Analysis of exceeding the standard of air pollutants in Wuhan
It can be seen from equation 1 that the OSM not only reflects whether the pollutant exceeds the standard but also reflects the degree of the pollutant exceeding the standard. When the OSM is positive, it means the pollutant is over-standard. When it is negative, it means that the pollutant meets the requirements and does not exceed the standard. The greater the OSM, the greater the degree of pollutants exceeding the standard. Applying the collected sample data to calculate the OSM of the corresponding air pollutants in Wuhan, the results are shown in Figure 1. PM2.5, PM10, SO2, and NO2,
As shown in Figure 1, analysis of the overall change trend revealed that the OSM of most of the pollutants have decreased compared with 2014, that is, the concentration of pollutants has dropped. Compared with last year, the OSM of O3 in the first month and the SO2 and O3 in the second month have increased, but it is still negative, which means that although the concentration of these pollutants has increased this year, but still meet the standards. The OSM of CO is reduced and remains negative, that is, the concentration of CO is still in compliance with the standard. The OSM of NO2 has decreased, that is, the concentration has decreased, and in the past two years, there has been a tendency to transition to the standard state. As for PM10 and PM2.5, although their OSM decreased, they only showed a positive value in February 2020. Over the past seven years, the OSM of PM10 and PM2.5 has been relatively large, which means that the main pollutant in Wuhan is PM10 and PM2.5 (PM). Hence, this article focuses on the GRA of PM.
Grey correlation analysis of air quality in Wuhan
To explore the feasibility of applying GRA to analyze the change of air pollutant concentration, this paper conducted a grey correlation analysis on the concentration change of the main pollutants-PM in Wuhan.
In this article, regarding the concentration limits as a reference sequence, and the pollutant concentrations on the statistics date as comparative sequences, the GRD of them directly reflects the air quality. The greater the GRD, the better the air quality. This article takes PM as an example for GRA, and the results are shown in Figure 2.
As shown in Figure 2, according to the change trends of GRD, it is found that the GRD of PM has increased significantly compared with 2014. Comparing with last year, the situation is the same. These trends are consistent with the results of OSM analysis, which shows that it is feasible to apply GRA to analyze the change trend of pollutants