Shell Chukchi Sea EP Revision 2

Environmental Impact Assessment

Attachment A

1 March 2015

Shell Chukchi Sea Outer Continental Shelf Lease 

Exploration Plan Revision 2

Environmental Impact Assessment – Attachment A

Arctic Offshore Air Quality Impacts

Recommendations for Appropriate Criteria

for Determining Significance Under NEPA

Executive Summary

The Bureau of Ocean Energy Management (BOEM) is charged with evaluating the impacts of air 

emissions associated with oil and gas exploration activities on the Outer Continental Shelf (OCS) under 

two different statutory/regulatory programs: (1) compliance with BOEM’s Air Quality Regulatory 

Program (AQRP) (which addresses onshore impacts of emissions from OCS sources), and (2) the “hard 

look” at potential environmental impacts required for every major federal action under the National 

Environmental Policy Act (NEPA). Section 7.0 of the Revised Outer Continental Shelf Lease Exploration 

Plan, Chukchi Sea, Alaska (EP Revision 2) demonstrates that Shell’s proposed operations are exempt 

from further air quality review under the terms of BOEM’s AQRP because the relevant emissions impacts 

onshore are negligible, requiring no further analysis for purposes of agency review of EP Revision 2. In 

its NEPA analysis of Shell’s prior exploration plans, BOEM utilized the analyses of air quality impacts 

prepared in support of the Clean Air Act permits Shell obtained from the Environmental Protection 

Agency (EPA). Because Congress has now changed jurisdiction for protection of air quality in the OCS 

offshore of the North Slope Borough of Alaska from the EPA to BOEM and Shell will not have a Clean 

Air Act permit from EPA, air quality impacts will no longer be analyzed under EPA procedures and 

standards. As such, BOEM now has an opportunity to identify an appropriate methodology to evaluate air 

quality impacts for potential significance under NEPA.

In the past, BOEM in Alaska established NEPA significance thresholds for onshore air quality impacts 

based upon Clean Air Act standards, including the National Ambient Air Quality Standards (NAAQS) 

and the Prevention of Significant Deterioration (PSD) increments. See, e.g., BOEM, Environmental 

Assessment for Shell’s 2011 Revised Chukchi Sea Exploration Plan (OCS EIS/EA BOEM 2011-061, 

Dec. 2011) (EA for EP Revision 1), Appendix B. These standards may continue to be applicable in the 

onshore environment as “significant impact” criteria under NEPA. But, while BOEM formerly used the 

NAAQS and PSD increments as default indicators of NEPA significance in the Arctic offshore 

environment, reference to those EPA standards is not necessary under NEPA because of the remoteness 

of the emissions sources and the very limited exposure of humans to project emissions in the offshore. 

Specifically, the NAAQS were established by the EPA to protect nationwide air quality in areas 

reasonably accessible to the general public, in order to protect the health of the most vulnerable 

population and to protect the quality of the environment generally.a Because emissions from Shell’s 

project will impact only remote and inaccessible offshore areas, where comparatively healthy people are 

present, if at all, only for limited periods of time and receptors in the ecosystem are transient, the NAAQS 

are not appropriate benchmarks for use in BOEM’s analysis of the offshore air quality impacts of Shell’s 

proposed operations in the Chukchi Sea.

 

a

42 USC § 7409, U.S. Clean Air Act: national primary and secondary ambient air quality standards.
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This document defines a set of more suitable offshore criteria to protect the health of the limited numbers 

of persons who work in offshore Arctic Ocean areas as well as subsistence hunters and fishermen in the 

Chukchi Sea, a few of whom may occasionally encounter some ancillary aspect of Shell’s operations.b

Shell developed these criteria after reviewing scientific evidence and Occupational Safety and Health 

Administration (OSHA) state and federal standards. The criteria adopted are more protective than 

OSHA’s exposure standards, and thus have a built-in margin of safety. They represent proposed 

maximum concentration limits for Shell’s operations. The criteria are set at levels adequate to ensure no

significant impacts on the health of exposed workers and subsistence hunters and fishermen (if any), and 

are also not expected to cause significant impacts to marine life and other environmental resources

present in the offshore regions of the Arctic Ocean. These criteria for significant offshore air quality 

impacts are as follows:

