Environ. Sci. Technol. 1999, 33, 4188-4193
Ambient Concentrations and Elemental Compositions of PM10 and PM2.5 in Four Chinese Cities F. WEI,† E. TENG,† G. WU,† W. HU,† W. E. WILSON,‡ R. S. CHAPMAN,‡ J . C . P A U , ‡,# A N D J . Z H A N G * ,§ China National Environmental Monitoring Center, Beijing, P.R. China, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, and Environmental and Occupational Health Sciences Institute, 170 Frelinghuysen Road, Piscataway, New Jersey 08854-1179
Three size fractions of particulate matter (PM), i.e., fine particles (PM2.5), coarse particles (PM2.5-10), and PM10, were measured at the school yards of eight elementary schools in four large Chinese cities during 1995 and 1996. These schools, one located in an urban district and one in a suburban district in each city, served as principal bases for an air pollution epidemiologic study. All PM samples were collected on Teflon filters using dichotomous samplers and analyzed gravimetrically for PM mass concentrations. A subset of the samples collected were analyzed for elements using a standard XRF technique. Annual means of PM10 concentrations, in which 52-75% were PM2.5, ranged from 68 to 273 µg/m3 across the eight sampling sites. Within each city, the urban site had higher annual means of all measured PM size fractions. Reported in the paper were also the concentrations of eight elements which were likely to be associated with urban pollution sources. The concentrations of these elements were found to be substantially higher in fine particles than in coarse particles, suggesting that urban pollution may have a larger impact on fine particles. This is further supported by the results from comparing elemental enrichment factors for fine particles with those for coarse particles. It is clearly demonstrated that the elements were enriched more in fine particles than in coarse particles.
Introduction Health effects of exposure to ambient particulate matter (PM) have been investigated extensively in epidemiologic studies mainly in North America and Europe (1-34). However, the public health effects of ambient PM exposure have not yet been fully characterized. The available database remains subject to important uncertainty in several key areas including (1) the community health effects of long-term ambient PM exposure; (2) the relative health importance of size fractions and chemical constituents of complex atmospheric particles; and (3) the ethnic, demographic, and other factors that influence susceptibility to adverse PM effects. Resolution of these and other uncertainties will require much further * Corresponding author phone: (732)445-0158; fax: (732)445-0116; e-mail:
[email protected]. † China National Environmental Monitoring Center. ‡ U.S. Environmental Protection Agency. § Environmental and Occupational Health Sciences Institute. # Formerly with U.S. EPA, currently a private consultant. 4188
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FIGURE 1. Map of China, showing the four study cities of Lanzhou, Wuhan, Chongqing, and Guangzhou. research and will be essential to achieving adequate understanding of the public health effects of ambient PM exposure. Such understanding will in turn be essential to ensure that air quality standards for PM are duly protective but not unduly stringent. From 1993 through 1996, a large epidemiologic study of children’s and adults’ respiratory health, in relation to longterm PM exposure, was conducted in the four large Chinese cities of Lanzhou, Chongqing, Wuhan, and Guangzhou (see Figure 1 for locations of these cities) (35). In each city, two elementary schools were selected to provide the subject pool: one school was in an urban district and the other was in a suburban district. The study included measurements of PM10 and PM2.5 in the yard of each participating school during 1995 and 1996. In this paper, we report concentrations of PM10, PM2.5, and coarse fraction of PM10 measured in the schoolyards. We also attempt to provide source information using the measured elemental compositions of fine and coarse fractions of PM10. Besides providing exposure bases for our epidemiologic analysis, the results presented in this paper would contribute to limited knowledge of PM10 and PM2.5 levels and their elemental compositions in urban and suburban atmospheres in China (36, 37).
