With growing vehicle numbers and the shift to new energy vehicles, traffic non-exhaust emissions (NEEs), especially tire and brake wear particles (TBWPs), have become a prominent urban air pollutant. TBWPs contain various organics harmful to the respiratory system. Epigenetics bridges environmental exposure and sustained lung injury, yet TBWP-related epigenetic toxic mechanisms remain poorly summarized. This review summarizes in vitro animal and epidemiological evidence to illustrate TBWP-induced pulmonary toxicity via epigenetic pathways such as DNA methylation changes, non-coding RNA dysregulation, and chromatin remodeling, alongside oxidative stress, inflammation, and genotoxicity. We point out key research gaps and discuss epigenetic changes as promising biomarkers. Building integrated epigenetic toxicology systems will help advance pollution risk assessment focused on toxicity rather than pollutant mass.

Vehicular exhaust represents a major anthropogenic source of atmospheric volatile organic compounds (VOCs), which serve as critical precursors for atmospheric ozone and PM2.5 formation, and characterizing its emission profile and associated health risks provides essential scientific basis for establishing effective emission control standards. Given that Three-Way Catalysts (TWC) currently represent an effective technology for controlling conventional pollutants, this study investigates their indirect benefits for VOC emission reduction on high-mileage China V vehicles. Exhaust samples were collected across multiple driving speed segments and start-up temperature conditions to analyze vehicle VOC emission factors, ozone formation potential, and both non-carcinogenic and carcinogenic health risks. Research findings indicate that renewing the TWC can reduce total emissions of VOCs by more than 88%. Notably, replacing aged TWCs eliminates acrolein, reduces benzene, and lowers 1,3-butadiene emissions, while post-replacement priority pollutants shift to xylenes, ethylbenzene, and acetaldehyde. Alkanes warrant mass-based controls, alkenes demand reactivity management, halogenated VOCs require carcinogenic risk regulation, and both OVOCs and aromatics necessitate integrated health-environmental mitigation strategies targeting their distinct toxic mechanisms. This study provides a new perspective on treatment of in-use vehicle aging TWC from the aspects of emissions, environmental impact, and health risks from a single-vehicle case.

Nitrous oxide (N2O) is a long-lived greenhouse gas with a global warming potential far exceeding that of carbon dioxide and methane. Despite its environmental significance, N2O emissions from modern light-duty vehicles remain poorly characterized under real-world conditions and across emerging powertrain technologies. In this comprehensive study, a diverse fleet of light-duty gasoline vehicles (LDGVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and a light-duty diesel vehicle (LDDV) was systematically investigated using both Worldwide harmonized Light vehicles Test Cycles (WLTC) and Real Driving Emissions (RDE) tests. Detailed analyses were conducted to evaluate operating condition distributions and the coupling relationships among N2O emissions, vehicle driving characteristics, and conventional regulated pollutants. The results demonstrate strong technology-dependent differences. The diesel vehicle exhibited the highest emission factor, primarily driven by non-selective reactions in the aftertreatment system. For gasoline and hybrid vehicles, comparisons between WLTC and RDE revealed that real-world stochastic driving significantly exacerbates transient N2O emissions. Notably, hybrid vehicles exhibited unique N2O profiles highly dependent on their energy management strategies, where frequent engine start-stops and recurring catalyst light-off behaviors dominantly influenced N2O formation. To quantitatively disentangle these complex interactions, a data-driven framework was further implemented. By training models with real-time kinematic parameters (velocity, acceleration, vehicle specific power) and instantaneous exhaust compositions, the feature importance was extracted to precisely identify the primary driving factors for each propulsion system. Ultimately, these multi-dimensional insights provide direct guidance for calibration strategies targeting N2O mitigation in next-generation emission control systems.

Secondary organic aerosol (SOA), formed via complex chemical mechanisms, is a major contributor to atmospheric aerosol pollution and climate forcing worldwide. Aqueous-phase oxidation serves as an important pathway for SOA formation, with aqueous SOA (aqSOA) exhibiting light absorption across the ultraviolet-visible range. This study investigates the formation and absorption properties of aqSOA in the Sichuan Basin, China. Results indicate that aqSOA mainly originated from aged biomass-burning emissions through aqueous-phase processing rather than from gas-phase photochemical oxidation, particularly under high aerosol liquid water content conditions during pollution periods. Substantial enhancement of brown carbon absorption by SOA was observed between 370 and 660 nm (27.5 %-43.2 %). These findings highlight the significant contribution of aqSOA formation from aged biomass-burning emissions to the brown carbon budget and absorption, especially at night. The mean aerosol absorption & Aring;ngstr & ouml;m exponents between 370 and 880 nm (AAE370-880) were 1.95, which is higher than the values reported for fresh and photochemically aged biomass-burning emissions. This study elucidates the formation and light-absorbing characteristics of aqSOA derived from aged biomass-burning emissions and highlights the important role of aqueous-phase reactions in aerosol pollution and radiative absorption.

China VI vehicle emission standards reduce primary exhaust pollutants, but impacts on secondary air pollution are less understood. We studied photochemical aging of hot-start exhaust from a China VI gasoline vehicle using smog-chamber experiments, focusing on semi- and intermediate-volatility organic compounds (S/IVOCs) and oxygenated volatile organic compounds (OVOCs) under variable oxidative conditions. Over OH exposures equivalent to 0.6-5.8 days, nonmethane organic gases (NMOGs) rapidly depleted, while low-molecular-weight OVOCs formed continuously. Secondary aerosol formation exhibited nonlinear dependence on oxidative capacity. Under low OH, secondary organic aerosol (SOA) dominated particle mass, whereas at high OH, secondary inorganic aerosol─mainly ammonium nitrate─accounted for 55-85% of total secondary aerosol mass, promoted by enhanced oxidation and ammonia availability. S/IVOCs contributed 54-88% of predicted SOA despite low NMOG fractions, while VOC/OVOC-based predictions underestimated SOA under high oxidation. Increasing OH exposure decreased SOA carbon oxidation state, reflecting a transition from functionalization to fragmentation chemistry. Health risk assessment indicated that photochemical aging increases noncarcinogenic risk via OVOC formation but decreases carcinogenic risk as aromatics oxidize. Overall, China VI vehicles remain efficient sources of secondary particulate pollution under oxidant- and ammonia-rich conditions, highlighting the importance of including secondary products in air quality and health impact assessments.

As tailpipe standards tighten, evaporative emissions have become a major VOC source. Current whole-vehicle regulations overlook the distinct contributions of canister bleed versus non-canister emissions, hindering accurate assessment and control. We developed a synchronized method coupling mini- and variable-temperature SHED to separately measure both sources during diurnal tests. Testing China 6 vehicles under the standard certification protocol, non-canister emissions averaged 170.3 ± 49.1 mg/day, while canister emissions averaged only 3.2 ± 1.2 mg/day, a ratio of ∼59:1. Across test conditions, non-canister emissions exceeded canister emissions by ∼19-fold on average. Canister emissions were highly condition-dependent, reaching 18 times the baseline under off-cycle conditions, with VOC composition shifting toward more reactive species (alkenes, aromatics) and ozone formation potential rising to nearly 600% of certification levels. In contrast, non-canister emissions remained stable in both composition and magnitude. These findings support a shift from mass-based whole-vehicle limits to differentiated, species-resolved strategies. Our streamlined method enables separate yet simultaneous testing of both source types, offering a practical approach for next-stage evaporative standards and progress toward near-zero emissions.