 PM2.5 and PM10: 500 μg/m3 (1-hour average concentration, not to be exceeded)

 NO2: 3,760 μg/m3 (2 ppm) (1- hour average concentration, not to be exceeded)

 CO: 55,000 μg/m3(50 ppm) (1-hour average concentration, not to be exceeded)

 SO2: 5,200 μg/m3 (2 ppm) (1-hour average concentration, not to be exceeded)

Assuming emissions from Shell’s operations would not cause an exceedance of any of these criteria at 

offshore locations where third-party boats and vessels may experience emissions from the project, the 

emissions would be deemed not to have a significant impact requiring preparation of an Environmental 

Impact Statement.

Analysis

1. BOEM Needs to Determine Independent Criteria for NEPA Significance

Now that Congress has transferred from EPA to BOEM jurisdiction for air quality impacts on the OCS 

offshore of the North Slope Borough of Alaska, BOEM must develop an appropriate method for its 

NEPA analysis of those impacts. In the past, BOEM has used the analyses performed for EPA permits to 

inform its NEPA analysis of Shell’s Alaska air quality impacts, but EPA analyses will no longer be 

available or appropriate for BOEM’s use.

Shell expects that BOEM will continue to apply the Clean Air Act-based criteria it has developed in the 

past to determine whether and under what control scenarios Shell’s air emissions will have a significant 

impact on onshore air quality for purposes of NEPA. Those criteria will remain keyed to the NAAQS 

applicable to the onshore area and the increment (or some fraction thereof) that would be applicable to the 

source if it were still regulated by EPA under its PSD rules. Going forward, the most significant change 

will be in how offshore air impacts are evaluated for significance under NEPA, i.e., whether a project’s 

estimated air emissions will have a “significant” impact such that an Environmental Impact Statement is 

required under NEPA.

Onshore Emissions

BOEM’s current approach to determining “significance” of onshore emissions is exemplified in BOEM’s 

EA for EP Revision 2.. In that EA, BOEM evaluated projected onshore and offshore air quality impacts 

 

b

 Subsistence hunting and fishing rarely, if ever, take place more than 30 miles offshore. The Discoverer and Polar Pioneer will 

operate more than twice that far offshore. Any project-related emissions that persons may encounter will almost certainly be 

limited to emissions from supply boats transiting to or from the Discoverer and Polar Pioneer. Shell accordingly believes that 

compliance with the proposed air quality limits should be evaluated only at points located within the subsistence areas designated 

under Figure 3.11.6-11 in the EIA for EP Revision 2. 
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from Shell’s project against applicable NAAQS, while also examining whether in any case air quality 

impacts from Shell’s emissions would exceed 50 percent of either the NAAQS or the “maximum 

allowable increase,” i.e., the applicable PSD increment. EA at 67-68, Tables 28 and 29. BOEM 

concluded that the proposed action would be “compliant with the federal air quality standards and without 

potential to cause or contribute to any violation of the NAAQS, which define healthful outside air quality. 

. . . As such, the level of effect on air quality caused by the Proposed Action is considered minor . . . .” Id. 

at 70-71.c BOEM has provided further clarification on determination of the significance levels of onshore 

emissions for the Chukchi Lease Sale 193 area. Under the Supplemental Environmental Impact Statement 

for Lease Sale 193 (OCS EIS/EA BOEMRE 2011-041, Nov. 2011), BOEM determined a significant 

effect when the project-related emissions cause an increase in pollutant concentrations over the nearest 

onshore area of at least 20 square kilometers that exceed 50 percent of NAAQS and maximum allowable 

increases (MAIs).

