Reevaluating the black carbon in the Himalayan and Tibetan Plateau : concentration and deposition

Black carbon (BC) is the second most important warming component in the 20 atmosphere after CO2. The BC in the Himalayan and Tibetan Plateau (HTP) has shaped the evolution of the Indian Monsoon and accelerated the retreat of glaciers, thereby resulting in serious consequences for billions of Asian residents. Although a number of related studies of this region have been conducted, the BC concentration and deposition indexes remain poorly understood. Because of the presence of arid environments and 25 the potential influence of carbonates from mineral dust (MD), the reported concentrations of BC from the HTP are overestimated. In addition, large discrepancies in the deposition of BC have been reported from lake cores, ice cores, snowpits and models. Therefore, the actual BC concentration and deposition values in this sensitive region must be determined. A comparison between the BC values of acid (HCl) 30 1 Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-209, 2017 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 3 April 2017 c © Author(s) 2017. CC-BY 3.0 License.


Introduction
The Himalayan and Tibetan Plateau (HTP) is the highest plateau in the world and represents the source region of approximately ten large rivers in Asia; moreover, this region is sensitive to climate change (Huang et al., 2008;Kang et al., 2010;Bolch et al., BC.This conclusion cannot be blindly applied to other areas because of the complexities mid-latitude environments around the world (e.g., arid areas and deserts with heavy dust storm events).For example, IC accounts for roughly 8% (Cao et al., 2005) and 10% (Ho et al., 2011) of the TC particles with diameters less than 2.5 μm 95 (PM2.5)during dust storm periods in northern China.Similar phenomena have been found for both PM2.5 and total suspended particle (TSP) samples in southern Europe (Sillanpää et al., 2005;Perrone et al., 2011).Because TSP contains more MD than PM2.5, it should contain a higher ratio of IC.In that study mentioned above from the United States (Chow and Watson, 2002), the authors suggested that "Acidification may be 100 advisable when sampling particle sizes larger than 2.5 μm, when samples are acquired at locations where carbonate carbon is expected to be high, or when >800 ℃ temperatures are applied during thermal evolution carbon analysis".
The above suggestion is well adapted for the study of HTP carbonaceous aerosols (CAs).Similar to northern China, large sand dunes and deserts are widely distributed 105 across the western HTP (Liu et al., 2005), and dust storms frequently occur in winter and spring (Wang et al., 2005;Fang et al., 2004).Thus, IC may account for a large portion of the CAs of the HTP.Unfortunately, the potential contributions of IC to TC and BC in HTP aerosols have been overlooked (Cong et al., 2015;Ming et al., 2010;Aiken et al., 2014;Cao et al., 2010;Zhao et al., 2013;Li et al., 2016b).Additionally, 110 IC contributions may be high because almost all of the reported data on CAs are based on the TSP content, which contains large volumes of coarse particles derived directly from MD.Therefore, TC and BC concentrations for the HTP are likely overestimated.
In fact, all published papers on aerosols collected from remote areas of the HTP have identified MD components, although none of these studies have directly discussed this 115 issue or evaluated the effects of IC.For example, mineral aerosols and fugitive dust collected from the Lulang station of the southeastern HTP account for a large part of the TSP in spring when dust storms frequently occur (Zhao et al., 2013) (Fig. 1).In addition, the aluminum concentrations of TSP increase considerably during dust storm events occurring at the Namco station of the central HTP, which clearly implies the 120 contributions of MD (Kang et al., 2015).Similarly, the dust loading derived from the Ca 2+ of the TSP samples collected at the Everest station reveal relatively constant MD levels throughout the year (Cong et al., 2015) .
Therefore, the contributions of IC to the TC and BC in the HTP aerosols must be quantitatively evaluated.In this study, the TSP samples of two remote stations of the 125 HTP were collected to evaluate the contributions of IC to the TC and BC.Seasonal variations in the extent of overestimations of TC and BC and possible causes were also examined.Finally, the corrected TC and BC concentrations of these two stations were determined based on previously published data (Ming et al., 2010;Cong et al., 2015).
