香港城门隧道和美国麦克亨利堡隧道的实际车辆排放特征。

Xiaoliang Wang, Andrey Khlystov, Kin-Fai Ho, Dave Campbell, Judith C Chow, Steven D Kohl, John G Watson, Shun-Cheng Frank Lee, Lung-Wen Antony Chen, Minggen Lu, Steven Sai Hang Ho
{"title":"香港城门隧道和美国麦克亨利堡隧道的实际车辆排放特征。","authors":"Xiaoliang Wang, Andrey Khlystov, Kin-Fai Ho, Dave Campbell, Judith C Chow, Steven D Kohl, John G Watson, Shun-Cheng Frank Lee, Lung-Wen Antony Chen, Minggen Lu, Steven Sai Hang Ho","doi":"","DOIUrl":null,"url":null,"abstract":"<p><strong>Introduction: </strong>Motor vehicle exhaust is an important source of air pollutants and greenhouse gases. Concerns over the health and climate effects of mobile-source emissions have prompted worldwide efforts to reduce vehicle emissions. Implementation of more stringent emission standards have driven advances in vehicle, engine, and exhaust after-treatment technologies as well as fuel formulations. On the other hand, vehicle numbers and travel distances have been increasing because of population and economic growth and changes in land use. These factors have resulted in changes to the amount and chemical composition of vehicle emissions.</p><p><p>Roadway tunnel studies are a practical way to characterize real-world emissions from the on-road vehicle fleet in an environment isolated from other combustion pollution sources. Measurements in the same tunnel over time allow evaluation of vehicle emission changes and the effectiveness of emission reduction measures. Tunnel studies estimate the impacts of vehicle emissions on air quality and traffic-related exposures, generate source profile inputs for receptor-oriented source apportionment models, provide data to evaluate emission models, and serve as a baseline for future comparisons.</p><p><p>The present study characterized motor vehicle emission factors and compositions in two roadway tunnels that were first studied over a decade ago. The specific aims were to (1) quantify current fleet air pollutant emission factors, (2) evaluate emission change over time, (3) establish source profiles for volatile organic compounds (VOCs) and particulate matter ≤2.5 μm in aerodynamic diameter (PM<sub>2.5</sub>), (4) estimate contributions of fleet components and non-tailpipe emissions to VOCs and PM<sub>2.5</sub>, and (5) evaluate the performance of the latest versions of mobile-source emission models (i.e., the EMission FACtors vehicle emission model used in Hong Kong [EMFAC-HK] and the MOtor Vehicle Emission Simulator used in the United States [MOVES]).</p><p><strong>Methods: </strong>Measurements were conducted in the Shing Mun Tunnel (SMT) in Hong Kong and the Fort McHenry Tunnel (FMT) in Baltimore, Maryland, in the United States, representing the different fleet compositions, emission controls, fuels, and near-road exposure levels found in Hong Kong and the United States. These tunnels have extensive databases acquired in 2003-2004 for the SMT and 1992 for the FMT. The SMT sampling was conducted during the period from 1/19/2015 to 3/31/2015, and the FMT sampling occurred during the periods from 2/8/2015 to 2/15/2015 (winter) and 7/31/2015 to 8/7/2015 (summer). Concentrations of criteria pollutants (e.g., carbon monoxide [CO], nitrogen oxides [NOx], and particulate matter [PM]) were measured in real time, and integrated samples of VOCs, carbonyls, polycyclic aromatic hydrocarbons (PAHs), and PM<sub>2.5</sub> were collected in canisters and sampling media for off-line analyses. Emission factors were calculated from the tunnel measurements and compared with previous studies to evaluate emission changes over time. Emission contributions by different vehicle types were assessed by source apportionment modeling or linear regression. Vehicle emissions were modeled by EMFAC-HK version 3.3 and MOVES version 2014a for the SMT and the FMT, respectively, and compared with measured values. The influences of vehicle fleet composition and environmental parameters (i.e., temperature and relative humidity) on emissions were evaluated.