With diagnostic reports and principal component analysis (PCA), industrial sites and urban areas were affected by the local emission of AVOCs. On the other hand, the effect of vehicle exhaust gases in the center and highway was more dominant with the seasonal northwesterly wind in autumn and winter. OFPs of AVOCs and BVOCs were high in most sampling sites during summer with the influence of seasonal wind and sea-land breeze with high BVOC reactivity.
There was predominant pollution by AVOCs in Ulsan during all seasons with the strong effect of secondary formation potential from BVOCs in summer. With BVOCs emitted by trees and AVOCs transported by industrial facilities, secondary formation in Ulsan should be controlled by monitoring the concentration and pollution characteristics of AVOCs and highly reactive BVOCs.
Introduction
- Volatile organic compounds (VOCs)
- Anthropogenic volatile organic compounds (AVOCs)
- Biogenic volatile organic compounds (BVOCs)
- Secondary formation of VOCs
- Objective of this study
Nevertheless, they show considerable reactivity in atmospheric chemistry, which has an impact on the global carbon cycle (Klinger et al., 2002). It is reported that isoprene is released mainly from broadleaf plants among BVOCs (Aydin et al., 2014). Although studies on the effects of AVOCs have been ongoing in Korea, there has been little research on the secondary formation by BVOCs (Choi et al., 2017; Kim et al., 2013).
Parameters such as ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP), which are based on measured reactivity and yields from laboratory experiments, have been widely used to evaluate the effects of VOC on the secondary formation (Duan et al. , 2008). Only one modeling study predicted SOA production during Ulsan's heat wave in terms of secondary formation (Yang et al., 2020).
Materials and Methods
- VOC sampling
- Sampling sites
- Active and passive air samplings
- Meteorological and criteria air pollution data
- Analysis and Quality Assurance/Quality Control (QA/QC)
- Target Compounds
- TD-GC/MS
- QA/QC
- Estimation of Ozone and SOA formation
- Ozone formation potential (OFP)
- SOA formation potential (SOAFP)
- Data analysis
- Wind field
- Conditional bivariate probability function (CBPF)
- Statistical analysis
270 samples were collected every 3 h with a sequential tube sampler (STS-25, Perkin Elmer, USA) equipped with a pump (MP-Σ30KNII, Sibata, Japan) at a flow rate of 50 ml/min and adsorbent tubes (Carbotrap 300, Supelco, USA), filled with multilayer adsorbent (Carbotrap C, Carbotrap B and Carbosieve S-III) (Figures 7, 8). Methyl tert-butyl ether (MTBE), benzene, toluene, ethylbenzene, m,p-xylenes, o-xylene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene and naphthalene are selected based on high emissions and concentrations from previous studies and emission data from industries in Ulsan and a list of photochemically reactive precursors (Kim et al., 2019). The MDL samples were analyzed using the same analytical procedure as the real samples.
To evaluate the contribution of individual VOCs to the ozone formation potential (OFP), Propylene-Equivalent (Prop-Equiv) concentration was proposed by Chameides (Chameides et al., 1992) calculated by eq.5. SOAFPi is the SOA formation potential of VOC (i), Ci is the measured concentration of VOC (i) (µg/m3), and SOA yield (i) is the stoichiometric constant for SOA formation from VOC (i) (Pandis et al., 1992).
Result and discussion
Concentration
- AAS VOCs concentration
- PAS VOCs concentration
Monoterpenes are known to be actively emitted with a high correlation with temperature (Kaser et al., 2013; Tingey et al., 1980). For the concentration fraction in Figure 13, there was a higher concentration fraction of BVOCs in summer (8%) than in autumn (2%) and winter (1%). Temporal variation of VOC concentration of AAS. a) Concentration trend of Σ24 VOCs, (b) Concentration trend of AVOCs and BVOCs, (c) Isoprene and Monoterpene trend, and (d) concentration fraction of AVOCs and BVOCs in summer, autumn and winter.
In Figure 15, Although it is well known that isoprene and monoterpenes are highly emitted during the day with increased temperature and light intensity, only the average concentration of isoprene emitted from broad leaves was higher during the day than at night and was moderately correlated with temperature and solar radiation in summer (Spearman's correlation, r = 0.697, r = 0.650, p < 0.01) (Fillella & Penuelas, 2006; . Ghirardo et al., 2010; Guenther et al., 1993). Due to its high volatility and absence of storage in plants, isoprene is mainly emitted into the atmosphere as soon as it is synthesized, resulting in high daytime concentrations (Ghirardo et al., 2010). On the other hand, the average concentrations of monoterpenes emitted from conifers and some broad leaves were higher at night than during the day in summer, similar to previous studies in urban areas (Hellén et al., 2012; Panopoulou et al., 2020).
Emission is regulated by both the concentration of monoterpenes in tissues and temperature-dependent vapor pressure (Laffineur et al., 2011; Lerdau et al., 1994; Lerdau et al., 1997). This causes an accumulation of monoterpenes in the night atmosphere and a rapid decrease in concentration in the morning due to mixing onset and a rapid oxidation reaction by sunlight (Järvi et al., 2009; Li et al., 2020). Benzene and toluene are known to be released by petrochemical processes (Lv et al., 2021; Watson et al., 2001).
