A Comparative Study of Chemical Databases for Fine Particle Chinese

Environ. Sci. Technol. 2000, 34, 4687-4694

A Comparative Study of Chemical Databases for Fine Particle Chinese Aerosols ZHIQUN ZHANG† AND SHELDON K. FRIEDLANDER* Department of Chemical Engineering, University of California, Los Angeles, California 90095-1592

A chemical database for PM2.5 and PM2.0 aerosols has been assembled for various sampling sites in China. The primarily urban sites, sampled from 1980 to 1993, include Beijing, Tianjin, Wuhan, Lanzhou, and Guangzhou. From 13 to 22 inorganic chemical elements were measured but few secondary and organic compounds. Previous source resolution studies are briefly summarized. A mass balance for the Beijing aerosol indicates that the three largest components are carbon-containing matter (∼50%), (NH4)2SO4 (∼18%), and silicon compounds (∼12% expressed as silica). Silicon concentrations in Beijing and Lanzhou were 26-36 times higher than Los Angeles. The fine silicon probably comes from coal combustion, crustal sources, and rice straw burning, but the relative amounts are not certain. Mass concentration data for Chinese cities were compared among themselves and with downtown Los Angeles using scatter diagrams. Compositions of the Beijing aerosol were generally higher than Los Angeles; the Beijing PM2.0 mass in 1992-1993 was about 5 times that of Los Angeles PM2.5 in 1986. In addition to significant changes over the years measurements were made, seasonal and regional variations were also observed. Mass fractions of crustal elements Ca, Al, Mn, Ti, and Fe in Beijing were higher than Los Angeles, while Cu, Pb, Zn, Cr, and Ni were lower. For Lanzhou (1983) and Tianjin (1984), most PM2.5 components show higher concentrations than central Beijing.

Introduction Epidemiological studies indicate an association between atmospheric particulate pollution and adverse health effects (1-3). Particulate matter with aerodynamic diameter less than 2.5 µm (PM2.5) is of most concern (4, 5). The United States Environmental Protection Agency (USEPA) has established a new PM2.5 National Ambient Air Quality Standard (6). However, a cause-and-effect relationship between specific chemical and/or physical agents in the atmospheric aerosol and health effects has not been established (7). Chinese economic, industrial, and demographic characteristics are sufficiently different from those of North America and Europe to warrant a comparative study of atmospheric aerosol compositions. The purpose of this paper is to compare Chinese fine aerosol (PM2.0 and PM2.5) databases among themselves and with Los Angeles. Such a study would have the following applications: * Corresponding author phone: (310)825-2206; fax: (310)206-4107; e-mail: [email protected]. † On leave from the Department of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China. 10.1021/es001147t CCC: $19.00 Published on Web 10/03/2000

 2000 American Chemical Society

1. Few data are available on health effects of fine particle air pollution in China. Assembling and comparing Chinese fine aerosol databases would help in planning health related studies such as those referenced above. 2. PM2.5 accounts for about 30-40% of the total suspended particulate (TSP) mass in Chinese urban aerosols (8, 9). Chinese aerosol compositions also vary significantly among sites and with the year of measurement and the season. Comparing Chinese fine aerosol databases can help in developing regional and global particulate air pollution control strategies. Of interest in this respect are recent studies suggesting aerosol effects on agricultural yields in China (10). 3. “Harmonizing” international standards for particulate matter requires the development of suitable databases and the identification of data gaps. Comparing aerosol databases for different nations will help in the development of worldwide air quality control strategies. Methodologies applicable to the comparative study of aerosol databases have been discussed by Wongphatarakul et al. (11). Three methods of comparison were applied to the PM2.5 aerosol databases at seven locations around the world, including five urban sites in Los Angeles, Philadelphia, Taipei, Ostrava, Teplice, and two nonurban sites in the Amazon Basin and Hortobagy National Park (Hungary). The three approaches include log-log scatter diagrams of chemical components, hierarchical cluster analysis, and correlation coefficients. In the first approach, the enhancement or depletion of individual chemical species at two different locations is shown by plotting mass concentrations for each chemical component at one sampling site against another and calculating the coefficient of divergence (CD) for the spread. In the second method, statistical procedures are used to identify and group sampling sites with similar aerosol chemical compositions. Finally, the spatial variation of aerosol chemical components in a given region is characterized by calculating the correlation coefficient among sampling sites. Of these methods, scatter diagrams provide the most easily visualized images for both quantitative and qualitative purposes. This method is used in this paper.