</p><p><strong>Results: </strong>In the SMT, emissions of PM<sub>2.5</sub>, sulfur dioxide (SO<sub>2</sub>), and total non-methane hydrocarbons (NMHCs) markedly decreased from 2003-2004 to 2015: SO<sub>2</sub> and PM<sub>2.5</sub> were reduced by ~80%, and total NMHCs was reduced by ~44%. Emission factors of ethene and propene, key tracers for diesel vehicle (DV) emissions, decreased by ~65%. These reductions demonstrate the effectiveness of control measures, such as the implementation of low-sulfur fuel regulations and the phasing out of older DVs. However, the emission factors of isobutane and <i>n</i>-butane, markers for liquefied petroleum gas (LPG), increased by 32% and 17% between 2003-2004 and 2015, respectively, because the number of LPG vehicles increased. Nitrogen dioxide (NO<sub>2</sub>) to NOx volume ratios increased between 2003-2004 and 2015, indicating an increased NO<sub>2</sub> fraction in primary exhaust emissions. Although geological mineral concentrations were similar between the 2003-2004 and 2015 studies, the contribution of geological materials to PM<sub>2.5</sub> increased from 2% in 2003-2004 to 5% in 2015, signifying the continuing importance of non-tailpipe PM emissions as tailpipe emissions decrease. Emissions of CO, ammonia (NH<sub>3</sub>), nitric oxide (NO), NO<sub>2</sub>, and NOx, as well as carbonyls and PAHs in the SMT did not show statistically significant (at <i>P</i> < 0.05 based on Student's <i>t</i>-test) decreases from 2003-2004 to 2015. The reason for this is not clear and requires further investigation.</p><p><p>A steady decrease in emissions of all measured pollutants during the past 23 years has been observed from tunnel studies in the United States, reflecting the effect of emission standards and new technologies that were introduced during this period. Emission reductions were more pronounced for the light-duty (LD) fleet than for the heavy-duty (HD) fleet. In comparison with the 1992 FMT study, the 2015 FMT study demonstrated marked reductions in LD emissions for all pollutants: emission factors for naphthalene were reduced the most, by 98%; benzene, toluene, ethylbenzene, and xylene (BTEX), by 94%; CO, NMHCs, and NOx, by 87%; and aldehydes by about 71%. Smaller reductions were observed for HD emission factors: naphthalene emissions were reduced by 95%, carbonyl emissions decreased by about 75%, BTEX by 60%, and NOx 58%.</p><p><p>The 2015 fleet-average emission factors were higher in the SMT for CO, NOx, and summer PM<sub>2.5</sub> than those in the FMT. The higher CO emissions in the SMT were possibly attributable to a larger fraction of motorcycles and LPG vehicles in the Hong Kong fleet. DVs in Hong Kong and the United States had similar emission factors for NOx. However, the non-diesel vehicles (NDVs), particularly LPG vehicles, had higher emission factors than those of gasoline cars, contributing to higher NOx emissions in the SMT. The higher PM<sub>2.5</sub> emission factors in the SMT were probably attributable to there being more double-deck buses in Hong Kong.</p><p><p>In both tunnels, PAHs were predominantly in the gas phase, with larger (four and more aromatic rings) PAHs mostly in the particulate phase. Formaldehyde, acetaldehyde, crotonaldehyde, and acetone were the most abundant carbonyl compounds in the SMT. In the FMT, the most abundant carbonyls were formaldehyde, acetone, acetaldehyde, and propionaldehyde. HD vehicles emitted about threefold more carbonyl compounds than LD vehicles did. In the SMT, the NMHC species were enriched with marker species for LPG (e.g., <i>n</i>-butane, isobutane, and propane) and gasoline fuel vapor (e.g., toluene, isopentane, and <i>m/p</i>-xylene), indicating evaporative losses. Source contributions to SMT PM<sub>2.5</sub> mass were diesel exhaust (51.5 ± 1.8%), gasoline exhaust (10.0 ± 0.8%), LPG exhaust (5.0 ± 0.5%), secondary sulfate (19.9 ± 1.0%), secondary nitrate (6.3 ± 0.9%), and road dust (7.3 ± 1.3%). In the FMT, total NMHC emissions were 14% and 8% higher in winter than in summer for LD and HD vehicles, respectively. Elemental carbon (EC) and organic carbon (OC) were the major constituents of tunnel PM<sub>2.5</sub>. De-icing salt contributions to PM<sub>2.5</sub> were observed in the FMT in winter.