ACS ES&T Air最新文献

{"title":"Source-Resolved Inversion of Elemental Carbon Emissions in California Using Log-Space Bayesian Inference","authors":"Jie Zhang,&nbsp;Ling Jin,&nbsp;Xiaodan Xu,&nbsp;Soroush E. Neyestani,&nbsp;Xinyi Zhang,&nbsp;Tin Ho,&nbsp;Jiachen Zhang,&nbsp;James Butler,&nbsp;Chelsea V. Preble,&nbsp;Thomas W. Kirchstetter,&nbsp;Qi Ying,&nbsp;Zichong Chen,&nbsp;Anna Spurlock,&nbsp;Hanna Breunig","doi":"10.1021/acsestair.6c00105","DOIUrl":"10.1021/acsestair.6c00105","url":null,"abstract":"<p>Elemental carbon (EC), operationallyquantified by thermal-opticalanalysis, is widely used as a proxy for black carbon (BC) relevantto short-term climate forcing and public health. Current EC emissioninventories remain highly uncertain, with persistent discrepanciesbetween bottom-up and top-down estimates. In this study, we developa source-resolved, log-space Bayesian inversion framework appliedto estimate California’s statewide EC emissions in 2019. Byintegrating surface EC measurements from the EPA’s Air QualitySystem network with high-resolution source contributions simulatedby a chemical transport model, we identify a one-third underestimationin the existing statewide EC inventory, requiring an increase of thetotal from a prior of 8.58 [5.49–13.75] Gg year^–1 to a posterior estimate of 12.78 [10.71<strong>–</strong>15.37]Gg year^–1. This discrepancy is primarily drivenby substantial underestimations in the power and industrial and off-roadmobile sectors. Furthermore, population-weighted exposure analysisreveals a marked sectoral divergence between emission mass and healthburden: off-road mobile sources dominate both emissions and exposure,accounting for 31% of statewide exposure, while residential wood combustioncontributes 26% of total exposure despite comprising only 19% of totalemissions, due to its source proximity to population. These findingsunderscore the need to update sector-specific EC speciation profilesand demonstrate that mitigation strategies targeting off-road mobilesources and residential wood combustion are critical for reducingEC-related health impacts in California.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1911–1921"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148656476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Elevated Environmental Lead Concentrations Following a Major Urban Fire","authors":"Sam J. Silva,&nbsp;Seth G. John,&nbsp;A. Joshua West,&nbsp;Mia Bradshaw,&nbsp;Yadan Hu,&nbsp;Cecilia M. John,&nbsp;Kyeong Pil Kong,&nbsp;Catherine Odendahl,&nbsp;Nataly Pineda,&nbsp;Adam Ross,&nbsp;Brian Schlaff,&nbsp;Nismata Sigdel,&nbsp;Katherine Thomas","doi":"10.1021/acsestair.6c00015","DOIUrl":"10.1021/acsestair.6c00015","url":null,"abstract":"<p>The Eaton Canyonfirestorm burned thousands of acres of urban land,devastating local communities and destroying nearly 20,000 structures.Measurements of roadside dust, stormwater runoff, and atmosphericaerosols show that this fire was a source of lead (Pb) into the urbanenvironment. Lead concentrations in roadside dust within the urbanburn scar were significantly elevated immediately after the fire,remaining high through repeat rainfall events but decreasing overthe course of subsequent months. During active structure fires, highaerosol lead was observed in the smoke plume. Lead in roadside rainwaterwas elevated in the urban burn area after the first rain. The sourceof lead in all cases is likely burning structures, which containedlead in paint and plumbing, resulting in widespread urban lead concentrationsin excess of healthy thresholds set by regulators.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1789–1796"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148666622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CIMS Detection of Hydroxymethyl Hydroperoxide: Insights into Alkene Ozonolysis in a Variety of Environments","authors":"Andrew J. Lindsay,&nbsp;Khaled Shaifullah Joy,&nbsp;Lee V. Feinman,&nbsp;Kyle Banecker,&nbsp;Brigitte M. Weesner,&nbsp;Amalia Muñoz,&nbsp;Esther Borrás,&nbsp;Mila Ródenas,&nbsp;Teresa Vera,&nbsp;Rubén Soler,&nbsp;Ezra C. Wood","doi":"10.1021/acsestair.6c00053","DOIUrl":"10.1021/acsestair.6c00053","url":null,"abstract":"<p>Hydroxymethyl hydroperoxide(HMHP, CH₂OHOOH) is producedfrom