Traffic-related air pollution and the local burden of childhood asthma in Bradford, UK

Background: Asthma is the most common chronic disease in children. Traffic-related air pollution (TRAP) may be an important exposure contributing to its development. In the UK, Bradford is a deprived city suffering from childhood asthma rates higher than national and regional averages and TRAP is of particular concern to the local communities. Aims: We estimated the burden of childhood asthma attributable to air pollution and specifically TRAP in Bradford. Air pollution exposures were estimated using a newly developed full-chain exposure assessment model and an existing land-use regression model (LUR). Methods: We estimated childhood population exposure to NOx and, by conversion, NO2 at the smallest census area level using a newly developed full-chain model knitting together distinct traffic (SATURN), vehicle emission (COPERT) and atmospheric dispersion (ADMS-Urban) models. We compared these estimates with measurements and estimates from ESCAPE's LUR model. Using the UK incidence rate for childhood asthma, meta-analytical exposure-response functions, and estimates from the two exposure models, we estimated annual number of asthma cases attributable to NO2 and NOx in Bradford, and annual number of asthma cases specifically attributable to traffic. Results: The annual average census tract levels of NO2 and NOx estimated using the full-chain model were 15.41 and 25.68 μg/m3, respectively. On average, 2.75 μg/m3 NO2 and 4.59 μg/m3 NOx were specifically contributed by traffic, without minor roads and cold starts. The annual average census tract levels of NO2 and NOx estimated using the LUR model were 21.93 and 35.60 μg/m3, respectively. The results indicated that up to 687 (or 38% of all) annual childhood asthma cases in Bradford may be attributable to air pollution. Up to 109 cases (6%) and 219 cases (12%) may be specifically attributable to TRAP, with and without minor roads and cold starts, espectively. Conclusions: This is the first study undertaking full-chain health impact assessment of TRAP and childhood asthma in a disadvantaged population with public concern about TRAP. It further adds to scarce literature exploring the impact of different exposure assessments. In conservative estimates, air pollution and TRAP are estimated to cause a large, but largely preventable, childhood asthma burden. Future progress with childhood asthma requires a move beyond the prevalent disease control-based approach toward asthma prevention