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

          Fig. 3 e Top 10 species contributing to SOAP on (a) winter normal days, (b) winter polluted days, (c) summer normal days,
          and (d) summer polluted days.

                                                              acetaldehyde. In contrast, in summer, acetaldehyde made the
                                                              largest contribution, 22.00% and 21.61% on the normal and
                                                              polluted days, respectively, followed by n-hexanal. These re-
                                                              sults infer the importance of more rigorously controlling the
                                                              emission of alkenes, such as ethylene, during winter, and
                                                              OVOCs, such as acetaldehyde, during summer to address the
                                                              ozone pollution problem in Beijing.

                                                              2.5.  Health risk assessment

                                                              Haze in Beijing constitutes a large concentration of VOCs,
                                                              and some of these species may pose a threat to the health
                                                              of the public. Probability and deterministic were used to es-
                                                              timate the risk of inhalation of VOCs to humans, and the
                                                              risk of inhalation was divided into carcinogenic and non-
                                                              carcinogenic (Choi et al., 2011). USEPA (2009) developed an
          Fig. 4 e Variation in the contribution of VOC components to
                                                              inhalation dosimetry methodology to estimate human health
                                                              risks associated with the inhalation of VOCs. The hazard ratio
                                                              (HR) and the lifetime cancer risk (LCR) were calculated to es-
             Fig. 5 shows the top 10 OFP species across the seasonal  timate the non-carcinogenic and carcinogenic health risks
                                                              using Equations (4)e(6) (Tohid et al., 2019).
          days studied. Among the top 10 species, alkenes, aromatics,
          and OVOCs contributed the most to the OFP, regardless of the  EC
          seasons days studied. The OFP values of the top 10 species  HR ¼ RfC  1000                       (4)
          were higher during the polluted days than during the normal
          days. In winter, ethylene contributed the most to the total    CA  ET  EF
                                                              EC ¼                                          (5)
          OFP, accounting for 26.00% on the normal days and 27.64% on  365ðdays=yearÞ 24ðhours=dayÞ
          the polluted days, followed by propylene, m/p-xylene, and
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