This document contains EPA policy and, therefore, does 1

not establish or affect legal rights or obligations. It does

not establish a binding norm and it is not finally

determinative of the issues addressed. In applying this

policy in any particular case, the EPA will consider its

applicability to the specific facts of that case, the

underlying validity of the interpretations set forth in this

memorandum, and any other relevant considerations, including

MEMORANDUM

SUBJECT: Areas Affected by PM-10 Natural Events

FROM: Mary D. Nichols

Assistant Administrator

 for Air and Radiation (6101)

TO: Director, Air, Pesticides and Toxics Management

 Division, Regions I and IV

Director, Air and Waste Management Division,

 Region II

Director, Air, Radiation and Toxics Division,

 Region III

Director, Air and Radiation Division,

 Region V

Director, Air, Pesticides and Toxics Division, 

 Region VI

Director, Air and Toxics Division

Purpose

This memorandum sets forth the Environmental Protection

Agency's (EPA's) policy for protecting public health in areas

where the PM-10 (particulate matter having a nominal

aerodynamic diameter less than or equal to 10 microns)

national ambient air quality standards (NAAQS) are violated

due to natural events. This policy will be followed in

implementing the PM-10 NAAQS until it is superseded. The 1
any that may be required under applicable law and regulations.

need for revisions to this policy will be considered by EPA,

State agencies and the Federal Advisory Committee Act's

Particulate Matter/Ozone/Regional Haze Subcommittee if the

NAAQS for particulate matter are revised.

Three categories of natural events have been identified

as affecting the PM-10 NAAQS: (1) volcanic and seismic

activity, (2) wildland fires, and (3) high wind events. These

PM-10
3

 Other types of temporary or exceptional events that can 2

impact ambient PM-10 concentrations are structural fires,

chemical spills, industrial accidents, and clean-up activities

following a major disaster. The EPA's Guideline on the

Identification and Use of Air Quality Data Affected by

Exceptional Events , July 1986, is still applicable for

treating air quality data resulting from these types of

exceptional, anthropogenic events.

natural events are defined further below. If other

significant categories of natural events are identified, they

may be added tothis policy in the future. 2

Background

Prior to the 1990 Clean Air Act Amendments (Act), the

Guideline on the Identification and Use of Air Quality Data

Affected by Exceptional Events (exceptional events guideline)

and Appendix K to 40 CFR, part 50, were issued by EPA to

address, in part, the situation where natural sources strongly

influence an area's PM-10 air quality. To avoid imposing

potentially unreasonable State implementation plan (SIP)

requirements on such areas, EPA provided for the exclusion of

certain natural source data from nonattainment determinations. 

Thus, Appendix K provides, in part, that measured exceedances

of the PM-10 NAAQS in an area may be discounted from decisions

regarding nonattainment status if the data are shown to be

influenced by uncontrollable events caused by natural sources

of particulate matter. The 1986 exceptional events guideline

contains EPA's guidance regarding the process States should

follow when dealing with PM-10 air quality data that may be

eligible for the adjustments authorized under section 2.4 of

Appendix K.

Subsequently, the Act added section 188(f) which provides

EPA with discretionary statutory authority to waive either a

specific attainment date or certain planning requirements for

serious PM-10 nonattainment areas that are impacted

significantly 

by nonanthropogenic sources. The EPA states in current PM-10

guidance documents that it interprets the section 188(f)

waiver provision to mean that the data exclusion policy

contained in Appendix K and the procedures described in the

exceptional events guideline no longer apply. 
4

 The air quality is considered unhealthy whenever the 24- 3

hour PM-10 NAAQS is exceeded. The short-term PM-10 NAAQS is

exceeded when the 24-hour average PM-10 concentration is

Under this natural events policy, those statements no

longer reflect EPA's interpretation of the relationship

between the section 188(f) waiver provision, Appendix K, and

the exceptional events guideline and should be treated as

revised to the extent described herein. 

In establishing this natural events policy, EPA now

believes that, under certain circumstances, it is appropriate

to again exclude PM-10 air quality data that are attributable

to uncontrollable natural events from the decisions regarding

an area's nonattainment status. The discussion in the

Appendix at the end of this memorandum briefly describes the

legal rationale underlying this revised interpretation.

