## 3 Results and Discussion
### Meteorological Conditions and Pollutant Concentrations  
As shown in Figure 3a, the wind direction was northeesterly on the afternoon of 10 June, and it persisted until the evening of 12 June. As explained in Section 3.1, the northeesterly winds aided the transport of particles across Wuhan, which was within a relatively weak low-pressure system during 9-13 June, as shown in Figure 3b. These meteorological conditions were not conducive to the dissipation of atmospheric particles and thus, led to the accumulation of pollutants in localized areas when the particulate matter arrived over Wuhan. Before the haze event, surface temperature exhibited a characteristic diurnal variation; however, during the haze event, surface temperature increased dramatically between noon on 11 June and the evening of 13 June. During this period, there was no visible diurnal change in temperature, which remained at 35-40 \({}^{\circ}\)C. [PERSON] and [PERSON] have both reported that particles have a heating effect on the environment during haze episodes [16,18]. Due to biomass combustion, the number of soot particles increases significantly, which can be revealed through the enhanced BC mass concentration, as discussed in the next paragraph. Soot pollutants can heat the atmosphere and affect the radiative effect of aerosols on the atmosphere [19,20]. It can be seen from Figure 3c that there was also significant diurnal change in RH before the haze event, but that RH remained at the high level of 60%-70% during the haze event of 11-13 June. Visibility also decreased to about 1 km by noon on 11 June and these conditions lasted until noon on 12 June. The minimum visibility reported was 0.72 km.  
Figure 3d shows that the mass concentrations of PM\({}_{2.5}\) and BC increased sharply in the morning of 11 June and reached maximum values of 597 and 18 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\), respectively, at noon on the same day. During the haze period, the mean PM\({}_{2.5}\) and BC mass concentrations were approximately 9.9 (332.79  
Figure 3: Time series variations of meteorological parameters and pollutant mass concentrations (BC and PM\({}_{2.5}\)) at LIESMARS site during 6–14 June 2012. **(a)** Wind direction (degrees) and wind speed (m\(\cdot\)s\({}^{-1}\)); **(b)** Temperature (\({}^{\circ}\)C) and atmospheric pressure (hPa); **(c)** Visibility (km) and relative humidity (%), and **(d)** BC and PM\({}_{2.5}\) mass concentrations and ratio between BC and PM\({}_{2.5}\).  
versus_ 33.66 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\)) and 3.2 times (9.67 _versus_ 2.99 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\)) greater, respectively, than during the non-haze period. Because of the large quantities of highly concentrated particles that were transported to the local area within a short time, the mass concentration of particles remained at a high level during 11-13 June. Before the haze period, BC/PM\({}_{2.5}\) was maintained at \(\sim\)0.13, but it decreased rapidly to 0.025 once the haze developed and remained \(<\)0.1 (\(\sim\)0.06) throughout the days of haze. This indicates that the quantities of both non-BC and BC aerosols increased significantly. However, the proportion of non-BC aerosols increased more rapidly than that of BC aerosols. The statistical information regarding the meteorological parameters and particle concentrations measured during the experiment is summarized in Table 1.