Offshore Emissions

While the significance levels BOEM developed for air quality impacts in the onshore environment may 

remain applicable to onshore impacts, Congress’s decision to change jurisdiction for OCS air quality 

impacts offshore of the North Slope Borough from EPA to BOEM makes it necessary for BOEM to 

update its methodology for evaluating offshore air impacts. Clean Air Act Section 328(b) requires only 

that BOEM “coordinate” air pollution control regulations for OCS sources and adjacent onshore areas. In 

contrast, Section 328(a) requires EPA to regulate OCS sources specifically to “attain and maintain” the 

NAAQS and to comply with subchapter I of the Clean Air Act (stationary source requirements). Because 

Congress chose in Section 328(b) not to require that sources in areas of the OCS administered by BOEM 

meet the NAAQS and the Clean Air Act (CAA) stationary source provisions, BOEM has both the 

discretion and obligation to thoughtfully regulate OCS sources within its jurisdiction, independent of 

these EPA standards. To assist BOEM with the NEPA analysis, Shell has developed proposed standards 

of NEPA significance that are more appropriate to the offshore environment and to the small population 

of workers in the region and subsistence hunters who might be briefly exposed at offshore locations to the 

air quality impacts from the project.

2. Clean Air Act Standards Are Not Appropriate Thresholds for Offshore NEPA 

Significance Levels

The NEPA significance levels BOEM has used for onshore analysis are not appropriate for offshore 

analysis in the Arctic for several reasons. First, as discussed in detail below, the NAAQS, on which the 

significance levels rely, were designed for areas accessible to the public, and do not provide meaningful 

information on the significance of air quality impacts upon a remote and inaccessible region such as the 

Chukchi Sea OCS. Second, the impacts of offshore emissions to the human and natural environment 

offshore will be different from the impacts to the onshore environment because the affected environment 

is different. Third, information on background air quality is different onshore versus offshore. Finally, and 

most important, both the human and fauna populations offshore are transient, and thus are extremely 

unlikely to remain in a fixed location exposed to air pollution for the duration of a day, let alone a full 

drilling season.

 

c

 For air quality impacts, BOEM’s NEPA “significance threshold” is that the project’s emissions would cause at an onshore 

location (1) a violation of a NAAQS or (2) an increase in pollutant concentrations that would (a) exceed half of any NAAQS

except for ozone, (b) exceed half of the maximum allowable increase (increment) under EPA’s PSD rules, or (c) exceed half of 

the ozone NAAQS including precursor emissions of VOCs and NOX. EA, App. B at B-1. 
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A. NAAQS Are Broad Nationwide Standards With Limited Relevance to Arctic OCS Operations

Some advocacy groups have suggested that BOEM should apply Clean Air Act standards, such as the 

NAAQS, in its NEPA analysis of the offshore air quality impacts of Shell’s proposed Chukchi Sea 

operations. However, those Clean Air Act standards are not legally binding on BOEM as applied to the 

Arctic offshore regiondand, more important, are not designed for an environment such as the Arctic 

Ocean. The CAA and its amendments mandated uniform nation-wide standards that are designed to 

protect public health and welfare everywhere in the United States. The CAA promotes the 

implementation of air quality controls to limit the exposure of the general public to unhealthy 

concentrations of pollutants in the air. The keystone of the CAA as originally enacted was Title I, Part A, 

Section 109, which established NAAQS. The NAAQS are designed to provide a set of concentration 

criteria to protect the public health and public welfare with a margin of safety. The CAA defines the 

NAAQS as a set of “primary” standards that are implemented to protect human health, and “secondary” 

standards that protect the general welfare. The CAA required EPA to establish NAAQS based on current 

scientific knowledge and studies and to update the NAAQS on a five-year schedule to incorporate new 

information.

B. EPA’s Definition of Ambient Air is Not Appropriate for Remote OCS Operations

The primary NAAQS are ambient air pollution concentration thresholds that should not be surpassed in 

areas accessible to the general public. The CAA does not define “ambient air” or the “general public,” 

leaving the definition and interpretation of these terms to the enforcing agency to allow flexibility in its 

implementation. EPA adopted the following definition of ambient air: “Ambient air means the portion of 

the atmosphere, external to buildings, to which the general public has access.” 40 CFR 50.1(e).