Ammonia (NH3) emitted from light-duty gasoline vehicles equipped with three-way catalysts (TWCs) is an important precursor to secondary aerosols, yet its dynamic formation mechanisms under transient vehicle operation and varying aftertreatment conditions remain insufficiently understood. In this study, a comprehensive investigation was conducted to examine NH3 emission characteristics and catalyst-level formation behavior by integrating vehicle emission evaluations, data-driven attribution analysis, and catalyst characterizations. Extensive chassis dynamometer tests revealed that NH3 emissions exhibited strong dependence on driving conditions and temperature, occurring mainly during cold-start and low-speed acceleration phases, and were positively correlated with CO emission rates. Catalyst aging status showed a non-monotonic impact on NH3 emissions. To link macroscopic emission behaviors with catalyst-related influencing factors, an ensemble learning model coupled with the SHapley Additive exPlanations (SHAP) framework was employed. The attribution analysis indicated that catalyst-temperature-related parameters showed the highest model-associated contributions under most tested scenarios, whereas CO-related exhaust conditions became more important for model prediction during cold-start operation and severe catalyst degradation. Guided by these macroscopic insights, further catalyst performance tests, characterizations, and in situ evaluations suggested that the Pd/Rh ratio substantially influenced NO conversion behavior and the product distribution of NH3 and N2O. Furthermore, hydrothermal aging promoted noble metal agglomeration and altered surface chemical properties, thereby affecting NO conversion efficiency and NH3 formation pathways. This study provides data-driven evidence and catalyst-level insights for understanding NH3 by-product emissions from the tested gasoline vehicle aftertreatment systems, and offers useful implications for mitigation strategies in broader TWC-equipped gasoline vehicles.

Greenhouse gas (GHG) emissions are a major driver of global climate change, with motor vehicles, particularly heavy-duty trucks (HDTs), emerging as significant contributors. Although extensive research has been conducted on gaseous pollutants, studies focusing on GHG emissions under the context of carbon neutrality remain relatively limited. This study evaluates the emissions of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) from 13 in-use trucks with varying aftertreatment technologies, including the first assessment of GHG emissions from HDTs equipped with dual-SCR. The results show that CO2 emission from HDTs were 392.4-841.6 g/km in trucks at standard conditions, with strong correlation to vehicle weight (r = 0.91). N2O emissions rose with advanced aftertreatment: S3 (DOC + DPF + SCR + ASC) emitted 146.4 mg/km, 3-8 times higher than S1 (no SCR)-S2 (SCR). S4 (SCR + ASC + DOC + DPF + SCR + ASC) reduced N2O by 15.4% compared to S3, highlighting improved urea dosing. N2O contribution to Global Warming Potential (GWP) increased from 1.2% (S1) to 4.4% (S4). CH4 emissions were fuel-dependent: diesel trucks showed negligible values (<0.03 g/kWh), while The natural gas truck emitted more CH4 under higher payload (>0.035 g/kWh), with cold starts causing more 20-fold increases. Ambient temperature increased CO2 emissions at -10 °C by up to 22%, while N2O emission trends diverged between S3 and S4 due to differences in aftertreatment architecture. These findings highlight the need for future regulations to further strengthen the control of conventional gaseous pollutants while avoiding the exacerbation of GHG emissions, seeking a balance between the two.

Mobile source (MS) emission control is increasingly important for achieving further air quality improvement. This study examined the atmospheric impacts of mobile-source-related PM2.5 (MS-PM2.5), with particular attention to emerging contributors, including non-exhaust emission processes and unregulated low-volatility organic compounds. From 2011 to 2019, MS-PM2.5 concentrations in eastern China decreased by approximately 13%. However, the contribution of MS to total PM2.5 increased by 3.5%, and non-road sources were found to pose higher environmental risks than on-road sources. Meanwhile, low-volatility organic compounds showed increasing contributions to organic aerosol formation, highlighting the growing importance of previously underrepresented emission components. Deaths attributable to PM2.5 pollution (DAPP) from MS increased by 44.6%, and their share of total DAPP rose by 5.9%. These findings indicate that MS-related health impacts remain substantial under improving air quality conditions. Future MS control strategies should therefore place greater emphasis on non-road sources and emerging emission processes that remain poorly regulated.

Vehicular emissions are a primary source of volatile organic compounds (VOCs), which drive urban ozone and secondary organic aerosol formation while posing direct risks to human health. Progressive emission standards and the widespread adoption of hybrid electric vehicles have successfully reduced total hydrocarbon outputs, establishing them as central strategies for climate and air quality management. However, the influence of these technological shifts on the molecular speciation of emissions-and their associated environmental and toxicological trade-offs-remains poorly understood, potentially masking hidden health risks. Here we apply a concentration-reactivity-toxicity framework to characterize species-resolved VOC emissions across conventional and hybrid vehicles under progressive emission standards. While stricter regulations reduced total VOC emissions by 75% in conventional vehicles, the relative contribution of highly reactive oxygenated VOCs (OVOCs) surged from 20% to 35%. Notably, a modern hybrid vehicle emitted nearly twice the mass of OVOCs (25.4 mg km-1) compared to its conventional counterpart (13.3 mg km-1), driven by frequent engine start-stop cycles that reduce aftertreatment efficiency. This distinct operational profile allows us to identify specific compounds-namely, vinyl acetate and methyl t-butyl ether-as molecular markers for hybrid powertrains in our study. Consequently, despite superior fuel economy, this tested hybrid vehicle exhibited a 69% increase in non-carcinogenic health risks and nearly double the carcinogenic risk, overwhelmingly dominated by aromatics and toxic OVOCs such as acrolein. Furthermore, while absolute emissions declined, persistent aromatics continued to account for over 70% of the secondary organic aerosol formation potential. These findings highlight a critical tension between fuel efficiency advancements and toxicological impacts, suggesting that future emission regulations must transition from total mass limits to species-specific controls to fully safeguard public health.

The polycyclic aromatic hydrocarbons present in vehicle exhaust, including both particulate and gaseous components, constitute a yet inadequately regulated threat to environmental health. However, there has been no systematic review on the emission characteristics and toxicity mechanism of polycyclic aromatic hydrocarbons in vehicle exhaust. Through comprehensive analysis, it was revealed that while high-ring particulate polycyclic aromatic hydrocarbons, especially Benzo[a]pyrene and Dibenz[a,h]anthracene, exhibit greater toxicity, the gaseous fraction of polycyclic aromatic hydrocarbons demonstrates higher emission levels and bioavailability, an aspect frequently underestimated in vehicle exhaust assessments. Meanwhile, engine type, emission standards, fuel type, driving conditions, and temperature largely affect the emission factors and compositional makeup of polycyclic aromatic hydrocarbons. This review, from the dual perspectives of emissions and toxicity, systematically analyzed the emission characteristics and influencing factors of polycyclic aromatic hydrocarbons from vehicle sources, as well as the toxicity mechanism, provided ideas for the formulation of future motor vehicle regulations that balance air quality improvement and public health protection, and also offered support for whether polycyclic aromatic hydrocarbons control should be included in future emission standards.

