Impact of Dust Storms on NPAHs and OPAHs in PM 2 . 5 in Jinan , China , in Spring 2016 : Concentrations , Health Risks , and Sources

To better understand the influence of dust storms on nitrogen polycyclic aromatic hydrocarbons (NPAHs) and oxygen polycyclic aromatic hydrocarbons (OPAHs), PM2.5 was collected using prebaked quartz filters at Shandong University, Jinan, China, in spring 2016. The concentrations of 16 NPAHs and 5 OPAHs in PM2.5 were measured using gas chromatographymass spectrometry. The highest concentration of NPAHs was recorded during dust storm 1 (DS1; 4.62 ng m), which was higher than those recorded during haze (2.28 ng m) and on clear days (0.17 ng m). The concentrations of 2+3N-FLA and 9N-ANT were considerably higher during haze and dust storms. The total concentration of OPAHs was highest during haze (7.72 ng m) and was 2–4.2 times higher than those during DS1, dust storm 2 (DS2), dust storm 3 (DS3) (all 2.38– 3.07 ng m) and on clear days (1.82 ng m). The three most abundant OPAHs were 9-fluorenone, 9,10-anthraquinone, and naphthalene-1-aldehyde during all studied periods. The 2+3N-FLA/1N-PYR ratio indicated that NPAHs were dominated by secondary generation throughout the sampling period and that dust storm days were more conducive to the secondary generation of NPAHs than were hazy days. During dust storms, NPAHs and OPAHs were influenced by longdistance transport originating in Mongolia and Inner Mongolia. NPAHs and OPAHs in PM2.5 were mainly derived from vehicle exhausts, solid fuel combustion, secondary generation, and crustal sources throughout the sampling period. The highest ∑BaPeq value (0.0928 ng m) was recorded during DS2. The incremental lifetime cancer risk and total risk on hazy days and the three dust storm episodes were higher than those on clear days.