These sites are located next to shipbuilding industries and these compounds are reported to originate from painting and coating processes (Datta & Philip, 2012; Yuan et al., 2010). In a previous study in Ulsan, four large industrial complexes (petrochemical, non-ferrous, automotive, and shipbuilding) were clearly the main sources of VOCs (Kim et al., 2019). Sites U1 and U7 are located near conifers known to emit mainly monoterpenes (Aydin et al., 2014; Chang et al., 2021).
Source identification
- Diagnostic ratio
- CBPF
- PCA
Also, X/E ratios in winter showed low ratios with the dominant northwesterly seasonal wind reducing the emission effect from the industrial area on the east coast in Ulsan and stale air mass could be transported over a long distance (Vuong et al., 2020). On the other hand, CP of m,p-xylene and o-xylene was high in the eastern part of the sample site which is a shipbuilding and automotive industry site. With the 95th percentile data in Figure S6, m,p-xylene and o-xylene showed high CP from the southeast section which is in the same direction as the 75th percentile data.
From the diurnal patterns in Figure S7, isoprene showed high CP during the day with an easterly wind, but no pollution at night. On the other hand, monoterpenes showed high CP from the northwest part near the sampling site in Figure 20. From the diurnal patterns in Figure S7, monoterpenes showed higher CP at night when there was a slow wind.
In the fall, the CPs of the 75th percentile data for AVOCs and BVOCs were high from the northwest. In the AVOCs, the CP of benzene was imported from the northwest region and was characterized by high emissions from highway vehicle exhaust. Ethylbenzene, m, p-xylenes and o-xylene CPs of the 95th percentile showed high CP from the southeastern part.
Even in autumn, high from the industrial area could be transported to urban areas and cause pollution when the southeast wind blew. In winter, there were similar 75th percentile CPs of AVOCs and BVOCs from the northwest, and CPs from the southeast were observed. With CP from the northwest, CP of AVOCs from the southeast could be emitted from industrial facilities.
Formation potential of SOA and ozone from VOCs
- OFP estimation from AAS
- OFP estimation from PAS
- SOAFP estimation from AAS
- SOAFP estimation from PAS
It also showed high ozone formation potential, ranking second among all VOC species measured in summer. In Figure 24 there is the OFP contribution of different VOC species in summer, autumn and winter. On the other hand, the VOC species that contributed the most to ozone formation potential were m,p-xylenes (27% and 24%) in autumn and summer.
Using the OFP contribution fraction of VOC species at industrial sites, urban sites, and rural sites during sampling periods in Figure 25, different OFP contribution fractions were observed. Although the contribution of BVOCs is high, the effect of AVOCs in rural areas is not negligible. In autumn and winter, toluene and benzene were the dominant VOC species that formed STD.
Also, the SOAFP contribution characteristics of BVOCs were different from the OFP contribution with the low contribution of monoterpenes. Figure 30 shows the SOAFP contribution of different VOC species in summer, autumn and winter. Compared to summer, the contribution of BVOCs has been reduced to 4% in autumn and 0% in winter.
The reduced SOAFP contribution of BVOCs was estimated using the relationship between lower BVOCs concentration and emissions from reduced plant activities in the cold season. In Figure 31, there are SOAFP contribution fractions of VOC species at industrial sites, urban sites, and rural sites during sampling periods. The top 5 VOC species that contributed to the concentration were BTEX and their concentration contribution was 79%.
Conclusion
Concentration, sources and ozone formation potential of volatile organic compounds (VOCs) during ozone episode in Beijing. Spatial and seasonal variation and source apportionment of volatile organic compounds (VOCs) in a heavily industrialized region. Volatile organic compounds (VOCs) during non-haze and haze days in Shanghai: characterization and secondary organic aerosol (SOA) formation.
Seasonal and diurnal variations of volatile organic compounds (VOCs) in Hong Kong's atmosphere. Characteristics of atmospheric volatile organic compounds (VOCs) in a mountainous forest area and two urban sites in southeastern China. Chlorinated volatile organic compounds (Cl-VOCs) in the environment: sources, potential human health impacts, and current remediation technologies.
Is it possible to predict the concentration of natural volatile organic compounds in the forest atmosphere. Spatial and temporal variations of volatile organic compounds using passive air samplers in the multi-industrial city of Ulsan, Korea. Characteristics of volatile organic compounds in the metropolitan city of Seoul, South Korea: diurnal variation, source identification, secondary organic aerosol formation and health risk.
Impact of biogenic volatile organic compounds on ozone production in the Taehwa Research Forest near Seoul, South Korea. Risk assessment of volatile organic compounds benzene, toluene, ethylbenzene and xylene (BTEX) in consumer products. Source profiles of volatile organic compounds (VOCs) measured in a typical industrial process in Wuhan, Central China.
Intraday and interday variations of 69 volatile organic compounds (BVOCs and AVOCs) and their source profiles at a semi-urban site. Source apportionment of volatile organic compounds: Implications for reactivity, ozone formation, and secondary organic aerosol potential.
