A birds-eye view of 4 smoke stacks, one releasing a large stream of pollution into the air around it.

Mercury and Air Toxics Standards

In 2012, the Envi­ron­men­tal Pro­tec­tion Agency (EPA) pub­lished a rule to reg­u­late emis­sions of mer­cury, acid gas­es and oth­er tox­ic pol­lu­tants from pow­er plants as appro­pri­ate and nec­es­sary” under the Clean Air Act. The Mer­cury and Air Tox­i­cs Stan­dards (MATS) rule places lim­its on the emis­sions of these haz­ardous pol­lu­tants (HAPs) that can cause dam­age to the brain, ner­vous sys­tem, and devel­op­ing fetus­es. Reduc­tions of HAPs also reduce emis­sions of oth­er harm­ful pol­lu­tants includ­ing, most sig­nif­i­cant­ly, large quan­ti­ties of par­tic­u­late mat­ter, gen­er­at­ing addi­tion­al, health-based co-benefits.

Defend­ing the MATS Rule Against Indus­try Attacks


A coali­tion of states and indus­try orga­ni­za­tions chal­lenged the 2012 MATS rule and in 2015, the Supreme Court held that EPA had erred in ade­quate­ly con­sid­er­ing the costs of reg­u­lat­ing mer­cury emis­sions and oth­er haz­ardous pol­lu­tants when mak­ing its appro­pri­ate and nec­es­sary” deter­mi­na­tion. In 2016, in response to the Supreme Court’s deci­sion, EPA released a sup­ple­men­tal appro­pri­ate and nec­es­sary” find­ing which fur­ther fleshed out the agency’s cost analy­sis, prompt­ing it to again con­clude that it was appro­pri­ate and nec­es­sary” to reg­u­late emis­sions of haz­ardous air pollutants.

  • April 2017

    In April 2016, states and indus­try groups opposed to the MATS rule chal­lenged the sup­ple­men­tal find­ing in the Dis­trict of Colum­bia Cir­cuit Court of Appeals. Fol­low­ing the change in admin­is­tra­tions, EPA request­ed that the Dis­trict of Colum­bia Cir­cuit delay oral argu­ments that were sched­uled for May 2017 to facil­i­tate a reg­u­la­to­ry reex­am­i­na­tion of the 2016 sup­ple­men­tal find­ing. Mass­a­chu­setts Attor­ney Gen­er­al Mau­ra Healey led a coali­tion of 17 attor­neys gen­er­al, which had inter­vened in the lit­i­ga­tion, in oppos­ing the con­tin­u­a­tion request, not­ing that EPA had not pro­vid­ed any basis for an unlim­it­ed con­tin­u­ance of the lit­i­ga­tion. In April 2017, the Dis­trict of Colum­bia Cir­cuit grant­ed EPA’s request for a con­tin­u­a­tion and placed the case in abeyance as EPA reviewed the 2016 sup­ple­men­tal finding.

  • Jan­u­ary-March 2019

    In Jan­u­ary 2019 and March 2019, new­ly sworn-in Michi­gan Attor­ney Gen­er­al Dana Nes­sel and Wis­con­sin Attor­ney Gen­er­al Josh Kaul with­drew their states, respec­tive­ly, from the lit­i­ga­tion in which they were part of the coali­tion of states and indus­try groups chal­leng­ing the 2016 sup­ple­men­tal finding.

  • May 2020

    In May 2020, the coal com­pa­ny West­more­land Min­ing Hold­ings filed a law­suit chal­leng­ing the EPA’s 2016 revised find­ing. In June 2020, Mass­a­chu­setts Attor­ney Gen­er­al Healey led a coali­tion of six­teen attor­neys gen­er­al in fil­ing a motion to inter­vene to defend the stan­dards. The attor­neys gen­er­al inter­vened in the lit­i­ga­tion because they believed the EPA could not be expect­ed to faith­ful­ly defend the stan­dards in court giv­en the agency’s new stance on the appro­pri­ate­ness of MATS.

Oppos­ing Attempts to Weak­en MATS through the Reg­u­la­to­ry Process


  • Feb­ru­ary 2019

    In Feb­ru­ary 2019, as lit­i­ga­tion over the 2016 sup­ple­men­tal find­ing remained in abeyance, EPA released a pro­posed rule that sought to reverse the find­ing that it is appro­pri­ate and nec­es­sary” for EPA to reg­u­late HAPs from pow­er plants under the Clean Air Act. In its pro­posed rule, EPA claimed that the Clean Air Act does not allow EPA to con­sid­er ben­e­fits asso­ci­at­ed with reduc­ing par­tic­u­late mat­ter emis­sions when eval­u­at­ing whether to reg­u­late HAPs under the Act. Based on its exclu­sion of co-ben­e­fits from the rule’s cost-ben­e­fit analy­sis, EPA assert­ed that it is no longer appro­pri­ate and nec­es­sary” to reg­u­late mer­cury, acid gas­es and oth­er tox­ic pol­lu­tants inso­far as the rule’s costs would out­weigh its rejig­gered benefits.

