Variation trends and principal component analysis of nitrogen oxide emissions from motor vehicles in Wuhan City from 2012 to 2017.

In addition to fine particulate matter and oxysulfides, nitrogen oxides (NOx) emitted by motor vehicles are among the most important pollutants affecting air quality and public health in those urban areas where centralized heating and chemical industry absent. We utilized correlation analysis (pearson correlation coefficient and spearman correlation coefficient) and principal component analysis (PCA) to identify the variation trends and main causes of NOx emissions from motor vehicles in Wuhan City. We considered the total number of motor vehicles (TN), ratios of motor vehicles of different emission standards (RE), rations of labeled motor vehicles (RL), and rations of motor vehicles' fuel types (RF). The results show that: 1) with an increase in the total amount of motor vehicles, the NOx emissions of motor vehicles have been decreasing since 2015; 2) three sub-categories (the ratio of the State III emission standard, the ration of yellow label diesel vehicles, and the ration of diesel vehicles) were recognized as key indexes of PE, PL and PF, respectively, in the PCA; 3) a new parameter, the ESindex is proposed as an index to represent the variation trend of the NOx emissions of motor vehicles in Wuhan City.