Measurements of 50 Non-polar Organic Compounds Including Polycyclic Aromatic Hydrocarbons, n-Alkanes and Phthalate Esters in Fine Particulate Matter (PM2.5) in an Industrial Area of Chiba Prefecture, Japan

Quantitative data of 50 non-polar organic compounds constituting PM2.5 were continuously collected and analyzed from June 2016 to October 2017 (approximately 17 months) at Ichihara, one of the largest industrial areas in Japan. Target non-polar organic compounds including 21 species of polycyclic aromatic hydrocarbons (PAHs), 24 species of n-alkanes and 5 species of phthalate esters (PAEs) were simultaneously measured by gas chromatography/mass spectrometry. Basically, the average concentrations of the total PAHs, n-alkanes and PAEs in each season remained nearly level, and seasonal variations were little throughout the study period. These results suggest that the emission sources, which are not influenced by the seasons, are the dominant inputs for the target organic compounds. Diagnostic ratios of PAHs, assessment of n-alkane homologue distributions, carbon preference index, and the contribution of wax n-alkanes from plants were used to estimate source apportionments. These results indicate that anthropogenic sources were the main contributor for most PAHs and n-alkanes throughout the study period. The concentrations of PAEs selected in this study were low because emission amounts of these chemicals were little within the source areas of the sampling site. To our knowledge, this study is the first attempt to simultaneously measure a high number of non-polar organic compounds in PM2.5 collected from the ambient air of Japan, and the resultant data will provide valuable data and information for environmental researchers.


INTRODUCTION
Particulate matter (PM) is an atmospheric pollutant that has received widespread concern as it causes public health problems and plays important roles in regulating regional and global climate (Fuzzi, et al., 2015;IPCC, 2013;WHO, 2013;Jacob, 1999).Among the PM, particle sizes with aerodynamic diameter less than 2.5 μm (PM 2.5 ) are particularly hazardous to public health because of their Measurements of 50 Non-polar Organic Compounds Including Polycyclic Aromatic Hydrocarbons, n-Alkanes and Phthalate Esters in Fine Particulate Matter (PM 2.5 ) in an Industrial Area of Chiba Prefecture, Japan ability to penetrate into the alveoli of lungs and they are therefore more likely to increase the incidence of respiratory and cardiovascular diseases (Ueda, 2011;Schwartz and Neas, 2000).
According to the information provided by the Ministry of the Environment Japan, 74.5% of stations monitoring general ambient air, and 58.4% of stations monitoring auto-exhaust emissions met environmental quality standards for PM 2.5 during the 2015 fiscal year (from April to March of the following year), and further countermeasures to reduce the level of PM 2.5 are required (http://www.env.go.jp/press/103858.html, in Japanese, Accessed on June 1, 2018).For an effective reduction of PM 2.5 levels, it is important to identify their emission sources and describe their chemical properties in the ambient air.Long time series of quantitative data of the chemical compositions that constitute PM 2.5 are necessary to provide the required information to achieve PM 2.5 reduction.
A wealth of publications have reported that the organic fraction of PM 2.5 consists of various kinds of organic compounds with different abundances in different areas of the world (Ichikawa et al., 2017;Mikuška et al., 2017;Ahmed et al., 2016;Fang et al., 2016;Li et al., 2016;Alves et al., 2015;Yadav et al., 2013;Park et al., 2006;Simoneit et al., 2004).Moreover, increasing attention has been paid to the study of the organic compounds in PM 2.5 to improve under standing of the emission sources and source apportionment.However, in Japan, most PM 2.5 studies have focused on metallic elements, carbonaceous components, and water-soluble inorganic components, and studies into organic compounds remain deficient.
Therefore, we intensively measured 50 different nonpolar organic compounds including 21 species of polycyclic aromatic hydrocarbons (PAHs), 24 species of n-alkanes and 5 species of phthalate esters (PAEs) in PM 2.5 in a long time series at Ichihara, a major industrial area in Japan.Selected non-polar organic compounds were simultaneously measured employing GC/MS.To the best of our knowledge, this paper is the first attempt to simultaneously measure as many non-polar organic compounds in PM 2.5 collected for a long time series (approximately 17 months) from the ambient atmosphere of Japan.Our results aim to provide useful insights and data for use in improving understanding of the target organic compounds in PM 2.5 and thereby contribute to better air quality management strategies.