EPA has interpreted the phrase “to which the general public has access” through a series of official 

memoranda and policy statements. These policy documents exempt that portion of the atmosphere over 

land that is controlled by a source where public access is precluded by a fence or other physical barrier.e,f

Ambient air is further limited by applying the NAAQS standards only to the portion of the atmosphere 

near ground level and building rooftop level, where the general public can reside. If the definition of 

ambient air were expanded to include all regions of the atmosphere that members of the public could 

theoretically access, even for short periods of time, air pollution control would be economically 

unfeasible. For example, the air aloft is accessible to the general public via aircraft, but the exposure 

period at any given point in a moving vehicle is limited and short compared to the health-based exposure 

periods recognized in the NAAQS. Thus, to balance the need for economic activity with the protection of 

human health, EPA has necessarily used common sense in interpreting its definition of ambient air, with 

recognition that even though access to a given area may not be absolutely impossible, that area cannot 

reasonably be considered ambient air.

In making case-by-case determinations of what is ambient air under the CAA, EPA and state agencies 

have struggled with applying the definition of “ambient air” over water. While EPA has determined that 

atmosphere over bodies of water reasonably accessible to the general public can fall within the agency’s 

definition of ambient air, the Alaska Department of Environmental Conservation (ADEC) has recognized 

that certain bodies of water and other geophysical barriers, if not reasonably accessible to the public, can 

represent a physical barrier that precludes public access.g The U.S. Court of Appeals for the Ninth Circuit 

 

d

42 USC § 7627(b).

e USEPA, Region I-IX Meteorologists, “Regional Meteorologists’ Memorandum,” dated May 16, 1985.

f Resisting Environmental Destruction on Indigenous Lands v. EPA, 704 F.3d 743, 753 (9th Cir. 2012) (REDOIL).

g ADEC Modeling Review Procedures Manual, Section 3.3, Sept. 14, 2011. 
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concurred, finding that it was “just common sense” that the agency be allowed some “leeway” in applying 

its land-based ambient air definition to overwater situations.h

The offshore region of the Chukchi Sea is not under EPA’s jurisdiction and the marine environment 

represents a formidable geographic barrier that limits reasonable access to the general public. The 

population that does access the offshore regions of the Chukchi Sea consists almost entirely of marinevessel occupants and subsistence hunters. Both of these populations are transient groups that access any 

point of the offshore region (usually not more than 30 miles offshore) only briefly. The NAAQS primary 

standards were established to protect the health of the most vulnerable members of the general public, not 

persons temporarily working or engaged in hunting and fishing offshore in the Chukchi Sea. Therefore, 

the NAAQS are not the appropriate standards to promote public health and public welfare in these 

offshore areas of the Chukchi Sea, and BOEM should not apply them in determining the significance of 

offshore air impacts.

EPA’s recent update of the 1-hour NAAQS for nitrogen dioxide (NO2) illustrates key differences between 

the exposure data EPA uses to set NAAQS under the CAA and the impact review BOEM is required to 

conduct under NEPA, and therefore why NAAQS are not appropriate criteria for BOEM’s NEPA review. 

First, in setting the new NO2 standard EPA cited findings that “traffic-related exposures can dominate 

personal exposures to NO2,” that “[w]hile driving, personal exposure concentrations in the cabin of a 

vehicle could be substantially higher than ambient concentrations measured nearby,” and that 

concentrations of nitrogen oxides (NOX), as well as carbon monoxide and ultrafine particulate matter 

(PM), “typically display peak concentrations on or immediately adjacent to roads.”i These largely urban 

exposure scenarios do not exist in the Arctic OCS. Second, EPA set the standard to protect sensitive 

groups in the population, noting that “subpopulations considered potentially more susceptible to the 

effects of NO2 exposure included persons with pre-existing respiratory disease, children, and the elderly.”j

It is unlikely that children, the elderly, and those with respiratory disease will be in the vicinity of the 

activities BOEM is reviewing.

C. Use of NAAQS for Offshore Significance Determinations is Not Consistent with BOEM’s 

Current Regulatory Approach

Air quality impacts attributable to oil and gas activities on the Outer Continental Shelf in portions of the 

Gulf of Mexico and offshore of the North Slope Borough of Alaska are governed by CAA Section 328(b), 

which instructs the Secretary of the Interior to “assure coordination of air pollution control regulation for 

Outer Continental Shelf Emissions and emissions in the onshore adjacent areas.”k BOEM has managed 

oil and gas emissions in the Gulf of Mexico under this standard for over twenty years, and now has

jurisdiction for the area of the Outer Continental Shelf offshore of the North Slope Borough of Alaska.