the reaction of water vapor with CH₂OO, which is thesimplest Criegee intermediate and is produced by the reaction of ozone(O₃) with a terminal alkene. After formation, HMHP is thoughtto have a considerable lifetime upward of 1 day due to its reactionwith OH, which produces formic acid and formaldehyde. HMHP measurementscan therefore provide meaningful insight into atmospheric oxidationprocesses, especially alkene oxidation. We demonstrate the abilityof iodide adduct chemical ionization mass spectrometry (I^–CIMS) to detect HMHP and show data from three measurement studiesthat span a range of chemical environments. Measurements of HMHP arepresented from a controlled chamber-based biomass burning (BB) O₃ oxidation experiment, from outdoor sampling periods in Boise,Idaho, during the summer with mixed rural/biogenic influences, andfrom Philadelphia during summer and late fall during time periodsof BB impact. Ambient HMHP concentrations ranged up to 100 pptv duringsummer at both field sites but rarely exceeded 10 pptv in the latefall. HMHP is often but not always correlated with OH oxidation productsdetected by I^–CIMS, including I(C₅H₁₀O₃)⁻ from isoprene hydroxy hydroperoxides(ISOPOOH) and isoprene epoxydiols (IEPOX), providing insight intothe relative importance of O₃ versus OH oxidation and alkenecomposition. The greatest observed HMHP mixing ratios exceeded 300pptv during an extended BB episode at the Philadelphia site causedby the historic Canadian wildfires of 2023 and were considerably greaterthan the chamber-simulated BB experiment. Given the age of the sampledair masses, these elevated concentrations suggest sustained productionand long-range transport of HMHP, highlighting that HMHP can accumulate,persist, and act as an important precursor to its degradation productsover long distances. Given how commonplace I-CIMS measurements havebecome in the past decade, measurements of HMHP may serve as a usefultool for assessing the budgets and chemistry of several importanttropospheric compounds, including Criegee intermediates, formaldehyde,and formic acid.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1832–1842"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148451145","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High-Latitude Urban Winter Aerosol Sources: Combustion, Dust, and Road Salt and the Role of Primary and Secondary Sulfur","authors":"Emily J. Costa,&nbsp;Maidot S. Bekele,&nbsp;Monica R. Mashkevich,&nbsp;Emily R. Lill,&nbsp;Judy Wu,&nbsp;Andrew L. Holen,&nbsp;Allison Moon,&nbsp;Becky Alexander,&nbsp;Zezhen Cheng,&nbsp;Nurun Nahar Lata,&nbsp;Swarup China,&nbsp;Jessie M. Creamean,&nbsp;Andrew P. Ault,&nbsp;Kerri A. Pratt","doi":"10.1021/acsestair.6c00130","DOIUrl":"10.1021/acsestair.6c00130","url":null,"abstract":"<p>Wintertime urban air pollution poses severe health risks.Yet,few studies have investigated the sources and aging of urban particulatematter at high latitudes, where low temperatures impact emissionsand particle chemistry. Atmospheric particles (0.18–3.2 μm)were collected from January to February 2022 during the Alaskan LayeredPollution and Chemical Analysis (ALPACA) field campaign in Fairbanks,Alaska. The morphology and elemental composition of 33,422 individualparticles were measured by computer-controlled scanning electron microscopywith energy-dispersive X-ray spectroscopy. The smallest measured particles(0.18–0.32 μm) were primarily fractal soot from residentialwood burning and fossil fuel combustion, and carbon, oxygen, and sulfur(C/O/S)-rich particles, most of which were aqueous/liquid (12 ±2% semisolid, by number). The largest particles (1.8–3.2 μm)were mechanically-generated road dust and road salt, as well as superaggregatesoot from inefficient combustion. Sulfur-containing fractal soot particlesprovide evidence of significant primary sulfur aerosol emissions.C/O/S, road salt, and dust particles showed evidence of secondarysulfur formation. The C/O/S particles reflect the transformation ofhygroscopic combustion particles to larger particles containing mainlysecondary organic and sulfate aerosol. These results demonstrate theheterogeneity of the high-latitude urban aerosol population and theparticipation of multiple sources in primary and secondary sulfurchemistry.