We investigated whether asthma attacks in asthmatic children were caused by short-term exposure to particulate matter(PM)_2.5.

Subjects were 411 patients who received inhalation therapy in National Fukuoka Hospital, from March to May 2013. All subjects were outpatients. We surveyed the air quality measurement results in the stations closest to the address of the patients. Data were used from the City of Fukuoka website data on air pollution. We carried out a case-crossover study and compared PM_2.5 concentration between 7 days after asthma attack occurred and the day asthma attack occurred and 1, 2 and 3 days before asthma attack occurred.

Highest hourly concentration of the day (OR 1.013, 95%CI 1.000-1.025) showed a significant association with 1 day before PM_2.5 concentration statistically. And 0-1 year-old infants were more vulnerable to the highest concentration of 1 day before PM_2.5 concentration(P < 0.05). Average concentration of NO₂ and O₃ and asthma attack also showed a significant association.

Maximal daily PM_2.5 concentrations within 24 hours prior to the attack affect asthma exacerbation. 0-1 year-old infants are particularly vulnerable to PM_2.5 concentration. Asthma exacerbation is aggravated by NO₂ and O₃ concentration on the day of the asthma attack.