Effects of chemical components and size fractions of particulate matters on visibility

Abstract

Airborne particulate matters were an important component of ambient air because of its significant effects on air quality, human health, regional visibility, and global climate change. High particulate matters were an important factor that causes low visibility. In this study, I investigated the relationships between visibility and PM2.5 concentration in the Tainan metropolitan area, southern Taiwan, from 2010 to 2018. The annual average PM2.5 concentration decreased from 37.0±19.4 μg/m3 in 2010 to 22.4±11.8 μg/m3 in 2018, while the annual average visibility increased from 8.53±4.56 km to 15.8±10.3 km in 2018. The 9-year annual average visibility was exponentially increased with the decreased annual average PM2.5 mass concentrations, expressing as Vis=587.2×PM2.5 -1.21 (where the unit in Vis is km and in PM2.5 is μg/m3, r value= -0.860). From 2010 to 2018, the visibility of the four seasons was the best in summer, with an average of 15.1±7.54 km, while the PM2.5 concentration in summer was the lowest, averaging only 15.5±7.88 μg/m3. The worst visibility was in the winter, with an average of only 6.62±6.18 km, while winter PM2.5 was the highest concentration, with an average of 40.5±16.9 μg/m3. Season visibility was also negatively correlated with PM2.5 concentration, expressing as Vis=157.9×PM2.5 -0.860 (r value= -0.866). The increasing trend in visibility was significantly related to the decreased concentration in PM2.5. The size distributions and concentrations of chemical composition during the Moon Festival such as nss-SO4 2- (2.9889±0.0300 μg/m3), NH4 + (0.9275±0.1131 μg/m3), and oxalate (0.0674±0.0227 μg/m3), respectively. Chemical compositions that mention above were major chemical composition effect on visibility due to photochemical reaction and similarly peak concentrations of these species occurred at 0.56 μm in the submicron droplet mode.