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1922–1934"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148672604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Photochemical Cloud Processing of Water-Soluble Organic Gases Produced by Aqueous-Phase Photooxidation of α-Pinene, d-Limonene, and Toluene","authors":"Matthew L. Zaragoza,&nbsp;Lisa M. Wingen,&nbsp;Sergey A. Nizkorodov,&nbsp;Annmarie G. Carlton","doi":"10.1021/acsestair.6c00044","DOIUrl":"10.1021/acsestair.6c00044","url":null,"abstract":"<p>Ambient water-soluble organic gases (WSOGs) are photochemicallyprocessed in atmospheric waters, which contributes to aqueous secondaryorganic aerosol (aqSOA). Chemical characterization of this atmosphericpathway has not been undertaken for monoterpene or aromatic oxidationproducts. In this work, gas-phase α-pinene, d-limonene, andtoluene were oxidized via O₃- and •OH-initiatedreactions. Resulting water-soluble oxidation products were collectedusing a mist chamber, in which WSOGs were scrubbed by aqueous droplets.WSOG samples were then subjected to aqueous-phase photooxidation toquantify aqSOA mass yields and characterize aqSOA chemical composition.AqSOA particle mass concentrations and O/C ratios increased with aqueous-phasephotooxidation time for monoterpene WSOGs, while only marginal increaseswere observed for toluene WSOGs. Mass spectra for α-pinene WSOGsshowed an abundance of small carboxylic acids (C₁–C₄) and monomeric (C₇– C₁₀) carbonylsformed during the aqueous-phase photooxidation. The α-pineneWSOGs exhibited a distinct molecular composition and underwent differentphotochemical processes when contrasted with water-soluble organicparticles (WSOPs) from the gas-phase oxidation of α-pinene.These results underscore the need for chemical-level characterizationof monoterpene-derived WSOGs to quantitatively evaluate their potentialcontribution to the global atmospheric aqSOA burden.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1811–1821"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148682560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Volatile Organic Compound Prediction Bias in a Regulatory Air Quality Model in Houston, Texas","authors":"William Vizuete,&nbsp;Evan Couzo,&nbsp;Alejandro Valencia,&nbsp;Kenneth Craig,&nbsp;Loredana Suciu,&nbsp;Bradley Flowers,&nbsp;Claudio Sanchez,&nbsp;Jaime Green","doi":"10.1021/acsestair.6c00027","DOIUrl":"10.1021/acsestair.6c00027","url":null,"abstract":"<p>This study evaluates the performance of a regulatoryair qualitymodel in simulating volatile organic compounds (VOCs) by comparingobserved concentrations with public and private surface monitoringdata. Significant negative biases were found, with normalized meanbias (NMB) values ranging from −33.18% for benzene to −71.62%for ethane, particularly during nighttime hours (10 p.m. to 6 a.m.).Median observed concentrations at monitors ranged from 0 to 6.84 ppbfor ethane, 1.48–2.87 ppb for propane, 0–0.37 ppb forbenzene, and 0.39–1.33 ppb for ethene, while median modeledconcentrations ranged from 1.29 to 2.21 ppb, 0.56–1.47 ppb,0.08–0.48 ppb, and 0.34–1.23 ppb for those same species.Trajectory analyses on high ozone days revealed air masses movingfrom industrial regions east of downtown Houston to downwind monitorsregistering large VOC discrepancies, suggesting potential errors inthe modeled emissions inventory. These errors may stem from the inventories’reliance on annual emission totals, average ozone season daily emissionrates, or averaged temporal profiles that do not capture short-termvariability. Additional errors may also stem from incomplete VOC speciation,and the reliance of averaged VOC speciation profiles in modeling inventorydevelopment. Ethane provides a unique speciation and quantificationchallenge because it is classified as an exempt VOC by the EPA andtherefore is not required to be reported by industry. To assess ozoneformation potential (OFP), the study incorporated both VOC abundanceand reactivity. Despite incomplete VOC measurements, observed OFPconsistently exceeded modeled OFP, indicating underrepresentationof reactive VOCs in the model. This discrepancy underscores limitationsin the emissions inventory and model representation of VOCs. A sensitivityanalysis doubling VOC emissions showed improved model performance,particularly for benzene and ethene, though alkane biases remainedrelatively unchanged. Overall, the findings highlight the need forrefined anthropogenic VOC emissions data from industrial sources foundin Houston, with emphasis on temporal resolution and speciation ofalkanes and aromatics. Improving the modeled emission inventory iscritical for enhancing model accuracy and understanding VOC-drivenozone formation.