Description of Policy

The policy described in this document addresses PM-10

NAAQS violations caused by natural events in areas designated

unclassifiable or attainment. It also addresses certain

reclassification and redesignation questions for PM-10

nonattainment areas. This policy applies at the time the

State determines that a PM-10 NAAQS has been violated due to

natural events and addresses the question of what should be

done to protect public health. The policy provides that EPA

will: (1) exercise its discretion under section 107(d)(3) not

to redesignate areas as nonattainment if the State develops

and implements a plan to respond to the health impacts of

natural events; and, (2) redesignate nonattainment areas as

attainment by applying Appendix K, on a case-by-case basis, to

discount data in circumstances where an area would attain but

for exceedances that result from uncontrollable natural

events. 

The guiding principles followed in developing this policy

are:

1. Protection of public health is the highest priority of

Federal, State, and local air pollution control agencies.

2. The public must be informed whenever the air quality in an

area is unhealthy. 3
5

greater than 150 micrograms per cubic meter (μg/m ). The 24- 3

hour NAAQS is violated when the expected number of days per

calendar year with a 24-hour average concentration above 150

μg/m is greater than 1.0, as determined by procedures 3

described in Appendix K.

3. All valid ambient air quality data should be submitted to

the EPA Aerometric Information Retrieval System (AIRS) and

made available for public access.

4. State and local agencies must take appropriate reasonable

measures to safeguard public health regardless of the source

of PM-10 emissions.

5. Emission controls should be applied to sources that

contribute to exceedances of the PM-10 NAAQS when those

controls will result in fewer violations of the standards.
6

 The EPA recognizes and endorses the Federal Wildland Fire 4

Policies adopted by the Departments of Interior and

Agriculture in December 1995. These policies refer to all

fires on sparsely populated lands managed by Federal agencies

(e.g., national parks, national forests, grasslands, etc.) as

wildland fires. The wildland fires term includes unwanted

fires that do not meet a prescription (wildfires), managementignited prescribed fires, and naturally-ignited fires that

meet a prescription (prescribed natural fire). Only wildland

fires that meet a prescription may be used to accomplish land

and resource management objectives. 

Definition of PM-10 Natural Events

Volcanic and seismic activities : Ambient PM-10

concentrations caused by volcanic eruptions or seismic

activity will be treated as due to natural events. Volcanic

eruptions contribute to ambient PM-10 concentrations in two

ways: (1) with emissions of primary PM-10 (e.g., ash), and

(2) with emissions of precursor pollutants (e.g., sulfur

dioxide) that react to form secondary particulate matter. 

Seismic activity (e.g., earthquakes) can also contribute to

ambient PM-10 concentrations by shaking the ground, causing

structures to collapse and otherwise raising dust (primary PM10 emissions).

Also, emissions caused by anthropogenic activities that

re-entrain volcanic ash during the first year (12 months)

following an event will be treated as due to the natural

event. One year is considered adequate time for cleaning ash

deposits from areas where anthropogenic activities (e.g.,

vehicle traffic) would cause reentrainment. After 1 year,

only emissions resulting from reentrainment of ash by high

winds will be treated as due to a natural event.

Wildland fires : Ambient PM-10 concentrations caused by

smoke from wildland fires will be treated as due to natural

events if the fires are unwanted fires, not designated or

managed as prescribed fires, and requiring appropriate

suppression action by the wildlands manager. 4

For the purposes of this policy, wildland fire natural

events are limited to unwanted fires that do not meet a

prescription (wildfires) and, therefore, require appropriate

suppression actions. Wildland prescribed fires, burning of
7

 BACM for PM-10 are techniques that achieve the maximum 5

degree of emissions reduction from a source as determined on a

case-by-case basis considering technological and economic

feasibility (59 FR 42010, August 16, 1994).

forest harvest residues, agricultural burning, and fires for

land clearing are not covered by this natural events policy. 

The EPA will develop broader guidance in the near future to

address issues raised by smoke emissions from wildland

prescribed fires and other policy issues surrounding

prevention of significant deterioration, conformity,

visibility protection programs and regional haze. 