BC deposition studies are closely related to studies of BC transport processes, 130 lifetime and radiative forcing.BC deposition can be measured directly from historical media, such as sediments (Gustafsson and Gschwend, 1998;Han et al., 2016) and ice core (Ming et al., 2007;Ruppel et al., 2014), estimated from BC concentrations in the atmosphere (Jurado et al., 2008) or calculated using models (Zhang et al., 2015).
Compared to the process of greenhouse gas emission, the BC deposition process 135 remains poorly defined and quantified (IPCC, 2013), especially in remote regions, such as the HTP, because of the presence of complex terrain and dynamic regimes (Bond et al., 2013;Bauer et al., 2013).Thus far, only three studies have directly reported on BC depositions in the HTP.
One model indicated that the BC deposits of the central HTP were 9 mg m -2 a -1 (Zhang 140 et al., 2015), which is roughly thirty times lower than the values found in two studies that evaluated lake cores of Namco Lake and Qinghai Lake (270-390 mg m -2 a -1 ) (Fig. 1) (Cong et al., 2013;Han et al., 2011).If the HTP BC is primarily derived from areas outside of the plateau because of long-range transport (Xu et al., 2009b;Luthi et al., 2015) and the BC of the lake sediment only reflects atmospheric deposition as declared 145 in the above mentioned articles based on lake cores (Cong et al., 2013;Han et al., 2011), then the above values should at least be comparable.Therefore, the discrepancies between these studies show that lake cores may overestimate BC deposition because pollutants in lake core sediments represent combined contributions from direct atmospheric deposition and lake catchment input (Yang, 2015).Although the two 150 Atmos.Chem. Phys. Discuss., doi:10.5194/acp-2017-209, 2017 Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 3 April 2017 c Author(s) 2017.CC-BY 3.0 License.studies on lake cores mainly attribute BC to regional (long-range transport) atmospheric deposition and show an increase in BC deposition in recent years, other potential influencing factors, such as catchment inputs, were not considered or were simply overlooked; however, these factors may have contributed significantly to lake core BC deposition.
155 Therefore, additional studies must be performed to provide more reliable values.
For instance, other researchers have reported on BC concentration and water accumulation levels in ice cores and snowpits from the HTP (Fig. 1) (Xu et al., 2009b;Li et al., 2016c;Li et al., 2016a;Ming et al., 2008).Although these studies did not report BC deposition patterns directly, BC deposition levels could be easily calculated out 160 from reported data.Because glaciers are generally located at the highest altitudes of a given region, they only receive wet and dry depositions of BC from the atmosphere.Thus, BC deposits in glacial regions are assumed to closely follow atmospheric depositions.In this study, the data cited above were used to investigate the differences in reported BC values and the potential reasons for such differences.In addition, 165 because the HTP is situated in a remote region, BC deposition patterns in the HTP must be compared to those of other areas (e.g., the Arctic, Europe and eastern China) to better understand the patterns.Finally, actual HTP BC deposition levels were presented.The Namco station is located in the center of the HTP.The Everest station is located on the northern slopes of the Himalayas.Both of these stations are generally considered to be located in remote areas of the HTP that receive BC transported over long ranges from South Asia, and several studies on BC have been conducted in this region (Chen et al., 2015;Cong et al., 2015;Ming et al., 2010;Li et al., 2016a).TSP samples were collected using 90 mm pre-combusted (550°C, 6 hours) quartz fiber filters (Whatman Corp) with a vacuum pump (VT 4.8,Germany).Because the pump was not equipped with a flow meter, the air volumes passing through each filter could not be determined (Li et al., 2016d); however, this did not influence the objectives of this study (e.g., relative concentrations of TC and BC in the original and acid-treated samples).Four field blank filters were also collected from each station by exposing the filters in each sampler without pumping.

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To compare the BC concentrations of the Namco Lake cores, two surface soils and four suspended particles of four rivers in the Namco Basin were collected during a period of peak river flow in 2015.A <20 μm fraction of these samples was extracted (Li et al., 2009) and treated (Han et al., 2015) to measure the BC concentrations.In addition, ten surface soil samples around the Everest station were collected to study the 190 pH values.