Chinese Aerosol Databases and Source Resolution Studies Studies of PM2.5 aerosol compositions in China have been made since the 1980s (12-22). Many of the measurements were made by research institutes of the Academia Sinica (Chinese Academy of Sciences) to perform source resolution for developing air pollution control strategies (8, 9, 17, 18, 21). Some of the work was carried out in cooperation with U.S. institutions, especially Florida State University (12, 1416, 22). The sampling sites were mostly located in large cities, including Beijing (the capital located in the northeast part of the country), Tianjin (the third largest city located 120 km southeast of Beijing), Wuhan (the largest city of Hubei Province in central China, near the Yangzi River), Lanzhou (a heavily industrialized city in the northwest), and Guangzhou (the largest city of Guangdong Province located in south China). However, the data sets were fragmentary and statistically very thin. We have used only a few of the aerosol databases for the following reasons. First, in several studies, results were presented as plots of concentrations, which were difficult to read accurately (12, 17, 19). Second, some researchers reported their measurements as mass fractions and/or mass concentration ratios without giving the total mass or referential concentrations (8, 20-22). In addition, VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 1. Chemical Characterization Studies of Fine Particulate Matter in China sampling site

measurement

sampling period

sampling device, analyzing method

ref

Beijing Dongdan Ave Dongsiliutiao

PM2.0 62 measurements 14 species, µg/m3 total mass

Forbidden City Zhangshan Park Wangfujing Ave Jingshan Park Qianmen Ave

PM2.0 22 measurements 18 species, µg/m3

Yianshan Beixinan CRAESa

PM2.0 62 measurements 14 species, µg/m3 total mass

Xinglong

PM2.0 4 measurements 17 species, µg/m3 PM2.0 1 measurement 21 species, µg/m3 PM2.0 2 measurements 18 species, µg/m3 PM2.0 2 measurements 18 species, µg/m3 PM2.0 4 measurements 22 species, µg/m3 b

Badaling Great Wall Shisanling Reservoir Wukesong Meteorological Tower

a

Downtown Area 6 Oct-6 Nov 1992 and 14 Dec 1992 -13 Jan 1993, 24-h samples, consecutive days Central Area 29-30 July and 23, 25 Dec 1980, 4-h samples

Hi-vol sampler with 2.0 µm size cut, ICP

9

seven-stage impactor, PIXE

16, 22

Suburban Area 6 Oct-6 Nov 1992 and 14 Dec 199213 Jan 1993, 24-h samples, consecutive days 11-13 Mar 1980, 12-h samples, consecutive days 1 Apr 1980, 4-h sample

eight-stage impactor, PIXE.

14

eight-stage impactor, PIXE.

15

29 Dec 1980, 4-h samples


16

26 Dec 1980, 4-h samples


16

18-23 July 1980, 6 and 10-h samples, random days,


12, 19

Hi-vol sampler with 2.0 µm size cut, ICP.

9

Downtown area (Hepin District)


Tianjin 12-18 Dec 1984 24-h sampling, consecutive days

Streaker sampler, PIXE

20

Downtown area

PM2.5 24 measurements 17 species, µg/m3b

Wuhan 19-30 Dec 1988 12-h samples, consecutive days

dichotomous sampler, XRF

20

Ceshisuo Haizhu Square Zhongshan Uni Xiguan Botanical Garden

PM2.3 4 measurements 20 species µg/m3 b

eight-stage impactor, PIXE

17

Xigu district


dichotomous sampler, XRF

18

Guangzhou 29-30 Mar, 16-17 Aug, 11 and 13 Oct, and 26 Dec 1984, 4-5-h samples, random days Lanzhou 7-20 Dec 1983 12-h samples, consecutive days