</p><p><p>Emission estimates by the EMFAC-HK agreed with SMT measurements for CO<sub>2</sub>; the modeled emission factors for CO, NOx, and NMHCs were 1.5, 1.6, and 2.2 times the measurements, respectively; and the modeled emission factor for PM<sub>2.5</sub> was 61% of the measured value in 2003. The EMFAC-HK estimates and SMT measurements for 2015 differed by less than 35%. The MOVES2014a model generally overestimated emissions of most of the pollutants measured in the FMT. No pollutants were significantly underestimated. The largest overestimation was observed for emissions measured during HD-rich driving conditions in winter.</p><p><strong>Conclusions: </strong>Significant reductions in SO<sub>2</sub> and PM<sub>2.5</sub> emissions between 2003 and 2015 were observed in the SMT, indicating the effectiveness of control measures on these two pollutants. The total NMHC emissions in the SMT were reduced by 44%, although isobutane and <i>n</i>-butane emissions increased because of the increase in the size of the LPG fleet. No significant reductions were observed for CO and NOx, results that differed from those for roadside ambient concentrations, emission inventory estimates, and EMFAC-HK estimates. In contrast, there was a steady decrease in emissions of most pollutants in the tunnels in the United States.</p>","PeriodicalId":74687,"journal":{"name":"Research report (Health Effects Institute)","volume":" 199","pages":"5-52"},"PeriodicalIF":0.0000,"publicationDate":"2019-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7282032/pdf/hei-2019-199.pdf","citationCount":"0","resultStr":"{\"title\":\"Real-World Vehicle Emissions Characterization for the Shing Mun Tunnel in Hong Kong and Fort McHenry Tunnel in the United States.\",\"authors\":\"Xiaoliang Wang, Andrey Khlystov, Kin-Fai Ho, Dave Campbell, Judith C Chow, Steven D Kohl, John G Watson, Shun-Cheng Frank Lee, Lung-Wen Antony Chen, Minggen Lu, Steven Sai Hang Ho\",\"doi\":\"\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p><strong>Introduction: </strong>Motor vehicle exhaust is an important source of air pollutants and greenhouse gases. Concerns over the health and climate effects of mobile-source emissions have prompted worldwide efforts to reduce vehicle emissions. Implementation of more stringent emission standards have driven advances in vehicle, engine, and exhaust after-treatment technologies as well as fuel formulations. On the other hand, vehicle numbers and travel distances have been increasing because of population and economic growth and changes in land use. These factors have resulted in changes to the amount and chemical composition of vehicle emissions.</p><p><p>Roadway tunnel studies are a practical way to characterize real-world emissions from the on-road vehicle fleet in an environment isolated from other combustion pollution sources. Measurements in the same tunnel over time allow evaluation of vehicle emission changes and the effectiveness of emission reduction measures. Tunnel studies estimate the impacts of vehicle emissions on air quality and traffic-related exposures, generate source profile inputs for receptor-oriented source apportionment models, provide data to evaluate emission models, and serve as a baseline for future comparisons.</p><p><p>The present study characterized motor vehicle emission factors and compositions in two roadway tunnels that were first studied over a decade ago. The specific aims were to (1) quantify current fleet air pollutant emission factors, (2) evaluate emission change over time, (3) establish source profiles for volatile organic compounds (VOCs) and particulate matter ≤2.5 μm in aerodynamic diameter (PM<sub>2.5</sub>), (4) estimate contributions of fleet components and non-tailpipe emissions to VOCs and PM<sub>2.5</sub>, and (5) evaluate the performance of the latest versions of mobile-source emission models (i.e., the EMission FACtors vehicle emission model used in Hong Kong [EMFAC-HK] and the MOtor Vehicle Emission Simulator used in the United States [MOVES]).