The metric recognized by the U.S. government for measuring aviation noise impacts on humans is an annual average of individual "noise events" measured in A-weighted decibels. It is important for activists engaged in airport planning issues to be aware that this metric was developed more than 25 years ago, has a very specific use, and has not been revised in light of continuing research on the effects of low-frequency noise on humans.
When Congress enacted the Noise Control Act in 1972 it directed the EPA to publish information on environmental noise. The result was an EPA report in 1974, "Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety" (EPA 550/9-47-004). In this report the EPA proposed the "day-night average sound level (DNL) as the best metric to describe the effects of noise on humans. This report, therefore, contains the only rationale for the DNL.
In 1979 the Federal Interagency Committee on Urban Noise was formed to provide a single forum in which noise abatement policy could be addressed by all federal agencies that had some responsibility for noise abatement. In 1980 FICUN published "Guidelines for Considering Noise in Land Use Planning and Control". Through this report FICUN established DNL as the descriptor to be used for all noise sources.
In 1990 the American National Standards Institute (ANSI) revised its 1980 standard on "Sound Level Descriptors for Determination of Compatible Land Use (ANSI S12.40-1990), in which the DNL is identified as "the acoustical measure to be used in assessing compatibility between various land uses and outdoor noise environment."
Finally, in 1992 the Federal Interagency Committee on Noise (successor to FICUN) issued a report "Federal Agency Review of Selected Airport Noise Analysis Issues" (available on the web at www.fican.org/pages/report.html ). This reports concludes that "there are no new descriptors or metrics of sufficient scientific standing to substitute for the present DNL cumulative noise exposure metric. The methodology employing DNL as the noise exposure metric and appropriate does-response relationships .. to determine noise impacts on populations is considered the proper one for civil and military aviation scenarios in the general vicinity of airports."
Note that the DNL is designed to evaluate land use compatibility based on human tolerance of noise in certain facilities. The use of DNL for any other purpose is an irrational and unwarranted extension of DNL to these other purposes, and should be challenged.
We need a white paper on the government's use of the DNL, and such a document, to have any credibility, must come from outside the government and without funding from the government.