Can Tennessee enforce its weather-modification ban on activities like cloud seeding when the chemicals are released in federally controlled airspace?

Plain-English summary

Tennessee passed legislation prohibiting the intentional injection, release, or dispersion of chemicals or substances into the atmosphere with the express purpose of affecting temperature, weather, or sunlight intensity. Tenn. Code Ann. § 68-201-122. Violation is a Class C misdemeanor with civil penalties up to $25,000 per day. The legislators who requested this opinion asked: can the state actually enforce that ban when the alleged activity happens in airspace the federal government controls?

The AG split the answer along two axes:

1. Ground-based weather modification (e.g., ground-based cloud seeding): Almost certainly enforceable. States exercise broad authority over land use and over activities physically conducted on the ground. No federal statute substantively regulates weather modification, and the Clean Air Act explicitly preserves state authority over emissions in this context.

2. Activities in navigable airspace (e.g., aircraft-based cloud seeding): Mixed. The Federal Aviation Act preempts the field of "aviation safety and efficient use of the airspace" but not all state regulation that touches airspace. The Clean Air Act expressly preempts state standards for aircraft engine emissions but not for non-emission releases. So enforcement against ground-launched activities is fine, enforcement against aircraft-mounted emission systems likely is not, and middle cases (e.g., a release from an aircraft that is not a propulsion emission) are uncertain.

What this means for you

If you operate or are considering a weather-modification project in Tennessee

The base prohibition applies state-wide. If your operation is purely ground-based (towers, ground-based generators, surface dispersion systems), the state can enforce against you, and there is no federal preemption defense. If your operation uses aircraft, your defense depends on what is being released and how. Aircraft engine emissions are protected by 42 U.S.C. § 7573's preemption clause. Releases that are not engine emissions, like dispersing seeding chemicals from a payload tank in flight, sit in unsettled territory and are not categorically preempted.

Practical step: get aviation and environmental counsel involved before the first flight. Document each release as either an engine-emission event (federally preempted defense) or a payload-discharge event (not categorically preempted). The line matters.

If you are an air-pollution-control staff attorney for Tennessee

This opinion gives you a litigation roadmap. For ground-based enforcement, the federal-preemption defense will fail. For aircraft-based enforcement targeting payload releases, you can argue the Clean Air Act preserves state authority via § 7416 because the activity is not an "aircraft engine emission" under § 7573. For aircraft engine emissions (combustion byproducts), expect a strong preemption defense under § 7573 and the FAA's exclusive jurisdiction over aircraft operations.

The FAA's own July 2023 fact sheet on state and local UAS regulation is your friend. The agency itself takes the position that federal preemption is "limited to the fields of aviation safety and efficient use of the airspace," not "altogether any state regulation purporting to reach into the navigable airspace." Cite it.

If you are a state legislator considering similar legislation

The AG opinion is a useful template for understanding which formulations survive preemption. Tennessee's statute is broad ("intentional injection, release, or dispersion of chemicals, chemical compounds, substances, or apparatus . . . with the express purpose of affecting temperature, weather, or the intensity of the sunlight"). That breadth gets you preemption-resistant ground-based coverage. If you also want airborne coverage, the safest design targets the purpose and the type of substance without targeting aircraft operations themselves. Specifying "ground-launched" or "ground-based" releases avoids the field that 49 U.S.C. § 40103(b)(1) reserves for the FAA.

If you defend an alleged violator

The strongest defenses, in order:
1. The activity was an aircraft engine emission and is preempted under 42 U.S.C. § 7573.
2. The activity was conducted in navigable airspace such that field preemption applies under 49 U.S.C. § 40103(b)(1) and the Federal Aviation Act, even if not strictly an aircraft emission.
3. The activity does not meet the statutory definition (no "express purpose of affecting temperature, weather, or the intensity of the sunlight").
4. The substances are not "chemicals, chemical compounds, substances, or apparatus" within the statute's contemplated scope (e.g., water vapor or ordinary aircraft exhaust).

