Source attribution and quantification of benzene event emissions in a Houston ship channel community based on real-time mobile monitoring of ambient air

ABSTRACT

A mobile laboratory equipped with a proton transfer reaction mass spectrometer (PTR-MS) operated in Galena Park, Texas, near the Houston Ship Channel during the Benzene and other Toxics Exposure Study (BEE-TEX). The mobile laboratory measured transient peaks of benzene of up to 37 ppb_v in the afternoon and evening of February 19, 2015. Plume reconstruction and source attribution were performed using the four-dimensional (4D) variational data assimilation technique and a three-dimensional (3D) micro-scale forward and adjoint air quality model based on mobile PTR-MS data and nearby stationary wind measurements at the Galena Park Continuous Air Monitoring Station (CAMS). The results of inverse modeling indicate that significant pipeline emissions of benzene may at least partly explain the ambient concentration peaks observed in Galena Park during BEE-TEX. Total pipeline emissions of benzene inferred within the 16-km² model domain exceeded point source emissions by roughly a factor of 2 during the observational episode. Besides pipeline leaks, the model also inferred significant benzene emissions from marine, railcar, and tank truck loading/unloading facilities, consistent with the presence of a tanker and barges in the Kinder Morgan port terminal during the afternoon and evening of February 19. Total domain emissions of benzene exceeded corresponding 2011 National Emissions Inventory (NEI) estimates by a factor of 2–6.

Implications: Port operations involving petrochemicals may significantly increase emissions of air toxics from the transfer and storage of materials. Pipeline leaks, in particular, can lead to sporadic emissions greater than in emission inventories, resulting in higher ambient concentrations than are sampled by the existing monitoring network. The use of updated methods for ambient monitoring and source attribution in real time should be encouraged as an alternative to expanding the conventional monitoring network.

Additional information

Funding

BEE-TEX was funded by the Fish and Wildlife Service of the U. S. Department of the Interior through Harris County, Texas.

Notes on contributors

Eduardo P. Olaguer

Eduardo P. Olaguer is the program director for Air Quality Science at the Houston Advanced Research Center in The Woodlands, TX.

Matthew H. Erickson

Matthew H. Erickson was until recently a postdoctoral research scientist at the Houston Advanced Research Center in The Woodlands, TX. He is now at the University of Houston.

Asanga Wijesinghe

Asanga Wijesinghe and Bradley S. Neish are research associates at the Houston Advanced Research Center in The Woodlands, TX.

Bradley S. Neish

Asanga Wijesinghe and Bradley S. Neish are research associates at the Houston Advanced Research Center in The Woodlands, TX.