Sampling Sites and Measurement Methods As shown in Figure 1, four geographically distinct cities were selected for the study. These cities were expected, based on data collected in the pilot phase of this study (35, 38), to exhibit a wide range of ambient levels of air pollutants such as PM, oxides of nitrogen (NOx), and sulfur dioxide (SO2). Lanzhou lies in northwestern China, with a population of about 1.5 million. The city is located in an east-west basin approximately 35 km long with a maximum north-south width of approximately 8 km. This topography results in a long-term inversion for about 310 days each year (39). Major air pollution sources include coal burning for industrial and domestic heating purposes and oil refinery industry. Wuhan is located in the middle of the Yangzi River Delta. It has a population of about 8 million, about half of which resides 10.1021/es9904944 CCC: $18.00
1999 American Chemical Society Published on Web 10/14/1999
TABLE 1. Sampling Sites in the Four Cities city
urban site
suburban site
Guangzhou Wuhan Lanzhou Chongqing
Ren-min-zhong-lu Huang-pi-jie Yu-zhong-jie Guany-ing-qiao
Hua-shi-fu-xiao Mo-shan Li-wu-tan Hong-yan
in central area of the city. Coal is commonly used for domestic cooking and heating and industrial processes. Chongqing, with a population of over 10 million, is a major industrial base in southwest China. The climate of Chongqing is mild with rich precipitation (average annual rainfall is 1100 mm). The frequency of windless days and inversion days is high, resulting in poor dispersion of air pollutants generated from combustion of coals with high sulfur content and high ash content and from motor vehicle emissions (40). Guangzhou is located in the southern coastline of China and has a population of about 7 million. The winter in Guangzhou is short and mild (temperature is >0 °C). The rainfall in Guangzhou (1355-2253 mm/year) is even greater than in Chongching. The residential population density is the highest (>175 000/km2) within the urban core of Guangzhou, where gas fuels are used as main fuel for domestic cooking. Coal is widely used for industrial purposes and still used in a small fraction of households. The city also has a large number of motor vehicles (41). Within each city, the two elementary schools (one in an urban district and the other in a suburban district) selected for PM monitoring and for subject recruitment were at least 30 km apart. The two districts, differing substantially in population and traffic densities, were also expected to differ significantly in ambient levels of air pollutants. The expected gradient of pollutant levels could provide a unique opportunity to study inter- and intracity exposure-effects relationships (35, 38). All PM samples were taken in the yards of the eight elementary schools from the four cities. The school (or district) names are listed in Table 1. Dichotomous samplers (Sierra-Anderson Model 241) were deployed to the sampling sites to collect PM samples. All the samplers were provided by U.S. EPA with certification as reference sampling devices. The samplers were equipped with an inlet with a 10-µm cutpoint. The particles smaller than 10 µm in aerodynamic diameter (PM10) entering the sampler were divided into two size fractions using a virtual impactor with a 2.5-µm cutpoint. These two fractions were usually referred to as fine particles (PM2.5) and course particles (PM2.5-10, i.e., 2.5 µm < particle diameter < 10 µm). The samplers were operated at a total flow rate of 16.7 L/min with 90% of the total flow passing the PM2.5 inlet and 10% of the total flow passing the PM2.5-10 inlet. Both fine and coarse particles were collected on 37-mm Teflon membrane filters (2-µm pore size) supported by polyolefin rings. The flow rate of each dichotomous sampler, equipped with a mass flow controller, was calibrated periodically with bubble flow meters to ensure a constant flow rate. Flow rate variations throughout each 24-h sampling were within (5%. All samples were taken for a 24-h sampling duration. Each filter was placed in a clean Petri dish during transport and storage. Presampling and postsampling weighing of filters were made using an electronic microbalance with a sensitivity of 10-6 g. A polonium 210 radioactive source was used as a static charge control device when weighing the filters. Prior to weighing, all filters were placed for at least 24 h in a standard weighing room, where temperature and relative humidity were controlled to 20 ( 2.5 °C and 50 ( 5%, respectively, at China National Environmental Monitoring Center. For every batch of 10 filters (either new or exposed), the 10th filter was reweighed and was within (5 µg of original weight. For every
batch of 20 filters, a blank filter was weighed or reweighed. The difference between two times of weighing of a blank filter was within 20 µg. At each of the eight sampling sites, approximately 15 samples (at least 12 samples) were successfully collected in each quarter of 1995 and 1996. These 24-h samples were collected on random days in each quarter. In total, approximately 1800 fine and coarse PM samples were collected at the eight sites during these 2 years. Approximately 300 out of the 1800 samples were hand-carried to U.S. EPA’s XRF laboratory in Research Triangle Park, NC, for elemental analysis. These samples were analyzed using nondestructive X-ray fluorescence spectrometer (XRF) custom-made by Lawrence Berkeley Laboratory (42). The instrument precision varies with the element and concentration. At high concentrations (greater than 1 µg/cm2) a precision of 6% can be expected for elements analyzed by two fluorescers (S, Cl, K, Ca, Mn, and Sr). For all other elements at high concentrations a precision of 8.6% can be expected. Based upon the analysis of NIST SRMs the accuracy was within (10%.