BOEM has not applied a project-specific NAAQS analysis in its review of air quality impacts in the Gulf 

of Mexico. However, BOEM has enforced air quality limitations on offshore sources to ensure protection 

of NAAQS onshore. This policy is consistent with a position that the offshore region is relatively 

inaccessible to the general public. Much of the region is frequented by marine traffic, but it is generally 

recognized that this population is transient and, as a result, the exposure periods considered in the 

NAAQS are not applicable. The reasoning behind the Gulf of Mexico exemption applies with even 

greater force in the Arctic Ocean given inherent limits on access due to remoteness and climatic extremes. 

 

h REDOIL, 704 F.3d at 753.

i

75 Fed. Reg. 6479 (Feb. 9, 2010), citing “Integrated Science Assessment for Oxides of Nitrogen-Health Criteria,” Section 2.5 

(EPA, 2007).

j

75 Fed. Reg. 6480 (Feb. 9, 2010).

k

42 USC § 7627(b).
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D. Using Clean Air Act Standards Would Compromise BOEM’s NEPA Analyses

For the reasons outlined above, the CAA and Alaska onshore air quality standards are not applicable nor 

are they appropriate to assess offshore air quality impacts under NEPA. The NAAQS and PSD increment 

limits are national standards that EPA applies to onshore (and some offshore) areas. EPA has no 

flexibility in applying the NAAQS and applicable increments; they are one-size-fits-all national 

standards. NAAQS and increments are appropriate to EPA’s statutory responsibilities under the Clean Air 

Act and may be acceptable proxies for determining the significance of OCS source emissions at onshore 

locations.

Were the NAAQS standards used as threshold criteria to define significant impacts to OCS air quality 

under NEPA, that approach actually would undermine BOEM’s effort to realistically assess these 

offshore environmental impacts. BOEM’s responsibility is to conduct a rigorous analysis of whether air 

quality impacts will be significant in a specific affected environment (here, the Burger Prospect some 60 

miles offshore which hosts limited numbers of transient individuals and an ever-changing collection of 

fauna). EPA’s national standards are based on assumptions that do not resemble offshore conditions and 

exposures. Under the conditions of the offshore Arctic, using the NAAQS and increment as criteria is 

overly conservative, misleading, and will necessarily predict “significant” environmental impacts where 

none will actually occur.

3. Shell’s Recommendations

Shell has developed more suitable criteria to govern offshore air quality related to its remote, offshore 

exploration activities in the Chukchi Sea. These proposed air quality standards for air pollutant 

concentrations in remote offshore regions of the Arctic Ocean consider the characteristics and activities of 

the population that accesses the region. The standards are appropriately based on the following 

assumptions:

 Short-term averaging periods due to transience (1 hour is appropriate).

 The population accessing the Arctic OCS region, particularly those who travel in boats far 

offshore to hunt, generally comprises persons for whom OSHA standards provide appropriate 

health protection.

l

Standards for NO2, PM2.5, PM10, carbon monoxide (CO), and sulfur dioxide (SO2) were developed by 

Shell based upon these assumptions, scientific evidence, and OSHA standards. Given these conditions, 

conservative standards for the offshore area are provided that are based on current occupational health 

standards or studies focused on non-medically compromised individuals.

NO2:

As discussed previously, NAAQS are not an appropriate set of criteria for assessing levels of impact in 

offshore Arctic areas. However, EPA has provided valuable information under NAAQS assessments that 

is relevant when evaluating acceptable air quality levels for offshore areas for the Arctic region in the 

Chukchi Sea. The EPA Integrated Science Assessment (ISA) for NO2

m

provides the basis for the current 

ambient concentration thresholds established in the NAAQS. The 1-hour NAAQS for NO2 (100 ppbn) has 

been established with regard to the most sensitive individuals. Sensitive asthmatics have shown the 

highest sensitivity to short-term NO2 exposure with increased airway response to concentrations as low as 

 

l Nevertheless, given that some members of the native population may be more susceptible to the health effects of air pollutant 

exposure due to genetic predisposition, and might conceivably engage in subsistence activities offshore, the standards are more 

stringent than the OSHA standards to even more fully protect the subsistence worker population.

m USEPA (2008): Integrated Science Assessment for Oxides of Nitrogen – Health Criteria, EPA/600/R-08/071.

n

1 part per million (ppm) = 1000 parts per billion (ppb).
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100 ppb after 60 minutes of exposure. Increased sensitivity is evident at 200-300 ppb for shorter, 30 

minute periods of exposure. Minimal airway response has been observed in healthy non-smoker nonasthmatics at levels as low as 1.5-2 ppm after continuous 1-hour exposure. Intermittent exposure to 2 ppm 

NO2 concentrations evoked no airway response in these individuals.

