An investigation of the relationship between total non-methane organic carbon and the sum of speciated hydrocarbons and carbonyls measured by standard GC/FID: measurements in the Los Angeles air basin

Simultaneous measurements of total non-methane organic carbon (TNMOC) and speciated volatile organic compounds (VOCs) were made with an instrument described in a companion paper. The ratio of the TNMOC to the speciated VOCs measurement indicates the “excess” VOCs that not detected by routine monitoring techniques. Measurements of ambient air were made in West Los Angeles, Burbank and Azusa, CA. Primary pollution sources are gasoline vapor and diesel exhaust were tested as well. These primary sources are, not surprisingly, measured well by the standard speciated analysis, with averages of 5–13% “excess” VOCs. The Burbank site, which is surrounded by freeways and light industry, had only 10–15% excess VOCs, as did UCLA during winter when there is minimal photochemistry. In contrast, averages of between 20% and 45% of the TNMOC was unmeasured by the standard chromatography at the UCLA and Azusa sites during summer. The dominant source of the unmeasured VOCs may be air that has been aged for more than 12 h, possibly for a day or more.