Model study of atmospheric aerosols in some typical places of China

J. Aerosol Sci., Vol. 22, Suppl. I, pp. $625-$628, 199I.

0021-8502/91 S3.00 +0.00 Pergamon Press plc

Printed in Great Britain.

MOOEL STUDY OF ATMOSPHERIC AEROSOLS IN SOME TYPICAL PLACES OF CHINA

Jun Xu, Huanting Hu and Jun Zhou Anhui I n s t i t u t e of Optics and Fine Mechanics, Academia Sinica, P.O. Box 1125, Hefei, P.R.China.

ABSTRACT Since 1983 the imaginary parts of r e f r a c t i v e index, elemental concentrations and size d i s t r i b u t i o n s of atmospheric aerosols have been measured in some typical regions of China,including T i a n j i n , Shenyang, Nanjing, Hefei and Shengzheng c i t e s , Fucun v i l l a g e , Bright Peak in Huangshan mountain (1840 m ASL), Yangbajin in Tibet (4300m ASL), South China Sea and coast. A large amount of data sets has been obtained and provides a batter understanding of the c h a r a c t e r i s t i c s of the aerosols. Based on these r e s u l t s , the China Atmospheric Aerosol Model has been developed. KEYWORDS Atmospheric a e r o s o l ; r e f r a c t i v e index;elemental concentration;size d i s t r i b u t i o n . CHARACTERISTICS OF Ni VALUES OF AEROSOLS The imaginary part of r e f r a c t i v e index (Ni) of atmospheric aerosol is an important parameter of absorption property of aerosol. Integrating Plate lIP) Method, proposed by Lin (1973) and improved by Weiss(1980), is quite simple and convenient. According to error analysis, Ni value of aerosol can be determined with an uncertainty of tess than 25%. Using this method, we have obtained the Ni values of aerosols in some places of China. They are shown in Table 1. Table 1 : Hi values of aerosols in some places of China Place .

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Shenyang Tianjin

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city city

Hefei city Shengzheng city Shengzheng city

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Time .

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05/01/8502/01/86-

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Dp > .

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I .

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Nr .

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I .

0.4#m 0.4#m

1.50 1.50

03/01/84I 0.4#m 08/15/89-08/17/89 0.4#m 08/15/89-08/17/89 1.0~m

1.50 1.50 1.50

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Ni .

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I .

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0.1000+0.020 0.0800+0.016 0.0600+0.025

0.1029 0.0277

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Comments .

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heavy i n d u s t r i a l c i t y industrial c i t y

middle city developing city developing city

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Tianjin Tianjin Nanjing Hefei

suburb suburb suburb suburb

02/01/8602/01/86I0/01/8603/01/84-

i 0.4/un i 1.50 , 0.4/un 1.50 I 0.4#m 1.50 l= 0.4~m 1.50

0.0760+0.010 0.0390+0.005 0.0530+0.011 0.0600+0.013

bottom of a tower top of tower (h=220m) eastern suburb western suburb

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Fucun v i t t a g e 111/01/85I 0.4/un Huangshan mountain110/01/85I 0.4/un South China Sea I07/14/89-07/25/891 0.4/un Taiwan S t r a i t 108/03/89-08/04/8910.4/.un Taiwan S t r a i t I08/03/89-08/04/891 1.0/un Dawanshan island 10/27/89-11/10/8910.4/un Shantou coast 07/29/89-08/02/89 0.4pJn Guangzhou wharf 08/07/89-08/09/89 O.4tun

i

1.50 i 0.0300+0.010 0.0120+0.007 I 0.0034 0.0082

1.50 I1.42 1.42 I1.42 1.50 1.50 1.50

0.0050 0.0200+0.008 0.0141 0.0320

rural Bright on the on the on the on the on the on the

Peak(1840m ASL) ship ship ship land land land

Dp=particte diameter; Nr,Ni=the real and imaginary part of r e f r a c t i v e index of aerosol. From table 1, we can see: (1) The mean Ni value is 0.080 in the c i t i e s of eastern China. I t is only 0.040 in New York (Lin et a l . , 1 9 7 3 ) . Most of the Ni values in urban sumnarized by Gerber et al.(1981) are tess than 0.05. Our high Ni values are retated to the coat as main energy resource in industry and livelihood a c t i v i t i e s in these c i t i e s . Shengzheng c i t y is near Hongkong. I t is a developing industrial c i t y . For the aerosols with diameter larger than 0.40 /un and 1 /tm, the Hi values are 0.1029 "and 0.0277 respectively. I t means the pottutants in Shengzheng c i t y are mostly composed of aerosol p a r t i c l e s with diameters from 0.4 p.m to 1.0 /un. (2) In suburbs of Tianjin, Nanjing and Hefei c i t i e s , the mean value of Ni is 0.063, which is obviousty smatter than the one in urban d i s t r i c t s . The largest Hi is 0.076 in the suburb of T i a n j i n , the biggest i n d u s t r i a l c i t y among them. The aerosol p a r t i c l e s were sampled simultaneously at the top of a meteorological tower with height of 220 m located in the suburb of Tianjin. Ni is 0.039 at the top, which is only about h a l f of the one on the ground.