1 Sampling Site Description
Sampling was conducted on the roof (12 m height above the ground) of the Chiba Prefectural Environmental Research Center (CERC).The CERC is located between the industrial zone of Tokyo Bay (a large industrial base including gas power plants, heavy petrochemical industries, and many light industries within ca. 2 km radius), and the residential zone of Ichihara, Chiba Prefecture, Japan (Fig. 1).The site is located approximately 200 m southeast of the Japanese National Route 16 (average weekday 24-hour traffic of 42,007 vehicles, of which 29.1% are large-sized vehicles).Ichihara is about 40 km southeast of central Tokyo, and the estimated population is nearly 277,000.

2 Sample Collection
PM 2.5 samples were collected on 47 mm diameter quartz filter (Pall Corp., 2500QAT-UP, Q-filter) from 13 June 2016 to 25 October 2017.The flow rate of the low volume air sampler (Rupprecht and Patashnick Co., Inc., Partisol-FRM Model 2000 Air Sampler) was 16.7 L/min with a constant sampling rate (accumulating to ca. 24 m 3 /d).From our previous study, daily air volumes per sample (24 m 3 /d) were too low to quantify some of the organic compounds present in relatively small amounts in the ambient atmosphere, so the samples in this study were sampled on a weekly basis (Ichikawa et al., 2017).Park et al. (2006) also pointed out the difficulty of detailed analysis of organic compounds by gas chromatography/mass spectrometry (GC/MS) from daily sampling, supporting the decision to analyze samples on a weekly basis.Some amount of organic compounds may be decomposed or evaporated from the Q-filter during the sampling.However, due to the reason mentioned above those were not taken into consideration in this study.
The sampling periods are described in Table 1.Based on the definition used by the Japanese Meteorological bon (OC) prior to sampling.However, combustion could activate the Q-filter, resulting in positive artifacts due to the absorption of gas phase organic materials onto the filter.As described in Section 2.3, gravimetric measurements of PM 2.5 collected in Q-filters were designed in this study and to eliminate the possible positive artifacts during transport, sampling and storage, Q-filters were not combusted.
Travel blank filters were prepared and placed in the same container as the samples and were transported and treated in the same way (e.g., making contact with the sampling devices, and being exposed to the conditions of the sampling site, storage, and all analytical procedures).Sample results reported in this paper were corrected based on the travel blank filters.
Sample filters were placed in petri dishes and enclosed in a sealed bag.All samples were stored in a freezer at -30°C until chemical analysis to prevent evaporation and degradation of components constituting PM 2.5 .A total of 68 effective samples were collected in this study, which included 3 blank samples.

3 PM 2.5 Mass Concentration
Both PM 2.5 sample filters and travel blank filters were weighed using an electronic microbalance (A&D Company Ltd., BM-20) with a reading precision of 1 μg.Prior to weighing, all Q-filters were kept under equilibrated conditions of constant temperature (21.5± 1.5°C) and relative humidity (35±5%) for at least 24 hours.An ionizing blower was used to eliminate the effects of static electricity on the weighing process.Obtained PM 2.5 mass (μg) was calculated by subtracting pre-weight from post-weight of the Q-filters.The PM 2.5 mass concentrations (μg/m 3 ) were calculated by PM 2.5 mass per total volume of suction.
For the accuracy testing of gravimetric measurement, PM 2.5 mass concentration was measured in parallel using an automatic instrument (Horiba Ltd., APDA-3750A) employing a beta-ray absorption technique.Automatic instrument was installed at the monitoring station of the CERC, at a height of 7 m above the ground.PM 2.5 mass concentrations observed by two different methodologies showed good positive correlation (n = 64, R = 0.84).

4 OC Measurement
The OC was measured by the thermal/optical reflectance carbon analysis system (Sunset Laboratory Inc., Lab OC-EC Aerosol Analyzer).The analytical condi-tions of the IMPROVE method (Chow et al., 1993) were used with the thermal optical reflection protocol (Chow et al., 2001).A total of four fractions (OC1, OC2, OC3, and OC4) and the optical pyrolysis correction of OC (PyC) were determined.The OC was calculated as OC1 + OC2 + OC3 + OC4 + PyC.