Heavy container trailers emit substantial quantities of tyre wear particles (TWPs) due to long-distance transportation, increasing ownership, and higher payloads. Owing to their multi-axle layouts, short-wheelbase and dual-tyre arrangement, these container trailers generate complex aerodynamic interactions that significantly influence TWPs dispersion, posing considerable challenges for efficient collection within such intricate flow fields. To address this issue, a comprehensive investigative framework and a novel collection strategy were both proposed. The Eulerian-Lagrangian approach, integrated with the Discrete Phase Model, was computationally implemented to validate the effectiveness and feasibility of the collection strategy. Equally important, a novel test rig was developed to conduct scaled-down experiments, along with a 3D-printed model, to validate the numerical model and simulation outcomes. To improve TWPs' collection efficiency, two collection channels and a rectification chamber were proposed to reconfigure the airflow and form TWPs-enriched passages, integrating porous filters for collection. The optimal placement and geometric arrangement of these channels were determined, with inlet angles of 70 degrees and 80 degrees for the first and second channels, respectively, and a 60 degrees triangular-shaped inlet for the third channel. The results show that a collection ratio exceeding 50% was achieved at a speed of 80 km/h in both laboratory experiments and numerical simulations. The maximum deviation between the simulation and experimental data was less than 6%, indicating high accuracy. These findings contribute to a better understanding of particulate matter dispersion and collection in a complicated flow field. In addition, this study provides valuable insights for policymakers, environmental researchers, trailer manufacturers, and tyre manufacturers in developing regulations and effective strategies to reduce TWPs' emissions.

Ammonia (NH3) emitted by light-duty gasoline vehicles (LDGVs) serves as a crucial precursor to secondary particulate matter. Complex nonlinear relationships are observed between NH3 emissions and various influencing factors. Hence, the development of a prediction model for vehicular NH3 emissions to evaluate actual levels is of utmost importance. In this study, Real Drive Emission (RDE) test results from LDGVs were selected as the dataset, and 4 ensemble learning algorithms, which were Random Forest, AdaBoost, XGBoost, and CatBoost, were employed to construct Model V1 with 13 input features and Model V2 with 9 features, tailored to different input data sources. Based on the models, the SHAP algorithm was utilized to assess the impact of relevant features. The model built on the CatBoost algorithm demonstrated the highest prediction accuracy, with 10-fold cross-validation yielding R2 values of 0.903 and 0.848, and MSE values of 0.00118 and 0.00166 for Models V1 and V2, respectively. The instantaneous NH3 emission prediction model provided a methodological framework for vehicle emission predictions.

The widespread use of retreaded tires has led to great concern about their uncertainty in terms of atmospheric pollution because their degraded tribological performance leads to emit more tire wear particles (TWPs) into the environment. This paper presented the features of TWPs from retreaded tire rubber via a self-developed rolling contact test rig. Normalized comparison, emission per unit worn mass and per kilometer were employed to compare the influence of the test parameters both on emission and on environmental impact quantitatively between the new tire rubber (N-TR) and tire rubber mixed with reclaimed rubber (RR-TR). The results showed that heavy load could induce retreaded tire emitting TWPs3.0 and 5.0 a maximum of 12–19

Traffic-related activity patterns, including transportation mode choices and time spent in transit, critically influence individuals’ exposure to air pollution. This study analyzed data from three cross-sectional surveys conducted in Lanzhou, China (2015-2020), to investigate variations in transportation behavior and their impact on daily cumulative PM2.5 inhalation exposure. Results showed that walking was the most frequently used mode, accounting for over 70% of trips, while car use involved the longest average travel time - exceeding 60 min per day. However, trends in mode share and usage time were not synchronized, and the use of different transportation modes was interrelated. Sociodemographic factors and built environment features near homes and workplaces were dynamically associated with transportation behaviors. Time spent in transit had the strongest influence on cumulative daily exposure, explaining more than 90% of the variation across modes. Open modes of transport were linked to the highest exposure levels due to elevated pollutant concentrations and increased inhalation rates, whereas car transportation resulted in the lowest exposure despite its longer duration. These findings underscore the need to incorporate transportation behavior into air pollution exposure assessments and suggest that transportation policies and infrastructure planning should align mobility objectives with public health priorities.

Greenhouse gas (GHG) emissions represent a pivotal driver of global climate change, with vehicular emissions, particularly from light-duty vehicles, emerging as a prominent source of GHGs. Despite extensive research on gaseous pollutants, studies on GHG emissions within the framework of carbon neutrality remain scarce. This study delves into the emission characteristics of three primary GHGs (carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)) from various light-duty vehicles, encompassing conventional gasoline and hybrid vehicles and bi-fuel taxis. As anticipated, with advancements in emission standards and powertrains, vehicular GHG emissions have significantly decreased. However, our findings also revealed surprising trends. While engine technology upgrades reduced CO2, they unexpectedly increased CH4 and N2O emissions. Additionally, hot starts, beneficial for reducing CO2 and CH4 emissions, caused heightened N2O emissions, which is noteworthy under operating conditions with frequent start–stop events. Intriguingly, compressed natural gas (CNG), generally perceived as cleaner, increased CH4 emissions. Regarding the impact of three-way-catalyst (TWC) converters on GHG emissions, under “TWC deteriorated” conditions, N2O emissions from CNG-powered vehicles were approximately 3 times higher than those under “TWC worked” conditions, which can be attributed to the significant increase in nitrogen oxides (NOx). Considering the global warming potential (GWP), the “TWC deteriorated” scenario paradoxically decreased GWP values, highlighting the complex interaction between emission control technologies and their environmental impacts. This study provides crucial insights into vehicular GHG emissions, which are essential for developing effective strategies aimed at mitigating emissions and enhancing the efficiency of emission control systems.

Chinese diesel trucks are the main contributors to NOx and particulate matter (PM) vehicle emissions. An increase in diesel trucks could aggravate air pollution and damage human health. The Chinese government has recently implemented a series of emission control technologies and measures for air quality improvement. This paper summarizes recent control technologies and measures for diesel truck emissions in China and introduces the comprehensive application of control technologies and measures in Beijing-Tianjin-Hebei and surrounding regions. Remote online monitoring technology has been adopted according to the China VI standard for heavy-duty diesel trucks, and control measures such as transportation structure adjustment and heavy pollution enterprise classification control continue to support the battle action plan for pollution control. Perspectives and suggestions are provided for promoting pollution control and supervision of diesel truck emissions: adhere to the concept of overall management and control, vigorously promote the application of systematic and technological means in emission monitoring, continuously facilitate cargo transportation structure adjustment and promote new energy freight vehicles. This paper aims to accelerate the implementation of control technologies and measures throughout China. China is endeavouring to control diesel truck exhaust pollution. China is willing to cooperate with the world to protect the global ecological environment. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

