Field survey of particulate matter mass concentration and exposure levels in a commercial garage in dalian, China

Highlights

• Spatial and temporal distribution of PM concentrations in a commercial garage.

• Personal particulate matter inhaled doses in the garage and outdoors.

• 22.2% of hourly averaged data exceeded the 70 μg/m³ PM_2.5 exposure recommends.

• Personal PM_2.5 mass dose in garage was more severe than outdoors at most time.

• Sole natural ventilation is insufficient to dilute particles in commercial garage.

Abstract

Due to the enclosed environment and large quantities of particulates in vehicle exhaust, shopping mall parking garages are a hotspot for exposure to pedestrians and staff. This study conducted two-week continuous field measurements focusing on traffic and pedestrian flows, thermal environment, and particle mass concentrations in a commercial garage in Dalian, China. The relationship between traffic flow and thermal environmental parameters, and its effect on particle mass concentration, was evaluated based on Pearson correlation analysis. The particle mass concentrations both inside and outside the garage, and the relative exposure in the garage compared to the rest of the day, were analyzed. Results demonstrated that hourly averaged PM_2.5 mass concentration exceeded China's 35 μg/m³ long-term (one year) and the 70 μg/m³ short-term (24 h) exposure limits by 54.8% and 22.2%, respectively. For 92% of the time, the PM_2.5 cumulative dose was higher inside the garage than outdoors. The available natural ventilation was insufficient to prevent unsafe levels of exposure to particulate matter in the garage.

Introduction

Traffic-related particle mass concentrations have been confirmed to have a harmful impact on human health (Liu et al., 2019; Šimić et al., 2020; Polednik and Piotrowicz, 2020). Asthma, cardiovascular disease, and lung cancer are all associated with traffic-related particles, especially nanoparticles (Pacitto et al., 2018; Rich et al., 2019; de Homdedeu et al., 2020). Thus, traffic-related particle exposure analysis needs to be at the forefront of research.

Parking garages, being enclosed spaces, are a hotspot for particle pollutants, including vehicular emissions. Furthermore, high particle exposure levels could negatively influence the health of persons spending extended periods in these garages, including operators, cleaners, and maintenance persons. Although car owners and passengers would generally transit quickly through garages, cumulative exposure over an extended period could also be harmful to health (Maynard et al., 2007; Samoli et al., 2016). Frequent peak exposure to nanoparticles is quite common in the context of garages, as high pollutant levels frequently occur in these settings. Daily integrated exposure is disproportionately high relative to time spent in these activities (Kim et al., 2007). Based on limited regulatory requirements in countries, including China, carbon monoxide (CO) has been the only measured index in the design and operation of ventilation system in garages (Krarti and Ayari, 2001; Chan and Chow, 2004; Sung et al., 2007; Ministry of Housing and Urban-Rural Development of the People’s Republic of China, 2015). While levels of particle pollutant should also be considered in ventilation system design and operation, particle mass concentration, and exposure levels in garages, are not yet sufficiently understood in the literature to be adequately addressed in ventilation system design and operation (Kim et al., 2007; Zhao et al., 2017; Zhao et al., 2018a, 2018b).

Numerous studies have focused on particle concentrations in enclosed transport spaces, such as tunnels (Knibbs et al., 2009; Alves et al., 2015), subways and buses (Targino et al., 2018; Velasco et al., 2019; Krecl et al., 2020), and underground garages (Kim et al., 2007; Zhao et al., 2017). Their results have confirmed that particle exposure levels are usually several times higher in confined (higher risk) forms of transport than in other transportation modes such as bicycling and walking in outdoor and indoor environments.

Thus, although, only 10% of the day is usually spent commuting, this contributes about 20% of daily exposure to pollutants including black carbon. This is accounted for by pollutant levels being much higher within enclosed transport spaces/a vehicle cabin. Black carbon is a strong marker of primary combustion particles, such as vehicle and biomass emissions (Dons et al., 2012; Williams and Knibbs, 2016; Carvalho et al., 2018). Thus, although the daily time spent in traffic is generally much less than that spent indoors, personal particulate exposure from transportation microenvironments (including garages) can be severe.

In our previous surveys on air quality in parking lots (Zhao et al., 2017; Zhao et al., 2018 a; Zhao et al., 2018 b), we found that unreasonable demands for energy and cost saving mean mechanical ventilation systems are shut off. Thus natural airflow becomes the sole source of ventilation in the majority of parking lots. With natural ventilation, gaseous pollutants such as CO can be efficiently diluted under certain conditions, while CO pollution levels have been found to be just over the 25 ppm recommendation issued by the World Health Organization (WHO) (Wang et al., 2008). However, particle exposure levels might be several times higher than the WHO recommendation (70 μg/m³ for 24 h exposure) if mechanical ventilation is not used during operating hours in garages in China, especially in winter when vehicles need to idle after starting (Wong et al., 2002; Li and Xiang, 2013; Obaidullah et al., 2013; Zhao et al., 2018). While CO has frequently been employed as an index for design of garage mechanical ventilation systems, further studies are required on the characteristics of PM_2.5 mass concentration distribution, along with variations in commercial garages with high traffic flow.

Therefore, this study focused on levels of exposure to particles in a commercial garage with high traffic flow and personnel movement, especially during weekends, in Dalian, China. The horizontal and vertical distributions of the time series particle concentrations inside the garage were examined. The results could reflect transient and cumulative exposure doses in enclosed commercial garages, providing information fundamental to air quality control and evaluation in garages.