{'fraction_non_alphanumeric': 0.04139654768413653, 'fraction_numerical': 0.03303913145356557, 'mean_word_length': 4.484472049689441, 'pattern_counts': {'":': 0, '<': 5, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 1, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Distribution and health risks of aerosol black carbon in a representative city of the Qinghai-Tibet Plateau

Although aerosol black carbon (BC) exerts strong influences on human health, research on potential health risks of aerosol BC around the Qinghai-Tibet Plateau is very limited. This is the very first study to investigate the distribution of aerosol BC in a typical city of the Qinghai-Tibet Plateau and the resulting health risks. The results showed that the maximal real-time (5-min monitoring interval) concentration of aerosol BC was 22.34 μg/m3, much higher than day- and week-averaged concentrations which were in the range of 1.28–6.15 and 1.93–4.63 μg/m3, respectively. The health risks were evaluated using four different health endpoints including low birth weight (LBW), percentage lung function decrement of school-aged children (PLFD), cardiovascular mortality (CM), and lung cancer (LC). The highest risks of LBW, PLFD, CM, and LC had reached 69.5, 184.4, 67.4, and 31.8 numbers of equivalent passively smoked cigarettes (PSC), respectively. The concentrations and health risks of aerosol BC in the study area are at a middle level among the global cities/regions. In comparison, the cities of the Qinghai-Tibet Plateau are experiencing high potential health risks resulting from aerosol BC to need more effective prevention and control of air pollution.


Introduction
Black carbon (BC), an important atmospheric aerosol that can deposit on environmental matrices, is generally created by weathering of graphitic carbon in rocks (Dickens et al. 2004) and the incomplete combustion of fossil fuels, vegetation, biofuels, and biomass (Cochrane 2003;Zhang and Wang 2011). BC generally possesses characteristics including high specific surface areas, variable particle size ranging from nanometers to mircometers, and a three-dimensional structure made up of stacked aromatic sheets (Koelmans et al. 2006). BC has been paid more attention due to its non-negligible contributions to global warming (Ramanathan and Carmichael 2008), strong relationship with persistent organic pollutants (Ni et al. 2014), and strong influences on human health (Koelmans et al. 2006;Shrestha et al. 2010).
The Qinghai-Tibet Plateau, covering a total area of approximately 3.0 × 10 6 km 2 (about 2.5 × 10 6 km 2 in China), has been called the Blast pure land^in China because of its high elevation and relatively severe natural conditions to prevent extensive anthropogenic activities. However, inorganic pollutants such as heavy metals and various organic pollutants have been frequently detected in different matrices of this area, exerting potential risks to the ecosystem and human health (Wu et al. 2016a, b).
Several recent studies on aerosol BC around the Qinghai-Tibet Plateau have been performed (Babu et al. 2011;Marinoni et al. 2010;Wang et al. 2016;Zhao et al. 2012).
The concentrations of aerosol BC are variable in different regions. Ma et al. (2003) investigated the concentrations of aerosol BC at Waliguan Observatory that is located on the top of Mt. Waliguan (an important mountain of the Qinghai-Tibet Plateau). The average concentration was 0.272 μg/m 3 . Cao et al. (2010) measured the concentrations of aerosol BC around the southeastern Qinghai-Tibet Plateau along the valley of the Yarlung Tsangpo River during winter. The average concentration of BC was 0.75 μg/m 3 which was significantly higher than the background concentrations (0.004-0.34 μg/ m 3 ) that were measured in the global background and remote regions. Ming et al. (2010) collected air and precipitation samples from Nam Co region of central Tibet. The highest concentration of BC in air and precipitation samples reached 0.239 μg/m 3 and 2158 μg/kg, respectively. Dumka et al. (2010) found that the concentrations of BC in a site of the Central Mt. Everest (29.4°N, 79.5°E) showed seasonal variations with the average value of 0.99 μg/m 3 . Engling et al. (2011) reported that the concentrations of aerosol BC at a monitoring station (25.01°N, 98.30°E) in Tengchong (located on the southeastern edge of the Qinghai-Tibet Plateau) varied from 0.043 to 1.471 μg/m 3 . It was also found that the concentrations of aerosol BC around cities/regions with a high population were significantly higher. Zhu et al. (2017) reported that the highest concentration of BC at an urban site in Lhasa (29.6°N, 91.1°E) and a remote site in Lulang (29.76°N, 94.73°E) reached 7.68 and 2.20 μg/m 3 , respectively. Moreover, some results showed that the concentrations of aerosol BC were affected by different factors such as altitude and meteorological conditions (Mao and Liao 2016;Zhao et al. 2017).