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Learn More CiteCitationCitation and abstractCitation and referencesMore citation options ShareShare onFacebookXWeChatLinkedInRedditEmailBlueskyJump toExpandCollapse ViewpointMarch 19, 2025Overlooked Underestimation of Mobile Sources Posing a Pronounced Imbalance in the HONO BudgetClick to copy article linkArticle link copied!Jia KeJia KeState Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, ChinaMore by Jia KeXinping Yang*Xinping YangState Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, China*[email protected]More by Xinping YangKeding Lu*Keding LuState Environmental Protection Key Laboratory of Atmospheric Ozone Pollution Control, State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China*[email protected]More by Keding Luhttps://orcid.org/0000-0001-9425-9520Mingliang FuMingliang FuState Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, ChinaMore by Mingliang FuYunjing WangYunjing WangState Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, ChinaMore by Yunjing Wanghttps://orcid.org/0000-0002-9467-190XHang YinHang YinState Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, ChinaMore by Hang YinYan Ding*Yan DingState Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, China*[email protected]More by Yan DingOpen PDFEnvironmental Science & TechnologyCite this: Environ. Sci. Technol. 2025, XXXX, XXX, XXX-XXXClick to copy citationCitation copied!https://pubs.acs.org/doi/10.1021/acs.est.5c02684https://doi.org/10.1021/acs.est.5c02684Published March 19, 2025 Publication History Received 25 February 2025Published online 19 March 2025article-commentary© 2025 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissionsThis publication is licensed for personal use by The American Chemical Society. ACS Publications© 2025 American Chemical SocietySubjectswhat are subjects Article subjects are automatically applied from the ACS Subject Taxonomy and describe the scientific concepts and themes of the article. Chemical reactions Coal Environmental chemistry Environmental modeling Redox reactions Gaseous nitrous acid (HONO), a pivotal precursor of hydroxyl radicals (OH) in the troposphere, has been recognized as a key initiator of atmospheric chemistry, and its formation has garnered significant global scientific interest. (1) Nevertheless, observed HONO concentrations are much higher than those predicted by chemical models even considering the known HONO formation pathways, indicating that exploring potential unknown HONO sources represents a crucial issue to be addressed. Studies have explored secondary sources involving homogeneous reactions of nitric oxide and OH, heterogeneous reactions of nitrogen dioxide, and photolysis of particulate nitrate, as well as the primary sources like coal combustion, traffic, biomass burning, soil, and livestock. (2) Mobile source emissions, a direct HONO source, can contribute up to 50% of urban HONO during haze episodes, (3) particularly with the substantial increase in vehicle ownership. Currently, scientists are predominantly focusing on secondary HONO formation mechanisms. However, should we consider whether the HONO emission from mobile sources, recognized as a significant primary source, has been comprehensively understood?Despite mobile sources being significant contributors to atmospheric HONO, their direct HONO emission measurements remain limited. Scientists commonly employed a HONO-to-NOx ratio of 0.8% in air quality models to estimate mobile source HONO emissions, (4) which has two limitations. First, the application of a fixed ratio to estimate mobile source HONO emissions relies on the assumption of a strong correlation between HONO and NOx emissions and the relatively constant emission ratio. However, increasing direct measurements reveal a wide variability in HONO-to-NOx ratios, (5) introducing significant uncertainty in estimating vehicular HONO emissions. Second, the fixed 0.8% ratio, derived from tunnel observation, (6) may not extend to other mobile sources like nonroad mobile machinery, ships, and aircraft, which remain understudied. These limitations likely cause over- or underestimation of mobile HONO emissions, highlighting a knowledge gap that could hinder tropospheric HONO budget closure.Gasoline VehiclesClick to copy section linkSection link copied!Over the past four decades, scientists have measured HONO emissions from gasoline-dominated fleets by tunnels and highways, and individual vehicles via chassis dynamometers. However, the sample size remains limited. Yang et al. (2024) (5) analyzed the limited data, revealing a general correlation between HONO and NOx emissions but a wide HONO-to-NOx ratio ranging within 0.01%∼5%─up to 2 orders of magnitude compared to the fixed 0.8% ratio. Individual vehicle tests show most ratios are below 0.8%, suggesting that the 0.8% ratio may overestimate gasoline vehicle HONO emissions. (5)Diesel VehiclesClick to copy section linkSection link copied!Diesel vehicles exhibit HONO emission factors up to 3 orders of magnitude higher than gasoline vehicles, potentially emerging as the primary contributors to vehicular HONO emissions. Nevertheless, individual vehicle measurements show a HONO-to-NOx ratio range for diesel vehicles of 0.3%∼3%, with the majority exceeding 0.8%. (5) This suggests that utilizing a fixed 0.8% value would significantly underestimate diesel vehicle HONO emissions. Moreover, some studies suggest the HONO-to-NOx ratio of 2.3% in diesel engines, (7) a rate likely increased with diesel particle filters. (8) Given their significant role in overall vehicular HONO emissions, it is evident that traditional estimation methods fall short in accurately assessing HONO emissions from diesel vehicles, often resulting in significant underestimation.Other Mobile SourcesClick to copy section linkSection link copied!HONO emissions from engine exhaust are well-recognized as a significant direct tropospheric HONO source, yet the majority of research focuses on gasoline and diesel vehicles, with limited attention to other mobile sources, like nonroad mobile machinery, ships, and aircraft.Most studies overlook ship emissions as a direct HONO source, and the few that consider them report inconsistent HONO-to-NOx ratios such as 0.51%, (9) 1.21%, (10) and 1.55%, (11) or assume a diesel-like ratio of 2.3%. Notably, these ratios are derived from ship plumes rather than in situ engine bench tests, but the emission characteristics of the two are not fully comparable. The uncertainty in ship HONO emissions further complicates the estimation of mobile source HONO emissions within models.Compared to ship emissions, HONO emissions from aircraft and nonroad mobile machinery have been largely overlooked. A handful of studies about aircraft examine HONO-to-NOx ratios of 0.82%∼6% (12) and HONO-to-NOy ratios (NOy = NOx+HNO3+PAN+alkylnitrates) of 0.5%∼7%. (13,14) Such high HONO-to-NOy ratios imply an even higher HONO-to-NOx ratio, further indicating the non-negligible significance of HONO emissions from aircraft. However, research on aircraft HONO emissions remains limited, with widely varying reported ratios, and most models have not yet considered them. To the best of our knowledge, only Yin et al. (2023) have reported nonroad mobile machinery HONO emissions using a 2.3% HONO-to-NOx ratio in inventories, (15) but no in situ measurements have been documented to date. Therefore, current air quality models overlook these HONO sources, increasing uncertainty in HONO budget exploration.Recommendations and OutlookClick to copy section linkSection link copied!Precise quantification of HONO emission is essential for identifying unknown HONO sources and addressing gaps in the HONO budget (Figure 1). This Viewpoint revisits the traditional methods for estimating mobile source HONO emissions, emphasizing their potential to significantly underestimate emissions. A major challenge contributing to this issue is the lack of a refined mobile source emission inventory. Herein, we recommend focusing on the following areas. (1) Developing in situ HONO measurement methods for different mobile sources, conducting precise testing on a large sample, with particular attention to emissions from high-emission vehicles, and constructing localized HONO fingerprint profiles. (2) Optimizing estimation methods for mobile source HONO emissions by adopting advanced technologies such as machine learning. (3) Establishing refined and localized emission inventories, categorized by vehicle/machinery types, emission standards, fuel types, and operational status, similar to the Tsinghua