2.2.Measurement of BC and elemental concentrations
The carbonates of the collected aerosol samples were removed by exposing a punch of samples to a vapor of 37% hydrochloric acid (HCl) for fumigation for 24 hours.
Then, the treated samples were stored at 60°C for over 1 hour to remove acid left on 195 the filter (Li et al., 2016a;Pio et al., 2007;Chen et al., 2013;Bosch et al., 2014).The OC and elemental carbon (EC, the common chemical/mass definition of BC) concentrations of both the original and treated samples were measured using the Desert Research Institute (DRI) Model 2001 Thermal/Optical Carbon Analyzer (Atmoslytic Inc., Calabasas, CA, USA) according to the IMPROVE-A protocol (Chow and Watson, 200 2002).The OC and BC concentrations were determined based on varying transmission signals.To evaluate the concentrations of MD, the elements of Ca, Fe, Al, and Ti in the aerosol samples were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES).Reported values were subtracted from the blank concentrations.The contributions of MD (Maenhaut et al., 2002) and total 205 carbonaceous aerosols (TCAs) (Ram et al., 2010) of the collected samples were calculated using the following equations: where Si is calculated from Al assuming an average ratio of Si/Al=2.5 (Carrico et al., 2003), and

Adoption and calculation of BC deposition data
Previously reported BC deposition data were adopted.In addition, the BC deposition levels from the Namco station and Qinghai Lake Basin were estimated from the average BC concentrations in the atmosphere and average precipitation levels using 215 the method described in detail in other works (Jurado et al., 2008;Fang et al., 2015) (Table .1).In brief, the annual atmospheric deposition of BC (μg m -2 a -1 ) was calculated as follows: FWD= 10 -3 .P0. Wp.CBC-TSP where FDD and FWD are the seasonal dry and wet deposition (μg.m -2 ); VD, P0 and Wp are the dry deposition velocity of aerosol (0.15 cm.s -1 ), the precipitation rate (mm) of a given season and the particle washout ratio (2.0×10 5 ), respectively; and CBC-TSP is

225
the BC concentration of the TSPs (μg.m -3 ).The seasonal BC concentrations from the Namco station were monitored by AE-31, and the average precipitation levels at the station were recorded from 2014-2015.The BC concentrations in Qinghai Lake are reported in (Zhao et al., 2015), and the average 1961-2010 precipitation levels recorded by the China Meteorological Administration from the Huangyuan station in the lake 230 basin were used.The values for these two areas used in the BC deposition calculations are shown in Table 1.(TCO, OCO and BCO) for the Namco and Everest stations were recorded as 0.81±0.13,0.78±0.10 and 0.53±0.37,respectively and 0.76±0.12,0.78±0.12and 0.65±0.26,respectively.As proposed in previous work (Chow and Watson, 2002), BC concentrations are more heavily influenced than OC and TC concentrations because carbonates are more prone to decomposition at high temperatures during OC and BC

245
analyses.The OC concentrations in the treated samples used in this study also decreased, indicating that carbonates can also decompose at low temperatures (Karanasiou et al., 2010).Seasonal TCA/TCo variations at the two stations differed (Fig. 2), and obvious seasonal variations of low and high TCA/TCo ratios appeared during the non-monsoon and monsoon periods for aerosols recorded at the Namco station, respectively (Fig. 2), 250 which is consistent with heavy dust storms occurring during non-monsoon periods.
However, the seasonal patterns of the TCA/TCO ratio at the Everest station were not obvious, in line with relatively stable seasonal variations of Ca 2+ recorded at this station (Cong et al., 2015).Moreover, the MD/(MD+TCA) levels recorded at the Namco station during non-monsoon periods were higher than those recorded during monsoon 255 periods, whereas the corresponding values at the Everest station were nearly the same during both periods (Fig. 3).Compared with those of other areas, the MD/(MD+TCA) values recorded at the two stations were higher than those recorded at the NCO-P station (70% and 73% during the pre-monsoon and monsoon periods, respectively) located on the southern slopes of the Himalayas (Decesari et al., 2010), which may be related to 260 the serious levels of South Asia pollutants at the NCO-P station and the polluted clouds that are easily transported to this station.Alternatively, the aerosols of the NCO-P stations may carry fine particles of PM10 with low levels of MD. two stations further demonstrates the contributions of CaCO3 to aerosol IC (Fig. 4).A similar phenomenon was also found in an aerosol study of southern Europe (Karanasiou et al., 2010), which implies that this is a common phenomenon found in arid regions.

