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Frontier of Environmental Science December 2013, Volume 2, Issue 4, PP.33-46

Personal Exposure to Fine Particulates and

Polycyclic Aromatic Hydrocarbons in an Office

Environment in Xi’an, China Hongmei Xu

1,2, Junji Cao

1,3†, Meiling Gao4, Kin Fai Ho

1,5, Xinyi Niu

1, Teresa L. Coons

6, Steven Sai Hang Ho

1,7,

Gehui Wang1, Zhuzi Zhao

1,2

1. Key Lab of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an,

710075, China

2. University of Chinese Academy of Sciences, Beijing, 100049, China

3. Institute of Global Environmental Change, Xi’an Jiaotong University, Xi'an, 710054, China

4. University of California, Berkeley, USA

5. School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China

6. Washington State University, USA

7. Hong Kong Premium Services and Research Laboratory, Lai Chi Kok, Kowloon, Hong Kong, China

†Email: cao@loess.llqg.ac.cn

Abstract

This study was conducted to evaluate the relationships between PM2.5 and associated polycyclic aromatic hydrocarbons (PAHs) in

indoor and outdoor environments, identify likely PAH sources, determine personal exposures, and estimate the toxicity and

carcinogenic risks. Monitoring was conducted in Xi’an, China on consecutive weekdays (July 6 to 24, 2009) from 8am to 8 pm. The

average PM2.5 personal exposure mass concentration (66.4 μg m-3) was lower than that outdoors (80.5 μg m-3), but the average total

PAH concentration in the personal exposure samples (179.8 ng m-3) was higher than outdoors (114.9 ng m-3). In addition, two distinct

relationships between personal exposure and outdoor PAH concentrations were observed; these could be explained by the subjects’

time-activity patterns. PAHs toxicity risks were estimated from the BaP-equivalent concentrations in the personal samples and

determined to be 45.8 ng m-3 on average. Applying the unit risk method, an estimated 8 cancer cases (range: 2 to 30) per million office

workers would be expected from the inhalation of PM2.5-bound PAHs.

Keywords: PM2.5; PAH; Personal Exposure; Toxicity Risk; Office Workers

1 INTRODUCTION

Rapid and sustained economic and population growth in China has led to frequent air pollution episodes and increased

incidences of respiratory disease [1,2,3]

. Two sources of fine particulate matter (PM2.5, PM with aerodynamic equivalent

diameters ≤ 2.5 μm) exposure, ambient air pollution and household air pollution, were the fourth and fifth leading death

risks in China, respectively [4]

. Total PM2.5 burden in China–the combination of ambient air pollution, household air

pollution, and second-hand tobacco smoke–is very large [4]

. An estimated 300,000 deaths annually are attributed to urban

air pollution in China alone [5]

.

Much of PM2.5 is produced by anthropogenic activities. PM2.5 has been found to be especially toxic to humans because

these particles are small enough to penetrate deeply into the lungs where they then can be transferred into the

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bloodstream [1]

. PM2.5-associated PAHs have also gained attention owing to their toxicity, carcinogenicity and

mutagenicity [6,7]

. Several studies have demonstrated an association between specific PAHs and early genetic damage

associated with breast and lung carcinogenesis [8,9]

. Outdoors, PAHs are generated from various natural sources, such as

forest fires and volcanic eruptions, but they are also produced from anthropogenic sources, mainly motor vehicle exhaust,

the incomplete combustion of fossil fuels for heat or power generation, and fugitive emissions from industries [10,11,12]

.

Indoor PAHs are produced from cooking and from wood and coal burning for heat; they also can be transferred indoors

either from nearby sources or long-range transport [13,14,15]

.

Modern humans spend most of their lives indoors [13,16]

, but few studies have assessed the relationship between ambient

PM2.5 or PAH concentrations and personal exposure. Investigations of exposures in an urban office environment can

provide important insights into the overall exposure to PM2.5 and to PAHs and the health implications of that exposure

for office workers. Hence, the aims of this study were to evaluate the relationships between PM2.5 and associated PAHs

in indoor and outdoor environments, identify likely PAH sources, determine personal exposures, and estimate the

toxicity and carcinogenic risks from the exposure to PAHs.

2 MATERIALS AND METHODS

2.1 Participant Selection

Four participants (identified as AA, BB, CC, and DD) were selected from four different offices in the Institute of Earth

Environment, Chinese Academy of Sciences (IEECAS, 34°13'49.68"N, 108°52'59.05"E). Located in the Hi-Tech Zone

in urban Xi’an, the Institute hosts scientists and graduate students, some of whom both live and work there. The selected

participants (non-smokers, female, ages 24 to 29) spent their time in similar indoor microenvironments and worked in

the same building complex. During the study, the participants maintained activity logs to document the amount of time

spent in different locations and sources of direct exposure, such as cooking or being in an area where people were

smoking.

