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JOUR NAL O F E NVI R ONM E NT AL S C I E NC ES 79 (2019 ) 1 – 10       3


                                                               (peroxy acetyl nitrate), acetonitrile and methyl chloride (CH 3 Cl)
                                                               which are typical tracers of specific emissions were selected as
                                                               inputs for the model. PAN is a secondary product and could be
                                                               used as the tracer for secondary formation in the PMF model
                                                               (Guven and Olaguer, 2011), while ACN and CH 3 Cl are tracers of
                                                               biomass burning (Yuan et al., 2010). The detailed description of
                                                               the model configuration and data processes can be found in
                                                               previous studies (Ling et al., 2017; Yuan et al., 2012). Briefly, the
                                                               model was tested with different numbers of factors and the
                                                               most optimum source profiles and contributions were deter-
                                                               mined based on the correlations between the modeled and
                                                               observed data as well as the comparisons of the modeled
                                                               profiles with the results from emission-based measurements
                                                               and other PMF model simulations (HKEPD, 2015; Wang et al.,
                                                               2014; Yuan et al., 2013; Liu et al., 2009).


                                                               2. Results and discussion

                                                               2.1. Overall results of isoprene, MACR and MVK

                                                               The time series of isoprene, MACR and MVK concentrations as
           Fig. 1 – Location of the sampling site and its surrounding  well as the meteorological parameters during the study period
           areas in the Pearl River Delta region (blue dot is the location if  are shown in Fig. 2. The overall average mixing ratios of
           Heshan district in Jiangmen city).                  isoprene, MACR and MVK during the entire sampling period
                                                               (30 days in total) were 151 ± 17, 91 ± 6 and 79 ± 6 pptv, with
                                                               the median values of 60, 59 and 38 pptv, respectively. The
                                                               levels of isoprene dropped to an average value of 75 ± 7 pptv
           while their concentrations were quantified based on the  due to the decrease in temperature from 02 November
           calibration curves of standard and zero air samples. The  onwards (p < 0.05). In this study, daily variations of MACR
           configuration, quality control and assurance, and the analyt-  and MVK at the HS presented three patterns: (1) comparable
           ical performance of the system have been provided in the  mixing ratios were observed for MACR and MVK for ~10%
           previous study (Shao et al., 2009).                 (three sampling days in total) of the total sampling days (p >
                                                               0.05) with average mixing ratios of isoprene, MACR and MVK
           1.3. Positive matrix factorization (PMF) model      being 52 ± 11, 37 ± 4 and 36 ± 6 pptv, respectively; (2) the
                                                               mixing ratio of MACR was much higher than MVK on eighteen
           The PMF (version 4.0) model was applied to the observed VOC  sampling days ([MACR] > [MVK], p < 0.05) with the average
           data to explore the sources of MACR and MVK at the HS.  mixing ratios of isoprene, MACR and MVK being 147 ± 20,
           Although, a total of 58 NMHCs were identified in the present  85 ± 8, and 39 ± 3 pptv, respectively; and (3) higher mixing
           study, not all were utilized in PMF due to the fundamental  ratios were observed for MVK than MACR on nine sampling
           assumption of non-reactivity and/or mass conservation of the  days ([MVK] > [MACR], p < 0.05) with average mixing ratios of
           model (Zhang et al., 2012). Furthermore, the aim of this study  isoprene, MACR and MVK being 193 ± 38, 106 ± 10, 153 ±
           was to investigate the source attributions of MACR and MVK  13 pptv, respectively. The second pattern was consistent with
           based on the observed NMHC data rather than identifying the  those observed at an urban site in Beijing during summer
           sources of the NMHCs (He et al., 2018). As such, species that  non-haze days and winter haze days (Rao et al., 2016). This
           are typical tracers of the sources were selected as the input for  indicates that biogenic emissions and photooxidation of
           the PMF model (Chen et al., 2013). It should be noted that a  isoprene were not important sources of MACR and MVK.
           single VOC may be a tracer for several emissions. For example,  Furthermore, the higher MACR and MVK levels in Beijing were
           isoprene is an important biogenic NMHC in the PRD region.  related to variations in gasoline and diesel vehicle emissions
           Aromatics, such as benzene, toluene, ethylbenzene, and  as indicated by the principal component analysis (Rao et al.,
           xylenes, could be emitted from both vehicular exhausts and  2016). The third pattern was consistent with the findings of
           solvent usage while alkenes, such as ethene, propene, and  previous studies which indicated that the mixing ratios of
           butene, are tracers for incomplete combustion (i.e., vehicular  MVK were usually higher than those of MACR if photooxida-
           emissions) (Guo et al., 2011; Lau et al., 2010; Ho et al., 2009; Liu  tion of isoprene was the dominant source of MACR and MVK
           et al., 2008). Furthermore, previous studies have demon-  (Guo et al., 2012 and references therein). This could be
           strated that C 3 –C 4 alkanes are typical tracers of vehicular  attributed to the longer lifetime of MVK as well as the higher
           exhaust (although they could also be emitted from liquefied  production rate of MVK from photooxidation of isoprene in
           petroleum gas (LPG)) while C 5 –C 6 alkanes, n-octane, and their  contrast to MACR. Nevertheless, the large daily variations of
           isomer are mainly related to gasoline vehicle emissions (Liu et  MACR and MVK indicated the influence of other sources other
           al., 2008). In total, 18 NMHCs, together with MACR, MVK, PAN  in addition to photooxidation of isoprene at the HS.
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