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Atmospheric Environment 39 (2005) 5113–5124

www.elsevier.com/locate/atmosenv

Characteristics of vertical profiles and sources of PM2.5, PM10

and carbonaceous species in Beijing

C.Y. Chana,�, X.D. Xub, Y.S. Lia, K.H. Wonga, G.A. Dingb,L.Y. Chana, X.H. Chengb

aDepartment of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong KongbChinese Academy of Meteorological Sciences, Beijing, China

Received 3 December 2004; received in revised form 1 May 2005; accepted 19 May 2005

Abstract

In August 2003 during the anticipated month of the 2008 Beijing Summer Olympic Games, we simultaneously

collected PM10 and PM2.5 samples at 8, 100, 200 and 325m heights up a meteorological tower and in an urban and a

suburban site in Beijing. The samples were analysed for organic carbon (OC) and elemental carbon (EC) contents.

Particulate matter (PM) and carbonaceous species pollution in the Beijing region were serious and widespread with

86% of PM2.5 samples exceeding the daily National Ambient Air Quality Standard of the USA (65 mgm�3) and the

overall daily average PM10 concentrations of the three surface sites exceeding the Class II National Air Quality

Standard of China (150mgm�3). The maximum daily PM2.5 and PM10 concentrations reached 178.7 and 368.1mgm�3,

respectively, while those of OC and EC reached 22.2 and 9.1 mgm�3 in PM2.5 and 30.0 and 13.0 mgm�3 in PM10,

respectively. PM, especially PM2.5, OC and EC showed complex vertical distributions and distinct layered structures up

the meteorological tower with elevated levels extending to the 100, 200 and 300m heights. Meteorological evidence

suggested that there exist fine atmospheric layers over urban Beijing. These layers were featured by strong temperature

inversions close to the surface (o50m) and more stable conditions aloft. They enhanced the accumulation of pollutants

and probably caused the complex vertical distributions of PM and carbonaceous species over urban Beijing. The built-

up of PM was accompanied by transport of industrial emissions from the southwest direction of the city. Emissions

from road traffic and construction activities as well as secondary organic carbon (SOC) are important sources of PM.

High OC/EC ratios (range of 1.8–5.1 for PM2.5 and 2.0–4.3 for PM10) were found, especially in the higher levels of the

meteorological tower suggesting there were substantial productions of SOC in summer Beijing. SOC is estimated to

account for at least 33.8% and 28.1% of OC in PM2.5 and PM10, respectively, with higher percentages at the higher

levels of the tower.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Particulate matter; Urban air pollution; Emission source; Atmospheric stability

e front matter r 2005 Elsevier Ltd. All rights reserve

mosenv.2005.05.009

ing author. Tel.: +1852 2766 4475;

4 6389.

ess: cececychan@polyu.edu.hk (C.Y. Chan).

1. Introduction

The 2008 Summer Olympic Games will be hosted by

Beijing, the capital of China. An important factor

determining the success of the Olympic Games is air

d.

ARTICLE IN PRESSC.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–51245114

quality. Exposure to airborne particulate matter (PM) is

associated with increased mortality and morbidity (Pope

III et al., 2002; Ostro et al., 1999). No broad consensus

has been reached on the effects of ambient PM on

exercising athletes and sport performance. However,

athletes are at considerable risk of inhaling elevated

levels of PM and its toxic constituents. This is because

there is a proportionate increase in the quantity of

pollutants inhaled with increased rate of breathing

during exercise coupled with a larger fraction of air

inhaled through the mouth, effectively bypassing the

normal nasal filtering process. Also, the increased air

flow velocity carries pollutants deeper into the respira-

tory tract.

In recent years, elevated pollution with PM10 con-

centration as high as 400 mgm�3 has been reported for

Beijing (e.g. Ando et al., 1994; Ning et al., 1996; He et

al., 2001). Shi et al. (2003) reported that particles in the

respirable (o2.5 mm) fraction account for 99% of the

total particles in airborne PM samples in Beijing.

Various sources including vehicular emission, coal and

bio-fuel burning emissions, and fugitive dust emission

from unpaved surfaces have been proposed to be

important sources of pollutants in the Beijing region

(e.g. He et al., 2004; Shi et al., 2003; Dan et al., 2004).

David and Guo (2000) found that mineral constituents

make up a large mass of the small particles in aerosols,

which may reflect the emissions from construction

activities. Duan et al. (2004) however suggested with

correlation relationship between organic carbon (OC)

and water soluble potassium that biomass burning is a

significant source of urban aerosol in Beijing.

In the summer of 2003 during the anticipated month

of 2008 Olympic Games, we conducted an intensive

observational study of air pollution up a 325-m-high

meteorological tower, and two sites in urban and

suburban areas of Beijing. The study, as part of the

environmental improvement efforts of Beijing, aims at

understanding the physical and chemical processes

leading to air pollution in Beijing and providing

scientific evidence for building up a ‘‘green’’ Beijing for

hosting the Olympic Games. To our knowledge, this is

the first study in Beijing that vertical distributions of PM

and associated carbonaceous species were measured. In

this paper, the characteristics and vertical variations of

PM10 and PM2.5, and carbonaceous species of PM are

presented. Their causes and implications for the sources

and origins of PM will also be discussed.