INTRODUCTION
In recent years, air pollution has been a critical issue in China, and organic pollutants in the atmosphere have attracted considerable attention because of their persistence and mutagenicity.Many studies have been conducted on polycyclic aromatic hydrocarbons (PAHs) (Lee et al., 1995;Cheruyiot et al., 2015), nitrogen polycyclic aromatic hydrocarbons (NPAHs), and oxygen polycyclic aromatic hydrocarbons (OPAHs) (Xia et al., 2013;Wei et al., 2015).Currently, many studies have researched on PAHs in particles at home and abroad, which mainly focused on the concentration, sources and cancer risk (Da et al., 2015;Pongpiachan, 2016;Yang et al., 2017).Furthermore, the concentration, distribution, and origin of PAH derivatives in the atmosphere in cities, rural areas, traffic sites (Ringuet et al., 2012a, b, c), indoor and outdoor sites, and during special periods such as the Beijing Olympic Games (Wang et al., 2011b) have been studied, but few studies have focused on dust storms (Hou et al., 2006;Wang et al., 2009;Wang et al., 2012).The dust storm can affect the chemicals of fine particles, the concentration of secondary species and size distribution (Alghamdi et al., 2015;Pu et al., 2015;Xu et al., 2017).Economic development in East Asia may have caused increases in NO 2 , organic pollutants, and soot.Furthermore, because desert dust can reflect sunlight into space, absorb solar radiation, and provide an alkaline environment for the absorption of acid gases, the presence of dust in China can increase the complexity of particles (Wang et al., 2009).
In spring, many cities in China such as Beijing, Qingdao, and Shanghai are affected by dust storms (Guo et al., 2004;Sun et al., 2010).Dust storms in East China mainly originate from the Taklimakan and Gobi Deserts (Peltier et al., 2008;McNaughton et al., 2009;Uno et al., 2009).Many studies have focused on inorganic elements, soluble water ions, and organic carbon and elemental carbon in dust storms (Nie et al., 2012;Wang et al., 2016), but very few have studied organic pollutants in the particles of dust storms (Hou et al., 2006), especially NPAHs and OPAHs, which are sometimes more carcinogenic and mutagenic than their parent compounds (Durant et al., 1996;Durant et al., 1998;Lundstedt et al., 2007).Although the concentrations of certain NPAHs are much lower than those of their parent PAHs, some NPAHs exhibited high direct teratogenicity in animal assays (Pitts Jr et al., 1978) and which was confirmed rapidly in assays based on human cells (Durant et al., 1998).The particle properties like particle size, surface area, and the contents of organic matter and soot carbon, as well as physicochemical properties of PAH derivatives can affect the gas/particle partitioning of NPAHs and OPAHs (Li et al., 2016).NPAHs and OPAHs are mainly distributed on fine particles in particle matters, the part of OPAHs and NPAHs bound to particles smaller than 2.5 µm was upper than 85% (Ringuet et al., 2012c).The results of a recent study showed that PM 2.5 exposed to organic chemistry in urban areas and desert PM 2.5 abundant in microbial elements are crucial factors contributing to lung disease, and that desert PM 2.5 may have a greater impact on human respiratory health than does urban PM 2.5 abundant in organic chemicals (He et al., 2016).NPAHs come from primary emissions and secondary generation through radical reactions between PAHs and OH, NO 3 radicals.High levels of atmospheric oxidants such as ozone and nitrogen oxides in the region could promote the transformation of PAHs into their derivatives (Lin et al., 2015).Once released into the air, many NPAHs in the atmosphere are highly persistent and can be transported from their original source over long distances (Nielsen, 1984;Ciccioli et al., 1996).During long-distance transport, Asian dust aerosols can react with various chemicals, condense with other particles, and provide a reaction location in the atmosphere for carrying many chemicals together with the original soil constituent.In addition, the physical and chemical properties of the dust particles may undergo several changes (Hwang et al., 2008).
To contribute to the literature on NPAHs and OPAHs in atmospheric particulate matters during dust storms, this study investigated (1) the compositions and concentrations of NPAHs and OPAHs in PM 2.5 during dust storms, hazy days and clear days in Jinan; (2) the sources of NPAHs and OPAHs; (3) the cancer risk associated with NPAHs and OPAHs; and (4) the impact of air mass transport on NPAHs and OPAHs.

Sampling
Experiments were conducted from March 18 to May 7, 2016, at Shandong University (36°40′N 117°03′E), Jinan, Shandong Province.We divided samples into haze, dust storms, and clear days according to the monitoring of PM 10 and PM 2.5 values, as shown in Table 1.The sampling site was 20 m above ground on the rooftop of a teaching building on campus (Fig. 1).All PM 2.5 samples were collected using medium-volume air samplers (TH-150A, Wuhan Tianhong Instrument, China) at a rate of 100 L min -1 .Daytime samples were collected from 8:00 am-7:30 pm and nighttime samples were collected from 8:00 pm-7:30 am the following day, with collection periods of 11.5 h for both samples.Particles were collected on quartz filters prebaked at 600°C for 6 h to remove the interference of organic matter.After sampling, the samples were wrapped in aluminum foil that had been baked in advance at 600°C for 6 h and were stored in a freezer at -20°C prior to analysis.
The analysis was conducted using Agilent gas chromatograph (GC; 7890A, Palo Alto, USA) system with a triple quadrupole mass spectrometer (MS/MS, 7001B, Boston, USA) utilizing negative chemical ionization to selectively detect mass.For the analysis of NPAHs and OPAHs, a capillary column (HP-5MS, 30 m × 0.25 mm × 0.25 µm, USA) was used for GC separation.The GC oven was programmed initially to 60°C.The temperature was subsequently increased at a rate of 15 °C min -1 up to 150°C.Subsequently, the temperature was programmed to increase by 5 °C min -1 up to 300°C, where it was held for 15 min.

