1. Scientific Uncertainties (Challenges) and Science Policy Decisions (Judgments) in Setting National Ambient Air Quality Standards
Ronald H. White, M.S.T.
Johns Hopkins Bloomberg School of Public Health
Session : Using Science to Inform Air Pollution Policy
135th American Public Health Association
Annual Meeting & Exposition
November 5, 2007

2. EPA NAAQS Review Process (2007 +)

3. Science Policy Issues in Ambient Air Quality Standard-setting Process
Hazard Assessment
Selection of critical adverse health
effect(s)
Identification of
sensitive populations
Toxicity of components (PM)
Exposure Assessment
Personal exposure v. central site
monitoring
Measurement error
Low level data availability
Exposure/Dose–Response Assessment
Selection of exposure-response
function
- threshold v. non-threshold
- single studies v. meta-analyses
- single city v. multiple city studies
Risk Characterization
Central v. 95th percentile risk
Sensitivity analysis
Uncertainty analyses
- model uncertainty
- parameter uncertainty
Background Levels Assessment
Variation in regional/local background
levels
Projection of changes in future
background levels
Policy Assessment – Revise NAAQS?
Quantification/distribution of residual risks and sensitive populations
Cumulative exposures and risk factors NO
YES
Conduct Risk Analysis
for Alternative Standard(s)
Safety Factor
Needed? (MoS) NO
YES
Select Revised Standard
Science Policy Issues in Ambient Air Quality Standard-setting Process

4. Hazard Assessment Issues
Identifying adverse health effects
Weight of evidence (how much information is enough?)
Emerging evidence (when do we know enough?)
Biomarkers of pre-clinical effects (moving “upstream”)
Identification of sensitive groups
Expanding identification of sensitive groups (who do we protect?)
Sub-group population variability
Toxicity of components (PM)
Potential role of different PM components with various health effects

5. Air Pollution Adverse Health Effects
Death
Lung Cancer Incidence
CV + Respiratory Hospital
Admissions
Adverse Birth
Outcomes
Asthma
Incidence
Decrements in lung
function development
CV + Respiratory ER/
Physician Visits
Exacerbation of CV + Respiratory
Disease Requiring Medication
Reduction in Respiratory and/or CV Function with Clinical Symptoms
that Impair Normal Activity
Severity of Health Effect
Increase in Respiratory and/or CV Clinical Symptoms
that Do Not Impair Normal Activity
Decreased Health-Related Quality of Life
Magnitude of Impacted Population
Modified from ATS, 2000

6. PM Inhalation Lungs Heart Blood Vasculature Brain
Inflammation
Oxidative stress
Accelerated progression
and exacerbation of COPD
Increased respiratory symptoms
Effected pulmonary reflexes
Reduced lung function
Heart
Altered cardiac
autonomic function
Increased dysrhythmic susceptibility
Altered cardiac repolarization
Increased myocardial
ischemia
Blood
Altered rheology
Increased coagulability
Translocated particles
Peripheral thrombosis
Reduced oxygen saturation
Systemic Inflammation
Oxidative Stress
Increased CRP
Proinflammatory mediators
Leukocyte & platelet activation
Vasculature
Atherosclerosis,
accelerated progression of and destabilization of plaques
Endothelial dysfunction
Vasoconstriction and Hypertension
Brain
Increased cerebrovascular ischemia
PM-related mechanistic pathways and indicators of adverse health effects
From Dockery & Pope, A&WMA, 2006

7. Defining Sensitive Groups
“Ambient air quality is sufficient to protect the health of such persons whenever there is an absence of adverse effects on the health of a statistically related sample of persons in sensitive groups from exposure to ambient air. An ambient air quality standard, therefore, should be the maximum permissible ambient air level of an air pollution agent or class of such agents (related to a period of time) which will protect the health of any group of the population.
For purposes of this description, a statistically related sample is the number of persons necessary to test in order to detect a deviation in the health of any person within such sensitive group which is attributable to the condition of ambient air.” (emphasis added)
Senate Committee on Public Works –
Legislative History of the Clean Air Act
Amendments of 1970