2.2 Sample Collection

PM2.5 personal exposure filter samples were collected continuously and simultaneously for the four participants on

weekdays (July 6 to 24, 2009) from 8 am to 8 pm local time (total 12 hr). Samples were collected using URG-2000

PM2.5 personal sampling devices (URG Corp., Chapel Hill, USA) each of which consisted of a filter-holder containing a

25-mm quartz filter (QM/A®, Whatman Inc., UK), a mini-PM2.5 cyclone, and a 3 L min

-1 AirLite Sample Pump. Before

sampling, the quartz filters were pre-combusted at 800C for at least 4 hr to remove adsorbed organic vapors. A blank

filter was collected for each batch to account for contamination from handling and the weighing steps. The pumps were

wrapped in sound-deadening material and placed in a waist pack for the participants to wear. The samplers were

connected to the pumps, and the participants kept the sampling inlets within the breathing zone distance (~0.2 m from

the nose and mouth). Flow rates were tested at the beginning and the end of each sampling period. The exposed sample

filters were placed in petri dishes and then stored at -20C before analysis to prevent the volatilization of the PAHs.

Ambient PM2.5 samples were also collected from 8 am to 8 pm local time (in parallel with the personal sampling) with

the use of a URG-3000N ambient sampler that was deployed on the rooftop of IEECAS building complex (~10 m above

the ground and 30 m from road traffic). This ambient sampling device used 37-mm quartz filters (QM/A®, Whatman Inc.,

UK), and operated at a standard flow rate 22 L m-1

. The start and end times were recorded in a sampling log along with

notes on unusual weather or traffic events. After sampling, the ambient aerosol filters were removed, equilibrated,

weighed, and stored using the same methods as those for personal exposure samples. A total of 15 samples were

collected from each of the four participants; this resulted in a total of 60 personal exposure and 15 outdoor samples for

the gravimetric analyses.

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2.3 Analyses

All quartz sample filters were weighed before and after sampling to determine the accumulated PM2.5 mass

concentrations. The filters were weighed using a Sartorius ME 5-F electronic microbalance (±1 μg sensitivity, Sartorius,

Gottingen, Germany)[17]

. The equilibration and weighing steps were repeated until a difference of < 5 µg was achieved.

Due to the high PM2.5 mass correlations among the four individuals [18]

, one punch (0.5 cm2) from each personal

exposure filter were combined (total 2.0 cm2) for the PAH analyses of the personal samples. Two punches (each punch

was 0.5 cm2; 1.0 cm

2 in total) were taken from each outdoor sample to provide sufficient mass for the ambient PAHs

analysis.

Solvent extraction (SE) followed by gas chromatography/mass spectrometry (GC/MS) was used to determine the PAH

concentrations. Filter punches were extracted three times, each time with 5 mL of a mixture of dichloromethane/

methanol (2:1, v/v) for 10 min with ultrasonication. After concentration, the extracts were incubated with 50 μL of

N,O-bis-(trimethylsilyl)trifluoroacetamide with 1% trimethylsilyl chloride and 10 μL of pyridine at 70C for 3 hr. The

derivatized extracts were analyzed with a Agilent 4890 5975 gas chromatography/mass selective detector system

(Agilent Technologies, Inc., Santa Clara, CA. USA). The GC/mass spectrometer GC/MS response factors were

determined using authentic standards. Average recoveries of all the standards were ~70%. Detailed information on the

procedures used for PAHs pretreatment and analysis along with QA/QC information has been presented in Wang et al. [19]

. Field blank filters were analyzed using these same procedures. The results of the blank analyses showed no serious

contamination (< 5.0% of the PAH concentrations of samples). The data reported are all corrected for the blanks.

Thirteen PAHs were identified and quantified in this study; these were fluorine (FLO, 3-ring), phenanthrene (PHE,

3-ring), anthracene (ANT, 3-ring), fluoranthene (FLU, 4-ring), pyrene (PYR, 4-ring), benzo[a]anthracene (BaA, 4-ring),

chrysene and triphenylene (CT, 4-ring), benzo[b]fluoranthene (BbF, 5-ring), benzo[k]fluoranthene (BkF, 5-ring),

benzo[a]pyrene (BaP, 5-ring), indeno[1,2,3-cd]pyrene (IcdP, 6-ring), dibenzo[a,h]anthracene (DahA, 5-ring), and

benzo[g,h,i]perylene (BghiP, 6-ring).

2.4 Air Exchange Rate Experiment

An experiment was conducted to determine the rate at which outdoor air was transferred into the office environment

from the air conditioning system and from leaks in doors, windows, etc; this was done to understand the role of the air

exchange in terms of PAH exposure. Carbon dioxide gas (gas cylinder, 5000 ppm CO2) was released into an office with

the windows and doors closed in the building complex. The CO2 source was removed when the concentration reached

5000 ppm in the office. A handheld Q-TRAK air quality real-time instrument (TSI Inc., MN, USA) was used to measure

the CO2 concentrations. Multiple locations in the office were measured to ensure CO2 was well-mixed throughout the

room. The air conditioner was then turned on high until the CO2 concentration fell below the background, indoor level

(700 ppm).

