Before Elrod, Chief Judge, and Davis, Jones, Smith, Stewart, Richman, Southwick, Haynes, Graves, Higginson, Willett, Ho, Duncan, Engelhardt, Oldham, Wilson, and Douglas, Circuit Judges.* Per Curiam:** The en banc court heard oral argument in this matter in May 2023. That was more than eighteen months ago. Moreover, the parties in this case have already endured multiple appeals and remands back to the district court, over the course of nine years.1 Another remand would mean that the appellate proceedings in this matter will have delayed resolution of this case by over a decade. Justice delayed is justice denied. Had we known that it would take a year and a half after en banc oral argument to issue an opinion, we would not have granted en banc rehearing. We accordingly AFFIRM the judgment of the district court, dated March 2, 2021.2 W. Eugene Davis, Circuit Judge, concurring, joined by Stewart, Southwick, Haynes, Graves, Higginson, and Douglas, Circuit Judges: We concur in the per curiam opinion for the reasons it expresses. However, we would prefer to affirm the district court’s April 26, 2017 judgment for the reasons expressed in the opinion below. * * * Plaintiffs-Appellees Environment Texas Citizen Lobby, Inc. and Sierra Club, on behalf of their members, brought this Clean Air Act (“CAA”) citizen suit against ExxonMobil Corporation and its affiliates (“Exxon”) seeking civil penalties, payable to the U.S. Treasury, for thousands of unauthorized emissions from Exxon’s Baytown, Texas complex between October 2005 and September 2013. The principal issue before the en banc Court is whether Plaintiffs’ members, who live, work, and recreate near Exxon’s facility, have a sufficient “personal stake”[1] in curtailing Exxon’s ongoing and future unlawful emissions of hazardous pollutants. We conclude that the district court correctly held that Plaintiffs established standing for each of their claims and did not abuse its discretion in awarding a penalty of $19.95 million against Exxon to deter it from committing future violations. Accordingly, we would AFFIRM the district court’s 2017 judgment.[2] BACKGROUND This suit’s twelve-year factual history is recounted in greater detail in the district court’s[3] and this Court’s prior opinions.[4] Briefly stated, Exxon owns and operates a complex in the city of Baytown consisting of a refinery, olefins plant, and chemical plant (collectively the “Complex”). It is the largest petroleum and petrochemical complex in the United States and covers 3,400 acres, with a circumference of almost 13.6 miles. And, of relevance here, the Complex is located near several residential areas in Baytown, with some homes as close as 2,000 yards from its fence line. The Complex is governed by emission permits issued under Title V of the CAA. The Texas Commission on Environmental Quality (“TCEQ”) and the United States Environmental Protection Agency (“EPA”) are jointly responsible for enforcing these permits and regulating Exxon’s emissions at the Complex. In order to monitor compliance, state regulations require Exxon to document and, in some instances, self-report incidents of noncompliance with its permits.[5] On December 13, 2010, Plaintiffs Environment Texas Citizen Lobby, Inc. and Sierra Club, on behalf of their members, sued Exxon for its ongoing permit violations under the CAA’s citizen-suit provision, 42 U.S.C. § 7604(a)(1). Plaintiffs’ members include individuals who live, work, and recreate next to the massive Baytown Complex and have suffered physical, psychological, curtailment, and aesthetic injuries as a result of Exxon’s ongoing unlawful emissions. Plaintiffs requested relief in the form of civil penalties, payable to the U.S. Treasury, to deter Exxon from continuing to violate its permits in the future.[6] It is undisputed that Exxon has a history of repeatedly violating its Title V permits. During the pendency of this suit, Exxon stipulated to spreadsheets documenting its thousands of permit violations between October 2005 and September 2013.[7] Throughout this eight-year claims period, Exxon committed on average more than one permit violation per day, resulting in the unlawful emission of nearly ten million pounds of pollutants. Out of the ten million pounds unlawfully emitted from the Complex, nine million pounds were “criteria pollutants” which the EPA has determined “cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare.”[8] In February 2014, following a thirteen-day bench trial in which twenty-five witnesses testified and 1,148 exhibits were admitted, the district court found that although Plaintiffs had Article III standing, only a few days of Exxon’s violations were “actionable” under the CAA.[9] The court therefore declined to impose civil penalties. Plaintiffs appealed. A panel of this Court reversed and remanded, holding that the district court had analyzed “actionability” too narrowly.[10] On remand, the district court again found that Plaintiffs had standing and held that Exxon was liable for 16,386 days of violations and imposed a $19.95 million civil penalty.[11] This time, Exxon appealed, challenging the district court’s judgment on the issues of standing, affirmative defenses, and penalty factors.[12] A divided panel of this Court held that Plaintiffs had established the injury-in-fact and redressability prongs of Article III standing, but ordered a “limited remand” for additional analysis on which of Exxon’s violations satisfied the “fairly traceable” requirement of standing.[13] The panel majority provided a “rubric” to guide the district court’s traceability analysis on remand. On the second remand, the district court applied the panel’s “rubric” and held that Plaintiffs established traceability for 3,651 days of violations and reduced the penalty award to $14.25 million.[14] For the second time, Exxon appealed the district court’s standing and penalty holdings, and the same divided panel of this Court affirmed.[15] In response, the full Court ordered rehearing en banc and vacated the second and third panel opinions.[16] Now, before the en banc court, Exxon maintains that Plaintiffs lack standing because their members only “correlated” their injuries to five emissions events (representing only forty days of violations), and Exxon has already taken “corrective actions” as to those five events. Accordingly, Exxon contends we should vacate the district court’s judgment and dismiss the case. Plaintiffs argue that under established precedent they have standing and urge us to affirm the district court’s 2017 judgment. LAW & DISCUSSION CAA’s Citizen-Suit Provision The CAA’s citizen-suit provision authorizes “any person” to bring a civil action against another “person . . . who is alleged to have violated (if there is evidence that the alleged violation has been repeated) or to be in violation . . . of an emission standard or limitation under [the Act].”[17] The CAA in turn defines “emission standard” or “emission limitation” as “a requirement established by the State or the [EPA] Administrator which limits the quantity, rate, or concentration of emissions of air pollutants on a continuous basis.”