Field Study on Online Monitoring Network of Air Toxics and
Tracking near a Petrochemical Industrial Park
Yu-Cheng Chen, Chin-Yu Hsu, Yue-Liang Leon Guo
National Institute of Environmental Health Sciences, National Health Research Institutes, Miaoli, Taiwan
A field study on onsite-continuous monitoring networks of air toxics was performed for
exposure assessment and source tracking near a petrochemical industrial park with mixtures of
manufacturing facilities and residential, urban and rural areas. The automatic monitoring networks of
air toxics utilizing high-performance portable VOC analyzers and anemometers were deployed at four
sites. More than 14,000 data sets were collected from the three-month continuous onsite monitoring.
The source directions were observed using the receptor model in cooperating with ambient VOCs and
wind information in each monitoring site. Our developed monitoring technique can be used to capture
the peak concentration of targeted VOCs and identity the geographical directions of pollutants, which
serves the purpose of exposure assessment of air toxics in the community level and tracking pollutants
for emission reduction.
INTRODUCTION
Air quality issues to public health have been attracting concerns globally. According to a World
Health Organization (WHO) report published in 20161, more than 90% of the world’s population is
exposed to air pollutants exceeding recommended limits. Air pollution is mainly from anthropogenic
sources such as traffic exhausts and emissions from various industrial manufacturing processes.
Among air pollutants, volatile organic compounds (VOCs) are one of the primary contributors to
PM2.5 and the formation of photochemical oxidants (monitored by photochemical assessment
monitoring station [PAMS]). Some VOCs are classified as Air Toxics (also known as Hazardous Air
Pollutants [HAPs]), which are associated with adverse effects on human health, including cancer,
reproductive effects, and respiratory illness, even under trace level exposure2. Air Toxics with various
compounds are still measured by offline canister sampling in accordance with laboratory toxic organic
(TO) methods, since diversified local specific sources make online monitoring challenging. A couple
field studies at industrial parks based on the offline method combined with cross-analysis of the
inventory data base were able to depict background VOC concentrations as well as abundant types of
VOCs3,4. However, lacking temporal resolution of the offline method makes it difficult to capture a
full picture of the emission status; especially for random emissions, such as fugitive emissions,
equipment leaks, emissions from malfunctioning processes, which usually generate air pollutant with a
high level.
Recently, an on-site continuous VOC monitoring network along fencelines of a mega steel
manufacturing plant was successfully demonstrated to be a feasible solution enabling effective
pollution source identification, earlier leakage detection, evaluation of VOC reduction control, and
precise exposure assessment5. In this study, the monitoring scope is extended to cover bigger regions
with mixtures of industrial parks, residential areas, urban and rural areas, which presents more
challenges for monitoring technique due to diverse sources, compounds, geography and climate.
EXPERIMENTAL METHODS Site Selection and System Setup for Monitoring Network
The Renda Petrochemical Industrial Park (RPIP) in southern Taiwan consists of over thirty
industrial plants and four waste water treatment facilities. Four sampling sites were selected to monitor
ambient VOCs using a continuous online air toxics monitoring network as shown in Figure 1. Each site
represents its unique geographic location in corresponding to the Industrial Park. Site A is located 3.6
km west of the RPIP. In this study, the site was influenced by winds from sea during winter season.
Site B is located only 1.6 km south of RPIP, which likely receives the highest VOC levels from the
Industrial Park. Site C is located at 30 km north-east of RPIP. The location is far away from both the
industrial park and metropolitan cities. Site C served as reference site (rural area), in which
background VOCs were more related to the natural environment from local farms and forests. Site D is
located in a metropolitan city 8.8 km south of RPIP with several small manufacturing facilities nearby.
As a result, it may receive combination of VOCs from RPIP, traffic emission, and the local
manufacturing facilities.
Each monitoring site was equipped with an anemometer on the roof of the building and a stand-
alone chassis with the online toxic VOCs monitoring system on the ground, as shown in Figure 1. The
online toxic VOCs chassis system consists of an automatic gas chromatography (Auto-GC) analyzer
MiTAP P310 (Tricorntech Corp., Taipei, Taiwan) capable of continuously measuring fourteen specific
VOCs related to industrial and traffic emissions, including Vinyl Chloride Monomer (VCM) , 1,3-
Butandiene, Benzene, Toluene, Ethylbenzene, m,p-Xylene, o-Xylene, Acetone, Propene, Ethyl
Acetate, 2-Butanone, 1,2-Dichlorobenzene and 1,4-Dichlorobenzene. The MiTAP system was
connected with a sampling tube extending to the roof for VOC collection at the same location as the
anemometer. In addition, the chassis was equipped with an automatic calibration system (ACS), which
served as a regular quality check for the MiTAP analyzer. Finally, a mini-computer was used to collect
the VOC analysis results from MiTAP and wind field information from the anemometer. In this study,
the automatic air toxic monitoring system was setup to output concentration of targeted 14 VOCs and
corresponding wind field data for every 30 minutes. The full data set was then uploaded to the cloud
through 4G wireless communication as shown in Figure 1. Meanwhile, canister field samples were also
manually collected weekly at each location and analyzed by both MiTAP and lab GC/MS for parallel
comparison.
Figure 1. Locations and site setups of online air toxics monitoring network.
