# Improving PM2.5 Concentration Forecast with the Identification of Temperature Inversion
## 2 Literature Review  
### Analysis of PM\({}_{2.5}\) Concentration in Taiwan  
The west coast of central and southern Taiwan, which accommodates petrochemical complexes, coal combustion power plants, industrial parks, and national highways, is notorious as one of the heaviest-polluting regions in Taiwan [6]. Moreover, the PM\({}_{2.5}\)/PM\({}_{10}\) ratio for central and southern Taiwan is around 61-67%, which is higher than the 54-59% measured for northern Taiwan [7]. These studies show that the air pollution in central and southern Taiwan is not only higher than that in northern Taiwan, but its apportionment is also more harmful to human health. Several studies have been conducted in these regions to explore the pollution apportionment and transportation routes. The back trajectory model was applied in [8] and it was found that winter aerosols concentrate at Changhua county because of the northwestern wind passing over Mongolia, northern China, and central-western Taiwan. Meanwhile, the southwestern wind in spring and summer blows the soil and crustal elements in the air from the river banks and carries the emissions from coal and oil combusions at the petrochemical complex and the power plants. A case study of 22 polycyclic aromatic hydrocarbons (PAHs) was conducted in the same place [2]. The receptor-based apportionment model is applied to analyze the PAH compounds. The lifetime excess cancer risk (ECR) from inhalation exposure to PAHs is \(4.7\times 10^{-5}\), which is nearly fifty times higher than the guideline limit (\(10^{-6}\)) released by United States Environmental Protection Agency (USA EPA). [PERSON] and [PERSON] [6] studied the meteorological influence on PM\({}_{2.5}\) concentrations in Yunlin County which is near to two large-scale coal-fired power plants and one petrochemical complex. It is shown that the weather pattern with a continental anticyclone or a stagnant local circulation results in high PM\({}_{2.5}\) concentrations from industrial production. Kaohsiung is another southern Taiwanese city which has high pollution concentrations due to industrialization. [PERSON] et al. [9] studied the factors most influencing PM\({}_{2.5}\) intensities in Kaohsiung and found that the most abundant PM\({}_{2.5}\) chemical components were SO\({}_{4}^{2-}\), NO\({}_{3}^{-}\), elemental and organic carbon. SO\({}_{4}^{2-}\) constitutes 29.8% of the PM\({}_{2.5}\) mass and it is formed by the oxidation of SO\({}_{2}\) emitted from diesel vehicles and coal/oil combustion which are strongly related to oil and steel industries in Kaohsiung. A population-based study [10] conducted by Chang Gung Memorial Hospital (the largest medical service system in Taiwan) in 2012 showed that the number of emergency room visits for respiratory disease are highly associated with the increase in ambient PM\({}_{2.5}\) concentrations. This phenomenon is more significant for southern Taiwanese districts. Aside from the industrial production and traffic emissions, some particular anthropogenic activities occasionally trigger pollution events. On every 9 January of the lunar calendar, Taoists burn incense and joss papers at homes and temples to celebrate the birthday of the First God. A case study [11] has shown that there is a rapid increase of PM\({}_{2.5}\) concentrations in almost all residential regions of Taiwan during the religion ritual. In Chinese custom, families gather outdoors to attend moon-watching activities at the Mid-Autumn Festival (MAF) Day (15 August of the lunar calendar). In Taiwan, the moon-watching activities are a barbecue festival, and many people gather at households or in the streets. [PERSON] et al. [12] studied the relationship between the MAF phenomenon and the PM\({}_{2.5}\) variations. The result shows that the PM\({}_{2.5}\) mass concentration is the highest during the MAF, followed by the period leading up to the MAF, and it is the lowest after the MAF.