PM2.5 was collected in Nagoya, a major city in the central part of Japan (latitude 35°18?N, longitude 136°91?E; Fig. 1). Nagoya has a MK-2461 of more than 2,200,000. Sampling of PM2.5 was conducted for 23.5 h using a low-volume air sampler (FRM-2000, R&P) from April 2003 to March 2004 at an urban site in Nagoya. Two PM2.5 samples were collected in parallel, one onto polytetrafluoroethylene (PTFE) filters (TK15-G3M, Pallflex) and the other onto quartz-fiber filters (2500QAT-UP, Pallflex); antigens samples were collected at a flow rate of 16.7 L min− 1. The quartz-fiber filters were pre-heated at 900 °C for 3 h to remove residual carbon prior to sampling. The PTFE filters were conditioned in a constant temperature and humidity room (20 ± 0.5 °C, 50 ± 3% relative humidity (RH)) for 24 h prior to weighing. Then, these samples were stored at − 25 °C in a freezer until further analysis.