Abstract  We use the fractional aerosol optical depth (AOD) values derived from Multiangle Imaging Spectroradiometer (MISR) aerosol component measurements, along with aerosol transport model constraints, to estimate ground-level concentrations of fine particulate matter (PM2.5) mass and its major constituents in the continental United States. Regression models using fractional AODs predict PM2.5 mass and sulfate (SO4) concentrations in both the eastern and western United States, and nitrate (NO3) concentrations in the western United States reasonably well, compared with the available ground-level U.S. Environment Protection Agency (EPA) measurements. These models show substantially improved predictive power when compared with similar models using total-column AOD as a single predictor, especially in the western United States. The relative contributions of the MISR aerosol components in these regression models are used to estimate size distributions of EPA PM2.5 species. This method captures the overall shapes of the size distributions of PM2.5 mass and SO4 particles in the east and west, and NO3 particles in the west. However, the estimated PM2.5 and SO4 mode diameters are smaller than those previously reported by monitoring studies conducted at ground level. This is likely due to the satellite sampling bias caused by the inability to retrieve aerosols through cloud cover, and the impact of particle hygroscopicity on measured particle size distributions at ground level.

Abstract  BACKGROUND: Numerous studies have shown that ambient air pollution and smoking are both associated with increased mortality, but until now there has been little evidence as to whether the effects of these 2 factors combined are greater than the sum of their individual effects. We assessed whether smokers are subject to additional mortality risk from air pollution relative to never-smokers. METHODS: This study included 10,833 Chinese men in Hong Kong who died at the age of 30 or above during the period 1 January to 31 December 1998. Relatives who registered for deceased persons were interviewed about the deceased's smoking history and other personal lifestyle factors about 10 years before death. Poisson regression for daily number of deaths was fitted to estimate excess risks per 10 microg/m increase in particulate matter with aerodynamic diameter <10 microm (PM10) in male smokers and never-smokers in stratified data, and additional excess risk for smokers relative to never-smokers in combined data. RESULTS: In smokers there was a significant excess risk associated with PM10 for all natural causes and cardio-respiratory diseases for men age 30 years or older and men 65 or older. For all natural causes, greater excess risk associated with PM10 was observed for smokers relative to never-smokers: 1.9% (95% confidence interval = 0.3% to 3.6%) in men age 30 and older and 2.3% (0.4% to 4.3%) in those age 65 and older. CONCLUSIONS: Ambient particulate air pollution is associated with greater excess mortality in male smokers compared with never-smokers.

Abstract  Objective: It is still unknown whether specific components in fine particles are associated with heart rate variability (HRV) reduction. Methods: We recruited 46 patients with or at risk for cardiovascular diseases to measure 24-hour HRV by ambulatory electrocardiographic monitoring. Fixed-site air-monitoring stations were used to represent participants' exposures to particles with aerodynamic diameters less than 10 ?m (PM10) and 2.5 ?m (PM2.5), and particulate components of sulfate, nitrate, organic carbon (OC) and elemental carbon, and gaseous pollutants. Results: We found that HRV reduction was associated with sulfate, OC, and PM2. 5 but not with the other five pollutants in single-pollutant models. Sulfate was found to remain in significant association with HRV reduction adjusting for OC and PM2.5 in three-pollutant models. Conclusions: Exposures to sulfate and OC in PM2.5were associated with HRV reduction in patients with or at risk for cardiovascular diseases.

Abstract  Objective: The authors conducted an investigation of the association between air pollution and arrhythmia. Methods: A prospective panel study (October 2000-April 2001) was conducted in Erfurt, Germany. Fifty-seven men with coronary heart disease were subjected to six 24-hour electrocardiogram recordings. Runs of supraventricular and ventricular tachycardia were associated with continuous ultrafine particle counts (UFP), accumulation mode particle counts (ACP), PM2,5, and gaseous pollutants. Poisson and linear regression models were applied adjusting for trend, weekday, and meteorologic data. Results: Elevated concentrations of UFP, ACP, PM2,5, and nitrogen dioxide increased the risk for supraventricular runs and the number of ventricular runs at almost all lags. Statistically significant associations were found predominantly in the previous 24 to 71 hours and with the 5-day moving average. Conclusion: Elevated concentrations of fine and ultrafine particle increased the risk of arrhythmia in men with coronary heart disease.