CRAES ) Chinese Research Academy of Environmental Science.

some measurements were made over a few days, and no long-time data series were available (14-17, 19). Since differences in chemical component concentrations at different sites are caused not only by true chemical variations but also by sampling and measurement artifacts, data based on only a few measurements were generally not used. Table 1 summarizes the PM2.0 and PM2.5 databases; most of the measurements were made in the Beijing region during the early 1980s and in 1992-1993. The aerosols were sampled primarily using seven or eight stage cascade impactors. Chemical components were analyzed by a variety of methods of multielement analysis, including X-ray fluorescence (XRF), particle induced X-ray emissions (PIXE), instrument neutron 4688

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b

Concentrations shown only in figures.

activation analysis (INAA), inductively coupled plasma emission spectroscopy (ICP), and ion chromatography (IC). Of the 13-22 chemical species analyzed in the fine fraction, most were inorganic elements (9, 14-20); few data were available for secondary or carbon containing components. Beijing, located at a latitude similar to New York City, is about 50 m above sea level. It has approximately 13 million people; the population density exceeds 5500 people per square kilometer compared with about 2900 for Los Angeles. The city is about 400 km from the Gobi Desert to the northwest and surrounded by mountains on the western, northern, and eastern sides with an opening to the southeast about 120 km from the Yellow Sea. Beijing’s climate is somewhat

humid with significant seasonal winds. From November to April, the prevailing airflow from the northwest is dry and dusty. At other times, the local wind is mild but usually rotates over the city, leading to the trapping of pollutant emissions that disperse with difficulty. Beijing is a major industrial center with mechanical, chemical, metallurgical, textile, and electronic industries the most important. Its urban areas account for only 7% of the city, but hold about 50% of the population, 60% of the industrial production, 80% of the structures, and 80% of the energy consumption. These features produce a high level of particulate pollution; atmospheric visibility in the region has decreased from about 18 km in the 1950s to less than 10 km in the 1990s. Based on the data shown in the references listed in Table 1, source resolution studies have been made for Beijing (9), Lanzhou (18), and Wuhan (20). Two types of receptor models were employed: the chemical mass balance (CMB) method (23), which has been widely used in China (8, 9, 20), and target transformation factor analysis (TTFA), which has been applied in Lanzhou (18) and Wuhan (20). In Beijing, major sources of fine particles are motor vehicles, coal combustion, and crustal material (9). However, their contributions vary with sites and seasons significantly. For example, in Dongsiliutiao (a residential site with heavy traffic in downtown areas), motor vehicle emissions account for about 56% of the PM2.0 in autumn but only 32.4% in winter. On the other hand, coal burning contributes about 25% to fine particle mass in autumn but rises to 50.2% in winter due to the heavy use of coal for residential heating. For Beixinan, a metallurgical industry area, coal burning and crustal sources are generally higher than at other Beijing locations; motor vehicles account for 25 to 32%, coal burning 37 to 43%, and crustal 28 to 32%. Emission sources for Wuhan and Lanzhou differ from those for Beijing. Motor vehicles contributions are reduced to 0.7% and 10.6%, respectively, while coal burning is highest with 5 contributions up to 36.4% and 33.8%, respectively (18, 20). Other major sources for Wuhan include biomass burning (which ranks second with 36.2%), followed by secondary sources with 24.7% (20). For Lanzhou, the metallurgical industry and construction materials (cement, glass, etc.) are the second and third largest sources with average contributions of 22.4% and 15.4%, respectively (18). The time periods covered in the source resolution studies were short, about three months for Beijing 1992-1993 and a few weeks for Lanzhou in 1983 and Wuhan in 1988. For the three cities, coal combustion is usually the largest single source of fine particle mass. This is probably the case for most Chinese cities. Crustal contributions are more important in northern China because of transport from northwest desert areas. Particle size and composition data are needed for sites dominated by desert aerosols.