High Winds : Ambient PM-10 concentrations due to dust

raised by unusually high winds will be treated as due to

uncontrollable natural events under the following conditions: 

(1) the dust originated from nonanthropogenic sources, or (2)

the dust originated from anthropogenic sources controlled with

best available control measures (BACM). 5

 The BACM must be implemented at contributing

anthropogenic sources of dust in order for PM-10 NAAQS

exceedances to be treated as due to uncontrollable natural

events under this policy. Therefore, BACM must be implemented

for anthropogenic dust sources contributing to NAAQS

exceedances in attainment and unclassifiable areas and in

moderate PM-10 nonattainment areas. In unclassifiable and

attainment areas, BACM must be implemented for those

contributing sources for which it has been defined within 3

years after the first NAAQS violation attributed to high wind

events or from the date of this policy. In these same areas,

implementation should be as expeditious as practicable for

sources for which BACM are undefined.

The conditions that create high wind events vary from

area to area with soil type, precipitation and the speed of

wind gusts. Therefore, the State must determine the unusually

high wind conditions that will overcome BACM in each region or

subregion of the State.

Response to NAAQS Violations

If natural events cause ambient concentrations of PM-10

to violate a NAAQS, a plan should be developed to address

future 
8

 The annual PM-10 NAAQS is violated if the expected 6

average annual arithmetic mean concentration for the past 3

calendar years is greater than 50 μg/m . Several elevated 24- 3

hour PM-10 concentrations caused by natural events can

potentially cause the annual NAAQS (which is an annual

arithmetic mean of 24-hour concentrations) to be exceeded. If

natural events cause the annual NAAQS to be violated, one NEAP

for the area will cover both the 24-hour and annual NAAQS.

events. A natural events action plan (NEAP) should include 6

commitments to:

1. Establish public notification and education programs. 

Such programs may be designed to educate the public about the

short-term and long-term harmful effects that high

concentrations of PM-10 could have on their health and inform

them that: (a) certain types of natural events affect the air

quality of the area periodically, (b) a natural event is

imminent, and (c) specific actions are being taken to minimize

the health impacts of events.

2. Minimize public exposure to high concentrations of PM-10

due to future natural events. Programs to minimize public

exposure should: (a) identify the people most at risk, (b)

notify the at-risk population that a natural event is imminent

or currently taking place, (c) suggest actions to be taken by

the public to minimize their exposure to high concentrations

of PM-10, and (d) suggest precautions to take if exposure

cannot be avoided.

3. Abate or minimize appropriate contributing controllable

sources of PM-10. Programs to minimize PM-10 emissions may

include: 

(a) volcanic and seismic activities - cleaning ash and

dust deposits from areas where it would be re-entrained into

the air by anthropogenic activities; 

(b) wildland fires - prohibition of other burning

activities during wildland fire events and steps to minimize

fuel loadings in areas vulnerable to fire. Appropriate

suppression actions, as determined by the wildlands manager,

should be taken for fires that do not meet a prescription. 

The Federal Wildland Fire Policies require that fire

management plans (FMP) be developed
9

 FMP are not in place for all Federal lands at this time. 7

These plans will be developed by Federal land managers in

conjunction with all stakeholders including Federal, State and

local air management agencies. The FMP will integrate fire,

as a natural ecological process, into land and resource

management plans and will form the basis for management

actions taken on wildland fires. The FMP must include

prescriptions for any use of fire to meet land and resource

management objectives.

The EPA anticipates that FMP will achieve an acceptable

balance between forest health and public health concerns. 

Public health concerns caused by the potential effects of

smoke on air quality from wildland fires will be addressed in

FMP through smoke management plans and other measures. Smoke

management plans attempt to minimize smoke impacts by

monitoring fire behavior, meteorology and air quality during

the fire and by publicly announcing forecasts of likely smoke

conditions in communities impacted by ongoing fires. Since

FMP will treat fire as a natural ecological process, the

impact of wildland fires on air quality and regional haze is

expected to increase in the future. Therefore, EPA will

encourage Federal land management agencies to support air

quality monitoring near fires, to assess

air and haze impacts, and to develop a fire information data

base and regional-scale smoke management plans. 

for all Federal lands with burnable vegetation. It is 7

anticipated that a goal of FMP will be to prevent NAAQS

exceedances caused by wildland fires. Therefore, EPA

envisions treating future FMP as acceptable plans for

mitigating the public health impacts of smoke from wildland

fires on Federal lands. Similar FMP should be developed to

serve the same purpose for State and private wildlands.

