;In this study, data collected from Pinglin air quality station are using to investigate the correlation of air pollution from road transport with suburban valley topographic air quality. The research aims include understanding the Pinglin area air quality changes in recent years, analyzing air quality in weekdays and holidays, investigate the air pollution that may influence from neighboring regions and explore on the contribution and characteristics of secondary aerosol pollution by fractional actinic intensity.
According to the results from the monitoring of Pinglin air quality station from 2013 to 2017, the gaseous pollutants NOx, SO2, and CO were all far below the air quality standards, while the particulate pollutants TSP, PM10, and PM2.5 were also usually been lower than the standards either, shows that the air quality in the area is in good condition. To further compare NOx and CO concentrations, when the daily traffic volume (using Pinglin interchange car numbers as the traffic assessment indicator ) is in the fourth quartile of all traffic volume, the corresponding average concentration is greater than the daily traffic volume in the first quartile about 20.0% and 4.5% higher. Also, compared with the correlation of NOx and CO, when the relative humidity is less than 70%, the correlation coefficient r of NOx and CO concentration is 0.61 (R2=0.369) and it is moderately correlated. However, as the ambient humidity increases, the correlation coefficient between NOx and CO are getting lower. The decrease in r may be due to the fact that when the humidity in the environment is higher, NO2 in NOx is more soluble in water than CO and forms nitric acid and nitrous acid. Therefore, when the relative humidity is lower, the correlation between the NOx and CO concentrations is higher.
Based on the assessment of the air quality that may be affected by the neighboring regions, comparing the EPA′s Keelung air quality station on the north side of Pinglin with different wind speeds, the result shows that when the average daily wind speed at the Keelung station increases, the PM10 concentrations at the two stations in Keelung and Pinglin are more correlated with each other. Therefore, in addition to local traffic pollution emissions, when the wind speed in neighboring areas is high, it may also bring pollutants located in the upwind area into Pinglin.
In addition, the secondary aerosol evaluation results from the graded actinic intensity shows that when the average O3 concentration (based on the O3 average of the EPA Keelung, Xizhi, and Yilan stations) is less than 40 ppb from June to August, the correlation between PM10 and CO in Pinglin station is better (r=0.64, R2=0.416), so it is inferred that the secondary aerosol generated by the photochemical reaction may also increase the suspended particulate concentration (PM10, PM2.5) in the Pinglin region. In summer, high sunlight intensity and high ozone concentration may have a greater influence.