[Temporal Evolution and Source Appointment of Black Carbon Aerosol in Ordos During Summer and Autumn 2019]

In this study, black carbon (BC) aerosols were continuously observed using a seven-channel aethalometer (AE-33) in Ordos from August 12 to October 4, 2019; using this data combined with article matter (PM), pollutant gas, and meteorological element data; a HYSPLIT model; and potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models, we analyzed the temporal evolution and potential source appointment and main influence areas of BC. The results showed that the average of ρ(BC) was 882 ng·m^-3, accounting for 6.08% of PM_2.5. The ρ(BC) was mainly concentrated at 200-1000 ng·m^-3, accounting for 55.9% of the total samples. In different BC mass concentration ranges, BC_liquid was the mainstay, with an average proportion of 86%. The diurnal variations in BC and PM_2.5 showed unimodal distributions, with peaks at 08:00 and 10:00, respectively, and peak concentrations increased by 24.3% and 47.2%, respectively. The diurnal variation in BC_solid showed a bimodal distribution, with peaks at 08:00 and 20:00, respectively. The diurnal variation in the BC_liquid showed a unimodal distribution with a peak at 08:00. The strong correlation between BC and NO₂ indicated a greater impact of vehicle emissions on BC concentration, whereas the weak correlation between BC and SO₂ indicated a lower impact of industrial emissions on BC concentration. The dominant air masses affecting the Ordos could be divided into four categories. The southern air masses (35.6%) had the highest mass concentration of atmospheric pollutants, followed by the local air masses (26.9%) and the northwest air masses (18.8%), and the northeast air masses (18.7%) had the lowest mass concentration of pollutants. The influence of the Ordos on the downstream areas was mainly divided into the northeast air masses (40.9%), the northwest air masses (30.4%), and the southeast air masses (28.7%). High CWT value areas of BC were mainly located in the southern Yan'an-Tongchuan-Baoji-Hanzhong areas and Lvliang-Linfen-Sanmenxia-Nanyang areas. They were two long and narrow transmission belts with a weight mass concentration exceeding 1400 ng·m^-3. High CWT value areas of BC had the greatest impact on the Wuhai-Bayannaoer-Baotou-Hohhot regions, with a weight concentration exceeding 900 ng·m^-3. The long-range transportation of BC could reach the Yulin-Yan'an-Tongchuan-Baoji areas in the south, the Shuozhou-Datong-Beijing areas in the east, and the Xilin Gol League-Xing'an League-Hulunbuir areas in the northeast.