In contrast, material balances may be inappropriate where material is consumed or chemically combined in the process, or where losses to the atmosphere are a small portion of the total process throughput. As the term implies, one needs to account for all the materials going into and coming out of the process for such an emission estimation to be credible. If representative source-specific data cannot be obtained, emissions information from equipment vendors, particularly emission performance guarantees or actual test data from similar equipment, is a better source of information for permitting decisions than an AP emission factor.
When such information is not available, use of emission factors may be necessary as a last resort. Whenever factors are used, one should be aware of their limitations in accurately representing a particular facility, and the risks of using emission factors in such situations should be evaluated against the costs of further testing or analyses. A factor's rating is a general indication of the reliability, or robustness, of that factor.
This rating is assigned based on the estimated reliability of the tests used to develop the factor and on both the amount and the representative characteristics of those data. In general, factors based on many observations, or on more widely accepted test procedures, are assigned higher rankings. Conversely, a factor based on a single observation of questionable quality, or one extrapolated from another factor for a similar process, would probably be rated much lower.
Because ratings are subjective and only indirectly consider the inherent scatter among the data used to calculate factors, the ratings should be seen only as approximations. AP factor ratings do not imply statistical error bounds or confidence intervals about each emission factor.
At most, a rating should be considered an indicator of the accuracy and precision of a given factor being used to estimate emissions from a large number of sources. This indicator is largely a reflection of the professional judgment of AP authors and reviewers concerning the reliability of any estimates derived with these factors. Because emission factors can be based on source tests, modeling, mass balance, or other information, factor ratings can vary greatly.
Some factors have been through more rigorous quality assurance than others. Two steps are involved in factor rating determination. The first step is an appraisal of data quality, the reliability of the basic emission data that will be used to develop the factor. The second step is an appraisal of the ability of the factor to stand as a national annual average emission factor for that source activity.
The quality rating of AP data helps identify good data, even when it is not possible to extract a factor representative of a typical source in the category from those data. For example, the data from a given test may be good enough for a data quality rating of "A", but the test may be for a unique feed material, or the production specifications may be either more or less stringent than at the typical facility.
The AP emission factor rating is an overall assessment of how good a factor is, based on both the quality of the test s or information that is the source of the factor and on how well the factor represents the emission source.
Higher ratings are for factors based on many unbiased observations, or on widely accepted test procedures. For example, ten or more source tests on different randomly selected plants would likely be assigned an "A" rating if all tests are conducted using a single valid reference measurement method.
Likewise, a single observation based on questionable methods of testing would be assigned an "E", and a factor extrapolated from higher-rated factors for similar processes would be assigned a "D" or an "E". What is an EF? To constitute an emission factor, we need to produce a dataset which describes and quantifies the activity generating GHG. Kyoto Protocol GHG. Nitrogen trifluoride NF 3 has been recently added. In the countries where data are not specific, organisations are reluctant to apply international values since the accuracy of the results is not guaranteed due to difference between the localisations.
Indeed, the calculation of carbon footprints is then based on generic data that can be totally different to the real situation, and thus have a high uncertainty. This has major impact on the credibility of any results coming from any calculation method. SO 2 and NO x are criteria pollutants regulated by the U.
They are not greenhouse gases. EPA is a source for emission factors for all greenhouse gases and other emissions factors. Learn more: How much carbon dioxide is produced per kilowatthour of U. Where greenhouse gases come from.
In most cases, these factors are simply averages of all available data of acceptable quality, and are generally assumed to be representative of long-term averages for all facilities in the source category i. This page includes both the existing procedures and the review draft for the proposed new procedures. Uncertainty is dependent on the kind of emissions released, the number of tests used to determine the emissions factor, the appropriate decision level or percentile within the distribution range, and the number of similar emissions units within a specific area.
EPA released a draft review for public comment on April 24, Since the posting of the Draft Emission Factor Uncertainty Assessment for comment on April 24, , we have received numerous inquiries from interested stakeholders questioning whether the Agency intends to include the effect of uncertainty on a source's applicable emission-related requirements, or whether states or local authorities need to apply the effect of uncertainty to determine area compliance with NAAQS standards.
As originally stated in the Draft Assessment, we do not attempt to evaluate or provide guidance on the application of emissions factor uncertainty in making environmental decisions. Moreover, any such decisions would be made only after a formal notice and comment rulemaking process.
0コメント