Air pollution lab reports from Los Angeles

THE FRANKLIN INSTITUTE LABORATORIES FOR RESEARCH AND DEVELOPMENT NICOL H. SMITH, DIRECTOR AIR

POLLUTION LAR REPORTS FROM LOS ANGELES BY

EDGAR R STEPHENS*

One of the goals of research on the Los Angeles smog problem has been to find an explanation for the high concentrations of ozone during It has been shown in the laboratory1 that high consmog attacks. centrations of ozone are produced by reactions between nitrogen dioxide and organic compounds in artificial sunlight. Franklin Institute research has demonstrated that the ozone concentration can build up to high levels because of the simultaneous formation of Compound X, a chemical identified as peroxyacyl nitrite. INLET

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This is a very Schematic of the ultra-long-path infrared absorption cell and spectrometer. versatile and powerful analytical tool, and provides the only method for detecting and identifying the unsuspected or unknown gaseous constituents of smog as found in Los Angeles -especially unstable chemical compounds like peroxyacyl nitrite. * Dr. Stephens, Leader of the Laboratories’ Air Pollution Research Group, and Mr. Philip Hanst, Senior Research Chemist of that Group, have been stationed in Los Angeles since The mobile lab August, 19.56, in charge of the Laboratories’ Mobile Air Pollution Laboratory. was designed and built by the staff to extend research studies that began, and are still going on, in the Institute’s Philadelphia laboratories. Both phases of this project are supported by the American Petroleum Institute. r JOUR. FRANKLIN INST., Vol. 260, p. 140 (1955). 349

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The role of peroxyacyl nitrite is as follows: Nitrogen dioxide, a man-made pollutant, decomposes in sunlight to form nitric oxide and The atomic oxygen combines with the normal oxygen atomic oxygen. But the nitric oxide is removed from of the atmosphere to form ozone. the scene by reacting with organic pollutants to form the peroxyacyl nitrite (Compound X). If the nitric oxide were not removed, it would react with the ozone ; thus it would prohibit the ozone from building up to the high concentrations found in smog. To complete the cycle, the peroxyacyl nitrite itself is decomposed slowly by sunlight to produce nitrogen dioxide, the substance which began the cycle. Thus the nitrogen dioxide is used over and over again to produce ozone. Using an early model of the long-path infrared absorption cell in our Philadelphia lab, we studied nitrogen dioxide reactions with organic compounds (synthetic smog) and discovered that the peroxyacyl nitrite

Infrared spectrum of peroxyacyl nitrite prepared from diacetyl and NOI.

was a major product in addition to ozone. We also found that this compound, along with ozone, is formed when auto exhaust is diluted with air and irradiated with artificial sunlight. The only way to check the prediction that peroxyacyl nitrite would be found in actual smog was to take a long-path cell to Los Angeles. Consequently a new cell was built, installed in the mobile laboratory, and taken to the West Coast. The prediction has been confirmed ; it has been found that peroxyacyl nitrite is formed simultaneously with ozone in the atmosphere of the Los Angeles basin when smog is formed. The infrared absorption spectrum of this unusual compound as prepared in the laboratory is shown in the illustration. It was identified in the atmosphere in Los Angeles by this characteristic absorption spectrum.