2. Experiment

2.1. Vertical profile measurement and sampling

The field experiment was performed from 10 to 25

August 2003. The experiment consisted of two parts.

The first part measured the vertical variations of PM2.5

and PM10 in the lower BL of Beijing city up a

meteorological tower of the Institute of Atmospheric

Physics, Chinese Academy of Sciences (CAS). The tower

is 325m in height and is divided into 15 zones. It is

situated in the north of Beijing city at around 8 km from

the Olympic Sports Centre. The tower is surrounded by

buildings of 30–60m height, which are situated at

around 50m from the tower. A total of eight sets of

portable air samplers (MINIVOL, AIRMETRICS,

USA) were used for simultaneous collection of samples

at 8, 100, 200 and 325m heights up the tower. The

samplers have a flow of 570.5 Lmin�1. At each of these

heights, a pair of samplers with PM10 and PM2.5 inlets

was installed. The sampling duration was 24 h. During

sampling, air is drawn through a particle size separator

with PM10 and PM2.5 cut point and then through a

47mm Whatman quartz microfibre filter (QM/A) which

collects the particles in the air stream. The filters were

pre-heated at 800 1C for 3 h before use and were placed

in clean polyethylene petri dishes and wrapped with

Teflon tape before and after field measurements.

Three sets of portable monitors (DustTrak, TSI

Model 8520) were used to measure the real-time PM10

and PM2.5 concentrations at 8, 100 and 325m heights.

The monitor works under the laser photometer principle

with light scattering technique. The monitor works in

the range of 0.001–100mgm�3 (calibrated to respirable

fraction of standard ISO 12103-1, A1 test dust) and

measures particles size ranging from 0.1 to approxi-

mately 10mm (upper limit is dependent on flow rate).

The sampling flow rate is 1.7 Lmin�1. The concentra-

tions of PM with aerosol diameter less than 10 and

2.5mm (PM10 and PM2.5) are distinguished by an

impactor installed in the inlet of the monitor. In the 15

zones of the tower, standard meteorological parameters

including wind speed and direction, air temperature,

relative humidity and others were routinely measured.

The meteorological measurements were subjected to

standard quality control and assurance procedures

specified by CAS.

2.2. Surface measurement and sampling

Samplings were also performed in an urban station

and a suburban station of metropolitan Beijing (Fig. 1)

by MINIVOL Samplers. The urban station is located in

the Chinese Academy of Meteorological Sciences

(CAMS), which is situated in the northwest of Beijing

city (Fig. 1), at the top of a 6-storey building with the

sampling inlet at around 25m above ground. The

suburban station is the Southern Observational Base

(SOB) of CAMS, which is located in a village in the

southeast at around 5 km outside the Fifth Ring Road

(FRR) which was still under construction. The sampling

inlet was situated on the rooftop of a 3-storey building

ARTICLE IN PRESS

Fig. 1. Map showing Beijing city and the sampling sites.

PM :y = 1.09x - 13.98

R2 = 0.99

PM : y = 1.18x - 19.73

R2 = 1.00

PM : y = 0.32x + 11.842.5

2.5

10

10

R2 = 0.99

PM :y = 0.39x + 11.35

R2 = 1.00

0

100

200

300

400

0 100 200 300 400 500 600 700

Mini-volume, DustTrak (µg /m3)

TE

OM

(µ

g/m

3 )

Mini-Volume

DustTrak

Fig. 2. Comparison of the daily PM2.5 and PM10 concentra-

tions measured by TEOM, and Mini-volume and DustTrak

samplers.

C.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–5124 5115

of around 15m above ground. It is relatively far away

from pollutant sources in urban Beijing. Similar to those

up the meteorological tower, a pair of samplers with

PM10 and PM2.5 inlets was installed at each of these

sites.

2.3. Organic and elemental carbon (EC) analysis

An open top balance (Metter AE163) with an

accuracy of 0.01mg was used to weigh the mass of filter

papers. The filters were conditioned in electronic

desiccators with 40% relative humidity before and after

sample collection for 24 h. The filters were stored in the

petri dishes, covered after conditioning and weighting,

and stored in a refrigerator at about 4 1C before

chemical analysis to prevent loss of volatile components

due to evaporation. The samples were analysed by an

OC/EC analyser (Thermal/Optical Carbon Analyzer

Model 2001). The IMPROVE thermal/optical reflec-

tance (TOR) protocol described by Chow and Watson

(2002) and Cao et al. (2003) was used for carbon

analysis. A 0.526-cm2 punch of a sampled quartz filter

was heated at various temperatures in helium atmo-

sphere to evolve OC and in 2% oxygen atmosphere to

evolve EC. The carbon evolved at each temperature is

oxidized to carbon dioxide and then reduced to

methane, with a flame ionization detector for quantifica-

tion.

2.4. Quality control and assurance

In order to make direct comparison of the PM2.5 and

PM10 concentrations measured by different instruments

working under various principles with different mea-

surement techniques, we had conducted a performance

test for the DustTrak analyzer and MINIVOL samplers.

