New study finds asthma morbidity in children is enhanced in areas with high traffic-related air pollution near the home
Results from a new study by researchers at the University of California Irvine support a growing body of scientific literature indicating that sensitive populations, including children, certain ethnic groups and people of lower socioeconomic status, are more vulnerable to the effects of high exposures to traffic-related air pollution.
The UC Irvine study, which examined the effect of chronic exposure in asthmatic children living in homes near traffic pollution, was led by Ralph J. Delfino, MD, PhD, at the Department of Epidemiology. Asthma is a chronic inflammatory disorder of the airways; chronic inflammation is associated with airway (bronchial) hyperresponsiveness that leads to recurrent episodes of wheezing, breathlessness, chest tightness, and coughing. The study was funded by the California Air Resources Board (ARB) and benefited from funding by the South Coast Air Quality Management District (SCAQMD).
Overall, acute worsening of asthma was associated with short-term elevations of air pollution, particularly in asthmatic children living near high traffic roadways. It is the first study to show increased sensitivity to daily air pollution exposures in asthmatic children living in homes in areas with higher levels of air pollution from traffic, compared to asthmatic children exposed to lower levels of traffic-related pollution.
We found consistent results that acute asthma morbidity is increased in relation to short-term (1 to 7 days) elevations in various indicators of air pollution from fossil fuel combustion sources (including traffic), particularly during the cool seasons. … The analytic results of the importance of the spatial variation in residential TRAP [traffic-related air pollution] imply that associations of asthma hospital morbidity with ambient CO, NO2, NOx, and PM2.5, particularly during the colder seasons, are enhanced among subjects living in areas with high traffic-related air pollution near the home (≤500 m), including ultrafine and fine particles.
This suggests that associations reported in the time-series literature may underestimate effects of ambient air pollutants on asthma morbidity for pediatric populations so exposed as a result of acutely-increased vulnerability or chronically-increased susceptibility.—Delfino et.al
While numerous studies have linked fine particulate pollution (PM2.5) exposures to respiratory illnesses, including asthma, there is a lack of information about the health effects of exposure to particulate pollution from different sources. Assessing the health impacts from exposure to fine particle pollution from a variety of important sources could help ARB to better target sources of PM2.5 for future control measures.
The UC Irvine study consisted of four tasks:
To estimate exposures for children with asthma to primary and secondary organic aerosols.
To assess the risk of emergency department visits and hospital admissions for asthma in children from exposure to both traffic-related particles near their homes and local ambient primary and secondary organic aerosols and O3.
To stratify subjects based on recurrence of hospital encounters in order to assess whether children with multiple encounters show the strongest associations with air pollutants.
To assess effect modification of associations by subject demographic and socioeconomic characteristics.
The study is a case-crossover analysis in which subjects acted as their own control in a conditional logistic regression model adjusted for confounders. Research data included 11,390 emergency room visits and hospital admissions made by 7,954 children ages 0 to 18 between 2000 and 2008.
The UC Davis/California Institute of Technology (UCD/CIT) Source Oriented Chemical Transport Model was used to output daily POA (primary organic aerosols) and SOA (secondary organic aerosols) at a 4x4 km resolution. Model output included size-resolved mass, speciation, and source apportionment. Traffic-related air pollution (TRAP) was assessed using CALINE4 dispersion models at subject residential locations averaged seasonally and weekly.
Key findings included:
Associations of asthma with ambient pollution, including carbon monoxide, oxides of nitrogen and PM2.5, were stronger among children exposed to high traffic-related air pollution at their homes, suggesting this is a vulnerable population.
Hospital encounters for asthma were linked to PM2.5 and ozone in warm months, and with PM2.5, carbon monoxide, nitrogen dioxide and oxides of nitrogen in the cool season.
Hispanic and African American children, as well as those without private insurance, tended to live in areas associated with higher levels of traffic-related air pollution, further increasing their vulnerability.
ARB said that the results of the study, “Risk of Pediatric Asthma Morbidity from Multi-Pollution Exposures,” provide additional evidence to support ARB’s regulations to reduce traffic-related air pollution.
Ralph J. Delfino, Michael J. Kleeman, Jun Wu, Daniel J. Gillen, Bruce Nickerson (2015) “Risk of pediatric asthma morbidity from multipollutant exposures” Final report, California Air Resources Board Contract Nº 10-319