An Integrated Approach to Characterize Temporal-Spatial Variations in PM2.5 Concentrations at the Ground Level and Its Implication on Health Impact Assessments

Although PM2.5 concentrations measured by the governmental air quality monitoring station (AQMS) have been widely used for conducting exposure assessments, it might be not able to reflect the residents' exposures, especially for those associated with ground emissions. The present study was conducted in a city area for 1 year. A mobile monitoring station (MMS) was established to measure the PM2.5 concentrations at the ground level. A significant linear relationship (R-2 = 0.53) was found between the MMS-measured concentrations and the corresponding concentrations obtained from the AQMS (15 m above the ground level), and the former was similar to 1.11 times (95% CI: 1.08-1.15) in magnitude higher than that of the latter. To characterize the spatial variation of the area, the MMS-measured values were further classified into three different regions. A consistent trend was found in the present study for all collected data as industry region approximately equal to or the image of urban region > harbor region. The aforementioned results clearly indicate that the residents' ambient PM2.5 exposures do have spatial differences. Seven-year AQMS-measured concentrations (i.e., AQMS(7-yr)) were used to establish the long-term PM2.5 concentrations at the ground level (i.e., MMS7-yr) of the three different regions using the linear regression equations obtained from the MMS and AQMS. Health impact functions and local health data were used to quantify the PM2.5-attributable health burden for both AQMS(7-yr) and MMS7-yr, respectively. Results show that the former is similar to 10.4% lower in magnitude than the latter in the estimated lung cancer death attributed fraction (AF). In particular, the decrease of unit PM2.5 (mu g/m(3)) would lead to a 0.75 and 0.71% decrease in the estimated AF of lung cancer death for AQMS(7-yr) and MMS7-yr, respectively. As a result, directly using AQMS(7-yr) would lead to an underestimation of similar to 1,000 lung cancer deaths annually in Taiwan in comparison with those using MMS7-yr. The aforementioned results clearly indicate the importance of characterizing ground-level exposures for assessing the health impact of residents, and the methodology developed by the present study would be helpful for solving the aforementioned problem.