In brief, the DustTrak analyzer and MINIVOL sampler

were calibrated against standard gravimetric samplers

(Tapered Element Oscillating Microbalance, TEOM,

1400a) that are specified in the Federal Reference

Method (FRM) before deploying the instruments for

observation. In the test, DustTrak, MINIVOL and

TEOM samplers with PM10 and PM2.5 inlet were used to

measure the PM2.5 and PM10 simultaneously in the

CAMS for 5 days. The Spearman’s correlations between

the concentrations measured by the samplers were

assessed and their correlation relationships were ob-

tained through regression analysis (Fig. 2). In this paper,

all the PM concentrations have been converted to high

volume sampler scales using the slope and intercept

obtained from the regression analysis between concen-

trations measured by DustTrak analyzer and MINIVOL

sampler, and sampler of FRM as shown in Fig. 2.

The MINIVOL samplers were also subjected to a

parallel comparison before the field study. The relative

deviations of the measured concentrations from 12

samplers from the average values were within 5%. The

DustTrak analyzer was pre-calibrated against Arizona

Test Dust (ISO 12103-1) by the manufacturer every 6

months and before the field experiment. The test dust

has a wide size distribution covering the entire detected

size range of the instrument. As part of the quality

control and assurance procedures, the DustTrak analy-

zers were also subjected to daily zero check by attaching

an HEPA filter to the sampling inlet. The OC/EC

analyser was calibrated with 5.0% CH4 gas (traceable to

N.I.S.T.) every day. Replicate analysis of samples was

preformed at a rate of one per groups of five or 10

samples depending on the performance of the analytical

system. Field and laboratory blank filters were also

analysed and the OC and EC quantities in the samples

were corrected by subtracting the average concentra-

tions of the blanks from the sample values. The

detection limits of EC and OC were less than 1.0 mgm�3

for quartz fiber filter. The difference between the

replicate samples and original run samples was found

ARTICLE IN PRESSC.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–51245116

to be smaller than 5% for TC (total carbon), and 10%

for OC and EC.

3. Results and discussions

3.1. Elevated concentrations of PM2.5, PM10, OC and

EC

Elevated concentrations of PM2.5, PM10, OC and EC

were observed at all the sites. Table 1 summarizes the

PM2.5 and PM10 concentrations and their relative ratios

(PM2.5/PM10) in percentage of a total of 120 samples

collected up the meteorological tower, 30 samples at

CAMS and 30 samples in suburban Beijing. At the three

surface sites (SB, CAMS and 8m altitude), the average

daily concentrations of PM2.5 and PM10 ranged from

90.6 to 113.5mgm�3 and 166.6 to 251.4mgm�3 respec-

tively, with the highest values at the suburban site. At

the non-surface sites on the meteorological tower, the

average daily concentrations of PM2.5 and PM10 were

75.0–89.0mgm�3 and 139.4–148.5mgm�3, respectively.

For all six sites, the maximum daily PM2.5 and PM10

concentrations reached 178.7 and 368.1mgm�3, respec-

tively, while their maximum hourly concentrations

reached 300.4 and 374.3mgm�3, respectively. The

diurnal hourly PM2.5 and PM10 concentrations averaged

over the measurement period at the three meteorological

tower sites reached even higher levels with their

maximum concentrations exceeding 150 and 200 mgm�3,

respectively (Fig. 3). The PM2.5/PM10 ratios at the

surface sites ranged from 37.5% to 85.1% with

noticeably higher average values of 56.1–66.5% at

urban and elevated sites. At the suburban site, the

average PM2.5/PM10 ratio was 43.9%.

Table 2 summarizes the OC and EC concentrations of

a total of 73 samples selected for analysis, among which

Table 1

Summary of PM2.5 and PM10 concentrations and their ratios

PM2.5 (mgm�3) PM1

Daily Hourly Daily

Range Average Range Average Rang

Altitudes 325 3.5–133.7 75.0 2.9–279.3 87.1 18.6

200 14.0–160.2 87.3 NM NM 17.7

100 25.2–147.9 89.0 13.0–230.0 77.0 32.3

8 23.5–178.7 106.5 4.9–300.4 101.1 52.2

CAMS 30.4–159.2 90.6 NM NM 51.9

SB 83.5–162.8 113.5 NM NM 176.4

Overall 3.5–178.7 93.6 2.9–300.4 88.5 18.6

aBased on simultaneous daily data; NM: no measurement.

half are for the surface sites and another half for non-

surface sites. The overall average OC and EC concen-

trations in PM2.5 were 19.2 (range of 7.0–32.7) and 7.0

(1.6–13.1) mgm�3, respectively while those in PM10 were

23.5 (8.2–40.5) and 8.5 (2.7–16.6) mgm�3, respectively,

with noticeably higher values at surface sites, especially

for EC and OC in PM10 at the suburban site. The OC/

EC ratios ranged from 1.8 to 5.1 for PM2.5 and 2.0 to 4.3

for PM10 with an overall average of 2.9 in both PM2.5

and PM10. Noticeably, the OC/EC ratios in both PM2.5

and PM10 increased gradually from the 8 (2.6 and 2.7,

respectively) to 325m (3.5 and 3.4, respectively) heights.

