Thursday, March 24, 2011

EPA science advisers call once again for tougher national smog standard

From a letter from EPA's Clean Air Science Advisory Committee (CASAC) to EPA Administrator Lisa Jackson:

While we are concerned that EPA’s most recent request for additional CASAC advice is redundant with our past reviews, we nonetheless are pleased for the opportunity to reaffirm our previous advice and we are submitting this letter and the attached consensus advice to further assist EPA as it takes action following this additional scientific input from CASAC.

Here we reaffirm that the evidence from controlled human and epidemiological studies strongly supports the selection of a new primary ozone standard within the 60 – 70 ppb range for an 8-hour averaging time...

As you give consideration to the revision of the NAAQS, we offer the following summary of findings in the evidence available through 2006:
• The evidence available on dose-response for effects of ozone shows associations extending to levels within the range of exposures currently experienced in the United States.
• There is scientific certainty that 6.6-hour exposures with exercise of young, healthy, nonsmoking adult volunteers to concentrations ≥ 80 ppb cause clinically relevant decrements of lung function.
• Some healthy individuals have been shown to have clinically relevant responses, even at 60 ppb.
• Since the majority of clinical studies involve young, healthy adult populations, less is known about health effects in such potentially ozone sensitive populations as the elderly, children and those with cardiopulmonary disease. For these susceptible groups, decrements in lung function may be greater than in the healthy volunteers and are likely
to have a greater clinical significance.
• Children and adults with asthma are at increased risk of acute exacerbations on or shortly after days when elevated ozone concentrations occur even when exposures don't exceed the NAAQS concentration of 75 ppb.
• Large segments of the population falls into what EPA terms a “sensitive population group,’’ i.e., those at increased risk because they are more intrinsically susceptible (children, the elderly, and individuals with chronic lung disease) and those who are more vulnerable due to increased exposure because they work outside or live in areas that are more polluted than the mean levels in their communities.
• CASAC unanimously reaffirms its support for the previously recommended selection of an 8-hour average ozone NAAQS within the range proposed by EPA (60 to 70 ppb).

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