These defenses get progressively weaker. The first is strongest because the federal text is express. The fourth is fact-dependent and likely fails for traditional cloud-seeding chemicals (silver iodide, sodium chloride).

Common questions

Q: What is "weather modification" under Tennessee law?
A: Section 68-201-122 prohibits the intentional injection, release, or dispersion of chemicals, chemical compounds, substances, or apparatus into the atmosphere with the express purpose of affecting temperature, weather, or the intensity of the sunlight. The classic examples are cloud seeding (silver iodide, sodium chloride for precipitation enhancement) and proposed solar radiation management techniques (sulfur aerosol injection).

Q: What are the penalties?
A: A knowing violation is a Class C misdemeanor with criminal fines up to $10,000 per day per violation under § 68-201-112. Civil penalties up to $25,000 per day per violation under § 68-201-116(b)(1). The Air Pollution Control Board or Commissioner of Environment and Conservation can also abate violations as public nuisances.

Q: Why does federal preemption come into play at all?
A: Two federal regimes. First, the Clean Air Act expressly preempts state regulation of aircraft engine emissions. 42 U.S.C. § 7573. Second, the Federal Aviation Act gives the FAA "exclusive sovereignty" over U.S. airspace and authority to regulate flight operations. Tennessee's law could in some applications conflict with those.

Q: Does the state have any authority over its airspace at all?
A: Yes, partial. Tennessee Code Annotated § 42-1-102 declares that "[s]overeignty in the space above the lands and waters of this state is declared to rest in the state, except where granted to and assumed by the United States." The U.S. Supreme Court in Braniff Airways recognized that the federal declaration of sovereignty "did not expressly exclude the sovereign powers of the states" and was "an assertion of exclusive national sovereignty" only as against other nations.

Q: Is cloud seeding (which has happened in many states for decades) actually banned now in Tennessee?
A: Yes, if conducted within Tennessee's borders for the purpose of affecting weather. The statute is new (2024) and is broad. There are no carve-outs for established cloud-seeding programs.

Q: What about a federal weather-modification project conducted in Tennessee airspace?
A: That would invoke a different preemption analysis (the federal-instrumentality doctrine and the Supremacy Clause more broadly). The opinion does not address that scenario. Federal projects would not be subject to state criminal enforcement.

Q: Could the state enforce against a person who orders weather modification from Tennessee but the actual release happens out of state?
A: The opinion does not address extraterritorial enforcement. Courts generally apply criminal statutes only to conduct with a sufficient nexus to the state. A purely out-of-state release with no Tennessee impact would face significant jurisdictional hurdles.

Background and statutory framework

Tennessee's weather-modification ban is part of an amendment to the Tennessee Air Quality Act, codified at Tenn. Code Ann. § 68-201-122. The Act predates this provision and provides the enforcement machinery: Class C misdemeanor penalties under § 68-201-112, civil penalties under § 68-201-116, and public-nuisance abatement authority for the Air Pollution Control Board.

The federal preemption analysis turns on three doctrines:

• Express preemption. A federal statute uses explicit language to displace state law. The Clean Air Act does this for aircraft engine emission standards in 42 U.S.C. § 7573.
• Conflict preemption. State law makes compliance with federal law impossible or stands as an obstacle to congressional purposes. This doctrine has been narrowed in recent Supreme Court cases like Kansas v. Garcia.
• Field preemption. Federal law occupies an entire regulatory field, leaving no room for state supplementation. The Federal Aviation Act is widely understood to occupy the field of aviation safety and efficient airspace use, but the FAA itself reads that field narrowly.

The opinion's analytical move is to separate the purpose of the regulation (weather modification, traditionally a state-regulated field) from the medium of the regulated conduct (atmospheric release, sometimes overlapping with federal aviation regulation). When the regulation targets weather modification on the ground, no federal field is implicated. When it targets aircraft engine emissions, § 7573 expressly preempts. The middle ground (aircraft-mounted, non-emission releases of weather-modification chemicals) is the genuinely uncertain space.

