# Vertical Measurement of Equivalent Black Carbon Concentration at Low Altitude
## 3 Results and Discussion
### eBC Concentrations and Temperatures in Winter, Spring, Summer and Early Autumn
The average eBC concentrations from an altitude of 10 m to 130 m were \(0.93\pm 0.68\)\(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\). The eBC concentrations measured in the morning on the ground were lower than those measured in the late morning, which is contrary to the eBC situation in winter. Figure 4f shows the temperature inversion at an altitude from 20 m to 40 m in the morning and in the late morning. The inversion blocks the transfer from the ground to high altitude, thus the air mass on the ground is stagnant, causing the high eBC concentration on the ground. It is interesting to note that no vertical temperature gradient was observed at night. Average wind speed and direction during the measurements on 27 May 2017 were 2.7 m/s and 280\({}^{\circ}\), respectively. Moderate wind speed seems to partly affect the high eBC concentration on the ground level similarly to the case of winter. Figure 4g shows eBC concentrations measured on 21 June show the BC situation in the middle of summer. The temperature was highest as can be seen in Figure 4h. The temperature inversion around h = 30-60 m in the morning seems to cause the high BC at h = 40 m. The level of eBC concentrations were low except at 40 m in the morning. Temperature profiles after 19:00 were more stable than those before noon. The eBC concentrations was similar regardless of the time when the measurements were done. Average eBC concentrations from the ground to 130 m were \(1.01\pm 0.49\)\(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\). The temperature profile shows the temperature inversion from an altitude of 30 m to 60 m in the morning and from an altitude of 30 m to 40 m close to noon. The high eBC concentration at 40 m in the morning is associated with the temperature inversion. It is thought that BC particles generated at the ground  
Figure 4: Vertical profiles of eBC concentration and temperature at low altitude: (**a**) eBC concentrations in late winter; (**b**) Temperatures in late winter; (**c**) eBC concentrations in spring; (**d**) Temperatures in spring; (**e**) eBC concentrations in early summer; (**f**) Temperatures in early summer; (**g**) eBC concentrations in summer; (**h**) Temperatures in summer; (**i**) eBC concentrations in summer and early autumn; (**j**) Temperatures in summer and early autumn. were elevated up to 40 m and the stable layer created between 30 m and 60 m due to the temperature inversion prevented the BC from being lifted above 40 m. Average wind speed and direction during the measurements on 21 June 2017 were 6.7 m/s and 263\({}^{\circ}\), respectively. We observed eBC concentrations on August 19 th as shown in Figure 4i to ascertain whether the BC situation in the late summer and early autumn is same as before or not. The temperature was still high as shown in Figure 4j. The temperature inversion near noon around h = 0-40 m seems to keep the air mass stagnant. The level of eBC concentrations were low due to intermittent drizzle. Sudden heavy shower and rain at night hindered us from operating the drone, thus there was no data at night. This exemplifies the unavailability of drone system for the atmospheric measurements in some weather conditions including strong wind or heavy rain. Temperature profiles in the late morning showed a weak temperature inversion but other cases did not. Average eBC concentrations from the ground to 130 m were 0.75 \(\pm\) 0.48 \(\upmu\)g/m\({}^{3}\). The eBC concentration was the lowest among other cases. The temperature profile shows the temperature inversion from an altitude of 30 m to 60 m and from 90 m to 110 m in the late morning. Average wind speed and direction during the measurements on 19 August 2017 were 5.5 m/s and 87\({}^{\circ}\), respectively. As for the relationship between the eBC concentrations and the wind speed, eBC concentrations on the ground were low in strong wind days, while eBC concentrations on the ground were high in moderate wind days. Exceptionally, the eBC concentration on the ground on 30 April was high despite the strong wind.