Can air pollution negate the health benefits of cycling and walking?

Active travel (cycling, walking) is beneficial for the health due to increased physical activity (PA). However, active travel may increase the intake of air pollution, leading to negative health consequences. We examined the risk–benefit balance between active travel related PA and exposure to air pollution across a range of air pollution and PA scenarios.The health effects of active travel and air pollution were estimated through changes in all-cause mortality for different levels of active travel and air pollution. Air pollution exposure was estimated through changes in background concentrations of fine particulate matter (PM_2.5), ranging from 5 to 200 μg/m3. For active travel exposure, we estimated cycling and walking from 0 up to 16 h per day, respectively. These refer to long-term average levels of active travel and PM_2.5 exposure.For the global average urban background PM_2.5 concentration (22 μg/m3) benefits of PA by far outweigh risks from air pollution even under the most extreme levels of active travel. In areas with PM_2.5 concentrations of 100 μg/m3, harms would exceed benefits after 1 h 30 min of cycling per day or more than 10 h of walking per day. If the counterfactual was driving, rather than staying at home, the benefits of PA would exceed harms from air pollution up to 3 h 30 min of cycling per day. The results were sensitive to dose–response function (DRF) assumptions for PM_2.5 and PA.PA benefits of active travel outweighed the harm caused by air pollution in all but the most extreme air pollution concentrations.     

Years of life lost and morbidity cases attributable to transportation noise and air pollution: A comparative health risk assessment for Switzerland in 2010

BackgroundThere is growing evidence that chronic exposure to transportation related noise and air pollution affects human health. However, health burden to a country of these two pollutants have been rarely compared.AimsAs an input for external cost quantification, we estimated the cardiorespiratory health burden from transportation related noise and air pollution in Switzerland, incorporating the most recent findings related to the health effects of noise.MethodsSpatially resolved noise and air pollution models for the year 2010 were derived for road, rail and aircraft sources. Average day-evening-night sound level (Lden) and particulate matter (PM₁₀) were selected as indicators, and population-weighted exposures derived by transportation source. Cause-specific exposure–response functions were derived from a meta-analysis for noise and literature review for PM₁₀. Years of life lost (YLL) were calculated using life table methods; population attributable fraction was used for deriving attributable cases for hospitalisations, respiratory illnesses, visits to general practitioners and restricted activity days.ResultsThe mean population weighted exposure above a threshold of 48 dB(A) was 8.74 dB(A), 1.89 dB(A) and 0.37 dB(A) for road, rail and aircraft noise. Corresponding mean exposure contributions were 4.4, 0.54, 0.12 μg/m³ for PM₁₀. We estimated that in 2010 in Switzerland transportation caused 6000 and 14,000 YLL from noise and air pollution exposure, respectively. While there were a total of 8700 cardiorespiratory hospital days attributed to air pollution exposure, estimated burden due to noise alone amounted to 22,500 hospital days.ConclusionsYLL due to transportation related pollution in Switzerland is dominated by air pollution from road traffic, whereas consequences for morbidity and indicators of quality of life are dominated by noise. In terms of total external costs the burden of noise equals that of air pollution.     

Effect of air pollution and racism on ethnic differences in respiratory health among adolescents living in an urban environment

Recent studies suggest that stress can amplify the harm of air pollution. We examined whether experience of racism and exposure to particulate matter with an aerodynamic diameter of less than 2.5 µm and 10 µm (PM_2.5 and PM₁₀) had a synergistic influence on ethnic differences in asthma and lung function across adolescence. Analyses using multilevel models showed lower forced expiratory volume (FEV₁), forced vital capacity (FVC) and lower rates of asthma among some ethnic minorities compared to Whites, but higher exposure to PM_2.5, PM₁₀ and racism. Racism appeared to amplify the relationship between asthma and air pollution for all ethnic groups, but did not explain ethnic differences in respiratory health.     

Is physical activity a modifier of the association between air pollution and arterial stiffness in older adults: The SAPALDIA cohort study

Introduction and objectives

Air pollution and insufficient physical activity have been associated with inflammation and oxidative stress, molecular mechanisms linked to arterial stiffness and cardiovascular disease. There are no studies on how physical activity modifies the association between air pollution and arterial stiffness. We examined whether the adverse cardiovascular effects of air pollution were modified by individual physical activity levels in 2823 adults aged 50–81 years from the well-characterized Swiss Cohort Study on Air Pollution and Lung and Heart Diseases (SAPALDIA).