The opinion notes that "[f]ield preemption of state law is disfavored" (citing the Fifth Circuit's McCraw decision) and that even Kansas v. Garcia signaled the Supreme Court's willingness to rein in implied preemption. Both points support narrower preemption of Tennessee's law than a maximalist reading might suggest.

Citations and references

Statutes:
- Tenn. Code Ann. § 68-201-122 (Weather modification ban)
- Tenn. Code Ann. § 68-201-112 (Air Quality Act enforcement)
- 49 U.S.C. § 40103 (Federal Aviation Act airspace authority)
- 42 U.S.C. § 7573 (Clean Air Act aircraft emission preemption)
- 42 U.S.C. § 7416 (Clean Air Act state authority)

Cases:
- Murphy v. NCAA, 584 U.S. 453 (2018), preemption framework
- Kansas v. Garcia, 589 U.S. 191 (2020), narrowing implied preemption doctrine
- Braniff Airways, Inc. v. Neb. State Bd. of Equalization & Assessment, 347 U.S. 590 (1954), federal airspace sovereignty does not erase state authority
- Gustafson v. City of Lake Angelus, 76 F.3d 778 (6th Cir. 1996), FAA's exclusive authority over airspace regulation
- Riggs v. Burson, 941 S.W.2d 44 (Tenn. 1997), Tennessee Supreme Court on FAA airspace authority

Source

• Landing page: https://www.tn.gov/attorneygeneral/opinions.html
• Original PDF: https://www.tn.gov/content/dam/tn/attorneygeneral/documents/ops/2025/op25-006.pdf

Original opinion text

STATE OF TENNESSEE
OFFICE OF THE ATTORNEY GENERAL
February 28, 2025
Opinion No. 25-006
Enforceability of Prohibition on Weather Modification Activities

Question 1
Does Tenn. Code Ann. § 68-201-112 allow Tennessee to enforce Tenn. Code Ann. § 68-
201-122 when there is injection, release, or dispersion of the prohibited material into federally
controlled airspace, or airspace that is otherwise under the jurisdiction of the federal government?

Opinion 1
It depends. A court would likely find some attempts to enforce Tenn. Code Ann. § 68-
201-122 expressly or impliedly preempted, but not others.

Question 2
If not, in what other manner, if any, can Tennessee enforce Tenn. Code Ann. § 68-201-122
when there is injection, release, or dispersion of the prohibited material into federally controlled
airspace, or airspace that is otherwise under the jurisdiction of the federal government, for the
purposes of the release of chemicals, chemical compounds, substances, or other apparatus?

Opinion 2
See Response to Question 1. Tennessee can likely enforce Tenn. Code Ann. § 68-201-122
to ground-based activities that involve injection, release, or dispersion of material into the air. But
to the extent the question contemplates enforcement of § 68-201-122 to emissions, the federal
Clean Air Act may preempt enforcement. And for releases occurring in navigable airspace, a court
may find § 68-201-122 impliedly preempted depending on the facts.

ANALYSIS

A recent amendment to the Tennessee Air Quality Act ("the Act"), codified in Tenn. Code
Ann. § 68-201-122, provides that "[t]he intentional injection, release, or dispersion, by any means,
of chemicals, chemical compounds, substances, or apparatus within the borders of this state into
the atmosphere with the express purpose of affecting temperature, weather, or the intensity of the
sunlight is prohibited." Tenn. Code Ann. § 68-201-122. Like other violations of the Act,
violations of § 68-201-122 trigger the enforcement mechanisms outlined in Tenn. Code Ann. § 68-
201-112. Under that statutory section, a person who knowingly violates a provision of the Act
commits a Class C misdemeanor and is subject to a fine "not to exceed ten thousand dollars
($10,000) per day per violation." Tenn. Code Ann. § 68-201-112(a). "In addition to the criminal
penalties of § 68-201-112," any person who violates a provision of the Act "shall be subject to a
civil penalty of up to twenty-five thousand dollars ($25,000) per day for each day of violation."
Tenn. Code Ann. § 68-201-116(b)(1). Moreover, if the Air Pollution Control Board or the
Commissioner of Environment and Conservation finds that a provision of the Act has been violated
and that the violation constitutes a public nuisance, "the board or commissioner has authority to
abate any such public nuisance in the manner provided by the general law relating to the abatement
of public nuisances." Tenn. Code Ann. § 68-201-112(d).