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YUN Xu et al.

(3) Fucun v i l l a g e is Located in southern Anhui province. The mountainous measurement s i t e is the Bright Peak of Huangshan mountain(1840 m ASL). The Ni values of both rural and remote aerosol, given by Gerber et e l . (1981), are 0.003-0.025 and 0.001-0.005 respectively. But, the averages of Ni are 0.012 end 0.030 respectively at the Bright Peak and Fucun v i l l a g e , which are e t i t t l e larger. (4) Sea aerosols come from pet of sea waves and burst of a i r bubbles so that the main composition is NeC[, which is a kind of weak absorption substance. Table 1 shows that the Ni values increase gradually as the measurement s i t e is moving from the South China Sea to the coast, to the C i t i e s . For the aerosols with diameter larger than 0.4 pm, Ni values are 0.0034 over South China Sea, and 0.0082 over the Taiwan S t r a i t . ALthough they ere Larger than 0.006 and 0.002 given by Selby et al.(1976), they are s t i l l within the Ni range summarized by Gerber et a[.(1981). (5) Aerosol p a r t i c l e s were also sampled in the suburb of Hefei once per ten days in 1987 end 1988. Ni was 0.069 during Nov.1987-May 1988. The Largest Ni value of 0.086 was obtained in December, which is related to the c o a l - f i r e d smoking dust for heating in winter. Ni is 0.050 in June-Oct. 1987. Some factors may cause the decrease, such as no-heating in the warm period. CHARACTERISTICS OF SIZE DISTRIBUTIONS OF AEROSOLS The instrument for thispurpese is an Optical Particle Counter (OPC), which consists of an optical system with a 60" scattering angle and a .~ulse height analyzer with 18 channels. The characteristics of the particle number or volume density distrlbutions measured with the OPC would vary in a marked degree Qith the particle refractive index, especially with its imaginary part (Hu et al.1986). Therefore, all of the measured size distributions have been corrected with the measured Ni at the respective places. The main characteristics are:

(I) ~he numbs, density distributions maybe fit by Junge model (dN/dtog r=cr "Y) or Oiermendjan model (dN/dlog r=ar exp(-cr )). ALl correlation coefficients are higher than 95~ except in Tibet. The Junge exponent y reveals the relative proportion of large particles. The average values of y are 1.88±0.30, 2.59±0.43, end 2.72±0.49 in urban, suburb, and rural regions, respectively. The proportion of large particles is the lowest in the countryside, especially in Huangshan mountain, where the y is 2.81. It should be pointed out that the relative deviations of y are only about ±5% at Fucun and each urban site, which may be relevant to the stable background aerosol in the countryside or the prevailing local particle sources in each urban site. However, in the suburb of Hefei and at Bright Peak, the deviations are about ±20%. It is possible that different messes dominate alternatively in the suburbs because of a lack of prevailing local particle sources. The Latter case may be related to the fact that the Bright Peak site is either above or within the haze layer. In the urban region, not only is the proportion of large particles greater, but large particles are also the most abundant. Nc represents the concentration of aerosols with radius larger than I Am. in the urban region Nc is 56.2 particles/cm**3. An Nc of 78.8 particles/cm**3 in the urban of Tianjin is two times more than that in Hefei, which indicates the pollution in Tianjin is more serious. In contrast, large particles are quite rare with Nc of 0.77 pertictes/cm**3 in the countryside, especially at Bright Peak where Nc is only 0.20 partictes/cm**3. The even smeller values of Nc appear at the Bright Peak when it is above the haze layer, the average is only 0.047 partictes/cm**3. For the sea aerosols with radius~0.2 /un, the total concentration PN on the coast is larger than South China Sea. The PN values were measured before end after the Typhoon of No.8908 over South Chins Sea in July, 1989, they are 3.280 particles/cm**3 and 20.030 particles/cm**3 respectively. Thus, it can be seen that stormy waves have an important effect on PN values. The PN values are 134.258perticles/cm**3 over Taiwan strait, 182.359 particles/cm**3 in Dawanshan island, and 245.076 particles/cm**3 in Guangzhou wharf. This difference is mainly caused by the air pollution on the coast. As a remote site, Yangbajin is located in Tibet (30°06'N; 90°31,E, 4300 m ASL). The PN value (r~O.2 /~m) was measured in July of 1991. It is 0.838 partictes/cm**3 and the lowest in all the above-mentioned sites. For the aerosols with 0.2pm
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Fig.1. Representative volume d i s t r i b u t i o n s at Bright peak, Fucun v i l l a g e and Hehei.