Long-term air pollution exposure and lung function in 15 year-old adolescents living in an urban and rural area in Germany: The GINIplus and LISAplus cohorts

IntroductionThe impact of outdoor air pollution exposure on long-term lung development and potential periods of increased lung susceptibility remain unknown. This study assessed associations between early-life and current residential exposure to air pollution and lung function at 15-years of age in two German birth cohorts.MethodsFifteen year-old participants living in an urban and rural area in Germany underwent spirometry before and after bronchodilation (N = 2266). Annual average (long-term) exposure to nitrogen dioxide (NO₂), particles with aerodynamic diameters less than 2.5 μg/m³ (PM_2.5) mass and less than 10 μg/m³ (PM₁₀) mass, PM_2.5 absorbance and ozone were estimated to each participant's birth-, 10- and 15-year home address using land-use regression and kriging (ozone only) modelling. Associations between lung function variables and long-term pollutant concentrations were assessed using linear regression models adjusted for host and environmental covariates and recent short-term air pollution exposures.ResultsLong-term air pollution concentrations assessed to the birth-, 10- and 15-year home addresses were not associated with lung function variables, before and after bronchodilation, in the complete or study area specific populations. However, several lung function variables were negatively associated with long-term NO₂ concentrations among asthmatics. For example, NO₂ estimated to the 15-year home address was associated with the ratio of forced expiratory volume in one second to forced vital capacity (FEV₁/FVC) and the mean flow rate between 25% and 75% of FVC (−3.5%, 95% confidence interval [−6.0, −1.0] and −297.4 ml/s [−592.6, −2.1] per 5.9 μg/m³ increase in NO₂, respectively). Nearly all effect estimates for the associations between the short-term PM_2.5 mass, PM₁₀ mass and ozone concentrations and the lung function variables were negative in the complete population.ConclusionsEarly-life and current long-term air pollution exposures and lung function at the age of 15 years were not associated in the complete study population. Asthmatics may represent a vulnerable group.     

The associations between traffic-related air pollution and noise with blood pressure in children: Results from the GINIplus and LISAplus studies

Although traffic emits both air pollution and noise, studies jointly examining the effects of both of these exposures on blood pressure (BP) in children are scarce. We investigated associations between land-use regression modeled long-term traffic-related air pollution and BP in 2368 children aged 10 years from Germany (1454 from Munich and 914 from Wesel). We also studied this association with adjustment of long-term noise exposure (defined as day–evening–night noise indicator “Lden” and night noise indicator “Lnight”) in a subgroup of 605 children from Munich inner city. In the overall analysis including 2368 children, NO₂, PM_2.5 mass (particles with aerodynamic diameters below 2.5 μm), PM₁₀ mass (particles with aerodynamic diameters below 10 μm) and PM_2.5 absorbance were not associated with BP. When restricting the analysis to the subgroup of children with noise information (N = 605), a significant association between NO₂ and diastolic BP was observed (−0.88 (95% confidence interval: −1.67, −0.08)). However, upon adjusting the models for noise exposure, only noise remained independently and significantly positively associated with diastolic BP. Diastolic BP increased by 0.50 (−0.03, 1.02), 0.59 (0.05, 1.13), 0.55 (0.03, 1.07), and 0.58 (0.05, 1.11) mmHg for every five decibel increase in Lden and by 0.59 (−0.05, 1.22), 0.69 (0.04, 1.33), 0.64 (0.02, 1.27), and 0.68 (0.05, 1.32) mmHg for every five decibel increase in Lnight, in different models of NO₂, PM_2.5 mass, PM₁₀ mass and PM_2.5 absorbance as the main exposure, respectively. In conclusion, air pollution was not consistently associated with BP with adjustment for noise, noise was independently and positively associated with BP in children.     