The air exchange rate (AER) was calculated based on the following equation [20,21]

:

C(t) = C(0)e-kt

1)

where C(0) is the initial concentration of CO2, C(t) is the concentration of CO2 after time t, and k is a rate constant (that

is, the AER) in units of reciprocal time.

3 RESULTS AND DISCUSSION

3.1 Exposure to PM2.5

1) Personal-outdoor Associations of PM2.5 Concentrations

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The arithmetic mean mass concentrations of the four personal exposure PM2.5 samples ranged from a low of 58.6 μg m-3

(subject CC) to a high of 73.5 (BB) μg m-3

, and these were generally lower than outdoor PM2.5 concentrations, which

averaged 80.5 μg m-3

(Table 1). Ratios of personal exposure to outdoor mass concentrations (P/O) ranged from 0.7 to 0.9.

The P/O ratios less than unity can be interpreted as an indication that the PM2.5 loadings were lower in the offices

compared with the outdoor air, that is, lower exposure indoors compared with outdoors. A scatter-plot of personal versus

outdoor PM2.5 mass concentrations is presented in Fig. 1. Overall, the PM2.5 mass concentrations showed a strong

correlation between the personal exposure and outdoor samples (R = 0.81), with the R values for the four subjects

ranging from 0.79 to 0.87. The slope of the regression (0.6) implies that the filters on the air conditioners removed some

of the PM or that the PM was prevented from entering the offices by some other means. The intercept (24.3) of the

regression might imply that there is a background source for indoor PM.

FIG. 1 RELATIONSHIP BETWEEN PERSONAL EXPOSURE (P) AND OUTDOOR (O) PM2.5 MASS CONCENTRATIONS

TABLE 1 PERSONAL EXPOSURE (P) AND OUTDOOR (O) PM2.5 MASS CONCENTRATIONS IN XI’AN

Type of

Sample Na

PM2.5 concentration (μg m-3)

P/O ratio Rb

Mean Range

Subject AA 15 69.6 25.9 – 181.3 0.9 0.83

Subject BB 15 73.5 30.6 – 186.0 0.9 0.87

Subject CC 15 58.6 28.4 – 123.6 0.7 0.86

Subject DD 15 63.9 26.0 – 114.7 0.8 0.79

Outdoor 15 80.5 32.3 – 236.8 N/Ac N/A

aN is the number of samples

bR is the P/O correlation coefficient

cNA is not applicable

0 50 100 150 200 250 3000

50

100

150

200

0

50

100

150

200

Per

sonal

exposu

re P

M2.5

(ug m

-3)

Outdoor PM2.5

(ug m-3)

Y= 0.6X + 24.3

R=0.81 N=52 P<0.0001

AA

BB

CC

DD

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Regulatory standards have not been established in China for either personal exposure or indoor PM2.5 concentrations, and

few studies have focused on personal exposure to PM in office settings. Nevertheless, the results from our study can be

compared with those from other areas. Summer PM2.5 concentrations reported by Sangiorgi et al. [22]

for various office

settings in Milan, Italy were 14.5, 13.3, 20.0, and 23.3 μg m-3

, while the corresponding outdoor PM2.5 concentrations

were 19.5, 20.2, 32.1, and 37.0, respectively. The US EPA also completed the collection phase of the cross-sectional

Building Assessment Survey and Evaluation (BASE) study in 2000 [23]

. The PM2.5 indoor concentrations from that study

ranged from 1.3 to 24.8 μg m-3

in 100 office buildings across the USA, with a geometric mean of 7.2 μg m-3

, and the

outdoor concentrations ranged from 4.5 to 47.4 μg m-3

, with a geometric mean of 14.7 μg m-3

[23]

. A detailed study of

PM2.5 distributions in three non-residential indoor environments (museum, print industry, and office) in Athens, Greece

found mass concentrations of 20.3, 65.0, and 30.7 μg m-3

, respectively [24]

. In comparison, the PM2.5 mass loadings in the

personal exposure samples from our study were much higher than all of those just mentioned.

2) Impacts of the Time Spent Outdoors and Office Air Exchange Rate

The participants spent the majority of their time indoors (average = 93%, range: 89–97%); the percentages of time spent

outdoors were 7, 3, 5, and 11% for subjects AA, BB, CC, and DD, respectively (Fig. 2). The correlation coefficients (R

values) for linear regressions of the personal exposure PM2.5 mass concentrations versus the time spent outdoors by the

participants (four inset figures in Fig. 2) were 0.75, 0.34, 0.32, and -0.16, indicating modest or no correlations between

the outdoor activity time and personal PM2.5 exposure [25,26]

. This is likely because the variability in personal exposure

PM2.5 mass was as much a result of the differences between the indoor/outdoor PM2.5 loadings as the amount of time

spent outdoors [26,27]

. Moreover, it's worth mentioning that DD, who spent the greatest percentage of time outdoors,

showed a negative correlation between variables, which also was the weakest of the relationships. Furthermore, the

activity logs indicate that DD was the most mobile of the subjects, and that person also spent more time moving between

microenvironments where the PM2.5 loadings were likely variable.

