The Effects of Policy-Driven Air Quality Improvements on Children's Respiratory Health

Introduction: Ambient air pollution causes substantial morbidity and mortality in the United States and worldwide. To reduce this burden of adverse health effects, a broad array of strategies to reduce ambient air pollution has been developed and applied over past decades to achieve substantial reductions in ambient air pollution levels. This has been especially true in California, where the improvement of air quality has been a major focus for more than 50 years. Direct links between regulatory policies, changes in ambient pollutant concentrations, and improvements in public health have not been extensively documented. Data from the Children's Health Study (CHS), a multiyear study of children's respiratory health development, offered a unique opportunity to evaluate the effects of long-term reductions in air pollution on children's health.

Methods: We assessed whether changes in ambient air quality and emissions were reflected in three important indices of children's respiratory health: lung-function growth, lung-function level, and bronchitic symptoms. To make the best use of available data, these analyses were performed across the longest chronological period and largest CHS population available for the respective lung-function or bronchitic symptoms data sets. During field study operations over the course of the CHS, children's health status was documented annually by testing lung-function performance and the completion of standardized questionnaires covering a broad range of respiratory symptoms. Air quality data for the periods of interest were obtained from community monitoring stations, which operated in collaboration with regional air monitoring networks over the 20-year study time frame. Over the 20-year sampling period, common protocols were applied to collect data across the three cohorts of children. Each cohort's data set was assessed to investigate the relationship between temporal changes in lung-function development, prevalence of bronchitic symptoms, and ambient air pollution concentrations during a similar, vulnerable adolescent growth period (age 11 to 15 years). Analyses were performed separately for particulate matter ≤10 µm in aerodynamic diameter (PM₁₀), particulate matter ≤2.5 µm in aerodynamic diameter (PM₂.₅), ozone (O₃), and nitrogen dioxide (NO₂). Emissions data and regulatory policies were collected from the staff of state and regional regulatory agencies, modeling estimates, and archived reports.

Results: Emissions in the regions of California studied during the 20-year period decreased by 54% for oxides of nitrogen (NOₓ), 65% for reactive organic gases (ROG), 21% for PM₂.₅, and 15% for PM₁₀. These reductions occurred despite a concurrent 22% increase in population and a 38% increase in motor vehicle miles driven during that time frame. Air quality improved over the same time frame, with reductions in NO₂ and PM₂.₅ in virtually all of the CHS communities. Annual average NO₂ decreased by about 53% (from ~41 to 19 ppb) in the highest NO₂-reporting community (Upland) and by about 28% (from ~10 to 7 ppb) in one of the lowest NO₂-reporting communities (Santa Maria). Reductions in annual average PM₂.₅ concentrations ranged from 54% (~33 to 15 µg/m³) in the community with the highest concentration (Mira Loma) to 13% (~9 to 8 µg/m³) in a community with one of the lowest concentrations (Santa Maria). Improvements in PM₁₀ and O₃ (measured during eight daytime hours, 10 AM to 6 PM) were most evident in the CHS communities that initially had the highest levels of PM and O₃. Trends in annual average NO₂, PM₂.₅, and PM₁₀ ambient air concentrations in the communities with higher-pollution levels were generally consistent with observed trends in NOₓ, ROG, PM₂.₅, and PM₁₀ emissions.

Conclusions: This study provides evidence that multiyear improvements in air quality and emissions, primarily driven through a broad array of science-based regulatory policy initiatives, have resulted in improved public health outcomes. Our study demonstrates that improvements in air quality, brought about by science-based regulatory actions, are associated with improved respiratory health in children. These respiratory health metrics include reductions in respiratory symptoms and improvements in lung-function development in a population widely accepted to be at risk and highly vulnerable to the effects of air pollution. Our research findings underscore the importance of sustained air regulatory efforts as an effective means of achieving improved respiratory health in communities and regions affected by airborne pollution.