Aerosol BC poses potential risks to the human health (Koelmans et al. 2006;Louwies et al. 2015;Shrestha et al. 2010). BC has been reported to be an important cause for several human cardiovascular and respiratory diseases (Koelmans et al. 2006). Blood pressure increases when exposure concentration of BC increases, which potentially induces cardiovascular morbidity and mortality (Louwies et al. 2015). It is also found that particle size of BC is in a close relationship with its harmful effects (Ni et al. 2014;Shrestha et al. 2010). To the best of our knowledge, the information on the health risks posed by BC especially around the Qinghai-Tibet Plateau has been very limited until now. Therefore, it is necessary to perform research work on the health risks posed by aerosol BC of the Qinghai-Tibet Plateau. This study performed a series of experiments to explore the distribution of aerosol BC around a typical city of the Qinghai-Tibet Plateau and evaluate the potential health risks posed by aerosol BC. The objective of this study is to provide comprehensive information on the aerosol BC and its adverse side, especially in the high-elevation regions such as the Qinghai-Tibet Plateau.

Study area and aerosol BC monitoring strategy
Xining, the capital city of Qinghai Province and a representative city of the Qinghai-Tibet Plateau, was selected as the study area (Fig. S1). As the economic, political, and cultural center of Qinghai Province, Xining is also one of the most advanced and populated cities in the Qinghai-Tibet Plateau. Xining covers a total area of 7424 km 2 but only with 4.7% of urban region (Tan et al. 2017). The population of Xining in 2013 was 2.268 million (Tan et al. 2017).
Serving as landmark sites of Xining, a total seven sites were selected as target monitoring sites (Fig. S1). Near a coach station, Site XR is located at Xinning Road that bears heavy daily traffic. The daily amount of vehicles circulating on Site XR reached 44,000, and 80% of vehicles were gasolineengine cars based on our observation and estimation. Site CP is situated at Center Plaza that is the local traffic hub of Xining. The daily amount of vehicles circulating on Site CP reached 53,000, and 75% of vehicles were gasoline-engine cars. Site QU is located at Qinghai University campus that is suburb of Xining. Sites RS and XA are situated at railway station and airport, respectively. The daily amount of vehicles circulating on the adjacent streets of Sites RS and XA reached 62,000 and 28,000, respectively. The gasoline-engine cars on streets near Sites RS and XA accounted for approximately 75 and 90% of the total vehicles, respectively. Site GIP is seated at Ganhe Industrial Park that consists of many factories and companies. The distance between Site GIP and the nearest industrial stack is approximately 3000 m and this factory has been closed. Site DC is located in Datong County (a county that belongs to Xining) and near Datong aluminum factory which is an important enterprise of Qinghai Province. The distance between Site DC and the industrial stacks is approximately 500 m.
Monitoring of aerosol BC was performed from 21 February 2017 to 20 May 2017. Four time intervals including morning (7:30-9:00), noon-afternoon (12:00-14:00), afternoon (17:30-18:30), and evening (21:30-22:30) were chosen for BC monitoring because these time intervals represent the typical work-life pace of Xining. Each sampling site was monitored for a whole week in one monitoring experiment because of very limited in situ monitoring device.