Actual BC concentrations of two stations and implications
In summary, we clearly showed that the presence of carbonates from MD has 285 led to overestimations of the HTP TC levels in the TSP samples by roughly 19±13% and 24±12% for the Namco and Everest stations, respectively, which were higher than the corresponding value of 10% found for coarse particles of the central Mediterranean region of Europe (Perrone et al., 2011).In addition, the related BC values were overestimated by approximately 47±37% and 35±26%, respectively, thus implying that 290 the actual BC concentrations at these two stations were lower than previously reported values by approximately one half and two thirds.Therefore, based on previously reported BC concentrations (Ming et al., 2010;Cong et al., 2015), the actual BC concentrations at the Namco and Everest stations were estimated at 44 ng m -3 and 164 ng m -3 , respectively.

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Although carbonates decompose at a relatively high temperature of roughly 800°C, the presence of carbonates leads to an overestimation of both BC and OC concentrations because certain components of carbonates appear in very fine particles, which leads to carbonate decomposition at relatively low temperatures.A similar phenomenon was found via the measurement of BC levels in ambient samples in southern Europe ( Karanasiou et al., 2010).In addition, the BC and OC concentrations measured in the acid-treated samples presented several uncertainties.First, the acid-treated ambient samples transfer components of OC to BC, which leads to increased BC concentrations (Jankowski et al., 2008).However, this phenomenon was not common in the aerosol samples examined in this study, although several samples showed higher BC 305 concentrations in the acid-treated samples at both stations (Fig. 2).Because BCA can not be higher than BCo, those samples with BCA/BCO above one was set as one in calculation of the average value at two stations.Finally, the generally lower TC values found in the acid-treated samples clearly showed that carbonates contributed to the TC contents in the studied aerosol samples.

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The influence of carbonate carbon on TC has been observed for PM2.5 samples from arid areas (Zhao et al., 2015;Karanasiou et al., 2010), where this phenomenon should be more obvious for TSP samples.Because dust storms of the northern and western parts of the HTP are more severe than those of the two studied stations during the non-monsoon period, the effect of carbonates on the concentrations of OC and BC 315 should be more pronounced in such areas and must be seriously considered in future studies.The BC values of the TSP samples in the northern HTP have also been reported (Cao et al., 2005;Ho et al., 2011), it is naturally inferred that these BC concentrations are likely overestimated by at least 45%.Correspondingly, related studies on other issues, such as BC radiative forcing and atmospheric transport models, in the HTP based 320 on in situ BC concentrations must be adjusted.

Actual BC deposition in the HTP
In general, the BC deposition levels measured via different methods should be consistent for a given region.For instance, in the seriously polluted region of eastern China (Chen et al., 2013;Yan et al., 2015), the BC deposition level recovered from a 325 lake core was 1,660 mg m -2 a -1 (Han et al., 2016), which is consistent with the values of northern China calculated from the BC concentrations in aerosols (Fang et al., 2015) and determined via in situ monitoring (Tang et al., 2014) (Table 2).Similarly, a BC deposition level of 50 mg m -2 a -1 was measured from a lake core in Sweden (North Europe), and this value was similar to that of ice cores (76 mg m -2 a -1 ) drilled from glaciers in Switzerland (West Europe) (Preunkert et al., 2000;Jenk et al., 2006).
Therefore, lake cores from polluted areas of East Asia and less polluted areas of Europe closely reflect atmospheric BC deposition levels.For remote areas, the BC deposition levels measured from an ice core in the Arctic and from deep ocean sediment samples from the western South Atlantic were comparable of 27 mg m -2 a -1 and 10 mg m -2 a -1 , 335 respectively (Lohmann et al., 2009;Ruppel et al., 2014).

Overestimated BC deposition from lake cores of the HTP
Large discrepancies were found among the reported BC deposition values in the HTP.BC deposition levels derived from lake cores from Namco Lake (NMC09) and Qinghai Lake were 260 mg m -2 a -1 and 270-390 mg m -2 a -1 , respectively, which re much 340 higher than those derived from ice core and snowpit samples of the HTP (Table 2).We proposed that the BC deposition in the lake cores of Qinghai Lake mainly reflected atmospheric deposition followed by catchment inputs.However, the NMC09 value of Namco Lake was mainly influenced by catchment inputs.
Lake core-derived BC deposition in Qinghai Lake was only 2-3 times higher 345 than that estimated from the BC concentrations of PM2.5 in the atmosphere (Zhao et al., 2015).Because PM2.5 does not include all particles in the atmosphere, the actual BC concentration in the atmosphere should be higher than that of PM2.5; therefore, the atmospheric BC deposition should be more similar to that of a lake core.In addition, a previous study showed that roughly 65% and 22% of the deposition in surface 350 sediments of Qinghai Lake results from atmospheric deposition and catchment inputs (Wan et al., 2012), further demonstrating the significant effects of atmospheric deposition on lake core sediments.Therefore, if the BC concentrations in atmospheric particles and catchment inputs are the same, then the atmospheric BC deposition measured from the Qinghai Lake cores is overestimated by approximately 35%.

