Quantification of Ethylene Emissions from Petrochemical Industries in Houston, Texas: Large Disagreements with Emission Inventories

Reactive alkenes from petrochemical industries are known to play an important role in the formation of ozone in Houston, Texas. In this work we developed a fast-response detector of ethylene based on laser photo-acoustic spectroscopy (LPAS) and used it onboard the NOAA WP-3D aircraft to measure ethylene in industrial plumes around Houston in the summer of 2006. The new LPAS instrument was evaluated by comparison with measurement results from a whole air sampler (WAS), and the two measurements agreed within the combined measurement uncertainties. Emission fluxes of ethylene were estimated (1) by integrating the measured ethylene concentration across the width of industrial plumes, (2) by multiplying the concentration with the orthogonal wind speed measured from the aircraft, and (3) by assuming that the emissions are homogeneously distributed across the height of the boundary layer as estimated using aircraft ascents and descents. The estimated ethylene fluxes were compared with the results of simultaneous Solar Occultation Flux (SOF) measurements inside a mobile laboratory, and the agreement was within a factor of 2. Previous work had indicated that current inventories underestimate alkene emissions in Houston by 1-2 orders of magnitude. These findings were confirmed both by the aircraft and SOF measurements. The measured mixing ratios of ethylene were compared between the results from 2006 and an earlier mission in 2000. In contrast with CO and acetylene, which are predominantly from traffic, ethylene and its photoproduct formaldehyde showed significant decreases between 2000 and 2006.