Molini M. Patel

Air pollution and childhood asthma: recent advances and future directions

Purpose of review Current levels of air pollution are consistently associated with asthma development and morbidity among children, suggesting that current regulatory policies may be insufficient. This review will describe recent studies that have examined specific emission sources or components of pollutants that may be associated with pediatric asthma and identify subpopulations that may be particularly susceptible to the effects of air pollution exposure. Recent findings Important advances include new characterizations of the effects of traffic-related air pollution in urban areas. They also include the application of novel exposure and outcome measures such as pollution estimates derived from land use regression modeling and biological markers of airway inflammation. Additionally, studies have identified host susceptibility characteristics that may modify responses to air pollution exposure, including polymorphisms in oxidative stress genes and epigenetic alterations. Summary Identifying specific sources and toxic constituents of air pollution and accurately assessing air pollutant-related asthma outcomes are needed to better direct control strategies. Further research is needed to identify additional host factors that confer increased susceptibility to air pollution exposure. Future therapy to reduce the adverse effects of air pollution on respiratory disease will likely depend on targeting susceptible populations for intervention.

Ambient Metals, Elemental Carbon, and Wheeze and Cough in New York City Children through 24 Months of Age

RATIONALE The effects of exposure to specific components of ambient fine particulate matter (PM(2.5)), including metals and elemental carbon (EC), have not been fully characterized in young children. OBJECTIVES To compare temporal associations among PM(2.5); individual metal constituents of ambient PM(2.5), including nickel (Ni), vanadium (V), and zinc (Zn); and EC and longitudinal reports of respiratory symptoms through 24 months of age. METHODS Study participants were selected from the Columbia Center for Childrens Environmental Health birth cohort recruited in New York City between 1998 and 2006. Respiratory symptom data were collected by questionnaire every 3 months through 24 months of age. Ambient pollutant data were obtained from state-operated stationary monitoring sites located within the study area. For each subject, 3-month average inverse-distance weighted concentrations of Ni, V, Zn, EC, and PM(2.5) were calculated for each symptom-reporting period based on the questionnaire date and the preceding 3 months. Associations between pollutants and symptoms were characterized using generalized additive mixed effects models, adjusting for sex, ethnicity, environmental tobacco smoke exposure, and calendar time. MEASUREMENTS AND MAIN RESULTS Increases in ambient Ni and V concentrations were associated significantly with increased probability of wheeze. Increases in EC were associated significantly with cough during the cold/flu season. Total PM(2.5) was not associated with wheeze or cough. CONCLUSIONS These results suggest that exposure to ambient metals and EC from heating oil and/or traffic at levels characteristic of urban environments may be associated with respiratory symptoms among very young children.

Traffic-Related Particulate Matter and Acute Respiratory Symptoms among New York City Area Adolescents

Background Exposure to traffic-related particulate matter (PM) has been associated with adverse respiratory health outcomes in children. Diesel exhaust particles (DEPs) are a local driver of urban fine PM [aerodynamic diameter ≤ 2.5 μm (PM2.5)]; however, evidence linking ambient DEP exposure to acute respiratory symptoms is relatively sparse, and susceptibilities of urban and asthmatic children are inadequately characterized. Objectives We examined associations of daily ambient black carbon (BC) concentrations, a DEP indicator, with daily respiratory symptoms among asthmatic and nonasthmatic adolescents in New York City (NYC) and a nearby suburban community. Methods BC and PM2.5 were monitored continuously outside three NYC high schools and one suburban high school for 4–6 weeks, and daily symptom data were obtained from 249 subjects (57 asthmatics, 192 nonasthmatics) using diaries. Associations between pollutants and symptoms were characterized using multilevel generalized linear mixed models, and modification by urban residence and asthma status were examined. Results Increases in BC were associated with increased wheeze, shortness of breath, and chest tightness. Multiple lags of nitrogen dioxide (NO2) exposure were associated with symptoms. For several symptoms, associations with BC and NO2 were significantly larger in magnitude among urban subjects and asthmatics compared with suburban subjects and nonasthmatics, respectively. PM2.5 was not consistently associated with increases in symptoms. Conclusions Acute exposures to traffic-related pollutants such as DEPs and/or NO2 may contribute to increased respiratory morbidity among adolescents, and urban residents and asthmatics may be at increased risk. The findings provide support for developing additional strategies to reduce diesel emissions further, especially in populations susceptible because of environment or underlying respiratory disease.

Traffic-related air pollutants and exhaled markers of airway inflammation and oxidative stress in New York City adolescents.