3.2. Comparison with other olympic games hosting cities

The results suggested that the pollution associated

with PM and carbonaceous species is serious and

widespread in the urban and suburban areas, and

extended to the lower part of the BL of Beijing. In fact,

the average daily concentration of PM2.5 (93.6 mgm�3)

in Beijing during the measurement period far exceeded

the 24-h National Ambient Air Quality Standard

(NAAQS) of the USA (65 mgm�3). A total of 74 among

86 samples, which accounted for 86% of the data,

exceeded this standard. The overall average concentra-

tion of PM10 of the three surface sites also exceeded the

Class II National Air Quality Standard (NAQS) of

China for PM10 (GB3095-1996) of 150 mgm�3. The

PM2.5 and PM10 as well as OC and EC concentrations

found in this study are much higher than those reported

for summertime in other cities around the world (Table 3).

For instance, Chaloulakou et al. (2003) reported a

summertime average of 73.9 mgm�3 for PM10 and

39.4mgm�3 for PM2.5 in Athens, Greece, which hosted

the 2004 summer Olympic Games. Querol et al. (2001)

reported average values of 15–35mgm�3 for PM2.5 and

20–60mgm�3 for PM10 in the Barcelona metropolitan

0 (mgm�3) PM2.5/PM10 (%)a

Hourly Daily

e Average Range Median Range Average

–220.2 139.4 4.5–336.2 108.2 28.8–65.5 56.4

–243.6 141.1 NM NM 56.9–79.1 66.5

–261.6 148.5 19.2–269.4 92.4 39.8–78.0 61.2

–300.3 169.1 10.4–374.3 131.1 45.0–85.1 62.2

–271.2 166.6 NM NM 46.3–63.8 56.1

–368.1 251.4 NM NM 37.5–52.6 43.9

–368.1 169.4 4.5–374.3 111.1 28.8–85.1 58.0

ARTICLE IN PRESS

0

50

100

150

200

250

0:00 4:00 8:00 12:00 16:00 20:00

Hour (LST) Hour (LST)

PM

2.5(µ

g/m

3 )

8m100m325m

0

50

100

150

200

250

0:00 4:00 8:00 12:00 16:00 20:00

PM

10(µ

g/m

3)

8m100m325m

Fig. 3. Diurnal variations of average PM2.5 and PM10 concentrations at 8, 100 and 325m heights averaged over all days of

measurement.

Table 2

Summary of average OC, EC and SOC concentrations and OC/EC ratios

PM2.5 PM10

OC (mgm�3) EC (mgm�3) OC/EC SOC OC (mgm�3) EC (mgm�3) OC/EC SOC

mgm�3 % mgm�3 %

Altitudes 325 14.7 4.5 3.5 6.6 46.8 21.4 6.5 3.4 8.5 39.7

200 17.2 5.6 3.1 7.0 40.4 18.2 5.9 3.2 6.5 37.1

100 19.1 7.1 3.0 6.2 34.7 22.8 8.6 2.7 5.8 27.4

8 21.7 8.8 2.6 5.7 26.6 25.0 9.6 2.7 5.9 24.3

CAMS 19.7 6.7 3.0 7.5 36.5 25.6 8.7 3.0 8.4 32.2

SB 22.2 9.1 2.5 5.7 26.3 30.0 13.0 2.4 4.3 15.3

Overall 19.2 7.0 2.9 6.5 33.8 23.5 8.5 2.9 6.6 28.1

C.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–5124 5117

area, Spain, which hosted the Games in 1992. Kim et al.

(1999) reported values of 10.0 and 7.6mgm�3 for OC

and EC in PM2.5 in Seoul, Korea, which hosted the

Games in 1988. Chow et al. (1994) reported an average

of 8.3 and 2.4 mgm�3 in PM2.5 for OC and EC,

respectively, in Los Angels, USA, which hosted the

Games in 1984.

Table 3 compares the summertime PM2.5, PM10, OC

and EC concentrations found in this study for Beijing

city to those reported in the literature. The PM2.5

concentrations found in this study are lower than that

(144.9792.6mgm�3) measured in a site in Beijing city

reported by He et al. (2004). They are however much

higher than that (76 mgm�3) reported by He et al. (2001)

for Chegongzhuang of Beijing city and that (25713 and

46728mgm�3) reported by Shi et al. (2003) for two

summer periods of urban Beijing. The PM2.5 and PM10

concentrations found in suburban SB (113.5 and

251.4mgm�3, respectively) were higher than those

reported by Shi et al. (2003) for a satellite town at

Nankou (44714 and 25711 mgm�3 for PM10 and

PM2.5, respectively) and a clean air site at Ming Tombs

Reservoir (49723 and 32730 mgm�3 for PM10 and

PM2.5, respectively) of Beijing. The OC and EC

concentrations in PM2.5 found in this study were the

highest among those measured in summertime by Dan

et al. (2004) for rural and urban Beijing and by He et al.

