Misunderstanding what must be reported

One of the most common errors is failing to understand which pollutants must be included. Under the AERR, states and delegated agencies must report annual emissions of criteria air pollutants (CAPs) including sulfur dioxide, nitrogen oxides, volatile organic compounds, carbon monoxide, lead, particulate matter (PM₂.₅ and PM₁₀), and ammonia. These pollutants drive national air quality planning and modeling.

Using incorrect or incomplete emission calculations

Facilities often make calculation errors when converting raw activity data into emissions. Many rely on outdated emission factors or incomplete process data. EPA urges states and regulated entities to use standardized estimation guidance from the Emission Inventory Improvement Program (EIIP) whenever possible. But companies may choose default factors without confirming they apply to the specific process, control efficiency, fuel type, or measurement method.

Under EPA’s proposed AERR revisions, if approved, the agency will require more detailed stack information such as release point coordinates, exhaust parameters, control device data, and stack test results. Failure to collect these details early can lead to rushed estimates or missing data.

Misreporting source categories

Another major issue is misidentifying emission sources. AERR distinguishes between point, nonpoint, mobile, and portable sources. Mislabeling a source may cause a facility to submit incomplete inventories or fail to meet the required reporting frequency. For example, point sources often require annual reporting, while nonpoint sources may follow triennial schedules.

Similarly, GHGRP reporting is broken into numerous subparts that define equipment types, fuel suppliers, industrial processes, and CO₂ injection activities. Companies sometimes choose the wrong subpart or assume their process is exempt, leading to incomplete data submissions.

Incorrect use of thresholds and applicability

Both AERR and GHGRP have emission-based thresholds. Companies frequently make errors when determining:

• Whether they meet AERR Type A point source criteria;
• Whether they exceed GHGRP reporting thresholds (generally 25,000 metric tons CO₂e annually); and
• Whether HAP emissions exceed thresholds when HAP reporting is required by a state.

These mistakes usually occur when internal data systems lack consistent tracking or when actual emissions deviate from potential to emit estimates used in permitting.

Missing documentation and recordkeeping

EPA requires extensive documentation for emissions calculations, monitoring methods, stack tests, control equipment operation, and assumptions. GHGRP rules include detailed monitoring, QA/QC, missing data, and record retention requirements. Under proposed AERR rules, companies will also need to submit performance test and evaluation data. Missing or incomplete records often lead to rejected inventories.

Failing to track regulatory updates

Both AERR and GHGRP are undergoing major revisions. EPA’s proposed AERR updates aim to convert some triennial reporting to annual schedules, add HAP reporting, expand mobile source requirements, and require more detailed facility level data. Meanwhile, GHGRP is facing proposed cuts that eliminate reporting requirements for many source categories while delaying petroleum and natural gas reporting until 2034.

Companies that rely on outdated guidance or assume reporting rules remain static at risk of major compliance failures.

Improving AEI quality and compliance

Avoiding common errors begins with three fundamentals:

• Use current regulatory guidance, emission factors, and calculation tools;
• Maintain complete process data, stack test records, and QA/QC documentation; and
• Assign knowledgeable staff to track AERR, GHGRP, and state-level changes.

Key to Remember: Accurate air emissions inventories play a crucial role in protecting public health, supporting air quality regulation, and demonstrating corporate responsibility. By understanding the most common pitfalls, companies can improve compliance and reduce costly reporting errors.