The ISA also directs attention to NO2 exposure by laboratory animals that demonstrate increased airway 

responsiveness after 6-12 weeks of exposure to a concentration of NO2 at 1-4 ppm. This suggests that 

animals are sensitive to NO2 at a similar concentration range as humans. Therefore, it is appropriate that 

the primary and secondary criteria level for NO2 be roughly equivalent. Secondary criteria for NO2 are 

also relevant to the protection of coastal regions from nitrogen deposition that may contribute to a 

disturbance of the biological balance by encouraging algal growth.o Deposition is primarily a concern in 

onshore coastal regions where build-up of nitrates in coastal estuaries may disrupt biological balances.p

OSHA has established air quality limits for a range of pollutants to protect the health of laborers in the 

workplace. Though the established levels are less stringent than the NAAQS, the standards have been 

recognized as conservative levels of protection for the average healthy worker in the United States. The 

OSHA standard for NO2 is defined in Table Z-1 of OSHA Standard 1910.1000 (29 CFR 1910.1). Under 

the OSHA standard, NO2 must not exceed 5 ppm at any time. 

Given the scientific research and OSHA standards presented here, an NO2 criteria concentration level in 

the range of 2 to 5 ppm (3760-9400 μg/m3) over a 1-hour average period is a reasonable and conservative 

level of health protection for that population that may be exposed to pollutants in the offshore regions of 

the Chukchi Sea.

PM2.5 and PM10:

The 2009 EPA Integrated Science Assessment for Particulate Matterqindicates health effects are 

generally more related to long-term exposure and the NAAQS values are based on distribution of deaths 

and hospitalizations with relation to PM2.5 concentration. The EPA notes in the 2011 Particulate Matter 

Policy Statementrthat “protection from long term and short term PM2.5 exposure is most effectively and 

efficiently provided by relying primarily on the annual standard, with the 24-hour standard providing 

supplemental protection for days with high peak concentration.” This statement demonstrates the EPA’s 

interpretation of the ISA findings that PM2.5 exposure is generally a concern for longer (>1 hour) 

exposures.

The OSHA standard for respirable fraction (PM10) of suspended particulates, otherwise not regulated 

under another standard, is 5,000 μg/m3, averaged over an 8-hour workday. This value is considerably 

higher than the 24-hour NAAQS of 150 μg/m3for PM10 or 35 μg/m3for PM2.5. The most stringent OSHA 

standard for any respirable dust material is 500 μg/m3 for Paraquat, a highly toxic compound.

The current NAAQS include standards for both PM10 and PM2.5. PM2.5 is of greater concern because 

particles in this size range stay airborne longer, can penetrate deeper into the lungs, and are generally 

comprised of the more toxic compounds. When determining criteria, it is highly conservative to set the 

same concentration threshold value for both PM10 and PM2.5, given an appropriate health-based limit for 

PM2.5 exposure. This approach effectively assumes that all PM10 is PM2.5 for the sake of environmental 

assessment. The 24-hour average concentration NAAQS for PM2.5 is roughly a quarter of the PM10

 

o USEPA (2008): Integrated Science Assessment for Oxides of Nitrogen and Sulfur -- Ecological Criteria, EPA/600/R08/O82F.

p

Id.

q USEPA (2009): Integrated Science Assessment for Particulate Matter, EPA/600/R-08/139F.

r USEPA (2011): Policy Assessment for the Review of the Particulate Matter National Ambient Air Quality Standards, EPA452/R-11-003.
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NAAQS concentration; it is therefore more conservative to apply a health-based criteria threshold for 

PM2.5 that is less than a quarter of the OSHA respirable fraction limit (PM10).