Effects of air pollution on exhaled nitric oxide in children: Results from the GINIplus and LISAplus studies

Most previous studies which have investigated the short-term effects of air pollution on airway inflammation, assessed by an increase of exhaled nitric oxide (eNO), have been conducted among asthmatic children. Few studies have considered this potential association among non-asthmatics. Furthermore, although both short- and long-term effects of air pollution on eNO had been reported separately, studies which include both are scarce. We explored associations between 24 h NO₂ and PM₁₀ (particles with aerodynamic diameters below 10 μm) mass with eNO in 1985 children (192 asthmatics and 1793 non-asthmatics) aged 10 years and accounted for the long-term effects of air pollution by adjusting for annual averages of NO₂, PM₁₀ mass, PM_2.5 mass (particles with aerodynamic diameters below 2.5 μm) and PM_2.5 absorbance, using data from two German birth cohorts in Munich and Wesel. In total, robust associations between 24 h NO₂ and eNO were observed in both single-pollutant (percentage change: 18.30%, 95% confidence interval: 11.63–25.37) and two-pollutant models (14.62%, 6.71–23.11). The association between 24 h PM₁₀ mass and eNO was only significant in the single-pollutant model (9.59%, 4.80–14.61). The same significant associations were also observed in non-asthmatic children, while they did not reach significant levels in asthmatic children. Associations between annual averages of ambient air pollution (NO₂, PM₁₀ mass, PM_2.5 mass and PM_2.5 absorbance) and eNO were consistently null. In conclusion, significantly positive associations were observed between short-term ambient air pollution and eNO. No long-term effects of air pollution on eNO were found in this study.     

Associations between short-term exposure to particulate matter and ultrafine particles and myocardial infarction in Augsburg,Germany

BackgroundShort-term exposure to increased particulate matter (PM) concentration has been reported to trigger myocardial infarction (MI). However, the association with ultrafine particles remains unclear.ObjectivesWe aimed to assess the effects of short-term air pollution and especially ultrafine particles on registry-based MI events and coronary deaths in the area of Augsburg, Germany.MethodsBetween 1995 and 2009, the MONICA/KORA myocardial infarction registry recorded 15,417 cases of MI and coronary deaths. Concentrations of PM < 10 μm (PM₁₀), PM < 2.5 μm (PM_2.5), particle number concentration (PNC) as indicator for ultrafine particles, and meteorological parameters were measured in the study region. Quasi-Poisson regression adjusting for time trend, temperature, season, and weekday was used to estimate immediate, delayed and cumulative effects of air pollutants on the occurrence of MI. The daily numbers of total MI, nonfatal and fatal events as well as incident and recurrent events were analysed.ResultsWe observed a 1.3% risk increase (95%-confidence interval: [−0.9%; 3.6%]) for all events and a 4.4% [−0.4%; 9.4%] risk increase for recurrent events per 24.3 μg/m³ increase in same day PM₁₀ concentrations. Nonfatal events indicated a risk increase of 3.1% [−0.1%; 6.5%] with previous day PM₁₀. No association was seen for PM_2.5 which was only available from 1999 on. PNC showed a risk increase of 6.0% [0.6%; 11.7%] for recurrent events per 5529 particles/cm³ increase in 5-day average PNC.ConclusionsOur results suggested an association between short-term PM₁₀ concentration and numbers of MI, especially for nonfatal and recurrent events. For ultrafine particles, risk increases were notably high for recurrent events. Thus, persons who already suffered a MI seemed to be more susceptible to air pollution.     

Exposure to fine particulate matter during pregnancy and risk of term low birth weight in Jinan,China, 2014–2016

Background

Existing studies exploring the association between low birth weight (LBW) and maternal fine particulate matter (aerodynamic diameter < 2.5 μm, PM_2.5) exposure have presented equivocal results, and one of the possible reasons for this finding might be due to relatively low maternal exposures. In addition, relatively narrow maternal exposure windows to PM_2.5 have not been well established for LBW.