</p><p><strong>Methods: </strong>Measurements were conducted in the Shing Mun Tunnel (SMT) in Hong Kong and the Fort McHenry Tunnel (FMT) in Baltimore, Maryland, in the United States, representing the different fleet compositions, emission controls, fuels, and near-road exposure levels found in Hong Kong and the United States. These tunnels have extensive databases acquired in 2003-2004 for the SMT and 1992 for the FMT. The SMT sampling was conducted during the period from 1/19/2015 to 3/31/2015, and the FMT sampling occurred during the periods from 2/8/2015 to 2/15/2015 (winter) and 7/31/2015 to 8/7/2015 (summer). Concentrations of criteria pollutants (e.g., carbon monoxide [CO], nitrogen oxides [NOx], and particulate matter [PM]) were measured in real time, and integrated samples of VOCs, carbonyls, polycyclic aromatic hydrocarbons (PAHs), and PM<sub>2.5</sub> were collected in canisters and sampling media for off-line analyses. Emission factors were calculated from the tunnel measurements and compared with previous studies to evaluate emission changes over time. Emission contributions by different vehicle types were assessed by source apportionment modeling or linear regression. Vehicle emissions were modeled by EMFAC-HK version 3.3 and MOVES version 2014a for the SMT and the FMT, respectively, and compared with measured values. The influences of vehicle fleet composition and environmental parameters (i.e., temperature and relative humidity) on emissions were evaluated.</p><p><strong>Results: </strong>In the SMT, emissions of PM<sub>2.5</sub>, sulfur dioxide (SO<sub>2</sub>), and total non-methane hydrocarbons (NMHCs) markedly decreased from 2003-2004 to 2015: SO<sub>2</sub> and PM<sub>2.5</sub> were reduced by ~80%, and total NMHCs was reduced by ~44%. Emission factors of ethene and propene, key tracers for diesel vehicle (DV) emissions, decreased by ~65%. These reductions demonstrate the effectiveness of control measures, such as the implementation of low-sulfur fuel regulations and the phasing out of older DVs. However, the emission factors of isobutane and <i>n</i>-butane, markers for liquefied petroleum gas (LPG), increased by 32% and 17% between 2003-2004 and 2015, respectively, because the number of LPG vehicles increased. Nitrogen dioxide (NO<sub>2</sub>) to NOx volume ratios increased between 2003-2004 and 2015, indicating an increased NO<sub>2</sub> fraction in primary exhaust emissions. Although geological mineral concentrations were similar between the 2003-2004 and 2015 studies, the contribution of geological materials to PM<sub>2.5</sub> increased from 2% in 2003-2004 to 5% in 2015, signifying the continuing importance of non-tailpipe PM emissions as tailpipe emissions decrease. Emissions of CO, ammonia (NH<sub>3</sub>), nitric oxide (NO), NO<sub>2</sub>, and NOx, as well as carbonyls and PAHs in the SMT did not show statistically significant (at <i>P</i> < 0.05 based on Student's <i>t</i>-test) decreases from 2003-2004 to 2015. The reason for this is not clear and requires further investigation.</p><p><p>A steady decrease in emissions of all measured pollutants during the past 23 years has been observed from tunnel studies in the United States, reflecting the effect of emission standards and new technologies that were introduced during this period. Emission reductions were more pronounced for the light-duty (LD) fleet than for the heavy-duty (HD) fleet. In comparison with the 1992 FMT study, the 2015 FMT study demonstrated marked reductions in LD emissions for all pollutants: emission factors for naphthalene were reduced the most, by 98%; benzene, toluene, ethylbenzene, and xylene (BTEX), by 94%; CO, NMHCs, and NOx, by 87%; and aldehydes by about 71%. Smaller reductions were observed for HD emission factors: naphthalene emissions were reduced by 95%, carbonyl emissions decreased by about 75%, BTEX by 60%, and NOx 58%.