5 Organic Compounds Measurement
The measured non-polar organic compounds in this study were 21 species of PAHs, 24 species of n-alkanes and 5 species of PAEs, producing a total of 50 species.Details of these compounds, including individual abbreviations, are presented in Tables 2 and 3.

5. 2 GC/MS Analysis
Analysis of the target organic compounds in the PM 2.5 samples was carried out by GC/MS (6890 GC/5973 MSD, Agilent Technology) under the following conditions: capillary column DB-5MS (length; 60 m, internal dia meter; 0.25 mm, film thickness; 0.25 μm film thickness, Agilent J&W) was used for separation of the compounds; high-purity helium was used as the carrier gas with flow rate of 1.0 mL/min; sample injection amount was 1 μL in splitless mode; the GC oven temperature was initially held at 100°C for 1 min, increasing 20°C/ min until 270°C and held for 17 min, increasing 15°C/ min until 320°C and then held for 32 min; the injection temperature was set to 280°C and the MS source and       4. The individual organic compounds and IS substances were determined by comparing retention times and mass spectrum peaks with those of authentic standards.The five-point calibration curves were plotted based on the IS method for individual compounds and all of the compounds showed good linearity with the Pearson's correlation coefficients of R>0.95.
A recovery test (n = 4) was performed to validate the pretreatment method.Known amounts of individual organic compounds were spiked to the blank Q-filter and then prepared and handled by exactly the same pro-cedures as those used for the PM 2.5 samples.The average recovery for PAHs, n-alkanes and PAEs were 88-110%, 78-130% and 73-91%, respectively (Tables 2  and 3).In addition to the organic compounds described in Tables 2 and 3, we examined naphthalene (NaP), acenaphthene (Ace) and acenaphthylene (Acy) in PAHs, n-dodecane (C 12 ), n-tridecane (C 13 ), n-tetradecane (C 14 ), n-pentadecane (C 15 ), and n-hexadecane (C 16 ) in n-alkanes and diethyl phthalate (DEP), dibutyl phthalate (DBP) and dicyclohexyl phthalate (DCHP) in PAEs; however, the recovery percentages of those compounds were not acceptable.Therefore, these were eliminated from the analyte candidates in this study.The unacceptable recovery percentages for these compounds may have been due to vaporization loss during the evaporation process (NaP, Ace, Acy, and C 12 -C 16 ) and a high level of background contaminations (DEP, DBP, and DCHP).
The limit of detection (LOD) for the individual organic compounds is provided in Tables 2 and 3.It was calculated using the standard deviation of standard solution values (n = 7) multiplied by 3. Measurement data below the LOD were replaced with the value of LOD/2 for the calculations in this study.

1 Temporal Variations of PM 2.5 Mass
Concentration and OC A summary of average concentrations of PM 2.5 , OC and OC/PM 2.5 and their ranges in each season are shown in Table 2.These observations are also plotted in Fig. 2 to reveal the temporal variation of PM 2.5 and OC results.During the study period, PM 2.5 and OC had higher concentrations from October 2016 (autumn) to May 2017 (spring) compared with other periods.This implies that PM 2.5 and OC vary seasonally.PM 2.5 and OC showed similar variation patterns over time, and their Pearson's correlation coefficient (R) was 0.80.The overall average value of OC/PM 2.5 was 17%, which is in good agreement with the value of 19.7% from our previous publication (n = 373) based on data obtained at the same study site (Ichikawa et al., 2015).These results indicate that OC is one of the major chemical components that contributes to PM 2.5 mass concentration.Identifying the different proportions of organic compounds could help to identify OC source.