(2001) for urban Beijing. Dan et al. (2004) reported

minimum OC/EC ratios of 0.8–1.0 for PM2.5 at several

sites in Beijing compared to 1.8 found in this study. It

should be noted that concentrations of carbonaceous

species, especially OC measured from different analy-

tical techniques can vary substantially. The above

comparisons suggested that the PM levels in Beijing

have strong spatial and temporal variations in summer.

3.3. Vertical distributions of PM2.5, PM10, OC and EC

We noted from Table 1 that the average PM2.5 and

PM10 concentrations showed a general decreasing trend

ARTICLE IN PRESS

Table 3

Comparison of summertime PM2.5, PM10, OC and EC concentrations in the Beijing region with those around the world

PM10 PM2.5

Conc. (mgm�3) Conc. (mgm�3) OC (mgm�3) EC (mgm�3) OC/EC SOC

mgm�3 %

Beijing, Chinaa,b 68733 25–46

Beijing, Chinaa,c 10.773.6 5.772.9 2.2 37–59

Beijing, Chinaa,d 76 13.42 6.27 2.14

Beijing, Chinaa,e 144.9792.6 12.474.4 5.472.6 2.470.4

Seoul, Koreaa,f 9.97 7.57 1.3

Los Angles, USAa,g 8.3 2.4 3.5

Long Beach, USAg 3.4

Anaheim, USAg 3.9

Edison, USAh 3.4

Aveiro, UKi 2.4

Bringham, Uka,i 3.1 65

Coimbraa,i 2.58 50

Los Angles, USAa,j 40–80

Athens, Greecek 73.9721.5 39.4712.4

Barcelona, Spainl 20–60 15–35

Beijing, Chinam 169.0 93.6 19.2 7.0 2.9 6.8 36.3

aUrban areas.bShi et al., 2003.cDan et al. 2004.dHe et al., 2001.eHe et al., 2004.fKim et al., 1999.gChow et al., 1994.hChow et al., 1996.iCastro et al., 1999.jTurpin and Huntzicker, 1995.kChaloulakou et al., 2003.lQuerol et al., 2001.mThis study.

C.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–51245118

with increasing height up the meteorological tower.

Further study revealed that the daily average PM2.5 and

PM10 concentrations displayed complex vertical varia-

tions and a layered structure. Fig. 4 shows typical and

average profiles of PM2.5, PM10, EC and OC up the

meteorological tower. The profiles of PM10 can be

divided into two groups. In most profiles, PM10 showed

a more or less linear decreasing trend with height,

similar to that of the average profile (Fig. 4a). Such a

decreasing trend of PM10 concentration is similar to that

measured over a well-exposed street in an urban area of

Hong Kong (Chan and Kwok, 2000) suggesting PM10

was predominately emitted from ground level sources.

However, in another group of profile such as that on 12

(Fig. 4a), 13, 17, 19 and 21 August (not shown), PM10

showed a normal decreasing trend below 200m. How-

ever, it increased with height from 200m height to reach

170–190 mgm�3 range at 325m height.

PM2.5 showed more significant and complex vertical

variations. On average, PM2.5 at 100m height showed a

comparable concentration of 89.0mgm�3 compared to

that at 200m height of 87.3mgm�3 despite the decreas-

ing trend (Table 1) (Fig. 4b). The variation patterns of

daily profile can be classified into four groups. In the

first group represented by the profiles on 11 (Fig. 4b),

13, 15, 20, 23 and 24 August (not shown), PM2.5

decreased linearly with height similar to the average

profile of PM10. In a case on 11 August, PM2.5 decreased

substantially from 77mgm�3 at the 8m height to less

than 5 mgm�3 at 325m height. This group of profile is

similar to the overall average profile (Fig. 4b). The

second group is represented by the profiles on 10 (not

shown) and 22 August (Fig. 4b), in which the decreasing

trend was distorted as PM2.5 increased from 8 to 100m

height where it formed a local concentration peak. In

group three, a similar increasing trend also occurred

from 100 to 200m height on 12, 14 (Fig. 4b), 17 and 18

August (not shown). The PM2.5 concentration on these

days decreased noticeably from 8 to 100m height from

where it started to increase significantly to form a local

ARTICLE IN PRESS

0

90

180

270

360

80 120 160 200

0 30 60 90 200

Hei

ght,

m

8/22

8/12

average0

90

180

270

360

0 10 20 30 40

0 10 20 40

Hei

ght,

m

8/188/22average

0

90

180

270

360

1050 15

1050 15

Hei

ght,

m

8/188/22average

0

90

180

270

360

Hei

ght,

m

8/118/228/148/21average

0

90

180

270

360

Hei

ght,

m

8/108/22average 0

90

180

270

360

Hei

ght,

m8/108/22average

(a) (c) (e)

(b) (d) (f)

Fig. 4. Representative and average vertical profiles of PM2.5, PM10, OC and EC concentrations up the meteorological tower: (a) PM10

(mgm�3); (b) PM2.5 (mgm�3); (c) OC in PM10 (mgm

�3); (d) OC in PM2.5 (mgm�3); (e) EC in PM10 (mgm

�3); (f) EC in PM2.5 (mgm�3).