 

(c) High winds - application of BACM to any sources of

soil that have been disturbed by anthropogenic activities. 

The BACM application criteria require analysis of the

technological and economic feasibility of individual control

measures on a case-by-case basis. The NEAP should include

analyses of BACM for contributing sources. The BACM for

windblown dust include, but are not limited to, application of

chemical dust suppressants to unpaved roads, parking lots and

open areas; dust suppression at construction sites; use of

conservation farming practices on agricultural lands; tree
10

rows and other physical wind breaks; restricting or

prohibiting recreational off-road vehicle activities; and use

of surface coverings. If BACM are not defined for the

anthropogenic sources in question, step 4 below is required.

4. Identify, study and implement practical mitigating

measures as necessary. The NEAP may include commitments to

conduct pilot tests of new emission reduction techniques. For

example, it may be desirable to test the feasibility and

effectiveness of new strategies for minimizing sources of

windblown dust through pilot programs. The plan must include

a timely schedule for conducting such studies and implementing

measures that are technologically and economically feasible.

5. Periodically reevaluate: (a) the conditions causing

violations of a PM-10 NAAQS in the area, (b) the status of

implementation of the NEAP, and (c) the adequacy of the

actions being implemented. The State should reevaluate the

NEAP for an area every 5 years at a minimum and make

appropriate changes to the plan.

Form and Timing of the Response

The NEAP should be developed by the State air pollution

control agency in conjunction with the stakeholders affected

by the plan. Development of a NEAP for wildland fires should

include input from Federal, State and private land managers in

areas vulnerable to fire. Also, agencies responsible for

suppressing fires and the citizens in the affected area should

be involved in developing the plan. Development of a NEAP for

high- wind events should include input from Federal, State and

private managers of open desert lands, rangelands,

agricultural lands; the construction industry; and

organizations promoting the use of recreational off-road

vehicles. Development of a NEAP for volcanic and seismic

activities should include input from geophysicists and public

works officials who will be responsible for ash removal and

disposal. The plan should include documented agreements among

the stakeholders as to planned actions, the implementation

schedule, and the parties responsible for carrying out those

actions.

At a minimum, States should develop NEAP for any areas

where natural events cause or have caused a PM-10 NAAQS to be

violated within 18 months of the violation or the date this

policy is issued. The NEAP should be made available for public
11

review and comment and may, but are not required to, be

adopted as revisions to the SIP if current SIP rules are not

revised. Final plans should be submitted to EPA for review

and comment. 

Documentation of Natural Events 

In circumstances where a State has reason to believe that

natural events have caused measured exceedances of the NAAQS,

the State is responsible for establishing a clear causal

relationship between the measured exceedance and the natural

event. Supporting documentation concerning the natural event

could include filter analysis, meteorological data (e.g., wind

speed and wind direction to support a source receptor

relationship), modeling and receptor analysis, videos and/or

photographs of the event and the resulting emissions, maps of

the area showing sources of emissions and the area affected by

the event, and news accounts of the event.

In the case of high-wind events where the sources of dust

are anthropogenic, the State must document that BACM were

required for those sources, and the sources were in compliance

at the time of the high-wind event. If BACM are not required

for some dust sources, the NEAP developed must include

agreements with appropriate stakeholders to minimize future

emissions from such sources using BACM. 

The type and amount of documentation provided for each

event should be sufficient to demonstrate that the natural

event occurred, and that it impacted a particular monitoring

site in such a way as to cause the PM-10 concentrations

measured. This documentation should also provide evidence

that, absent the emissions from the natural event,

concentrations of PM-10 at the monitoring site under

consideration would not cause a NAAQS exceedance. 

