6.4 Nonpoint HAP Augmentation

For nonpoint sources, we derived HAP augmentation ratios from the emission factors used to develop the EPA nonpoint source estimates. Most EPA nonpoint HAP emission estimates are computed in EPA nonpoint database “tools” (e.g., previously discussed wagon wheel, oil and gas tool). Starting with the 2020 NEI, we removed HAP VOCs from the wagon wheel tool to reduce the resources required to package and process the wagon wheel data, and ensure that both SLT and EPA data would utilize EIS HAP Augmentation factors for computing VOC HAPs, streamlining quality assurance if/when emission factors for VOC or VOC HAPs changed.

EPA also generates HAPs with CAPs in stand-alone databases such as those used for agricultural burning and livestock waste. Because we used the same emission factors for these augmentation ratios, the ratios of HAP to CAPs for augmented S/L/T agency data are the same as the HAP to CAP ratios for the EPA-only data. For access by non-EIS users, the zip file called “HAPAugmentation_2023NEI_17apr2026”, on the “2023 NEI Supplemental data FTP site”, provides the emission ratios that the EPA used for augmenting nonpoint data. The nonpoint HAP augmentation factors were updated as compared to what was used for the 2020 NEI, particularly for residential wood combustion, oil and gas, and new sources such as structure and motor vehicle fires. The EPA staff responsible for the nonpoint sectors use their discretion for how to augment HAP emissions and work with the S/L/T agencies to reflect as complete and accurate set of pollutants as possible for the many source types. In general, if a S/L/T agency submitted a partial list of the HAPs that would be augmented for a given category, then we allowed the missing HAPs to be gap-filled with the HAP augmentation data. These missing HAPs are determined by comparing the Expected Pollutant List for Nonpoint SCCs with those that S/L/T agencies submitted. However, this approach has a risk of potentially violating VOC mass balance, whereby the sum of the VOC HAPs exceeds the VOC total. Thus, special cases occur when such problems are identified. In the limited cases where this occurred, we applied the business rules defined in Section 3.4.2 in the “2023 NEI Plan” to tag out S/L/T data causing this violation; in this case, S/L/T-submitted HAP-VOCs were replaced with HAP augmentation (generally based on S/L/T-submitted VOC) -based HAP-VOC estimates.