Background The main sources of indoor pollution in exhibition halls are exhibition materials and exhibits. Especially in large exhibitions where there are numerous and varied exhibition materials and insufficient time for volatilization, the indoor air pollution may post potential health risks to the large number of participants.

Objective This study investigates the indoor air pollution status of large-scale exhibitions and the health risks of employees, aiming to provide a scientific basis for the improvement of indoor air quality of large-scale exhibitions and the formulation of effective control measures.

Methods Formaldehyde, benzene, toluene, xylene, ammonia, and total volatile organic compounds (TVOC) were monitored in 9 exhibition halls of a large-scale exhibition center in Shanghai from July to September in 2019 and 2020 respectively, and evaluated in accordance with Hygienic indicators and limits for public places (GB 37488-2019). The health risk assessment model of the U.S. Environmental Protection Agency was used to perform health risk assessment of employees. In addition, the monitoring results in different ventilation conditions and of different exhibits were analyzed and compared.

Results The overall qualified rate of indoor air in the selected large exhibition center in Shanghai was 96.3% (182/189). The unqualified indoor air pollutants included formaldehyde (98.4% qualified), ammonia (99.5% qualified), and TVOC (98.4% qualified). In the "fresh air+doors open" mode, the M (P₂₅, P₇₅) concentrations of the four indoor air pollutants were 0.041 (0.033, 0.047), 0.028 (ND, 0.039), 0.006 (ND, 0.020), and 0.100 (0.062, 0.190) mg·m^-3, respectively; in the "fresh air+return air+doors closed" mode, the concentrations of the four indoor air pollutants were 0.050 (0.038, 0.063), 0.040 (0.035, 0.070), 0.019 (ND, 0.028), and 0.155 (0.095, 0.253) mg·m^-3, respectively. The concentrations of above four indoor air pollutants in the mode of "fresh air+doors open" were all lower than those in the mode of "fresh air+return air+doors closed". The concentrations of toluene and xylene were lower than the limits of detection, and showed no differences between different ventilation modes (P>0.05). As to the results in different exhibition halls, the formaldehyde concentration in exhibition halls displaying clothing and footwear0.087 (0.079, 0.091) mg·m^-3 was higher than that in exhibition halls displaying games and animation derivative products0.053 (0.045, 0.057) mg·m^-3 (Z=-5.45, P < 0.001). There was no difference in the concentrations of ammonia, benzene, toluene, xylene, and TVOC in the exhibition halls of different exhibits (P>0.05). The results of health risk assessment of staff in the exhibition center showed that the carcinogenic risks of males and females were 4.2×10^-5 and 3.8×10^-5 respectively, indicating an acceptable level and a low risk. The total hazard indexes for males and females were 0.0250 and 0.0219 respectively, both indicating a low risk.

Conclusion This study shows that some indoor air pollutants in the selected large-scale exhibition center exceed the national standards. Ventilation mode and exhibit type have an impact on indoor air pollutant concentration. Both the carcinogenic and non-carcinogenic risks of employees are at acceptable levels.