Characterization of dilution conditions for diesel nanoparticle inhalation studies.
Diesel exhaust nanoparticles easily coagulate during transportation from the engine to the inhalation chamber, depending on concentrations and residence times. Although dilution is effective in suppressing coagulation growth of nanoparticles, volatile organic carbon (OC) evaporates as a result of dilution. Thus, the design of an inhalation facility to investigate the health effects of nanoparticle-rich exhaust is important. In this study, we determined the optimum dilution conditions in consideration of coagulation growth and evaporation of OC for inhalation studies of nanoparticle-rich diesel exhaust. We found that a short residence time prevented coagulation growth in the primary dilution tunnel after the primary dilution or before the diluted exhaust reached the inhalation chamber after the secondary dilution. However, due to the longer residence time in the inhalation chamber, the coagulation growth occurred in the inhalation chamber depending on secondary dilution ratio which controlled exposure dose (particle concentration in the inhalation chamber). We determined that the secondary dilution ratio for the high-concentration chamber should be around 4.5 times to prevent coagulation growth and to obtain the desired exposure dose. We also found that the loss of OC was relatively independent of the secondary dilution ratio when the secondary dilution ratio was more than 10 times because it seemed to reach a gas-particle equilibrium in the inhalation chamber. We therefore set the secondary dilution ratios for the middle- and low-concentration chambers to 13.5 and 40.5 times, respectively.
Fujitani
Yuji
Y
National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Japan. fujitani.yuji@nies.go.jp
Hirano
Seishiro
S
Kobayashi
Shinji
S
Tanabe
Kiyoshi
K
Suzuki
Akira
A
Furuyama
Akiko
A
Kobayashi
Takahiro
T
D000280:Administration, Inhalation; D001273:Atmosphere Exposure Chambers; D002244:Carbon / Q000008:administration & dosage / Q000737:chemistry; D007201:Indicator Dilution Techniques; D019570:Inhalation Exposure; D053758:Nanoparticles / Q000008:administration & dosage / Q000032:analysis*; D010316:Particle Size; D001335:Vehicle Emissions / Q000032:analysis*; D014835:Volatilization
D001335:Vehicle Emissions; D002244:Carbon