Quality Assurance
Prior to onsite deployment, the MiTAP auto-GC analyzer was calibrated with targeted standard
VOC gases, with concentrations ranging from 2 ppbv to 50 ppbv respectively to ensure system
performance as results depicted in Figure 2 (a). To ensure data quality during monitoring period, the
ACS system was used to automatically perform daily checks on MiTAP response with the same
targeted standard VOC gas mixture (10 ppbv) as the results shown in Figure 2 (b). The system resumed
field sample monitoring once passing the ACS quality test. Under the circumstance that the on-site
ACS check result is out of targeted specification (e.g., > 30% concentration deviation), a notification
message will be sent to designated personnel via internet for immediate response.
Figure 2. Illustration of quality checks. a) In-house calibration, b) On-site daily auto check with ACS.
RESULTS
In this study, a total of 14,765 data sets were collected from the monitoring network (Nov. 1,
2016 ~ Feb. 28, 2017). Figure 3 shows the three-month average concentrations of targeted VOCs
measured from four sites respectively. The average concentrations for most VOCs are below 2 ppbv,
which is comparable to weekly off-line GC-MS measurements with canister samplings. Slightly higher
concentrations of industrial specific VOCs were observed at Sites A and B near the industrial park as
compared to Site C (reference area). However, since random or unexpected VOC emissions may
occur only within a day or several hours from a nearby industrial sources, the average concentration
measure tends to mask the importance of actual VOC excursion events.
Figure 3. Three-month average concentrations of VOCs as measured from 4 different sites.
In contrast to the average concentration measure (which leads the similar conclusions from the
off-line method), the advanced analysis with a temporal concentration trends combining information
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Site A Site B Site C Site D
Benzene Toluene Ethylbenzene mp-Xylene o-Xylene Acetone
Propene VCM 1,3-Butadiene 2-butanone Ethyl Acetate
Location
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(p
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from continuous monitoring data, all individual targeted VOCs, wind speed/direction, and network
layout, is able to depict more comprehensive patterns of ambient air pollutants regarding source,
location, transportation, background level, and even episode. Here, Figure 4 illustrates several
examples observed in various scenarios.
Figure 4(a) shows that the acetone concentration at reference Site C has a periodic fluctuation
in concentrations with consistently higher values during daytime (~2 ppbv) than nighttime (~1 ppbv).
It is suspected due to natural environment emissions from plants, trees, or the breakdown of organics
due to higher temperatures during the daytime. Although there is a slightly higher concentration for
acetone at other sites, no apparent periodic trend is observed, possibly due to random local emission
activities. Figure 4(b) shows that an excursion of the high concentration for VCM (~20 ppbv) occurred
during the evening of Dec. 13 at Site B, which is closest to the industrial park. The same VCM
excursion can also be found at Site A with a relatively lower concentration (~7 ppbv). Since the
excursion occurs in the early evening, the west wind at Site A could have potentially assisted pollutant
propagation to this location. Figures 4(c) and (d) show several events of propene and 1,3-butadien
excursions at both Sites B and D. The wind field at Site B is mostly from the northwest, with
significantly higher concentrations than those observed by Site D in a farther south location, indicating
that the emission sources are from the Industrial Park in the north of Site B. Figures 4(e) and (f) show
the temporal concentration trends of benzene and toluene, which are associated with both industrial
and traffic emissions. Site C shows much lower concentrations compared to other sites, which is due to
limited human activity at the corresponding location. Sites B and D show higher concentrations but do
not present apparent correlation between the locations. The benzene at Site D tends to have higher
concentrations during early morning and evening, suggesting more traffic emission is relevant. In
addition, Site B shows random higher concentrations during different times, indicating the combination
of industrial and traffic emission sources.
Figure 4. Example of VOC concentration excursions observed by the monitoring network.
The receptor model in cooperation with VOC concentration and wind-rose analysis is used to
trace the emission sources as illustrated in Figure 5. It can be seen that VMC with the highest
concentration at Site B was measured in the north, clearly indicating the emission source is directly
from the north facility, inside the industrial park. While VCM with a relatively lower concentration
was also observed at Site D, the wind-rose plot shows local high concentrations from different wind
directions. It is suspected that the emission sources are from local manufacturing plants near Site D.
For the case of 1,3-butadien, the highest concentration is also obtained from Site B. However, the
wind-rose shows that 1,3-butadien is from a north-north west direction, indicating a different emission
source from the VCM plant inside the industrial park. The benzene concentration shows the similar
result as 1,3-butadien observed at Site B, indicating the benzene concentration at Site B is dominated
by industrial emission from the industrial park. On the contrary, the benzene concentrations measured
at the other three sites do not show apparent emission sources from industrial park, which suggests that
benzene is dominated by local activities such as traffic emission.
Figure 5. Concentration wind-rose plots for toxic VOCs source tracking (Receptor model).
SUMMARY
An online continuous toxic VOC monitoring network over a large region of mixed industrial
and residential areas is demonstrated to be effective in providing comprehensive status for emission
patterns, source tracking, excursion types, general background concentration, and transportation. With
objective selections of site locations and VOC species, the monitoring network provides solutions,
enabling effective assessments of human exposure to air toxic pollution as well as air toxic impacts on
the environment.
ACKNOWLEDGMENT
This study was funded under the project No. EM-105-PP-13 supported by the National Institute
of Environmental Health Sciences, National Health Research Institutes (NHRI) in Taiwan. We would
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(Site C)
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also thank the TricornTech Corporation (Ching-Lin Hsiao, Li-Peng Wang, and Tsung-Kuan A. Chou)
supporting the monitoring network with a MiTAP auto-GC analyzer.
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