Ambient Fine Particle Concentrations Research Articles

Estimating PM2.5 concentrations in a central region of China using a three-stage model

ABSTRACT Owing to uneven environmental monitoring site distribution, there are significant spatial data gaps for concentrations of ambient fine particles with diameters ≤ 2.5 µm (PM2.5) obtained using traditional monitoring methods. Satellite products are an alternative data source for locations where monitoring sites are unavailable. The Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) product has been widely used in PM2.5 assessment for years; however, it has obvious data gaps in winter. Here, the Visible Infrared Imaging Radiometer Suite (VIIRS) AOD was applied to supplement MODIS AOD data to obtain a fused AOD dataset. A three-stage model consisting of a corrected AOD model, mixed effects model, and geographically weighted regression model was developed and used with meteorological and vegetation factors to estimate PM2.5. Results showed overall model fitting by cross-validation (CV) with an R2 of 0.92, mean absolute error of 5.72 µg/m3, and root mean square error of 7.15 µg/m3. The combination of MODIS AOD and VIIRS AOD was a suitable method for enhancing AOD coverage. The CV R2 value of the three-stage model (0.92) was higher than that of the two-stage model (0.9). Hence, the three-stage model could achieve a better fit in estimating PM2.5 on a regional scale.

Road traffic-induced particle matter dispersion in a calm wind environment at the main roundabout in Douala, central Africa


 
 
 
 Introduction: Road traffic emissions are among the most significant sources of pollution in Douala, Cameroon's economic town, alongside industrial operations. The morning and the evening are two times of the day when traffic is heavier and the winds are also at their calmest. The majority of the non-exhaust Particulate Matters (PMs) produced by autos is re-suspended road contaminants. The purpose of this research is to estimate fine particle dispersion in conditions of calm winds.
 Materials and methods: In one of Douala's roundabouts, the Gaussian Plume model is employed to calculate the PM concentration under calm winds conditions. Different vehicle classes (HDV: Heavy Duty Vehicles, LDV: Light Duty Vehicles, PC: Passenger Cars) are used to figure out the amount of PMs they produce. Measurements of ambient fine particle concentrations are made with the OC-300 laser dust particle detector.
 Results: The results made it possible to compare actual measurements of PM2.5, PM10 (300±150 μg/m3 and 650±150 μg/m3, respectively) with simulated values (PM2.5, PM10: 310 μg/m3 and 631 μg/m3, respectively). The difference between in-situ and computed values can range from 10 to 132 μg/m3. From 6 to 10 AM, the population's exposure to PM pollution is more severe. It has also been demonstrated that there is a significant association between traffic flow and PM Concentration during the dry season (R2=0.921). With increased traffic flow intensity, particle concentration levels rise.
 Conclusion: The concentration threshold stays above the World Health Organization (WHO) limits regardless of the approach. Furthermore, this paper provides important information about Douala's pollution levels.
 
 
 

Neurodegenerative hospital admissions and long-term exposure to ambient fine particle air pollution

Long-term exposure to ambient fine particle (PM2.5) concentrations has been associated with an increased rate or risk of neurodegenerative conditions, but individual PM sources have not been previously examined in relation to neurodegenerative diseases. Using the Statewide Planning and Research Cooperative System database, we studied 63,287 hospital admissions with a primary diagnosis of either Alzheimer's disease, dementia, or Parkinson's disease for New York State residents living within 15 miles from six PM2.5 monitoring sites. In addition to PM2.5 concentrations, we studied seven specific PM2.5 sources: secondary sulfate, secondary nitrate, biomass burning, diesel, spark-ignition emissions, pyrolyzed organic rich, and road dust. We estimated the rate of neurodegenerative hospital admissions associated with increased concentration of PM2.5 and individual PM2.5 sources average concentrations in the previous 0-29, 0-179, and 0-364days. Increases in ambient PM2.5 concentrations were not consistently associated with increased hospital admissions rates. Increased source-specific PM2.5 concentrations were associated with both increased (e.g., secondary sulfates and diesel emissions) and decreased rates (e.g., secondary nitrate and spark-ignition vehicular emissions) of neurodegenerative admissions. We did not observe clear associations between overall ambient PM2.5 concentrations or source-apportioned ambient PM2.5 contributions and rates of neurologic disease hospitalizations.

Hypertension Editors' Picks: Air Pollution.

