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A passive air sampler was used to monitor the concentration and contamination profile of 18 polychlorinated biphenyls (PCBs) in the atmosphere over the urban and industrial area of Gaolan, a city in northwest China, during the non-heating and heating seasons of 2018, and the sources, pollutant transport, and the health risks of PCB exposure were analyzed and assessed using principle component analysis, trajectory modeling, and inhalation exposure modeling. The atmospheric concentration in the study area ranged from 110.2 to 429.9 pg·m -3 , and the highest average concentration was found at the industrial estate. Tetra-PCBs and penta-PCBs were the dominant homologue groups, and the percentage of tetra-PCBs increased in the heating season. Combustion and industrial thermal processes, PCB-containing electrical equipment, and the combined source of volatilization from paint, combustion, and industrial thermal processes were considered to be the main sources, and the source of combustion and industrial thermal processes contributed the largest proportion of PCBs at 40.8%. Largely, the emission of UP-PCBs would significantly influence PCB pollution in the study area. Trajectory analysis results illustrated that PCBs emitted from sources in the study area would be transmitted to Lanzhou City atmospherically; local pollution would be the main source of PCBs contamination in the study area during the non-heating season, while the atmospheric input of PCBs transmitted from the northwest region would be another source during the heating season. Health risk analysis showed that the non-cancer risk of PCBs exposure was low in all age groups; however, lifetime cancer risks exceeded 10 -6 . PCBs emitted from combustion and industrial thermal processes sources would have a strong impact on resident exposure to PCBs, and adverse health effects would be caused due to long-term inhalation exposure of the inhabitants to PCBs contamination in the study area.

Aerosol acidity is closely related to particle properties and the explosive growth of secondary particles. Aerosol pH is difficult to measure directly but can be estimated indirectly by thermodynamic equilibrium modeling. ISORROPIA-Ⅱ is one of the most commonly used thermodynamic models and includes different modes (forward and reverse) and aerosol states (stable and metastable). Studies have shown that the calculated pH results vary with the selected mode and phase state. In addition to the selection of modes and phases, there are also other factors that influence the modeling results. In order to explore the appropriate mode and phase selection of ISORROPIA-Ⅱ as well as the factors influencing the model results under the air pollution characteristics of typical Chinese cities, the simulation results of different modes and aerosol states were analyzed by using online hourly data for Tianjin. The results showed that the pH calculations using the forward mode and metastable state were satisfactory at a higher RH. With increased temperature, the pH, aerosol water content, and concentration proportion in the aerosol phase of semi-volatile components all decreased. RH affected aerosol pH by influencing the aerosol water content and concentration of semi-volatile components. An increased cation concentration led to an increased pH and NH 3 concentration but a decreased HNO 3 concentration, whereas an increased anion concentration had the opposite effect. Ca 2+ , SO 4 2- , NO 3 - , and NH 4 + had a great influence on pH. Compared with SO 4 2- , NO 3 - had less effect on pH. Sensitive areas exist in the influence of NH 4 + on pH, and a high NH 4 + concentration did not cause a continuous pH increase. This study can improve the understanding of aerosol pH simulation using ISORROPIA-Ⅱ, and provides reference for research on the pH-related secondary generation mechanism, semi-volatile component gas-particle distribution, and pollution control measures.