FIG. 2 RELATIONSHIPS BETWEEN THE PERSONAL EXPOSURE TO PM2.5 AND TIME SPENT OUTDOORS

The activity logs showed that the participants’ office windows and doors were always closed and the air conditioners

were always turned on high. The high R values (0.79–0.87, Fig.1) for the linear regressions of outdoor versus personal

exposure PM2.5 mass concentrations indicate the offices had good ventilation and frequent air exchange [28]

. Indeed, the

average AER was 1.36 hr-1

for the four offices in the study. This value is comparable to other indoor microenvironments

0 50 100 150 2000

10

20

30

40

Y=-0.03 X + 11.2

R=-0.16 N=11 P=0.6346

Personal exposure PM2.5

(ug m-3

)

Tim

e sp

ent

outd

oor

(%)

DD

0 50 100 150 2000

10

20

30

40

Y=0.3 X - 2.3

R=0.32 N=6 P=0.5311

Personal exposure PM2.5

(ug m-3

)

Tim

e sp

ent

outd

oor

(%)

CC

0 50 100 150 2000

10

20

30

40

Personal exposure PM2.5

(ug m-3

)

Y=0.1 X + 2.9

R=0.34 N=6 P=0.5095

Tim

e sp

ent

outd

oor

(%)

BB

0 50 100 150 2000

10

20

30

40 Y=0.2 X - 3.4

R=0.75 N=11 P=0.0076

Personal exposure PM2.5

(ug m-3

)

T

ime

spen

t outd

oor

(%)

AA

AA BB CC DD0

5

10

15

20

25

30

35

0

5

10

15

20

25

30

35

Tim

e sp

ent

outd

oors

(%

)

Tim

e sp

ent

outd

oors

(hour)

Participant

Time spent outdoors (hour) Time spent outdoors (%)

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in China where air exchange rates were 1.37 hr-1

in a classroom, 1.91 hr-1

in a reading room, and 1.22 hr-1

in a dormitory

and in an urban area California (USA) where the air-exchange rate in summer was 1.13 hr-1

[21,29]

. If the AER for an

office is low, indoor air pollutants can accumulate to levels that could pose health risks. However, in our study, PM2.5

was typically higher for the outdoor air samples than for the personal samples, and a modest air exchange rate would be

beneficial to the office workers because it would prevent the infiltration of the outdoor air. On the other hand, as

illustrated below, exposure to other pollutants such as PAHs, also are affected by human activities as well as the AER.

3.2 Exposure to PAHs

Thirteen PAHs were detected in all samples, and the average concentrations and standard deviations of the sums of these

PAHs (ΣPAHs ) were 179.8 ± 157.7 ng m-3

and 114.9 ± 116.2 ng m-3

in the personal exposure and ambient PM2.5

samples, respectively (Table 2 and Fig. 3). The PAHs for daily average personal exposure samples ranged from 35.0 (23

July) to 555.8 ng m-3

(10 July) while the PAHs for ambient PM2.5 ranged from 31.0 (22 July) to 487.9 ng m-3

(14 July). A

time-series plot shows that the variations in the PAH concentrations in the two different kinds of samples were not

synchronous (Fig. 3). The average P/O ratio for ΣPAHs was 1.6 and ranged from 0.2 to 6.5. Indeed, the P/O ratios for

were less than 1.0 on only four of the sampling days (26.7% of the samples), and therefore, in contrast to the PM2.5

loadings discussed above, most of the personal exposure samples had higher PAH concentrations than the outdoor ones.

TABLE 2 CONCENTRATIONS OF 3- to 6-RING PAHS IN PERSONAL EXPOSURE AND OUTDOOR SAMPLES

PAH Number

of Rings

Personal Exposure (P) Outdoor (O)

P/O Average

(ng m-3)

Standard

deviation

Average

(ng m-3)

Standard

deviation

3-ring PAHs 19.9 15.5 5.8 6.1 3.4

4-ring PAHs 36.7 33.6 23.4 26.0 1.6

5-ring PAHs 75.4 68.2 51.2 53.7 1.5

6-ring PAHs 47.8 62.0 34.4 31.4 1.4

Total PAHs 179.8 157.7 114.9 116.2 1.6

FIG. 3 TIME SERIES OF PERSONAL EXPOSURE AND OUTDOOR PAH CONCENTRATIONS (ng m-3

) IN XI’AN

7/6

7/7

7/8

7/9

7/1

0

7/1

3

7/1

4

7/1

5

7/1

6

7/1

7

7/2

0

7/2

1

7/2

2

7/2

3

7/2

4

7/2

5

0

100

200

300

400

500

600

0

100

200

300

400

500

600

PA

Hs

con

cen

trat

ion

s (n

g m

-3)

Personal exposure

Outdoor concentration

PA

Hs

con

cen

trat

ion

s (n

g m

-3)

Date

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Based on the activity logs, none of participants cooked, cleaned, or were exposed to tobacco smoke during the collection

of the personal exposure samples. No obvious sources for the PAHs were noted except for the printing and computer

equipment in the office. Participants spent an average of 93% of their time indoors; most of their time outdoors was

spent in environments where the PAH concentrations were likely high (e.g., walking near roadways or riding buses).