Hypertension Editors' Picks: Air Pollution.

Wintertime Wood Smoke, Traffic Particle Pollution, and Preeclampsia.

Previous studies have reported associations between ambient fine particle concentrations and preeclampsia; however, the impact of particulate pollution on early- and late-onset preeclampsia is understudied. Furthermore, few studies have examined the association between source-specific particles such as markers of traffic pollution or wood combustion on adverse pregnancy outcomes. Electronic medical records and birth certificate data were linked with land-use regression models in Monroe County, New York for 2009 to 2013 to predict monthly pollutant concentrations for each pregnancy until the date of clinical diagnosis during winter (November-April) for 16 116 births. Up to 30% of ambient wintertime fine particle concentrations in Monroe County, New York is from wood combustion. Multivariable logistic regression was used to separately estimate the odds of preeclampsia (all, early-, and late-onset) associated with each interquartile range increase in fine particles, traffic pollution, and woodsmoke concentrations during each gestational month, adjusting for maternal characteristics, birth hospital, temperature, and relative humidity. Each 3.64 µg/m3 increase in fine particle concentration was associated with an increased odds of early-onset preeclampsia during the first (odds ratio, 1.35 [95% CI, 1.08-1.68]), second (odds ratio, 1.51 [95% CI, 1.23-1.86]), and third (odds ratio, 1.25 [95% CI, 1.06-1.46]) gestational months. Increases in traffic pollution and woodsmoke during the first gestational month were also associated with increased odds of early-onset preeclampsia. Increased odds of late-onset preeclampsia were not observed. Our findings suggest that exposure to wintertime particulate pollution may have the greatest effect on maternal cardiovascular health during early pregnancy.

Changes in the relationship between ambient fine particle concentrations and childhood lung function over 5 years

Exposure to ambient fine particles, particulate matter with an aerodynamic diameter of ≤2.5 μm (PM2.5), is a public health concern. Concentrations of ambient PM2.5 have changed temporally in the past 10 years after a series of action policies for improving air quality were implemented in Taiwan. In this study, temporal changes in the relationship between PM2.5 and lung function among children were investigated. A nationwide respiratory health survey was conducted among Taiwanese elementary and middle school students in 2011 and again in 2016-2017. A questionnaire was administered to students, for whom forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1) were measured using spirometry. During the study period, monthly concentrations of ambient PM2.5 were obtained from the monitoring stations of the Environmental Protection Administration. Lung function measurements were compared with ambient PM2.5 exposure using mixed-effects models. In the 2011 survey (mean PM2.5: 40.6 μg/m3), exposure to PM2.5 in the preceding 1-2 months was associated with a 2.2% decrease (95% confidence interval [CI]: -4.1%, -0.3%) in FVC and a 2.3% decrease (95% CI: -4.0%, -0.5%) in FEV1. By contrast, a significant relationship between PM2.5 concentrations and lung function was not observed in the 2016-2017 survey (mean PM2.5: 30.0 μg/m3). As improvement in air quality over time, the negative relationship between PM2.5 and childhood lung function tend to be not significant.

Long-term exposure to ambient fine particulate matter and liver enzymes in adults: a cross-sectional study in Taiwan

ObjectivesAnimal experiments indicate that exposure to particulate matter (PM) can induce hepatotoxic effects but epidemiological evidence is scarce. We aimed to investigate the associations between long-term exposure to PM air...

Influence of Outdoor Source on The Variations of Indoor PM2.5 Concentration and Its Morphological Properties in Roadside School Environment

Particles with aerodynamic diameters equal or less than 2.5 µm, which are known as fine particles (PM2.5), are major air pollutants that could seriously impact ambient and indoor air quality. The air quality in school environments less than 500 m away from the roadside is potentially affected by vehicles through exhaust emissions. Thus, the concentrations of ambient and indoor fine particles (PM2.5) were measured using a portable outdoor beta-attenuation monitor and an optical indoor direct reading monitor in two naturally ventilated school environments for 8 h during the teaching and learning sessions. In addition, meteorological parameters such as temperature, relative humidity and wind speed were measured under ambient and indoor conditions. PM2.5 samples were also collected and morphologically characterised. Pearson’s correlation was applied to identify the relationship between the ambient and indoor conditions of PM2.5, temperature, relative humidity and wind speed. Results showed that the indoor and outdoor PM2.5 in selected schools were varied. The concentration of indoor PM2.5 was higher than that of outdoor PM2.5 in both schools. Pearson’s correlation showed a significant correlation between indoor and outdoor PM2.5 in schools A (p = 0.006, r = 0.54) and B (p = 0.001, r = 0.74). In addition, ambient temperature, relative humidity and wind speed are the important factors that affect the outdoor concentrations of PM2.5.