</p><p><p>The 2015 fleet-average emission factors were higher in the SMT for CO, NOx, and summer PM<sub>2.5</sub> than those in the FMT. The higher CO emissions in the SMT were possibly attributable to a larger fraction of motorcycles and LPG vehicles in the Hong Kong fleet. DVs in Hong Kong and the United States had similar emission factors for NOx. However, the non-diesel vehicles (NDVs), particularly LPG vehicles, had higher emission factors than those of gasoline cars, contributing to higher NOx emissions in the SMT. The higher PM<sub>2.5</sub> emission factors in the SMT were probably attributable to there being more double-deck buses in Hong Kong.</p><p><p>In both tunnels, PAHs were predominantly in the gas phase, with larger (four and more aromatic rings) PAHs mostly in the particulate phase. Formaldehyde, acetaldehyde, crotonaldehyde, and acetone were the most abundant carbonyl compounds in the SMT. In the FMT, the most abundant carbonyls were formaldehyde, acetone, acetaldehyde, and propionaldehyde. HD vehicles emitted about threefold more carbonyl compounds than LD vehicles did. In the SMT, the NMHC species were enriched with marker species for LPG (e.g., <i>n</i>-butane, isobutane, and propane) and gasoline fuel vapor (e.g., toluene, isopentane, and <i>m/p</i>-xylene), indicating evaporative losses. Source contributions to SMT PM<sub>2.5</sub> mass were diesel exhaust (51.5 ± 1.8%), gasoline exhaust (10.0 ± 0.8%), LPG exhaust (5.0 ± 0.5%), secondary sulfate (19.9 ± 1.0%), secondary nitrate (6.3 ± 0.9%), and road dust (7.3 ± 1.3%). In the FMT, total NMHC emissions were 14% and 8% higher in winter than in summer for LD and HD vehicles, respectively. Elemental carbon (EC) and organic carbon (OC) were the major constituents of tunnel PM<sub>2.5</sub>. De-icing salt contributions to PM<sub>2.5</sub> were observed in the FMT in winter.</p><p><p>Emission estimates by the EMFAC-HK agreed with SMT measurements for CO<sub>2</sub>; the modeled emission factors for CO, NOx, and NMHCs were 1.5, 1.6, and 2.2 times the measurements, respectively; and the modeled emission factor for PM<sub>2.5</sub> was 61% of the measured value in 2003. The EMFAC-HK estimates and SMT measurements for 2015 differed by less than 35%. The MOVES2014a model generally overestimated emissions of most of the pollutants measured in the FMT. No pollutants were significantly underestimated. The largest overestimation was observed for emissions measured during HD-rich driving conditions in winter.</p><p><strong>Conclusions: </strong>Significant reductions in SO<sub>2</sub> and PM<sub>2.5</sub> emissions between 2003 and 2015 were observed in the SMT, indicating the effectiveness of control measures on these two pollutants. The total NMHC emissions in the SMT were reduced by 44%, although isobutane and <i>n</i>-butane emissions increased because of the increase in the size of the LPG fleet. No significant reductions were observed for CO and NOx, results that differed from those for roadside ambient concentrations, emission inventory estimates, and EMFAC-HK estimates. In contrast, there was a steady decrease in emissions of most pollutants in the tunnels in the United States.</p>\",\"PeriodicalId\":74687,\"journal\":{\"name\":\"Research report (Health Effects Institute)\",\"volume\":\" 199\",\"pages\":\"5-52\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2019-03-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7282032/pdf/hei-2019-199.pdf\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Research report (Health Effects Institute)\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Research report (Health Effects Institute)","FirstCategoryId":"1085","ListUrlMain":"","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0