Results and Discussion PM Concentrations. Annual means (both arithmetic and geometric means) and ranges of the three size fractions of PM measured at the eight sites are summarized in Table 2. The results indicate (1) that all measured PM size fractions were higher at the urban sampling site in each of the four cities; (2) that the urban-suburban differences were smaller in PM2.5 levels than in PM10 levels in three of the four cities (the two differences were about the same in Guangzhou); (3) that there was a gradient in PM levels across the four cities; and (4) that PM2.5/PM10 ratios, derived from annual arithmetic means, ranged from 52% to 75% (see Table 3). In addition, by examining seasonal variations in both years, we observed the levels of both fine and coarse PM in all eight sites were noticeably higher in the winter (due to emissions from space heating). In 1996, China promulgated a set of national air quality standards for PM10. The middle standards (class II), applicable to residential areas, are 100 µg/m3 for annual average and 150 µg/m3 for 24-h average. Among the eight sampling sites (school yards), only the Wuhan suburban site and the Chongqing suburban site had PM10 annual averages (AM) below 100 µg/m3 but still above the U.S. PM10 annual standard of 50 µg/m3. Fine particles (e.g., PM2.5) has not been regulated in China. In 1997, the U.S., for the first time, has promulgated National Ambient Air Quality Standards for PM2.5 in addition to the PM10 standards (43). The new PM2.5 standards are an annual average of 15 µg/m3 and a 24-h average of 65 µg/m3. This annual PM2.5 standard (15 µg/m3) was exceeded by 3-10 times at the eight sampling sites in 1995 and 1996. The daily PM2.5 standard (65 µg/m3) was also exceeded frequently at the eight sites (see Table 4). Elements in Fine and Coarse Particles. The following 17 elements were determined quantitatively using the XRF technique: calcium (Ca), aluminum (Al), arsenic (As), bromine (Br), chlorine (Cl), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), phosphorus (P), potassium (K), selenium (Se), silicon (Si), sulfur (S), titanium (Ti), and zinc (Zn). A hierarchical clustering technique was used to group these 17 elements (44). The results from the cluster analysis of fine PM elements and coarse PM elements are shown in Figures 2 and 3, respectively. The dendrogram for fine particles indicates a large difference between two groups of elements: Ti, Ca, Fe, Si, and Al in a group and the rest of the elements in the other group. The dendrogram for coarse particles shows a similar clustering pattern: Ti, Ca, Fe, Si, Al, P, K, and Mn in a group and the rest of the elements in the other group. The group of elements gathered in the right VOL. 33, NO. 23, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Ambient Concentrations (µg/m3) of Fine PM, Coarse PM, and PM10 Meaured at the Eight Sites in 1995 and 1996 urban site
difference (%)
suburban site
city
year
PM
N
range
GM
AM
SD
N
range
GM
AM
SD
GM
AM
Guangzhou
1995
fine coarse PM10 fine coarse PM10 fine coarse PM10 fine coarse PM10 fine coarse PM10 fine coarse PM10 fine coarse PM10 fine coarse PM10
49 49 48 70 70 70 46 46 46 48 48 48 51 51 51 62 62 62 57 57 57 61 61 61
25-506 1-255 80-558 17-402 9-227 67-560 6-199 1-130 18-329 12-215 8-164 30-351 2-899 6-493 50-1224 11-268 12-284 51-473 17-262 4-153 39-383 13-243 13-96 26-304
132 74 234 117 61 193 53 54 118 59 35 101 102 112 230 81 71 160 96 62 166 67 34 105