Abstract  The National Children's Study is considering a wide spectrum of airborne pollutants that are hypothesized to potentially influence pregnancy outcomes, neurodevelopment, asthma, atopy, immune development, obesity, and pubertal development. In this article we summarize six applicable exposure assessment lessons learned from the Centers for Children's Environmental Health and Disease Prevention Research that may enhance the National Children's Study: a) Selecting individual study subjects with a wide range of pollution exposure profiles maximizes spatial-scale exposure contrasts for key pollutants of study interest. b) In studies with large sample sizes, long duration, and diverse outcomes and exposures, exposure assessment efforts should rely on modeling to provide estimates for the entire cohort, supported by subject-derived questionnaire data. c) Assessment of some exposures of interest requires individual measurements of exposures using snapshots of personal and microenvironmental exposures over short periods and/or in selected microenvironments. d) Understanding issues of spatial-temporal correlations of air pollutants, the surrogacy of specific pollutants for components of the complex mixture, and the exposure misclassification inherent in exposure estimates is critical in analysis and interpretation. e) "Usual" temporal, spatial, and physical patterns of activity can be used as modifiers of the exposure/outcome relationships. f) Biomarkers of exposure are useful for evaluation of specific exposures that have multiple routes of exposure. If these lessons are applied, the National Children's Study offers a unique opportunity to assess the adverse effects of air pollution on interrelated health outcomes during the critical early life period.

Abstract  We report on the first application of a novel fast on-road sensing method for measurement of particulate emissions of individual passing passenger cars. The study was motivated by the shift of interest from gases to particles in connection with strong adverse health effects. The results correspond very much to findings by Beaton et al. (Science, May 19,1995) for gaseous hydrocarbon and CO emissions: A small percentage of "superpolluters" (here 5%) account for a high percentage (here 43%) of the pollution (here elemental carbon). We estimate that up to 50% of the particulate emissions of vehicles could be avoided on the basis of the present legislation, if on-road monitoring would be applied to enforce maintenance. Our fast sensing method for particles is based on photoelectron emission from the emitted airborne soot particles in combination with a CO2 sensor delivering a reference.

Abstract  BACKGROUND: Few studies of air pollutants address morbidity in preschool children. In this study we evaluated bronchitis in children from two Czech districts: Teplice, with high ambient air pollution, and Prachatice, characterized by lower exposures. OBJECTIVES: Our goal was to examine rates of lower respiratory illnesses in preschool children in relation to ambient particles and hydrocarbons. METHODS: Air monitoring for particulate matter < 2.5 microm in diameter (PM(2.5)) and polycyclic aromatic hydrocarbons (PAHs) was conducted daily, every third day, or every sixth day. Children born May 1994 through December 1998 were followed to 3 or 4.5 years of age to ascertain illness diagnoses. Mothers completed questionnaires at birth and at follow-up regarding demographic, lifestyle, reproductive, and home environmental factors. Longitudinal multivariate repeated-measures analysis was used to quantify rate ratios for bronchitis and for total lower respiratory illnesses in 1,133 children. RESULTS: After adjustment for season, temperature, and other covariates, bronchitis rates increased with rising pollutant concentrations. Below 2 years of age, increments in 30-day averages of 100 ng/m(3) PAHs and of 25 microg/m(3) PM(2.5) resulted in rate ratios (RRs) for bronchitis of 1.29 [95 % confidence interval (CI), 1.07-1.54] and 1.30 (95% CI, 1.08-1.58), respectively; from 2 to 4.5 years of age, these RRs were 1.56 (95% CI, 1.22-2.00) and 1.23 (95% CI, 0.94-1.62), respectively. CONCLUSION: Ambient PAHs and fine particles were associated with early-life susceptibility to bronchitis. Associations were stronger for longer pollutant-averaging periods and, among children > 2 years of age, for PAHs compared with fine particles. Preschool-age children may be particularly vulnerable to air pollution-induced illnesses.