C.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–5124 5119

peak at 200m height before picking up another notice-

able decreasing trend upwards. In the final group, PM2.5

concentration on 19 (not shown) and 21 August

(Fig. 4b) showed a similar decreasing and increasing

trend at 8–100m and 100–200m heights, respectively.

However, the rates of decrease and increase were much

less noticeable and the latter increasing trend extended

to upper level at 325m height. The PM2.5/PM10 ratio did

not show an apparent vertical distribution pattern.

The vertical profiles of OC and EC also showed

complex variation patterns although the sample sizes

were relatively small (5–8 samples at each zone). The

average profiles of OC and EC in PM2.5 showed a linear

decreasing trend with height (Fig. 4d and f). The features

of these profiles were shared by those on 13, 18 and 22

August (Fig. 4d and f) for PM2.5, and 10, 18 (Fig. 4c and

e) and 20 August for PM10. The other profiles were

featured by the existence of sharp increases in OC and

EC concentrations with height from 8 to 100m,

100–200m and 200–325m heights. These sharp increases

resulted in layered structure in this group of OC and EC

profiles. For instance, there were substantial increases of

EC in PM10 from 7.4 mgm�3 at 8meter heights to

12.3mgm�3 at 100m heights on 22 August (Fig. 4e). In

another case on 10 August, both OC and EC in PM2.5

showed significant decreases from 8 to 100m height,

followed by significant increases from 100 to 200m

height and decreases from 200 to 325m height (Fig. 4d

and f). There were increasing trends in the OC/EC ratios

in both PM2.5 and PM10 (Table 2). This is probably due

to the fact that there was relatively higher percentage of

SOC in the OC at the higher zones of the meteorological

tower as results of the photochemical SOC formation

during the transport of primary pollutants from the

surface to the higher levels.

3.4. Effects of atmospheric layers on vertical distributions

of PM2.5, PM10, OC and EC

The elevated PM2.5, PM10 and carbonaceous species

in urban Beijing resulted from the stable atmospheric

conditions during the experimental period. Fig. 5 shows

ARTICLE IN PRESS

-15

-10

-5

0

5

10

15

208/

10

8/12

8/14

8/16

8/18

8/20

8/22

8/24

EL

R,o C

/km

240-320 m 140-240 m

47-140 m 8- 47 m

SALR

DALR

0

50

100

150

200

8/10

8/12

8/14

8/16

8/18

8/20

8/22

8/24

PM

2.5, µ

g/m

3

325m 200 m

100 m 8mCAMS SB

0

100

200

300

400

8/10

8/12

8/14

8/16

8/18

8/20

8/22

8/24

PM

10, µ

g/m

3

325m 200m

100m 8m

CAMS SB

(a) (b)

(c)

Fig. 5. Variations of (a) environmental lapse rates (ELR), (b) PM2.5 and (c) PM10 concentrations from 10 to 24 August 2003.

C.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–51245120

the temperature lapse rates or environmental lapse rate

(ELR) calculated by using the temperature difference

measured between 8 and 47m, 47 and 140m, 140 and

240m and 240 and 320m during the measurement

period. The ELR determined in this way can be viewed

as a representation of the stability of the atmospheric

layers between the paired altitudes. The atmospheric

layers, with an exception of that centred at around

100m height, were stable during the period. In

particular, the layer close to the surface, represented

by the one between 8 and 47m, with the exception of 3

days in the early part of the measurement period, was

always stabilized by strong temperature inversions. The

wind measurements at the 8m height of the meteor-

ological tower (not shown) revealed that the inversions

were usually accompanied by much more variable wind

when compared with that at higher altitudes. The daily

average wind speed was usually less than 3m s�1. For

other layers, the ELRs frequently fell below the

saturated adiabatic lapse rate (SALR) of 5.4 1Ckm�1,

which indicates a stable atmosphere or between the

SARL and the dry adiabatic lapse rate (DALR) of

9.8 1Ckm�1, indicating conditional instability. These

atmospheric conditions limited the dispersion of PM2.5

and PM10 and their precursors emitted from various

sources close to the surface, and enhanced the formation

of secondary aerosol and secondary organic carbon

(SOC) when other favourable conditions, such as

availability of strong sunlight, are prevalent. In fact,

we noted that the temporal variations of PM2.5 and

PM10 concentrations from 13 to 21 August (Fig. 5b and

c) followed closely that of the ELR. Hence, the high

PM2.5 and PM10 levels measured in this study, in

particular at the surface sites, were partly due to the

low wind speed and prevalent stable atmospheric

conditions.

