Environ. Sci. Technol. 2004, 38, 3396-3404
Laboratory and Field Measurements of Dry Deposition of Sulfur Dioxide onto Chinese Loess Surfaces ATSUYUKI SORIMACHI,† K A Z U H I K O S A K A M O T O , * ,† M I O S A K A I , † HIDEKAZU ISHIHARA,‡ TSUTOMU FUKUYAMA,§ MASAHIRO UTIYAMA,§ HONGJIE LIU,| WEI WANG,| DAGANG TANG,| XUHUI DONG,⊥ AND HAO QUAN⊥ Graduate School of Science and Engineering and Faculty of Engineering, Saitama University, 255 Shimo-ohkubo, Sakura, Saitama 338-8570, Japan, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan, Chinese Research Academy of Environmental Sciences, Lishuiqiao, Anwai, Beijing 100012, China, and Sino-Japanese Friendship Center for Environmental Protection, No. 1 Yuhuinanlu, Chanyangqu, Beijing 100029, China
Laboratory and field measurements were conducted to examine dry deposition of SO2 onto Chinese loess surfaces using native soil sampled in the loess plateau, China. The field tests were employed in Beijing and Lanzhou, China, by directly measuring the dry deposition of SO2 on soil, which uses soil put on a collector as an SO2 passive sampling medium. In the laboratory, a high rate of uptake to SO2 deposition for Chinese soil surfaces due to the highly alkalinity was found. The uptake of SO2 deposition was dependent on the pH soil and relative humidity. Furthermore, we evaluated some factors that affect the measurement precision: response of SO2 uptake, repeatability, recovery factor, and variability associated with the weight and the surface coverage on the collectors. As a result, it was shown that the measurement precision was primarily related to the ratio of the SO2 deposition amount relative to the sulfur content of the original soil. This result was consistent with the field observations. The laboratory and field results indicated an excellent agreement on the SO2 uptake inherent in the results from the soil surfaces in different regions.
Introduction In the United States, Canada, and Europe, quite a number of measurements of dry deposition have been carried out in recent years (1-3), and estimates of dry deposition on local and regional scales have improved with the development of empirical descriptions based on flux measurements (4-7). In contrast, in East Asia, few direct dry deposition measurements have been made, despite the growing concern about the environmental impact of sulfur dioxide emissions (8). In * Corresponding author e-mail: sakakazu@ env.gse.saitama-u.ac.jp; phone: +81-48-858-3519; fax: +81-48-8589542. † Graduate School of Science and Engineering, Saitama University. ‡ Faculty of Engineering, Saitama University. § National Institute for Environmental Studies. | Chinese Research Academy of Environmental Sciences. ⊥ Sino-Japanese Friendship Center for Environmental Protection. 3396
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 38, NO. 12, 2004
only a few cases, the dry deposition velocity of SO2 has been estimated by the inferential approach based on data obtained in North America and Europe (9-11). Dry deposition on a surface varies with factors such as the weather, the atmospheric conditions close to the surface, the physicochemical and biological properties of the surface (e.g., plant physiology), and the composition of various types of surface water lying on the vegetation or soil (3). It is therefore important to evaluate the uncertainties inherent in the results from surfaces in different regions. In northern China, there are vast arid areas, for example, the loess plateau and the Gobi Desert. Because airborne particles derived from such areas are alkaline, they play an important role in buffering and neutralizing acidifying substances (12, 13). Examining the extent of uptake of acidic gases over such areas may provide interesting information about the transport and fate of these gases. However, the vast areas and various compositions of soil make dry deposition measurements difficult. Furthermore, if micrometeorological methods were employed, they would be expected to entail huge expenditures of money, time, and effort. In this paper, we employed the laboratory and field measurements of the dry deposition of SO2 onto Chinese loess surfaces.