[18] Congress enacted the citizen-suit provision to “encourage citizen participation in the enforcement of standards and regulations established under th[e Clean Air] Act . . . and intended the section to afford citizens very broad opportunities to participate in the effort to prevent and abate air pollution.”[19] If a defendant is found liable, the district court is authorized “to apply any appropriate civil penalties.”[20] If imposed, civil penalties are deposited into a “special fund” in the United States Treasury.[21] In determining whether to assess a penalty and, if so, in what amount, district courts must consider seven enumerated factors, including: “the size of the business, the economic impact of the penalty on the business, the violator’s full compliance history and good faith efforts to comply, the duration of the violation . . . , payment by the violator of penalties previously assessed for the same violation, the economic benefit of noncompliance, and the seriousness of the violation.”[22] The court may also consider any unenumerated factors “as justice may require.”[23] If the court finds a penalty appropriate, the amount must be within the statutory cap in light of the Act’s language that penalties “may be assessed for each day of violation.”[24] Article III Standing Although the CAA authorizes “any person” to bring suit, that person must still meet “the irreducible constitutional minimum of standing” in order to file suit in federal court.[25] Standing is a legal question that we review de novo.[26] But we review findings of fact related to standing for clear error.[27] The requirement of Article III standing “ensures that the parties before us retain a ‘personal stake’ in the litigation.”[28] To establish such a “personal stake,” a plaintiff bears the burden of showing (1) an injury in fact,(2) fairly traceable to the defendant’s challenged conduct, (3) that is likely redressable by the requested relief.[29] Although “the proof required to establish standing increases as the suit proceeds, the standing inquiry remains focused on whether the party invoking jurisdiction had the requisite stake in the outcome when the suit was filed.”[30] In cases that proceed to trial, standing must be established by a preponderance of the evidence.[31] In cases like this where Plaintiffs are organizations suing on behalf of their members, the organization must demonstrate that: “(a) its members would otherwise have standing to sue in their own right; (b) the interests it seeks to protect are germane to the organization’s purpose; and (c) neither the claim asserted nor the relief requested requires the participation of individual members in the lawsuit.”[32] The dispute here turns on whether Plaintiffs’ members, “any one of them,” would have standing to sue in their own right.[33] Finally, “standing is not dispensed in gross; rather, plaintiffs must demonstrate standing for each claim that they press and for each form of relief that they seek (for example, injunctive relief and damages).”[34] The application of this fundamental tenet of our standing jurisprudence is at the heart of this case. Specifically, the parties dispute: (1) whether the standing analysis for citizen suits seeking civil penalties is prospective or retrospective; and (2) how to define a “claim” under the CAA for purposes of standing. We address these two issues first given their broader impact on our standing analysis before turning to whether Plaintiffs have established the three prongs of standing in this case. The Standing Analysis for Civil Penalties is Prospective. The form of relief a plaintiff seeks impacts our standing analysis.[35] For example, when a plaintiff seeks compensatory damages in a tort suit, we consider standing through the lens of the plaintiff’s past harm. On the other hand, when a plaintiff seeks prospective relief, we consider standing through the lens of the plaintiff’s continuing or future harm. The question here is under which category civil penalties—which are not paid to individual plaintiffs but instead to the U.S. Treasury to deter future violations—fall. Exxon contends that civil penalties should be analyzed retrospectively as in cases seeking past damages, whereas Plaintiffs argue civil penalties are a form of prospective relief similar to an injunction. We find that Plaintiffs have the superior argument in light of Supreme Court precedent that has repeatedly characterized citizen-suit claims for civil penalties as seeking prospective forms of relief. First, in Middlesex County Sewerage Authority v. National Sea Clammers Association,[36] the Supreme Court addressed whether the Clean Water Act’s (“CWA”)[37] citizen-suit provision authorizes an implied private cause of action for damages. The Court held it did not, noting that the CWA contemplates “only prospective relief” in citizen suits, either in the form of an injunction or the imposition of civil penalties.[38] Next, in Gwaltney of Smithfield, Ltd. v. Chesapeake Bay Foundation, Inc., plaintiffs brought a citizen suit seeking declaratory and injunctive relief, civil penalties, and attorney’s fees under the CWA against a meat-packing plant.[39] The plaintiffs alleged Gwaltney repeatedly violated its permit conditions by exceeding its effluent limitations for five separate pollutants between 1981 and 1984.[40] But Gwaltney’s last recorded violation occurred several weeks before the plaintiffs filed suit, thus raising the question whether the CWA allows citizen suits for wholly past violations.[41] The Court held the CWA does not provide jurisdiction over wholly past violations because “the harm sought to be addressed by the citizen suit lies in the present or the future, not in the past.”[42] Specifically, the Gwaltney Court noted that the citizen-suit provision “does not authorize civil penalties separately from injunctive relief; rather, the two forms of relief are referred to in the same subsection, even in the same sentence.”[43] It further observed that this “connection between injunctive relief and civil penalties” is absent from the provision authorizing the Administrator of the EPA to bring an action for civil penalties, in which it “is little questioned” that civil penalties may be recovered for wholly past violations.[44] The Court also took note of the fact that “[m]embers of Congress frequently characterized the citizen suit provisions as ‘abatement’ provisions or as injunctive measures.”[45] In Steel Co. v. Citizens for a Better Environment, the Court held that an environmental group seeking civil penalties for a steel manufacturer’s wholly past violations of the Emergency Planning and Community Right-To-Know Act failed to satisfy the redressability requirement for standing.[46] Specifically, the Court held because civil penalties are payable to the U.S. Treasury, they cannot be considered “as a sort of compensation or redress to respondent.”