This time-activity pattern was reflected in the lower 12-hr average PAH concentrations in ambient PM2.5 samples

compared with the personal exposure samples. Although the time spent outdoors everyday by participants was short

(even zero hours on occasion for two participants who sometimes stayed in the Institute), the time outdoors usually

involved the daily commute. This led to the subjects’ exposure to higher PAH concentrations from motor vehicle

emissions.

To the best of our knowledge, no studies to date have investigated personal exposure to PM2.5-bound PAHs near

roadways in Xi’an. Fortunately, data for traffic police exposed to PAHs during the summer in Tianjin provide a point of

comparison for understanding the ambient PAH concentrations found in our study [30]

. The mean concentration of the

sum of thirteen PAHs collected from roadway intersections in Tianjin was 867.5 ng m−3

, and that was much higher than

the average for samples collected on a school campus which also was in Tianjin (ΣPAHs: 19.5 ng m−3

). In comparison,

the personal PAHs in our study were five orders of magnitude lower than what found in Tianjin roadside samples. This

suggests that personal exposure to PAHs can be strongly affected by outdoor activity patterns, and in particular, the time

spent in specific microenvironments where the pollutants are in high concentrations.

The mean concentrations of individual PAH in the personal exposure and outdoor samples are shown in Fig.4. IcdP was

the most abundant PAH followed by BbF and BaP. The mean IcdP concentrations were 31.6 and 26.9 ng m-3

in the

personal exposure and outdoor samples, respectively, and it accounted for 17.6% to 23.4% of the ΣPAHs. BaP is one of

the most potent carcinogens among the known PAHs, and it has been considered a general indicator of carcinogenicity [19,31,32]

; the average BaP concentrations were 28.4 for the personal exposure samples and 21.7 ng m-3

for the outdoor

samples. These levels are more than 20 times the concentration limit in the air-quality guidelines of the World Health

Organization (1.0 ng m-3

), and they also exceeded the BaP limit in the China National Ambient Air Quality Standards

(2.5 ng m-3

for 24-hr average in PM10) [33]

and in the China National Indoor Air Quality Standards (1.0 ng m-3

for 24-hr

average in PM10) [34]

. Note that the last two standards just referenced are for PM10 and not PM2.5 as was measured in our

study; indeed, the concentrations in our samples would have been higher if we had collected and analyzed larger

particles. Although the total PAH and BaP concentrations may have declined in Xi’an [19,35]

, the loadings are still high,

and the potential for adverse health effects remains a cause for concern.

FIG. 4 INDIVIDUAL PAH ABUNDANCE (%) IN PERSONAL EXPOSURE AND OUTDOOR SAMPLES IN XI’AN

fluoren

e

phenanthrene

anthracene

fluoranthene

pyrene

benz[a]anthracene

triphenylen

e

benzo[b]fluoranthene

benzo[k]fluoranthene

benzo[a]pyrene

indeno[1,2,3-cd]pyrene

dibenz[a,h]anthracene

benzo[g,h,i]pery

lene

0

5

10

15

20

25

0

5

10

15

20

25

Ab

un

dan

ce (

%)

Ab

un

dan

ce (

%)

Personal exposure

Outdoor concentration

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Comparisons of the PAH concentrations grouped by ring structure for the personal exposure and outdoor samples are

shown in Table 2. The average contribution of 3-ring PAHs was 11.1% for the personal exposure samples, and that was

much higher than in the outdoor PM2.5 samples (5.1%); in fact, the P/O ratio for 3-ring PAHs was 3.4. In contrast, the

concentration percentages of 4-, 5-, and 6-ring PAHs in personal exposure and outdoor samples were much more similar

(20.4 and 20.3% for 4-ring PAHs, 41.9 and 44.6% for 5-ring PAHs, 26.6 and 30.0% for 6-ring PAHs, respectively). The

average P/O ratios for the 4-, 5- and 6-ring PAHs ranged from 1.6 to 1.4; and they varied inversely with the PAHs’

boiling points; that is, lower P/O ratios were observed for the PAHs with higher boiling points.

This difference in P/O ratios is most likely because the 3- and 4-ring PAHs (molecular weight, MW < 252) typically

exist in both the vapor and particulate phases while the 5- and 6-ring PAHs (MW ≥ 252) are mainly in the particulate

phase [7,32,36]

. According to gas-particle distribution theory, the 5- and 6-ring PAHs should be more stable and less

volatile than the 3-ring PAHs. This means that compared with the higher MW PAHs, the 3-ring PAHs are more likely to

vaporize in the warm summer air and then infiltrate into the offices through the doors and windows. In our study, the

average outdoor temperatures reached 31.1C; this was approximately 7C higher than in the offices (mean 24.4C).