University MEIC model (http://meicmodel.org.cn), for integration into air quality models. (4) Incorporating HONO emissions from mobile sources into emission standards, but we acknowledge that it is challenging to control HONO emissions from mobile sources at this stage due to the lack of a clear understanding of their emission characteristics. Overall, we believe that the overlooked and potentially significantly underestimated mobile source HONO emissions could be a crucial factor contributing to the nonclosure HONO budget. Addressing these knowledge gaps in a refined understanding of mobile source HONO emissions could elucidate the missing HONO sources, a globally concerned issue, from the perspective of primary direct emission.Figure 1Figure 1. Schematic diagram of the source and removal mechanisms of HONO.High Resolution ImageDownload MS PowerPoint SlideAuthor InformationClick to copy section linkSection link copied!Corresponding AuthorsXinping Yang - State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Email: [email protected]Keding Lu - State Environmental Protection Key Laboratory of Atmospheric Ozone Pollution Control, State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China; https://orcid.org/0000-0001-9425-9520; Email: [email protected]Yan Ding - State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Email: [email protected]AuthorsJia Ke - State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, ChinaMingliang Fu - State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, ChinaYunjing Wang - State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; https://orcid.org/0000-0002-9467-190XHang Yin - State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, ChinaFundingThe authors thank the National Natural Science Foundation of China (Grant 42205111), the Open Research Fund of Key Laboratory for Vehicle Emission Control and Simulation of the Ministry of Ecology and Environment, Chinese Research Academy of Environmental Sciences (Grant VECS2024K11), and the Fundamental Research Funds for the Central Public-interest Scientific Institution (Grant 2024YSKY-03) for supporting this work.NotesThe authors declare no competing financial interest.ReferencesClick to copy section linkSection link copied! This article references 15 other publications. 1Xue, C. Substantially Growing Interest in the Chemistry of Nitrous Acid (HONO) in China: Current Achievements, Problems, and Future Directions. Environ. Sci. Technol. 2022, 56 (12), 7375– 7377, DOI: 10.1021/acs.est.2c02237 Google Scholar1Substantially Growing Interest in the Chemistry of Nitrous Acid (HONO) in China: Current Achievements, Problems, and Future DirectionsXue, ChaoyangEnvironmental Science & Technology (2022), 56 (12), 7375-7377CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society) There is no expanded citation for this reference. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhsVKgt77J&md5=1ba459fb3756c7ce37f34de36d69b4862Zhang, Q.; Liu, P.; Wang, Y.; George, C.; Chen, T.; Ma, S.; Ren, Y.; Mu, Y.; Song, M.; Herrmann, H.; Mellouki, A.; Chen, J.; Yue, Y.; Zhao, X.; Wang, S.; Zeng, Y. Unveiling the underestimated direct emissions of nitrous acid (HONO). Proc. Natl. Acad. Sci. U. S. A. 2023, 120 (35), e2302048120 DOI: 10.1073/pnas.2302048120 Google ScholarThere is no corresponding record for this reference.3Zhang, W.; Tong, S.; Ge, M.; An, J.; Shi, Z.; Hou, S.; Xia, K.; Qu, Y.; Zhang, H.; Chu, B.; Sun, Y.; He, H. Variations and sources of nitrous acid (HONO) during a severe pollution episode in Beijing in winter 2016. Science of The Total Environment 2019, 648, 253– 262, DOI: 10.1016/j.scitotenv.2018.08.133 Google ScholarThere is no corresponding record for this reference.4Ye, C.; Lu, K.; Ma, X.; Qiu, W.; Li, S.; Yang, X.; Xue, C.; Zhai, T.; Liu, Y.; Li, X.; Li, Y.; Wang, H.; Tan, Z.; Chen, X.; Dong, H.; Zeng, L.; Hu, M.; Zhang, Y. HONO chemistry at a suburban site during the EXPLORE-YRD campaign in 2018: formation mechanisms and impacts on O3 production. Atmospheric Chemistry and Physics 2023, 23 (24), 15455– 15472, DOI: 10.5194/acp-23-15455-2023 Google ScholarThere is no corresponding record for this reference.5Yang, X.; Fu, M.; Liao, S.; Tu, Z.; Feng, W.; Wang, Y.; Jiang, H.; Tian, Q.; Yin, H.; Zheng, J.; Ding, Y. Revisiting the estimation indicator for HONO emissions from light-duty vehicles. Journal of Hazardous Materials 2024, 479, 135642, DOI: 10.1016/j.jhazmat.2024.135642 Google ScholarThere is no corresponding record for this reference.6Kurtenbach, R.; Becker, K. H.; Gomes, J. A. G.; Kleffmann, J.; Lorzer, J. C.; Spittler, M.; Wiesen, P.; Ackermann, R.; Geyer, A.; Platt, U. Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel. Atmos. Environ. 2001, 35 (20), 3385– 3394, DOI: 10.1016/S1352-2310(01)00138-8 Google Scholar6Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnelKurtenbach, R.; Becker, K. H.; Gomes, J. A. G.; Kleffmann, J.; Lorzer, J. C.; Spittler, M.; Wiesen, P.; Ackermann, R.; Geyer, A.; Platt, U.Atmospheric Environment (2001), 35 (20), 3385-3394CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.) Simultaneous measurements of nitrous acid and nitrogen dioxide using a differential optical absorption spectroscopy system, nitric oxide by an in situ chemiluminescence analyzer, and carbon dioxide by a gas chromatog. technique were carried out in the Kiesbergtunnel, Wuppertal, Germany. At high traffic d., HONO concns. of up to 45 ppb by vol. (ppbv) were obsd. However, at low traffic d., unexpectedly high HONO concns. of up to 10 ppbv were measured that were caused by heterogeneous HONO formation on the tunnel walls. In addn. to the tunnel campaigns, emission measurements of HONO, NO2, NO, and CO2 from different single vehicles (a truck, a diesel, and a gasoline passenger car) were also performed. For the correction of the HONO emission data, the heterogeneous HONO formation on the tunnel walls was quantified by two different approaches: (a) in different NO2 emission expts. in the tunnel without traffic and (b) on tunnel wall residue in the lab. The HONO concn. cor. for heterogeneous formation on the tunnel walls, in relation to the CO2 concn., can be used to est. the amt. of HONO that is directly emitted from the vehicle fleet. From the measured data, emission ratios (e.g., HONO/NOx), and emission indexes (e.g., mg HONO/kg fuel) were calcd. The calcd. emission index of 88 ±18 mg HONO/kg fuel allows an estn. of the HONO emission rates from traffic into the atm. Furthermore, the heterogeneous formation of HONO from NO2 on freshly emitted exhaust particles is discussed. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXks1aru7s%253D&md5=5e4fa5a123fe0e84f764930b956948e77Gutzwiller, L.; Arens, F.; Baltensperger, U.; Gäggeler, H. W.; Ammann, M. Significance of semivolatile diesel exhaust organics for secondary HONO formation. Environ. Sci. Technol. 2002, 36 (4), 677– 682, DOI: 10.1021/es015673b Google Scholar7Significance of Semivolatile Diesel Exhaust Organics for Secondary HONO FormationGutzwiller, Lukas; Arens, Frank; Baltensperger, Urs; Gaeggeler, Heinz W.; Ammann, MarkusEnvironmental Science and Technology (2002), 36 (4), 677-682CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society) The atm. origin of nitrous acid (HONO) is largely unknown despite its estd. importance as an OH source during daytime due to its rapid photolysis. Recently, primary HONO contained in automobile exhaust as well as secondary HONO formation on soot particles were invoked as possible HONO sources, but none of them is able to account for the obsd. HONO to NOx ratios of up to 0.04 in the atm. Semivolatile and/or water-sol. species contained in diesel exhaust are significantly involved in secondary HONO formation. These species are not assocd. with soot when the exhaust exits the tailpipe. To quantify these species and to assess the reaction kinetics leading to HONO, expts. were performed in which filtered but hot diesel exhaust gas interacted with a glass surface as well as a water film mimicking dry and wet surfaces to which exhaust might be exposed. A fraction of 0.023 of the NOx emitted was heterogeneously converted to HONO, which is at least three times more than the primary HONO emissions by diesel engines and a fraction of 50 larger than HONO formed on diesel soot particles that do not contain the semivolatile orgs. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XjtF2qug%253D%253D&md5=f1431cb10c62c3d6c855588c16506e4b8Liang, Y.; Zha, Q.; Wang, W.; Cui, L.; Lui, K. H.; Ho, K. F.; Wang, Z.; Lee, S.-c.; Wang, T. Revisiting nitrous acid (HONO) emission from on-road vehicles: A tunnel study with a mixed fleet. J. Air Waste Manage. Assoc. 