Abstract  The size and composition of ambient airborne particulate matter is reported for winter conditions at five locations in (or near) the San Joaquin Valley in central California. Two distinct types of airborne particles were identified based on diurnal patterns and size distribution similarity: hygroscopic sulfate/ammonium/nitrate particles and less hygroscopic particles composed of mostly organic carbon with smaller amounts of elemental carbon. Day-time PM10 concentrations for sulfate/ammonium/nitrate particles were measured to be 10.1 μg m-3, 28.3 μg m-3, and 52.8 μg m-3 at Sacramento, Modesto and Bakersfield, California, respectively. Nighttime concentrations were 10-30% lower, suggesting that these particles are dominated by secondary production. Simulation of the data with a box model suggests that these particles were formed by the condensation of ammonia and nitric acid onto background or primary sulfate particles. These hygroscopic particles had a mass distribution peak in the accumulation mode (0.56-1.0 μm) at all times. Daytime PM10 carbon particle concentrations were measured to be 9.5 μg m-3, 15.1 μg m-3, and 16.2 μg m-3 at Sacramento, Modesto, and Bakersfield, respectively. Corresponding nighttime concentrations were 200-300% higher, suggesting that these particles are dominated by primary emissions. The peak in the carbon particle mass distribution varied between 0.2-1.0 μm. Carbon particles emitted directly from combustion sources typically have a mass distribution peak diameter between 0.1-0.32 μm. Box model calculations suggest that the formation of secondary organic aerosol is negligible under cool winter conditions, and that the observed shift in the carbon particle mass distribution results from coagulation in the heavily polluted concentrations experienced during the current study. The analysis suggests that carbon particles and sulfate/ammonium/nitrate particles exist separately in the atmosphere of the San Joaquin Valley until coagulation mixes them in the accumulation mode.

Abstract  The San Joaquin Valley (SJV) in California has one of the most severe particulate air quality problems in the United States during the winter season. In the current study, measurements of particulate matter (PM) smaller than 10 μm in aerodynamic diameter (PM10), fine particles (PM1.8), and ultrafine particles (PM0.1) made during the period December 16, 2000-February 3, 2001, at six locations near or within the SJV are discussed: Bodega Bay, Davis, Sacramento, Modesto, Bakersfield, and Sequoia National Park. Airborne PM1.8 concentrations at the most heavily polluted site (Bakersfield) increased from 20 to 172 μg/m3 during the period December 16, 2000-January 7, 2001. The majority of the fine particle mass was ammonium nitrate driven by an excess of gas-phase ammonia. Peak PM0.1 concentrations (8-12 hr average) were ∼2.4 μg/m3 measured at night in Sacramento and Bakersfield. Ultrafine particle concentrations were distinctly diurnal, with daytime concentrations ∼50% lower than nighttime concentrations. PM0.1 concentrations did not accumulate during the multiweek stagnation period; rather, PM0.1 mass decreased at Bakersfield as PM1.8 mass was increasing. The majority of the ultrafine particle mass was associated with carbonaceous material. The high concentrations of ultrafine particles in the SJV pose a potential serious public health threat that should be addressed.

