## 2 Study Area and Data Analysis
### Data and Analysis  
Particulate matter concentrations of PM\({}_{10}\), PM\({}_{2.5}\) and PM\({}_{1}\) were measured by a German GRIMM-1107 Dust Meter (approved by the Ministry of Environment, Korean Government), which was installed at the Gangwon Meteorological Administration (128.9\({}^{\circ}\) longitude; 37.75\({}^{\circ}\) latitude; 20 m above sea level) located in the downtown area of Gangneung city. The dust meter, devised to measure 15 sizes of dust particles (>0.3 \(\upmu\)m to 20.0 \(\upmu\)m), can measure the concentration of particulate matter (\(\upmu\)g/m\({}^{3}\)) at a 5-min interval, and the concentrations are again summed into PM\({}_{10}\) (the total amount of a particle size of 10 \(\upmu\)m or less), PM\({}_{2.5}\) (with the total amount of 2.5 \(\upmu\)m size or less), and PM\({}_{1}\) (with the total amounts of 1 \(\upmu\)m size or less). Then the concentrations of PM\({}_{10}\), PM\({}_{2.5}\), and PM\({}_{1}\) are recalculated as the 1 h-averaged value and these concentrations were used as the basic data for this study.  
Hourly based PM\({}_{10}\) and PM\({}_{2.5}\) data measured at Beijing city, China (especially, the South-3 rd ring road observation point) were acquired through the internet with a website address ([[https://quotsoft.net/air/](https://quotsoft.net/air/)]([https://quotsoft.net/air/](https://quotsoft.net/air/)) or [[http://www.bjmemc.com.cn/](http://www.bjmemc.com.cn/)]([http://www.bjmemc.com.cn/](http://www.bjmemc.com.cn/)) accessed on 20 March 2021). Since most of the yellow dusts, originated from the Gobi Desert and arid Inner Mongolia, pass through Beijing city to the downwind region by the northerly wind or northwesterly wind and reach Gangneung city in the eastern coast of Korea, the PM concentrations at Gangneung city are directly affected by the PM concentrations of Beijing city, still containing much of the dusts originated from the desert and arid area of northern China.  
Normally, the transport time of the dusts of Beijing city to Gangneung city takes approximately two days under a relatively strong northwesterly wind of about 8 m/s to 10 m/s (i.e., over 10 m/s in the origin of the yellow dust storm), because the distance between Beijing city and Gangneung city is about 1400 km. Thus, in order to investigate the effect of PMs of Beijing city on the air quality at Gangneung city, two days early pollution data of Beijing are needed. Hourly based meteorological data measured at Gangneung, Korea were obtained from a website address ([[https://data.kma.go.kr/](https://data.kma.go.kr/)]([https://data.kma.go.kr/](https://data.kma.go.kr/)) 15 February 2021).  
In this study, the correlation coefficients and predictive regression equations among PM\({}_{10}\), PM\({}_{2.5}\) and PM\({}_{1}\) of Gangneung city associated with PM\({}_{10}\) and PM\({}_{2.5}\) of Beijing city were investigated in three divided periods of 18 March to 28 March, before the inflow of yellow dust (00:00 LST, 18 March to 00:00 LST, 21 March 2015), during the inflow (01:00 LST, 21 March to 00:00 LST, 23 March), and after the inflow (01:00 LST, 23 March to 00:00 LST, 27 March). Thus, statistical models were obtained through multiple regression analyses using IBM SPSS Statistics-25. For testing the goodness of the predicted values of PM\({}_{10}\), PM\({}_{2.5}\) and PM\({}_{10}\) concentrations, the predicted values were compared to the observed ones.  
Figure 1: Topographical feature in the north-eastern Asia including the Gobi Desert (large red ellipse), Beijing city (China; red square) and Gangneung city (Korea; small red circle).