2017, 67 (7), 797– 805, DOI: 10.1080/10962247.2017.1293573 Google ScholarThere is no corresponding record for this reference.9Sun, L.; Chen, T.; Jiang, Y.; Zhou, Y.; Sheng, L.; Lin, J.; Li, J.; Dong, C.; Wang, C.; Wang, X.; Zhang, Q.; Wang, W.; Xue, L. Ship emission of nitrous acid (HONO) and its impacts on the marine atmospheric oxidation chemistry. Sci. Total Environ. 2020, 735, 139355, DOI: 10.1016/j.scitotenv.2020.139355 Google ScholarThere is no corresponding record for this reference.10Gu, R.; Wang, W.; Peng, X.; Xia, M.; Zhao, M.; Zhang, Y.; Liu, Y.; Shen, H.; Xue, L.; Wang, T.; Wang, W.; Wang, Y. n. Nitrous acid in the polluted coastal atmosphere of the South China Sea: Ship emissions, budgets, and impacts. Sci. Total Environ. 2022, 826, 153692, DOI: 10.1016/j.scitotenv.2022.153692 Google ScholarThere is no corresponding record for this reference.11Guo, Y.; Wang, S.; Gao, S.; Zhang, R.; Zhu, J.; Zhou, B. Influence of ship direct emission on HONO sources in channel environment. Atmos. Environ. 2020, 242, 117819, DOI: 10.1016/j.atmosenv.2020.117819 Google ScholarThere is no corresponding record for this reference.12Lee, B. H.; Santoni, G. W.; Wood, E. C.; Herndon, S. C.; Miake-Lye, R. C.; Zahniser, M. S.; Wofsy, S. C.; Munger, J. W. Measurements of Nitrous Acid in Commercial Aircraft Exhaust at the Alternative Aviation Fuel Experiment. Environ. Sci. Technol. 2011, 45 (18), 7648– 7654, DOI: 10.1021/es200921t Google Scholar12Measurements of Nitrous Acid in Commercial Aircraft Exhaust at the Alternative Aviation Fuel ExperimentLee, Ben H.; Santoni, Gregory W.; Wood, Ezra C.; Herndon, Scott C.; Miake-Lye, Richard C.; Zahniser, Mark S.; Wofsy, Steven C.; Munger, J. WilliamEnvironmental Science & Technology (2011), 45 (18), 7648-7654CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society) The Alternative Aviation Fuel Expt., conducted in Jan. 2009 in Palmdale, California, quantified aerosol and gaseous emissions from a DC-8 aircraft equipped with CFM56-2C1 engines using traditional and synthetic fuels. This study examd. HNO2 and NOx (NO + NO2) emissions measured 145 m behind the grounded aircraft. A fuel-based emission index (EI) for HNO2 increased ∼6-fold from idle to take-off conditions, but leveled off between 65 and 100% of max. rated engine thrust; the EI for NOx increased continuously. At high engine power, NOx EI was greater when burning traditional (JP-8) vs. Fischer-Tropsch fuels; HNO2 exhibited the opposite trend. Also, H2O2 was identified in exhaust plumes emitted only during engine idle. Chem. reactions responsible for emissions and comparison to previous measurement studies are discussed. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtVCrsbvP&md5=dbbdbf362019bd6733768d7bd3c10e6613Wood, E. C.; Herndon, S. C.; Timko, M. T.; Yelvington, P. E.; Miake-Lye, R. C. Speciation and chemical evolution of nitrogen oxides in aircraft exhaust near airports. Environ. Sci. Technol. 2008, 42 (6), 1884– 1891, DOI: 10.1021/es072050a Google Scholar13Speciation and Chemical Evolution of Nitrogen Oxides in Aircraft Exhaust near AirportsWood, Ezra C.; Herndon, Scott C.; Timko, Michael T.; Yelvington, Paul E.; Miake-Lye, Richard C.Environmental Science & Technology (2008), 42 (6), 1884-1891CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society) NOx measurements from a variety of com. aircraft engines as part of the JETS-APEX2 and APEX3 campaigns showed NOx (NOx = NO + NO2) is emitted primarily as NO2 at idle thrust and NO at high thrust. A chem. kinetics combustion model reproduced obsd. NO2 and NOx trends with engine power and shed light on relevant chem. mechanisms. Exptl. evidence is presented of rapid conversion of NO to NO2 in the exhaust plume from engines at low thrust. This rapid conversion and the high NO2:NOx emission ratios obsd. were unrelated to O3 chem. NO2 emissions from a CFM56-3B1 engine accounted for ∼25% of NOx emitted below 3000 ft (916 m) and 50% of NOx emitted below 500 ft (153 m) during a std. International Civil Aviation Organization landing/take-off cycle. HONO accounted for 0.5-7% of NOy emissions from aircraft exhaust, depending on thrust and engine type. Implications for photochem. near airports resulting from aircraft emissions are discussed. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXitFeht7o%253D&md5=203318b11fd98cd0f85090b490124dbe14Jurkat, T.; Voigt, C.; Arnold, F.; Schlager, H.; Kleffmann, J.; Aufmhoff, H.; Schaeuble, D.; Schaefer, M.; Schumann, U. Measurements of HONO, NO, NOy and SO2 in aircraft exhaust plumes at cruise. Geophys. Res. Lett. 2011, 38 (10), L10807, DOI: 10.1029/2011GL046884 Google ScholarThere is no corresponding record for this reference.15Yin, X.; Tang, F.; Huang, Z.; Liao, S.; Sha, Q.; Cheng, P.; Lu, M.; Li, Z.; Yu, F.; Xu, Y.; Shao, M.; Zheng, J. Developing a model-ready highly resolved HONO emission inventory in Guangdong using domestic measured emission factors. Science of The Total Environment 2023, 899, 165737, DOI: 10.1016/j.scitotenv.2023.165737 Google ScholarThere is no corresponding record for this reference.Cited By Click to copy section linkSection link copied!This article has not yet been cited by other publications.Download PDFFiguresReferences Get e-AlertsGet e-AlertsEnvironmental Science & TechnologyCite this: Environ. Sci. Technol. 2025, XXXX, XXX, XXX-XXXClick to copy citationCitation copied!https://doi.org/10.1021/acs.est.5c02684Published March 19, 2025 Publication History Received 25 February 2025Published online 19 March 2025© 2025 American Chemical Society. 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Find more information on the Altmetric Attention Score and how the score is calculated.Recommended Articles FiguresReferencesAbstractHigh Resolution ImageDownload MS PowerPoint SlideFigure 1Figure 1. Schematic diagram of the source and removal mechanisms of HONO.High Resolution ImageDownload MS PowerPoint SlideReferences This article references 15 other publications. 1Xue, C. Substantially Growing Interest in the Chemistry of Nitrous Acid (HONO) in China: Current Achievements, Problems, and Future Directions. Environ. Sci. Technol. 2022, 56 (12), 7375– 7377, DOI: 10.1021/acs.est.2c02237 1Substantially Growing Interest in the Chemistry of Nitrous Acid (HONO) in China: Current Achievements, Problems, and Future DirectionsXue, ChaoyangEnvironmental Science & Technology (2022), 56 (12), 7375-7377CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society) There is no expanded citation for this reference. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XhsVKgt77J&md5=1ba459fb3756c7ce37f34de36d69b4862Zhang, Q.; Liu, P.; Wang, Y.; George, C.; Chen, T.; Ma, S.; Ren, Y.; Mu, Y.; Song, M.; Herrmann, H.; Mellouki, A.; Chen, J.; Yue, Y.; Zhao, X.; Wang, S.; Zeng, Y. Unveiling the underestimated direct emissions of nitrous acid (HONO). Proc. Natl. Acad. Sci. U. S. A. 2023, 120 (35), e2302048120 DOI: 10.1073/pnas.2302048120 There is no corresponding record for this reference.3Zhang, W.; Tong, S.; Ge, M.; An, J.; Shi, Z.; Hou, S.; Xia, K.; Qu, Y.; Zhang, H.; Chu, B.; Sun, Y.; He, H. Variations and sources of nitrous acid (HONO) during a severe pollution episode in Beijing in winter 2016. Science of The Total Environment 2019, 648, 253– 262, DOI: 10.1016/j.scitotenv.2018.08.133 There is no corresponding record for this reference.4Ye, C.; Lu, K.; Ma, X.; Qiu, W.; Li, S.; Yang, X.; Xue, C.; Zhai, T.; Liu, Y.; Li, X.; Li, Y.; Wang, H.; Tan, Z.; Chen, X.; Dong, H.; Zeng, L.; Hu, M.; Zhang, Y. HONO chemistry at a suburban site during the EXPLORE-YRD campaign in 2018: formation mechanisms and impacts on O3 production. Atmospheric Chemistry and Physics 2023, 23 (24), 15455– 15472, DOI: 10.5194/acp-23-15455-2023 There is no corresponding record for this reference.5Yang, X.; Fu, M.; Liao, S.; Tu, Z.; Feng, W.; Wang, Y.; Jiang, H.; Tian, Q.; Yin, H.; Zheng, J.; Ding, Y. Revisiting the estimation indicator for HONO emissions from light-duty vehicles. Journal of Hazardous Materials 2024, 479, 135642, DOI: 10.1016/j.jhazmat.2024.135642 There is no corresponding record for this reference.6Kurtenbach, R.; Becker, K. H.; Gomes, J. A. G.; Kleffmann, J.; Lorzer, J. C.; Spittler, M.; Wiesen, P.; Ackermann, R.; Geyer, A.; Platt, U. Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel. Atmos. Environ. 