Incorporating long-term satellite-based aerosol optical depth, localized land use data, and meteorological variables to estimate ground-level PM concentrations in Taiwan from 2005 to 2015.

Satellite-based aerosol optical depth (AOD) is now comprehensively applied to estimate ground-level concentrations of fine particulate matter (PM). This study aimed to construct the AOD-PM estimation models over Taiwan. The AOD-PM modeling in Taiwan island is challenging owing to heterogeneous land use, complex topography, and humid tropical to subtropical climate conditions with frequent cloud cover and prolonged rainy season. The AOD retrievals from the MODerate resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua satellites were combined with the meteorological variables from reanalysis data and high resolution localized land use variables to estimate PM over Taiwan island from 2005 to 2015. Ten-fold cross validation was carried out and the residuals of the estimation model at various locations and seasons are assessed. The cross validation (CV) R based on monitoring stations were 0.66 and 0.66, with CV root mean square errors of 14.0 μg/m (34%) and 12.9 μg/m (33%), respectively, for models based on Terra and Aqua AOD. The results provided PM estimations at locations without surface stations. The estimation revealed PM concentration hotspots in the central and southern part of the western plain areas, particularly in winter and spring. The annual average of estimated PM concentrations over Taiwan consistently declined during 2005-2015. The AOD-PM model is a reliable and validated method for estimating PM concentrations at locations without monitoring stations in Taiwan, which is crucial for epidemiological study and for the assessment of air quality control policy.