[47] Finally, in Friends of the Earth, Inc. v. Laidlaw Environmental Services (TOC) Inc., the Supreme Court considered a CWA citizen suit against Laidlaw, a hazardous waste incinerator, that repeatedly discharged various pollutants into the North Tyger River.[48] The district court found that Laidlaw exceeded its mercury discharge limits on 489 occasions between 1987 and 1995 and imposed a civil penalty of $405,800.[49] On appeal, Laidlaw argued that members of the environmental organizations lacked standing because they were not suffering from a continued injury redressable by civil penalties given that Laidlaw had come into compliance after suit was filed.[50] The Court disagreed and held that plaintiffs had standing under Article III to pursue their suit for civil penalties. Specifically, the Court reaffirmed its holdings in Gwaltney and Steel Co., but clarified that plaintiffs can seek civil penalties for violations ongoing or threatened at the time suit was filed.[51] The Laidlaw Court’s standing analysis focused on affidavits submitted by plaintiffs’ members who lived[52] or recreated downstream from Laidlaw’s facility. The members averred that they terminated their recreational activities in or around the North Tyger River based on their concerns about the harmful effects to their health from Laidlaw’s illegal discharges.[53] Some of the members used the river a couple of miles downstream from the facility, whereas others recreated up to forty miles downstream.[54] The Court found that these were cognizable injuries given “that environmental plaintiffs adequately allege injury in fact when they aver that they use the affected area and are persons ‘for whom the aesthetic and recreational values of the area will be lessened’ by the challenged activity.”[55] Laidlaw disputed that the plaintiffs established the injury-in-fact prong of standing given that the district court’s penalty analysis found Laidlaw’s permit violations did not result in “any health risk or environmental harm.”[56] The Court rejected this argument and clarified that “[t]he relevant showing for purposes of Article III standing . . . is not injury to the environment but injury to the plaintiff” and that to “insist upon the former rather than the latter . . . is to raise the standing hurdle higher than the necessary showing for success on the merits.”[57] Although the issue in Laidlaw was whether plaintiffs had standing to seek civil penalties, the Court relied on a case involving standing to seek an injunction when setting forth the appropriate inquiry. It observed that in the context of an injunction, a plaintiff has standing if he has a reasonable fear that it is likely that a recurrence of the unlawful conduct will occur.[58] The Court then closed the circle by stating that it was undisputed that Laidlaw’s unlawful conduct—discharging mercury in excess of its permit limits—was occurring at the time the complaint was filed and that there was “nothing ‘improbable’ about the proposition that a company’s continuous and pervasive illegal discharges of pollutants into a river would cause nearby residents to curtail their recreational use of that waterway and would subject them to other economic and esthetic harms.”[59] As to redressability, the Court explained that civil penalties redress the injuries of plaintiffs facing ongoing violations because they “encourage defendants to discontinue current violations and deter them from committing future ones.”[60] In underscoring the deterrent effect of penalties, the Court acknowledged that “penalties may serve, as an alternative to an injunction, to deter future violations and thereby redress the [plaintiffs'] injuries.”[61] To summarize, the above cases make clear the following: (1) citizen- suit plaintiffs may only pursue prospective forms of relief; (2) civil penalties are a form of prospective relief because they deter future violations; and (3) the standing analysis for suits seeking injunctive relief applies equally to suits seeking civil penalties. In light of the above precedent, both this Court and our sister circuits have consistently applied Laidlaw‘s prospective standing analysis to citizen-suit cases seeking injunctive relief and civil penalties alike.[62] On the other hand, Exxon, despite numerous opportunities, has not cited (and we have not found) any case law that has applied its proposed backwards-looking approach to standing focused on individual past violations to a citizen suit seeking civil penalties. This is not to say that a defendant’s past violations are irrelevant. For example, plaintiffs’ injuries from past violations that remain ongoing can provide valuable insight into whether they face a “real and immediate threat of repeated injury.”[63] Additionally, as discussed below, courts must consider a defendant’s past violations in assessing an appropriate civil penalty. However, the fact that past violations play a role in calculating the amount of civil penalties or determining the imminence of future injuries does not undermine the forward-looking nature of civil penalties for purposes of standing. Therefore, consistent with controlling Supreme Court precedent, our own post-Laidlaw precedent, our sister circuits’ precedent, and the views of the EPA,[64] we conclude that civil penalties are a form of prospective relief and that the same standing analysis applies regardless of whether a citizen suit requests injunctive relief or the assessment of civil penalties. * * * Essentially ignoring the above Supreme Court caselaw, Exxon makes several erroneous arguments in favor of a retrospective approach to standing.[65] As a legal matter, Exxon asserts that because the CAA states that a “penalty may be assessed for each day of violation,”[66] the standing analysis is necessarily retrospective and analogous to a damages suit. There are two main problems with Exxon’s retrospective approach to standing. First, Exxon’s contention contravenes “[p]erhaps the most fundamental aspect of the standing doctrine” which is that standing is separate from the merits of the case.[67] This is because the amount of penalties assessed against a defendant pertains to the merits of the case rather than the question of standing. As the Supreme Court in Steel Co. pointed out, standing is a threshold issue that is wholly separate from the merits inquiry given that “the Article III requirement of remediable injury in fact . . . has nothing to do with the text of the statute relied upon.”