Triggering of Neurodegenerative Hospital Admissions and Emergency Room Visits by Fine Particle Concentrations in Six Urban Centers in New York State: The New York State Accountability Study

Emerging evidence has linked exposure to ambient fine particle (PM2.5) concentrations with an increased incidence of neurodegenerative conditions such as dementia, Alzheimer’s disease (AD), and Parkinson’s disease (PD). Previous studies have not examined the association between ambient PM2.5 concentrations and exacerbations of symptoms, which would further add to the public health burden of these chronic neurodegenerative conditions. Using the Statewide Planning and Research Cooperative System (SPARCS) database, we retrieved all hospital admissions (inpatient) and emergency room visits (outpatient) with a primary diagnosis of one of three neurodegenerative disease subtypes for NYS residents living within 15 miles from PM2.5 monitoring sites in Buffalo, Rochester, Albany, Queens, Bronx, and Manhattan from 2005-2016. Using quasi-Poisson regression models adjusting for temperature, relative humidity, and secular trends in hospitalization rates, we examined the association between daily inpatient and outpatient neurodegenerative hospitalizations and ambient PM2.5 concentrations estimated for short-term and long-term time windows: concurrent exposure as well as lagged by 14, 30, 180, and 365 days. A total of 63,287 inpatient admissions and 14,288 outpatient visits for the three neurodegenerative conditions occurred during the study period. Interquartile range (IQR) increases in PM2.5 concentration were not associated with increased rates of inpatient AD and dementia hospitalizations. However, increased rates of PD hospital admissions were associated with increased PM2.5 concentrations in the previous 14 days (rate ratio (RR) = 1.04; 95% confidence interval (CI) = 1.00-1.09), and 30 days (RR=1.06; 95% CI=1.00-1.12). For outpatient visits, an increased rate of AD was associated with increased PM2.5 in the past 365 days (RR=1.77; 95% CI = 1.03-3.03). Thus, ambient PM2.5 exposure may be associated with exacerbations of symptoms among patients with neurodegenerative disease.

Ambient wintertime particulate air pollution and hypertensive disorders of pregnancy in Monroe County, New York

Previous studies have reported associations between ambient fine particle (PM2.5) concentrations and hypertensive disorders of pregnancy (HDP). However, none have examined whether ultrafine particles (UFP; < 100 nm), accumulation mode particles (AMP; 100-500 nm), markers of traffic pollution (black carbon; BC), or wood burning (Delta-C; (30% of ambient wintertime PM2.5 in Monroe County, NY is from wood burning)) are associated with an increased odds of HDP. We estimated the odds of HDP associated with increased concentrations of PM2.5, UFP, AMP, BC, and Delta-C in each gestational month during winter months. Electronic medical records and birth certificate data were linked with land-use regression models in Monroe County, New York in 2009-2013 to predict monthly pollutant concentrations during winter (November-April) based on maternal residential address for 16,637 births. Using multivariable logistic regression, we estimated the odds of HDP associated with each interquartile range (IQR) increase in PM2.5, UFP, AMP, BC, and Delta-C concentrations during each gestational month, adjusting for maternal characteristics, birth hospital, temperature, and relative humidity. Each 0.52 µg/m3 increase in Delta-C concentration during the 7th gestational month was associated with an increased odds of HDP (odds ratio (OR) = 1.21; 95% confidence interval (CI) = 1.01, 1.45), with a similar sized estimate in month 8 (OR = 1.18; 95%CI = 0.98, 1.43). Non-statistically significant increased odds of HDP associated with IQR increases in BC concentrations during months 3 (OR = 1.12; 95%CI = 0.98, 1.28) and 7 (OR = 1.12; 95%CI = 0.96, 1.29) were observed. Increased odds of HDP were not observed for PM2.5, UFP, or AMP. Our findings suggest that maternal exposure to wood smoke in Monroe County during winter is associated with an increased odds of HDP during late gestation. Additional studies are needed to evaluate the effect of wood smoke on HDP and to explore effects on other pregnancy outcomes.