摘要

从美国的隧道研究中可以观察到,在过去 23 年中,所有测量到的污染物排放量都在稳步下降,这反映了在此期间引入的排放标准和新技术的效果。与重型车(HD)相比,轻型车(LD)的排放减少更为明显。与 1992 年的 FMT 研究相比,2015 年的 FMT 研究表明,轻型车所有污染物的排放量均显著减少:萘的排放系数减少最多,达 98%;苯、甲苯、乙苯和二甲苯 (BTEX) 减少 94%;一氧化碳、非甲烷总烃和氮氧化物减少 87%;醛类减少约 71%。HD排放因子的减少幅度较小:萘排放减少了95%,羰基排放减少了约75%,BTEX减少了60%,氮氧化物减少了58%。2015年,SMT的一氧化碳、氮氧化物和夏季PM2.5的车队平均排放因子高于FMT。在SMT,一氧化碳排放量较高,这可能是由于香港车队中摩托车和液化石油气车辆的比例较大。香港和美国的柴油车的氮氧化物排放系数相似。不過,非柴油車輛,特別是石油氣車輛的排放因子較汽油車輛為 高,導致深圳灣口岸的氮氧化物排放量較高。在两条隧道中,多环芳烃主要存在于气相中,而较大的多环芳烃(四环及更多芳香环)则主要存在于颗粒相中。甲醛、乙醛、巴豆醛和丙酮是深圳地铁中含量最高的羰基化合物。在 FMT 中,最多的羰基化合物是甲醛、丙酮、乙醛和丙醛。高排放车辆排放的羰基化合物是低排放车辆的三倍。在 SMT 中,NMHC 物种富含液化石油气(如正丁烷、异丁烷和丙烷)和汽油燃料蒸气(如甲苯、异戊烷和间/对二甲苯)的标记物,表明蒸发损失。SMT PM2.5 质量的来源贡献是柴油废气(51.5 ± 1.8%)、汽油废气(10.0 ± 0.8%)、液化石油气废气(5.0 ± 0.5%)、二次硫酸盐(19.9 ± 1.0%)、二次硝酸盐(6.3 ± 0.9%)和道路扬尘(7.3 ± 1.3%)。在 FMT 中,LD 和 HD 车辆在冬季的非甲烷总排放量分别比夏季高 14% 和 8%。元素碳(EC)和有机碳(OC)是隧道 PM2.5 的主要成分。香港环境监测和分析中心对二氧化碳的排放估算与深圳地铁的测量结果一致;一氧化碳、氮氧化物和非甲烷总烃的模拟排放系数分别是测量值的1.5倍、1.6倍和2.2倍;PM2.5的模拟排放系数是2003年测量值的61%。2015 年的 EMFAC-HK 估计值与 SMT 测量值相差不到 35%。MOVES2014a 模型普遍高估了大多数在 FMT 中测量到的污染物的排放量。没有污染物被明显低估。高估幅度最大的是冬季高密度驾驶条件下测得的排放量:结论:从 2003 年到 2015 年,SMT 观察到二氧化硫和 PM2.5 的排放量显著减少,这表明针对这两种污染物的控制措施非常有效。虽然异丁烷和正丁烷的排放量因液化石油气车队规模的扩大而增加,但 SMT 的非甲烷总排放量减少了 44%。一氧化碳(CO)和氮氧化物(NOx)的排放量没有明显减少,这与路边环境浓度、排放清单估算和香港环境管理与监测中心(EMFAC-HK)估算的结果不同。相比之下,美国隧道中大多数污染物的排放量都在稳步下降。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Real-World Vehicle Emissions Characterization for the Shing Mun Tunnel in Hong Kong and Fort McHenry Tunnel in the United States.

Real-World Vehicle Emissions Characterization for the Shing Mun Tunnel in Hong Kong and Fort McHenry Tunnel in the United States.

Real-World Vehicle Emissions Characterization for the Shing Mun Tunnel in Hong Kong and Fort McHenry Tunnel in the United States.

Introduction: Motor vehicle exhaust is an important source of air pollutants and greenhouse gases. Concerns over the health and climate effects of mobile-source emissions have prompted worldwide efforts to reduce vehicle emissions. Implementation of more stringent emission standards have driven advances in vehicle, engine, and exhaust after-treatment technologies as well as fuel formulations. On the other hand, vehicle numbers and travel distances have been increasing because of population and economic growth and changes in land use. These factors have resulted in changes to the amount and chemical composition of vehicle emissions.

