Importance of Correct Data for Emission Inventories
January 25, 2018

Oil and gas companies prepare air emission inventories for several reasons. These include compliance with regulatory requirements and company internal policies. Emission inventories for oil and gas operations are used to determine emissions from venting sources, fugitive sources and combustion sources. These can be based on potential to emit (PTE) emissions (as used for air permits) or for actual emissions based on operations during a selected period. Direct measurement, engine emission stack testing, emission factors and process simulators are used to quantify emissions.


Emission inventories are important because these records impact air permit types, compliance costs and are used by governmental agencies (EPA, State environmental regulators) to verify compliance and to determine if new regulations are needed. Using accurate data inputs is vital.

Below is a general description of the emission inventory process with some tips to help ensure the correct data is gathered.

Air emission inventories are used to prepare:

  1. Air permit applications – new facilities and modifications to existing facilities.
  2. Criteria pollutants and hazardous air pollutants (HAPs) emissions reports
  3. Greenhouse gas (GHG) reports to EPA and certain States (e.g., California) and for voluntary reporting programs.
  4. Annual reports to regulatory agencies (e.g., NSPS OOOO and OOOOa)

The types of data used for emission inventories can be grouped as:

  1. DESCRIPTIVE data – includes data that are constants or nearly constant and are used as inputs to emission calculation equations and models. Descriptive data includes operating parameters (pressure, temperature), equipment make/model/rating, fuel type, dates of construction and installation, expected throughputs, expected flare/venting volumes, capacities, vent/stack/exhaust dimensions, flash gas analyses, sales/fuel gas analyses, etc.
  2. ACTIVITY data – used for actual emissions calculation for a specified period (typically for a calendar year). This data includes actual natural gas, crude oil, produced water throughput; equipment runtime; amount of fuel used; volumes flared or vented – routine and upset volumes.

Sources for descriptive and activity data are:

  1. Field site visits to gather process and equipment data from existing facilities.
  2. Company operations and engineering departments engineering consultants
  3. Equipment suppliers’ product specification data

 Reasons to use a system that gathers accurate, correct and complete data include.  

  1. Ensure all emission sources and required data are included in the inventory.
  2. Obtain and use correct inputs for calculations.
  3. Gather the data once to limit multiple iterations for data gathering, calculations and document preparation.  Changes to the data used after calculations, application forms and reports are completed or already underway adds to the cost.
  4. Accurate data ensures that the emission controls ordered and used are appropriately designed and sized.
    1. Direct measurement data (e.g, storage tank vent gas IQR) assists with correct design and sizing of VRUs and enclosed vapor combustors (VCU).
    2. Engine emission stack testing data can help ensure regulatory limits are met.
  5. Calculate the correct PTE emissions to obtain the appropriate type of air permit (minor source or major source).
  6. Ensure correct fees are paid for annual emission inventories.
    1. Facilities with major source air permits (e.g., Title V) are required to report actual annual emissions to State permitting agencies.
    2. Fees are assessed based on the reported annual total criteria pollutants and possibly for HAPs emissions.
    3. The reporter will generally pay air pollutant fees based on a dollar per ton of emissions reported.

System for Gathering Emission Inventory Data

  1. Create a form to gather and record descriptive data needed.
    1. Use one form that covers multiple inventory types (e.g., air permit applications criteria pollutants, HAP, GHG annual reports) that are expected for the company’s operations.
    2. Attach to the form relevant analytical and product data sheets that are needed.
  2. For existing facilities, complete the descriptive data collection form during a site visit with onsite data that is available. Supplement site visit data with data available from company operations/engineering departments and/or equipment vendors.
  3. New (not constructed) facility descriptive data can be supplied by a combination of company operations/engineering departments and equipment vendors. Site visits to facilities can be conducted to verify data for actual operating parameters and equipment installed.
  4. Take digital pictures of the facility, equipment, emission exhausts/stacks/vents, equipment name plates, emission control equipment, etc. Consider using video with audio narration to record pertinent data for the facility and equipment.
  5. For the location of the facility, the latitude and longitude (use 5 decimals) used is generally the front gate.
    1. If air dispersion modeling (e.g., larger major sources and nonattainment areas) will be required, then the latitude and longitude of each emission exhaust stack will be needed.
    2. For the NSPS OOOOa Compliance and Emissions Data Reporting Interface (CEDRI) annual reports, the need latitude and longitude of each storage tank and well to 5 decimals.
  6. For annual emission inventory reports, prepare and use a form (paper or electronic) to record actual operating ACTIVITY data for each of the emission sources at the facility. Daily records are best to ensure complete data for the reporting period. Conduct a quality check of data gathered on a quarterly basis.

For more details on air emission inventories see HY-BON/EDI blog topic at: Oil and Gas Air Emission Inventories

Collect the Correct Data and Stay in Compliance

HY-BON/EDI offers air emission inventory services for oil and gas operators as a part of our IQR Emissions Survey services. Our experienced IQR team members are ready for the following:

  1. Gather descriptive data during facility site surveys and by working with your technical representatives. The data gathered is supplied to the client in completed spreadsheet forms.
  2. Prepare spreadsheet forms to collect activity data for emission calculations.
  3. Calculate emissions based on data supplied.

HY-BON/EDI can also assist your company with NSPS OOOO and OOOOa compliance. Our thorough understanding of oil and gas processes and expertise with storage tank emission controls (VRUs, VRTs, VCUs) and leak monitoring makes us a leader in providing certainty to your compliance needs.

Our IQR Emissions Services (LDAR) services include fugitive leak monitoring that meets NSPS OOOOa requirements. Our IQR services can also assist with storage tank emissions measurement and emission controls selection for your facility.

Contact us today #-hbX/B\J$fZ]#[=?ujiGTdW3zg and #-hbX/B\J$fZ9s*j]#[yiUHLJ%VRcVIFWtX.