[68] It is only if standing is established that a court proceeds to the merits, which in environmental cases seeking civil penalties is the calculation of an appropriate penalty amount. The district court’s consideration of a defendant’s past violations for purposes of calculating the appropriate amount of penalties has no impact on the preliminary question of standing. We thus reject Exxon’s attempt to infuse our standing analysis with considerations that pertain to the merits of this case. The second problem with Exxon’s retrospective argument is that even assuming arguendo that the CAA’s penalty assessment provisions are relevant to standing, these provisions are entirely consistent with the view that civil penalties are a prospective form of relief for purposes of standing. The basis for Exxon’s argument that the standing analysis in CAA citizen suits is retrospective is its assertion that “penalties are assessed for past violations” and that Plaintiffs here “seek” a penalty for each day a violation occurred. But in making this argument, Exxon mischaracterizes the role that past violations play in the overall penalty calculation analysis. Under the CAA, courts cannot simply award penalties in isolation for each day a violation occurred. Indeed, as we have previously recognized, a “district court is not bound to impose the maximum penalty afforded under the statute” (i.e., awarding the maximum penalty for each day of violation), and to the contrary, it “is required to consider a myriad of factors, some of which are mitigating in nature, when determining the appropriate civil penalty.”[69] In accordance with the text of the CAA and our precedent, the district court in this case did not assess a penalty for each day of violation. Instead, it landed on a $19.95 million penalty after analyzing and balancing each of the statutory factors. Additionally, because the $19.95 million penalty did not come close to reaching the per day of violation cap ($573.51 million), the court did not expressly consider the number of days of violations and did not assess a penalty for each day a violation occurred.[70] Exxon next contends that the CAA’s seven penalty factors, which focus on past violations, further support its argument that standing must be evaluated retrospectively. But Exxon’s argument relies on the flawed premise that consideration of a defendant’s past unlawful conduct alters the forward-looking nature of civil penalties. As a general matter, courts often consider past behavior in suits for injunctive relief given that “past wrongs are evidence bearing on whether there is a real and immediate threat of repeated injury.”[71] In the context of civil penalties, it makes sense that a defendant’s history of noncompliance would be relevant to setting a penalty amount that is sufficient to deter its ongoing or future violations of a specific emissions limit. The CAA’s seven enumerated factors reflect this focus on deterrence. For example, the economic benefit a defendant receives from noncompliance—arguably the most important factor[72]—”is of key importance if the penalties are to successfully . . . deter violations.”[73] Similarly, factors such as the number, duration, and seriousness of the defendant’s past violations are relevant given that more long-term violations of a serious nature may require a higher financial incentive in order to compel future compliance. We therefore find nothing in the text of the CAA’s penalty factors undermines the prospective nature of civil penalties for purposes of standing. Exxon seeks to avoid this conclusion by arguing that the statutory factors are not focused on deterrence but instead are “particularly associated with the goal of retribution,” which is “inherently backward-looking.” Exxon cites to Tull v. United States for the proposition that civil penalties serve multiple purposes besides deterrence, given that the “legislative history of the [Clean Water] Act reveals that Congress wanted the district court to consider the need for retribution and deterrence, in addition to restitution, when it imposed civil penalties.”[74] However, as pointed out by the dissent in Laidlaw, Tull was a case involving civil “penalties pursued by the government, not by citizens.”[75] And the legislative history cited by the Court in Tull pertains to the EPA’s penalty authority and its policies in suits seeking civil penalties under the CWA and CAA.[76] This is a significant difference in terms of evaluating the various purposes of civil penalties because unlike citizen suits, the EPA may seek penalties for wholly past violations.[77] In sum, nothing in the text of the CAA’s penalty provisions undermines a forward-looking approach to standing in a citizen suit and instead the statutory text is entirely consistent with Laidlaw‘s view that penalties are meant to deter a defendant from continuing to violate its permits in the future. In the alternative, Exxon argues that even if suits seeking civil penalties are analyzed under a forward-looking standing analysis, as a factual matter Plaintiffs have not established standing here because: (1) the district court previously denied their claim for injunctive relief, and (2) Plaintiffs waived their forward-looking theory of standing. We find both of Exxon’s arguments unavailing. The district court’s denial of Plaintiffs’ claim for injunctive relief on the merits (after finding Plaintiffs had standing to seek such relief) is immaterial to whether Plaintiffs have standing to seek another type of prospective relief. In fact, Exxon’s argument to the contrary was rejected by the Court in Laidlaw which held that the “[d]enial of injunctive relief does not necessarily mean that the district court has concluded there is no prospect of future violations for civil penalties to deter.”[78] Finally, the extensive trial record in this case refutes Exxon’s assertion that the forward-looking nature of civil penalties “is not the theory on which this case was pleaded and tried.” Starting with the case pled: Plaintiffs’ complaint is focused on their ongoing injuries and their risk of increased harm in the future. Specifically, Plaintiffs pled that they “have members who are worried that in the future they will breathe illegal emissions from the Baytown Complex, and that future illegal emissions will result in the formation of dangerous ozone, create serious health problems, and interfere with their ability to carry on ordinary activities.” They also alleged that “[a]bsent an appropriate order from this Court, Defendants will continue to violate the Act as described in Counts I through VII.” Furthermore, Plaintiffs did not seek damages for themselves. And even if they had, as noted above, there is no law allowing such retrospective relief under the citizen-suit statute.