The four ELRs, which varied significantly, suggested

that fine layers exist in the lower BL of Beijing. As

shown in Fig. 5a, there was a very stable layer below

50m altitude. Interestingly, right above this layer, there

was a layer extending roughly from 50 to 160m with

unstable atmospheric conditions because of enhanced

temperature decrease with increasing height. This

temperature drop might be due to the distortion of the

temperature profile caused by wind blowing above the

rooftop of the surrounding buildings. However, more

ARTICLE IN PRESSC.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–5124 5121

evidence is needed to verify this hypothesis. The ELRs

determined from the temperature measurements at 47

and 147m heights also revealed that the atmospheric

layer centred at 100m altitude was relatively more

natural or unstable than other layers. This layer was

capped above by two layers with higher stability. Thus,

we believe that the unstable condition of the layer

centred at 100m was the cause of lower PM concentra-

tion measured at this height. The existence of atmo-

spheric layers with varying degree of atmospheric

stability may be the reason for complex vertical

distributions of the PM, OC and EC at the four altitudes

of the meteorological tower. However, more evidence is

needed to substantiate this conjecture.

3.5. Sources of PM2.5 and PM10

We noted that the PM2.5 and PM10 concentrations

showed substantial variations during the measurement

period and the occurrence of elevated concentration

episodes were accompanied with a wind from the

southwest. Fig. 6 presents the wind roses measured at

the 325m level of the meteorological tower, which

represented the prevalent wind of urban Beijing. The

wind data at other zones also showed a similar

behaviour. The wind was mainly from the northwest

sector on 10 and 11 August (not shown) when the lowest

PM levels were measured. The wind was accompanied

by rainy weather that led to a scavenging of PM2.5 and

PM10. It gradually changed to low northerly on 12

August when the highest PM2.5 (163mgm�3) and PM10

(368mgm�3) levels were measured in suburban southeast

Beijing and there was a sharp change in PM2.5 and PM10

levels at urban sites. The wind shifted to blow from the

southwest direction from 13 (not shown) to 20 August,

when the highest PM levels were recorded at the urban

sites (Fig. 5b and c). An episodic high PM concentra-

tions with PM2.5 ranging from 133.7 to 178.7 mgm�3 and

PM10 from 220.2 to 350.4mgm�3 were recorded on 18

August at all the sites with this wind direction. In this

episode, the PM2.5 concentration at all the urban sites

was noticeably higher than that at the suburban site.

The wind changed to more southerly on 21 August and

fluctuated between southerly and northerly on 22 (not

shown) and 23 August when PM2.5 and PM10 dropped

to lower levels. There are large-scale industrial com-

plexes including the Capital Steel Plants in the southwest

region of Beijing city. Thus, the southwest wind brought

in large amount of pollutants emitted from the industrial

activities from this sources region. This together with the

highest PM and carbonaceous measured in our sub-

urban site, which is located at the southeast direction,

suggested that the suburban and rural areas in the south

are a predominant source region for urban Beijing.

The PM2.5 and PM10 concentrations, their temporal

variations and relative ratio at the suburban site during

the measurement period showed substantial variations

from those at the urban site (Fig. 5b and c. These

differences suggest that there exists a complex emission

pattern in the Greater Beijing region. In summer, the

contributions of coal and biofuel burning emissions

from commercial and domestic stoves and heating

facilities in urban Beijing are relatively low when

compared with the emissions from over 2 million

vehicles in the region. The majority of vehicles in China,

in particular motorcycles, are poor in quality, and the

combination of poor-quality fuel, inferior engines and

insufficient use of emission control technologies such as

catalytic converters, lead to elevated pollutant emissions

(Chan et al., 2002). Testing shows that emission levels of

Chinese autos are similar to those of cars used in the

USA in the early 1980s (He, 2003). Although there has

been a stricter fuel and vehicle control program in

Beijing these years, the increase in the number of

vehicles may have compensated the control efforts and

caused the high PM levels.

Also Beijing city is configured such that it is served by

several ring roads with heavy traffic (Fig. 1). This may

also have enhanced built-up of PM. In fact, the

occurrence of the maximum PM2.5 and PM10 concentra-

tions at the morning hours with maximum traffic (Fig. 3)

and high concentrations at the evening rush hours

(19:00–21:00) tended to reinforce our conclusion that

emissions from traffic are the predominant source of

PM2.5 and PM10 in urban Beijing. The continuous

increase in PM concentrations from 22:00 to midnight

were due to the accumulation of PM in the shallower BL

as radiative cooling continued as it progressed from the

evening to the midnight. Also, diesel trucks, which are

usually heavily loaded and emit large amounts of PM,

especially fine particles, are not allowed to enter the

urban areas (Fourth Ring Road) of Beijing from around

7:00 to 22:00. The contribution of PM emitted from

these high emitting trucks might have caused the

continuous increases in PM2.5 and PM10 in the late

evening and midnight.

We also believe that the emission from construction

activities is an important source of PM measured.

Large-scale infrastructure and construction activities

are common in urban Beijing and its vicinity in recent

years. The constructions of the Fourth Ring Road and

(FRR) as well as the Olympic Games facilities are such

examples. In fact, some parts of the CAMS premises

were undergoing renovation works and there were some

construction activities in the surroundings of CAMS

during the measurement period. Also, the FRR is not

far away from our suburban site and its construction

activities were at full strength during the measurement

period. Thus, fugitive dust generated from these

activities may be a vital source of high levels of PM2.5

and PM10 measured in this study. In fact, this may have

been reflected by the lower values of PM2.5/PM10 ratios

ARTICLE IN PRESS

Fig. 6. Wind-rose for the 325m level on the meteorological tower.