2. 1 PAHs
PAHs are derived exclusively from the incomplete combustion and pyrolysis of organic materials contained in fossil fuels, coal fuels, lubricant oils, biomass, etc., and are ubiquitous environmental contaminants (Alves, 2008;Park et al., 2006;Simoneit, 2002).There are studies indicating or suggesting the linkage between PAH properties and human health problems such as cancer (IARC, 2013(IARC, , 2010)).
Measurement values of individual PAHs in each sea-   son are shown in Table 2.The summed concentration of 21 species of PAHs is expressed as PAHs.Fig. 3 shows temporal variations of PAHs obtained through the long time series analysis.Winter 2016 showed the highest average PAH concentration (4.0 ng/m 3 ) during the study period and other studies conducted in Japan support our results (Suzuki et al., 2015;Kume et al., 2007;Kakimoto et al., 2002).There were a few samples in early summer ( July) and early winter (December-January) showing an elevated level of PAHs; however, most of the samples were below 4 ng/m 3 during the study period and the seasonal variation was little.Kume et al. (2007) have analyzed 21 species of PAHs in PM 2.5 from February 2001 to January 2002 in Shizuoka, Japan, and their result did not show strong seasonal variations, implying similarity to our result.This result suggests that the emission sources, which are not influenced by the seasons, are the dominant inputs for PAHs within the source areas of the sampling site.The overall mean concentration of PAHs was 2.9 ng/m 3 , which accounts for 0.030% and 0.19% of PM 2.5 and OC, respectively.Also, PM 2.5 and OC have positive correlation with PAHs with the Pearson correlation coefficient (R) of 0.57 and 0.42, respectively.Our result is approximately one to two orders of magnitude lower than those observed in China (Wang et al., 2016(Wang et al., , 2015)).Although the individual amounts of organic compounds and their percentages accounting for PM 2.5 and OC are small, they could be used as molecular markers for source apportionment, which will be discussed later.
As is evident from Table 2, the lighter weight PAHs ( 3-rings = Fl + Phe + Ant) were much lower than that of the heavier weight PAHs ( 4-rings = Fluor + Py + BcP + BaA + Chry + 7,12DaA; 5-rings = BbF + BjF + BkF + BeP + BaP + 3MC + DBahA; 6-rings = IP + BghiP + DBalP + DBaiP + DBahP) throughout the year.This is probably because the 3-ring PAHs have relatively higher vapor pressures compared with the higher weight PAHs and tend to partition in the gas phase.The 4-ring PAHs can exist in both gas and particulate phases, whereas the 5-ring and 6-ring PAHs are mainly condensed/adsorbed onto particle phases (Zhang et al., 2016).Among the 4, 5, and 6-ring PAHs, 5-ring PAHs were found to be dominant throughout the year.In summer and autumn, average values of 6-ring PAHs were higher than those of 4-ring PAHs.However, the opposite results were obtained in spring and winter.These results could be attributed to the atmospheric temperature (summer>autumn>spring >winter, Table 2), since 4-ring PAHs have lower vapor pressures than 6-ring PAHs.
The highest average concentrations measured in each season among all the PAHs were as follows; BbF and IP in summer 2016, IP in autumn 2016, Fluor in winter 2016, Fluor in spring 2017, IP in summer 2017, and IP in autumn 2017.Although WHO has not drafted a guideline for BaP, it is classified as carcinogenic to humans (Group 1) by the IARC (2012), and is probably the most studied PAH.BaP concentrations were above the LOD for all the samples, but no BaP values exceeded 1 ng/m 3 which is an annual mean value for the protection of human health as set out in the Directive 2004/107/EC (EU, 2004).
Measurement values of n-alkane homologues in each season are shown in Table 3.The sum of C 17 -C 40 n-alkane concentrations is expressed as n-alkanes.Fig. 4 describes the temporal variation of n-alkanes during the study period and the relative abundances of individual n-alkanes normalized by C 29 , which is one of the most abundant n-alkanes, are presented in Fig. 5 to visually confirm the distribution profile in each season.Winter 2016 showed the higher average n-alkanes concentration (21 ng/m 3 ) than the other seasons.A few samples in late autumn of 2016 (October-November) and early winter of 2016 (December-January) showed relatively elevated n-alkanes concentration; however, most of the samples had concentrations below 20 ng/m 3 (overall average of 14 ng/m 3 ) during the study period and the seasonal variation was little.This result suggests that the emission sources, which are not influenced by the seasons, are the dominant inputs for n-alkanes within the source areas of the sampling site.The highest n-alkanes concentration was observed in late summer of 2017, when all of the n-alkane homologues appeared at high concentrations.The overall mean concentration of n-alkanes accounted for 0.14% and 0.84% of PM 2.5 and OC, respectively.Also, PM 2.5 and OC have positive correlation with n-alkanes with the Pearson correlation coefficient (R) of 0.57 and 0.80, respectively.