Quality Control
Field blank and solvent blank experiments were conducted to control the data quality.Target detection NPAHs and OPAHs were not detected in the blank samples.Two types of spiked perdeuterated NPAH surrogates (100 ng), including 3-nitrofluoranthene-d 9 and 2-nitrofluorene-d 9 , were added to control the experimental performance.The recoveries of 2-nitrofluorene-d 9 and 3-nitrofluoranthene-d 9 were 95 ± 22% and 83 ± 11%, respectively.The method recoveries were obtained by adding the NPAH and OPAH standards to cleaned filters, which were subsequently analyzed using the same experimental procedure.The method recoveries were 90 ± 14% for NPAHs and OPAHs.The measured data were not corrected with the blank sample data, surrogates, or method recoveries.One duplicate sample was analyzed for every 10 samples, and the variation was averaged with 10.28% for NPAHs and OPAHs.

Cancer Risk Assessment
The incremental lifetime cancer risk (ILCR) was calculated to evaluate the risk of exposure to PM 2.5 with NPAHs and OPAHs based on the United States Environmental Protection Agency's Risk Assessment Guidance (Lu et al., 2016).The equation used to calculate ILCR in regard to inhalation was as follows: where C is the total BaP equivalent carcinogenic potency (BaPeq) concentration (ng m -3 ), IRinhalation is the inhalation rate (m 3 day -1 ), ED is the exposure duration (years), EF is the exposure frequency (day year -1 ) and a value of 350 was used to calculate the inhalation of PAHs in 1 year (Lu et al., 2016), BW is the body weight (kg), ALT is the life span for cancerogenic substances (years), and CSF inhalation is the carcinogenic slope factor (per mg kg -1 day -1 ).The value of CSF for BaP inhalation was 3.14 (mg kg -1 day -1 ) -1 (Chen and Liao, 2006).The equation used to calculate the total BaP toxic equivalency was as follows: Here, NPAH i is the concentration of individual NPAHs.TEF i is the toxic equivalency factor for carcinogens, which reflects the carcinogenicity of individual NPAHs.In this study, we assigned the BaPeq concentration of NPAHs to C in Eq. ( 1).The ILCR for BaPeq (total BaP toxic equivalency) was estimated for people in different age groups, including infants, toddlers, children, adolescents, and adults.The total BaPeq values obtained using Eq. ( 2) during haze, DS1, DS2, DS3, and on clear days were used to calculate ILCRinhalation.

Concentrations and Compositions of NPAHs and OPAHs in PM 2.5
The average concentration of NPAHs for three dust storms (2120.80pg m -3 ) and the concentration of NPAHs for haze (2281.33 pg m -3 ) were higher than annual concentration of 15 NPAHs (1730 pg m -3 , PM 2.5 ) during 2012-2013 in Beijing (Lin et al., 2015) and concentration of 8 NPAHs (103.9 ± 67.4 pg m -3 ) outdoor of a middle school in Xi'an, respectively (Wang et al., 2017b).The concentration of NPAHs of clear days was a little lower than mean annual concentration of 12 NPAHs (200 pg m -3 ) in Xi'an during 2008-2009 (Bandowe et al., 2014).The concentrations of NPAHs and OPAHs in PM 2.5 samples during haze, DS1, DS2, DS3, and on clear days are listed in Table 2.The order of NPAH concentrations was DS1 > Haze > DS2 > DS3 > Clear days.The dominant NPAHs were 2+3N-FLA and 9N-ANT in all periods, accounting for 45%-92% of all NPAHs.The concentrations of 2+3N-FLA and 9N-ANT were significantly higher during hazy and dust storm days than on clear days (Table 2).The concentration of 9N-ANT was highest on hazy days, whereas that of 2+3N-FLA was highest during dust storms.The proportions of 2+3N-FLA in ∑NPAHs during DS1, DS2, and DS3 was higher than those on hazy and clear days, and the proportion of 9N-ANT during haze was higher than those during the DS1, DS2, DS3, and on clear days (Fig. 2).2+3N-FLA was generated from secondary formation (Arey et al., 1986;Wang et al., Regarding OPAHs, the three dominant OPAHs were 9-FO, 9,10-ATQ, and 1-NALD in all periods, accounting for 97%-99% of all OPAHs.The concentrations of OPAHs in hazy days, DS1, DS2, DS3 (2.38-7.72 ng m -3 ) were lower than 5 OPAHs in PM 2.5 in Beijing during 2012-2013 (55.9 ng m -3 ) and 3 OPAHs in PM 2.5 in Xi'an from 16 th to 30 th May 2012 (outdoor: 19.1 ng m -3 ) and were higher than concentration of 5 OPAHs in Beijing Olympics period (504.6 ± 195.4 pg m -3 ) (Wang et al., 2011b;Lin et al., 2015;Wang et al., 2017a).The order of OPAH concentrations was Haze > DS1 > DS3 > DS2 > Clear days (Table 2).The origin and generation mechanism of the OPAHs are not yet clear.Studies have shown that 9-FO and 9,10-ATQ are derived from primary emissions and oxidation generation (Souza et al., 2014).The concentration of OPAHs during haze was 2-4.2 times higher than that during dust storms and on clear days, suggesting that hazy days can promote the accumulation of OPAHs.In previous studies, the bad meteorological conditions of hazy days are unfavorable for the dispersion of pollutants like fine particulates (Wang et al., 2006;Tan et al., 2009).This may have positive impact on the accumulation of OPAHs.The concentration and components of OPAHs during dust storms were similar to those on clear days (Fig. 3), suggesting that dust storms had no impact on OPAHs.