355
Correspondingly, catchment inputs account for a large proportion of the NMC09 samples.Because of its inert characteristics, BC is widely distributed throughout environmental materials, such as soil and river sediments (Cornelissen et al., 2005;Bucheli et al., 2004).Therefore, river inputs contribute to sediments as well as to BC deposits.For instance, BC concentrations within the <20 μm fraction of surface soil and sediment in the Namco Basin reach 0.78±0.48mg g -1 , which close to that of the Namco Lake cores of 0.74 mg g -1 .In addition, several findings have demonstrated the contributions of catchment inputs to Namco Lake cores as shown in the following sections.
First, a large glacial area (141.88 km 2 ) is distributed across the Namco Basin 365 (Fig. 5), and large volumes of glacier meltwater and sediment pour directly into the lake (Wu et al., 2007).For example, increases in glacier meltwater in the Namco Basin triggered by increasing temperatures and precipitation account for roughly 50.6% of the lake's volume and have augmented the lake volume over the last 30 years (Zhu et al., 2010).Originating at high-elevation glacier terminals, these rivers flow at a steep angle, 370 and large volumes of suspended allochthonous sediments are transported into Namco Lake annually (Doberschütz et al., 2014).For instance, one study of the Zhadang glacier basin found remarkably high pollutant yields from the source river water because of the steep gradient (Sun et al., 2016).Similarly, abnormally high BC deposition levels in Europe were also observed in lake cores of a glacier feed lake as a result of glacier 375 meltwater effects (Bogdal et al., 2011).
Second, previous studies on the accumulation rates of lake cores have revealed significant contributions of riverine particles.The accumulation rates of Namco Lake cores (core 08-1) are consistent with the precipitation variations recorded in the Namco Basin over the last 60 years (Fig. 5A) (Wang et al., 2011), which indicates that heavy 380 precipitation promotes the transportation of large riverine particles to the lake, thus increasing the accumulation rates in the lake cores.Interestingly, the mean grain size of another lake core (core NMC09) showed a significantly positive relationship with precipitation (Fig. 5B), thus reflecting the same phenomenon that catchment inputs cause lake core accumulations (Li et al., 2014).Because the drill sites of these two lake 385 cores are located not at the same site (Fig. 5), their similar catchment input characteristics reflect a common feature of Namco sediment.As shown above, the BC concentrations of fine fraction of river sediments are nearly equivalent to those of lake cores, so that additional catchment inputs will increase the BC deposition levels within lake cores.Third, the atmospheric deposition of BC calculated from BC concentrations in the atmosphere is much less significant than the deposition of BC recorded in the Namco Lake cores (Fig. 6), further reflecting the dominant contributions of catchment inputs relative to atmospheric inputs in lake cores.
Our findings indicate that variations in BC depositions in Namco Lake mainly 395 reflected catchment inputs rather than atmospheric inputs; thus, atmospheric deposition plays a minor role relative to catchment inputs.Qinghai Lake and Namco Lake are the two largest lakes in the HTP, and they were assumed to be weakly influenced by catchment inputs.However, the above discussion shows that catchment inputs play a dominant role in the sediment formation of these lakes.Because most lakes in the HTP 400 have increased in area over the last 20 years (Zhang et al., 2016), this phenomenon likely occurs in many other lakes of the HTP, especially in small lakes scoured by glacier feed streams (Bogdal et al., 2011).Therefore, caution should be exercised when studying the atmospheric deposition of pollutants (e.g., BC) into the sediments of small lakes in the HTP.405