FIGURE 1. Beijing PM2.0 chemical compositions (July 1980) are higher than those for PM2.5 in downtown Los Angeles (1986) except for Cu. *SoCAB database for downtown Los Angeles, January 2-December 28, 1986, 24 h sampling, every sixth day, dp < 2.5 µm (37). **Average of 5 sites in central Beijing around Tiananmen Square, July 29-30, 1980, 4 h sampling, consecutive days, do < 2.0 µm (16).

FIGURE 2. Chemical composition differences between Beijing PM2.0 (1992-1993) and Los Angeles PM2.5 (1986) tended to increase compared with Figure 1. *SoCAB database for downtown Los Angeles, January 2-December 28, 1986, 24 h sampling, every sixth day, dp < 2.5 µm (37). **Average of 2 sites in downtown Beijing, December 14, 1992-January 13, 1993, 24 h sampling, consecutive days, dp < 2.0 µm (9).

Mass Balance for the Beijing Fine Aerosol Of the seven studies of the Beijing aerosol listed in Table 1, only one (9) includes data for the total fine particle mass, in addition to various chemical components. These data can be used to prepare a mass balance for the separate components, which should sum to the total measured mass concentration. Among the Beijing data that include fine particle mass are the 1992-1993 measurements (9) shown in Figure 5. These data include measurements of fine aerosol mass and a variety of inorganic elements. However, data for silicon, magnesium, sodium, and carbon were not reported. In the absence of such data, we have used the results of Winchester et al. (16) for Si and Wang et al. (21) for Mg and Na. In the absence of data for carbon in the fine aerosol, we have used the data reported by Dod et al. (13) for total C in PM12 determined by oxidizing the collected aerosol and measuring CO2.

Table 2 shows a mass balance for the Beijing aerosol for a period during the winter based on limited data sets gathered by four different research groups over the period 1980 to 1994; the sulfate concentration was calculated from the sulfur data for 1992-1993 (9). There are major uncertainties in the carbon containing components; data on the nitrate, ammonium, and water portions are not available. It is likely that a significant fraction of the carbon components measured in the PM12 is present in the fine particles. For example, measurements in Philadelphia and Camden for the eastern United States show that almost all of the PM10 elemental and organic carbon are present in the PM2.5 fraction (24). In the absence of other information, it is assumed in Table 2 that all the PM12 carbon is present in the fine particles. This assumption, which overestimates the fine particle carbon, is balanced (to an unknown extent) by the mass of hydrogen, VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. PM2.0 chemical compositions measured by different groups in Beijing show an increase between 1992 and 93 and 1980, except for chromium. *Average of 5 sites in central Beijing around Tiananmen Square, December 23 and 25, 1980, 4 h sampling, random days, dp < 2.0 µm (16). **Average of 2 sites in downtown Beijing, December 14, 1992-January 13, 1993, 24 h sampling, consecutive days, dp < 2.0 µm (9).

FIGURE 5. PM2.0 chemical compositions in downtown Beijing show a fairly good agreement between the autumn and winter measurements in 1992-1993. *Average of 2 sites in 24 downtown Beijing, October 6-November 6, 1992, 24 h sampling in consecutive days, dp < 2.0 µm (9). **Average of 2 sites in downtown Beijing near Tiananmen Square, December 14, 1992-January 13, 1993 in consecutive days, dp < 2.0 µm (9).

TABLE 2. Mass Balance of the Beijing Aerosol (Various Time Periods 1980-1994) chemical componenta

av concn,b µg/m3

year and PMx measured or estimated

A. Primary (Inorganics Reported as Equivalent Oxides) 1. A12O3 6.7c 1992-1993, PM2.0 2. Fe2O3 3.3c 1992-1993, PM2.0 3. CaO 5.2c 1992-1993, PM2.0 4. K2O 2.4c 1992-1993, PM2.0 5. SiO2 20.7d 1980, PM2.0 6. MgO 2.9e 1993-1994, PM1.1 7. Na2O 2.6e 1993-1994, PM1.1 1. (NH4)2SO4 2. NH4NO3

