Analysis of the Effect of Meteorological Factors on PM 2 . 5-Associated PAHs during Autumn-Winter in Urban Nanchang

The objectives of this study were to examine the association between PM2.5-associated polycyclic aromatic hydrocarbons (PAHs) and their meteorological factors, and the relationship between PM2.5-associated PAH concentrations and temperature, air pressure and air humidity. Data collected by Center for Disease Control (CDC) in Nanchang urban areas during the fall and winter seasons of 2014–2015 were analyzed by using high performance liquid chromatography (HPLC). Our study showed that the PM2.5 mass concentration had a mean of 0.088 μg m. Our results showed that the total concentration of PAHs in Nanchang was 22.54 ng m (RSD: 8.50) and 15 different types of PAHs examined in this study all exceeded the China national standard. Multiple regression analysis revealed that the daily average concentration of total PAH was significantly associated with the temperature and daily minimum humidity (p < 0.05), but not daily wind speed and rainfall. Principal component analysis and characteristic ratio study indicated that the source of PAHs in PM2.5 were mainly from vehicle exhaust and coal and gas combustion in Nanchang.


INTRODUCTION
Haze weather is a state of atmosphere and is defined as excess level of all kinds of suspended particles in the atmosphere due to the formation of core substance floating in the air, smoke, dust and other particles (Li et al., 2014).Haze is different from fog since the latter is a naturally occurred phenomenon due to more condensed water in the air.Haze weather is mainly the formation of man-made pollution of the environment, combined with low temperature, low air velocity and other natural conditions leading to very limited spread of pollutants.In recent years, haze has occurred frequently in most cities in China (Kong et al., 2015;Li et al., 2016).As a major component of haze, particulate matter PM 2.5 is known to cause serious illness to human body such as the respiratory and cardiovascular + These authors contributed equally to this manuscript.systems (Samat et al., 2015;Anyenda et al., 2016).Different profiles and distribution patterns of individual PAHs in PM 2.5 are characteristic of different sources of air pollution (Wang et al., 2007).According to the "2012 Chinese cancer registry annual report", the total cancer cases in China reached 3.12 millions in 2009, indicating an average of 8,550 new cases per day, and six people diagnosed with malignant tumor per minute.National cancer mortality rate in China is 180.5/100,000 with estimated death of 2.7 millions every year (about 7,300 people die of cancer every day).Currently, about 20.0%-30.0% of cancer patients can survive for five years and the national cancer cases went up to 3.64 million in 2015.Among all reported cancer cases in China, lung cancer has the highest fatality rate and the current haze whether in China has been directly linked to the high incidence of lung cancer.Recent reports have indicated the culprit of haze, particulate matter PM 2.5 , to be a serious health risk to human body, the polycyclic aromatic hydrocarbons adhered on the surface of the PM 2.5 is a persistent organic pollutant with carcinogenicity effect to humans (Choi et al., 2015;Dauner et al., 2016;Pongpiachan, 2016).Currently, there have been some reports emphasizing on the content and source of polycyclic aromatic hydrocarbons in PM 2.5 (Geng et al., 2014;Cvetkovic et al., 2015;Zhao et al., 2015;Wang et al., 2016).However, little is currently known regarding how meteorological factors influence the concentration and variation of PM 2.5 -associated PAHs (Li et al., 2012, Dan et al., 2004).In particular, recent studies have shown that meteorological factors in different climatic conditions could have different effects on PM 2.5 (He et al., 2014;Liu et al., 2015;Zhang et al., 2015b).Therefore, there is a need to sexamine meteorological factors and to understand concentration and distribution of PM 2.5 -associated PAHs.Currently, rapid development of economics and the building booms has resulted in serious pollution of the air in many major cities in China, like Nanchang (SBJX, 2014a; Wang et al., 2015), thus it become important and necessary to study those factors that are associated with PAHs in PM 2.5 .

Sampling of Atmospheric PM 2.5
The Qing Yun Pu division of Jiangxi Center for Disease Control (CDC) collected the data.The PM 2.5 samples were collected from several monitoring locations of Qing Yun Pu district between 10th to 16th of each month from September 2014 to February 2015.These sampling locations had continuous airflow and were free of major pollution sources or obstacles within one-kilometer radius.With airflow velocities of 100 L min -1 , traffic PM 2.5 samplers containing glass fiber membranes were chosen and vertically placed 10-15 meters above the ground.Samples were collected at every other 10 minutes interval and each sampling time was 10 minutes and a total of ≥ 20 hours per sampling day.

Meteorology and National Monitoring Point Data
Data was collected every day for the test period from the environmental air quality monitoring station in Nanchang and collected samples were measured for SO 2 , NO 2 , PM 10 , CO, O 3 and PM 2.5.Other factors such as the daily temperature, relative humidity, atmospheric pressure (maximum, minimum and average), daily precipitation, and wind speed.