Hence, setting aside the differences in the PAH emission sources and other factors, a larger fraction of the 3-ring PAHs

would condense onto particles in the cooler office air compared with the warmer outdoor environment.

Comparisons with the results of previous studies of personal exposure to PM2.5 and associated PAHs shows that the

exposure in Xi’an is much lower than in Beijing (559.4 ng m-3

in 2007 winter) [37]

but higher than in Guangzhou or

Tianjin, China [13,30]

, Shizuoka, Japan [38]

, Bangkok, Thailand [39]

, and Porto, Portugal [40]

. The level of exposure in Xi’an

is ten to one hundred times higher than what is typical in the USA [41,42]

, and this high level of the personal exposure to

PAHs deserves serious attention in future air pollution and human health studies.

3.3 Implications for PAH Sources

A scatter plot of the total PAH concentration outdoors versus personal exposure (Fig. 5a) shows two different

relationships, one with R = 0.61 (line I) and the other R = 0.94 (line II). The difference in the slopes of lines I and II

(0.18 and 4.57) indicates that there were two types of exposure to PAHs, and these were most likely a function of the

individuals’ time-activity patterns. This finding is important because it illustrates how normal day-to-day activities can

influence one’s exposure to this group of pollutants. For regression line I (below the 1:1 diagonal line), all of the

personal exposure PAH concentrations were much higher than the matching outdoor data. Although our outdoor

monitoring site did not capture the roadside PAH concentrations, the high personal exposure PAHs can best be explained

by the relatively long time (>1 hr) the participants spent outdoors each day; this included time spent commuting in

heavily trafficked areas where PAH concentrations were likely high. Regression line II (above the 1:1 diagonal line)

reflected relatively shorter outdoor exposure times (<1 hr each day on average); this relationship was seen for

participants on days when they did not commute or when they spent the entire day indoors where PAH concentrations

were most likely low.

Diagnostic ratios of atmospheric PAHs with similar MWs have been used for source identification studies [43,44]

. The

personal exposure samples from our study had average values of 0.24 for ANT/(ANT+PHE) and 0.62 for

IcdP/(IcdP+BghiP); in comparison, the corresponding ratios were ~0.11 and 0.75 for the outdoor samples (Fig. 5b). The

bulk of the outdoor data plotted around the vertical line at 0.1 for ANT/(ANT+PHE), and this indicates that the

contributions of petrogenic and pyrogenic sources to the outdoor PAHs were roughly equal. In contrast, most of the

personal exposure samples plotted in the center of Fig. 5b, and this is consistent with a predominant influence from

pyrogenic sources. Almost all of the data points plotted above the upper horizontal line at 0.5 for the IcdP/(IcdP+BghiP)

ratio, indicating that most of the samples had strong influences from grass, wood, and coal combustion although some of

them evidently also were affected by petroleum combustion.

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FIG. 5(a) CORRELATIONS OF OUTDOOR AND PERSONAL EXPOSURE PAH CONCENTRATIONS; (b)

CORRELATIONS BETWEEN PAH DIAGNOSTIC RATIOS [ANT/(ANT+PHE) AND IcdP/(IcdP+BghiP)] FOR

PERSONAL EXPOSURE AND OUTDOOR SAMPLES

3.4 Toxicity and Carcinogenic Risk of PAHs in Personal PM2.5

It is well established that many PAHs are mutagenic and carcinogenic, and their health risks can be assessed by

calculating BaP-equivalent ([BaP]eq) concentrations [9]

. The widely used procedures of the Office of Environmental

Health Hazard Assessment (OEHHA) of the California Environmental Protection Agency (CalEPA) are often used to

calculate inhalation cancer risks [45,46]

. The [BaP]eq for each personal exposure sample was calculated from the

PM2.5-bound PAH concentration combined with the toxicity equivalency factors (TEFs) of target compounds [47,48]

as

shown in equation (2).

Σ[BaP]eq = Σ (Ci × TEFi) (2)

where Ci is the concentration of target compound i (ng m-3

), and TEFi is the TEF of the target compound i. The

inhalation cancer risk associated with exposure to the PAHs can be calculated as follows:

Inhalation cancer risk = Σ[BaP]eq × UR[BaP] (3)

where UR[BaP] (unit risk), which is the inhalation cancer unit risk factor of BaP, which is defined as the number of

people at risk of contracting cancer from the inhalation of a BaP equivalent concentration of 1 ng m-3

in a lifetime of 70

years. The UR[BaP] value from the CalEPA is 1.1 × 10-6

(unit risk) [45,46]

. Assuming that the career of a typical employee

spans ~35 years; and adjusting for evenings, weekends, and holidays; that employee would spend ~12 years in the office

environment. Therefore, the estimated average UR[BaP] value for the subjects in our study would be 1.8 × 10-7

(unit

risk).