B. Secondary 31.9c 1992-1993, PM2.0 unknown

ref

9 9 9 9 16 21 21 9

C. Water unknown

FIGURE 4. Beijing PM2.0 chemical compositions show a significant seasonal dependence in 1980. *Average of 5 sites in central Beijing around Tiananmen Square, July 29-30, 1980, 4 h sampling, consecutive days, dp < 2.0 µm (16). **Average of 5 sites in central Beijing around Tiananmen Square, December 23 and 25, 1980, 4 h sampling, random days, dp < 2.0 µm (16). oxygen, and other elements associated with carbon that are lost when the aerosol is oxidized to carbon dioxide. Recognizing these many uncertainties, Table 2 shows that a mass balance on the Beijing aerosol can be closed at least approximately; the three largest components are carboncontaining particulate matter (∼50%), (NH4)2SO4 (∼18%), and SiO2 (∼12%). The single most important assumption is that the very high carbon-containing component measured by Dod et al. (13) in PM12 is for the most part associated with fine particles, PM2.0. The carbon component measured in 1983 and reported in this reference probably originates primarily from coal burning. In Beijing, there were over 1.5 million small-sized household stoves in the 1980s used for residential cooking and heating during winter associated with low temperature coal burning (25). Studies by Ge et al. (26) showed that emissions from low temperature coal burning were dominated by carbon components (>90%); contributions of particulate emissions from small scale heating sources 4690

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total C in PM12 1. elemental C 2. organic C total accounted for measured total

D. Carbon Containing 98/115.4 f,g 1983, PM12 49/57.7 ≈40-50%TC, PM12 49/57.7 ) TC-EC, PM12 174/191 181c 1992-1993, PM2.0

13 13 9

a

Trace elements with mass concentrations less than 1 µg/m3 not included. b Assumed in oxidized forms as shown. c Two-site time average measured by Zhang et al. for Dec 1992-Jan 1993 (9). d Fivesite time average measured by Winchester et al. for Dec 1980 (16). e Based on time average mass fractions measured by Wang et al. for Dec 1993-Feb 1994 (21). f Two time averages measured by Dod et al. for the two periods in Dec 1-15 and Dec 16-31, 1983 (13). g Assuming all of the carbon in PM12 is present in PM2.0 (see discussion in text).

are disproportionately larger than from power plants, even though power plants burned much larger quantities of coal. Since carbon containing components strongly absorb and scatter light, the high concentrations of the atmospheric carbon may significantly reduce visibility. It has also been suggested that aerosol light extinction reduces rice and winter wheat yields (10). Most of the aerosol sulfate probably results from the oxidation of SO2, released from coal combustion (9, 13). The magnitude of the silicon component (∼12% expressed as SiO2) is a surprising feature of the Table 2 mass balance. The origin of the SiO2 is discussed in the next section.

