Sources and physicochemical characteristics of black carbon aerosol from the southeastern Tibetan Plateau: internal mixing enhances light absorption

Abstract

Abstract. Black carbon (BC) aerosol has important effects on the climate and hydrology of the Tibetan Plateau (TP). An intensive measurement campaign was conducted at Lulang (∼ 3300 m a.s.l. – above sea level), southeastern TP, from September to October 2015, to investigate the sources and physicochemical characteristics of refractory BC (rBC) aerosol. The average rBC mass concentration was 0.31 ± 0.55 µg m−3, which is higher than most prior results for BC on the TP. A clear diurnal cycle in rBC showed high values in the morning and low values in the afternoon. A bivariate polar plot showed that rBC loadings varied with wind speed and direction, which also reflected the dominant transport direction. The estimated net surface rBC transport intensity was +0.05 ± 0.29 µg s−1 m−2, indicating stronger transport from outside the TP compared with its interior. Cluster analysis and a concentration-weighted trajectory model connected emissions from north India to the high rBC loadings, but the effects of internal TP sources should not be overlooked. The average mass median diameter (MMD) of rBC was 160 ± 23 nm, with smaller MMDs on rainy days (145 nm) compared with non-rainy days (164 nm). The average number fraction of thickly coated rBC (FrBC) was 39 ± 8 %, and it increased with the O3 mixing ratios from 10:00 to 14:00 LT, indicating that photochemical oxidation played a role in forming rBC coatings. The average rBC absorption enhancement (Eabs) was estimated to be 1.9, suggesting that light absorption by coated rBC particles was greater than for uncoated ones. The Eabs was strongly positively correlated with the FrBC, indicating an amplification of light absorption for internally mixed rBC. For rBC cores < 170 nm, Eabs was negatively correlated with MMD, but it was nearly constant for rBC cores > 170 nm. Our study provides insight into the sources and evolution of rBC aerosol on the TP, and the results should be useful for improving models of the radiative effects of carbonaceous aerosols in this area.

Deposition of Organic and Black Carbon: Direct Measurements at Three Remote Stations in the Himalayas and Tibetan Plateau

“…The high BC scavenging ratios at this station could also be explained by the aging of aerosols during the longrange transport from South Asia (Li, Bosch, et al, 2016;Lüthi et al, 2015;Yang et al, 2018). The scavenging ratios for both WIOC and BC at the Lulang and Everest stations were relatively low compared to those at Nam Co Station because the atmospheric concentrations of WIOC and BC at the former two stations were much higher than those at Nam Co Station (Table S2) due to the large influence of local emissions Wang et al, 2018). In contrast, the concentrations of WIOC and BC in precipitation at these two stations were slightly higher than or comparable to those at Nam Co Station (Table 1).…”

Intra-regional transport of black carbon between the south edge of the North China Plain and central China during winter haze episodes

“…3.3 BC/PM 2.5 and BC/CO ratios BC/PM 2.5 and BC/CO ratios are widely used to identify the sources of BC Wang et al, 2011;Verma et al, 2010;Chow et al, 2011). Generally, ratios of BC/PM 2.5 from mobile sources (0.059-0.74) and area sources (0.032-0.33) are higher than those from industrial sources (0.0046-0.03).…”

Seasonal contrast in size distributions and mixing state of black carbon and its association with PM1.0 chemical composition from the eastern coast of India

“…Absence of day time enhancement of nitrate and ammonium indicated that photochemical production may not be significant or possibly destruction (evaporative loss, i.e., Even though it is very difficult to determine the coating material on the BC particles that exist in a multi-component organic, inorganic aerosols, gaseous vapours system, the above discussion suggests two contrasting possibilities of coating material on BC: (a) concurrent peaks in RCT (as seen in Figure 8) and sulphate during the diurnal cycles indicates that the most probable material for the coating is sulphate, whereas (b) possibility of organic matter acting as coating material cannot be ruled out because observed minima in the mass fraction of organics during RCT peaks (during dawn and afternoon 5 hours) suggested a possible loss of organic vapours through condensation on large number of pre-existing BC particles, thereby contributing to their coating. Boundary layer dynamics and source processes play an important role not only on particle loading but also in determining the coating Gong et al, 2016;Thamban et al, 2017;Wang et al, 2018). Increased ventilation during day time due to enhanced boundary layer heights dilutes aerosol concentrations, thereby reduces competition among particles for adsorption of condensable vapours.…”

“…A summary of MMD values reported in the literature with different emission sources and atmospheric conditions along with the present values is made in Table-3. Several earlier publications reported a range of MMD values (0.100-0.170 µm) for 30 urban regions with near source fossil fuel emissions (McMeeking et al, 2010;Liu et al, 2014;Laborde et al, 2013;Cappa et al, 2012;Kondo et al, 2011;Cheng et al, 2018), whereas, urban/continental outflows depict MMDs in the range of 0.140-0.180 µm (Shiraiwa et al, 2007;Wang et al, 2018). The MMD values are ~0.211 ± 0.014 µm for fresh biofuel/crop residue sources (Raatikainen et al, 2017), and in the range ~0.220-0.240 µm for aged BC from biomass burning sources (Liu et al,. https://doi.org /10.5194/acp-2019-376 Preprint.…”