Monitoring and modeling the mass, heavy metal and ion species dry deposition in central Taiwan

Abstract

Dry deposition flux and particle concentration of mass, Ca²⁺, Mg²⁺, Cl⁻ and SO₄ ^2‐were measured by dry deposition plates and NRI (Noll Rotary Impactor), MOUDI (Micro‐Orifice Uniform Deposit Impactor), respectively in the ambient air of Chung‐Hsing University and Tung‐Hai University in central Taiwan from November 1995 to January 1996. AAA‐680/G flame atomic absorption spectrophotometer was used to measure the metals Ca²⁺ and Mg²⁺ and a I. C. (DIONEX DX‐100 Ion Chromatography) was used to measure the ions Cl⁻ and SO₄ ^2‐ species. The CHU sampling site was divided into two parts to discuss the influence of coarse particle on the concentration and deposition velocities. The average mass concentration (without NRI sampler) for thefine and coarse particles were 21.6, 23.8 and 19.8, 21.6 μg/m³ in CHU and THU sampling site, respectively. By the same token, the average mass concentration (with NRI sampler) for the fine and coarse particles were 26.4 and 30.9 μg/m³ in CHU sampling site, separately. The results indicated that the average deposition velocities were 1.34, 1.11, 1.19, 0.11 and 0.27 (cm/sec) for mass, Ca²⁺, Mg²⁺, Cl⁻ and SO₄ ^2‐, respectively in CHU area with NRI sampler. And the results also displayed the average deposition velocities were 1.58, 1.23, 1.64, 0.52 and 0.58 (cm/sec) for mass, Ca²⁺, Mg²⁺, Cl⁻ and SO₄ ^2‐, separately in CHU sampling site without NRI sampler. The deposition velocities were 3.93, 2.69 and 2.23 (cm/sec) for mass, Ca²⁺ and Mg²⁺, respectively in THU sampling site without NRI sampler. Thus, this study showed that the coarse particle did have significant influence on the urban and suburban area of central Taiwan. In the ambient air of CHU the correlation coefficient of average wind speed with average mass flux (R²) is 0.65 This phenomena can be further verified by the sampling site of THU (R² = 0.76). The results indicated that fine particles (dp < 2.5 μm) occupied only about 4.65% and 7.20% for mass in CHU and THU sampling site, respectively. The calculated dry deposition coarse particle flux (dp > 2.5 μm) is much higher than dry deposition fine particle flux for mass even though the concentration distribution for the coarse and fine particle are insignificantly different. The calculated results displayed coarse particle occupied the majority (> 91.6%) of the total dry deposition in either urban or suburban area for mass, metal (Ca²⁺, Mg²⁺) and ions (Cl⁻, SO₄ ^2‐). The correlation coefficient (R²) of total mass flux and coarse / fine particle concentration are 0.76 and 0.076, separately. And the results suggest that the magnitude of the flux is strongly dependent on coarse particle concentration and independent of the fine particle concentration.

Key words:

• dry deposition
• metal
• ion
• coarse particle
• fine particle

Notes

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