Origins of High Fine Silicon Concentrations High concentrations of fine particle silicon were observed for Beijing in 1980 (16) and for Lanzhou in 1983 (18) by different research groups using different sampling methods. The PM2.5 silicon concentration in Los Angeles was only about 0.27 µg/m3, whereas for the two Chinese urban sites, the fine silicon mass had values of 7.01 and 9.68 µg/m3. Of the fine silicon mass, more than 80% was associated with particles smaller than 0.25 microns. The origin of the submicron silicon in Chinese urban aerosols has been explained by referring to the mechanisms of coal combustion (19, 27). Briefly, Si(IV) in coal ash, e.g. SiO2, is reduced by carbon during combustion to Si(II), forming volatile SiO, at high temperatures. After release to the atmosphere, the vaporized SiO is oxidized to silica and rapidly condenses to form particulate matter or collects on the surface of existing particles. Little aluminum vaporizes during combustion and appears in the submicron fractions. Silicon vaporization and subsequent condensation during coal combustion have been well documented (28-30). The vaporization of silicon during combustion depends on the nature and type of the coal burned (29). As an example, the mass fraction of submicron silica in combustion fume at 1750 K is less than 4% for lignite but more than 40% for bituminous coal (30). In Teplice, a heavy coal burning industrial city in the Czech Republic, measurements during 1992-1994 showed that the mass concentrations of PM2.5 silicon in the local atmospheric aerosols were not high, amounting to only 0.2-0.3 µg/m3 in summer and 0.4-0.9 µg/m3 in winter (31). On the other hand, the vaporization rates of Si and the composition of coal burning emissions vary with combustion temperature by over 4 orders of magnitude in the range 16003000 K (30). Ge et al. (26) found that the composition of emissions differ greatly for coal burning at high and low temperatures. Laboratory measurements of emissions from the burning of Chinese coal showed that the mass ratio of Si/Al in the smoke plume was only 2.57 (20, 26), whereas the observed Si/Al ratio in Beijing fine mode aerosols ranged from 6.92 to 10.46 (16). These observations and the Si/Al difference suggest that, in addition to coal combustion, there may be other important sources of fine silicon in the Beijing and Lanzhou aerosols. First, crustal sources may contribute to aerosol silicon. Gordon (32) found that about 60% and 80% of the fine Si concentrations in Philadelphia and Watertown (Massachusetts) result from soil dust. Pitchford et al. (33) used optical and scanning electron microscopy to examine the morphology of silicon-enriched submicron aerosols sampled at Zion National Park in the southwest U.S.A.; the results showed clearly that silicon in submicron particles in the atmosphere was not a product of combustion but crustal in origin. Beijing and Lanzhou are both located in the northern China where soil and dust storms are common during winter and spring. According to an inventory by Xuan (34), some 43 million tons/year of dust for the area are emitted from crustal sources in Northern China with emission rates increasing from east to west by 5 orders of magnitude. The heavy dust emission suggests that crustal material is probably a more important source of fine silicon, compared to approximately 8000 tons/ year of particulate emissions from residential coal burning in Beijing (26). However, it is very difficult to compare the regional estimate for crustal sources with the local value for coal burning. Biomass burning may be another source of atmospheric fine silicon. Of the variety of biomass materials that have been studied, rice straw has the highest silicon content, amounting to 10-15% of dry matter (35). The other major components are oxygen (∼40%) and carbon (∼35%). How-

ever, the chemistry of biomass burning is not well understood. It is not known whether rice straw burning releases SiO to the atmosphere, as in the case of coal combustion discussed above. In one study, the average mass fraction of silicon in the fine particles emitted from rice straw burning was only about 0.5% (36). Our approximate calculations indicate that biomass burning is probably not a major source. We conclude that the relative importance of the various sources of silicon containing particulate matter is still not known. More measurements of atmospheric silicon are needed to confirm the observations made almost 20 years ago by different groups in different cities using different methods. Also needed are studies on aerosol formation during rice straw burning under conditions similar to those in China. Summarizing our mass balance results, there are major uncertainties for the Beijing aerosol in the amount of each of the three largest components measured in different time periods, 1983 for the carbon, 1992-1993 for the sulfate, and 1980 for the silica. New measurements of these components are essential to test the Beijing data. In the sections that follow, the Chinese chemical databases are compared with Los Angeles and with each other.

Comparison Studies: Concentration Scatter Diagrams Concentration diagrams are log-log scatter plots of the concentration or mass fraction of the chemical components at one sampling site against those at another. The doublelogarithmic scale is used because of the large spread in concentrations for the individual chemical components. A diagonal line divides the diagram into two different regions, the one above the line showing enhancement and the one below depletion of the individual chemical components with respect to the reference site shown on the abscissa. The diagonal line with unit slope represents a hypothetical case in which the mass concentrations for each component at the two sampling sites are equal. The coefficient of divergence (CD), a self-normalizing parameter, can be used to measure the spread of the data points for the two databases

CDjk )

x ( ) 1

p

xij - xik

∑x p i)1

ij

2

(1)