2. 3 PAEs
PAEs are widely manufactured as plasticizers to make plastic materials flexible, and also in building materials, food, drinking water, soil, medical devices, cosmetics, children's toys, and other products (Wang et al., 2017;Yao et al., 2016;Chou and Wright, 2006).Several epidemiological studies have demonstrated that human exposure to PAEs can induce adverse effects, and PAEs are suspected to be endocrine disruptors, which has stimulated public concern (Okamoto et al., 2011;Chou and Wright, 2006;Duty et al., 2005Duty et al., , 2003)).To our knowledge, there is no previous publication involving the measurement of PAEs in PM 2.5 collected from the ambient atmosphere of Japan.
Measurement values of PAEs in each season are shown in Table 3.The summed concentration of 5 species of PAEs is expressed as PAEs.Fig. 6 presents the temporal variation of PAEs during the study period.
Average PAEs was found to be higher (0.51 ng/m 3 ) in summer 2017 than in other seasons; however, average PAEs in summer 2016 (0.26 ng/m 3 ) was about half the summer 2017 value, so there was no clear seasonal pattern.One sample in late summer of 2017 showed a relatively high level of PAEs (1.8 ng/m 3 ); however, most of the obtained data were below 1 ng/ m 3 during the study period and thus no clear seasonal variation was observed.The reason is uncertain but the PAEs were extremely low in autumn 2017.The overall mean concentration of PAEs was 0.36 ng/ m 3 , which was one and two orders of magnitude lower than PAHs and n-alkanes, respectively.Also, PM 2.5 and OC did not indicate correlation with PAEs.Therefore, the target PAEs were not substantially emitted within the source area of the sampling site; however, PAEs those were not measured in this study might be contained in high concentrations in PM 2.5 , so further research should target these nondetected compounds.
Most fresh exhaust emissions typically contain almost the same amount of BeP and BaP.However, BaP more easily degraded than BeP by photochemical reactions in the ambient atmosphere.The atmospheric lifetime of BaP is estimated as ten times shorter than that of BeP (Kalberer et al., 2002).Therefore, the increment of BeP/(BeP + BaP) can be used as in indicator of the degree of photochemical degradation (i.e., aging) of compounds in the atmospheric environment (Wang et al., 2015;Shen et al., 2013;Alves et al., 2009).The seasonal variation of calculated BeP/(BeP + BaP) in this study ranged from 0.38-0.58.Freshly released BeP/ (BeP+BaP) should have a ratio close to 0.50 (MikuŠka et al., 2015;Park et al., 2006), suggesting that most of the PM 2.5 containing BaP and BeP was emitted from local or nearby regional sources throughout the study period.