Your question about enforcing § 68-201-122, namely your concern that certain airspace is
"under the jurisdiction of the federal government," implicates the doctrine of federal preemption.

Preemption Doctrine. The Supremacy Clause provides that the "Constitution, and the
Laws of the United States which shall be made in Pursuance thereof . . . shall be the supreme Law
of the Land." U.S. Const., art. VI, cl. 2. That Clause provides "a rule of decision" for determining
whether federal or state law applies in a particular situation. Armstrong v. Exceptional Child Ctr.,
Inc., 575 U.S. 320, 324 (2015). If "a state law confers rights or imposes restrictions that conflict
with the federal law," "the federal law takes precedence and the state law is preempted." Murphy
v. NCAA, 584 U.S. 453, 477 (2018).

Any preemption of state law must "stem from either the Constitution itself or a valid statute
enacted by Congress." Kansas v. Garcia, 589 U.S. 191, 202 (2020). In some cases, a federal
statute "may preempt state authority by so stating in express terms," express preemption. Pac.
Gas & Elec. Co. v. State Energy Res. Conservation & Dev. Comm'n, 461 U.S. 190, 203 (1983).
But the Supreme Court has long recognized that "preemption may also occur by virtue of
restrictions or rights that are inferred from statutory law." Garcia, 589 U.S. at 203. That implied
preemption takes two forms: conflict preemption and field preemption.

The conflict preemption doctrine has evolved over time. At the founding, courts looked
only to "whether the ordinary meaning of federal and state law directly conflict." Id. at 214
(Thomas, J., concurring) (quotations omitted). Over time, though, the Supreme Court loosened
the conflict inquiry and held state laws preempted if they stood "as an obstacle to the
accomplishment and execution of the full purposes and objectives of Congress." Hines v.
Davidowitz, 312 U.S. 52, 67 (1941); see also Matthews v. Centrus Energy Corp., 15 F.4th 714,
720 (6th Cir. 2021). That purposes-and-objectives inquiry has been widely criticized because "[a]
free wheeling judicial inquiry into whether a state statute is in tension with federal objectives
would undercut the principle that it is Congress rather than the courts that pre-empts state law."
See, e.g., Gade v. Nat'l Solid Wastes Mgmt. Ass'n, 505 U.S. 88, 111 (1992) (Kennedy, J.,
concurring in part and concurring in judgment). And in recent years, the Court has reined in the
doctrine. In Garcia, for example, the Court emphasized that "[t]he Supremacy Clause gives
priority to 'the Laws of the United States,' not the criminal law enforcement priorities or
preferences of federal officers." 589 U.S. at 212. And it noted that preemption cannot be based
on "a 'freewheeling judicial inquiry into whether a state statute is in tension with federal
objectives.'" Id. at 202 (quoting Chamber of Com. of U.S. v. Whiting, 563 U.S. 582, 607 (2011)
(plurality)).

Field preemption, another species of implied preemption, likewise rests on a shaky
foundation. Under the field preemption doctrine, courts determine "if the federal law so
thoroughly occupies the legislative field 'as to make reasonable the inference that Congress left no
room for the States to supplement it.'" Riggs v. Burson, 941 S.W.2d 44, 49 (Tenn. 1997) (quoting
Fid. Fed. Sav. & Loan Ass'n v. de la Cuesta, 458 U.S. 141, 153 (1982)). But that just begs the
question of "what field" and why preempt the field if Congress provided no instruction to do so.
In this vein, it is noteworthy that the jurisprudential framework for analyzing federal preemption
has been roundly criticized or questioned by judges and commentators alike. See, e.g., Garcia,
589 U.S. at 214 n.* (Thomas, J., concurring) ("I am also skeptical of field pre-emption . . . ."). And
unsurprisingly, "[f]ield preemption of state law is disfavored." Nat'l Press Photographers Ass'n
v. McCraw, 90 F.4th 770, 796 (5th Cir. 2024).

