VOCs are an important precursor of secondary organic aerosol (SOA) and ozone (O3), which causes atmospheric pollution and damage to human respiratory and nervous systems. Underground parking garages are characterized by concentrated emissions of exhaust and evaporation, within a semi-closed space in which the concentration of pollutants continues accumulating. Serving as a passage they must walk through, it poses a threat to the health of residents. Here, the air of an underground parking lot of a residential building in Tianjin was studied. Volatile organic compound (VOCs) samples were collected for nine days. VOCs characteristics and fleet activity were analyzed based on vehicle flow data obtained from the parking lot entry/ exit management system. Ozone formation potential (OFPs),·OH radical reaction rate, and secondary organic aerosol formation potential (SOAPs) were used to comprehensively evaluate VOCs atmospheric reactivity in the parking garage and to evaluate human health risks. These results were compared with published data from other studies on traffic pollution. The results showed: ① the rise in VOCs concentration with inbound/ outbound traffic flow peak appeared synchronously, namely during morning and evening rush hours. VOCs concentration was (463.76 ±148.42)μg·m -3 and (391.47 ±135.37) μg·m -3 in the morning rush hour and (334.29 ±176.57) μg·m -3 and (416.20 ±134.64) μg·m -3 in the evening rush hours. Although cars barely left or drove into the garage at night, VOCs concentrations at night [(320.33 ±115.57) μg·m -3 on weekdays and (364.77 ±155.32) μg·m -3 on weekends] were still higher than those at noon [(255.76 ± 103.65) μg·m -3 and (350.91 ± 108.73) μg·m -3] owing to diurnal emissions when vehicles were parked. Moreover, the proportion of olefin at night was significantly higher than that at other periods, because a higher proportion of olefin was the main characteristic of diurnal breathing emissions. During the sampling period, the ρ (VOCs) of the parking lot were 4.39-6.46 times the atmospheric ρ (VOCs) of the same period. ② The proportion of alkanes and aromatics on weekdays and weekends was 37.33%-44.57% and 31.83%-48.81%, respectively. The proportion of alkynes and OVOCs was 10.22%- 19.13% and 2.46%- 5.05%, respectively. The proportion of halo-hydrocarbons in each period was the lowest, ranging from 0.40% to 1.77%. Alkenes and aromatics contributed the most to OFPs and L·OH (84.10%-88.04%). Aromatics contributed the most to SOAPs in every period (98. 03%-98. 99%). These results indicated that aromatics and olefins had strong atmospheric reactivity and were the main pollutants emitted by motor vehicles. For example, m/ p-xylene and other active components contributed more to the secondary generation, and their content should be reduced first when gasoline is upgraded. ③ Health risk evaluation results showed that the non-carcinogenic risk index (HI) in the parking lot ranged from 0. 9-0.55, indicating no health risk. The carcinogenic risk in each period was 1.56-3.11 times higher than the threshold value (1 ×10 -6). As the parking lot is a place residents must pass through every day, mechanical ventilation measures should be opened to ensure adequate air circulation. © 2022 Science Press. All rights reserved.