Daytime and Nighttime Concentrations of NPAHs and OPAHs
The daytime and nighttime concentrations of 16 NPAHs and 5 OPAHs during haze, DS1, DS2, DS3, and on clear days are shown in Fig. 4. The nighttime concentrations of all NPAHs and OPAHs were higher than the daytime concentrations.It's similar to Wu et al. (2012) that the concentration of NPAHs were higher in nighttime than in daytime at a roadside site.And in the study of Ringuet et al. (2012a) the nighttime concentration of OPAHs were higher than daytime at both traffic site and suburban site.Possibly because that NPAHs and OPAHs can be photolyzed during the day and are easily accumulated at night (Albinet et al., 2007) and the life span of NPAHs is 0.5-22 h (Kameda, 2011).In this study, the nighttime concentrations of 1N-PYR and 7N-BaA were higher than the daytime concentrations (Fig. 5), which is not in agreement with the result of Ringuet et al. (2012a).One previous study showed that 1N-PYR was emitted from vehicles (Albinet et al., 2007).In this study, a strong correlation was observed between 1N-PYR and 7N-BaA (R 2 = 0.75, P < 0.01) (Table 3), suggesting that 7N-BaA was the primary source in the  vehicle emissions.Diesel engines can discharge NO x in the atmosphere (Jiang et al., 2016).In this study, the mean concentration of NO 2 was higher in nighttime (63.91 µg m -3 ) than in daytime (18.92 µg m -3 ), which may be due to a large number of trucks entering Jinan at nighttime.Therefore, the daytime and nighttime concentration differences of 1N-PYR and 7N-BaA may be related to the large number of trucks entering Jinan at nighttime, which increases of NO x through exhaust emissions and the atmosphere boundary layer at night decreased, thereby rendering the diffusion of pollutants difficult.The concentrations of 9N-ANT and 2+3N-FLA were higher at nighttime than in the daytime.9N-ANT was derived from primary emissions and secondary formation (Ringuet et al., 2012a) and 2+3N-FLA was formed through radical-initiated reactions of FLA with NO 3 and OH radical (Wang et al., 2011b).In the present study, the 9N-ANT concentrations were significantly correlated with 2+3N-FLA (R 2 = 0.90, P < 0.01), suggesting that the generation pathway of 9N-ANT was similar to that of 2+3N-FLA.