Exposures to ambient diesel exhaust particles have been associated with respiratory symptoms and asthma exacerbations in children; however, epidemiologic evidence linking short-term exposure to ambient diesel exhaust particles with airway inflammation is limited. We conducted a panel study with asthmatic and nonasthmatic adolescents to characterize associations between ambient diesel exhaust particle exposures and exhaled biological markers of airway inflammation and oxidative stress. Over four weeks, exhaled breath condensate was collected twice a week from 18 asthmatics and 18 nonasthmatics (ages 14-19 years) attending two New York City schools and analyzed for pH and 8-isoprostane as indicators of airway inflammation and oxidative stress, respectively. Air concentrations of black carbon, a diesel exhaust particle indicator, were measured outside schools. Air measurements of nitrogen dioxide, ozone, and fine particulate matter were obtained for the closest central monitoring sites. Relationships between ambient pollutants and exhaled biomarkers were characterized using mixed effects models. Among all subjects, increases in 1- to 5-day averages of black carbon were associated with decreases in exhaled breath condensate pH, indicating increased airway inflammation, and increases in 8-isoprostane, indicating increased oxidative stress. Increases in 1- to 5-day averages of nitrogen dioxide were associated with increases in 8-isoprostane. Ozone and fine particulate matter were inconsistently associated with exhaled biomarkers. Associations did not differ between asthmatics and nonasthmatics. The findings indicate that short-term exposure to traffic-related air pollutants may increase airway inflammation and/or oxidative stress in urban youth and provide mechanistic support for associations documented between traffic-related pollutant exposures and respiratory morbidity.

Modeling spatial variations of black carbon particles in an urban highway-building environment.

Highway-building environments are prevalent in metropolitan areas. This paper presents our findings in investigating pollutant transport in a highway-building environment by combing field measurement and numerical simulations. We employ and improve the Comprehensive Turbulent Aerosol Dynamics and Gas Chemistry (CTAG) model to simulate the spatial variations of black carbon (BC) concentrations near highway I-87 and an urban school in the South Bronx, New York. The results of CTAG simulations are evaluated against and agree adequately with the measurements of wind speed, wind directions, and BC concentrations. Our analysis suggests that the BC concentration at the measurement point of the urban school could decrease by 43-54% if roadside buildings were absent. Furthermore, we characterize two generalized conditions in a highway-building environment, i.e., highway-building canyon and highway viaduct-building. The former refers to the canyon between solid highway embankment and roadside buildings, where the spatial profiles of BC depend on the equivalent canyon aspect ratio and flow recirculation. The latter refers to the area between a highway viaduct (i.e., elevated highway with open space underneath) and roadside buildings, where strong flow recirculation is absent and the spatial profiles of BC are determined by the relative heights of the highway and buildings. The two configurations may occur at different locations or in the same location with different wind directions when highway geometry is complex. Our study demonstrates the importance of incorporating highway-building interaction into the assessment of human exposure to near-road air pollution. It also calls for active roles of building and highway designs in mitigating near-road exposure of urban population.

RESPIRATORY IMPACTS OF TRAFFIC-RELATED PARTICLE EXPOSURES ON URBAN YOUTH

Diesel exhaust particles (DEP) produce and or exacerbate airway inflammation in animal models, and have been associated with increased respiratory symptoms and diminished lung function in epidemiology studies. DEP is an important component of fine particulates in many urban areas. We hypothesized that respiratory symptom prevalence would differ across two schools that varied with respect to diesel traffic impacts, and that day to day changes in symptoms would correlate with daily concentrations of black carbon, a surrogate for DEP. One school was located along a major highway in an inner city neighborhood; the other was located in a suburban neighborhood upwind of the city. Air monitoring was carried out on the roofs of the two schools for hourly black carbon concentrations and integrated PM2.5 filters. In addition, a meteorological station was established on each school to assess wind speed and direction. Daily symptoms were assessed over a 4–6 week period at each school, with approximately 40 students participating at each school. On average, elemental carbon (EC) levels were approximately 3 fold higher on the urban schools vs. the suburban. Students from the urban school reported having higher bus and truck traffic in busy street close to their homes. Asthma prevalence (evaluated as ever having had diagnosed asthma by a physician) was higher at the urban school (p 0.007). This prevalence remained higher after controlling for differences in SES and ethnicity. In addition, daily symptoms were analyzed in relation to daily EC concentrations. Results of this study highlight the potential health impacts of emissions from traffic sources in inner city locations. This work was funded by NIEHS under grant ES011379.