Using a Mobile Measurement to Characterize Number, Surface Area, and Mass Concentrations of Ambient Fine Particles with Spatial Variability during and after a PM Episode

Fine particles play a key role in regional air quality deterioration. Commonly used central-site monitoring data, which offer rough determinations of spatial particulate matter (PM) distributions, is insufficient to estimate potential local emissions or population exposure levels. This study characterizes the spatial variability of fine particles in suburban and rural regions during and after a winter episode of elevated PM (PM episode). Commercial instruments of high time resolution in a mobile laboratory platform were deployed to measure the distribution, number, surface area, and mass concentrations of fine particles. Spatial variations of those particle properties were mainly affected by regional feature, PM episode, local primary source and wind speed. Particle concentrations and size distributions were found to differ considerably during and after PM episode. The PM episode was found to exhibit a lower degree of spatial concentration contrast with respect to particle number, surface area and mass, where similar particle size patterns were distributed across all study regions with decreased particle number under nucleation and Aitken modes and increased number under the accumulation mode. The mobile measurement may supplement information on spatial particle distributions for estimating levels of population exposure and for characterizing detailed physical properties of short-term, high-exposed scenarios.

Impact of wood combustion for secondary heating and recreational purposes on particulate air pollution in a suburb in Finland.

Little information is available on the concentrations of ambient fine particles (PM2.5) in residential areas where wood combustion is common for recreational purposes and secondary heating. Further, the validity of central site measurements of PM2.5 as a measure of exposure is unclear. Therefore, outdoor PM2.5 samples were repeatedly collected at a central site and home outdoor locations from a panel of 29 residents in a suburb in Kuopio, Finland. Source apportionment results from the central site were used to estimate the contributions from local sources, including wood combustion, to PM2.5 and absorption coefficient (ABS) at home outdoor locations. Correlations between the central and home outdoor concentrations of PM2.5, ABS, and their local components were analyzed for each home. At the central site, the average PM2.5 was 6.0 μg m(-)(3) during the heating season, and the contribution from wood combustion (16%) was higher than the contribution from exhaust emissions (12%). Central site measurements predicted poorly daily variation in PM2.5 from local sources. In conclusion, wood combustion significantly affects air quality also in areas where it is not the primary heating source. In epidemiological panel studies, central site measurements may not sufficiently capture daily variation in exposure to PM2.5 from local wood combustion.

Evaluation of the impact of low emission zone and heavy traffic ban in Munich (Germany) on the reduction of PM₁₀ in ambient air.

Concentrations of ambient fine particles (PM10: particles with an aerodynamic diameter ≤ 10 µm) are still exceeding current air quality standards in many European cities. In Munich (Germany), low emission zone and transit bans for heavy-duty vehicles were introduced in 2008 aiming at reduction of traffic emissions contribution to PM10. The effects of those measures on PM10 mass concentrations in Munich were investigated with a semiparametric regression model for modeling PM10 levels adjusted for time, background pollution, public holidays and wind direction. The reduction of PM10 concentration after the introduction of the measures was larger at a traffic monitoring site (13.0 %, 19.6 % in summer, and 6.8 % in winter) and smaller in urban background (4.5 %, 5.7 % in summer, and 3.2 % in winter). The effect was most pronounced on Fridays and on the weekends in summer.

Ambient fine particulate air pollution triggers ST-elevation myocardial infarction, but not non-ST elevation myocardial infarction: a case-crossover study

