Size and seasonal distributions of airborne bioaerosols in commuting trains

Aerobiological studies in commuting trains in northern Taiwan were carried out from August, 2007 until July, 2008. Two six-stage (>7 μm, 4.7∼7 μm, 3.3∼4.7 μm, 2.1∼3.3 μm, 1.1∼2.1 μm, 0.65∼1.1 μm) cascade impactors of 400 orifices were used to collect viable bacteria and fungi, respectively. The levels of carbon monoxide (CO), carbon dioxide (CO2), formaldehyde (HCHO), temperature, and relative humidity in the commuting trains were also recorded during the sampling period. Results show that bacterial concentrations ranged from 25 to 1530 CFU m−3, and averaged 417 CFU m−3. The fungal concentrations ranged from 45 to 1906 CFU m−3, and averaged 413 CFU m−3. Additionally, the highest fractions occurred in the fifth stage (1.1∼2.1 μm) for both bacteria and fungi. The respirable fractions, Rb and Rf, for bacteria and fungi were 62.8% and 81.4%, respectively, which are higher than those in other studies. Furthermore, the bacterial concentration reached its highest level in autumn, and its lowest level in winter. However, the fungal concentration was highest in spring and lowest in winter. Though the total bacterial or fungal concentration did not exceed the recommendation standard in Taiwan, the relatively high respirable fraction in commuting trains probably implies a higher adverse health risk for sensitive commuters. This study further conducted multiple regression analysis to determine the relationship of various stage fractions of airborne bacteria and fungi with indoor air pollutants (CO and HCHO) and environmental parameters (CO2, temperature, and relative humidity). The correlation coefficients of multiple regression analysis for total bacteria and fungi concentrations with indoor air pollutants and environmental parameters were 0.707 (p < 0.00376) and 0.612 (p < 0.00471), respectively. There are currently no formally regulated laws for indoor air quality (IAQ) in Taiwan, and this preliminary study can provide references to the Taiwan government on IAQ management.