Characteristic Ratios of NPAHs
Previous studies have analyzed the characteristic ratios of NPAHs, mainly involving 2+3N-FLA/1N-PYR and 2+3N-FLA/2N-PYR.To evaluate whether NPAHs mainly originate from primary emissions or secondary formation, the 2+3N-FLA/1N-PYR ratio was calculated.1N-PYR is emitted primarily from diesel engines (Paputa-Peck et al., 1983;Nielsen, 1984).Furthermore, in atmospheric environments, the secondary generation of 1N-PYR is negligible compared to the primary emission (Ringuet et al., 2012a).2N-FLA is formed in air through radical-initiated reactions with NO 2 , which are initiated by the OH radical during the daytime and NO 3 radical at nighttime (Arey et al., 1986;Atkinson et al., 1987;Wang et al., 2011b).In Fan et al. (1996), a 2N-FLA/1N-PYR ratio higher than 5 was used to indicate NPAHs originating from secondary formation.However, in the process of measuring NPAHs for this study, 2N-FLA and 3N-FLA are indistinguishable with the analytical technique.Many studies have used the 2+3N-FLA/1N-PYR instead of 2N-FLA/1N-PYR because the amount of 3-nitrofluoranthene in the atmosphere is much lower than that of 2-nitrofluoranthene (Feilberg and Nielsen, 2000;Bamford and Baker, 2003).The 2+3N-FLA/1N-PYR ratios of PM 2.5 for every day and night are shown in Fig. 6(a).As can be seen, all 2+3N-FLA/1N-PYR ratios are higher than 5, indicating that the NPAHs mainly originated from secondary generation in all the sampling periods.The highest value of 2+3N-FLA/1N-PYR was 197.36 on the night of April 2, 2016, during DS1.Furthermore, during DS2 and DS3, the ratio of 2+3N-FLA/1N-PYR showed a clear upward trend.The mean values of 2+3N-FLA/1N-PYR during DS1 (113.5),DS2 (24.5), and DS3 (25.2) were higher than those during haze (18.2) and on clear days (17.0), suggesting the dust storms could promote the secondary generation of NPAHs.The 2+3N-FLA/1N-PYR ratios on April 22 and May 6 (the first days of DS2 and DS3, respectively) were slightly lower than those on clear days.Furthermore, the 2+3N-FLA/1N-PYR ratios on April 23 and May 7 (the second days of DS2 and DS3, respectively) were higher than those on clear days, indicating that the secondary generation of NPAHs increased during dust storms.There are many conditions that affect the secondary generation of NPAHs such as the levels of PAHs, atmospheric oxidants as O 3 and NO x and the ambient temperature and so on (Wilson et al., 1995;Lin et al., 2015).This phenomenon may be related to the heterogeneous reaction of NO 2 on the surface of particulate matters (Nie et al., 2012).NO 2 can undergo photochemical heterogeneous reactions on the surfaces of solid aromatic compounds (George et al., 2005).
2N-PYR is formed from the gas phase reaction of pyrene with the OH radical not from the reaction with the NO 3 radical (Arey et al., 1986;Zielinska et al., 1986;Atkinson, 1990).2N-FLA is formed through gaseous reactions between FLA and OH and is the only NPAHs product formed by the initiated reaction of FLA with NO 3 (Zielinska et al., 1986).2N-FLA/2N-PYR ratios have been used to evaluate the secondary formation of NPAHs mainly based on gaseous reactions with OH or NO 3 (Arey et al., 1989;Atkinson and Arey, 1994;Bamford and Baker, 2003;Reisen and Arey, 2005;Albinet et al., 2007;Albinet et al., 2008;Zimmermann et al., 2012).2N-FLA/2N-PYR ratios lower than or equal to 10 indicate the dominance of OH-initiated reactions, whereas those greater than 100 indicate that the NO 3 radical reaction dominates NPAHs formation (Albinet et al., 2007;Albinet et al., 2008).The 2+3N-FLA/2N-PYR ratios were calculated and are shown in Fig. 6(b).During haze and on clear days, the ratios were approximately 10, suggesting that secondary NPAHs were mainly formed through initiated reactions with the OH radical.The 2+3N-FLA/2N-PYR ratios higher than or approximately 100 were present during DS1 and DS3, indicating that the reactions with the NO 3 radical greatly contributed to the secondary formation of NPAHs.Moreover, the ratios were approximately 10 during DS2, which indicates that the secondary formation of NPAHs was dominated by initiated reactions with the OH radical.
There was no obvious consistency during DS1, DS2, and DS3.Further research is required to determine whether dust storms can affect the pathway of the secondary generation of NPAHs.