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Model study of atmospheric aerosols

From F i g . l , we can see that the presence of the accumulation mode (A-mode, r < l . 0 /=,) is a special c h a r a c t e r i s t i c of the r u r a l aerosols ( F i g . l , a). The middle mode (M-mode, 1/un3/un) p r e v a i l in suburbs and urban area ( F i g . l , b). The peak value of M-mode is very small tn r u r a l regions, but o f t e n dominant at suburb and urban s i t s . The peak value in p o l l u t e d regions is 1-3 order of magnitude g r e a t e r than that in r u r a l regions, i t can be deduced that the M-mode is generated from some a r t i f i c i a l a r t i c l e sources, which may a f f e c t the suburbs severely, and the r u r a l regions s l i g h t l y . A distinctive eature can be seen from the d i s t r i b u t i o n s at each region. The f i t parameters of the A- andC- modes at r u r a l s i t e s are n e a r l y the same as S h e t t t e ' s data (Shettte et e[.,1979). The mode radius value of Vo in the C- mode is near[y equat to the A-mode value in the Huangshanmountain, and only three times more than the A-mode value in Fucun due to a tack of coarse p a r t i c l e s .

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(S) Before Typhoon. 14-15,7,%989.

A f t e r Typhoon. 20-25,7,1989.

Fig.2. Size distribution measured over South China Sea. Fig.2 d i s p l a y the representationmeasurements before and a f t e r the Typhoon of No.8908 in July, 1989 over South China Sea. Because of the Typhoon e f f e c t , the volume density d i s t r i b u t i o n s have been changed from muttimode (Fig.2, a) to dominant Middle mode (Fig.2, b). Stormy waves make a great c o n t r i b u t i o n to p a r t i c l e s from 1 to 3 gm. CHARACTERISTICS OF ELEMENTAL CONCENTRATIONSOF AEROSOL The c o l l e c t i n g f i l t e r s is Nuclepore, whose pore diameter is 0.2 or 0.4 /u~. Samples were analyzed by PIXE method. The aerosol d e n s i t i e s and concentrations of the elements, whose atomic numbers are l a r g e r than 12, are reported here. The elemental concentrations are strongly d i s t i n c t i v e f o r the aerosols sampled in the above various regions.

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1 - i n s h o r e sea; Z-open see; 3 - B r i g h t peek; 4 - r u r a l ; 5-Hefel s~ourb 6 - T i a n j i n suburb; 7 - T . j . 220m h i g h , 8 - T . j . urban; 9-Senyan u r ~ n . F i g . 3 . Aerosot a e n s i t y in d ( f f e r e n t type r e g i o n s .

At St p

s Ct ~ Ca ri v

Cr ~n Fe M! CU 2J1 41 Pb Se 5r Sr

F i g . 4 . Etessents of aerosol at inshore see(Or')1), open s e e ( l ~ 3 ) and Bright p e a k ( ~ ) .

(1) The concentration of Ct element over South China Sea is the highest in eastern China. I t s average value is high to 557 ng/m**3, which is about 40 times as large as that in mountainous region (see F i g . 4 ) . I t is the reason that the aerosols in ocean region contain large amount of NaC[. Oppositely, concentration of S element is only about 14 ng/m**3. I t seems that S element from the land has s l i g h t e f f e c t on the aerosols in the ocean region. There are some marked d i f f e r e n c e s f o r the aerosols in the inshore and the open see. Because of the i n d u s t r i a l p o l l u t i o n and the dusts from the land, the concentrations of Si,K,Fe, end Ca elements in the inshore sea are much higher than the ones in the open sea.

$628

¥uN Xu et al.

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Ct I;

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Cr ~

Fe ~t Cu Zn A= PI~ Se a r s r

E[e~nts of a e r o s o l s mt Refei s u b u r b ( c ~ ) , Tianjin su~Jrb( ~ ] and T i i l n j f n 220m h i g h ( ~ ) .