+ xik

where j and k stand for two sampling sites, p is the number of investigated components, and xij and xik represent the average mass concentrations of a chemical component i at sites j and k (11). If the CD approaches zero, the two sampling sites are similar. If the CD approaches one, the two sampling sites are very different. An aerosol database for downtown Los Angeles, a part of the Southern California Air Basin (SoCAB), was used as a reference for comparing the Chinese data sets. The Los Angeles database covered the period January 2 to December 28, 1986 with 24 h sample collections every sixth day on Teflon filters using an AIHL-design cyclone separator operating at 24.8 L/min (37). Taking account of the statistical weakness of the assembled Chinese databases, only a limited set of special issues is addressed below based on the largest measurement sets (9, 16, 18, 20). Figures 1 and 2 compare the concentrations of Beijing PM2.0 components in 1980 and 1992-1993 with downtown Los Angeles PM2.5 in 1986. As expected, the scatter plots showed a large difference in chemical compositions with CDs of 0.587 and 0.697, respectively. Concentrations of trace elements in central Beijing during the summer of 1980 were generally higher than downtown Los Angeles in 1986, except for copper (Figure 1). In particular, the mass concentration of fine silicon was 26-36 times that of downtown LA. Figure 2 shows that for the winter of 1992VOL. 34, NO. 22, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 6. The similarity of PM2.0 compositions between Dongdan and Dongsiliutiao (1992-1993) suggests the close resemblance of atmospheric fine aerosol sources in downtown Beijing. *Commercial area in downtown Beijing, December 1992-January 1993, 24 h sampling, consecutive days, dp < 2.0 µm (9). **Residential area in downtown Beijing, December 1992-January 1993, 24 h sampling, consecutive days, dp < 2.0 µm (9).

FIGURE 7. PM2.0 chemical compositions in Beixinan and downtown Beijing (1992-1993) show the regional effect of industrial particulate emissions from the Capital Iron & Steel Works. *Average of 2 sites in downtown Beijing, December 1992-January 1993, 24 h sampling, consecutive days, dp < 2.0 µm (9). ** Industrial area near the Capital Iron & Steel Works in northwestern Beijing, December 14, 1992January 13, 1993, 24 h sampling, consecutive days, dp < 2.0 µm (9).

1993, Beijing concentrations relative to Los Angeles were significantly greater; the total mass of the Beijing aerosol was about 5 times that of downtown LA. Data for Si were not reported in the 1992-1993 Beijing study (9). Figure 3 compares the 1980 winter data (10 samples) with the 1992-1993 winter data (31 samples) for Beijing aerosols. The concentrations of all components except for chromium were substantially higher in 1992-1993, probably due to the rapid growth of industrial and automobile emissions. However, the winter 1980 data were based on only 2 days of sampling (16), and the 1992-1993 measurements were made by other researchers using different methods (9). In addition, the two sampling sites were not identical; this probably contributed to the differences in results. The effect of the season on the Beijing aerosol is shown in Figures 4 and 5, which compare the 1980 and 1992-1993 data at the same sampling sites for different times of year. For central Beijing in 1980, the components Pb, Zn, Br, Fe, Cu, and S were higher in summer aerosols, while Si, Ca, Al, Ti, Cr, and Mn were higher in winter (Figure 4). However, measurements in 1992-1993 indicated that the concentrations of all chemical species in winter aerosols were generally higher than in autumn (Figure 5). Reasons for the seasonal variability of Beijing aerosol compositions are not clear; they may be related to the heavy coal burning during wintertime (9), the changes in meteorological conditions between seasons, and the different measurement methods. Local variations of the Beijing aerosol are illustrated in Figure 6, which compares 1992-1993 Dongsiliutiao and Dongdan aerosols, both in downtown areas, showing a strong similarity with the CD of 0.148. The 1980 data of Winchester et al. (16) also show a strong similarity between central Beijing and Shisanling Reservoir, a suburban area about 40 km apart in the north direction. The results suggest that the regions extending from central Beijing to northern suburban areas are well mixed. However, Beixinan and downtown Beijing differ significantly (Figure 7). Emissions from metallurgical processes and coal burning sources enrich the Beixinan aerosol in elements such as Fe, Mn, Cr, Ti, and Al; in downtown areas, the heavy traffic produces higher concentrations of Pb, Zn, and Cu from motor vehicle emissions. The consistency of the aerosol databases for two northern Chinese cities was tested by comparing Xigu, Lanzhou PM2.5 (1983)

FIGURE 8. PM2.5 aerosol compositions in Xigu Lanzhou (1983) are much higher than central Beijing (1980) due to industrial activities including power generation, aluminum processing, petrochemical producing, and glass manufacturing. *Average of 5 sites in central Beijing around Tiananmen Square, December 23 and 25, 1980, 4 h sampling, random days, dp < 2.0 µm (16). **Average of 2 sites in Xigu Lanzhou, December 7-20, 1983, 24-h sampling, consecutive days, dp < 2.5 µm (18).