C.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–51245122

measured at the CAMS and suburban site as fugitive

emissions from construction activities are relatively

richer in larger size particles.

3.6. Correlations and sources of carbonaceous species

The relationship between OC and EC is very useful in

assessing the origin of carbonaceous particles. In our

samples, the OC–EC correlations (r2 ¼ 0:74 in PM2.5

and 0.82 in PM10) were strong. Such good OC–EC

correlation indicates that they are emitted from a

predominant single source (Park et al., 2001), probably

vehicle emissions as both OC and EC are emitted

significantly from internal combustion engines, espe-

cially diesel vehicles. A primary OC/EC ratio of 2.2

(Turpin and Huntzicker, 1991) or 2.0 (Chow et al., 1996)

was usually regarded as an indication of the existence of

secondary organic particles. We are not sure if these

ARTICLE IN PRESSC.Y. Chan et al. / Atmospheric Environment 39 (2005) 5113–5124 5123

ratios are applicable to the Beijing region as the emission

pattern there may be different from that in the

developed western countries. Nevertheless, the high

OC/EC ratio found in this study tends to suggest that

there were substantial formations of SOC in the Beijing

region during the experimental period. In fact, we noted

that the OC/EC ratios of all samples, with exception of

four samples, were larger than 2. The frequent sunny

days, high solar intensity and the stable atmospheric

conditions during the measurement period together with

large amount of SOC precursor hydrocarbons emitted

from various sources might have enhanced SOC

production. In fact, the elevated concentration of

volatile organic compounds and ozone, a secondary

pollutant, simultaneously measured in these sites (not

shown) also suggested that there were abundant SOC

precursors and enhanced formations of secondary

pollutants in the Beijing region during the measurement

period.

Table 2 also summarizes the SOC estimated using the

minimum OC/EC ratio method proposed by Turpin and

Huntzicker (1995) and Castro et al. (1999) in addition to

the measured OC and EC concentrations. In the

calculation, the minimum OC/EC ratio of 1.8 and 2.0

for PM2.5 and PM10, respectively, were adopted. These

values were observed on 10 and 22 August when rainy

and cloudy weather prevailed and limited photochemical

reactions occurred. The average concentrations of SOC

in all samples were 6.5 and 6.6mgm�3 in PM2.5 and

PM10, respectively, which accounted for 33.8% and

28.1% of OC, respectively. Formation of SOC involves

complex chemical reactions between its precursors

emitted predominantly from ground level and trans-

ported sources. It is thus reasonable to see an increasing

trend in the percentages of SOC up the meteorological

tower (Table 1). It should be pointed out that if lower

minimum OC/EC ratios, such as those reported in the

literature, are adopted for calculation, the SOC esti-

mated will be much larger. Also, the method proposed

by Turpin and Huntzicker (1995) uses OC and EC

concentrations measured at noontime when photoche-

mical production of SOC is most active. Our OC and EC

data covered the whole diurnal cycle including the

nighttime, when photochemical production of SOC is

minimal. Thus, the actual SOC produced should be

higher than those estimated. Hence, SOC, other than

emissions from vehicular exhaust and construction

activity is an important source of OC and thus PM in

Beijing.

4. Conclusions

The results of this study showed that PM2.5, PM10 and

carbonaceous species pollution were serious and wide-

spread in urban and suburban areas of Beijing. Such

high pollution levels were due to the accumulation of

pollutants as results of the prevalent stable atmosphere

during the measurement period and transport of

industrial emission from the region southwest of Beijing

city. There exist complex emission sources in Beijing.

Emissions from road traffic and construction activities

as well as SOC formed from locally emitted pollutants

are important sources of PM. PM and their OC and EC

components showed complex vertical distributions and

layered structures over urban Beijing. Our analysis

suggested that these layers are caused by fine atmo-

spheric layers with varying degree of atmospheric

stability and temperature inversions in the lower BL

over urban Beijing. Exposure to high levels of PM,

especially fine particulate, OC and EC has important

health implications. Although no clear evidence has

been found on the effects of ambient PM on the

exercising athletes and sport performance, the elevated

levels of PM, OC, EC and associated toxic chemicals in

the Beijing region can be a potential risk to the athletes

and the large number of Olympic Games audiences.

Thus, in order to provide a ‘‘green’’ environment for

hosting the 2008 Summer Olympic Games, much more

efforts have to be spent to control the emission sources.

As revealed in this study, there exist complex PM

patterns in the Beijing region and more research efforts

are needed to pinpoint more clearly the predominant

sources before cost-effective control strategies can be

devised.

Acknowledgements

This study is supported by The Hong Kong Poly-

technic University (A502 and A504), Research Grant

Council of Hong Kong (PolyU 529/03) and Chinese

Ministry of Science and Technology (G1999045700). We

thank the Institute of Atmospheric Physics for providing

the meteorological tower for measurement works.

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