Results: The average concentration of particulate matter was 181.3 g/m3 and 97.1g/m3 before and after the ban respectively. The total numbers of ER visits for pediatric patients were 6453 and 6865 in period 1 and period 2 respectively. Of those, 313 were due to asthma in period 1 and 223 in period 2. The number of asthma-related visits was significantly reduced during period 2. When we looked at the monthly distribution of visits, asthma-related visits were significantly reduced during October, November and December of period 2 compared to the same months of period 1, while it was significantly increased during the month of June.
Discussion: This study shows that a ban on diesel engine resulted in a decrease in the air concentration of particulate matter and was associated with a reduction in the number of emergency room visits for acute asthma. This reduction was most marked during the season of viral respiratory infections. We postulate that a reduction in the concentration of air pollutants was protective against viral-induced asthma exacerbations.