The enforcement of § 68-201-122 implicates each of these preemption doctrines. And,
given the state of federal law, the analysis differs depending on where the base of the prohibited
weather modification activity occurs. As explained below, although we believe that a court is
likely to conclude that Tennessee can generally enforce the statute as applied to activities
conducted from a base on the ground, there is a risk that a court could hold that enforcement is
preempted as applied to activities occurring in navigable airspace.

Enforcement of § 68-201-122 to activities in navigable airspace. Numerous federal
statutes address issues implicating activities in navigable airspace. A court would likely find at
least some applications of enforcing § 68-201-122 preempted by these laws. But no federal law
cleanly preempts enforcement of § 68-201-122 wholesale to activities in navigable airspace.

Start with 49 U.S.C. § 40103(a)(1). That provision states that "[t]he United States
Government has exclusive sovereignty of airspace of the United States." 49 U.S.C. § 40103(a)(1).
On its face, this declaration of sovereignty might appear to suggest that the federal government
exercises exclusive dominion over the entirety of the skies. In reality, though, § 40103(a)(1) does
much more limited work. The congressional acts on which § 40103(a)(1) is based, including the
Air Commerce Act of 1926, make clear that "Congress used this section to declare sovereignty
only internationally" and "did not intend to trample on the sovereignty of states' airspace rights."
Stephen J. Migala, UAS: Understanding the Airspace of States, 82 J. Air. L. & Com. 3, 15 (2017).
Indeed, when the United States Supreme Court engaged with the Air Commerce Act of 1926 in
Braniff Airways, Inc. v. Nebraska State Board of Equalization & Assessment, it recognized that
the congressional declaration of sovereignty "was an assertion of exclusive national sovereignty"
and that the legislation "did not expressly exclude the sovereign powers of the states." Braniff
Airways, Inc. v. Neb. State Bd. of Equalization & Assessment, 347 U.S. 590, 595 (1954).

Other federal statutes implicating the use of navigable airspace do expressly preempt state
law. Under 42 U.S.C. § 7573, "[n]o State or political subdivision thereof may adopt or attempt to
enforce any standard respecting emissions of any air pollutant from any aircraft or engine thereof
unless such standard is identical to a standard applicable to such aircraft under this part." 42 U.S.C.
§ 7573. Although precedent on this section is "sparse," Codoni v. Port of Seattle, No. 2:23-cv-
795-JNW, 2024 WL 4882015, at 11 (W.D. Wash. Nov. 25, 2024), preemption concerns would
be particularly acute if a state regulation, as applied in a given case, would necessitate aircraft
alterations. Id. at 12; see also California v. Dep't of the Navy, 624 F.2d 885, 888 (9th Cir. 1980)
(opining that 42 U.S.C. § 7573 "was not intended to be preclusive of all state regulation of the
field of aircraft engines" and agreeing that it is "concerned with direct state regulation of aircraft
or aircraft engines or with other state regulation which would affect the aircraft or engine"). This
statute, though, may not be implicated in most contemplated enforcement efforts pertaining to the
prohibition in § 68-201-122. As one commentator has discussed, "[t]he Clean Air Act's mobile
source program . . . largely targets emissions from the operation of engines rather than intentional
releases conveyed by the mobile sources themselves." Tracy D. Hester, Remaking the World to
Save It: Applying U.S. Environmental Laws to Climate Engineering Projects, 38 Ecology L.Q.
851, 879 (2011).

