Regional and Urban Air Quality in East Asia: Taiwan

Abstract

AbstractTaiwan is located downwind of a variety of regional sources of air pollutants transported particularly during the seasons of East Asian winter monsoon. In addition, western Taiwan is a highly populated and urbanized/industrialized area, where the air quality is subject to the influences of local air pollution. To mitigate the impacts of air pollution, a series of control strategies have been developed and enforced during the last couple of decades, which evolved conceptually from being technically oriented in the 1970s to being cost-benefit oriented since 2003. Along with the efforts in controlling air pollutants emitted from various sources, a significant improvement in air quality has been evidenced by monitoring data. Here, the time series of the ambient levels of respective criteria air pollutants in Taiwan for the period of 1996–2020 are presented. It is noteworthy that the ambient levels of O3 in all air quality districts in Taiwan have almost leveled off in the past 25 years, while all the other criteria air pollutants (PM10, PM2.5, CO, NOx, and SO2) exhibited consistently a declining trend. Moreover, the data on the chemical speciation of PM2.5 shows that the secondary aerosols (i.e., ammonium, sulfate, nitrate, and organic matter) remained the major constituents of PM2.5, which did not change significantly in the last two decades. Given the observed facts, it is inferred that the air quality in Taiwan is strongly subject to the impacts of photochemical reactions. As a result, in addition to the elevated ozone level, the production of secondary organic aerosols and ultrafine particles, as well as their impacts on atmospheric visibility, are expected to be major challenges in the near future.