(2) Huangshan mountain is f a r from c i t i e s and i t s Bright Peak is high above the ground, so the atmospheric aerosols there would not be affected markedly by the i n d u s t r i a l p o l l u t i o n in c i t i e s and the Local l i v e l i h o o d activities. The aerosol density (33.2 #g/m**3) and concentrations of a l l elements at Bright Peak are the Lowest in eastern China except South China Sea and may be accepted as the background values f o r the aerosols in eastern China. The aerosol density is 42.8 #g/m**3 at Fucun v i l l a g e , which is a L i t t l e higher than the one at Bright Peak. However, i t is only one s i x t h of the one in Shenyang urban. Because of the c o a t - f i r e d smoke, the concentrations of S and Pb in Shenyang urban are 2 or 3 times as large as that at Bright Peak. (3) The aerosol density and elemental concentrations of the aerosol in T i a n j i n suburb are not markedly d i f f e r e n t fnomthe ones in T i a n j i n urban because of the r a p i d l y developing industry and t r a f f i c in the suburb. The aerosol density in T i a n j i n suburb is 2.2 times a s large as that in Hefei suburb, and the concentrations of Si, Ca, CL, Mn, Fe, and Zn elements, related to the p o l l u t i o n of the construction, the industry and the t r a f f i c in T i a n j i n suburb are above 3 times as large as the ones in Hefei suburb. Obviously, T i a n j i n is a more s e r i o u s l y p o l l u t a n t c i t y . The measurement results in Shenyang and T i a n j i n urban i n d i c a t e t h a t t h e i r aerosol d e n s i t i e s are about 8 times as large as the background value and t h e i r elemental concentrations are the highest in eastern China (see Fig.3). In the c i t i e s , there a r e 12 elements whose concentrations a r e about 20 times as large as the background values (see Fig.5). Among them, At, Si, Ca, and Ti are r e l a t e d to the cement ash and the s o i l dust; the burning and c o a t - f i r e d smoke make the concentrations of CI, Fe, and Pb elements increasing; Pb and Br are also related to the exhaust of automobiles; and the high concentration of K, Cr, Mn, and Zn elements are the resutts of the i n d u s t r i a l p o l l u t i o n . The concentration of Br in T i a n j i n and Pb in Shenyang a r e 190 times and 387 times respectively as large as the background values. Therefor, the p o l l u t i o n is serious in the i n d u s t r i a l c i t i e s of eastern China. (4) At the top of the meteorological tower (220 m high) Located in the suburb of T i a n j i n , the aerosot d e n s i t y is h a l f of the one near the ground (see Fig.3). Near the ground, the concentrations of 10 elements, such as At, Si, CI, Ca,Ti, Hn, Fe, Zn, and Pb, are above 3 times as Large as the ones at the tower top (see F i g . 6 ) . The concentration d i f f e r e n c e in Ca element is even high to about 26 times. I t seems that the p o l l u t a n t s r e l a t e d to the above-mentioned 10 e|ements accumulate in the layer near the ground. Oppositely, the concent r a t i o n s of S and Br elements f o r the aerosol at the tower top are close to the ones r e s p e c t i v e l y f o r the aerosol near the ground. REFERENCES [1] Gerber, H.E.and E.E. Hindman, 1981: F i r s t International gorkshop on Light Absorption by Aerosol P a r t i c l e s : Background, A c t i v i t i e s and Preliminary Results, Bull. Ameri. Meteor. Soc., 62:1321-1327. [2] Chin-I Lin, M. Baker, and R. J Chartson, 1973: Absorption c o e f f i c i e n t of Atmospheric Aerosol: a Method f o r Measurement, Algol. Opt.. 12. [3] Huanting Hu et at. 1988: Effect of P a r t i c l e Refractive Index on the Accuracy of Aerosol Measurement with Optical P a r t i c l e Counters. Sic. Bul., 33, 429-432. [4] Cooke,D.D.,and M.Kerker, 1975: Response Calculations f o r Light Scattering Aerosol P a r t i c l e Counters. APPt.ODt. 14.734-739. [5] E.M.Patterson et at, 1980. Global Measurements of Aerosol in Continental and Marine Regins: Concentrations, Size D i s t r i b u t i o n s , and Optical Properties. J. Geophys. Res. 85,7561- 7376, 1980. [6] Selby, J. E., E. P Shettte, and R. A. Hcclatchey. 1976. Atmospheric transmittance from 0.25 to 28.5 /u~: supplement Lowtran 3B. AFGL-TR-76-0258. Environmental Paper 587,27-34. [7] Shettle, E. P. and R. W. Fenn, 1979: Models f o r the aerosol of the tower atmospher and the e f f e c t s of humidity v a r i a t i o n s on t h e i r optical properties. Rep, AFGL-TR-79-0241,94 pp. [8] Huanting Hu, Jun Xu et el, 1986, " The Characteristics of Aerosol O i s t r i b u t i o n in Some Places of China ", published at the Beijin~ International Radiation Symposium. 26-30 August 198~.