The area of greatest uncertainty regarding federal preemption in navigable airspace comes
from the Federal Aviation Act. Under 49 U.S.C. § 40103(b)(1), "[t]he Administrator of the Federal
Aviation Administration shall develop plans and policy for the use of the navigable airspace and
assign by regulation or order the use of the airspace necessary to ensure the safety of aircraft and
the efficient use of airspace." 49 U.S.C. § 40103(b)(1). Section 40103(b)(2) provides that "[t]he
Administrator shall prescribe air traffic regulations on the flight of aircraft" for, among other
things, "protecting individuals and property on the ground," 49 U.S.C. § 40103(b)(2)(B), and
"using the navigable airspace efficiently." 49 U.S.C. § 40103(b)(2)(C).

These provisions have served as the foundation for a well-entrenched judicial
understanding that state and local control is preempted as it concerns the areas of airspace use and
the regulation of aircraft in flight. In Gustafson v. City of Lake Angelus, for instance, the Sixth
Circuit cited to these provisions in connection with its acknowledgment that "the FAA has
exclusive authority in regulating the airspace over the United States." Gustafson v. City of Lake
Angelus, 76 F.3d 778, 783 (6th Cir. 1996). Similarly, in the previously cited Riggs decision, the
Tennessee Supreme Court referenced 49 U.S.C. § 40103(b)(1) in support of its observation that
there was "congressional intent to place exclusive authority for regulating the airspace above the
United States with the Federal Aviation Administration." Riggs, 941 S.W.2d at 49.

But accepting that the Federal Aviation Act likely preempts some sphere of state law, that
does not mean that all state or local regulation is prohibited by the mere fact that it could have
some effect on the use of airspace. As a recent fact sheet issued by the Federal Aviation
Administration explains, federal field preemption of airspace matters is itself specifically limited
to the fields of aviation safety and efficient use of the airspace. State and Local Regulation of
Unmanned Aircraft Systems (UAS) Fact Sheet ("FAA Fact Sheet") (July 14, 2023). Laws "aimed
at objectives other than aviation safety or airspace efficiency that do not impair the reasonable use
by [unmanned aircraft systems] of the airspace" are likely not to be subject to field or conflict
preemption. The FAA Fact Sheet even states that "[r]estrictions on how [unmanned aircraft
systems] are utilized (i.e., conduct) instead of where they may operate in the airspace would more
likely be consistent with Federal preemption principles." In other words, the exclusivity of the
Federal Aviation Administration's jurisdiction is cabined to "certain regulatory fields, not over
certain airspace."

Applying those principles here leaves little doubt that federal law does not altogether
preempt § 68-201-122. Tennessee Code Annotated § 68-201-122 does not directly involve the
regulation of aircraft or navigable airspace. It broadly addresses weather modification in broad
terms. And as explained infra, that field as a whole, regulation of weather modification, is not
federally preempted.

Any preemption analysis of § 68-201-122 will turn on particular applications of the law.
It is certainly foreseeable that a court might find enforcement of § 68-201-122 preempted as
applied to certain attempts to regulate operations of aircraft in navigable airspace. But unless a
court adopts a broad view of field preemption (broader than even the approach adopted by the
federal government), some regulation of weather modification activities in navigable airspace
would likely be permitted. And any preemption challenge would have to overcome the assumption
that a state's police powers are not to be superseded absent clear congressional purpose, Riggs,
941 S.W.2d at 48, and the reality that "states have traditionally had primary carriage of weather-
modification regulations."

Enforcement of § 68-201-122 to ground-based activities. The prospect of preemption
differs for the enforcement of § 68-201-122 to ground-based activities.

States exercise broad authority with respect to activities occurring on land, even if those
ground-based activities implicate the usage of navigable airspace. This Office has previously
concluded that States "retain regulatory authority over the decision of whether land may be used
as an airport or heliport." Tenn. Att'y Gen. Op. 93-04 (Jan. 13, 1993). And courts have generally
distinguished the "United States' sovereign regulation of the airspace over the United States and
the regulation of aircraft in flight" from regulation involving local control of land. Gustafson, 76
F.3d at 783. As one court stated, there is "no conflict between . . . [non-federal] regulatory power
over land use, and the federal regulation of airspace." Condor Corp. v. City of St. Paul, 912 F.2d
215, 219 (8th Cir. 1990). So the federal laws addressing navigable airspace seem unlikely to pose
any preemption problem for enforcing § 68-201-122 with respect to ground-based weather
modification activities, such as ground-based cloud seeding.

