SmB 6 , a well-known Kondo insulator, exhibits a transport anomaly at low temperature. This anomaly is usually attributed to states within the hybridization gap. Recent theoretical work and transport measurements suggest that these in-gap states could be ascribed to topological surface states, which would make SmB 6 the first realization of topological Kondo insulator. Here by performing angle-resolved photoemission spectroscopy experiments, we directly observe several dispersive states within the hybridization gap of SmB 6 . These states show negligible k z dependence, which indicates their surface origin. Furthermore, we perform photoemission circular dichroism experiments, which suggest that the in-gap states possess chirality of the orbital angular momentum. These states vanish simultaneously with the hybridization gap at around 150 K. Together, these observations suggest the possible topological origin of the in-gap states.

Abstract. Long-term continuous measurements of total gaseous mercury (TGM=gaseous elemental mercury (GEM)+ reactive gaseous mercury (RGM)) were conducted simultaneously along with meteorological variables and a suite of trace gases at an urban site in Nanjing, China from 18 January to 31 December 2011. Measurements were conducted using a high resolution mercury vapor analyzer (Tekran 2537B) with 5-min time resolution. The average concentration of TGM was 7.9 ± 7.0 ng m −3 with a range of 0.8-180 ng m −3 over the study period. TGM concentrations followed a typical lognormal pattern dominated by a range of 3-7 ng m −3 , which was significantly higher than the continental background values (∼1.5 ng m −3 ) in Northern Hemisphere. The mean seasonal TGM concentrations decreased in the following order: summer, spring, fall, and winter. This seasonal pattern was quite different from measurements at most other sites around the world. We attributed high monthly average concentrations to the re-volatilization of deposited mercury during the warm season due to high temperatures and greater solar radiation. Previous modeling studies suggested that Nanjing and the surrounding region have the largest Chinese natural emissions during the summer. Positive correlations between temperature, solar radiation, and TGM concentration combined with no correlation between CO and TGM in summer provide a strong indication that natural sources are important in Nanjing while most sharp peaks were caused by anthropogenic sources. TGM concentrations in Nanjing exhibited a noticeable diurnal pattern with a sharp increase after sunrise and peak of greater than 8 ng m −3 during 7-10 a.m. local time. Further, seasonally averaged diurnal cycles of TGM exhibited considerably different patterns with the largest variation in spring and insignificant fluctuations in winter. Using HYSPLIT backwards trajectories from six clusters, it was indicated that the highest TGM concentrations, 11.9 ng m −3 , was derived from local air masses. The cleanest air masses, with an average TGM concentration of 4.7 and 5.9 ng m −3 , were advected from the north via fast transport facilitated by sweeping synoptic flows.

An online coupled regional climate-chemistry model called RegCCMS is used to investigate the interactions between anthropogenic aerosols and the East Asian summer monsoon (EASM) over East Asia. The simulation results show that the mean aerosol loading and optical depth over the region are 17.87 mg/m 2 and 0.25, respectively. Sulfate and black carbon (BC) account for approximately 61.2% and 7.8% of the total aerosols, respectively. The regional mean radiative forcing (RF) is approximately À3.64, À0.55, and +0.88 W/m 2 at the top of the atmosphere for the total aerosol effect, the total aerosol direct effect, and the BC direct effect, respectively. The surface direct RF of BC accounts for approximately 31% of the total RF of all aerosols. Because of the total aerosol effect, both the energy budgets and air temperature are considerably reduced in the region with high aerosol loadings, leading to decreases in the land-ocean air temperature gradient in summer. The total column-absorbed solar radiation and surface air temperature decrease by 8.4 W/m 2 and 0.31 K,respectively. This cooling effect weakens horizontal and vertical atmospheric circulations over East Asia.The wind speed at 850 hPa decreases by 0.18 m/s, and the precipitation decreases by 0.29 mm/d. The small responses of solar radiation, air temperature, and atmospheric circulations to the BC warming effect are opposite to those of the total aerosol effect. The BC-induced enhancement of atmospheric circulation can increase local floods in south China, while droughts in north China may worsen in response to the BC semidirect effect. The total aerosol effect is much more significant than the BC direct effect. The East Asian summer monsoon becomes weaker due to the total aerosol effect. However, this weakness could be partially offset by the BC warming effect. Sensitivity analyses further indicate that the influence of aerosols on the EASM might be more substantial in years when the southerlies or southwesterlies at 850 hPa are weak compared with years when the winds are strong. Changes in the EASM can induce variations in the distribution and magnitude of aerosols. Aerosols in the lower troposphere over the region can increase by 3.07 and 1.04 μg/m 3 due to the total aerosol effect and the BC warming effect, respectively.