Impact of personally measured pollutants on cardiac function

Epidemiological studies have shown associations between ambient air pollution and changes in heart rate variability (HRV). However, studies using personal air pollution measurements, especially with exposure averages <24 h, are still rare.Between February and March 2008 HRV data as well as personal exposure to particulate matter <2.5 μm (PM_2.5), and particle number concentrations (PNC) were collected in five volunteers for up to 8.3 h on a 5 min resolution. Information about the participant's whereabouts was also collected. Mixed models were used to analyze concurrent and up to 30 min delayed effects of air pollutants as well as being in traffic on 5 min-averages of heart rate (HR), high and low frequency power (HF and LF), standard deviation of all normal-to-normal intervals (SDNN), and the root mean square of successive interval differences (RMSSD). Results are presented as %-change from the mean per increase in interquartile range of air pollutant.In total, 474 5-min segments were available for analysis. We observed concurrent and delayed reductions in SDNN of about 0.8–1.0% in association with a 5.4 μg/m³ increase in PM_2.5. However, being in traffic by car led to an increase of about 20% 10–14 min and 15–19 min later. An increase in PM_2.5 or PNC was associated with lagged decreases for RMSSD and HF. We detected concurrent reductions in RMSSD (−17.6% [95%-confidence interval: 29.1; −4.3]) when being in traffic by bike/foot. Being in traffic by car was associated with an immediate reduction in LF while more delayed increases in LF were observed when being in traffic by bike/foot. Air pollution and traffic effects on HR were less consistent.These rapid changes in HRV within 30 min might be mediated by the autonomic nervous system in response to direct reflexes from receptors in the lungs.     

Association between PM10 concentrations and school absences in proximity of a cement plant in northern Italy

Dusts are one of the main air pollutants emitted during cement manufacturing. A substantial part of these are breathable particles that are less than 10 μm in diameter (PM₁₀), which represent a potential threat for the health of the exposed population. This study aimed at evaluating the short-term effects of PM₁₀ concentrations on the health of children, aged 6–14 years, who attended the schools in Fumane (Italy), in proximity (1.2 km) to a large cement plant. School absenteeism was used as a proxy indicator of child morbidity. Time series of daily school absences and PM₁₀ concentrations were collected for 3 school-years from 2007 to 2010 (541 school-days, 462 children on average). The associations between PM₁₀ concentrations and school absence rates in the same day (lag0) and in the following 4 days (lag1 to lag4) were evaluated using generalised additive models, smoothed for medium/long term trends and adjusted for day of the week, influenza outbreaks, daily temperature and rain precipitations. The average concentration of PM₁₀ in the period was 34 (range: 4–183) μg/m³. An average 10 μg/m³ increase of PM₁₀ concentration in the previous days (lag0–4) was associated with a statistically significant 2.5% (95%CI: 1.1–4.0%) increase in the rate of school absences. The highest increase in the absence rates (2.4%; 95%CI: 1.2–3.5%) was found 2 days after exposure (lag2). These findings provide epidemiological evidence of the acute health effects of PM₁₀ in areas with annual concentrations that are lower than the legal European Union limit of 40 μg/m³, and support the need to establish more restrictive legislative standards.     

Associations between ambient air pollution and bone turnover markers in 10-year old children: Results from the GINIplus and LISAplus studies

Negative associations between bone turnover markers and bone mineral density have been reported. In order to study the association between ambient air pollution and bone turnover markers, as indicators of bone loss, we investigated associations between land-use regression modeled air pollution (NO₂, PM_2.5 mass, PM_{2.5 – 10} [coarse particles], PM₁₀ mass and PM_2.5 absorbance) and bone turnover markers in 2264 children aged 10 years. Serum osteocalcin and C-terminal telopeptide of type I collagen (CTx), measured by Modular-System (Roche), were the two bone turnover markers considered in this analysis. In total population, NO₂, PM_{2.5 – 10} and PM₁₀ mass exposure were positively and significantly associated with both osteocalcin and CTx. A 2.5 (95% CI: 0.6, 4.4) ng/ml increase in osteocalcin and a 24.0 (95% CI: 6.7, 41.3) ng/L increase in CTx were observed per IQR (6.7 μg/m³) increase in NO₂, independent of socioeconomic status, sex, age, pubertal status, fasting status and total physical activity. The estimated coefficients were 3.0 (95% CI: 0.1, 5.8) for osteocalcin and 32.3 (95% CI: 6.1, 58.5) for CTx with PM_{2.5 – 10}; 3.2 (95% CI: 0.0, 6.4) for osteocalcin and 30.7 (95% CI: 1.7, 59.7) for CTx with PM₁₀. Children living close to a major road (≤ 350 m) had higher levels of both osteocalcin (1.4 [−1.2, 4.0] ng/ml) and CTx (16.2 [−7.4, 39.8] ng/L). The adverse impact of ambient air pollution on bone turnover rates observed in one of the study areas showed stimulation of more such studies.     

