SOUTHERN CALIFORNIA AIR-QUALITY STUDY - A SEARCH FOR METHYL NITRATE

Methyl nitrate, CH3ONO2, was measured by electron capture gas chromatography (EC-GC) under conditions which allowed resolution of methyl nitrate, PAN, and several chlorinated hydrocarbons. Calibrations involved both EC-GC and NOx chemiluminescence and were in agreement with independent calibrations involving i.r. spectroscopy. The rate constant for photolysis of methyl nitrate in sunlight was < 2.3 × 10-6 s-1. Detection limits of field instruments were 0.1-0.4 ppb. Some 3000 EC-GC chromatograms grams of ambient air recorded between June and December 1987, during the Southern California Air Quality Study (SCAQS) at up to nine Southern California locations yielded only seven possible, but unlikely observations of methyl nitrate. Thus, methyl nitrate was only a minor component among nitrogenous air pollutants during SCAQS. The measured CH3ONO2/PAN ratios of <0.003-0.2 during SCAQS are discussed in terms of available kinetic data for PAN unimolecular decomposition (a major source of methyl nitrate), PAN thermal decomposition and CH3ONO2 photolysis. © 1990.