2001, 35 (20), 3385– 3394, DOI: 10.1016/S1352-2310(01)00138-8 6Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnelKurtenbach, R.; Becker, K. H.; Gomes, J. A. G.; Kleffmann, J.; Lorzer, J. C.; Spittler, M.; Wiesen, P.; Ackermann, R.; Geyer, A.; Platt, U.Atmospheric Environment (2001), 35 (20), 3385-3394CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Science Ltd.) Simultaneous measurements of nitrous acid and nitrogen dioxide using a differential optical absorption spectroscopy system, nitric oxide by an in situ chemiluminescence analyzer, and carbon dioxide by a gas chromatog. technique were carried out in the Kiesbergtunnel, Wuppertal, Germany. At high traffic d., HONO concns. of up to 45 ppb by vol. (ppbv) were obsd. However, at low traffic d., unexpectedly high HONO concns. of up to 10 ppbv were measured that were caused by heterogeneous HONO formation on the tunnel walls. In addn. to the tunnel campaigns, emission measurements of HONO, NO2, NO, and CO2 from different single vehicles (a truck, a diesel, and a gasoline passenger car) were also performed. For the correction of the HONO emission data, the heterogeneous HONO formation on the tunnel walls was quantified by two different approaches: (a) in different NO2 emission expts. in the tunnel without traffic and (b) on tunnel wall residue in the lab. The HONO concn. cor. for heterogeneous formation on the tunnel walls, in relation to the CO2 concn., can be used to est. the amt. of HONO that is directly emitted from the vehicle fleet. From the measured data, emission ratios (e.g., HONO/NOx), and emission indexes (e.g., mg HONO/kg fuel) were calcd. The calcd. emission index of 88 ±18 mg HONO/kg fuel allows an estn. of the HONO emission rates from traffic into the atm. Furthermore, the heterogeneous formation of HONO from NO2 on freshly emitted exhaust particles is discussed. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXks1aru7s%253D&md5=5e4fa5a123fe0e84f764930b956948e77Gutzwiller, L.; Arens, F.; Baltensperger, U.; Gäggeler, H. W.; Ammann, M. Significance of semivolatile diesel exhaust organics for secondary HONO formation. Environ. Sci. Technol. 2002, 36 (4), 677– 682, DOI: 10.1021/es015673b 7Significance of Semivolatile Diesel Exhaust Organics for Secondary HONO FormationGutzwiller, Lukas; Arens, Frank; Baltensperger, Urs; Gaeggeler, Heinz W.; Ammann, MarkusEnvironmental Science and Technology (2002), 36 (4), 677-682CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society) The atm. origin of nitrous acid (HONO) is largely unknown despite its estd. importance as an OH source during daytime due to its rapid photolysis. Recently, primary HONO contained in automobile exhaust as well as secondary HONO formation on soot particles were invoked as possible HONO sources, but none of them is able to account for the obsd. HONO to NOx ratios of up to 0.04 in the atm. Semivolatile and/or water-sol. species contained in diesel exhaust are significantly involved in secondary HONO formation. These species are not assocd. with soot when the exhaust exits the tailpipe. To quantify these species and to assess the reaction kinetics leading to HONO, expts. were performed in which filtered but hot diesel exhaust gas interacted with a glass surface as well as a water film mimicking dry and wet surfaces to which exhaust might be exposed. A fraction of 0.023 of the NOx emitted was heterogeneously converted to HONO, which is at least three times more than the primary HONO emissions by diesel engines and a fraction of 50 larger than HONO formed on diesel soot particles that do not contain the semivolatile orgs. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XjtF2qug%253D%253D&md5=f1431cb10c62c3d6c855588c16506e4b8Liang, Y.; Zha, Q.; Wang, W.; Cui, L.; Lui, K. H.; Ho, K. F.; Wang, Z.; Lee, S.-c.; Wang, T. Revisiting nitrous acid (HONO) emission from on-road vehicles: A tunnel study with a mixed fleet. J. Air Waste Manage. Assoc. 2017, 67 (7), 797– 805, DOI: 10.1080/10962247.2017.1293573 There is no corresponding record for this reference.9Sun, L.; Chen, T.; Jiang, Y.; Zhou, Y.; Sheng, L.; Lin, J.; Li, J.; Dong, C.; Wang, C.; Wang, X.; Zhang, Q.; Wang, W.; Xue, L. Ship emission of nitrous acid (HONO) and its impacts on the marine atmospheric oxidation chemistry. Sci. Total Environ. 2020, 735, 139355, DOI: 10.1016/j.scitotenv.2020.139355 There is no corresponding record for this reference.10Gu, R.; Wang, W.; Peng, X.; Xia, M.; Zhao, M.; Zhang, Y.; Liu, Y.; Shen, H.; Xue, L.; Wang, T.; Wang, W.; Wang, Y. n. Nitrous acid in the polluted coastal atmosphere of the South China Sea: Ship emissions, budgets, and impacts. Sci. Total Environ. 2022, 826, 153692, DOI: 10.1016/j.scitotenv.2022.153692 There is no corresponding record for this reference.11Guo, Y.; Wang, S.; Gao, S.; Zhang, R.; Zhu, J.; Zhou, B. Influence of ship direct emission on HONO sources in channel environment. Atmos. Environ. 2020, 242, 117819, DOI: 10.1016/j.atmosenv.2020.117819 There is no corresponding record for this reference.12Lee, B. H.; Santoni, G. W.; Wood, E. C.; Herndon, S. C.; Miake-Lye, R. C.; Zahniser, M. S.; Wofsy, S. C.; Munger, J. W. Measurements of Nitrous Acid in Commercial Aircraft Exhaust at the Alternative Aviation Fuel Experiment. Environ. Sci. Technol. 2011, 45 (18), 7648– 7654, DOI: 10.1021/es200921t 12Measurements of Nitrous Acid in Commercial Aircraft Exhaust at the Alternative Aviation Fuel ExperimentLee, Ben H.; Santoni, Gregory W.; Wood, Ezra C.; Herndon, Scott C.; Miake-Lye, Richard C.; Zahniser, Mark S.; Wofsy, Steven C.; Munger, J. WilliamEnvironmental Science & Technology (2011), 45 (18), 7648-7654CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society) The Alternative Aviation Fuel Expt., conducted in Jan. 2009 in Palmdale, California, quantified aerosol and gaseous emissions from a DC-8 aircraft equipped with CFM56-2C1 engines using traditional and synthetic fuels. This study examd. HNO2 and NOx (NO + NO2) emissions measured 145 m behind the grounded aircraft. A fuel-based emission index (EI) for HNO2 increased ∼6-fold from idle to take-off conditions, but leveled off between 65 and 100% of max. rated engine thrust; the EI for NOx increased continuously. At high engine power, NOx EI was greater when burning traditional (JP-8) vs. Fischer-Tropsch fuels; HNO2 exhibited the opposite trend. Also, H2O2 was identified in exhaust plumes emitted only during engine idle. Chem. reactions responsible for emissions and comparison to previous measurement studies are discussed. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhtVCrsbvP&md5=dbbdbf362019bd6733768d7bd3c10e6613Wood, E. C.; Herndon, S. C.; Timko, M. T.; Yelvington, P. E.; Miake-Lye, R. C. Speciation and chemical evolution of nitrogen oxides in aircraft exhaust near airports. Environ. Sci. Technol. 2008, 42 (6), 1884– 1891, DOI: 10.1021/es072050a 13Speciation and Chemical Evolution of Nitrogen Oxides in Aircraft Exhaust near AirportsWood, Ezra C.; Herndon, Scott C.; Timko, Michael T.; Yelvington, Paul E.; Miake-Lye, Richard C.Environmental Science & Technology (2008), 42 (6), 1884-1891CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society) NOx measurements from a variety of com. aircraft engines as part of the JETS-APEX2 and APEX3 campaigns showed NOx (NOx = NO + NO2) is emitted primarily as NO2 at idle thrust and NO at high thrust. A chem. kinetics combustion model reproduced obsd. NO2 and NOx trends with engine power and shed light on relevant chem. mechanisms. Exptl. evidence is presented of rapid conversion of NO to NO2 in the exhaust plume from engines at low thrust. This rapid conversion and the high NO2:NOx emission ratios obsd. were unrelated to O3 chem. NO2 emissions from a CFM56-3B1 engine accounted for ∼25% of NOx emitted below 3000 ft (916 m) and 50% of NOx emitted below 500 ft (153 m) during a std. International Civil Aviation Organization landing/take-off cycle. HONO accounted for 0.5-7% of NOy emissions from aircraft exhaust, depending on thrust and engine type. Implications for photochem. near airports resulting from aircraft emissions are discussed. >> More from SciFinder ®https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXitFeht7o%253D&md5=203318b11fd98cd0f85090b490124dbe14Jurkat, T.; Voigt, C.; Arnold, F.; Schlager, H.; Kleffmann, J.; Aufmhoff, H.; Schaeuble, D.; Schaefer, M.; Schumann, U. Measurements of HONO, NO, NOy and SO2 in aircraft exhaust plumes at cruise. Geophys. Res. Lett. 2011, 38 (10), L10807, DOI: 10.1029/2011GL046884 There is no corresponding record for this reference.15Yin, X.; Tang, F.; Huang, Z.; Liao, S.; Sha, Q.; Cheng, P.; Lu, M.; Li, Z.; Yu, F.; Xu, Y.; Shao, M.; Zheng, J. Developing a model-ready highly resolved HONO emission inventory in Guangdong using domestic measured emission factors. Science of The Total Environment 2023, 899, 165737, DOI: 10.1016/j.scitotenv.2023.165737 There is no corresponding record for this reference.