BackgroundWe and others have shown that increases in particulate air pollutant (PM) concentrations in the previous hours and days have been associated with increased risks of myocardial infarction, but little is known about the relationships between air pollution and specific subsets of myocardial infarction, such as ST-elevation myocardial infarction (STEMI) and non ST-elevation myocardial infarction (NSTEMI).MethodsUsing data from acute coronary syndrome patients with STEMI (n = 338) and NSTEMI (n = 339) and case-crossover methods, we estimated the risk of STEMI and NSTEMI associated with increased ambient fine particle (<2.5 um) concentrations, ultrafine particle (10-100 nm) number concentrations, and accumulation mode particle (100-500 nm) number concentrations in the previous few hours and days.ResultsWe found a significant 18% increase in the risk of STEMI associated with each 7.1 μg/m3 increase in PM2.5 concentration in the previous hour prior to acute coronary syndrome onset, with smaller, non-significantly increased risks associated with increased fine particle concentrations in the previous 3, 12, and 24 hours. We found no pattern with NSTEMI. Estimates of the risk of STEMI associated with interquartile range increases in ultrafine particle and accumulation mode particle number concentrations in the previous 1 to 96 hours were all greater than 1.0, but not statistically significant. Patients with pre-existing hypertension had a significantly greater risk of STEMI associated with increased fine particle concentration in the previous hour than patients without hypertension.ConclusionsIncreased fine particle concentrations in the hour prior to acute coronary syndrome onset were associated with an increased risk of STEMI, but not NSTEMI. Patients with pre-existing hypertension and other cardiovascular disease appeared particularly susceptible. Further investigation into mechanisms by which PM can preferentially trigger STEMI over NSTEMI within this rapid time scale is needed.

Characteristics and Seasonal Variations in Mass and Multi-element Concentrations of Ambient Fine and Coarse Particles

Characteristics and Seasonal Variations in Mass and Multi-element Concentrations of Ambient Fine and Coarse Particles

OBESITY AND METABOLIC SYNDROME: RISK FACTORS FOR AIR POLLUTION RELATED ASTHMA HOSPITAL ADMISSIONS

Background and Aims: Obesity has been shown to be associated with the presence of asthma in children and, to a lesser extent, adults. Additionally, acute exposure to elevated ambient air pollution has been demonstrated to increase the risk of respiratory hospital admission. However, the effect modification of obesity and metabolic syndrome on the association between air pollution and asthma hospital admissions has yet to be determined. Methods: Data for unscheduled hospital admissions in New York City with a primary diagnosis of asthma was obtained for the years 2003-2006. A poisson generalized linear model was used to determine the association of a distributed lag model of ambient air pollution exposure with asthma hospital admissions for children (under 18), adults (18-64) and older adults (over 65). Additional analyses were conducted for children with a secondary diagnosis of obesity and adults with multiple secondary diagnoses corresponding with metabolic syndrome (i.e. hypertension, diabetes, hyperlipidemia, and obesity). Results: After controlling for meteorological variables, temporal trends, and other possible confounders, short-term changes in ambient fine particle, nitrogen dioxide, and ozone concentrations were significantly associated with an increased risk of asthma hospital admissions in all age groups. A significant increase in risk of asthma hospitalization due to elevated pollutant concentrations was also observed in children with a secondary diagnosis of obesity, as compared to non-obese children. Also, a significant increase in risk of hospitalization was observed in adults and older adults with at least three of the secondary diagnoses that constitute metabolic syndrome as compared those individuals without metabolic syndrome. Conclusions: Obesity in children and metabolic syndrome in adults are significant risk factors for air pollution related asthma hospital admissions. The identification of this susceptible subpopulation indicates an ongoing public health risk due to the increasing prevalence rates of both child obesity and metabolic syndrome in adults.

Spatial modeling of residential woodsmoke across a non-urban upstate New York region

Residential wood combustion is an important contributor to heating-season ambient fine particle concentrations in many regions of North America. We applied a measurement and modeling approach to evaluate the effect of wood combustion on local and regional air quality in a non-urban setting with complex topography—the Adirondacks region of New York State. Spatially resolved topographic, census, property assessment, and emissions survey data were used to model spatial variability of woodsmoke fine particulate matter (PM2.5) emissions across the region. This spatial emissions model was then used to locate fixed-site monitors and to design a mobile-monitoring campaign. Measurements using a dual-wavelength AethalometerTM enabled the discrimination of woodsmoke from other combustion sources. By comparing these Aethalometer measurements with nephelometer measurements of PM2.5 we determined that the majority of the PM2.5 measured in the Adirondacks during calm, cold winter nights came from wood combustion. We used the measurements of spatial variability in woodsmoke PM2.5 concentrations, the spatial emissions estimates, and additional geographic covariates to develop a spatial model of woodsmoke PM2.5. Considering those living in areas in the upper tertile of modeled woodsmoke concentrations as “exposed,” the model estimated that about 20% (~130,000 people) of the population in the study area were exposed to elevated woodsmoke. Further, the model demonstrates that U.S. census information can be combined with additional survey and property assessment data to provide a broadly applicable estimate of woodsmoke spatial patterns and population exposure. This approach is a promising method for screening potential woodsmoke problems, including those areas with complex terrains.

