A Californian-based study has looked in detail at air quality and the impact of traffic-related air pollution on premature¹ birth. Published in BioMed Central's open access journal Environmental Health, results from this study show that traffic-related air pollution, especially polycyclic aromatic² hydrocarbons³ (PAH多环芳烃), is associated with up to a 30% increase in premature births, and that seasonal⁴ changes and vicinity（临近，附近） to the coast affected⁵ concentration of toxic⁶ pollutants⁸ in the air. The study, based at the University of California, looked at 100,000 births, within a five mile radius⁹ of air quality monitoring stations. The study evaluated births spanning a 22 month period from June 2004, and used information provided by the California Department of Health about the births and the mothers, in addition to air pollution information from monitoring stations which measure concentrations of airborne toxic pollutants.

The researchers were able to analyse and compare exposures using three different information sources: government "criteria¹⁰ pollutant⁷" monitoring stations (including carbon monoxide, nitrogen dioxide, ozone¹¹, and fine particulate¹² matter), a traffic pollution model (Land Use Regression), and data about toxic chemicals collected by the South Coast Air Quality Management District. Once integrated, these data provided a new level of detail about the concentrations and location of individual pollutants. All statistical¹³ models were adjusted for maternal¹⁴ age, race/ethnicity, education and parity¹⁵.

Some pollutants were area specific, relating to industry and urbanization. However, overall exposure to critical pollutants such as PAH resulted in up to a 30% increase in the risk of premature birth. Other toxic substances, such as benzene（苯） and fine particulate matter from diesel¹⁶（柴油） fumes¹⁷ were associated with a 10% increase, while ammonium nitrate fine particles were associated with a 21% increase in premature birth. Concentrations of these pollutants were higher in winter and lower in coastal¹⁸ areas, indicating that local weather patterns played an important part in the dispersal of pollutants.

Dr Beate Ritz said, "Air pollution is known to be associated with low birth weight and premature birth. Our results show that traffic-related PAH are of special concern as pollutants, and that PAH sources besides traffic contributed to premature birth. The increase in premature birth risk due to ammonium nitrate（硝酸铵） particles suggests secondary pollutants are also negatively impacting the health of unborn babies. To reduce the effects of these pollutants on public health, it is important that accurate modeling of local and regional spatial¹⁹ and temporal air pollution be incorporated into pollution policies."