Occupational exposure to particulate matter from three agricultural crops in California

Agricultural work is a major contributor to California's and the nation's economy and employs a large number of workers. However, agricultural work can have numerous risks, such as exposure to elevated levels of particulate matter (PM) and other airborne pollutants with potential adverse health effects. To determine the magnitude of occupational exposures, PM levels were assessed for 89 workers from three major crops in California; almonds, melons and tomatoes. Personal samples were collected for PM_2.5 and inhalable PM using personal sampling equipment. Geometric mean concentrations from personal exposure for workers in almonds (inhalable PM = 4368 μg/m³, PM_2.5 = 122 μg/m³, N = 5), tomatoes (inhalable PM = 1410 μg/m³, PM_2.5 = 12 μg/m³, N = 33), and melons (inhalable PM = 1118 μg/m³, PM_2.5 = 19 μg/m³, N = 51) showed high PM exposure when working with these three crops. Large exposure differences by crop were more common than by task (i.e. harvesting, packing and weeding) among the three crops studied. This is the largest study of agricultural workers engaged in hand harvesting, a significant employer of farm labor, and relatively high levels of exposure to PM were measured.     

Waterpipe cafés are hazardous to your health: Determination of a waterpipe specific calibration factor

Introduction

The use of a waterpipe to smoke tobacco has emerged as a popular trend in the United States. Waterpipe smoking establishments have had an increasing presence in the U.S., despite smoke-free air legislation. Dangers of waterpipe smoking have been documented, but less data has been gathered about the waterpipe café itself. This project sought to determine a waterpipe-specific calibration factor (CF) for measuring waterpipe aerosol, and field-test this CF by conducting surveillance on the existing waterpipe cafés of western and central New York.

Effects of commuting mode on air pollution exposure and cardiovascular health among young adults in Taipei,Taiwan

The association between traffic-related air pollution and adverse cardiovascular effects has been well documented; however, little is known about whether different commuting modes can modify the effects of air pollution on the cardiovascular system in human subjects in urban areas with heavy traffic. We recruited 120 young, healthy subjects in Taipei, Taiwan. Each participant was classified with different commuting modes according to his/her own commuting style. Three repeated measurements of heart rate variability (HRV) indices {standard deviation of NN intervals (SDNN) and the square root of the mean of the sum of the squares of differences between adjacent NN intervals (r-MSSD)}, particulate matter with an aerodynamic diameter ≤2.5 μm (PM_2.5), temperature, humidity and noise level were conducted for each subject during 1-h morning commutes (0900–1000 h) in four different commuting modes, including an electrically powered subway, a gas-powered bus, a gasoline-powered car, and walking. Linear mixed-effects models were used to investigate the association of PM_2.5 with HRV indices. The results showed that decreases in the HRV indices were associated with increased levels of PM_2.5. The personal exposure levels to PM_2.5 were the highest in the walking mode. The effects of PM_2.5 on cardiovascular endpoints were the lowest in the subway mode compared to the effects in the walking mode. The participants in the car and bus modes had reduced effects on their cardiovascular endpoints compared to the participants in the walking mode. We concluded that traffic-related PM_2.5 is associated with autonomic alteration. Commuting modes can modify the effects of PM_2.5 on HRV indices among young, healthy subjects.     

Associations between particulate matter elements and early-life pneumonia in seven birth cohorts: Results from the ESCAPE and TRANSPHORM projects

Evidence for a role of long-term particulate matter exposure on acute respiratory infections is growing. However, which components of particulate matter may be causative remains largely unknown. We assessed associations between eight particulate matter elements and early-life pneumonia in seven birth cohort studies (N_total = 15,980): BAMSE (Sweden), GASPII (Italy), GINIplus and LISAplus (Germany), INMA (Spain), MAAS (United Kingdom) and PIAMA (The Netherlands). Annual average exposure to copper, iron, potassium, nickel, sulfur, silicon, vanadium and zinc, each respectively derived from particles with aerodynamic diameters ≤ 10 μm (PM₁₀) and 2.5 μm (PM_2.5), were estimated using standardized land use regression models and assigned to birth addresses. Cohort-specific associations between these exposures and parental reports of physician-diagnosed pneumonia between birth and two years were assessed using logistic regression models adjusted for host and environmental covariates and total PM₁₀ or PM_2.5 mass. Combined estimates were calculated using random-effects meta-analysis. There was substantial within and between-cohort variability in element concentrations. In the adjusted meta-analysis, pneumonia was weakly associated with zinc derived from PM₁₀ (OR: 1.47 (95% CI: 0.99, 2.18) per 20 ng/m³ increase). No other associations with the other elements were consistently observed. The independent effect of particulate matter mass remained after adjustment for element concentrations. In conclusion, associations between particulate matter mass exposure and pneumonia were not explained by the elements we investigated. Zinc from PM₁₀ was the only element which appeared independently associated with a higher risk of early-life pneumonia. As zinc is primarily attributable to non-tailpipe traffic emissions, these results may suggest a potential adverse effect of non-tailpipe emissions on health.     