Laboratory Measurements of the Heterogeneous Oxidation of Condensed-Phase Organic Molecular Makers for Motor Vehicle Exhaust

Triterpanoid hopanes and steranes are petroleum biomarkers used to apportion fine particulate matter to motor vehicle emissions. To investigate the chemical stability of these compounds, aerosolized motor oil was exposed to the hydroxyl radical (OH) in a smog chamber and the reaction rate constants of hopanes, steranes, and n-alkanes were measured. The experiments were conducted across a range of atmospheric conditions including low and high relative humidity (RH) and with mixtures of lubricating oil and secondary organic aerosol. Hopanes and steranes were found to react at atmospherically significant rates across the entire range of experimental conditions; they are estimated to have lifetimes on the order of several days at average summertime OH levels. The one experimental parameter that strongly influenced the effective rate constants was RH; oxidization of hopanes and steranes was about a factor of 4 slower at 75% RH than at 10% RH. Chemical mass balance (CMB) analysis was performed to illustrate the effects of oxidation on source apportionment estimates. As the extent of oxidation increases, traditional CMB analysis increasingly underestimates the contribution of gasoline vehicles butthe diesel estimates are largely unaffected. The results demonstrate that even modest levels of oxidation can alter policy-relevant conclusions about the total and relative contribution of gasoline and diesel vehicle emissions to ambient fine particle concentrations.

Acute Changes in Right Heart Pressures and Ambient Fine Particle Concentrations

Acute Changes in Right Heart Pressures and Ambient Fine Particle Concentrations

Impact of Exposure Error on the Relationship Between Traffic-Related Air Pollution and Heart Rate Variability (HRV)

TM6-O-05 Introduction: Numerous studies have shown associations between ambient fine particle (PM2.5) concentrations and heart rate variability (HRV). Previously, we reported results examining the association between ambient pollution and HRV for 18 individuals with chronic obstructive pulmonary disease (COPD) and 12 individuals with a myocardial infarction (MI). We found ambient concentrations of PM2.5 and the traffic-related elemental carbon (EC) and nitrogen dioxide (NO2) to have no effects on HRV among all individuals. When analyzed by subgroup, ambient PM2.5 was shown to result in significant increases in SDNN for COPD participants and nonsignificant decreases in MI participants. For EC and NO2, associations with SDNN showed similar, nonsignificant trends for COPD and MI participants. Other measures of HRV, including the parasympathetic indicators, r-MSSD, PNN50, and HF/LF, showed insignificant associations with all ambient measures. Methods: We compare pollutant-associated changes in HRV using ambient concentrations and personal exposures, which were measured for each participant 24 hours prior to each HRV measurement. Personal exposures to PM2.5, sulfate (SO42−), EC, and NO2 were measured using our multipollutant exposure monitor. Corresponding ambient concentrations were assessed using the average pollutant concentration measured at metropolitan Atlanta stationary ambient monitoring sites. The association between 24-hour ambient concentrations and personal exposures and HRV was examined using linear mixed-effects models (LME). Results: Similar to 24-hour ambient PM2.5 concentrations, 24-hour personal PM2.5 exposures were generally not significantly associated with any of the HRV measures. In contrast, personal EC and NO2 exposures averaged over the 24 hours prior to the HRV measurements were significantly associated with decreased HRV, particularly in rMSSD, PNN50, and HF, and with increased LF/HF. Among all participants, RMSSD decreased by 10.97% (95% CI, −18.00 to −3.34) for an IQR change in personal EC exposures (0.81 μg/m3). The magnitude of these associations was substantially stronger than those observed for corresponding 24-hour ambient concentrations and was strongest in MI participants. For example, an IQR change of 0.75 μg/m3 in personal EC exposures was associated with an overall 13.47% (95% CI, −23.81 to −1.73) decrease in RMSSD for MI participants as compared with a 7.53% (95% CI, −16.14 to 1.96) decrease in RMSSD for COPD participants. Similar findings were shown for NO2 and other HRV measures. Discussion and Conclusions: Results indicate decreased vagal tone in response to traffic pollutant exposures, which can best be detected with more precise measures of traffic pollutant exposures.