Geographic Factors Explain the Variability of Atmospheric Deposition of Sulfur and Nitrogen onto Coniferous Forests Within and Beyond the Tokyo Metropolis

Imamura, Naohiro; Levia, Delphis F.; Nanko, Kazuki; Tanaka, Nobuaki; Ohte, Nobuhito

Geographic Factors Explain the Variability of Atmospheric Deposition of Sulfur and Nitrogen onto Coniferous Forests Within and Beyond the Tokyo Metropolis

2020

Imamura, Naohiro | Levia, Delphis F. | Nanko, Kazuki | Tanaka, Nobuaki | Ohte, Nobuhito

With the continued growth of cities in many areas of the world, it is important to understand variations in atmospheric deposition in relation to site-specific geographic factors. Accordingly, this research investigated wet or bulk deposition (WD/BD) and dry deposition (DD) of SO₄²⁻, NO₃⁻, and NH₄⁺ onto Japanese cedar within the Tokyo metropolis and surrounding areas with the primary aim of evaluating which geographical factors most influence the deposition of pollutants. Two new sites were established and, along with five existing sites, comprised an array of sites with varied geographic settings (distance from the center of Tokyo, elevation, and azimuthal difference between slope aspect and dominant wind direction). Annual WD/BD and DD values of SO₄²⁻, NO₃⁻, and NH₄⁺ ranged from 9–35, 16–83, and 12–96 mmol m⁻² year⁻¹, respectively, and 1–25, − 5–104, and − 7–142 mmol m⁻² year⁻¹, respectively. Annual WD/BD values only showed a statistically significant difference with azimuthal difference for SO₄²⁻ and NH₄⁺. In contrast, annual DD values of SO₄²⁻, NO₃⁻, and NH₄⁺ were found to significantly decrease with distance from the center of Tokyo. In addition, site elevation was a significant factor influencing the DD of SO₄²⁻, NO₃⁻, and NH₄⁺ in linear regression models. Azimuthal difference was not significantly related to DD variability. Given these results, it is necessary to consider both the distance from emission source as well as the geographic factors of particular locations when evaluating the deposition of atmospheric pollutants from megacities to forested areas within and beyond the city.

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