Airborne Lead Standards

After 30 years, and a 2005 court order, last month, the US EPA finalized new primary and secondary national ambient air quality standards (NAAQS) for lead. The new primary and secondary standards for lead each tighten the limits of concentrated lead from 1.5 µg/m3 to 0.15 µg/m3 . The primary standard is the standard set to include a margin of safety for at-risk groups. The secondary standard is based on the estimated impact of airborne lead on the general welfare and environment. The new regulation also changes how lead in the air is sampled and how concentrated lead is tested, including the creation of a new federal reference method.

By January 2009, states must designate attainment, nonattainment and unclassifiable areas for the new lead standards. States’ plans to meet the standards are due in June 2013, and the new standards must be met by January 2017. The EPA estimates that currently 18 counties in 12 states do not comply with the new standards. States will be required to place monitors where sources of lead emissions exceed or are equal to one ton or more annually. In addition, monitors must also be placed in the 101 US urban areas with populations of more than 500,000. The EPA estimates that such requirements will increase the numbers of new monitors or relocated monitors by 236. Half of these are required to be operational by January 1, 2010, and the other half must be operational a year later.

A standard consists of four elements: indicator, averaging time, form and level. Only one of the four elements remains unchanged in the new lead NAAQS. The indicator for the lead NAAQS continues to be the concentration of lead in total suspended particulates (Pb-TSP). In addition to the lower level of 0.15 µg/m3 of lead in air, average time and form were revised to a maximum three-month rolling average evaluated over a three-year period, compared to the previous calculation that used the maximum value averaged over a calendar quarter.

For the collection and testing of samples to determine Pb-TSP, the regulation maintains the federal reference method set in 1978. The method specifies the use of a high-volume sampler. High-volume samplers draw air through an 8 in. x 10 in. filter at the rate of 70–100 m3 per hour. Flame atomic absorption spectrometry is the designated method for analysis of Pb-TSP. Since 1978, 21 equivalent methods for Pb-TSP testing have also been approved.

The changes to the lead NAAQS include the use under certain circumstances of particulate matter of up to 10 µm in diameter (Tb-PM10) as an indicator. These circumstances are when lead is not expected to be in large particles and when it can be shown that lead concentrations are not expected to have averages over three months of more than or equal to 0.1 µg/m3. Based on the federal reference method for coarse particulate matter of up to 10 µm in diameter, the sampling method for Tb-PM10 utilizes a low-volume sampler. A low-volume sampler draws air through a 47 mm diameter filter at the rate of 1 m3 of air per hour. An EPA spokesperson told IBO that the development of a federal reference method for low-volume lead samplers will take years. For the analysis of Pb-PM10, the new lead NAAQS designates XRF as the reference method, with alternative methods subject to approval.

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