A microAeth AE51 real-time monitor (Aethlab Inc., San Francisco, CA, USA) was used to in situ monitor the concentrations of aerosol BC. The air sample was collected on T60 Teflon coated glass fiber filter strip and the concentration of aerosol BC was determined using the 880-nm optical absorption. The data of BC concentrations were recorded real timely by AE51 monitor and exported by the computer workstation connected with AE51 monitor. The flow rate was set at 100 mL/min for all monitoring experiments. The time interval of AE51 measurements was set as 5 min. A total of 490 data regarding real-time (5-min monitoring interval) concentration of BC were obtained at each monitoring site.
The comparison on concentrations of BC at different sites or within different time intervals or days was evaluated by analysis of variance (ANOVA) with calculation of the least significant differences (LSD, P = 0.01).

Health risk assessment
Although aerosol BC is in a close relationship with several human cardiovascular and respiratory diseases and poses potential health risks to the public, the standard method for evaluating the health risks of BC has not yet been established. It might be feasible to use the equivalent numbers of passively smoked cigarettes (PSC) to express the health risks posed by aerosol BC since it is an airborne pollutant. Targeting at aerosol BC, a health risk assessment method based on environmental tobacco smoke (ETS) has been developed by van der Zee et al. (2016). The present study also used this method to evaluate the health risks posed by aerosol BC of Xining.
Four health endpoints including low birth weight (LBW) denoting a birth weight < 2.5 kg after 37-week gestation, percentage lung function decrement of school aged children (PLFD), cardiovascular mortality (CM), and lung cancer (LC) were selected to evaluate the health risks according to van der Zee et al. (2016). The equivalent amounts of PSC (N psc ) can be calculated as follows: , is the regression coefficient per cigarette; Δconcentration = 1 μg/m 3 for BC; ΔC refers to the difference between the monitored and background concentrations of aerosol BC; RR BC is relative risk for the association between BC and the health endpoint; RR ETS means relative risk for ETS exposure; N a represents the assumed number of cigarettes, which is 9 for children and 7 for adults according to van der Zee et al. (2016). A survey was performed to investigate the number of cigarettes smoked indoors by smokers in Xining. Approximately 550 smokers answered the questionnaires and they averagely smoke about 14 cigarettes per day. Therefore, the number of cigarettes smoked indoors assumed by van der Zee et al. (2016) is suitable for this study. Values of RR BC and RR ETS can be obtained from van der Zee et al. (2016). Xining lies approximately 90 km to the northeast of Waliguan Observatory that is relatively isolated from anthropogenic activities . Therefore, the background concentration of BC in this study was chosen as 0.272 μg/m 3 (data from Waliguan Observatory based on Ma et al. 2003).
Differences in health risks of BC at different sites or within different time intervals or days were determined by ANOVA (p = 0.01).

Results and discussion
Distribution of aerosol BC in the study area Aerosol BC was monitored with four time intervals in a day as described above, and on each day during a week so as to obtain 490 data for each monitoring site (Fig. S2). The statistical distribution of BC concentrations was shown by box plots in Fig. 1 and Figs. S3 and S4. Concentrations of aerosol BC at different sites showed significant difference according to ANOVA results (P < 0.01). Concentrations of BC at the same site varying with four time intervals or 7 days also exhibited significant difference based on ANOVA results (p < 0.01). Site DC possessed the highest week-averaged concentration of BC (4.63 μg/m 3 ) with standard deviation of 3.18 μg/ m 3 while Site XA showed the lowest value of 1.93 μg/m 3 (Fig. 1). The week-averaged concentrations of BC at the rest 5 sites ranged from 1.99 to 3.72 μg/m 3 (Fig. 1). For each site, concentrations of aerosol BC showed large fluctuations during the whole week. On Monday, the real-time (5-min monitoring interval) concentration of BC at Site DC reached the maximum value of 22.34 μg/m 3 . In comparison, the real-time concentration of BC reached its minimum value of 0.40 μg/m 3 at Site QU on Sunday (Fig. S2).