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Black carbon aerosol (BC) has a significant influence on regional climate changes because of its warming effect. Such changes will feed back to BC loadings. Here, the interactions between the BC warming effect and the East Asian monsoon (EAM) in both winter (EAWM) and summer (EASM) are investigated using a regional climate model, RegCM4, that essentially captures the EAM features and the BC variations in China. The seasonal mean BC optical depth is 0.021 over East Asia during winter, which is 10.5% higher than that during summer. Nevertheless, the BC direct radiative forcing is 32% stronger during summer (+1.85 W m−2). The BC direct effect would induce lower air to warm by 0.11–0.12 K, which causes a meridional circulation anomaly associated with a cyclone at 20°–30°N and southerly anomalies at 850 hPa over East Asia. Consequently, the EAM circulation is weakened during winter but enhanced during summer. Precipitation is likely increased, especially in southern China during summer (by 3.73%). Relative to BC changes that result from EAM interannual variations, BC changes from its warming effect are as important but are weaker. BC surface concentrations are decreased by 1%–3% during both winter and summer, whereas the columnar BC is increased in south China during winter. During the strongest monsoon years, the BC loadings are higher at lower latitudes than those during the weakest years, resulting in more southerly meridional circulation anomalies and BC feedbacks during both winter and summer. However, the interactions between the BC warming effect and EAWM/EASM are more intense during the weakest monsoon years.

Abstract.A comprehensive measurement study of mercury wet deposition and size-fractionated particulate mercury (Hg P ) concurrent with meteorological variables was conducted from June 2011 to February 2012 to evaluate the characteristics of mercury deposition and particulate mercury in urban Nanjing, China. The volume-weighted mean (VWM) concentration of mercury in rainwater was 52.9 ng L −1 with a range of 46.3-63.6 ng L −1 . The wet deposition per unit area was averaged 56.5 µg m −2 over 9 months, which was lower than that in most Chinese cities, but much higher than annual deposition in urban North America and Japan. The wet deposition flux exhibited obvious seasonal variation strongly linked with the amount of precipitation. Wet deposition in summer contributed more than 80 % to the total amount. A part of contribution to wet deposition of mercury from anthropogenic sources was evidenced by the association between wet deposition and sulfates, as well as nitrates in rainwater. The ions correlated most significantly with mercury were formate, calcium, and potassium, which suggested that natural sources including vegetation and resuspended soil should be considered as an important factor to affect the wet deposition of mercury in Nanjing. The average Hg P concentration was 1.10 ± 0.57 ng m −3 . A distinct seasonal distribution of Hg P concentrations was found to be higher in winter as a result of an increase in the PM 10 concentration. Overall, more than half of the Hg P existed in the particle size range less than 2.1 µm. The highest concentration of Hg P in coarse particles was observed in summer, while Hg P in fine particles dominated in fall and winter. The size distribution of averaged mercury content in particulates was bimodal, with two peaks in the bins of < 0.7 µm and 4.7-5.8 µm. Dry deposition per unit area of Hg P was estimated to be 47.2 µg m −2 using meteorological conditions and a size-resolved particle dry deposition model. This was 16.5 % less than mercury wet deposition. Compared to Hg P in fine particles, Hg P in coarse particles contributed more to the total dry deposition due to higher deposition velocities. Negative correlation between precipitation and the Hg P concentration reflected the effect of scavenging of Hg P by precipitation.

Black carbon (BC) aerosol is a significant, short-lived climate forcing agent. To further understand the effects of BCs on the regional climate, the warming effects of BCs from residential, industrial, power and transportation emissions are investigated in Asian regions during summer using the state-of-the-art regional climate model RegCM4. BC emissions from these four sectors have very different rates and variations. Residential and industrial BCs account for approximately 85% of total BC emissions, while power BCs account for only approximately 0.19% in Asian regions during summer. An investigation suggests that both the BC aerosol optical depth (AOD) and direct radiative forcing (DRF) are highly dependent on emissions, while the climate effects show substantial nonlinearity to emissions. The total BCs AOD and clear-sky top of the atmosphere DRF averaged over East Asia (100-130°E, 20-50°N) are 0.02 and + 1.34 W/m 2 , respectively, during summer. Each sector's BC emissions may result in a warming effect over the region, leading to an enhanced summer monsoon circulation and a subsequent local decrease (e.g., northeast China) or increase (e.g., south China) in rainfall in China and its surrounding regions. The near surface air temperature increased by 0.2 K, and the precipitation decreased by approximately 0.01 mm/day in east China due to the total BC emissions. The regional responses to the BC warming effects are highly nonlinear to the emissions, which may be linked to the influences of the perturbed atmospheric circulations and climate feedback. The nonuniformity of the spatial distribution of BC emissions may also have significant influences on climate responses, especially in south and east China. The results of this study could aid us in better understanding BC effects under different emission conditions and provide a scientific reference for developing a better BC reduction strategy over Asian regions.