[79] As to the case tried, Plaintiffs’ counsel’s closing argument made clear that each form of relief requested was targeted at reducing Exxon’s violations in the future: “We are asking the Court to declare Exxon to be violating the Clean Air Act. The plaintiffs are asking for the Court to issue an injunction to halt the violations of the Clean Air Act. The plaintiffs are asking the Court to appoint a special master to be in the complex to assure compliance, and the plaintiffs are asking the Court to impose a large penalty that will deter Exxon.” And most tellingly, Plaintiffs’ proposed findings of fact and conclusions of law argued that “[r]equiring a plaintiff to prove specific injury from each alleged past violation would serve no legitimate purpose in the standing inquiry, because the focus of the citizen enforcement suit (unlike that of a tort suit for compensation) is ‘primarily forward-looking.’” Plaintiffs went on to clarify that they were “ask[ing] the Court to impose penalties and injunctive relief to reduce the likelihood that Exxon will violate the Clean Air Act at these facilities in the future.” Finally, Plaintiffs maintained this forward-looking approach even after the district court denied their claim for injunctive[80] and declaratory relief. In Plaintiffs’ opening brief in ETCL II, they lay out their interest in seeking to deter Exxon from continuing to violate its emissions limitations going forward. In the “injury-in-fact” analysis of their brief, Plaintiffs note that their members have “concern[s] about future adverse effects from pollution.” In the “traceability” section of their brief, Plaintiffs focus on their members’ testimony “that their injuries are ongoing,” that they have fears about their future increased risk of cancer, and that such fears are “rationally related” to Exxon’s emission of particular chemicals. Finally, in addressing “redressability,” Plaintiffs argue that civil penalties “incentivize[] Exxon to be proactive about compliance in the future.” We therefore find that Plaintiffs have not waived their forward-looking standing argument and have sought prospective relief for their continuing and threatened injuries at each stage of this litigation. Because citizen-suit plaintiffs are limited to prospective relief, the same forward-looking standing analysis applies regardless of whether plaintiffs are seeking injunctive relief or civil penalties. This means that Plaintiffs here were required to prove the following to establish standing: an ongoing harm or the “real and immediate threat” of future harm, traceable to Exxon’s unlawful emissions ongoing at the time of suit, and redressable by the deterrent effect of civil penalties.[81] Definition of a Claim in a CAA Citizen Suit. Another foundational aspect of standing is that we consider it “on a claim-by-claim basis.”[82] The parties dispute what constitutes a “claim” for purposes of standing in a citizen suit brought under the CAA. Exxon contends that because the CAA permits courts to assess civil penalties for each day of violation, a “claim” for purposes of standing “refers to each day for which penalties are sought.” Under their definition, Exxon contends that to ensure standing is not dispensed in gross, Plaintiffs must prove “an injury-in-fact on each day of violation for which they seek a penalty” and “prove a causal connection between each day of violation for which they seek a penalty and an injury-in-fact.” Plaintiffs reject Exxon’s argument on the grounds that individual past violations are not separate claims under the CAA. Instead, they contend a claim is properly defined as consisting of repeated or ongoing violations of “an emission standard or limitation.”[83] In ETCL II, a panel of this Court ultimately adopted Exxon’s violation-by-violation based approach to standing.[84] Despite appearing to accept Plaintiffs’ definition of a claim, the panel determined that standing must be analyzed for each violation because “Clean Air Act penalties are tied to violations, not the broader claims . . . (that is, [a] group of violations of a particular emission standard).”[85] In arriving at this conclusion, the panel members in the majority acknowledged that it gave them “some pause” that “no court appears to have found standing for some Clean Air Act violations but not others.”[86] The panel majority also acknowledged that “[n]umerous cases have instead recognized standing in environmental citizen suits without separate analyses for each violation.”[87] However, it found these cases distinguishable on the grounds that they did not “involve the number and variety of violations that this case does (24 different pollutants).”[88] After further consideration and briefing, we conclude that the panel in ETCL II erred in requiring Plaintiffs to establish standing for each violation. The Supreme Court instructs that “[a]lthough standing in no way depends on the merits of the plaintiff’s contention that particular conduct is illegal, it often turns on the nature and source of the claim asserted.”[89] In this case, the statute Plaintiffs rely on, 42 U.S.C. § 7604, authorizes “any person” to “commence a civil action on his own behalf” “against any person . . . who is alleged to have violated (if there is evidence that the alleged violation has been repeated) or to be in violation of . . . an emission standard or limitation” set forth in a permit issued under the CAA. It is undisputed that a plaintiff may not file suit until a violation of an emission standard or limitation has been repeated in the past or occurred at least once before suit was filed and once after.[90] Therefore, under the language of the statute, a claim consists of at least two violations of “an emission standard or limitation.” We delved into what is meant by an “emission standard” under § 7604 in the first opinion issued by this Court.[91] We held, consistent with the approach taken in CWA cases, that the focus should be on a particular pollutant and whether that pollutant has been discharged at higher rates than authorized by a permit.[92] It therefore follows that a “claim” under the CAA arises when a particular pollutant has been emitted repeatedly in violation of a permit limit. Accordingly, in order to avoid dispensing standing in gross, Plaintiffs must establish that their members suffer from ongoing or imminently threatened injuries as a result of Exxon’s violations of each of its emission standards or limitations. Exxon does not dispute that under the CAA a single violation cannot constitute a claim, but instead maintains that a violation-by-violation approach to standing is necessary to ensure that citizens do not “secure civil penalties for violations that did not cause them injuries-in-fact.” This approach, which is a repackaging of Exxon’s prior argument about the retrospective nature of civil penalties, misunderstands the purpose of citizen suits and is at odds with Supreme Court precedent. Citizen-suit plaintiffs do not “secure” civil penalties as compensation for any injuries they may have suffered from past violations. The only benefit they receive from civil penalties is cleaner air in the future. This understanding of citizen suits is consistent with the above cited Supreme Court precedent that has characterized civil penalties, payable to the U.S. Treasury, as a forward-looking remedy imposed to deter a defendant from committing future violations. Moreover, it is the approach applied in Laidlaw where the Court did not conduct a separate standing analysis for each of the defendant’s 489 CWA violations. Instead, the Court concluded the district court “reasonably” assessed a $405,800 penalty not because of the number of past days of violations plaintiffs suffered, but because such a penalty carried a “deterrent effect that made it likely, as opposed to merely speculative, that the penalties would redress [plaintiffs'] injuries by abating current violations and preventing future ones.”