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1797–1810"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148624842","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Real-World Performance of Commercial Passive Formaldehyde Removal Products: Ineffectiveness and Undisclosed VOC Emissions","authors":"Yinxi Yao,&nbsp;Feiyang He,&nbsp;Zhipeng Tu,&nbsp;Haoyu Wei,&nbsp;Songdi Liao,&nbsp;Manni Zhu,&nbsp;Junyu Zheng,&nbsp;Yutong Liang","doi":"10.1021/acsestair.6c00046","DOIUrl":"10.1021/acsestair.6c00046","url":null,"abstract":"<p>Growingpublic concern over indoor formaldehyde (HCHO) pollutionhas driven rapid growth in the use of passive HCHO removal products,which are widely marketed as low-cost and electricity-free solutions.In China, monthly sales of such products have reached millions ofunits. However, their real-world performance and unintended impactson indoor air chemistry remain insufficiently characterized. Here,we evaluated the performance of five passive HCHO removal productsand their volatile organic compounds (VOCs) emissions in an unoccupiedoffice. None of the products measurably reduced HCHO concentrationsunder realistic conditions. In contrast, substantial VOC emissionswere observed. A product claimed to be terpene-based emitted 192 μgof VOCs per gram of product consumed, with emissions dominated byaromatic compounds (50.5%), while a titanium dioxide (TiO₂)-based product emitted 155 μg g^–1 and wasenriched in monoterpenoids (54.7%). Hazardous VOC signals, such asbenzene, toluene, and styrene, were detected, and monoterpene emissionsmay have implications for indoor secondary chemistry under certainconditions. These results indicate that manufacturer-claimed HCHOremoval efficiencies may substantially overestimate real-world performanceand that product use can introduce additional indoor air quality concerns,highlighting the need for greater oversight and real-world testingof consumer air-cleaning products.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1822–1831"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148666497","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"River and Coastal Water VOC Emissions Drive Spatial and Diurnal Air Quality Variability","authors":"Christopher R. Frobenius,&nbsp;Jena K. Herbst,&nbsp;Justin D. Hamlin,&nbsp;Benjamin Rico,&nbsp;Robert S. Pomeroy,&nbsp;Kimberly A. Prather","doi":"10.1021/acsestair.5c00514","DOIUrl":"10.1021/acsestair.5c00514","url":null,"abstract":"<p>As urbanization accelerates, accurately assessing theatmosphericconsequences of wastewater pollution has become increasingly important.Polluted rivers, overlooked in air quality inventories, can rivalor exceed other typically considered sources of airborne volatileorganic compounds (VOCs). In this study, we deployed continuous sorbenttube air sampling with Thermal Desorption Gas Chromatography MassSpectrometry (TD-GCMS) analysis, alongside purge and trap (P&amp;T)dissolved gas measurements over a 25-day period in the Tijuana RiverValley in San Diego, California, USA. Gas-phase VOC concentrationswere consistently higher near the Tijuana River compared to the coast,with air masses often enriched in sulfur-containing compounds, ethers,and aromatic species. Peak VOC abundance near the Tijuana River alignedwith river flow and turbulence at a previously identified TijuanaRiver hotspot, suggesting bubble-mediated transfer represents a keyemission pathway. More than 30% of the elevated VOC species in theair were also present in Tijuana River water, providing chemical evidenceof river-to-air gas transfer. These results extend the long-recognizedwater pollution crisis in the Tijuana River Valley, demonstratingthat polluted water bodies can serve as major and compositionallydistinct VOC sources in urban airsheds. By linking riverine VOC emissionsto atmospheric composition, this study provides a scalable methodfor diagnosing wastewater impacts and informing mitigation strategiesglobally.