Given the scientific research and OSHA standards presented here, PM2.5 and PM10 criteria concentration 

threshold of 500 μg/m3over a 1-hour average period would provide a reasonable and highly conservative 

level of health protection (considering that the OSHA standard of 5,000 μg/m3is based on 8-hour average

concentrations) for the population who might be exposed to pollutants in the offshore regions of the 

Chukchi Sea.

In terms of impacts on the environment, the primary concern being the health of marine life exposed to 

PM2.5 in the offshore regions, there is limited information concerning the impacts of deposited or airborne 

PM.r The body of scientific studies focused on health impacts of PM2.5 on animals is sparse, but effects 

are expected to be at the same concentrations as humans thus, the criteria for humans should be 

appropriate for protection of marine life.

CO:

The NAAQS for CO are based on clinical evidence that relate carboxyhemoglobin (COHb) to a number 

of health impacts. COHb is formed from the bonding of CO and hemoglobin in the blood that hinders the 

transport and delivery of oxygen throughout the body. The CO NAAQS were set to protect the health of 

those most vulnerable to the effects of COHb, which include those susceptible to exercise-induced angina, 

asthma, coronary artery disease, and myocardial ischemia. The developing young and elderly are also 

more sensitive to CO exposure. It has been noted that persons with normal healthy cardiovascular systems 

can tolerate “substantial concentrations of CO” if they increase cardiovascular output in response to 

higher COHb. Individuals with compromised systems have limited ability to respond to higher COHb, 

making them susceptible to even low concentrations of CO.s

The OSHA 8-hour exposure limit for CO is 55,000 μg/m3(50 ppm) (8-hour average). It has been found 

that a 1-hour exposure of up to 1,200 ppm would cause unpleasant but no dangerous symptoms.t The 

OSHA exposure limit is a reasonable primary and secondary threshold for workers and those engaged in 

subsistence activities in the Chukchi Sea. A conservative criteria level, based on the OSHA standard, 

would be 1-hour average threshold of 50 ppm.

SO2:

Short-term SO2 NAAQS have been established to protect the most susceptible individuals, which include 

severe asthmatics and those with pre-existing respiratory disease such as Chronic Obstructive Pulmonary 

Disease. SO2-related health impacts in healthy individuals have not been demonstrated at concentrations < 

1,000 ppb.u,vIncrease in respiratory symptoms have been observed in exercising asthmatics following 5 to 

10 minute exposure to SO2 levels as low as 200-300 ppb. Given these observations, the 1-hour SO2

NAAQS has been set at 250 ppb (not to be exceeded more than twice per year) to limit health impacts on 

the most susceptible individuals.

The OSHA permissible exposure limit is 5 ppm (13 mg/m3) (8-hour exposure). The California OSHA 

standard is lower, however, at 2 ppm. Shell has adopted a more protective and conservative value (given 

 

s USEPA (2010): Quantitative Risk and Exposure Assessment for Carbon Monoxide – Amended, EPA-452/R-10-009.

t Center for Disease Control, IDLHs for Carbon Monoxide: http://www.cdc.gov/niosh/idlh/630080.html.

u USEPA (2009): Risk and Exposure Assessment to Support the Review of the SO2 Primary National Ambient Air Quality 

Standards, EPA-452/R-09-007. 

v

Sulfur dioxide final acute exposure guideline levels (May, 2008).
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the temporal averaging period of the standard) of 2 ppmw(1-hour average concentration) to provide 

adequate protection of workers and subsistence hunters and fishermen on the Chukchi Sea.

The secondary NAAQS are established primarily to protect against the acidification of the environment 

from SO2 pollution. Build-up of SO2 in the air can lead to acid rain and deposition can increase the acidity 

of isolated marine environments, where pollutants can concentrate. These factors are not an issue over the 

offshore regions of the Arctic Ocean due to the lack of widespread SO2 sources. Acidification is primarily 

a concern in coastal areas due to the buildup of sulfur in estuaries and marshlands: similar buildup is 

impossible over the open ocean, where any deposited sulfur will disperse quickly. Impacts on marine life 

should be averted by adherence to health-based limits set for human exposure.

 

w

2 ppm = 2,000 ppb.