8. Ozone At-Risk Populations
Elderly (12% ≥65 yrs.)
Children (26% <18 yrs.)
People with respiratory disease
Asthma (7% of adults; 9% of children)
COPD (6% of adults)
Adults and children who regularly exercise outdoors
People engaged in physical activity (e.g. outdoor workers)
Ozone responders (15-20% of healthy adults?)
Adults with cardiovascular disease? (12% of adults)

9. Exposure – Response Issues
Threshold v. Non-threshold Functions
“…significant uncertainties continue to underlie the resulting risk estimates… a risk assessment based on studies that do not resolve the issue of a threshold is inherently limited as a basis for standard setting, since it will necessarily predict that ever lower standards result in ever lower risks, which has the effect of masking the increasing uncertainty as lower levels are considered”
EPA PM NAAQS Proposed Rule, 12/20/05

10. Exposure Assessment Issues
Personal exposure v. central site monitoring data correlations (PM v. gaseous pollutants)
Measurement error at very low concentrations
Limited data for very low exposure levels
Bell et al ozone mortality 98-city <40 ppb 30% of study days <20 ppb 73% of days excluded
Bell et al ozone mortality 98 city study <40 ppb 30% of study days <20 ppb 73% of days excluded

11. Background Pollution Levels Issues
Variability in modeled regional/local “natural” background levels (e.g., Ozone: 0.15 – 0.35 ppm)
Predicted increases in background ozone levels from global warming
Intercontinental transport

12. Policy Assessment
Non-threshold pollutants, residual risk and uncertainty (Is any level “safe”? What about a “margin of safety”?)
Cumulative exposures (“bright line” v. C x T)
Impact of other pollutant exposures and health risk factors (Cumulative health risk assessment)
Quantification of affected sensitive populations
Magnitude of sensitive group (how many is enough?)

13. Short-term Sulfur Dioxide NAAQS & Asthmatics
Compelling clinical studies from mid-late 1980s indicate when mild to moderate asthmatics breathing rapidly with exposed to SO2 concentrations of 0.60 ppm for five minutes, "substantial percentages (~25 percent)" experience effects "distinctly exceeding ... [the] typical daily variation in lung function" that asthmatics routinely experience”.
EPA finds that the severity of these atypical effects "is likely to be of sufficient concern to cause disruption of ongoing activities, use of bronchodilator medication, and/or possible seeking of medical attention” and “repeated occurrences of such effects should be regarded as significant from a public health standpoint." (emphasis added)
(EPA PM/SO2 SP and CD supplement (1994))

14. Short-term Sulfur Dioxide NAAQS & Asthmatics (2)
EPA exposure assessment estimates 180,000 to 395,000 annual “exposure events” i.e., heavily breathing asthmatics exposed to an SO2 levels > 0.60 ppm, affecting from 68,000 to 166,000 asthmatics
However, EPA concludes:
“5-minute peak SO2 levels do not pose a broad public health problem when viewed from a national perspective”
“short-term peak concentrations of SO2 do not constitute the type of ubiquitous public health problem for which establishing a NAAQS would be appropriate”
1998 U.S. Court of Appeals finds EPA decision not to set short-term SO2 NAAQS “arbitrary and capricious” and remands decision.
2005 Center for Biological Diversity lawsuit – review of SO2 NAAQS by late 2009.

15. Future Scientific Challenges in NAAQS Reviews
Increasing emphasis on identification of pre-clinical indicators of adverse health effects related to low ambient pollutant levels with associated measurement error issues
Inter-individual variability in genetic composition and underlying health status make detection of thresholds of effects in general population epidemiological studies unlikely
Accounting for impacts of multiple pollutant exposures and health risk factors

16. Techniques for Addressing Scientific Issues
Air Quality Standard-Setting Scientific Issues
Risk Assessment Sensitivity Analyses
Expert Panel Judgment
Probabilistic Risk
Assessment
Safety Factors
Identification of Critical Adverse Health Effect(s) No
Yes
Selection of Exposure-Response Function
Exposure Assessment
Error
Identification & Quantification of Sensitive Groups
Toxicity of PM Components
Background Concentrations
Pollutant Mixtures

17. "Precision is not reality” - Henri Matisse
“Politics is the art of making good decisions on insufficient evidence.”
- Lord Kennet