A study on the speciation of NOy and its implications for the atmospheric oxidation capacity in Taichung, Taiwan

This study investigates the speciation of the total oxides of nitrogen (NO_y) in Taichung, Taiwan, which is a highly developed urban area. Positive correlation between the daily mean of PM_2.5 and the daytime (8-hr) mean of O₃ shows that photochemical reactions are the major mechanisms underlying the observed air pollution phenomena. Furthermore, a strong linear correlation between the ambient levels of PM_2.5 and NO_z (NO_y-NO_x) found during the high PM episodes evidences that the atmospheric oxidation of NO_x is the key processes leading to the air quality deterioration in the urban area. An in-depth analysis on the variations in the NO_y composition as well as in the ozone precursors (VOCs and NOx) will be presented, and the significance of atmospheric oxidation capacity in the urban air quality is highlighted.