Effect of long-term exposure to air pollution on anxiety and depression in adults: A cross-sectional study

Background

The association between exposure to air pollutants and mental disorders among adults has been suggested, although results are not consistent.

Influenza vaccination and the endurance against air pollution among elderly with acute coronary syndrome

ObjectiveAir pollution, weather condition and influenza are known risk factors of acute coronary syndrome (ACS) among elderly people. The influenza vaccine (IV) has been shown to reduce major cardiovascular events. The purpose of this study was to compare resistance to air pollution and weather factors causing ACS between vaccinated and less-vaccinated elderly people.MethodsA case–crossover design was applied to 1835 elderly ACS patients who were obtained from the 1-million sample of Taiwan National Health Insurance Research Data with inclusion criteria: (1) the first diagnosis of ACS was in cold season and at age 68 or more, (2) had received the free IV program at least once during the period 3 years before the ACS. They were stratified into two groups: 707 had received flu vaccinations for all the 3 years and the remaining 1128 had not. The measurements of air pollutants, temperature, and humidity corresponding to each of the 3 days prior to the ACS diagnosis date were retrieved from the data banks of the Taiwan Environmental Protection Administration and Central Weather Bureau.FindingsIncreases in air pollution concentrations of CO, NO₂, PM₁₀ or PM_2.5 and decreases in temperature significantly influenced the risk of ACS for the non-continuously vaccinated elderly population; however, less significant effects were observed for the continuously vaccinated population.ConclusionConsecutive influenza vaccination may potentially offer resistance against the detrimental effects of air pollution and changes in temperature in frail elderly adults with ACS. Future studies are needed to directly assess the interaction effect between the vaccination and environmental factors on ACS.     

Chronic PM2.5 exposure and risk of infant bronchiolitis and otitis media clinical encounters

Chronic particulate matter less than 2.5 μm in diameter (PM_2.5) exposure can leave infants more susceptible to illness. Our objective is to estimate associations of the chronic PM_2.5 exposure with infant bronchiolitis and otitis media (OM) clinical encounters. We obtained all first time bronchiolitis (n = 18,029) and OM (n = 40,042) clinical encounters among children less than 12 and 36 months of age, respectively, diagnosed from 2001 to 2009 and two controls per case matched on birthdate and gestational age from the Pregnancy to Early Life Longitudinal data linkage system in Massachusetts. We applied conditional logistic regression to estimate odds ratios (OR) and confidence intervals (CI) per 2-μg/m³ increase in lifetime average satellite based PM_2.5 exposure_. Effect modification was assessed by age, gestational age, frequency of clinical encounter, and income. We examined associations between residential distance to roadways, traffic density, and infant bronchiolitis and OM risk. PM_2.5 was not associated with infant bronchiolitis (OR = 1.02, 95% CI = 1.00, 1.04) and inversely associated with OM (OR = 0.97, 95% CI = 0.95, 0.99). There was no evidence of effect modification. Compared to infants living near low traffic density, infants residing in high traffic density had elevated risk of bronchiolitis (OR = 1.23, 95% CI = 1.14, 1.31) but not OM (OR = 0.98, 95% CI = 0.93, 1.02) clinical encounter. We did not find strong evidence to support an association between early-life long-term PM_2.5 exposure and infant bronchiolitis or OM. Bronchiolitis risk was increased among infants living near high traffic density.     

A novel method to construct an air quality index based on air pollution profiles

Background

Air quality indices based on the maximum of sub-indices of pollutants are easy to produce and help quantify the degree of air pollution. However, they discount the additive effects of multiple pollutants and are only sensitive to changes in highest sub-index.