The State should also make the documentation of natural

events and their impact on measured air quality available to

the public for review. This may be accomplished through a

number of means, such as the publishing of newspaper

announcements, periodic reports on air quality in the area,

and through public hearings. This would serve to allow the

public an opportunity to comment on whether the causal

relationship between the natural event and the air quality

measurement is convincing. Also, open hearings, where State

and local regulatory boards review the documentation, are
12

 The 1990 Amendments to the Clean Air Act required that 8

control measures for anthropogenic sources in PM-10

nonattainment areas be implemented by the end of 1993. 

Therefore, this policy is made retroactive to January 1, 1994

so that NAAQS exceedances that may prevent areas from having

sufficient clean air quality data to meet the standards will

be covered by this policy.

useful forums in which to notify the public of potentiallyimportant policy decisions.

When air quality data affected by a natural event are

submitted to EPA for inclusion into the AIRS data base, the

State should request that a flag be placed on the data to

indicate that a natural event was involved. Documentation to

support the flagged data should be maintained by the State. A

copy of the documentation should be sent to the relevant EPA

Regional Office monitoring representative no later than 180

days from the time the exceedance occurred or from the date of

this policy for past events. The Regional Office will

acknowledge receipt of the documentation and confirm that the

natural event data were flagged within 60 days. 

Current PM-10 Nonattainment Areas

States may request that a moderate nonattainment area not

be reclassified as serious if it can be demonstrated that the

area would attain the standards by the statutory attainment

date but for emissions caused by natural events. Similarly,

States may request redesignation of nonattainment areas to

attainment if it can be demonstrated that the area would be

meeting the NAAQS but for the emissions caused by natural

events. This policy applies to emissions caused by natural

events that have occurred since January 1, 1994. 8

Approval of the above requests will be made by EPA on a

case-by-case basis as determined by the sufficiency of the

information submitted by the State to substantiate its claim. 

At a minimum, the State must have adopted a SIP for the area

which demonstrates that, but for the emissions from natural

events, the area would be able to attain the NAAQS. All of

the requirements under section 107(d)(3)(E) of the Act must

also be satisfied before an area can be redesignated to

attainment. Those requirements include the submittal of a

maintenance plan under section 175A, among other things. The
13

maintenance plan for areas affected by natural events must

include a NEAP. 

Failure to Submit a Natural Events Action Plan

If a State fails to submit an adequate NEAP within 18

months in response to violations of a PM-10 NAAQS, EPA will

notify the governor of the State that the area should be

redesignated as nonattainment. The EPA's action, in such

instances, would be authorized under the Act based on the

conclusion that the health of citizens affected by such events

is not being protected by the State.

Once the area violating the NAAQS is designated

nonattainment, the State will be required to adopt a

federally- enforceable SIP revision and address the sources of

PM-10 emissions. Most likely, the SIP revision will include

many of the same mitigative measures that could have been

included in a NEAP.
APPENDIX

INTERPRETATION OF THE CLEAN AIR ACT (ACT) AS AMENDED IN 1990

Section 107(d)(4)(B) of the Act, as amended in 1990,

provided EPA with the authority to designate initial areas as

nonattainment for PM-10. Where such determinations involved

an assessment of a potential PM-10 nonattainment area's air

quality data, Congress expressly required such assessments to

be made in accordance with Appendix K (section

107(d)(4)(B)(ii)). Since, upon enactment, Congress did not

alter or revise Appendix K in any way, all the provisions of

Appendix K, including section 2.4, remained applicable under

the Act. Among other things, section 2.4 authorizes EPA to

discount air quality data that are attributable to "an

uncontrollable event caused by natural sources" of PM-10. 

Consequently, if an area's nonattainment problem was

attributable to uncontrollable natural sources, application of

section 2.4 of Appendix K would allow the data from the

uncontrollable natural event to be excluded from regulatory

determinations regarding an area's nonattainment status.

The Act also added section 188(f) which specifically

addresses the adverse influence of nonanthropogenic PM-10

sources. This section provides EPA with discretionary

authority to waive a specific attainment date for all areas or

certain planning requirements for serious PM-10 nonattainment

areas that are significantly impacted by nonanthropogenic

sources.