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and central Beijing PM2.0 (1980). Figure 8 shows that Xigu is much more heavily polluted than Beijing. The same was true for downtown Tianjin (20) in 1984 when compared with Beijing.

Comparison Studies: Mass Fraction Diagrams The mass fraction is the ratio of the concentration of species i to the total mass concentration of the aerosol, defined by p

Ci ) xi/

∑x

i

(2)

i)1

where xi is the mass concentration of species i. Forming the mass fraction normalizes the aerosol composition and makes it possible to compare differences in composition independent of the total aerosol mass concentrations. Since the total

fractions of potassium are higher and sulfur are lower than downtown Los Angeles without significant seasonal difference as shown in Figure 10. Comparing the mass fraction diagram for Beijing vs Los Angeles (Figure 9, CD ) 0.466) with the corresponding concentration diagram (Figure 2, CD ) 0.697), we see that a smaller CD is associated with the mass fraction plot. This shows that by removing the effect of the total aerosol mass concentration on the data spread, the smaller spread due to the chemical variation by itself can be extracted in the mass fraction diagram.

Acknowledgments

FIGURE 9. Mass fractions of fine aerosol components show the importance of crustal elements in downtown Beijing (1992-1993) than in downtown Los Angeles (1986). *SoCAB database for downtown Los Angeles, January 2-December 28, 1986, 24 h sampling, every sixth day, 25 dp < 2.5 µm (37). **Average of 2 sites in downtown Beijing, December 14, 1992-January 13, 1993, 24 h sampling, consecutive days, dp < 2.0 µm (9).

FIGURE 10. Beixinan PM2.0 aerosols (1992-1993) show a large difference in mass fractions of chemical components compared with downtown Los Angeles (1986). *SoCAB database for downtown Los Angeles, January 2-December 28, 1986, 24 h sampling, every sixth day, dp < 2.5 µm (37). **Industrial area near the Capital Iron & Steel Works in northwestern Beijing, December 14, 1992-January 13, 1993, 24 h sampling, consecutive days, dp < 2.0 µm (9). 26 mass of Chinese aerosols in the fine fraction is not available for most of the reported data sets (8, 12, 14-22), the discussion is limited to data for the Beijing region in 1992-1993 (9). Figures 9 and 10 are mass fraction scatter diagrams showing results very different from the mass concentration diagrams; chemical species such as Zn, Pb, Cu, Ni, and Cr have much higher mass fractions in the 1986 downtown Los Angeles aerosols than those of Beijing in 1992-1993. These aerosol components are primarily contributed by sources of human origin. On the other hand, crustal elements such as Ca, Al, Mn, Ti, and Fe in Beijing PM2.0 aerosols show higher mass fractions than downtown LA. The mass fractions of potassium and sulfur show a different variation depending on sites and times. For downtown Beijing, the mass fraction of potassium in autumn is lower but becomes much higher than downtown Los Angeles in winter (Figure 9). Similarly, sulfur mass fractions are lower in downtown Beijing in autumn but increase in winter reaching the same level as downtown LA. For industrial areas such as Beixinan, the mass

This work was supported in part by U.S. Environmental Protection Agency Grant R821288. The contents of the paper do not necessarily reflect EPA views and policies. S. K. Friedlander is Parsons Professor of Chemical Engineering. Zhiqun Zhang is a Visiting Researcher at UCLA and Professor of Chemical Engineering at Beijing University of Chemical Technology.

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Received for review March 31, 2000. Revised manuscript received July 24, 2000. Accepted August 1, 2000. ES001147T

A Comparative Study of Chemical Databases for Fine Particle Chinese

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