Temporal determination of heavy metals in PM 2 . 5 from Guiyang , Guizhou province , southwestern China

Twelve hours integrated PM2.5 samples collected with a Weekly Air Particulate Sampler (URG Model 2000-01J) from September 2008 to November 2008 in Guiyang, China, were analyzed on the Kevex energy dispersive x-ray spectrometer (XRF) for elements. Monitoring results found elevated concentrations of heavy metals (Ti, Mn, Fe, Zn, and Pb) in PM2.5 in Guiyang. The average concentrations were 30±22 ng m for Ti, 250±400 ng m for Mn, 340±280 ng m for Fe, 290±330 ng m for Zn, and 130±130 ng m for Pb, respectively. Temporal variation patterns in the resulting data were also obtained. It is hypothesized that local anthropogenic sources and the seasonal variability result in the temporal variability.


Introduction
The fine particles in ambient air have been reported to be associated with many health problems (Kim et al., 2004).The fractions smaller than 2.5 µm (PM 2.5 ) are getting more and more attention worldwide, which can result in the prolonged exposure, promoting or aggravating health problems (Figueroa et al., 2006).Because the PM 2.5 has a long residential time of several days to weeks in atmosphere, it can travel hundreds to thousands of kilometers.Previous studies indicated that smaller particles of PM 2.5 are water soluble and hygroscopic, and make them bio-available (Raes et al., 2000;Heal et al., 2005).On the other hand, the PM 2.5 has high concentrations of toxic trace metals, such as chromium (Cr), cadmium (Cd), titanium (Ti), manganese (Mn), nickel (Ni), lead (Pb), arsenic (As), zinc (Zn), etc. (Singh et al., 2002).Those toxic heavy metals incorporated with PM 2.5 may enter the body through inhalation and have been suggested as causative agents associated with adverse respiratory health effects.
Guiyang, the capital of Guizhou province, southwestern China, is classified as one of the most seriously air polluted cities in China.Its climate represents a typical subtropical humid monsoon with an average annual temperature of 15 ºC and 1100-1400 mm of precipitation.It has 3.7 million populations in 2008.Because of the abundant coal resources in Guiyang, the air pollution caused by coal combustion emission is considered as the most critical environmental issue.

Materials and Methods
The PM 2.5 measurements at the Monitoring Station Agency (MSA) in Guiyang (E: 106º43'03", N: 26º33'56") were conducted on the roof of an 8-story building using a Weekly Air Particulate Sampler (URG Model 2000-01J).The MSA site is located in residential area with a number of local industries, including a large coal-fired utility (1.5 km south), a cement plant (3.5 km south), and several non-ferrous metal smelters.The PM 2.5 samples were collected onto filters (Millipore, PGTRISLIDE TM ) at a flow rate of 10 L min -1 .During the sampling campaign, 12-hour integrated samples were collected each day from 8:00am/8:00pm (Daytime) to 8:00pm/8:00am (Nighttime).The sampled filters were stored individually in petri dishes and were sealed in polyethylene bags with citric acid paper for preservation.The sampled filters were analyzed for elements using the Kevex energy dispersive X-ray fluorescence spectrometer (XRF) at USEPA's National Exposure Research Laboratory.The certified reference standards of SRM1833-1111 and SRM1832-249 were analyzed to monitor the accuracy of the spectrometer.Laboratory blanks, field blanks, and duplicate samples were also determined for data quality control and assessment.The average concentrations for each element reported were higher than the limit of quantification (LOQ), which is defined as ten times the standard deviation of a set of blanks.

Results and Discussion
Concentrations of PM 2.5 and heavy metals measured in 12-hour integrated samples were presented in Table 1.The PM 2.5 showed elevated concentrations with a range of 3.7 to 190 µg m -3 .Heavy metals concentrations in PM 2.5 , particularly Mn, Pb, and Zn, were highly elevated, ranging from 0.39 to 160 ng m -3 for Ti, 0.017 to 3980 ng m -3 for Mn, 11 to 1870 ng m -3 for Fe, 6.7 to 2160 ng m -3 for Zn, and 1.6 to 920 ng m -3 for Pb, respectively.
The distribution of the five heavy metals showed different temporal variation.High monthly average concentrations of Mn were record during September and October, while during September and November, the high levels of Ti, Fe, Zn, and Pb were presented.In the present study, notable diurnal variations characterized by reduced concentrations during daytime were observed among Mn, Fe, Zn, and Pb (Figure 1).
Strong anti-correlations was detected between PM 2.5 and wind speed (r=-0.31,p<0.01) as well as PM 2.5 and relative humidity (r=-0.46,p<0.01) (Table 2).The results confirm the fact that strong winds prevent the accumulation of air pollutants and that the rainfall constituted a mechanism of purification of the atmosphere.Table 2 presents also the correlations coefficient between PM 2.5 and Ti, Mn, Fe, Zn, Pb as well as between the five metal concentrations.All of the heavy metals were positive correlated with PM 2.5 and were positive correlated with each other, indicating that those heavy metals are readily bond to fine particles and seem to be associated with local sources.

Conclusions
This study presents ambient PM 2.5 as well as its heavy metals concentrations in Guiyang city, Guizhou province.

Fig. 1
Fig.1The average concentrations of PM 2.5 and heavy metals during daytime and nighttime in Guiyang

Table 1 .
E3S Web of Conferences DOI: 10.1051/ C Owned by the authors, published by EDP Sciences, 2013 The concentration range and average of the different components This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2 0 , which .permits unrestricted use, distributi and reproduction in any medium, provided the original work is properly cited.on,Articleavailable at http://www.e3s-conferences.orgor http://dx.doi.org/10.1051/e3sconf/20130120008

Table 2 .
The temporal variation patterns in the resulting data suggest local anthropogenic activities impacted the sites.Concentrations of heavy metals, particularly Mn, Pb, and Zn, were significantly elevated in PM 2.5 .Identification Correlations among PM 2.5 , heavy metals and meteorology parameters (WS-Wind Speed, RH-Relative Correlation is significant at the 0.01 level (2-tailed).*.Correlation is significant at the 0.05 level (2-tailed).and quantification of the major atmospheric PM 2.5 sources in and around Guiyang and development of a detailed emission inventory in Guiyang is needed to further elucidate PM 2.5 as well as trace elements distribution characteristics.