MAX-DOAS measurements of air pollution on the northern tip of Taiwan

Wind and weather in Taiwan are strongly influenced by the monsoons. Taiwan is on the lee side of the Asian winter monsoon, originating on the Asian continent. It receives continental air masses transported by the monsoon, thus air pollutants originating in the eastern and northern parts of China. While polluted air reaches Taiwan during winter monsoon, clean air masses from the remote western North Pacific are predominant in summer, making Taiwan an ideal location to investigate variations in atmospheric composition due to the monsoons. In addition to that, the monsoons themselves are also subject to regional climate changes in the future.

Since June 2023, a Multi-AXis-DOAS (MAX-DOAS) instrument has been installed at the Cape Fuguei Research Station (CAFE) at the northernmost point of Taiwan, measuring vertical and horizontal distributions of trace gases, including NO₂, SO₂, HCHO, and aerosols. The measurements aim to investigate local air pollution and study the impact of pollution export from mainland China on tropospheric composition and local air quality. The MAX-DOAS and the other measurements at the site will also be very valuable in the validation of the data products from the GEMS satellite.

The measurements are part of the project “Investigation of Pollution Transport to Taiwan” (IPToT), which has been established as a cooperation between the Insitute of Environmental Physics (IUP) of the University of Bremen (Germany) and the Research Center for Environmental Changes of the Academia Sinica (Taiwan), funded by the DFG (Deutsche Forschungsgemeinschaft).

Here, we present first MAX-DOAS observations and retrieved profiles of NO₂, SO₂, HCHO, and aerosols at this new station and compare them to collocated in-situ and (aerosol) LIDAR measurements. The data are evaluated for diurnal and weekly pollution signals and the dependency on the prevailing wind direction. A first comparison to satellite measurements is also shown.