Heavy container trucks generate disproportionately large quantities of tire-wear particles (TWPs) owing to their high axle loads, dual tires and long duty cycles. We investigate the gas-solid two-phase-flow capture of freshly emitted TWPs from the tractor unit using a porous filter that spans the full cross section of the collection duct. Porous filter placement together with inlet-outlet geometry was optimized through a coupled Eulerian-Lagrangian multiphase flow framework and verified with a 1:24 physical model on a bespoke test rig. The results showed that a suitably designed triangular inlet promotes the entrainment of TWPs into the capture duct, driven by the pressure differential between the internal and external flow regions. The optimal top angle of the triangular inlet was found to be 50 degrees. The rear outlet, incorporating an overhead cavity, effectively suppresses air backflow within the capture duct by reducing the static pressure in the vicinity of the outlet. Under the integrated front-rear configuration, the average capture ratios reached approximately 31.4% at 30 km/h, 44.1% at 60 km/h, and 50.9% at 90 km/h. An analogous comparison across studies suggests that the porous filter achieves approximately 6.7% higher capture efficiency than the adhesive method at 90 km/h. The experimental and simulation results exhibit good agreement both qualitatively and quantitatively. The proposed methodology offers guidance for mitigating secondary hazards associated with tire-wear emissions from the tractors of heavy container trucks.