Actual atmospheric BC deposition and potential uncertainties
BC deposits derived from ice cores and snowpits may be more similar to the actual values observed for the HTP, and this hypothesis is supported by the following findings.
First, BC deposition levels in the snowpits of different glaciers are consistent.For example, the estimated BC deposition levels of Laohugou, Tanggula, Zhadang, Demula 410 and Yulong are 25, 21.3, 20, 14.5 and 20.2 mg m -2 a -1 , respectively (Table 2), which reflects a homogeneous spatial distribution of BC deposition.The above values are also similar to those of ice cores described in other articles (e.g., 18 and 12 mg m -2 a -1 for the Muztagh Ata and Zuoqiupu glaciers, respectively (Xu et al., 2009b;Bauer et al., 2013), and 10.1 mg m -2 a -1 for the East Rongbuk glacier (Ming et al., 2008) (Table 2).

415
Second, these values are nearly equivalent to those of atmospheric BC deposits derived from completely different methods (e.g., Community Atmosphere Model version 5 (Zhang et al., 2015) and other models (Bauer et al., 2013) (Table 2).Third, the BC deposition levels of the snowpits/ice cores of the HTP are comparable to those of other remote areas (e.g., ice cores of the Arctic (Ruppel et al., 2014) and surface sediments of deep oceans (Lohmann et al., 2009).In summary, despite the complex topography of the HTP, atmospheric BC deposition in its glacial region presents a limited spatial discrepancy of 10-25 mg m -2 a -1 .
Despite recent technological achievements, accurately measuring BC concentrations in ambient samples still represents a challenge in atmospheric chemistry 425 research (Andreae and Gelencser, 2006;Bond et al., 2013).Because the methods used to measure BC concentrations and determine BC deposition levels described above are not the same, uncertainties will be introduced when directly comparing the results from different studies.For instance, different protocols used to determine temperature increases will lead to differences in the BC concentrations obtained via different 430 thermal-optical methods (e.g., NIOSH vs. IMPROVE) for the same sample (Karanasiou et al., 2015;Andreae and Gelencser, 2006).In general, BC concentrations derived from the IMPROVE method are 1.2-1.5 times higher than those derived from the NOISH method (Reisinger et al., 2008;Chow et al., 2009), and BC concentrations derived from the EUSAAR_2 temperature protocol are twice as high as those derived from the 435 NIOSH protocol (Cavalli et al., 2010).Furthermore, lake core samples must be pretreated by dissolution in HCl and HF several times, as well as centrifugation, transfer and filtration, prior to measurement via the thermal-optical method (Han et al., 2015).
This complex process and the thermal-optical method produce additional uncertainties.
However, because of the complex chemical properties of ambient samples, the "best" 440 thermal-optical protocol has not been identified (Karanasiou et al., 2015), and an exact ratio for BC produced from different methods is difficult to determine.For example, aerosols with high biomass-sourced concentrations correspond to larger differences among the BC results of different methods (Cheng et al., 2011).Therefore, in this study, although the direct comparison of BC concentrations and deposition levels across

Conclusions
The BC concentration and deposition levels in the HTP region, which presents the largest glacial area at middle latitudes, were investigated and reevaluated in this article.values derived from different methods and materials showed that because of catchment inputs, the BC deposition levels derived from lake cores of the HTP were higher than the actual atmospheric deposition values.The lake cores examined in this study were drilled from the two large Qinghai and Namco Lakes, and lakes of this size should only be slightly influenced by catchment inputs.Therefore, the catchment inputs into smaller 470 HTP lakes should be more intense, which should be considered in future studies.

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TSP samples were collected from the Namco Station for Multisphere Observation and Research (Namco station) and the Qomolangma Station for Atmospheric and Environmental Observation and Research (Everest station) (Fig. 1) from 2014 to 2016.

8
, we found that carbonate carbon contributes significantly to the BC concentrations as well as to the TC and OC concentrations of the aerosols at the Namco and Everest stations, especially during non-monsoon periods (winter and spring) when dust storms occur frequently at Namco station.The ratios of the TC, OC and BC levels of the aerosols treated with acid (TCA, OCA and BCA) to those of the original samples 240 Atmos.Chem.Phys.Discuss., doi:10.5194/acp-2017-209,2017 Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 3 April 2017 c Author(s) 2017.CC-BY 3.0 License.