Abstract  Background:In vivo animal experiments demonstrate neurotoxicity of exposures to particulate matter (PM) and ozone, but only one small epidemiological study had linked ambient air pollution with central nervous system (CNS) functions in children. Objectives: To examine the neurobehavioral effects associated with long-term exposure to ambient PM and ozone in adults. Methods:We conducted a secondary analysis of the Neurobehavioral Evaluation System-2 (NES2) data (including a simple reaction time test [SRTT] measuring motor response speed to a visual stimulus; a symbol-digit substitution test [SDST] for coding ability; and a serial-digit learning test [SDLT] for attention and short-term memory) from 1764 adult participants (aged 37.5 ± 10.9 years) of the Third National Health and Nutrition Examination Survey in 1988?1991. Based on ambient PM10 (PM with aerodynamic diameter <10 ?m) and ozone data from the EPA Aerometric Information Retrieval System database, estimated annual exposure prior to the examination were aggregated at the centroid of each census-block group of geocoded residences, using distance-weighted averages from all monitors in the residing and adjoining counties. Generalized linear models were constructed to examine the associations, adjusting for potential confounders. Results:In age- and sex-adjusted models, PM10 predicted reduced CNS functions, but the association disappeared after adjustment for sociodemographic factors. There were consistent associations between ozone and reduced performance in NES2. In models adjusting for demographics, socioeconomic status, lifestyle, household and neighborhood characteristics, and cardiovascular risk factors, ozone predicted high scores in SDST and SDLT, but not in SRTT. Each 10-ppb increase in annual ozone was associated with increased SDST and SDLT scores by 0.16 (95%CI: 0.01, 0.23) and 0.56 (95%CI: 0.07, 1.05), equivalent to 3.5 and 5.3 years of aging-related decline in cognitive performance. Conclusions:Our study provides the first epidemiological data supporting the adverse neurobehavioral effects of ambient air pollutants in adults.

Abstract  Several studies have documented potential health effects due to agricultural burning smoke. However, there is a paucity of literature characterizing community residents exposure to agricultural burning smoke. This study assesses personal exposures to particulate matter (PM) with aerodynamic diameters <2.5 mu m (PM sub(2.5)) from agriculture burning smoke (E sub(b)) for 33 asthmatic adults in Pullman, WA. PM sub(2.5) concentrations were measured on 16 subjects, inside of all but four residences, outside of 6 residences, and at a central site. The mean+/-standard deviation of personal exposure to PM sub(2.5) was 13.8+/-11.1 mu g m super(-3), which was on average 8.0 mu g m super(-3) higher during the agricultural burning episodes (19.0+/-11.8 mu g m super(-3)) than non-episodes (11.0+/-9.7 mu g m super(-3)). The levoglucosan (LG, a unique marker for biomass burning PM) on personal filter samples also was higher during the episodes than non-episodes (0.026+/-0.030 vs. 0.010+/-0.012 mu g m super(-3)). We applied the random component superposition model on central-site and home indoor PM measurements, and estimated a central-site infiltration factor between 0.21 and 2.05 for residences with good modeling performance. We combined the source apportionment and total exposure modeling results to estimate individual E sub(b), which ranged from 1.2 to 6.7 mu g m super(-3) and correlated with personal LG with an r of 0.51. The sensitivity analysis of applying the infiltration efficiency estimated from the recursive model showed that the E sub(b) (range: 1.3-4.3 mu g m super(-3)) obtained from this approach have a higher correlation with personal LG (r=0.75). Nevertheless, the small sample size of personal LG measurements prevents a comparative and conclusive assessment of the model performance. We found a significant between-subject variation between episodes and non-episodes in both the E sub(b) estimates and subjects activity patterns. This suggests that the LG measurements at the central site may not always represent individual exposures to agricultural burning smoke. We recommend collecting more microenvironmental samples to model the E sub(b) and more personal samples to validate the E sub(b) estimates.