Roadway tunnel studies are a practical way to characterize real-world emissions from the on-road vehicle fleet in an environment isolated from other combustion pollution sources. Measurements in the same tunnel over time allow evaluation of vehicle emission changes and the effectiveness of emission reduction measures. Tunnel studies estimate the impacts of vehicle emissions on air quality and traffic-related exposures, generate source profile inputs for receptor-oriented source apportionment models, provide data to evaluate emission models, and serve as a baseline for future comparisons.

The present study characterized motor vehicle emission factors and compositions in two roadway tunnels that were first studied over a decade ago. The specific aims were to (1) quantify current fleet air pollutant emission factors, (2) evaluate emission change over time, (3) establish source profiles for volatile organic compounds (VOCs) and particulate matter ≤2.5 μm in aerodynamic diameter (PM2.5), (4) estimate contributions of fleet components and non-tailpipe emissions to VOCs and PM2.5, and (5) evaluate the performance of the latest versions of mobile-source emission models (i.e., the EMission FACtors vehicle emission model used in Hong Kong [EMFAC-HK] and the MOtor Vehicle Emission Simulator used in the United States [MOVES]).

Methods: Measurements were conducted in the Shing Mun Tunnel (SMT) in Hong Kong and the Fort McHenry Tunnel (FMT) in Baltimore, Maryland, in the United States, representing the different fleet compositions, emission controls, fuels, and near-road exposure levels found in Hong Kong and the United States. These tunnels have extensive databases acquired in 2003-2004 for the SMT and 1992 for the FMT. The SMT sampling was conducted during the period from 1/19/2015 to 3/31/2015, and the FMT sampling occurred during the periods from 2/8/2015 to 2/15/2015 (winter) and 7/31/2015 to 8/7/2015 (summer). Concentrations of criteria pollutants (e.g., carbon monoxide [CO], nitrogen oxides [NOx], and particulate matter [PM]) were measured in real time, and integrated samples of VOCs, carbonyls, polycyclic aromatic hydrocarbons (PAHs), and PM2.5 were collected in canisters and sampling media for off-line analyses. Emission factors were calculated from the tunnel measurements and compared with previous studies to evaluate emission changes over time. Emission contributions by different vehicle types were assessed by source apportionment modeling or linear regression. Vehicle emissions were modeled by EMFAC-HK version 3.3 and MOVES version 2014a for the SMT and the FMT, respectively, and compared with measured values. The influences of vehicle fleet composition and environmental parameters (i.e., temperature and relative humidity) on emissions were evaluated.

Results: In the SMT, emissions of PM2.5, sulfur dioxide (SO2), and total non-methane hydrocarbons (NMHCs) markedly decreased from 2003-2004 to 2015: SO2 and PM2.5 were reduced by ~80%, and total NMHCs was reduced by ~44%. Emission factors of ethene and propene, key tracers for diesel vehicle (DV) emissions, decreased by ~65%. These reductions demonstrate the effectiveness of control measures, such as the implementation of low-sulfur fuel regulations and the phasing out of older DVs. However, the emission factors of isobutane and n-butane, markers for liquefied petroleum gas (LPG), increased by 32% and 17% between 2003-2004 and 2015, respectively, because the number of LPG vehicles increased. Nitrogen dioxide (NO2) to NOx volume ratios increased between 2003-2004 and 2015, indicating an increased NO2 fraction in primary exhaust emissions. Although geological mineral concentrations were similar between the 2003-2004 and 2015 studies, the contribution of geological materials to PM2.5 increased from 2% in 2003-2004 to 5% in 2015, signifying the continuing importance of non-tailpipe PM emissions as tailpipe emissions decrease. Emissions of CO, ammonia (NH3), nitric oxide (NO), NO2, and NOx, as well as carbonyls and PAHs in the SMT did not show statistically significant (at P < 0.05 based on Student's t-test) decreases from 2003-2004 to 2015. The reason for this is not clear and requires further investigation.

