An assessment of emission event trends within the Greater Houston area during 2003-2013

Emission events are upsets (unavoidable breakdowns in process or operation) or unscheduled maintenance, startup, or shutdown activities within industrial facilities that can release large amounts of pollutants for several hours or days, potentially causing air quality to exceed standards established to protect the environment and human health. The Greater Houston area is home to the largest petrochemical complexes in the United States, so the likelihood of emission events is higher in this area than in other areas in the nation. Notable emission events in the Greater Houston area have caused unexpected explosions, fires, and releases of toxic chemicals, which have killed workers and triggered various health issues among nearby communities. Understanding how to minimize these emission events can help protect the health of Houstonians. In this study, we analyzed emission event data for the Greater Houston area extracted from the Texas Commission on Environmental Quality (TCEQ) emission event database during 2003-2013 for criteria and other selected pollutants to identify annual and seasonal trends and industrial classification patterns. We evaluated 7273 emission events and found that total event incidents and releases from nitrogen oxides (NOX), carbon monoxide (CO), and sulfur dioxide (SO2) have generally decreased from 2003 to 2013, whereas particulate matter (PM) event emissions have generally increased during this period. Our seasonal analyses demonstrated that emission events were more likely to occur during winter for several pollutants. We also found that emission events were mainly generated from the chemical manufacturing and petroleum and coal products manufacturing industries. In addition, we found strong interrelationships between different pairs of pollutants during these emission events. We compared these results against regulatory policy and found potential gaps within the state regulations and TCEQ emission event database explaining our findings, and we provided recommendations on closing these gaps. Our study could drive policy change to lower emission events in the Greater Houston area, potentially improving air quality and reducing the health impacts from these events.