2 Historical Distribution, CPI and C wax of
n-Alkanes Table 3 and Fig. 5 indicate that C 23 -C 33 were the main homologues contributing to the n-alkanes.Previous research has shown that carbon number with a strong predominance of odd carbon number indicates a significant contribution from biogenic contributors (Rogge et al., 1993c), whose abundances of odd carbon number higher than 24 are approximately one magnitude higher than those of even carbon number.Whereas n-alkanes released from fossil fuel sources do not show such predominant tendency (Alves et al., 2009;Simoneit et al., 1991).Fig. 5 shows that oddnumbered carbon homologues were not dominant during the study period.Therefore, contributions arising from anthropogenic inputs might have been higher than biogenic inputs at the study site.
For the further interpretation of obtained data associated with n-alkanes, we used the carbon preference index (CPI) and contribution of plant wax to n-alkanes (C wax ) to assess the variability of sources, and they are listed in Table 6.The CPI can be used to distinguish biogenic and anthropogenic inputs.It is defined as the sum of the concentrations of the odd carbon number n-alkanes ( C odd ) divided by the sum of the concentrations of the even carbon number n-alkanes ( C even ), which was calculated as follows: C odd (C 17 to C 39 ) CPI = - -----------= ---------------------(1) C even (C 18 to C 40 ) Plant wax n-alkanes exhibit a strong odd carbon number predominance and thus increase the CPI value (Park et al., 2006).Conversely, anthropogenic inputs such as fossil fuels reduce the CPI value.The CPI typical values in the urban environment range from 1.1 to 2.0, while a CPI higher than 2.0 has a stronger biogenic influence (Alves et al., 2009).In the present study, the CPI values during the study period were in the range 0.73-3.2with an average of 1.5, as shown in Table 6.A CPI value above 2.0 was observed just in one sample in spring 2017 (CPI = 3.2, for 2-10 May), suggesting that most of the measured n-alkanes during the study period were anthropogenic in origin.
Another methodology to analyze the contribution of plant wax sources to n-alkanes can be expressed through C wax (Wang et al., 2015;Yadav et al., 2013;Alves, 2008;Park et al., 2006;Simoneit et al., 1991).C wax gives the percentage concentration input of wax n-alkanes from biogenic sources in sample.The C wax is calculated as follows: (C n-1 + C n+1 ) { C n -------------------} 2 C wax = -----------------------------------× 100 (2) n•Alkanes where n is the odd number of analyzed n-alkanes.Measured C n values below the LOD were replaced with the value of LOD/2, and the negative values of {C n -(C n-1 + C n+1 )/2} were determined as zero.Table 6 shows that the percentages of C wax were in the range of 4.3-53% with an average of 22%.The higher percentage values indicate greater contributions from biogenic sources (Wang et al., 2015).The highest C wax value of 53% was calculated from the same sample as CPI = 3.2, which could possibly mean that the contribution of biogenic sources was larger than sample during the period of 2-10 May 2017.Comprehensive evaluation including the historical distributions of n-alkanes homologues, CPI, and C wax , indicates that the observed n-alkanes may largely originate from anthropogenic sources for most of the samples in this study.Further identification of the emission sources of n-alkanes in PM 2.5 will be conducted in future research.

SUMMARY AND CONCLUSIONS
A long time series (approximately 17 months) of quantitative data of non-polar organic compounds constituting PM 2.5 was created from samples collected at Ichihara, one of the largest industrial areas in Japan.Sample collection and analysis took place continuously from June 2016 to October 2017.The target non-polar organic compounds were 21 species of PAHs, 24 species of n-alkanes, and 5 species of PAHs, and these were simultaneously measured using GC/MS.The results indicate that anthropogenic sources were the dominant inputs for the most PAHs and n-alkanes throughout the study period.Identification of the emission sources of individual organic compounds in PM 2.5 will be conducted in future research.To our knowledge, this paper describes the first attempt to measure such a large number of different nonpolar organic compounds in PM 2.5 from the ambient atmosphere of Japan to create a long time series.The findings will provide valuable data and information to environmental researchers.The main findings are as follows: (1) The average concentrations of PAHs, n-alkanes, and PAEs in each season remained nearly level (except for a few high PAHs in early winter and n-alkanes in late autumn and early winter), and no strong seasonal variations were observed throughout the study period.These results suggest that the emission sources, which are not influenced by the seasons, are the dominant inputs for the target organic compounds.
(2) The contributions of PAHs, n-alkanes, and PAEs to the PM 2.5 mass concentration were each less than 1%.
(3) The target PAEs were not substantially emitted within the source area of the sampling site.
(4) All of the calculated BeP/(BeP + BaP) ratios were close to 0.50, which indicates that PM 2.5 containing BaP and BeP were emitted from local or nearby regional anthropogenic sources throughout the study period.
(5) From the analysis of diagnostic ratios, gasoline, diesel and coal emissions could be possible anthropogenic sources of measured PAHs in this study.
(6) The distributions of n-alkane homologues and calculated results of CPI and C wax , indicate that n-alkanes at the study site may largely originate from anthropogenic sources.Further identification of the emission sources of n-alkanes in PM 2.5 will be conducted in future research.

Fig. 5 .
Fig. 5. Relative abundances of individual n-alkanes normalized by C 29 in each season.

Table 2 .
Temperature Except for the temperature, all of the measured values have been rounded to no more than three significant figures.

Table 4 .
Monitored target and qualifier ions, and internal standards used in SIM mode of GC/MS analysis.

Table 5 .
Comparison of PAHs diagnostic ratios from this study with those reported in previous studies.

Table 6 .
CPI and C wax obtained from the measurement results of individual n-alkanes.