Experimental Section Preparation of Soil and SO2 Sampler. Measurement of the SO2 dry deposition flux was carried out using native soil as an SO2 passive sampling medium. Native soil (Chinese loess) was collected from the following sites: Huining, Beijing, Wuchuan, Yinchuan, and Lanzhou [two different sites, Lanzhou(1) and Lanzhou(2)], located in the loess plateau (Table 1). The Huining soil, which was collected between 1.8 and 2.5 m depth, was obtained from National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan (14). The other soils were collected from the ground covering the depth zero (surface) to about 10 cm at each site. It was thought essential to facilitate comparison among the results from different soil samples. For this purpose, to ensure a uniform particle size distribution and surface condition, the Chinese loess samples were sieved through a 250-mesh sieve to remove plants, roots, and large particles and were ground in an agate mortar for 1 h to yield 1 g of powdered soil, which was further sieved with 440 mesh to sort out particles less than 32 µm in diameter. The resulting material was dried at 105 °C for at least 4 h in an electric oven. Furthermore, to investigate dependence of the acidity of the soil on SO2 deposition, diatomaceous earth (chemical grade, Wako Pure Chemical Industries, Ltd., Osaka) was used and was treated with phosphoric acid solution, ultrapure water, and sodium hydroxide solution to prepare three different acidities where the corresponding samples were referred to as DE 1, DE 2, and DE 3, respectively, in this paper (Table 1). Both the diatomaceous earth and the solvent were ultrasonically mixed, and after the filtration the residual material was dried. The solid material was treated to yield powdered soil by the same method as the Chinese loess samples as noted above. The samplers for measuring SO2 deposition were prepared by evenly distributing a known weight of the treated soil on the collectors (vide infra) and lightly tamping with the end of a stainless steel microspatula. The roughness of the finished soil surface was about 1 mm. The time required for this procedure was less than 3 min. Because of this short time and also because of low SO2 concentration generally expe10.1021/es034967p CCC: $27.50
2004 American Chemical Society Published on Web 05/15/2004
TABLE 1. pH (H2O) and Blank Levels of SO42- Content in Soil soil
pH (H2O)
SA (m2 g-1)
blank [mg of SO2 (g of soil)-1]
SD (σ) [mg of SO2 (g of soil)-1]
RSD (%)
n
LOD (3σ) (µg of SO2 m-2 s-1)a
LOQ (10σ) (µg of SO2 m-2 s-1)b
Huining Beijing Wuchuan Yinchuan Lanzhou(1) Lanzhou(2) Lanzhou(2)c DE 1 DE 2 DE 3
9.1 9.2 7.0 9.3 9.2 9.1 9.7 5.1 6.1 8.1
9.4 8.5 4.9 9.2 7.1 8.3 9.4 31.2 28.9 22.0
0.109 0.059 0.018 0.185 0.146 0.121 0.103 0.052 0.201 0.149
0.004 0.002 0.001 0.010 0.011 0.005 0.009 0.004 0.010 0.006
3.9 4.1 5.0 5.4 7.4 4.5 8.3 8.1 4.9 4.1
10 10 10 10 10 7 10 7 7 7
0.042 0.024 0.009 0.098 0.106 0.054 0.084 0.042 0.097 0.060
0.140 0.080 0.029 0.326 0.353 0.179 0.280 0.138 0.322 0.202
a LOD, limit of detection using 3 times the blank standard deviation 3σ, assuming a soil weight of 50 mg, a surface coverage of 353 mm2, and an exposure time of 12 h. b LOQ, limit of quantification. c Soil without grinding.
TABLE 2. Recovery Factor (RF) of SO2 and Repeatability in Dry Deposition Flux (F), As Shown by Relative Standard Deviation (RSD) Using the Lanzhou(2) Soil flow rate (L run min-1)
RH (%)
soil surface F (µg of SO2 m-2 RSD wt area exposure 2 (mg) (mm ) time (h) n s-1) (%)
1 2 3 4 5 6 7 8 9 10 11 12b 13b 14 15b 16 17b