[93] Exxon recognizes that neither Laidlaw nor other circuit court CAA and CWA cases have applied a violation-by-violation approach to standing.[94] Instead, relying on the panel’s decision in ETCL II, Exxon contends its novel approach is necessary here because Laidlaw and other circuit court cases are distinguishable because they did “not involve the number and variety of violations that this case does (24 different pollutants).”[95] In response, Plaintiffs contend that the number and seriousness of Exxon’s violations have “no bearing on whether Plaintiffs have an interest in Exxon complying with each of its permit limits in the future.” We see no reason why the unprecedented number and variety of violations at issue here require the application of a novel approach to standing focused on each past violation. Further, the number of violations and pollutants does nothing to change the fact that civil penalties are a prospective form of relief that requires a forward-looking approach to standing. And to adopt Exxon’s violation-by-violation approach would amount to making standing impossible to establish in cases involving sprawling industrial complexes that regularly emit an array of dangerous pollutants as compared to cases involving small facilities that commit few violations. Such an approach is inconsistent with Article III and would thwart the purpose of the citizen-suit provision.[96] Moreover, it would run afoul of TransUnion‘s instruction that courts “afford due respect to Congress’s decision to impose a statutory prohibition or obligation on a defendant, and to grant a plaintiff a cause of action to sue over the defendant’s violation of that statutory prohibition or obligation.”[97] Additionally, Exxon’s concern about the large number of violations with varying levels of seriousness is readily accounted for without upending well-established standing jurisprudence. For example, the wide number of pollutants Exxon emitted is accounted for by the fact that Plaintiffs must establish standing for each specific pollutant limit they seek to enforce. Crucially, under 42 U.S.C. § 7413(e)(1), the district court is already required to consider both the seriousness and duration of the defendant’s violations as part of its civil penalty analysis. Therefore “[i]f violations that are truly trivial become the targets of citizen suits, courts are fully capable of adjusting the penalties imposed for them to trivial levels.”[98] Accordingly, we analyze standing on a claim-by-claim basis, which under the CAA is not each violation, but each emission standard or limitation Plaintiffs seek to enforce. Injury-in-Fact. Having established the fundamentals of what constitutes a claim and how civil penalties are assessed for purposes of standing, we proceed to examine whether Plaintiffs established the three elements of standing here. The Supreme Court has described the injury-in-fact prong as the “‘[f]irst and foremost’ of standing’s three elements.”[99] In suits seeking prospective relief, “[a]n allegation of future injury may suffice if the threatened injury is certainly impending, or there is a substantial risk that the harm will occur.”[100] Past injuries, “though insufficient to confer standing, are still ‘evidence bearing on whether there is real and immediate threat of repeated injury.’”[101] Past injuries accompanied by “continuing, present adverse effects” also can satisfy the injury-in-fact requirement.[102] Here, four of Plaintiffs’ members—Diane Aguirre Dominguez, Marilyn Kingman, Richard Shae Cottar, and Sharon Sprayberry—testified at trial about the impact that Exxon’s unlawful emissions have on their lives. At the time of suit, one member lived one-quarter mile from the Complex in a townhouse “right across the street from both the chemical and olefins plant,” and another member lived a half-mile away from the Complex’s fence line.[103] The other two members regularly visited the Baytown area and recreated near the Complex.[104] In terms of their injuries, Plaintiffs’ members testified that they suffered from allergy and respiratory problems while living in or visiting Baytown and that the severity of their symptoms fluctuated based on their proximity to the Complex.[105] These members also testified that they regularly smelled unpleasant chemical odors,[106] and observed flares, smoke, and haze coming from the Complex.[107] This caused all four members to fear for their health[108] and safety.[109] Finally, two members testified that seeing flares, smoke, and haze, smelling chemical odors, and experiencing respiratory problems impacted their current and anticipated enjoyment of outdoor activities.[110] Supported by the above testimony, the district court applied well-established precedent to hold that Plaintiffs’ members suffered cognizable ongoing harms or showed a substantial risk that they will face similar injuries in the future.[111] Laidlaw is Directly Applicable Here. Exxon does not dispute that the above injuries are cognizable under Article III. Instead, Exxon argues that “[w]hen a civil penalty is sought for a ‘day of violation,’ a concrete injury is established only if there is evidence that the injury was actually experienced on that day—i.e., that an alleged violation that day ‘affect[ed] the plaintiff in a personal and individual way.’” Under this standard, Exxon concludes that Plaintiffs only offered evidence that their members suffered “concrete” injuries during five emissions events. This approach to injury-in-fact suffers from the same defect as several of Exxon’s other standing arguments: it is inconsistent with the most on- point Supreme Court case. The Supreme Court in Laidlaw did not require plaintiffs’ members to show that they were near the river or suffered some specific injury on each day a past violation occurred. Rather, the Court found that plaintiffs’ members’ current and future curtailment of their recreational activities based on their “reasonable concern” about the defendant’s upstream emissions was sufficient to establish an injury for all 489 violations.[112] Exxon’s insistence that Plaintiffs must submit proof that their members experienced an injury on each day a past violation occurred cannot be squared with Laidlaw‘s holding that citizen-suit plaintiffs’ ongoing or future injuries are cognizable for purposes of Article III standing.[113] This is because under Exxon’s erroneous approach to injury-in-fact, only past injuries, not ongoing or future ones, are cognizable. Take, for example, Plaintiffs’ members’ ongoing concerns about their future health and safety due to their continuing exposure to Exxon’s unlawful emission of harmful pollutants. Or consider members’ current and future decisions to refrain from outdoor activities, or to move away from the Complex, due to Exxon’s violations. Such ongoing and future injuries[114] are based on Exxon’s extensive history of past violations and the likelihood that it will commit similar violations in the future. These injuries cannot be tied to a specific day on which a past violation occurred and thus under Exxon’s approach would not be cognizable injuries.