  • March 2019

    In March 2019, a rep­re­sen­ta­tive of Mass­a­chu­setts Attor­ney Gen­er­al Mau­ra Healey tes­ti­fied in oppo­si­tion to EPA’s pro­posed rule at EPA’s pub­lic hear­ing on the pro­posed rule. The tes­ti­mo­ny not­ed that fail­ing to con­sid­er all of the costs and ben­e­fits asso­ci­at­ed with reduc­ing pow­er plant pol­lu­tion would vio­late the pur­pos­es of the Clean Air Act and fun­da­men­tal eco­nom­ic prin­ci­ples. The tes­ti­mo­ny also not­ed that EPA has no legal author­i­ty to reverse the appro­pri­ate and nec­es­sary” find­ing as the Clean Air Act only allows the agency to reverse such a find­ing if it can demon­strate that pow­er plants no longer pose an unac­cept­able risk to human health or the environment.

    Mass­a­chu­setts Attor­ney Gen­er­al Healey, on the same day as the tes­ti­mo­ny, led a coali­tion of 17 states in request­ing that EPA hold two addi­tion­al pub­lic hear­ings on the revised appro­pri­ate and nec­es­sary” find­ing. The let­ter from the attor­neys gen­er­al urged that EPA hold the addi­tion­al hear­ings so that parts of the coun­try most vul­ner­a­ble to haz­ardous air pol­lu­tants from pow­er plants could pro­vide pub­lic input on the proposal.

  • April 2019

    A coali­tion of 21 state attor­neys gen­er­al, led by Mass­a­chu­setts Attor­ney Gen­er­al Healey filed exten­sive com­ments object­ing to the pro­posed rule and urg­ing the agency to with­draw the pro­pos­al in April 2019. The com­ments not­ed that it remains appro­pri­ate and nec­es­sary” to con­trol HAPs emis­sions from pow­er plants as pow­er plants are the largest source of HAPs, which pose severe risks to human health. The evi­dence on record estab­lish­es the 2012 MATS rule helped achieve an eighty-six per­cent reduc­tion in mer­cury emis­sions and mas­sive” reduc­tions in oth­er HAPS from pow­er plants. Reduc­tions in HAPs have pro­vid­ed vast pub­lic health ben­e­fits and co-ben­e­fits at a bar­gain cost.

    The attor­neys gen­er­al also com­ment­ed that EPA’s attempt to revis­it its pri­or appro­pri­ate and nec­es­sary” find­ing is an unlaw­ful attempt by the agency to evade the Clean Air Act’s clear lim­its on EPA’s author­i­ty to reverse such a find­ing in the absence of evi­dence that pow­er plants no longer pose an unac­cept­able human health or envi­ron­men­tal risk. Addi­tion­al­ly, the com­ments also empha­sized that ignor­ing the human health co-ben­e­fits of reduc­ing par­tic­u­late mat­ter under the MATS rule is arbi­trary and capri­cious as those co-ben­e­fits are unavoid­able and substantial.

  • April 2020

    In April 2020, the EPA pub­lished its final rule rolling back the legal basis of the MATS rule. The rule revers­es the Oba­ma administration’s cost-ben­e­fit analy­sis and deter­mines that the cost to indus­try to com­ply with the exist­ing MATS rule out­weighs the ben­e­fits. To reach that con­clu­sion, the EPA dis­re­gard­ed the direct ben­e­fits to pub­lic health from reduced mer­cury emis­sions and the co-ben­e­fits from reduc­tions in fine par­tic­u­late pol­lu­tion. Cal­i­for­nia Attor­ney Gen­er­al Xavier Becer­ra issued a state­ment crit­i­ciz­ing the final rule for ignor­ing the ben­e­fits of lim­it­ing harm­ful air pol­lu­tion to pub­lic health and the environment.

  • July 2020

    In July 2020, Mass­a­chu­setts Attor­ney Gen­er­al Healey led a coali­tion of 21 states in fil­ing a peti­tion for review chal­leng­ing the final rule in the D.C. Circuit.