And no federal laws that we are aware of substantively regulate weather modification
efforts. Reporting requirements exist, see 15 U.S.C. § 330a, but "[a]ttempts to pass a
comprehensive weather modification policy at the federal level have failed." MacKenzie L. Hertz,
It's Raining, It's Pouring, Weather Modification Regulation is Snoring: A Proposal to Fill the Gap
in Weather Modification Governance, 96 N.D. L. Rev. 31, 46 (2021). "The federal government
has . . . left substantive weather modification regulation to state authorities."

In light of the foregoing, it is this Office's opinion that enforcement of § 68-201-122
relative to ground-based weather modification activities would be entirely consistent with the
historical liberty states have exercised, virtually unimpeded by the federal government, to regulate
in this area.

Nor does there appear to be any preemption issue under the federal Clean Air Act
concerning § 68-201-122's prohibition on the release of material involved in ground-based
weather modification efforts. First, it is not entirely clear that the framework of the Clean Air Act
would even apply to trigger any potential preemption concern. As one commentator has observed,
"[t]he Clean Air Act only applies to releases of 'pollutants' that meet statutory and regulatory
criteria," and "[h]istorical attempts to modify weather through cloud seeding or other rain-making
technology have fallen under separate state regulatory regimes rather than the Clean Air Act."
Yet, even if we assume that an "air pollutant" would be implicated by a given weather modification
activity, the prohibition represented by § 68-201-122 would still not appear to create any type of
preemption issue. Indeed, enforcing § 68-201-122 would be in furtherance of a statutorily imposed
ban on such emitted "pollutants" being released in a particular setting, and except for preemption
of certain state regulation pertaining to pollutant emissions from moving sources, "nothing in the
Clean Air Act precludes or denies the right of any state . . . to adopt or enforce any standard or
limitation respecting emissions of air pollutants, or any requirement respecting control or
abatement of air pollution." 61B Am. Jur. 2d Pollution Control § 147. The only statutory
qualification is that a State's exercise of such authority must simply be reflected in a policy that is
not less stringent than the Clean Air Act "if an emission standard or limitation is in effect under
an applicable implementation plan or under section 7411 or section 7412 of this title." 42 U.S.C.
§ 7416. Even if "air pollutants" are involved, there is thus leeway for Tennessee to operate
legislatively.

To recap our analysis, it is our opinion that the prospect of enforcing § 68-201-122 is
dependent on where the base of the prohibited weather modification activity occurs and what
activity is being regulated. Although a court is likely to conclude that Tennessee can generally
enforce the statute as applied to activities based on the ground, there is a risk that a court could
hold that enforcement is impliedly preempted for some attempts to regulate activities occurring in
navigable airspace. Moreover, to the extent there might be contemplated enforcement of the statute
relative to actual emissions produced by aircraft from flight operations, such enforcement is
susceptible to express preemption under the federal Clean Air Act.

JONATHAN SKRMETTI
Attorney General and Reporter

J. MATTHEW RICE
Solicitor General

MATTHEW KERNODLE
Assistant Attorney General

Requested by:
The Honorable Rusty Crowe
State Senator
Cordell Hull Building, Suite 720
425 Rep. John Lewis Way North
Nashville, Tennessee 37243

The Honorable Page Walley
State Senator
Cordell Hull Building, Suite 750
425 Rep. John Lewis Way North
Nashville, Tennessee 37243

The Honorable Janice Bowling
State Senator
Cordell Hull Building, Suite 718
425 Rep. John Lewis Way North
Nashville, Tennessee 37243

The Honorable Mark Pody
State Senator
Cordell Hull Building, Suite 754
425 Rep. John Lewis Way North
Nashville, Tennessee 37243