Abstract  Mucociliary transport is responsible for the cleansing of inhaled particles from the conducting airways of the lung. The characteristics of human tracheobronchial mucociliary transport have been investigated using radiotagged aerosols. These methods are critically reviewed together with alternative techniques. The role of predictive mathematical models of tracheobronchial clearance is discussed. Major findings regarding mucociliary clearance in health and the effects of drugs, inhaled pollutants, and disease are summarized. Throughout, areas requiring problem-solving are delineated.

Abstract  The report provides the Oversight Review Board`s (ORB`s) conclusions on the performance of the National Acid Precipitation Assessment Program (NAPAP) as requested by the Joint Chairs Council, and suggests lessons to be drawn from the NAPAP experience which may be of use in other similar endeavors.The ORB concludes that, taken as a whole, NAPAP was a successful enterprise which furthered effective decision making with respect to acid precipitation and other air quality matters, which improved scientific and technical understanding of underlying processes, and which provided an innovative institutional departure for addressing other problems at the intersection of science, technology and policy.

Abstract  An ambient carbon particulate monitor (ACPM), which is a commercially available instrument for automatic continuous measurement of particulate carbon, has been used in the recent studies. In order to investigate the amount of the positive artifact in the measurement of particulate carbonaceous substances by the ACPM, field duplicate experiments using two ACPMs and a parallel plate organic denuder were conducted in urban and rural atmosphere. The ACPM measurements without the denuder are at risk of overestimating the results for organic carbon (OC) and total carbon in aerosols because of the positive artifact derived from organic vapors in the sample air stream. On the other hand, the measurement of OC evolved at higher temperatures (250-340°C) and elemental carbon in aerosols are not significantly affected by the positive artifact. The ACPM measurements with the denuder give the lower-limit concentrations of particulate carbonaceous substances.

Abstract  BACKGROUND: Outdoor air pollution and lead exposure can disturb cardiac autonomic function, but the effects of both these exposures together have not been studied. METHODS: We examined whether higher cumulative lead exposures, as measured by bone lead, modified cross-sectional associations between air pollution and heart rate variability among 384 elderly men from the Normative Aging Study. We used linear regression, controlling for clinical, demographic, and environmental covariates. RESULTS: We found graded, significant reductions in both high-frequency and low-frequency powers of heart rate variability in relation to ozone and sulfate across the quartiles of tibia lead. Interquartile range increases in ozone and sulfate were associated respectively, with 38% decrease (95% confidence interval = -54.6% to -14.9%) and 22% decrease (-40.4% to 1.6%) in high frequency, and 38% decrease (-51.9% to -20.4%) and 12% decrease (-28.6% to 9.3%) in low frequency, in the highest quartile of tibia lead after controlling for potential confounders. We observed similar but weaker effect modification by tibia lead adjusted for education and cumulative traffic (residuals of the regression of tibia lead on education and cumulative traffic). Patella lead modified only the ozone effect on heart rate variability. CONCLUSIONS: People with long-term exposure to higher levels of lead may be more sensitive to cardiac autonomic dysfunction on high air pollution days. Efforts to understand how environmental exposures affect the health of an aging population should consider both current levels of pollution and history of lead exposure as susceptibility factors.

Abstract  Recent papers have reported that Asian dust events have been associated with increased risks of all-cause mortality and rates of respiratory illness. The current study was designed to estimate the relative risk of mortality associated with Asian dust events. We used the daily counts of non-accidental deaths, air pollution and meteorological data in Seoul, Korea from 2000 to 2004. We divided all days during the study period into two groups according to the presence or absence of Asian dust events. For each group, we conducted time-series analysis to estimate the relative risk of total non-accidental death when the concentration of each air pollutant increased by the inter-quartile range (IQR). The average concentrations of every air pollutant on the days without a dust event were lower than those on the days with such an event. We found that the effect sizes of air pollution on daily death rates in the model without Asian dust events were larger than those in the model with Asian dust events, and were statistically significant for all air pollutants (PM10, CO, NO2, and SO2) except for O-3. Our results Suggest that we are likely to underestimate the risk of urban air particles if we analyze the effect size of air pollution on daily mortality during Asian dust events. We hypothesize that the real health effect is much larger than previous results suggested.

