Experimental determination of reactive oxygen species in Taipei aerosols

The concentrations of reactive oxygen species (ROS) in various particle siz e fractions were determined for the Taipei aerosols and for particles in ve hicular exhausts. Sampling of particles was carried out at a sidewalk and a n underpass by a cascade impactor. The sampling duration was 3 h during day time at the sidewalk and 20-30 min during rush hours in the underpass. The collected particles were treated with a non-fluorescent probe dichlorofluor escin (DCFH2) that forms highly fluorescent dichlorofluorescin (DCF) when o xidized in the presence of ROS. Data on the fluorescence intensity of DCF w ere converted into equivalent hydrogen peroxide concentrations using calibr ation curves obtained from H2O2 assay. The equivalent H2O2 concentration wa s used as an indicator for the reactivity of ROS in particles. The concentr ation of ROS in ambient particles had good correlations with the intensity of photochemical reactions. The correlation coefficient between the ROS con centration and the O-3 concentration was higher for smaller particles. This indicates that the intensity of photochemical reactions is a major factor affecting ROS concentration in smaller particles, especially in ultrafine p articles (aerodynamic diameter <0.18 mum). Moreover, for the same mass conc entrations of particles, the content of ROS was found to be higher in small er particles, except for ultrafine particles. This pattern was observed onl y in the particles sampled at the sidewalk, and not those in the underpass. The results suggest that, for the same particle mass concentration, smalle r particles in ambient aerosols have higher ROS contents and, therefore, ma y have a greater potential to cause damage to the pulmonary cells. (C) 2001 Elsevier Science Ltd. All rights reserved.