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different studies presents certain limitations, large differences of approximately thirtyfold between the lake core and snowpit data are still reliable because of relatively small differences (roughly 2 times) in the BC concentrations derived by the different methods.450 15 Atmos.Chem.Phys.Discuss., doi:10.5194/acp-2017-209,2017 Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 3 April 2017 c Author(s) 2017.CC-BY 3.0 License.
glacial regions were similar to those obtained via models and consistent with values obtained for other remote areas around the world (e.g., Arctic and deep ocean areas); thus, they reflect the actual atmospheric deposition values of BC.Although the HTP is 475 located adjacent to seriously polluted regions of South Asia and East China, the HTP BC deposition levels are relatively low because of the high elevation.Finally, our results indicated that the atmospheric BC deposition values of the HTP ranged from 10 m -2 a -1 to 25 mg m -2 a -1 , with low and high values appearing in the central and peripheral areas of the HTP, respectively.480 16 Atmos.Chem.Phys.Discuss., doi:10.5194/acp-2017-209,2017 Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 3 April 2017 c Author(s) 2017.CC-BY 3.0 License.Atmos.Chem.Phys.Discuss., doi:10.5194/acp-2017-209,2017 Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 3 April 2017 c Author(s) 2017.CC-BY 3.0 License.Atmos.Chem.Phys.Discuss., doi:10.5194/acp-2017-209,2017 Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 3 April 2017 c Author(s) 2017.CC-BY 3.0 License.Atmos.Chem.Phys.Discuss., doi:10.5194/acp-2017-209,2017 Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 3 April 2017 c Author(s) 2017.CC-BY 3.0 License.

770Figure 1 Figure 2
Figure 1 Selected study sites covering the HTP stations, lakes and glaciers Figure 2 Seasonal variations in the BC and TC concentrations in the original and acid-treated samples of aerosols measured at the Namco and Everest stations.

Figure 3 Figure 4
Figure 3 Percentage of MD and TCA to their sum during both non-monsoon period and monsoon period at Namco station and Everest station.775

Figure 5 .
Figure 5. Similar variations in precipitation and mass accumulation rates (A) (Wang

Figure 6
Figure 6 Comparison of the atmospheric BC deposition levels derived from the 780 Figure 1 Figure 2

Figure 6 32
Figure 6 (Li et al., 2008)2002).Because of dry weather conditions, the pH values of soil around the Namco and Everest stations are as high as 8(Li et al., 2008)and 8.3, in a typical grassland region with limited amounts of locally sourced dust that during monsoon periods.Additionally, the Everest station is located in the rain shadow of the Himalayas; thus, precipitation levels recorded at the Everest station (179 mm from January 2014 to January 2015) are much lower than those recorded at the Namco station 270 9 Atmos.Chem.Phys.Discuss., doi:10.5194/acp-2017-209,2017 Manuscript under review for journal Atmos.Chem.Phys.Discussion started: 3 April 2017 c Author(s) 2017.CC-BY 3.0 License.at the same period of 302 mm, which results in high MD concentrations in the atmosphere of Everest station during monsoon periods.Potentially biased aerosol samples caused by carbonates have been proposed to occur in arid areas with alkaline soils (275 respectively, implying intensive carbonate contributions.During non-monsoon periods, MD is mainly transported by westerlies from the arid western HTP, where MD is distributed across large deserts with sand dunes; thus, the aerosol samples were influenced by MD that has a high concentration of carbonates.Finally, the significantly positive relationship (p<0.01) between Ca and IC (TCO-TCA) for the aerosols of these 280 Our findings indicated that carbonate carbon contributions from MD have led to overestimations in previously reported BC concentrations of TSPs from the remote 455 Namco and Everest stations in the central and southern HTP by approximately 47±37% and 35±26%, respectively.After omitting the contributions of carbonate carbon, the actual BC concentrations at the Namco and Everest stations should be 45 ng m -3 and 169 ng m -3 , respectively.In addition, the levels of OC and TC in the TSPs at the Namco and Everest stations were also overestimated by22±10% and 22±12%, 19±13% and 46024±12%, respectively.Large arid areas that receive low precipitation are distributed across the western and northern HTP; thus, the effects of carbonates on BC measurements should be more significant in such areas and must be considered in future related studies.In addition, TSP samples must be treated with acid to eliminate the effects of carbonates prior to measuring BC.A comparison between the BC deposition 465

Table 2
Monitored or recovered BC deposits (mg m -2 a -1 ) from the HTP and other regions of the world.