Abstract  #In Asia, limited literature has been published on the association between daily mortality and ambient air pollution. We examined the associations of daily cause-specific mortality with daily mean concentrations of particulate matter (PM) with a mass median aerodynamic diameter less than 10 mu m (PM10) in Wuhan, China using 4 years of data (2001-2004). There are approximately 4.5 million residents in Wuhan who live in the city core area of 201 km(2) where air pollution levels are higher and pollution ranges are wider than the majority of cities in the published literature. We use quasi-likelihood estimation within the context of the generalized additive models (GAMs) (natural spline (NS) models in R) to model the natural logarithm of the expected daily death counts as a function of the predictor variables. We found consistent PM10 effects on mortality with the strongest effects on lag 0 day. Every 10 mu g/m3 increase in PM10 daily concentration at tag 0 day was significantly associated with an increase in non-accidental (0.36%; 95% CI 0.19-0.53%), cardiovascular (0.51%; 95% CI 0.28-0.75%), stroke (0.44%; 95% CI 0.16-0.72%), cardiac (0.49%; 95% CI 0.08-0.89%), respiratory (0.71%; 95% CI 0.20-1.23%), and cardiopulmonary (0.46%; 95% CI 0.23-0.69%). In general, these effects were stronger among the elderly (>= 65 years or >= 45 years) than among the young. The exploration of exposure-response relationships between PM10 and cause-specific mortality suggests the appropriateness of assuming linear relationships, where the PM10 concentration in Wuhan ranged from 24.8 to 477.8 mu g/m(3). We conclude that there is consistent evidence of acute effects of PM10 on cardiopulmonary mortality. A linear no threshold exposure-response relationship is suggested between PM10 and the studied cause-specific mortality.

Abstract  BACKGROUND: Fine particulate matter has been linked to allergies by experimental and epidemiological data having used aggregated data or concentrations provided by fixed-site monitoring stations, which may have led to misclassification of individual exposure to air pollution. METHODS: A semi-individual design was employed to relate individual data on asthma and allergy of 5338 school children (10.4 +/- 0.7 years) attending 108 randomly chosen schools in 6 French cities to the concentrations of PM2.5 (fine particles with aerodynamic diameter 2.5 microm) assessed in proximity of their homes. Children underwent a medical visit including skin prick test (SPT) to common allergens, exercise-induced bronchial (EIB) reactivity and skin examination for flexural dermatitis. Their parents filled in a standardised health questionnaire. RESULTS: After adjustment for confounders and NO2 as a potential modifier, the odds of suffering from EIB and flexural dermatitis at the period of the survey, past year atopic asthma and SPT positivity to indoor allergens were significantly increased in residential settings with PM2.5 concentrations exceeding 10 microg/m3 (WHO air quality limit values). The relationships were strengthened in long-term residents (current address for at least 8 years). CONCLUSIONS: Findings support the hypothesis that changes in allergy prevalence observed in recent decades might be partly related to interactions between traffic-related air pollution and allergens. Further longitudinal investigations are needed to corroborate such results.

Abstract  Background: Many studies have shown a consistent association between ambient air pollution and an increase in death due to cardiovascular causes. An increase in blood pressure is a common risk factor for a variety of cardiovascular diseases. However, the association between air pollution and blood pressure has not been evaluated extensively. Methods: In this cross-sectional study, we measured blood pressure in 10 459 subjects who had a health examination from 2001 to 2003, and calculated individual’s exposure to ambient levels of air pollutants. To evaluate the relationship between exposure to air pollutants and blood pressure with respect to season, we performed a multiple regression analysis, separately, according to season, controlling for individual characteristics and meteorological variables. Results: In the warm-weather season (July–September), particulate air pollutant of <10 μm (PM10) and nitrogen dioxide (NO2) concentrations were significantly associated with measures of blood pressure. During cold weather (October–December), blood pressure was significantly associated with sulphur dioxide (SO2) and ozone (O3) concentrations. The significant association between PM10 or NO2 and blood pressure disappeared during the cold-weather season. Conclusion: We found a seasonal variation for the association between ambient air-pollutant concentrations and blood pressure.

