A variety of photochemical dispersion models have been developed to describe the quantitative relationships between ambient concentrations of precursor organic compounds and subsequent downwind concentrations of ozone. An important application of such models is to determine the degree of control of such organic compounds that is necessary to achieve compliance with ambient air quality standards for ozone. The method described can be used to obtain the requisite upwind NMOC measurements. This method is sort of a compromise between the continuous and GC methods. It combines cryogenic concentrations techniques used in the GC method for high sensitivity with the simple flame ionization detector (FID) for total NMOC measurements without the complex GC system necessary for species resolution. And because of the use of helium carrier gas, the FID has less response variation to various organic compounds than a conventional NMOC analyzer with direct air infusion.