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2 jour nal o f e nvironmental sciences 93 (2020) 1 e12

constant. Wang et al. (2016) conducted a related study on the
Introduction
variation characteristics and chemical reactivity of atmo-
spheric VOCs in a suburb of Beijing. The results show that
With the rapid development of the world economy and the
aromatics and alkenes are the main contributors to ozone
surge in population, environmental issues have become a generation. Hui et al. (2018) have reported that Wuhan belongs
persistent problem that cannot be ignored. Air pollution has
to a VOC limited area in terms of ozone generation by using
become a common problem that has received widespread the Empirical Kinetic Modelling Approach. Therefore, deter-
attention in recent years in China (Huang et al., 2016; Hui et al.,
mining the contribution of VOCs to O 3 formation is important
2019; Wei et al., 2018; Zhong et al., 2019). The occurrence of for local governments to control photochemical pollution.
haze, a common type of air pollution, is more frequent in
VOCs not only play an important role in atmospheric
Beijing, an international metropolis with more than 20 million
chemistry, but also are harmful to human health (Parra et al.,
people and nearly 6 million motor vehicles, owing to the rapid 2006). Toxic VOCs are mostly benzenes and halocarbons.
regional industrialization and urbanization. Studies have
Different species, different exposure times, and exposure
confirmed that short- or long-term exposure to haze pollution pathways have different health effects on humans. Extensive
is associated with cardiovascular and respiratory diseases,
studies have confirmed that VOCs are harmful to human health
premature death, and increased risk of cancer (Gao et al., 2017; owing to their toxicity, mutagenicity, and carcinogenicity (Gong
Lu et al., 2013). Thus, devising strategies to effectively control
et al., 2017; Tuet et al., 2017; Tyagi et al., 2016). The health risks
and prevent air pollution is pressing. Recently, studies have to the human body exposed to VOCs can be divided into
increasingly shown that volatile organic compound (VOC)
carcinogenic and non-carcinogenic effects (Jiang et al., 2017).
emissions play an important role in air pollution. Some VOCs, such as dichloromethane, trichloroethylene, and
VOCs refer to organic matters with boiling points below
BTEX, are classified as hazardous air pollutants. A great deal of
250 C at atmospheric pressure (Xu et al., 2016). These, including

research has been conducted on the health risk assessment of
non-methane hydrocarbons, halocarbons, BTEX (benzene, PM2.5 in Beijing (Song et al., 2019; Xu et al., 2018). In contrast,
toluene, ethylbenzene, and meta-, para-and ortho-xylenes), and
the health risk assessments for VOCs require further work.
oxygenated volatile organic compounds (OVOCs), which are In the present study, the concentrations of 99 VOCs were
emitted from various natural and anthropogenic sources. Ac-
measured using online instruments at an urban site in Beijing
cording to the atmospheric photochemical reactivity, VOCs can during winter from 15 December 2015 to 17 January 2016 and
be divided into two types: strong and weak photochemical ox-
summer from 21 July to 25 August 2016. All values were
ides. The former type can quickly participate in atmospheric measured at 10 am. The sampling period was divided into
chemical processes and is eliminated by reaction with atmo-
polluted days (air quality index (AQI) > 100) and “normal” days
spheric oxidants such as OH radicals and O 3 . Its lifetime in the (AQI 100). The variations in the type of VOCs, SOA formation
troposphere is short and its overall lifespan generally lasts from
potential, and ozone formation potential were analyzed dur-
several hours to one day. Therefore, such compounds are not ing the normal or polluted days of winter and summer. In
easy to grow. Distance transmission is mainly concentrated addition, a health risk assessment (carcinogenic risk and non-
near pollution sources. The latter is relatively stable and has a
carcinogenic risk) owing to inhalation exposure to specific
relatively long residence time in the atmosphere. Many studies VOCs was performed. Finally, the effects of local sources and
have shown that VOCs with a higher photochemical reactivity
long-distance sources on VOC pollution were assessed using
are generally important precursors to the formation of sec- the potential source contribution function (PSCF) during both
ondary organic aerosol (SOA) and ozone (Sun et al., 2016; Hui
sampling periods.
et al., 2018). VOCs can react with OH radicals, ozone, and ni-
trogen oxides (NO x ) in the atmosphere to form SOA. The sub-
sequent accumulation of SOA accelerates the formation of haze 1. Materials and methods
(Rao et al., 2016). Huang et al., 2014 have reported that the for-
mation of haze is greatly promoted by secondary aerosol for- 1.1. Site description
mation, contributing 30e77% and 44e71% of PM2.5 and organic
aerosol, respectively. Therefore, studying the formation pro- The sampling site was selected in Chaoyang District, Beijing,
cess of SOA is expected to further our understanding of the China (40 02 N, 116 24 E), which was near residential areas,

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formation of haze and reduce air pollution. schools, parks, and road junctions. Samples were collected at
VOCs are also of interest because of their participation in 10 am in winter from 15 December 2015 to 17 January 2016 and
tropospheric ozone formation, stratospheric ozone depletion, in summer from 21 July to 25 August 2016. Due to the appro-
and indirect global greenhouse effects (Jaars et al., 2018; Jiang priate temperature and solar radiation, the VOC concentration
et al., 2017). In the presence of solar radiation, VOCs, NO x , and of Beijing at 10 am was close to the daily average concentra-
CO can form O 3 through a series of chemical reactions (Kumar tion and was good to represent the daily concentration,
et al., 2014). Numerous studies have been carried out on the compared with the result of Gu et al., 2019.
potential contribution of VOCs to the formation of O 3 .
Bowman and Seinfeld (1994) and Carter (1996) have shown 1.2. Sampling and chemical analysis
that the composition of VOCs in the atmosphere is complex
and variable, and the ozone generation potential varies greatly VOCs were monitored by a gas chromatograph with flame
because of the difference in concentration of each component, ionization detector which was coupled to a mass spectrom-
concentration of free radicals, and photochemical reaction eter (6890/5973, Agilent Technologies; Santa Clara, CA, USA)