# Multivariate Regression Modeling for Coastal Urban Air Quality Estimates
## 3 Results
### Satellite Images of Yellow Dust Transport
Figure 3: Hourly distribution of (**a**) PM\({}_{10}\) and PM\({}_{2.5}\) concentrations (\(\upmu\)g/m\({}^{3}\)) and (**b**) SO\({}_{2}\) (\(\times\)1000), (**c**) CO (\(\times\)100), (**d**) O\({}_{3}\) (\(\times\)1000) and NO\({}_{2}\) (\(\times\)1000) concentrations (ppm) before, during and after the yellow sand period at the Okcheondong observation point in Kangnung city (Korea), corresponding to the PM concentrations on 16 to 25 March at the Yongdingmen observation point in Beijing city (China). In Figure 3, the PM\({}_{10}\) concentration before the Yellow Sand event at Kangnung was about 50.445 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{m}^{3}\). When the PM\({}_{10}\) concentration increased, the PM\({}_{2.5}\) concentration increased and had a mean value of 41.234 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{m}^{3}\). Both during the event (01:00 LST, 21 March to 00:00 LST, 23 March) and in the early stages after the event on 23 March, the PM\({}_{10}\) and PM\({}_{2.5}\) concentrations rapidly increased; however, the increase in PM\({}_{2.5}\) was much smaller than that in PM\({}_{10}\). This may be attributed to the intrusion of major coarse particles of yellow sand into Kangnung. After the event, the temporal distributions of PM\({}_{10}\) and PM\({}_{2.5}\) had a similar pattern, with similar magnitudes to those values of PM concentrations before the event with slightly different magnitudes. We further investigated the effect of the ground-based concentrations of SO\({}_{2}\), CO, O\({}_{3}\) and NO\({}_{2}\) at Kangnung in increasing the PM concentrations in Figure 3 before, during and after the yellow sand event from 00 LST, 18 March to 00 LST, 27 March. The SO\({}_{2}\), NO\({}_{2}\) and CO concentrations had a similar temporal tendency to some extent, whereas O\({}_{3}\) had an opposite tendency. The concentrations before and during the event were slightly higher than ones after the event; however, the CO concentration relatively unchanged. Figure 4: Hourly distributions of (**a**) air temperature (\({}^{\circ}\)C; TEMP), (**b**) wind speed (m/s; WIND) and (**c**) relative humidity (%; RH) at Kangnung in Korea (modified from [41]). In Figure 3d shows, as [PERSON] et al [42] explained, that when the O\({}_{3}\) concentration increases, the NO\({}_{2}\) concentration decreases. A diurnal NO\({}_{\text{X}}\) (= NO\({}_{2}\) + O\({}_{3}\)) cycle shows that NOx emitted from the vehicles on the road and heating boilers in residential areas undergoes its photochemical reaction into O\({}_{3}\) due to the increased daytime solar radiation, resulting in its decrease. In contrast, O\({}_{3}\) is reduced to NO\({}_{2}\) at night through the NOx cycle (i.e., no photochemical reaction of NO\({}_{2}\)), leading to a decrease in O\({}_{3}\) concentration. [PERSON] et al. [43] insisted that the decreases in PM\({}_{2.5}\) and NO\({}_{2}\) concentrations support the control of NO\({}_{\text{X}}\) to further reduce PM\({}_{2.5}\) pollution in China and result in the increase in O\({}_{3}\) concentrations. We investigated whether meteorological parameters could influence PM and gas concentrations for the whole research period in Figure 4. The daytime air temperature near the ground surface during the yellow sand event at Kangnung (from 01:00 LST, 21 March to 00:00 LST 23 March) was much higher than in other periods. The maximum wind speed also became much higher than in other periods. The wind speed should be over 10 m/s (gust wind) for the dust mobilization in the desert. After the dust raised from the desert surface was uplifted to about a 3 km height, it was then transported a by westerly wind of 8 m/s to 10 m/s and moved to the downwind site of Kangnung 1400 km away.