[115] We have no doubt that the above ongoing and future injuries are sufficiently concrete for purposes of standing. Indeed, the Court in Laidlaw found similar injuries satisfied the injury-in-fact requirement. And following Laidlaw, both this Court and our sister circuits have found similar ongoing and future injuries to be cognizable.[116] Accordingly, we reject Exxon’s retrospective approach to injury-in-fact. TransUnion is Inapposite. Exxon’s focus on linking members’ past injuries to past violations can be attributed to its reliance on TransUnion LLC v. Ramirez, a class action tort case seeking damages for past injuries.[117] In TransUnion, a class of consumers sued TransUnion, a credit reporting agency, under the Fair Credit Reporting Act.[118] The plaintiffs alleged that TransUnion had failed to use reasonable procedures to ensure the accuracy of their credit files.[119] Specifically, the class members asserted that TransUnion incorrectly included an alert in their files that their names matched those of individuals on the Treasury Department’s watch list for terrorists and other serious criminals.[120] The Supreme Court held that only the class members whose credit reports TransUnion had disseminated to third parties had standing because their reputations were harmed as a result of the disclosures.[121] The other class members whose reports had not been disseminated lacked standing because they could not demonstrate that TransUnion’s inclusion of misleading information in their files constituted a concrete harm.[122] In holding that many of the class members lacked standing because they failed to show they suffered an injury-in-fact, the Court reemphasized the principle that “Article III standing requires a concrete injury even in the context of a statutory violation.”[123] Exxon uses TransUnion‘s holding that the class members whose credit reports were not disseminated to third parties lacked standing to further its argument that Plaintiffs here have not established that each of their members suffered a “concrete” injury on each day a violation occurred. We disagree given that this case is distinguishable from TransUnion. Unlike in TransUnion, where each class member sought retrospective damages as compensation for their alleged past harms, Plaintiffs here seek a prospective remedy in the form of civil penalties, payable to the U.S. Treasury, to redress their members’ ongoing and future injuries. This results in two notable differences for purposes of standing. First, the relevant injury in a case seeking retrospective relief is different from the injury-in-fact analysis for suits, like this one, seeking prospective relief.[124] And second, unlike class action suits, as long as one of Plaintiffs’ members has standing, it is irrelevant whether any other members meet Article III’s standing requirement.[125] It is also worth noting the factual differences between this case and TransUnion. Unlike the class members in TransUnion who were unharmed aside from a statutory violation, Plaintiffs’ members’ injuries—interference with recreation, breathing and smelling polluted air, and allergy-like or respiratory problems—are the type of “physical, monetary, or cognizable intangible harm traditionally recognized as providing a basis for a lawsuit in American courts.”[126] Moreover, at the time Plaintiffs filed suit, their members suffered from the imminent threat of a future injury which was ultimately realized when Exxon continued to violate its permit limits after suit was filed. This is a sharp contrast to the Court’s finding in TransUnion that even if class members had sought prospective relief, their asserted injury—the potential that TransUnion could in the future disseminate their credit reports to third parties—was not sufficiently imminent to establish standing.[127] TransUnion simply reaffirms several basic principles of standing and does not stand for the proposition that citizen-suit plaintiffs seeking civil penalties must tie separate injuries to each alleged violation. For the foregoing reasons, the district court correctly held that Plaintiffs have satisfied the injury-in-fact requirement for standing as to all of Exxon’s violations, not just those forty days correlated at trial. Traceability. The second prong of standing “asks whether the [plaintiff's] injury is fairly traceable to the challenged action of the defendant, and not the result of the independent action of some third party not before the court.”[128] In other words, traceability ensures that the plaintiff has sued the right defendant.[129] The Supreme Court has generally found traceability lacking in cases where “the independent act of a third party was a necessary condition of the harm’s occurrence, and it was uncertain whether the third party would take the required step.”[130] On the other hand, the Court has been much more apt to find traceability when the plaintiff’s injury was “not dependent on speculation about the possible actions of third parties not before the court.”[131] The present case raises no concerns about chains of causation involving the actions of third parties. In particular, there is no allegation that pollution from a third party is the intervening cause of Plaintiffs’ members’ injuries.[132] And it requires no attenuated chain of causation or speculation about the actions of third parties to conclude that one of the largest petrochemical plants in the United States that has undisputedly emitted millions of pounds of dangerous pollutants unlawfully into the air contributed to the physical, aesthetic, and recreational injuries of people who lived next door. Plaintiffs’ case is therefore easily distinguishable from cases in which the Supreme Court has found a lack of traceability. Although there is no third party interrupting the chain of causation here, Plaintiffs still must establish that their members’ injuries are “fairly traceable” to Exxon’s unlawful conduct. Under Supreme Court precedent, this means that Plaintiffs must show that their members’ injuries were “likely caused by” Exxon,[133] or that their current or threatened injuries are “a consequence of [Exxon's] ongoing unlawful conduct.”[134] This causation standard is notably less demanding than proving tort causation.[135] The Cedar Point Framework. In Sierra Club, Lone Star Chapter v. Cedar Point Oil Co., our Court adopted a three-prong test first articulated by the Third Circuit that permits citizen-suit plaintiffs to establish traceability through circumstantial evidence.[136] Several of our sister circuits have subsequently adopted this test.