1. Introduction
The modern airport is a complex system with various types of facilities. Some components of the airport include air traffic control facilities, airfield including approach zones, a terminal complex, a utility communications network, supporting and service facilities, and ground access system [
1]. Among them, the terminal buildings are unique in that they usually operate on a 24-h basis throughout the year and directly interact with majority of the passengers and airport employees.
In recent years, the importance of air quality assessment at the airport has gradually been acknowledged. A number of studies on air quality have been conducted in various facilities at airports around the world. Typical air quality parameters include total volatile organic compounds (TVOC), ultrafine particles (UFP) (particle diameters are less than 0.1
m), fine particles (FP) or PM
2.5 (particle diameters are less than 2.5
m), and PM
10 (particle diameters are less than 10
m). For example, the TVOC and other gas pollutants were evaluated inside the control tower by Helmis et al. [
2], Mokalled et al. [
3], and Tsakas and Siskos [
4]. Helmis et al. [
2] also measured the indoor PM
2.5 and PM
10 mass concentration in the control tower [
2]. Lee et al. [
5] and Kungskulniti et al. [
6] used PM
2.5 as a parameter to assess indoor air quality in airport smoking rooms. More studies can be found on ambient air quality at or near the airport. Hsu et al. [
7,
8] monitored the UFP level near runways at two U.S. airports to evaluate the impact of aircraft emissions on ambient air quality. Stacey [
9] provided a most recent review of UFP related studies conducted at or near the airport with a focus on aircraft emission. Other studies have looked at particle size distributions in the ambient air near the airports, such as in Hudda et al. [
10], Masiol et al. [
11,
12], and Fanning et al. [
13]. However, indoor air quality studies inside the airport terminal buildings are still limited for good reasons. Access to terminals and gates typically requires a thorough security check. Only passengers with boarding passes can wait by the entrance. Researchers with single-use escort passes still need to be accompanied by the airport security personnel to obtain measurements. Furthermore, obtaining the pre-approval from regulatory agencies adds another layer of complexity during the preparation phase of gaining permission to access the study site. These hurdles often act as discouragement for researchers during site selection of indoor air quality studies.
The airport terminal buildings experience a high fluctuation in the number of passengers that move through various parts of the building as well as the auxiliary spaces. Studies have shown that human activities, such as walking, often lead to particle resuspension which is an important indoor source of particulate matter [
14,
15]. Aircraft also generate a significant amount of particulate matter [
16] as they idle near the ramps, taxi off the runway, and land onto the taxiways, which could infiltrate the building envelope and affect the air quality inside the terminal. Previous studies of airport workers have shown some evidence of correlation between chronic adverse respiratory symptoms and exposure to aviation fuel or jet stream exhaust [
17,
18]. Møller et al. [
19] measured the exposure to UFP for five occupational groups at the airport. Workers who resided in the terminal buildings were considered a low exposure group or control group in these studies compared to other workers whose activities were outdoor or in closer proximity to aircraft. However, passengers spend most of their time at the airport inside the terminal buildings. It is equally important to understand the air quality inside the terminal building as opposed to other parts of the airport. Two recent studies by Zanni et al. [
20] and Ren et al. [
21] have examined the FP concentrations in airport terminal buildings in Italy and China, respectively. Other air quality parameters measured in the studies include TVOC [
20] and UFP [
21]. Whereas Zanni et al. concluded that the building’s ventilation system appeared to be efficient in terms of filtration [
20], Ren et al. demonstrated that the building failed to provide sufficient protection for passengers from PM
2.5 and UFP exposures [
21]. Yet, neither study included the coarse particles PM
2.5–10 in the assessment. Brunekreef and Forsberg [
22] have discussed the epidemiological evidence for effects of coarse particles on health and emphasized the importance of studying and regulating coarse particles separately from fine particles. A recent study by Deng et al. [
23] found that coarse particles generated by crustal sources might have adverse health effects as strong as those of fine particles generated from combustion sources.
The objective of this paper was to conduct a pilot study with limited data to examine the mass concentrations of fine particles including PM1 and PM2.5, and coarse particles PM2.5–10 inside Terminal 3 of the Soekarno-Hatta International Airport (SHIA) in Jakarta. The feasibility of estimating particle infiltration using time-lagged regression was evaluated. In addition, the effect of aircraft and passenger traffic on the concentration of fine and coarse particles was investigated.
4. Discussion
The hypothesis tests showed that the indoor PM
2.5 and PM
2.5–10 were significantly lower than those outdoors, whereas the PM
1 concentration was comparable to the outdoor one. The estimated I/O ratios suggest that the air filtration system at the terminal was working effectively in removing PM
2.5 as compared to the reported ratios in Ren et al. [
21]. However, the removal of PM
1 was less efficient. The ANCOVA results revealed that passenger traffic was a significant factor that affected the indoor coarse particle concentrations, while aircraft traffic showed significant effect on fine particles. The combined results indicate that the terminal building HVAC system is efficient at protecting the passengers and employees from aircraft emissions and other outdoor particles. The change in indoor fine particle concentration was largely due to aircraft traffic, which was inevitable for an airport terminal building. On the other hand, the change in indoor coarse particle concentration was largely depending on the passenger movement and the concentration from the previous hour. This also reflects the ability of the coarse particles to remain in the building at the current air exchange rate. The additional air filtration and cleaning system inside the boarding bridge may reduce the particles brought into the terminal building by arriving passengers. Increased ventilation rate could also aid the removal of existing coarse particles in the terminal building. As summarized in [
42], other than the PM of outdoor origin, there were numerous potential indoor sources of PM. For a large and complex building such as the airport terminal, these sources include particle emission and resuspension, which were often linked to human activities [
42]. Studies have shown that bioaerosols emitted from damp surfaces, cleaning product residues, and cooking activities could contribute to indoor PM [
42]. Particle resuspension from activities such as walking and vaccuming, which are common for a terminal building, is also an important source of indoor PM [
14,
15,
43]. The indoor measurement conducted in this study was at a single location near the boarding gate. Therefore the main activity considered was the walking of passengers and the spatial coverage was rather limited. If resources permit, future studies could consider deploying multiple sensors at various representative sites inside the terminal to investigate the different PM contributions from different locations with various activities.
This study detailed the process of gaining access to the airport terminal building to conduct air quality measurements and could be beneficial to future studies at airports. Due to time and resource constraints, the measurements were only for a short period of time and the dataset was limited. Because the PM measurements were conducted using a light scattering monitor, the high level of humidity in Jakarta also resulted in data loss. The influence of humidity on the remaining optical measurements was evaluated by calculating the I/O ratios for subsets of the data with different RH cutoff values, and the results showed modest changes for the I/O ratios. In addition, as can be seen from
Figure 10, the peak traffic periods were not covered by this study. A permanent air quality monitoring program at the airport would allow data collection in longer terms and contributes to the growth of the airport indoor air quality knowledge base.