The EPA previously interpreted the inclusion of such an

express waiver provision in the 1990 Amendments as implying

that Congress may have intended to limit the application of

section 2.4 of Appendix K. The argument in support of this

interpretation was that in contrast to section 2.4 of Appendix

K, which contemplates the discounting of data due to emissions

from certain events, the section 188(f) waiver provisions

envisioned that adjustments prompted by adverse air quality

impacts that are attributable to data from natural

uncontrollable sources of PM-10 should be made only after all

the data have been considered and the area has been designated

nonattainment.

The EPA, however, believes that this is not the only

reasonable interpretation of the Act's provisions that is

possible. The EPA believes that the congressional directive

in section 107(d)(4)(B)(ii) to base designation decisions on
Appendix K, and the differences in how section 188(f) and

Appendix K address issues related to emissions from natural

sources, indicate that it is not necessary to conclude that

section 188(f) limits the application of section 2.4 of

Appendix K. Rather, it is possible to view both section

188(f) and section 2.4 of Appendix K as being operative and

dealing with related but distinct aspects of the issues

connected with emissions from natural PM-10 sources.

The starting point for this analysis is section

107(d)(4)(B)(ii), which, by operation of law, designated

nonattainment any area with data showing a violation of the

PM-10 NAAQS before January 1, 1989 "(as determined under part

50, appendix K of title 40 of the Code of Federal

Regulations)." In that section, Congress required the use of

Appendix K in designating areas nonattainment without

indicating that any portion of Appendix K was to be considered

invalid. Thus, that provision indicates that Congress

intended designation decisions to be based on that appendix,

including the procedures in section 2.4 regarding exceptional

events. 

Notably, section 2.4 defines an exceptional event as "an

uncontrollable event caused by natural sources of particulate

matter or an event that is not expected to recur at a given

location." Thus, exceptional events include both

uncontrollable natural sources and nonrecurring events related

to any kind of source of particulate matter. Section 2.4

further provides that data from such events may be discounted

(i.e., EPA may compensate for such data or exclude such data

entirely from decisions regarding an area). Consequently,

Appendix K contemplates that data from "exceptional events"

may be discounted, including, but not limited to, data due to

emissions from uncontrollable natural events. 

On the other hand, section 188(f), which was enacted by

Congress in the same amendments as section 107(d)(4)(B)(ii),

discusses PM-10 natural sources in terms of whether they are

"anthropogenic" or "nonanthropogenic." It does not discuss

such sources or emissions in the terms of Appendix K (i.e., it

does not discuss matters in terms of exceptional or

nonexceptional events, nor does it distinguish between

uncontrollable and controllable natural sources). In general,

section 188(f) provides that EPA may waive certain

requirements where EPA determines that anthropogenic sources

do not contribute significantly to a violation of the PM-10

standard, and that EPA may waive a specific attainment date if
it determines that the contribution of nonanthropogenic

emissions to a violation is demonstrated to be "significant."

As Congress, without express exception, directed the use

of Appendix K in determining whether areas were attaining the

PM-10 standard, EPA believes it is reasonable to interpret

section 188(f) as not limiting the use of that appendix,

provided that such an interpretation does not render section

188(f) invalid. The EPA believes that the approach taken in

this natural events policy does not do that, and that it

represents a reasonable harmonization of these provisions of

the Act and the language of Appendix K regarding exceptional

events.

Under EPA's revised interpretation, section 188(f)

continues to have force and effect. As section 188(f)

addresses the issues in terms of "anthropogenic" and

"nonanthropogenic" sources, not in terms of exceptional events

(which are defined in Appendix K as both uncontrollable

natural events and nonrecurring events from both natural and

other sources), it is possible to view the waivers of section

188(f) as being potentially applicable only to areas that are

designated nonattainment because the data do not qualify for

adjustment under Appendix K. For such areas, it may be

reasonable and appropriate to grant waivers from some

requirements that simply do not make sense in light of the

nature of the sources generating the PM-10 problem in the

area. Thus, EPA's new interpretation does not render section

188(f) meaningless. Consequently, EPA believes that the

exercise of its discretionary authority under Appendix K to

discount or de-weight air quality data that are affected by

uncontrollable natural sources of PM-10 is reasonable and

appropriate.