Abstract  Motor vehicles emit a cocktail of pollutants and are a major contributor to ground-level air pollution, but little is known regarding the ecological impacts of air pollution from roads on the surrounding vegetation. Data are presented on vegetation at three sites adjacent to two major motorways in the UK, comprising two woodland sites and one blanket bog site. Surveys of oak and beech tree health (at the woodland sites) and species composition (at the blanket bog site) were undertaken along transects away from the motorway. The oak tree health survey found increased defoliation and insect damage near to the motorway, and the beech tree health survey also found poorer crown condition close to the motorway. Vascular species composition showed a trend towards species adapted to higher N availability close to the motorway, while the moss Polytrichum commune showed a significant decline in frequency with distance from the motorway. The effect of the road was estimated to extend to approximately 100m at these three sites; this distance was consistent with the measured profile of NO2, which declined to background levels at about 100m. The results suggest that emissions of air pollutants can have significant ecological impacts on sensitive sites within 100m of major roads.

Abstract  Dicarboxylic acids in atmospheric aerosols have received much attention because of their potential roles in affecting the global climate. The composition and the sources of dicarboxylic acids in PM2.5 were studied at one remote and two urban sites in Hong Kong in the winter of 2000 and in the summer of 2001. Oxalate was the dominant dicarboxylic acid in all samples. The winter oxalate concentrations were high and spatially uniform, with an average value of 0.36 μg m−3, but the summer oxalate concentrations were low and had a large spatial variation. The influence of meteorological factors on the concentrations of dicarboxylic acids was also studied. The ratio of malonate to succinate was used to distinguish primary sources from secondary sources of these acids. This ratio at all three sites was close to that from direct vehicular exhaust in the winter, but it was close to that of secondary reactions in the summer. Hence, the acids were attributed to vehicular emissions in the winter and secondary sources in the summer. This hypothesis is also supported by a good correlation of oxalate with sulfate in the summer but a poor one in the winter. The correlations of oxalate with malonate, succinate, sulfate and K+ were also studied in terms of the routes of secondary formation of these dicarboxylic acids.

Abstract  Background: Short term increases in exposure to particulate matter (PM) air pollution are associated with increased cardiovascular morbidity and mortality. The mechanism behind this effect is unclear, although changes in autonomic control have been observed. It was hypothesised that increases in fine PM measured at the subjects' home in the preceding hour would be associated with decreased high frequency heart rate variability (HF-HRV) in individuals with pre-existing cardiac disease. Methods: Two hundred and eighty five daily 20 minute measures of HRV (including a paced breathing protocol) were made in the homes of 34 elderly individuals with (n=21) and without (n=13) cardiovascular disease (CVD) over a 10 day period in Seattle between February 2000 and March 2002. Fine PM was continuously measured by nephelometry at the individuals' homes. Results: The median age of the study population was 77 years (range 57-87) and 44% were male. Models that adjusted for health status, relative humidity, temperature, mean heart rate, and medication use did not find a significant association between a 10 ?g/m3increase in 1 hour mean outdoor PM2.5 before the HRV measurement and a change in HF-HRV power in individuals with CVD (3% increase in median HF-HRV (95% CI -19 to 32)) or without CVD (5% decrease in median HF-HRV (95% Cl -34 to 36)). Similarly, no association was evident using 4 hour and 24 hour mean outdoor PM2.5 exposures before the HRV measurement. Conclusion: No association was found between increased residence levels of fine PM and frequency domain measures of HRV in elderly individuals.