Page 7 - JES202001
P. 7

2                           JOUR NAL O F E N V I R ONM E NT AL S C I E NC ES 87 (202 0) 1 – 9



          100 nm could reach up to 30,000 cm −3  in the urban area of  environment and regional climate, but also have an important
          Beijing,  which  is  much  higher  than  Wu's  studies  hazard to human health.
                   −3
          (27,000 cm ) (Wu et al., 2008). It is known that aerosols can  Prior research on the chemical composition of particles in
          not only reduce the visibility, but also have an adverse effect  Beijing was mainly focused on fine particles, and it was also
          on the human respiratory and cardiovascular systems. The  mainly focused on some specific species in China and abroad
          World Health Organization (WHO) estimated that air pollu-  in recent years (Pathak et al., 2009; Ianniello et al., 2011), the
          tion was associated with approximately 300,000 premature  size distribution of aerosol chemical species (Guo et al., 2010;
          deaths per year in China (Duan et al., 2014).       Li et al., 2012), particle number concentration (Yue et al., 2011)
             Beside the mass concentration and the particle size, the  and new particle formation processes (Gao et al., 2012) have
          concentration of potential toxic metals of aerosols plays a  also been discussed. There were few measurements of PM 10 ,
          decisive role for the assessment of atmospheric pollution and  especially comprehensive analysis of the different chemical
          the hazards to human health (Limbeck et al., 2012; Sato et al.,  compositions of particles. To fully understand concentrations
          2008). Atmospheric heavy metals are continually being  and chemical compositions of atmospheric particles in
          deposited into the ground by dry and wet deposition, from  Beijing, daily PM 10 samples were collected at an urban site in
          where they could be absorbed by plant roots and stems or  Beijing during December, 2014–January, 2015. The concentra-
          impact soil enzyme activity, biological activity and biodiver-  tions of major components, their characteristics and compar-
          sity, resulting in persistent negative impacts on the ecosys-  ison in hazy and non-hazy days of PM 10 were discussed in
          tem biogeochemical cycles. The long-term existence of heavy  detail. The studies presented are expected to be useful in
          metals may pose a great potential threat to the environment,  making future PM pollution control policies.
          it can invade the respiratory system, induce heart disease,
          lung disease, reduce lung function, and even cause cancer
          (Fang, 2010). As, Cr, Ni, Pb and Cd have some carcinogenic  1. Experimental design
          capacity, As and Cd have potential teratogenic effects on the
          human body, and Pb and Hg are toxic to the fetus (Hu et al.,  1.1. Sample collection
          2012). High anthropogenic emissions of heavy metals enter
          into the biosphere in China, and these emissions far exceed  The sampling site was located on the roof of an office building
          those of other countries with increasing trend (Pacyna and  at the IAP (Institute of Atmospheric Physics, Chinese Acad-
          Pacyna, 2001). Studies have shown that about 70%–80% of  emy of Sciences) campus (116°22′ E, 39°58′ N) in the Haidian
          metal elements in the atmosphere are adsorbed on fine  District, Beijing, which is about 6 m above the ground. The site
          particles (Lv et al., 2005; Mohanra et al., 2004).  is in the middle of the North Third Ring Road and the North
             The scattering and extinction effects of atmospheric  Fourth Ring Road in Beijing, which is about 150 m eastern
          aerosols are affected by its own physical properties (including  from the east–west urban traffic main road, North Tucheng
          particle size distribution, mass concentration, etc.) and  Road, and is about 200 m from the Badaling Expressway
          chemical composition. Water-soluble compounds (nitrates,  (Fig. 1). It is surrounded by high-density roads, residential
          sulfates, ammonium salts, etc.), organic and elemental carbon  buildings and office buildings. There are no obvious industrial
          (OC and EC) are the main chemical components that reduced  sources of aerosols in the vicinity. Therefore, it can be
          visibility in hazy days. Nitrates and sulfates are one of the  considered as a typical urban site.
          most important extinction components in the atmosphere,  Sampling was conducted from December 29, 2014 to
          the visibility will significantly reduce with the increasing of  January 22, 2015 by a sampler (VFC-PM10, Thermo, USA).
          concentration. Concentrations of nitrates and sulfates have a  There was no precipitation during observation period. The
          close relationship with the acidity of atmospheric precipita-  quartz filters were baked at 800°C for 3 hr before using to
          tion. Water-soluble ions have strong hygroscopic property;  remove absorbed organic vapors. The sampling duration was
          they can promote the formation of cloud condensation nuclei,  24 hr and filters were changed at about 9:00 am. Two sets of
          and also affect the size, composition, number, acidity and life  samplers were used to take samples in turn. After collecting,
          time of aerosols due to their strong hygroscopic property  the sampler was ultrasonically cleaned and dried, and was left
          (Xiang et al., 2017). In the case of high relative humidity, the  for use the next day. The concentrations of all species were
          moisture-absorbing growth of water-soluble ions will en-  calculated by mass divided by sampling air flow rate.
          hance the extinction effect of aerosols, which will lead to a
          decrease in visibility.                             1.2. Chemical analysis
             Carbonaceous species are also important fraction in PM 10 .
          Based on thermal and optical properties, carbonaceous  After sampling, all the samples were wrapped in aluminum
          aerosols can be divided into EC and OC. OC is emitted by  foil and stored in a refrigerator (−18°C) to avoid sunlight and
          fossil fuel combustion or is formed by a complex process of  analyzed for chemical species in less than a month. Prior to
          secondary formation, including of a vast array of individual  extraction and digestion, each filter was cut into three equal
          organic species, such as formaldehyde, acetone and PAHs  parts. One of them was digested with nitric acid, hydrogen
          (Cao et al., 2003; Tang et al., 2006; Yang et al., 2011). EC, which  peroxide, and hydrofluoric acid at 180°C for 6 hr. The reagents
          is important for radiative forcing, can be emitted directly by  were all Merk ultra-pure reagents (6 mL HNO 3 +2mL
          incomplete combustion of e.g., biomass and fossil fuel (Xiang  H 2 O 2 + 0.1–1 mL HF Mixed acid system). After the permeation
          et al., 2017), mainly from primary emissions. Carbonaceous  solution  passed  through a  filter  (pore  size:  0.45 μm,
          species have a significant impact on the atmospheric  Membrana, Germany, Micro PES), an inductively coupled
   2   3   4   5   6   7   8   9   10   11   12