Sources of NPAHs and OPAHs Analyzed using Principal Component Analysis
In this study, principal component analysis was used to analyze the sources of NPAHs and OPAHs during all the sampling periods.Some major NPAHs and OPAHs were selected for analysis.The results shown in Table 4 reveal that three factors (PC1, PC2, and PC3 hereafter) explained 80.28% of the data variance.PC1, which explained 42.78% of the total variance, was highly loaded with 7,12-BaAQ, 9-FO, 1-NALD, 9,10-ATQ, 2N-PYR, 7N-BaA, and 1N-PYR (factor loading > 0.5).9-FO and 9,10-ATQ were dominant in solid fuel combustion (Shen et al., 2011).7N-BaA primarily had a diesel source (Paputa-Peck et al., 1983;Chiu and Miles, 1996;Bezabeh et al., 2003) in addition to gasoline (Albinet et al., 2007).The source of 1N-PYR was direct diesel emissions.Therefore, PC1 was mainly derived from solid fuel combustion and vehicle exhaust.PC2 was highly loaded with 2+3N-FLA and 9N-ANT (factor loading > 0.8) and explained 19.50% of the total variance.2+3N-FLA is generated from secondary reactions and 9N-ANT has two origins: primary emissions and secondary reactions (Albinet et al., 2008;Ringuet et al., 2012a).PC2 was mainly derived from secondary formation.PC3 (explaining 18.00% of the total variance) was regarded as dust storms with high loadings of Ca 2+ and Mg 2+ (factor loading > 0.8), and as suggested by previous studies, Ca 2+  and Mg 2+ were mineral ions that originated from crustal sources (Wang et al., 2006;Sun et al., 2010;Wang et al., 2011a).
During all sampling periods, NPAHs and OPAHs mainly originated from solid fuel combustion, diesel and gasoline vehicle primary emissions, secondary generation, and crustal sources.

Cancer Risk Assessment
There are no available toxic equivalency factor (TEF) values for OPAHs, and the TEF values of 6 NPAHs were available including 5N-ACE (0.01), 2N-FLO (0.01), 9N-ANT (0.0032), 2+3N-FLA (0.0026), 1N-PYR (0.1) and 6N-CHR (10) employed to evaluate the cancer risk (Durant et al., 1996;Wei et al., 2015).The total BaPeq concentrations calculated based on the TEF and NPAH concentrations are shown in Table 5.Samples collected during DS2 exhibited the highest ∑BaPeq value (0.0928 ng m -3 ).Furthermore, the ∑BaPeq values during haze and the three dust storms were all higher than those on clear days.The ILCR of inhalation values and the total risk for each specific age group are listed in Table 5.For all age groups, the ILCR and total risk during haze and dust storms were higher than those on clear days, revealing that the air pollution during haze and dust storms had a higher probabilistic health risk through NPAHs inhalation compared with that on clear days.The ILCR increased from infancy (0-1 years) to adulthood (30-70 years), except for during the toddler stage (1-6 years).These results agree with those of Lu et al. (2016), suggesting that the health risk for toddlers was higher than that for adults (18-30 years), although they were only exposed to NPAHs for 6 years.Further, the highest ILCR in all the study periods (Haze, DS1, DS2, DS3, and Clear days) was for adults (30-70 years).The total risk and the harm to human health caused by NPAHs increased with age in all periods.