Statistical Analysis
Descriptive statistics was used to summarize the air pollution indexes.Independent two-sample t-tests were conducted to compare the difference of PAHs in PM 2.5 between fall and winter times.Pearson ' s correlation coefficients were used to report the association between PAHs categories and meteorological factors.In addition, stepwise multiple linear regression analysis was conducted to investigate the most meteorological significant factors associated with total PAHs in PM 2.5 .Statistical software SPSS20 was used for data management and analyses.All statistical inferences were conducted at 5% alpha level.

Quality Control
Sample collection, preservation and storage, along with laboratory procedures for this study were carried out in highly strict accordance with the "Ambient air and stationary source emissions-determination of gas and particle-phase polycyclic aromatic hydrocarbons with gas chromatography/mass spectrometry" released by the Ministry of Environmental Protection of the People's Republic of China (MEPPRC).The sampling time was not less than 22 hours, which covered the rush hours.Qualified and trained graduate students from medical school of Nanchang universities, and researchers from Chinese Center for Disease Control and Prevention and Qing Yun Pu division of Jiangxi Center for Disease Control conducted the study, and collected and analyzed the data.Data were entered twice separately by two researchers into two different files and cross-checked to ensure no error.

The Concentration of Atmospheric PM 2.5 and Polycyclic Aromatic Hydrocarbons
As shown in Table 1, the average daily concentration of PM 2.5 in Nanchang city during the monitoring time was 0.088 mg m -3 (SD: 0.03), which is 0.013 mg m -3 higher than the Chinese standard of 0.075 mg m -3 (GB3095-1996) Thirty days among the total of 40-day monitoring time (> 71%), the monitored concentration of PM 2.5 is over the air quality standard.This is consistent with the 70.91% reported by the Environmental Protection Bureau of Nanchang city, indicating that PM 2.5 pollution is serious in Nanchang.In addition, total PAH concentration was 22.54 ng m -3 (SD: 8.47), which is very close to the value (21.48 ng m -3 ) reported from other rapid developing cities in China (Ray et al., 2012).Fifteen categories of PAHs tested in this study all exceeded the allowable concentrations of the national air quality standards (HJ646-2013).The concentrations of pyrene, fluoranthene benzo (b) and chrysene were highest.The concentrations of fluorine, acenaphthylene, dibenzo (a,h), anthracene and anthracene were the lowest; all the others below 1.00 ng m -3 (Table 1).
PAHs belong to a larger group of aromatic carbons consisting of 2 to 13 cyclic rings that are fused together.The PAHs with 2 to 3 fused benzene rings are classified as low molecular weight PAHs (LMW-PAHs), while the 4ringed PAHs are classified as middle molecular weight (MMW-PAHs), and the those with 5 to 7 rings are classified as higher molecular weight PAHs (HMW-PAHs) (Cheruyiot  et al., 2015).The results showed that different numbers of benzene ring for PAHs are distributed differently on the surface of PM 2.5 showing 4 rings > 2 rings > 3 rings > 5 rings > 6 rings (Fig. 1).The PAHs with number of 4 rings are most abundant and this may be largely due to the number of 4 ring PAHs are relatively less volatile.Due to dry weather in autumn and winter, less volatile and larger relative molecular mass PAHs enhanced their concentration on PM 2.5 particles surface (Zhu et al., 2011;Shi et al., 2015).
Table 2 shows the mean and SD's of the 15 different categories of PAHs.The mean of total PAH concentration level in the winter of 2015 (mean: 45. 53, SD: 15.15) was significantly higher than that determined in the fall of 2014 (mean: 13.91, SD: p < 0.05).In addition, the mean concentration for each type of 15 PAHs in winter was higher than that observed in the fall with the exception of acenaphthylene, which was detected only once in the fall and twice during the winter.
The correlation between the measured level of PAHs and meteorological factors that includes daily air pressure, temperature, humidity, precipitation, average wind speed, and sunshine time are presented in Table 3.The acenaphthylene level was excluded for this analysis due to its small sample size.As shown in Table 3, PAHs were negatively correlated with temperature and humidity.The multiple regression analysis showed that the total PAHs were significantly associated with daily temperature and daily minimum humidity (Table 4).These results are very similar to the findings recently reported by Liu and his co-workers (Liu et al., 2015).Monitoring deposition characteristics of air contaminant in different geographic sites and areas is of great importance in understanding the fate and distribution of these pollutants in the environment as well as the estimating potential exposure to the populations living in these locations (Suryani R. et al., 2015).However the effect of daily temperature and humidity were not found in some other studies conducted in Wuhan, Shenzhen and other southern areas in China (Sun et al., 2015;Zhang et al., 2015b).A very recent study have indicated that since there are no heating devices in south part of China, thus the impact of temperature, precipitation and relative humidity on the concentration of total PAH should be very limited (Zhang et al., 2015a).These findings suggest that different regional climate characteristics (Ray et al., 2012) could have different effects on PAHs and there is a need for more in-depth research to clarify linkage of daily temperature and humidity to PAH concentration.Guangzhou is a subtropical monsoon city with high humidity, high temperature and more rain weather, while Nanchang is a subtropical monsoon city with moist climate, especially in the fall and winter with low level of water precipitation (Huang et al., 2012).Thus, it is not impossible to conclude that the rainfall has very limited effect on the concentration of total PAH in atmospheric PM 2.5 in Nanchang, although the influence of temperature and humidity on the concentration of total PAH in atmospheric PM 2.5 is consistent with other studies (Zhang et al., 2015b).
The method used for factor analysis in this study is a commonly used one for the determination of the source of polycyclic aromatic hydrocarbons (Akhbarizadeh et al., 2016;Ma et al., 2016).Fifteen types of PAHs were extracted for two common factors of eigenvalues greater than 1, and the cumulative variance contribution rate was as high as 92.20%.The 4-ring, 5-ring, and 6-ring PAHs in principal component factor 1 are loaded on high side as shown in the factor loading/matrix results (Table 5), which indicates vehicle emissions to be the primary source of the pollution (Cai et al., 2014).The fluorene and acenaphthene in common  factors 2 are loaded on higher side belongs to low ring PAHs, which suggests that the sources of these PAHs are mainly from coal combustion (Jung et al., 2010;Samburova et al., 2016).These findings are similar to the study about polycyclic aromatic hydrocarbons in the atmosphere of two subtropical cities in southeast China conducted by Wu et al. (2014) and the study about polycyclic aromatic hydrocarbons in PM 2.5 and PM 2.5-10 during the autumn and winter time in Urumqi of China conducted by Yi et al. (2013).Both these studies employed the principal component analysis (PCA) as an exploratory tool to identify possible sources of particulate PAHs.Qing Yun Pu district belongs to the industrial zone of Nanchang city that administers a number of large industrial enterprises that account for nearly 50% of the economic contribution to the entire Nanchang industrial area (SBJX, 2014b).Moreover, the Qing Yun Pu district is at the center of Nanchang city, where the traffic is usually heavy.This result allows to conclude that air pollution in Qing Yun Pu district is largely due to automobile exhaust emissions and industrial pollution.

