Emissions Inventories for the Downstream Oil & Gas Sector: What are the Known Unknowns and why are They Important?

Characterizing emissions from large facilities such as refineries and large petrochemical plants involves several current challenges to better constraining key uncertainties. It is important to understand the path to protecting public health and the environment that starts with the identification of an air quality epidemiological impact, through development of emission factors, compilation of emissions inventories, different types of modelling, and culminating in the development of environmental regulation. Inaccurate information along this technical chain can ultimately lead to ineffective regulation that may be unnecessarily costly to operators and other stakeholders. 

Operators and regulators need a fuller understanding of uncertainty and where errors can occur, e.g., within emissions inventories or within modelling results. For instance, a detailed temporal resolution of emissions is especially important for modelling short-duration events such as summer ozone exceedances. But in the absence of more detailed information, photochemical modellers often have to apply default temporal profiles to reported annual totals of emissions. This process may well omit review by operators and inventory experts who have pertinent subject knowledge. Other issues include the use of unrepresentative emission factors, default stack parameters or inaccurate release point coordinates that can lead to invalid assessments of public health risks from air toxic emissions. 

As has happened in the past, developments in one oil & gas sector can ultimately percolate through to impact the whole industry. Strong public awareness in the US and in Europe of recent upstream unconventional onshore oil and gas development has driven academic research and increased regulators awareness of so-called fat-tails or super-emitters, e.g., short-duration events that generate large amounts of emissions. As the penetration of cheap citizen monitoring continues, scrutiny of larger, longer-established oil & gas facilities will increase and operators will need to be able to promptly respond with defensible documentation of effective and proportionate operational and environmental monitoring programmes. 

While emissions inventories already prioritise the use of plant or point specific data reported by industry over the traditional emission factor times activity approach, more detailed operator data could significantly refine our understanding of emissions inventories, thus providing a key contribution as environmental regulations are developed and reviewed by stakeholders. However, it is crucial that industry data always be thoroughly reviewed for quality in order to assure the public of its credibility.