.34]) found in the surface waxes of tobacco in such a form that they are distinguishable from other plant leaf waxes in the Los Angeles area.

Using the surface-wax tracer, the researchers determined that cigarette smoke contributes from 1.0 to 1.3 percent of the fine particle mass in the Los Angeles atmosphere.

"That they've identified these ambient air samples is incredible," says Douglas W. Dockery of the Harvard School of Public Health in Boston, "They're doing some really precise analysis here. Just extraordinary"