A steady decrease in emissions of all measured pollutants during the past 23 years has been observed from tunnel studies in the United States, reflecting the effect of emission standards and new technologies that were introduced during this period. Emission reductions were more pronounced for the light-duty (LD) fleet than for the heavy-duty (HD) fleet. In comparison with the 1992 FMT study, the 2015 FMT study demonstrated marked reductions in LD emissions for all pollutants: emission factors for naphthalene were reduced the most, by 98%; benzene, toluene, ethylbenzene, and xylene (BTEX), by 94%; CO, NMHCs, and NOx, by 87%; and aldehydes by about 71%. Smaller reductions were observed for HD emission factors: naphthalene emissions were reduced by 95%, carbonyl emissions decreased by about 75%, BTEX by 60%, and NOx 58%.

The 2015 fleet-average emission factors were higher in the SMT for CO, NOx, and summer PM2.5 than those in the FMT. The higher CO emissions in the SMT were possibly attributable to a larger fraction of motorcycles and LPG vehicles in the Hong Kong fleet. DVs in Hong Kong and the United States had similar emission factors for NOx. However, the non-diesel vehicles (NDVs), particularly LPG vehicles, had higher emission factors than those of gasoline cars, contributing to higher NOx emissions in the SMT. The higher PM2.5 emission factors in the SMT were probably attributable to there being more double-deck buses in Hong Kong.

In both tunnels, PAHs were predominantly in the gas phase, with larger (four and more aromatic rings) PAHs mostly in the particulate phase. Formaldehyde, acetaldehyde, crotonaldehyde, and acetone were the most abundant carbonyl compounds in the SMT. In the FMT, the most abundant carbonyls were formaldehyde, acetone, acetaldehyde, and propionaldehyde. HD vehicles emitted about threefold more carbonyl compounds than LD vehicles did. In the SMT, the NMHC species were enriched with marker species for LPG (e.g., n-butane, isobutane, and propane) and gasoline fuel vapor (e.g., toluene, isopentane, and m/p-xylene), indicating evaporative losses. Source contributions to SMT PM2.5 mass were diesel exhaust (51.5 ± 1.8%), gasoline exhaust (10.0 ± 0.8%), LPG exhaust (5.0 ± 0.5%), secondary sulfate (19.9 ± 1.0%), secondary nitrate (6.3 ± 0.9%), and road dust (7.3 ± 1.3%). In the FMT, total NMHC emissions were 14% and 8% higher in winter than in summer for LD and HD vehicles, respectively. Elemental carbon (EC) and organic carbon (OC) were the major constituents of tunnel PM2.5. De-icing salt contributions to PM2.5 were observed in the FMT in winter.

Emission estimates by the EMFAC-HK agreed with SMT measurements for CO2; the modeled emission factors for CO, NOx, and NMHCs were 1.5, 1.6, and 2.2 times the measurements, respectively; and the modeled emission factor for PM2.5 was 61% of the measured value in 2003. The EMFAC-HK estimates and SMT measurements for 2015 differed by less than 35%. The MOVES2014a model generally overestimated emissions of most of the pollutants measured in the FMT. No pollutants were significantly underestimated. The largest overestimation was observed for emissions measured during HD-rich driving conditions in winter.

Conclusions: Significant reductions in SO2 and PM2.5 emissions between 2003 and 2015 were observed in the SMT, indicating the effectiveness of control measures on these two pollutants. The total NMHC emissions in the SMT were reduced by 44%, although isobutane and n-butane emissions increased because of the increase in the size of the LPG fleet. No significant reductions were observed for CO and NOx, results that differed from those for roadside ambient concentrations, emission inventory estimates, and EMFAC-HK estimates. In contrast, there was a steady decrease in emissions of most pollutants in the tunnels in the United States.

求助全文
通过发布文献求助,成功后即可免费获取论文全文。 去求助
来源期刊
自引率
0.00%
发文量
0
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
确定
请完成安全验证×
copy
已复制链接
快去分享给好友吧!
我知道了
右上角分享
点击右上角分享
0
联系我们:info@booksci.cn Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。 Copyright © 2023 布克学术 All rights reserved.
京ICP备2023020795号-1
ghs 京公网安备 11010802042870号
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术官方微信