[137] To satisfy the Cedar Point test, a plaintiff is required to show that the defendant: (1) discharged some pollutant in concentrations greater than allowed by its permit (2) into a waterway[138] in which the plaintiffs have an interest that is or may be adversely affected by the pollutant and that (3) the pollutant causes or contributes to the kinds of injuries alleged by the plaintiffs.[139] As explained by the Third Circuit, this “test in no way replaces the three-prong test for standing under Article III,” and instead “merely enables a plaintiff to link an environmental injury to the defendant’s pollution when the plaintiff is unable to prove ‘to a scientific certainty’ that the defendant’s discharges (and not those of some other nearby polluter) caused the injury.”[140] Put differently, the Cedar Point test permits citizen-suit plaintiffs, like all other litigants, to rely on circumstantial evidence, such as “proximity to polluting sources” or “past pollution” to establish traceability.[141] In applying the Cedar Point test, we have cautioned that a plaintiff’s injuries cannot be considered “fairly traceable” to a particular defendant’s actions if the plaintiff is too far removed from the point of discharge.[142] In light of this concern, our post-Cedar Point caselaw has clarified that the three- part test is meant to account for geographic proximity.[143] In considering geographic proximity, we have distinguished between two types of plaintiffs: those who “sit[] squarely in the discharge zone of a polluting facility,” and those who are “so far downstream that their injuries cannot fairly be traced to that defendant.”[144] Only the more distant type of plaintiff must produce additional evidence that the pollutants or their effects could have reached them.[145] Plaintiffs’ Evidence Satisfied the Cedar Point Factors. Here, the district court, in a detailed opinion, applied Cedar Point and its progeny to find that Plaintiffs satisfied the fairly traceable element of standing.[146] At the outset of its traceability analysis, the district court cited our case, Texans United for a Safe Economy Education Fund v. Crown Central Petroleum Corp.,[147] for the proposition that “the plaintiffs['] injury does not have to be linked to exact dates that the defendant’s violations occurred, and the plaintiff does not have to ‘show to a scientific certainty that defendant’s [emissions], and defendant’s [emissions] alone, caused the precise harm suffered by the plaintiffs.’”[148] The court then noted that “[e]ven though Plaintiffs’ members’ injuries do not have to be linked to exact dates that the Events and Deviations occurred, Plaintiffs’ members correlated some of the experiences described . . . to five Events or Deviations.”[149] It is from this language that Exxon roots its argument that Plaintiffs have established standing for only five emissions events (which resulted in forty days of violations).[150] We agree with the district court that Plaintiffs adduced sufficient circumstantial evidence via the Cedar Point framework to establish the “fairly traceable” prong of standing. As to the first Cedar Point factor (the emission of pollutants in excess of permit limits), Exxon stipulated to various spreadsheets outlining its thousands of permit violations. Based on this evidence, the district court correctly found that Exxon discharged pollutants in greater concentrations than allowed by its permits.[151] As to the second Cedar Point factor (emissions have the potential to adversely affect an area in geographic proximity to plaintiffs), the district court credited Plaintiffs’ members’ testimony that Exxon’s emissions adversely affect or have the potential to adversely affect the area around the Complex where they live and visit. As noted above, at the time of suit, one member lived one-quarter mile from the Complex, and another lived a half- mile away. The district court relied on these members’ testimony that from their homes they could see flares, smoke, and haze originating from the Complex.[152] Additionally, they could smell chemical odors from their homes when the wind was blowing in from the Complex and noticed these odors became stronger closer to the Complex.[153] Finally, the court noted that members’ physical symptoms improved when they moved away from the Complex.[154] Moreover, we note that the injuries members suffered within a mile or two of the Complex are likely so “squarely in the [emission] discharge zone” that no further geographic analysis is necessary.[155] Regardless, Plaintiffs did provide additional evidence of geographic proximity, including from Exxon’s own air dispersion modeling of selected emissions events indicating that off- site pollutant levels exceeded safety standards on over 130 occasions. Additionally, Plaintiffs’ expert, Dr. Edward Brooks, opined that it was “very likely that health effects occurred in exposed neighborhoods bordering the complex” from Exxon’s emission of sulfur dioxide. He made similar conclusions for various other pollutants emitted by Exxon.[156] And Exxon’s own expert testified that the pollutants emitted from the Complex “can travel significant distances beyond the fence line of the complex.” Based on this evidence, the district court did not clearly err in finding that Plaintiffs established geographic proximity[157] and satisfied the second prong of the Cedar Point test. As for the final Cedar Point factor (pollutants cause or contribute to alleged injuries), in addition to the aforementioned testimony from Plaintiffs’ members, Plaintiffs also introduced expert testimony from Dr. Brooks about “the likelihood that particular emissions events at the Baytown Complex, in fact, created a[] risk of adverse health effects in the surrounding communities.” Plaintiffs also relied on testimony from Exxon’s own personnel and expert witnesses. Finally, they supplemented the above testimony with toxicological profiles and studies from various government agencies discussing the side effects of exposure to specific concentrations of the various pollutants Exxon emitted. Below, divided by each Count (or each emission standard or limitation if more than one exists within a Count), is a summary of the evidence Plaintiffs introduced about the potential health effects of the pollutants Exxon emitted. Count I and Count II encompass claims to enforce various pollutant- specific emission limits. Because each pollutant limit is a separate “emission standard or limitation,” we look at each pollutant individually. Some pollutants contribute to several of the members’ injuries and therefore may be listed twice. Odor-causing pollutants:Plaintiffs’ members’ injuries: Natural gas has a “pungent odor.” AmmoniaMembers testified that they & ammonium compounds have a “pungentsmelled “pungent” odors cleaning-type smell.” Sulfur dioxide (SO2 &emanating from the Complex, SOx) is a colorless gas with a pungent odorsuch as sulfur, rotten egg, that smells like rotten eggs. Hydrogen sulfidegasoline, sweet, and chemical is a colorless gas with a smell of rotten eggsodors. or fecal matter which is detectable even at
very low concentrations. Hydrochloric