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1758–1771"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148666634","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Health Benefits of Source-Specific Air Pollution Reductions Following Emission Regulations in New York City","authors":"Masha Pitiranggon,&nbsp;Sarah Johnson,&nbsp;Ariel Spira-Cohen,&nbsp;Rebecca Goldberg,&nbsp;Kazuhiko Ito","doi":"10.1021/acsestair.5c00435","DOIUrl":"10.1021/acsestair.5c00435","url":null,"abstract":"<p>PM_2.5 sourceapportionment and time-series models ofNO₂ and PM_2.5 with mortality and cardiovascularand asthma morbidity were employed to calculate short-term healthbenefits from pollution reductions in New York City across differentpolicy-relevant sectors from 2005 to 2019 (2008–2019 for residualoil) using U.S. Environmental Protection Agency’s BenMAP program.Short-term health risks of nickel and sulfate exposure were also estimatedto better understand source-specific risk. Nickel and sulfate servedas indicators for residual oil boilers and coal-fired power plants,while NO₂ indicated traffic and building boilers. Thisassessment’s strength is its use of concentration–responsefunctions developed specifically for our study period and population.Coal-fired power plant PM_2.5 saw the largest decline, avoidinghundreds of excess deaths, asthma hospitalizations, and cardiovascularemergency department visits and hospitalizations, and over 1000 asthmaemergency department visits, annually. Reductions in PM_2.5 from residual oil and traffic also led to meaningful health benefits.These substantial health benefits from declining use of coal-firedpower plants and residual oil boilers support continued systematicreductions in fossil fuel use. Declines in NO₂ exhibitedgreater health benefits than those for PM_2.5, despite asmaller percentage reduction, underscoring the potential benefitsof further NO_<em>x</em> mitigation, such as vehicleand building electrification.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1693–1703"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148672572","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Long-Term Trends in Nitrogen Oxides Emissions from Heavy-Duty Diesel Vehicles in California","authors":"Georges Saliba,&nbsp;Okjoo Park,&nbsp;Seungju Yoon,&nbsp;Jorn D. Herner,&nbsp;Chris Ruehl,&nbsp;Thomas D. Durbin,&nbsp;Kent Johnson,&nbsp;Arvind Thiruvengadam,&nbsp;Mark C. Besch","doi":"10.1021/acsestair.6c00066","DOIUrl":"10.1021/acsestair.6c00066","url":null,"abstract":"<p>Reducingnitrogen oxides (NO_<em>x</em>) in Californiais critical to improving air quality and meeting National AmbientAir Quality Standards for ozone and fine particulate matter. On-roadheavy-duty diesel vehicles (HDDVs) are a major source of NO_x. In this study, the impact of on-board diagnostic (OBD) HD regulationson tailpipe NO_x emissions during running hot in-use operations(exhaust temperature &gt;200 °C) was quantified; cold-start andlow-load operations which can significantly contribute to in-use NO_x emissions are not considered. Onboard NO_x emissionswere measured between 2013 and 2024 from class 7 and 8 HDDVs. Vehicleswere classified as pre-OBD engines equipped with an Engine ManufacturersDiagnostic (EMD) system, HD OBD phase-in engines, and HD OBD engines.HD OBD engines showed significant reductions in distance-based tailpipeNO_x emission factors (0.2 ± 0.3 g·mi^–1) compared to EMD engines (3.2 ± 1.9 g·mi^–1). HD OBD engines exhibited significantly lower tailpipe NO_x emissions even when compared to vehicles of the same age, likelyreflecting improved SCR control efficiencies to meet increasinglystringent OBD control thresholds. However, the data suggests evidenceof SCR deterioration in the in-use fleet. This study highlights thematuring of SCR technology and the efficacy of the OBD program inreducing HDDV NO_x emissions.</p>","PeriodicalId":100014,"journal":{"name":"ACS ES&T Air","volume":"3 7","pages":"1843–1852"},"PeriodicalIF":0.0,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148672603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}