160 99 257 140 74 215 70 63 133 75 49 124 141 132 273 94 87 181 113 70 183 76 38 115
97 64 107 85 43 101 47 31 65 56 40 84 135 85 189 49 55 92 63 33 78 36 20 48
51 51 51 74 74 74 46 46 46 50 50 50 52 52 52 60 60 60 55 55 55 57 57 57
23-186 1-260 47-301 16-179 1-176 34-314 9-105 1-100 29-203 7-132 7-55 27-174 20-395 6-192 41-540 19-345 8-217 43-547 2-223 4-81 15-304 17-154 5-128 38-206
68 41 122 54 26 86 51 28 86 39 19 61 94 57 162 67 51 124 79 26 109 60 23 90
79 59 137 62 38 100 57 38 95 46 21 68 118 74 192 80 61 140 97 31 128 68 29 97
44 47 60 27 22 38 24 25 39 29 11 34 88 45 112 53 38 82 54 18 69 31 23 40
48 45 48 54 57 55 4 48 27 34 46 40 8 49 30 17 28 23 18 58 34 10 32 14
51 40 47 56 49 53 19 40 29 39 57 45 16 44 30 15 30 23 14 56 30 11 24 16
1996 Wuhan
1995 1996
Lanzhou
1995 1996
Chongqing
1995 1996
t
t t t t t
t
t t t t
Difference ) (urban - suburban)/urban, indicating the difference in PM annual means between the urban and suburban sites in each city. t denotes not significantly different at alpha ) 0.05 by t-test, otherwise significantly different. Note: fine ) PM2.5, coarse ) PM2.5-10. N ) number of samples collected. AM ) arithmetic mean, GM ) geometric mean. SD ) standard deviation. PM 10 is log-normally distributed, and fine and coarse PM are near-log-normally distributed. a
TABLE 3. Average PM2.5/PM10 Ratios (%) Measured at the Eight Sites in 1995 and 1996a urban site
suburban site
city
year
N
PM2.5/PM10
N
PM2.5/PM10
Guangzhou
1995 1996 1995 1996 1995 1996 1995 1996
57 61 46 48 51 62 49 70
64.7 66.1 52.6 60.5 51.6 51.9 61.8 65.1
55 57 46 50 52 60 51 74
75.1 70.1 60.6 67.6 61.4 57.1 58.5 65.5
Wuhan Lanzhou Chongqing a
N ) number of samples collected.
TABLE 4. Percentage of days Exceeding the U.S. 24-h PM2.5 Standard city
year
urban site
suburban site
Guangzhou
1995 1996 1995 1996 1995 1996 1995 1996
84 87 46 44 80 66 77 64
59 39 39 14 73 55 67 51
Wuhan Lanzhou Chongqing
corner of the dendrograms are typical earth elements. The sources of these elements were most likely soil and dust. The group of elements gathered in the left corner of the dendrograms (e.g., S, Pb, As, Cl, Zn, Cr, Se) might be closely related to urban anthropogenic sources such as fossil fuel combustion and waste incineration (45, 46). The difference in clustering pattern between fine particles and course particles suggests that P, K, and Mn in coarse particles may 4190
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FIGURE 2. Complete linkage dendrogram for 17 elements in fine particles (PM2.5). mainly come from soil/dust sources; however, these elements in fine particles may result from urban pollution sources. Concentrations of the eight elements that were likely to be associated with anthropogenic pollution are reported in Tables 5 and 6 for fine PM and coarse PM, respectively. The results lead to the following findings: (1) The concentrations of these elements in coarse PM were higher in the urban site than in suburban site within each city. (2) The concentrations of most of these elements in fine PM were higher in the urban site than in the suburban site within each city (the exceptions were Zn in Chongqing and Cl in Lanzhou). (3) The concentration of each element in fine PM was substantially higher than that in coarse PM at each sampling site. The last finding described above suggests that pollutiongenerated elements may be gathered more in fine PM than in coarse PM. This can be further evaluated by examining enrichment factors of the elements in fine PM and coarse PM, as discussed in the following.