As part of our effort to evaluate the health effects of the PAHs, we calculated the individual [BaP]eq concentration levels

and the relative contributions for each of the thirteen measured PAHs in the personal exposure samples (Fig. 6). Fig. 6

shows that the [BaP]eq values for the various PAH species ranged from 0.02 (ANT) to 28.4 (BaP) ng m-3

(with a mean

value for the PAHs of 3.5 ng m-3

). Thus, the contributions from the individual PAHs to the total [BaP]eq concentrations

(Σ[BaP]eq) ranged from 0.004% for ANT to 61.9% for BaP. The [BaP]eq levels were dominated by BaP (28.4 ng m-3

or

61.9%) and DahA (10.2 ng m-3

or 22.2%); these two compounds accounted for more than 80% of the total [BaP]eqs. The

contributions of 5+6-ring PAHs to the Σ[BaP]eq concentrations followed the order BaP > DahA > IcdP > BbF > BkF >

BgihP; these compounds amounted to ~99.5% of the total due to their high absolute concentrations and high TEF values:

the 3+4-ring PAHs amounted to only 0.5% of Σ[BaP]eq. These results attest to a distinctly higher human-health risk for

the PAHs with MW ≥ 252 (~2 to 4 orders of magnitude higher) when compared with the MW < 252 PAHs.

0 100 200 300 400 500 600

0

100

200

300

400

500

600

Outd

oor

PA

Hs

(ng m

-3)

Personal exposure PAHs (ng m-3)

Y= 0.18 X + 36.83

R=0.61 N=10 P=0.0592

Y= 4.57 X - 79.93

R=0.94 N=5 P=0.0158

1:1 line

ⅡⅠ

（a）

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Petrogenic

Petroleum combustion

Grass, wood and

coal combustion

Pyrogenic

IcdP

/(Ic

dP

+B

ghiP

)

ANT/(ANT+PHE)

Personal exposure

Petrogenic

Outdoor

（b）

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FIG. 6 PERCENTAGES (%) OF [BaP]eq FOR INDIVIDUAL PAH SPECIES IN PERSONAL EXPOSURE SAMPLES (SEE

TEXT FOR DESCRIPTION OF PAH ABBREVIATIONS)

Furthermore, the mean Σ[BaP]eq for the entire personal exposure sampling period was 45.8 ± 43.0 ng m-3

(range:

8.7–164.6 ng m-3

): the highest value was found on 10 July and the lowest on 23 July. The maximum Σ[BaP]eq value was

more than 3.5 times the average. The excess inhalation cancer risk in the Xi’an urban office environment for a typical

career of 12 years averaged 8.3 × 10-6

(range: 1.6 × 10-6

to 3.0 × 10-5

). The median value of total inhalation risk was

6.9×10-6

, with 6.0×10−6

and 1.0×10-5

for the 5th and 95

th percentiles, respectively. Therefore, an estimated mean of 8

(range: 2 to 30) cases of cancer per million office workers in Xi'an can be expected from the inhalation of PM2.5-bound

PAHs.

The Xi’an Statistical Yearbook [49]

indicates that the total number of persons employed in enterprises, institutions,

agencies and related organizations in Xi’an was approximately 1.35 million at the end of 2009. Therefore, an estimated

11 cancer cases for these working employees can be attributed to the inhalation of PM2.5-bound PAHs. We should note

that this number of cases is most likely an underestimate because the assessment is based on summertime PAH

concentrations, which are lower than that in other seasons [19]

. This extremely high Σ[BaP]eq value and the

corresponding health risks should not to be neglected in Xi’an. Finally, it is important to note that the levels of PAHs and

other contaminants in the offices investigated here are surely much lower than in many other work environments, and

therefore, the investigations of PAH exposures should be expanded to include other workplaces where the impacts are

likely to be greater.

4 CONCLUSIONS

This study on personal exposure to PM2.5 and PAHs in Xi’an, China highlights the importance of understanding and

quantifying PAH sources and in determining how the exposures are affected by personal activity patterns. The personal

exposure PM2.5 mass concentrations for four subjects averaged over 15 days ranged from 58.6 to 73.5 μg m-3

(with the

average of 66.4 μg m-3

), and these were generally lower than the outdoor concentrations, which averaged 80.5 μg m-3

.

Overall, the mass concentrations showed a strong correlation between outdoor and personal exposure (R = 0.81), and the

slope of the regression for these two sets of samples implies that some of the outdoor PM was removed by the air

conditioning system or in other ways prevented from entering the offices.