Influence of Air Mass Transport on NPAHs and OPAHs
To better understand the influence of air mass transport on NPAHs and OPAHs pollution, the backward trajectory results calculated using the HYSPLIT model were used to analyze the origin and long-distance transport of air masses.The 72 h backward trajectories were calculated every 1 h at a distance of 50 m above ground.All the backward trajectories in Jinan for the different air periods (Haze, DS1, DS2, and DS3) were divided into four clusters for analysis.
Figs. 7(a), 7(b), 7(c), and 7(d) show the transport pathway with the percentages of each cluster for Haze, DS1, DS2, and DS3, respectively.For haze, cluster 1 accounted for 38% of all trajectories.Furthermore, high concentrations of NPAHs and OPAHs were associated with cluster 1, which originated from the yellow sea and passed through the eastern coastal areas of China and Shandong Province on route to the sampling site.These areas are economically developed and have high fuel consumption.Therefore, hazy days were easily affected by short-distance transport.During DS1, DS2, and DS3, the transport of air masses was similar.The three dust storms were all affected by clusters originating from Mongolia and Inner Mongolia and passing through Hebei Province on route to the sampling site (DS1, cluster 4 (50%); DS2, cluster 4 (33%); DS3, cluster 4 (48%)).The high concentrations of NPAHs and OPAHs were associated with cluster 4. Hebei Province is a developing district with many industries (Zhang et al., 2009) and high levels of NPAHs and OPAHs.Therefore, the dust storms were easily influenced by the long-distance transport of air masses.

CONCLUSION
The mean NPAH concentrations during haze, DS1, DS2, and DS3 were all higher than those on clear days.The highest average concentration of NPAHs occurred during DS1.The dominant NPAHs were 9N-ANT and 2+3N-FLA in all periods.The proportions of 2+3N-FLA in ∑NPAHs during DS1, DS2, and DS3 were higher than those during haze and on clear days, suggesting that dust storms could promote the secondary formation of 2+3N-FLA.The average concentration of OPAHs was highest during haze.The nighttime concentrations of NPAHs and OPAHs in PM 2.5 for all samples were higher than the daytime concentrations.The 2+3N-FLA/1N-PYR ratio indicates that NPAHs were dominated by the secondary generation during all sampling periods, and that the secondary formation of NPAHs was significantly enhanced during dust storms, especially DS1.In all the sampling periods, the NPAHs and OPAHs in PM 2.5 mainly originated from solid fuel combustion, diesel and gasoline vehicle primary emissions, the secondary generation, and crustal sources.The highest ILCR value was observed during DS2.Haze and dust storms had a higher probabilistic cancer risk through NPAHs inhalation than did clear days.Furthermore, among the specific age groups, adults (30-70 years) had the highest carcinogenic risk from NPAHs.The pollution of NPAHs and OPAHs was mainly influenced by short-distance transport from the yellow sea and over the eastern coastal areas of China during haze and by longdistance transport from Mongolia and Inner Mongolia during the dust storms.

Fig. 1 .
Fig. 1.The map of sampling site of Shandong University in Jinan, Shandong Province, China.

Fig. 5 .
Fig. 5.The daytime and nighttime concentrations of several main NPAHs and OPAHs in PM 2.5 samples.

Table 2 .
The mean concentrations of sixteen NPAHs and five OPAHs in Haze, DS1, DS2, DS3 and Clear days.
dichloromethane (J.T. Baker, USA) for 8 h.The temperature of the water bath was 57°C.Furthermore, one-third of all the samples were added to spiked perdeuterated NPAH surrogates (100 ng), including 3-nitrofluoranthene-d 9 and 2-nitrofluorene-d 9 , before Soxhlet extraction.The extracts were then concentrated to approximately 1 mL by rotary evaporation (RE201, Shanghai Bing Yue Corporation, China)

Table 4 .
Component matrix of PCA analysis for four OPAHs, six NPAHs and two water-soluble ions.

Table 5 .
The cancer risk assessment of NPAHs for different specific-age groups in Haze, DS1, DS2, DS3 and Clear days.