Concentrations of aerosol BC at different sites varied significantly and depended on each day of a whole week ( Fig.   Fig. 1 Box plots of concentrations of aerosol black carbon (BC) at seven monitoring sites. In each box, the bottom and top of the box illustrate the 25th and 75th percentiles; the mid-line of the box means the median value; the small box inside each box represents the average value; the bottom and top of the whiskers refers to the 10th and 90th percentiles; and the extreme values exceeding three times the 25th percentile are marked S3). The minimal day-averaged concentration of BC at all sampling sites was 1.28 μg/m 3 (Site GIP). Except Wednesday and Friday, Site DC possessed the maximal dayaveraged concentration of BC among all sites ranging from 4.39 to 6.15 μg/m 3 (Fig. S3). Among all sites, Sites CP and RS showed the maximal day-averaged concentration of BC with values of 4.94 and 5.35 μg/m 3 for Wednesday and Friday, respectively (Fig. S3). The maximal day-averaged concentration of BC at Sites XR, CP, QU, RS, DC, GIP, and XA occurred on Thursday, Wednesday, Thursday, Friday, Thursday, Monday, and Sunday with values of 4.06, 4.94, 2.77, 5.35, 6.15, 2.55, and 2.75 μg/m 3 , respectively (Fig. S3).
The concentrations of BC at seven sites also varied with four time intervals (Fig. S4). In the morning, the time-intervalaveraged concentrations of aerosol BC at seven sites reached the maximum values ranging from 3.02 to 6.13 μg/m 3 . Site DC showed the maximal time-interval-averaged concentrations of aerosol BC in the morning, noon-afternoon, afternoon, and evening with the values of 6.13, 3.33, 4.58, and 5.01 μg/m 3 , respectively.

Health risks of aerosol BC in the study area
Aerosol BC is closely associated with several human cardiovascular and respiratory diseases to pose potential risks to the human health (Koelmans et al. 2006;Louwies et al. 2015;Shrestha et al. 2010). Health risk assessment model was developed by van der Zee et al. (2016) to use four health endpoints including LBW, PLFD, CM, and LC for exploring potential health risks posed by aerosol BC. Therefore, health risks posed by aerosol BC of this study area were also evaluated by LBW, PLFD, CM, and LC, expressed into equivalent numbers of PSC (Figs. 2, 3, 4, and 5). Health risks posed by aerosol BC at different sites showed significant difference based on ANOVA results (p < 0.01). Health risks posed by aerosol BC at the same site varying with different time intervals or days also illustrated significant difference according to ANOVA results (p < 0.01).
Similar to concentration pattern, health risks of LBW calculated by real-time concentrations of BC at Site DC reached the maximal value with 69.5 equivalent numbers of PSC while that at Site QU showed the lowest value of 0.4 (Fig. 2). The week-averaged risks of LBW at seven sites ranged from 5.2 (Site XA) to 13.7 (Site DC) equivalent numbers of PSC. Day-averaged risks of LBW at Site DC reached the highest values varying from 13.0 to 18.5 equivalent numbers of PSC on each day of a week except Wednesday and Friday while Sites XA, GIP, and QU possessed the minimal day-averaged risks of LBW, showing significant difference in day-averaged risks (Fig. S5). The highest time-intervalaveraged risks of LBW occurred in the morning for all seven sites ranging from 8.7 to 18.5 equivalent numbers of PSC whereas Site DC possessed the highest time-interval-averaged risks of LBW in the morning, noon-afternoon, afternoon, and evening with the values of 18.5, 9.6, 13.6, and 14.9 equivalent numbers of PSC, respectively (Fig. S6). The minimal time-interval-averaged risks of LBW usually occurred in the time intervals of noon-afternoon and afternoon (Fig. S6).