The averages of the sums of the thirteen PAHs investigated were 179.8 ± 157.7 and 114.9 ± 116.2 ng m-3

in the personal

exposure (P) and outdoor (O) samples, respectively. The PAHs P/O correlations evidently were driven by the

individual’s time-activity patterns. The average P/O ratio for individual PAHs was 1.6 and ranged from 0.2 to 6.5. The

mean Σ[BaP]eq concentration for the ensemble of all personal exposure samples was 45.8 ± 43.0 ng m-3

(range: 8.7 to

164.6 ng m-3

). The PAHs diagnostic ratios indicate that the main sources of PAHs were anthropogenic, especially coal

0.35%

22.18%

6.89%

61.88%

1.9%

6.34%

0.31%0.09%0.02%0.02%0%0.01%0.01%

FLO

PHE

ANT

FLU

PYR

BaA

CT

BbF

BkF

BaP

IcdP

DahA

BghiP

6.3 %

1.9 %

22.2 %

6.9 %

61.9 %

0.8 %

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combustion and motor vehicle emissions.

The excess inhalation cancer risk derived from Σ[BaP]eq indicates that 8 persons (range: 2 to 30) per million office

workers in Xi'an would develop cancer due to their exposure to PM2.5-bound PAHs. It is important to note that the PM2.5

and PAH concentrations in the offices in this study are doubtlessly much lower than in many other workplace

environments, and so the cancer risks estimated here are likely toward the lower end of the risk spectrum. The study also

was conducted during the summer when the PAH concentrations were relatively low, so the overall risks are likely

higher. It is also worth emphasizing that this study highlights the potential impacts of PM2.5 and PAHs from mobile

sources; the study participants evidently were exposed during their commute despite the typically short duration of

exposure. Targeted sampling of specific microenvironments and further investigations of time-activity patterns would

benefit future studies and help determine the greatest PAH-related health risks.

ACKNOWLEDGMENTS

This study was supported by National Gongyi Project (201209007), Shaanxi Project (2012KTZB03-01), and the funding

from “US National Science Foundation East Asia Pacific Summer Institutes Program”.

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Authors1 Hongmei Xu (1986-), female, Chinese, a

PhD Candidate of Key Lab of Aerosol

Science & Technology, SKLLQG, Institute

of Earth Environment, Chinese Academy of

Sciences and University of Chinese

Academy of Sciences. Her research interests

are inorganic and organic compounds in

aerosol particles, their origins, and the

human health effects; personal exposure and related health risk

assessment and PM2.5 source apportionment.

Email: xuhongmei@ieecas.cn

2† Junji Cao (1971-), male, Chinese, Doctor, professor of Key Lab

of Aerosol Science & Technology, SKLLQG, Institute of Earth

Environment, Chinese Academy of Sciences and part-time

professor of Institute of Global Environmental Change, Xi’an

Jiaotong University. His research interests are PM2.5 and

carbonaceous aerosols, their origins, and effects on climate; and

indoor air pollutants and their effects on historical artifacts.

Email: cao@loess.llqg.ac.cn

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3 Meiling Gao (1984-), female, USA, a PhD Candidate of

University of California, Berkeley, USA. Her research interests are

air pollutants in indoor and outdoor environments, and the effects

of built environment on disparities in exposures and health in both

China and USA.

4 Kin Fai Ho (1974-), male, Chinese, Doctor, assistant professor

School of Public Health and Primary Care, The Chinese University

of Hong Kong and part-time professor of Key Lab of Aerosol

Science & Technology, SKLLQG, Institute of Earth Environment,

Chinese Academy of Sciences. His research interests are aerosol

chemistry and health, especially the physical and chemical

characteristics of gases and aerosols in the atmosphere from

different sources.

5 Xinyi Niu (1990-), female, Chinese, Master degree of Department

of Civil and Structural Engineering, Hong Kong Polytechnic

University. Her research interests are air pollutants, including

aerosol and gases in indoor environment.

6 Teresa L. Coons (1985-), female, USA, Master degree of science

in Department of Civil, Environmental, and Architectural

Engineering, Washington State University in 2009. Her research

interest is personal exposure and spatial variability of PM2.5 in

Colorado and China.

7 Steven Sai Hang Ho (1975-), male, Chinese, Doctor, Chief

Executive Officer of Hong Kong Premium Services and Research

Co. and part-time professor of Institute of Earth Environment,

Chinese Academy of Sciences. His research experiences are in

environmental sciences and analytical chemistry.

8 Gehui Wang (1968-), male, Chinese, Professor of the Key Lab of

Aerosol Science & Technology, SKLLQG, Institute of Earth

Environment, Chinese Academy of Sciences. His research interests

are atmospheric chemistry, especially the physical and chemical

characteristics of organic aerosols in the atmosphere and their

impacts on climate and human health.

9 Zhuzi Zhao (1985-), female, Chinese, a PhD Candidate of Key

Lab of Aerosol Science & Technology, SKLLQG, Institute of

Earth Environment, Chinese Academy of Sciences and University

of Chinese Academy of Sciences. Her research interest is the

carbonaceous aerosol and its origins in remote regions (e.g., Tibet

and Qinghai Lake).