A distant view of a smoggy city

Particulate Matter

Par­tic­u­late mat­ter (PM) pol­lu­tion is a mix­ture of sol­id par­ti­cles and liq­uid droplets found in the air that vary in size. PM comes from con­struc­tion sites, unpaved roads, fields, smoke­stacks or fires and has been asso­ci­at­ed with a wide range of health prob­lems, includ­ing car­dio­vas­cu­lar dis­ease, res­pi­ra­to­ry impacts and can­cer. PM pol­lu­tion is reg­u­lat­ed under the Clean Air Act’s Nation­al Ambi­ent Air Qual­i­ty Stan­dards (NAAQS) pro­gram as a cri­te­ria air pollutant. 

NAAQS Pol­i­cy Assessment


  • Sep­tem­ber 2019

    In Sep­tem­ber 2019, the Envi­ron­men­tal Pro­tec­tion Agency (EPA) released its draft Pol­i­cy Assess­ment regard­ing NAAQS for PM. The study is sup­posed to help the agency devel­op con­clu­sions about the ade­qua­cy of exist­ing PM stan­dards and poten­tial alter­na­tives under the NAAQS. The EPA made a num­ber of changes to the process for devel­op­ing the draft Pol­i­cy Assess­ment that have reduced the trans­paren­cy of the agency’s PM NAAQS review.

  • Novem­ber 2019

    In Novem­ber 2019, Cal­i­for­nia Attor­ney Gen­er­al Xavier Becer­ra led a coali­tion of six attor­neys gen­er­al in sub­mit­ting com­ments on the draft Pol­i­cy Assess­ment. The com­ments high­light­ed sev­er­al prob­lems with the draft Pol­i­cy Assessment’s devel­op­ment process, includ­ing the EPA’s con­sol­i­da­tion of key com­po­nents of the review process and elim­i­na­tion of oppor­tu­ni­ties for pub­lic com­ment on mul­ti­ple inter­im drafts of crit­i­cal doc­u­ments pro­duced as part of the review. Fur­ther, the attor­neys gen­er­al crit­i­cized dis­con­tin­u­a­tion of the long-stand­ing prac­tice that the Clean Air Sci­en­tif­ic Advi­so­ry Com­mit­tee PM Review Pan­el pro­vide analy­sis and feed­back on the agency’s review of the PM NAAQS. Address­ing the short­com­ings in the draft Pol­i­cy Assessment’s devel­op­ment process would help ensure that the final PM NAAQS stan­dard pro­tects pub­lic health and wel­fare with an ade­quate mar­gin of safe­ty as required by the Clean Air Act.

Strength­en­ing NAAQS


  • April 2020

    In April 2020, the EPA released a pro­posed deci­sion not to strength­en the NAAQS for PM. The EPA is required under the Clean Air Act to review the NAAQS for PM every five years and last revised the stan­dards in 2012.

  • June 2020

    In June 2020, New York Attor­ney Gen­er­al Leti­tia James led a coali­tion of 17 attor­neys gen­er­al in fil­ing com­ments object­ing to the EPA’s pro­posed deci­sion and urg­ing the agency to aban­don it. In their com­ments, the attor­neys gen­er­al not­ed that the pro­posed deci­sion con­tra­dicts over­whelm­ing evi­dence of the health harms asso­ci­at­ed with PM pol­lu­tion and ignores the advice and rec­om­men­da­tions of its own staff and oth­er sci­en­tif­ic experts. The attor­neys gen­er­al also flagged sig­nif­i­cant envi­ron­men­tal jus­tice con­cerns, giv­en the well-doc­u­ment­ed and dis­pro­por­tion­ate impact of PM pol­lu­tion on com­mu­ni­ties of color.

  • Novem­ber 2020

    In Novem­ber 2020, New York Attor­ney Gen­er­al Leti­tia James again led a coali­tion of 16 attor­neys gen­er­al in fil­ing com­ments call­ing on the EPA to strength­en the NAAQS for PM in light of new sci­ence that fur­ther con­firms that the cur­rent stan­dards are not ade­quate to pro­tect pub­lic health. The coali­tion high­light­ed a long-term study on the effects of PM on neu­ro­log­i­cal dis­or­ders in old­er Amer­i­cans that found an increased risk of Parkinson’s dis­ease, Alzheimer’s dis­ease, and relat­ed demen­tias based on long-term expo­sure to PM, even at lev­els low­er than the cur­rent nation­al stan­dards. The attor­neys gen­er­al also not­ed that mul­ti­ple stud­ies pub­lished since June 2020 found links between increased mor­tal­i­ty from COVID-19 and PM exposure.

  • Decem­ber 2020

    In Decem­ber 2020, dis­re­gard­ing the con­cerns of the attor­neys gen­er­al, the EPA pub­lished its final rule leav­ing the cur­rent NAAQS for PM unchanged. Cal­i­for­nia Attor­ney Gen­er­al Becer­ra con­demned the Trump administration’s deci­sion as despi­ca­ble” and high­light­ed the dis­pro­por­tion­ate impact the deci­sion will have on low-income com­mu­ni­ties, par­tic­u­lar­ly when cou­pled with a dead­ly res­pi­ra­to­ry pandemic.” 

  • Jan­u­ary 2021

    In Jan­u­ary 2021, Cal­i­for­nia Attor­ney Gen­er­al Becer­ra led a coali­tion of 17 attor­neys gen­er­al in fil­ing a peti­tion for review in the Court of Appeals for the D.C. Cir­cuit chal­leng­ing the Decem­ber 2020 rule leav­ing the cur­rent NAAQS for PM unchanged. In June 2021, the case was in abeyance.