Measurements of fugitive emission using the Solar Occultation Flux (SOF) method

The SOF method is an emerging remote sensing technique based on measuring infrared intensity of solar spectra from a mobile platform (car, boat). From the infrared solar spectra, utilizing known absorption features and with a good knowledge of wind profile, the total mass of ethylene, propylene, alkanes and several other species along the path of the solar light can be retrieved. The method is today used to screen and quantify VOC emissions from industrial conglomerates down to sub-areas in individual plants. The SOF method is usually combined with mobile DOAS by which it is possible to measure also SO 2, NO2 and formaldehyde. The SOF method has been applied in several larger campaigns in both Europe and the US and in more than 70 individual plant surveys over the last 10 years. In the various campaign studies it has been found that the measured emissions obtained with SOF are 5-10 times higher than the reported emission obtained by standard calculation methods. For instance in studies in Houston, TexAQS 2006 and campaigns 2009 and 2011, it was shown that the industrial releases of alkenes for the Houston Galveston area, on average, were 10 times higher than what was reported. For alkanes the discrepancy factor was about 8