CONCLUSIONS
The PM 2.5 mass concentration in fall and winter of Nanchang city was 0.088 ± 0.031 µg m -3 , ranged from 0.026 to 0.156 µg m -3 .71.43% of monitoring days exceeding the air quality standard in China.The total PAH concentration in PM 2.5 was 22.536 ± 8.469 ng m -3 , and 15 types of PAHs were detected to be over the allowable values of the national standard.The atmospheric PM 2.5 mass concentration and the concentrations of 15 kinds of PAHs were higher in winter than in autumn in Nanchang.Statistical analysis revealed that the total PAH concentration of atmospheric PM 2.5 to have a significantly negative correlation to daily average temperature and minimum humidity (P < 0.05), but effect from the daily average wind speed and average rainfall was not significant (P > 0.05).The polycyclic aromatic hydrocarbons in atmospheric PM 2.5 mainly come from vehicle exhaust, coal combustion and factory gas sources.These findings allow to suggest that industrial pollution and automobile exhaust pollution be the major source of air pollution in Nanchang.In addition, with the rapid industrialization in Nanchang city, the toxicity of PAHs in PM 2.5 could pose serious health risks to the public even in the suburban areas.Moreover, the carcinogenic risk of PAHs to the public can be more serious due to increasing traffic activity in the area.Therefore, more stringent measurement on the traffic control should be implemented in order to meet the new criterion on ambient air quality and to reduce the health risk to the public.In particular, more efficient emission control measures are desperately needed for controlling current air pollution in urban and suburban atmosphere of China.

Fig. 1 .
Fig. 1.Distribution of 16 kinds of PAHs in PM 2.5 in Nanchang city observed over 30 days from September 2014-February 2015.

Table 1 .
Concentrations of 15 categories of PAHs in PM 2.5 in Nanchang (ng m -3 ) observed over 30 days from September 2014 to February 2015.

Table 2 .
t means and SDs of different types of PAHs during the fall and winter in Nanchang.

Table 3 .
Correlations between PAHs and meteorological factors.Bolded numbers indicate significant correlation at 5% level.

Table 4 .
Most significant meteorological factors that are associated with PAHs*.Results were obtained from multiple stepwise linear regression analysis and R 2 of the regression model is 0.835.

Table 5 .
The biggest factor analysis of variance factor loading matrix table.