Non-methane hydrocarbon and organic gas emissions measured by a single instrument. Surrogate group of compounds identified for FTIR equivalent to FID NMHC. Oxygenated compounds included for FTIR measurement of real time NMOG emissions. Thresholds for including surrogates in spectral analysis developed to maximize S/N. Reduces noise in NMHC when methane is high and allows real time NMOG measurement.