Long-term (2005–2015) trends analysis of OMI retrieved NO2 columns in Taiwan

Özet

In this study, the monthly data retrieved from the Ozone Monitoring Instrument (OMI) have been used to estimate long-term trends of NO2 (2005–2015) in the entire Taiwan as well as in five representative city areas of Taiwan. The long-term NO2 data have been used for trend analysis and evaluated to find the extent of the effects of NOx emission reduction and related environmental regulations on the NO2 trend. Desirable policies and strategies for further reducing NOx emission have been also discussed. The corresponding reductions are 15–37% for the five city areas and 24% for the entire Taiwan over the 10-yr span. Clearly, the governmental policies/ measures enacted during this 10-yr period are responsible for the reduction of tropospheric NO2 column values. The OMI NO2 column values of four cities (i.e., Taipei, Taichung, Kaohsiung, and Douliu) are relatively highly correlated (r=0.70–0.95), indicating the cities have similar emission sources. Furthermore, the correlations between observed OMI NO2 columns and their emission NOx are all significant in the three metropolitan cities and the entire Taiwan (r=0.66–0.89). The correlation of OMI-based NO2 VCDs and ground-based NO2 levels is high in Kaohsiung (r=0.82) and moderate in Taipei and Taichung (r=0.60 and 0.59, respectively). The satellite retrieved OMI NO2 data clearly indicate their usefulness in evaluating decreasing trend of the NO2, a precursor gas of PM2.5 during the 10-yr span for the entire region of Taiwan and for the selected five cities.