The week-averaged health risks of PLFD at 7 sites illustrated significant difference (Fig. 3). The highest health risks of PLFD occurred in Site DC on Monday with 184.4 equivalent numbers of PSC while Site QU showed the lowest risks of PLFD on Sunday with 1.1 (Fig. 3). The week-averaged risks  Similar to LBW, the highest health risk of CM occurred at Site DC with 67.4 equivalent numbers of PSC while Site QU showed the lowest risk of CM with 0.4 (Fig. 4). The weekaveraged risks of CM at seven sites ranged from 5.1 (Site XA) to 13.3 (Site DC) equivalent numbers of PSC (Fig. 4). Except Wednesday and Friday, Site DC illustrated the highest dayaveraged risks of CM varying from 12.6 to 18.0 equivalent numbers of PSC while Sites XA, GIP, and QU showed the lowest day-averaged risks of CM, also exhibiting significant difference in day-averaged risks (Fig. S9). The maximal timeinterval-averaged risks of CM at all seven sites occurred in the morning ranging from 8.4 (Site GIP) to 17.9 (Site DC) equivalent numbers of PSC whereas Site DC possessed the maximal average risks of CM in all four time intervals (Fig. S10). The minimal time-interval-averaged risks of CM usually occurred in the noon-afternoon and afternoon (Fig. S10).
Compared with other three endpoints, health risks of LC showed relatively low values. Health risks of LC reached the highest value of 31.8 equivalent numbers of PSC at Site DC while Site QU showed the minimal risk of LC with 0.2 (Fig. 5), less than half of the corresponding risks of LBW and CM. The week-averaged risks of LC risks at seven sites ranged from 2.4 (Site XA) to 6.3 (Site DC) equivalent numbers of PSC (Fig. 5). Among all sites, day-averaged risks of LC at Site DC reached the highest values varying from 5.9 to 8.5 equivalent numbers of PSC on each day of a week except Wednesday and Friday while day-averaged risks of LC reached the highest values of 6.7 (Sites CP) equivalent numbers of PSC on Wednesday and 7.3 (Site RS) on Friday, respectively (Fig. S11). The maximal time-interval-averaged risks of LC occurred in the morning for all seven sites ranging from 4.0 (Site GIP) to 8.4 (Site DC) equivalent numbers of PSC whereas Site DC possessed the maximal time-intervalaveraged risks of LC for all four time intervals (Fig. S12). The minimal time-interval-averaged risks of LC usually occurred in the time intervals of noon-afternoon and afternoon (Fig.  S12).

Comparison on health risks of aerosol BC in different sites of the world
Besides concentration data of aerosol BC in Xining, this study also cited concentration data of aerosol BC in other 42 cities/ regions of 24 countries to make comparison on concentrations and potential health risks of BC in the study area and the other sites at a global scale (Table 1). The maximal concentration   To our knowledge, criterion for evaluating pollution by aerosol BC has not been established. Compared with other cities around the world, concentration of aerosol BC in Xining was at middle level, not very high or low enough, even among the cities of the Qinghai-Tibet Plateau (Table 1). However, the highest concentration of aerosol BC in this study area reached 22.34 μg/m 3 , still suggesting urgent need for air pollution control. Large amounts of small hydrocarbon molecules and polycyclic aromatic hydrocarbons (PAHs) are produced during the formation of BC particles (Ni et al. 2014). BC particles carrying PAHs react with chlorine to produce polychlorinated biphenyls (PCBs), polychlorinated dibenzopara-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) when chlorine presents during combustion (Ni et al. 2014). Due to a close relationship with persistent organic pollutants and human health, criterion establishment for assessing aerosol BC pollution should be put on the agenda as soon as possible.
There are not standard protocols for evaluating health risks of aerosol BC up to now. Therefore, a recently published method was selected to assess health risks of BC by using equivalent numbers of PSC in this study. Health risks posed by aerosol BC were expressed into four health endpoints so as to obtain comprehensive evaluation.