TABLE 5. Concentrations (ng/m3) of Elements Contained in Fine Particles at the Eight Sampling Sitesa city
siteb
N
Guanzhou
u
10
s
10
u
13
s
12
u
25
s
21
u
18
s
19
Wuhan
Lanzhou
Chongqing
a
AM GM AM GM AM GM AM GM AM GM AM GM AM GM AM GM
As
Cu
Pb
Se
Zn
Br
Cl
S
40.4 33.2 23.4 23.1 27.6 23.4 26.3 17.9 39.5 29.0 30.1 29.5 31.0 30.1 29.7 29.3
62.6 32.0 17.0 11.0 47.1 42.8 24.8 25.6 32.8 23.4 20.9 16.9 20.0 16.9 7.6 6.9
476 470 207 223 310 205 222 186 636 412 526 399 220 204 133 123
10.9 12.1 33.3 12.4 14.5 12.6 8.3 5.8 3.2 2.0 2.0 1.9 18.9 19.0 13.1 11.6
645 599 280 328 340 189 232 260 724 557 614 401 245 212 282 225
102 41.0 21.3 14.4 26.9 22.1 18.2 16.0 28.2 20.3 11.9 10.6 52.0 42.5 39.0 37.9
977 741 424 256 841 495 753 476 3540 2754 3952 3677 1826 1475 1328 1362
8033 7725 4499 3755 5886 4601 4744 3898 6207 4924 4495 3621 7822 7172 6212 6297
N ) number of samples; AM ) arithmetic mean; GM ) geometric mean. b Urban, u; suburban, s.
TABLE 6. Concentrations (ng/m3) of Elements Contained in Coarse Particles at the Eight Sampling Sitesa city
siteb
N
Guangzhou
u
10
s
10
u
13
s
12
u
25
s
21
u
18
s
19
Wuhan
Lanzhou
Chongqing
a
AM GM AM GM AM GM AM GM AM GM AM GM AM GM AM GM
As
Cu
Pb
Se
Zn
Br
Cl
S
8.0 6.6 3.0 2.7 4.1 3.4 3.3 3.0 10.7 5.9 7.2 4.5 5.7 3.7 3.7 2.6
36.2 21.5 3.5 2.3 23.9 25.2 9.2 3.0 18.9 17.1 10.6 12.2 8.4 8.0 5.2 4.6
104 69.3 21.1 12.8 30.0 23.8 19.1 15.6 155.1 51.3 66.1 19.8 69.9 52.5 26.6 19.2
2.2 1.8 1.6 1.0 1.4 1.4 1.1 1.1 1.5 1.4 1.6 1.5 3.4 1.5 1.5 1.0
248 164 44.1 42.8 76.7 56.7 25.7 15.7 142 95.1 56.7 32.1 94.1 77.1 49.2 35.8
17.5 8.2 1.4 1.2 2.2 1.6 1.6 1.5 2.6 2.3 2.1 2.0 8.3 4.3 3.8 2.2
874 666 192 157 513 427 159 106 393 378 249 233 728 774 289 164
2571 1881 373 238 710 670 438 329 1091 985 594 613 2067 1464 1138 961
N ) number of samples; AM ) arithmetic mean; GM ) geometric mean. b Urban, u; suburban, s.
FIGURE 3. Complete linkage dendrogram for 17 elements in coarse particles (PM2.5-10). The enrichment factor of element i, Ki, is defined as
Ki )
(Ci/Cn)aerosol (Ci/Cn)soil
where Ci is the concentration of element i of interest; Cn is the concentration of a reference element n; (Ci/Cn)aerosol represents the ratio derived from the concentrations of element i and element n in ambient aerosols; and (Ci/Cn)soil represents the ratio derived from the concentrations of
element i and element n in background soil. Reference elements selected for this purpose normally are those ones in the soil that are stable, spatially homogeneous, and least impacted by anthropogenic pollution. Here we selected Ti as the reference element n. The concentrations used for calculating (Ci/Cn)soil are the average background values of soil in China (in µg/g) [As ) 11.2, Cu ) 22.6, Pb ) 26.0, Se ) 0.29, Zn ) 74.2, Br ) 2.5, and Ti ) 3800 (47)] or the elemental abundance values in the earth crust (in µg/g) [S ) 260, Cl ) 130 (48)]. The elemental enrichment factors for fine and coarse PM are shown in Tables 7 and 8, respectively. Conventionally, a “cutoff” Ki value of 10 is used to distinguish between two types of atmospheric aerosols. If Ki < 10, element i is considered to have a significant dust/soil source and is termed nonenriched. If Ki > 10, element i is enriched and has a significant fraction which is contributed by nonmineral dust sources (49, 50). The results shown in Tables 7 and 8 indicate the following. (1) The enrichment factors (K) of As, Cu, Pb, Se, Zn, Br, Cl, and S were all .10 in fine PM measured in all sites and >10 in coarse PM measured in most sites (only K of Cu, As, and Br were