The maximal health risks of CRG reached 279.2, 740.7, 270.9, and 127.6 equivalent numbers of PSC for LBW, PLFD, CM, and LC, respectively. Ny-Ålesund showed the minimal health risks of LBW, PLFD, CM, and LC with 0.5, 1.4, 0.5, and 0.2 equivalent numbers of PSC, respectively. In Asia, India showed the most serious air pollution with BC concentration of 73.00 μg/m 3 , thus exerting health risks of LBW, PLFD, CM, and LC with 229.1, 607.8, 222.3, and 104.7 equivalent numbers of PSC, respectively. Besides USA, Canada in North America also showed relatively high health risks of LBW, PLFD, CM, and LC with 28.9, 76.8, 28.1, and 13.2 equivalent numbers of PSC. In terms of South America, Chili showed the highest health risks with 31.9, 84.6, 31.0, and 14.6 equivalent numbers of PSC for LBW, PLFD, CM, and LC, respectively. Among European countries, France exhibited the maximal health risks of LBW, PLFD, CM, and LC with 153.5, 407.2, 148.9, and 70.2 equivalent numbers of PSC, respectively. Fiji and Mali possessed the highest health risks of LBW/PLFD/CM/LC in Oceania and Africa, respectively, with 14.6/38.7/14.1/6.7 and 59.6/158.2/57.9/27.3 equivalent numbers of PSC, respectively.
Based on evaluation results, most of the cities (even for the cities located in the Qinghai-Tibet Plateau) around the world are experiencing the high health risks posed by aerosol BC (Table 1). Health risks of BC in Xining were lower than those in Shanghai, Xi'an, Karachi, Delhi, Kolkata, CRG, and Paris. Although more new methods are waiting to be developed for more precisely and comprehensively evaluating health risks of BC, the current results still suggest the needs for effective control of aerosol BC.

Possible factors affecting concentrations of aerosol BC in the study area
Industrial production contributes to concentrations of aerosol BC to a great extent. Site DC showed significantly higher concentrations of BC, which may be due to the nearby aluminum factory emission. Out of our expectation, concentrations of BC at Site GIP exhibited relatively normal values, which might be attributed to that over 70% of enterprises in this industrial park have been in stopping-production status since 2016. Therefore, distribution features of BC at Sites DC and GIP illustrate that anthropogenic activities such as industrial production and mining will contribute to concentrations of aerosol BC, which is also proved by Jaffe et al. (2015).
The traffic might be another important factor contributing to the concentrations of BC. Except Site DC, the highest concentrations of BC at the rest sites mainly occurred in the morning (exceeding 4 days out of a week), especially during workday. Vehicle exhaust, especially during rush hours, might offer concentrations of BC to great extent, which is also similar to the findings of other scientists Dutkiewicz et al. 2009;Ji et al. 2017;Patel et al. 2009;Rakowska et al. 2014). Aircrafts and trains are mainly used for inter-province transportation. Many flights and trains are arranged to depart in the morning, noon or early afternoon so that people have to arrive at airport or railway station by cars, taxi or bus in the morning. Therefore, it is reasonable that the highest concentrations of aerosol BC at Sites RS and XA occurred in the morning. Located on the arterial road and local traffic hub, the highest concentrations of aerosol BC at Sites XR and CP reflect the local life-work schedules that include commuting for work (workday morning and afternoon), morning market-shopping (weekend morning), and evening leisure. Interestingly, the highest real-time concentrations of aerosol BC at Site QU mainly occurred in the morning (4 days out of a week) and noon (3 days out of a week), which might be affected by other sources such as restaurant cooking besides traffic.

Conclusions
A total of seven sites of Xining were monitored a week with four time intervals of each day to obtain concentrations of aerosol BC. The real-time (5-min monitoring interval) concentrations of BC in the study area ranged from 0.40 to 22.34 μg/m 3 while the day-averaged and week-averaged concentrations of BC were in the range of 1.28-6.15 and 1.93-4.63 μg/m 3 , respectively. The highest time-interval-averaged concentrations of BC at seven sites occurred in the morning of each day. The health risks posed by aerosol BC were evaluated using LBW, PLFD, CM, and LC, with the highest values of 69.5, 184.4, 67.4, and 31.8 equivalent numbers of PSC, respectively. To the best of our knowledge, this is the first report on the health risks posed by BC in the Qinghai-Tibet Plateau. The health risks of BC showed the same pattern with concentration. Compared with other cities/regions around the world, the concentrations and health risks of BC in Xining were at the middle level. However, Xining and other cities of the Qinghai-Tibet Plateau are still experiencing high potential health risks posed by aerosol BC based on evaluation results to need effective prevention and control of air pollution.